A method for coordinated regulation of thermal stress of an air intake system of an aero-engine test chamber in a wide temperature range

Abstract

The present application relates to the technical field of multi-physical field coupling optimization of aero-engine test equipment, and specifically discloses a method for the coordinated regulation and control of thermal stress of an air intake system of an aero-engine test cabin in a wide temperature range, which comprises the following steps: constructing a three-stage progressive thermal-solid coupling finite element model of the air intake system, sequentially establishing a simplified model without expansion joints, a model with expansion joints, and a complete model with expansion joints and extending to the fixed point of the pipeline, and completing the calibration of the force boundary of the nozzle in combination with pipeline mechanics analysis; for the high and low temperature gas mixing section, the flow-thermal coupling simulation is used to optimize the cold / hot gas flow ratio and mixing structure, and the mixing uniformity index is quantified; the three-stage progressive thermal-solid coupling finite element model is constructed, and the pipeline mechanics software is used for bidirectional calibration, so that the boundary condition deviation between the local fine model and the simplified model of the whole pipeline is eliminated, the high-precision prediction of the deformation and thermal stress distribution of the pipeline system under the extremely wide temperature range is realized, and an accurate simulation basis is provided for the coordinated regulation and control of thermal stress.

Description

Technical Field

[0001] This invention relates to the field of multi-physics coupling optimization technology for aero-engine test equipment, and in particular to a method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test chamber. Background Technology

[0002] The wide-temperature-range aero-engine test chamber is the core equipment for conducting high-altitude simulation tests. Because the aero-engine test chamber needs to simulate the air environment encountered by the engine during takeoff, ascent, and cruise, it involves significant temperature changes with altitude and a large range of variations. The intake conditions involve transitions from normal to extreme. When designing the intake pipeline of the test chamber, multiple pipelines with different temperatures and flow rates are used to control the experimental conditions that cover the intake range of the aero-engine.

[0003] The existing technology has the following drawbacks: First, the simulation model lacks accuracy, does not include key structures such as expansion joints and the entire pipeline, and is not calibrated with professional mechanical software. This results in a deviation of orders of magnitude between the pipe force calculation results of the ANSYS local model and the CAESAR II full pipeline model, making it impossible to accurately predict the actual deformation and stress distribution. Secondly, the mixing process under extreme temperature differences of -70℃ to 600℃ lacks systematic fluid-thermal coupling analysis and fails to quantify the relationship between the ratio of hot and cold gases and uniformity, resulting in severe temperature gradients and frequent thermal shocks in the pipe junction area, which has become the main cause of structural failure. Third, in areas of sudden temperature change such as local heater inlet and outlet and cabin connection, there is a lack of quantitative criteria for transition zone design and thermal stress suppression, and a temperature difference of hundreds of degrees Celsius over a short distance causes severe stress concentration. Fourth, the mapping relationship between the stiffness of the expansion joint and the deformation of the pipeline and the force at the pipe opening is unclear, making it impossible to accurately match thermal displacement, resulting in excessive force at the equipment interface and loss of coaxiality control.

[0004] Therefore, a method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test cabin is proposed to solve the problems mentioned above. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test chamber, which can effectively solve the problems involved in the prior art.

[0006] The objective of this invention can be achieved through the following technical solution: This invention provides a method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test chamber, comprising the following steps: Step 1: Construct a three-level progressive thermo-solid coupled finite element model of the intake system. Sequentially establish a simplified model without expansion joints, a model with expansion joints, and a complete model with expansion joints extending to the fixed point of the pipe. Combine pipe mechanical analysis to complete the pipe force boundary calibration, realize high-precision simulation of the deformation and stress of the whole system, ensure that the simulation boundary is highly consistent with the actual engineering, and improve the credibility of thermal stress prediction. Step 2: For the high and low temperature gas mixing section, optimize the cold / hot gas flow ratio and mixing structure based on fluid-thermal coupling simulation, quantify the mixing uniformity index, reduce the local temperature gradient and thermal shock in the pipeline, effectively suppress the thermal shock in the mixing section, and improve the downstream temperature uniformity. Step 3: Set a gradient transition zone of 100mm to 1000mm at locations of sudden temperature changes, such as the inlet and outlet of the local heater and the connection between the pipe and the cabin, to determine the optimal range to suppress stress concentration caused by sudden temperature changes in the pipe wall, significantly alleviate local stress concentration caused by sudden temperature changes, and enhance structural safety. Step 4: Establish stiffness models for compound tie rod type and bend pressure balance type expansion joints, decouple the nonlinear mapping between expansion joint stiffness and pipe force and thermal displacement, clarify the nonlinear coupling law of stiffness-pipe force-thermal displacement, achieve precise matching between expansion joint stiffness and thermal displacement, and improve compensation efficiency. Step 5: Based on the deformation distribution of the entire pipeline, optimize the installation position and number of expansion joints, and achieve complete thermal displacement compensation and precise control of pipe force through stiffness gradient adjustment, thereby eliminating the pipeline thermal displacement blind zone and reducing the risk of equipment interface load. Step 6: Integrate multi-physics simulation verification under full working conditions, coordinate and control the mixing uniformity, transition zone design, and expansion joint parameters to ensure that the maximum equivalent stress is lower than the allowable value of the material, so that the system deformation and pipe force fully meet the standards, and ensure that the system stress and deformation under the entire working package are fully controllable, thus guaranteeing operational reliability.

[0007] Preferably, step 1 specifically includes: For the simulation analysis of the air intake system of the aero-engine test cabin, ANSYS Workbench was selected as the thermo-mechanical coupling simulation platform. The density, elastic modulus, Poisson's ratio, thermal conductivity and linear expansion coefficient of 316 stainless steel, S30408 ​​stainless steel and carbon steel in the full temperature range of -70℃ to 600℃ were defined to ensure the simulation authenticity of material properties at extreme temperatures. A three-level progressive thermo-solid coupled finite element model of the intake system was constructed sequentially, including a simplified model without expansion joints, a model with expansion joints, and a complete model with expansion joints extending to the fixed point of the pipeline. Temperature and pressure boundary conditions were set for low temperature of -70℃, high temperature of 550℃, and electric heating conditions of 600℃, respectively, to achieve a high-precision approximation of the deformation and stress of the entire system step by step. A full pipeline mechanical analysis model was established using CAESAR II software. The force and torque data of the inlet and outlet of the local heater and the interface of the cabin were extracted. The boundary conditions of the three-level progressive thermo-solid coupled finite element model of the air intake system were then used to calibrate the model, eliminate the bias of a single model, and improve the accuracy of the boundary conditions.

[0008] Preferably, step 1 further includes: For the simplified model without expansion joints, the branch pipelines are cut off to the expansion joint interface, and only the main body of the front compartment is retained. The basic deformation and thermal stress distribution law is solved, which effectively reduces the calculation scale of the model and quickly obtains the basic deformation and stress distribution law. In the model containing expansion joints, the equivalent stiffness method is used to simplify the bellows structure. The wall thickness, wave pitch and wave number parameters are set to restore the real stress characteristics of the compound tie rod type and the pressure balance type of the bend pipe expansion joint, accurately restore the stress behavior of the expansion joint, and improve the simulation accuracy of thermal displacement compensation. In the complete model including expansion joints and extending to the fixed point of the pipeline, fully constrained boundary conditions are set at the end of each branch pipeline. The calculation results of the pipe inlet force are compared with those of ANSYS and CAESAR II, so that the calculation deviation of the electric heater inlet force is less than 5%, ensuring the model boundary is real and reliable, and realizing high-precision prediction and calibration of the pipe inlet force.

[0009] Preferably, step 2 specifically includes: The core area of ​​the high-low temperature gas mixing section at the intersection of the main pipeline and the branch pipeline is extracted. The internal fluid domain is extracted by geometric filling. A three-dimensional unsteady flow thermal coupling numerical model is constructed to effectively capture the transient temperature changes in the mixing process and provide accurate boundaries for thermal stress analysis. By enabling the fluid energy equation, selecting the Realizable k-epsilon turbulence model and standard wall function, and setting the inlet and outlet boundaries of the gas mass flow at -70℃, 40℃, and 550℃, we can accurately simulate strong shear and backflow flow and improve the reliability of the mixing temperature field calculation. For two extreme temperature difference scenarios of 40℃ / -70℃ and 40℃ / 550℃, five sets of hot and cold gas flow ratio conditions were set up respectively. The mixing uniformity of temperature standard deviation was quantified, the flow guiding structure and the intersection angle of the pipeline were optimized, and the influence of the ratio on uniformity was revealed, effectively reducing local temperature gradient and thermal shock.

[0010] Preferably, step 3 specifically includes: Based on the full-system thermo-mechanical coupling simulation results, the air inlet and outlet of the electric heater, the connection between the main pipeline and the test chamber, and the junction of the hot and cold pipelines are identified as high-risk areas for temperature sudden changes. This effectively identifies the sources of thermal stress concentration and provides precise target locations for the design of the transition zone. For each location of abrupt temperature change, ten gradient transition zone length schemes of 100mm, 200mm, 300mm, 400mm, 500mm, 600mm, 700mm, 800mm, 900mm and 1000mm were set up to construct a complete length gradient sequence and systematically reveal the continuous influence of transition zone size on stress suppression. Thermo-structure interaction simulations were performed sequentially for each scheme, and the data of maximum pipe deformation, pipe nodal force and maximum equivalent stress were extracted. The quantitative correlation between transition zone length and thermal stress was established to provide data support for the selection of the optimal interval.

[0011] Preferably, step 3 further includes: Using the equivalent mechanical strength of 316 stainless steel (234 MPa) and S30408 ​​stainless steel (342 MPa) as the allowable thresholds for materials, the optimal transition zone length range at each temperature change location was screened to ensure that the selected transition zone length can reliably meet the material strength safety margin requirements. Based on the engineering installation space constraints and simulation data, 600mm to 700mm was determined as the optimal transition zone length range, so that the pipe wall temperature can smoothly and linearly transition within the transition zone, achieving the optimal balance between stable temperature transition and compact installation space. Based on the optimal transition zone length, the wall thickness, material grade, and gradient insulation structure of the temperature transition section are designed to eliminate stress concentration caused by steep temperature drops and rises, thus preventing thermal shock from damaging the integrity of the pipeline at the structural source.

[0012] Preferably, step 4 specifically includes: For compound tie rod type expansion joints and bend pressure balance type expansion joints, theoretical calculation models for axial stiffness and lateral stiffness of bellows wall thickness, wave number, wave pitch and tie rod structure are established respectively to ensure that stiffness calculation is based on evidence and to provide accurate theoretical benchmarks for subsequent simulations. In ANSYS, a detailed model of the expansion joint was completed. The spherical washer was set to be in non-separation contact, and the tie rod was set as a rigid body. The real force characteristics of the bellows expansion and contraction and the tie rod constraint were restored, and the force behavior of the expansion joint was realistically restored, thus improving the accuracy of thermal displacement simulation. By adjusting the elastic modulus, wall thickness, and wave number parameters of the bellows material, the stiffness of the expansion joint was adjusted to ensure that the simulated stiffness was consistent with the design target stiffness. The reference stiffness of the five core expansion joints was calibrated to ensure that the simulated stiffness was accurate and reliable, laying the foundation for the thermal stress control of the entire system.

[0013] Preferably, step 4 further includes: Six sets of gradient stiffness parameter schemes, both below and above the reference stiffness, were set up to conduct full-condition expansion joint stiffness simulations, ensuring that the simulation results cover extreme thermal displacement responses and avoiding the risk of extrapolating stiffness boundaries. Extract the force and thermal displacement data of the test chamber interface, electric heater inlet and outlet and each branch pipeline under different stiffnesses, establish the quantitative nonlinear mapping relationship between expansion joint stiffness and inlet force and thermal displacement, and realize the accurate quantitative characterization of the influence law of stiffness change on inlet force and thermal displacement. With the goal of achieving the required nozzle force and complete thermal displacement compensation, the optimal stiffness parameters of each expansion joint are determined, and the nonlinear coupling law of stiffness-nozzle force-thermal displacement is decoupled to ensure that the expansion joint can balance flexible compensation and controllable interface load under wide temperature range conditions.

[0014] Preferably, step 5 specifically includes: Based on the deformation distribution pattern of the entire pipeline, identify the high-risk pipe section locations with excessive pipe inlet force and excessive axial deformation, optimize the installation location and quantity of expansion joints, accurately locate weak links, and avoid blindly adding waste. In areas of concentrated deformation, additional double-rod type or bend-type pressure balance type expansion joints are installed as needed to form an expansion joint thermal displacement compensation system covering the entire pipeline, achieving coordinated absorption of thermal displacement throughout the pipeline with no compensation blind spots.

[0015] Preferably, step 6 specifically includes: An integrated multi-physics simulation environment covering all working conditions from -70℃ to 600℃ is used to conduct collaborative iterative simulation verification of parameters such as temperature uniformity of the mixing section, length of the temperature transition zone, and stiffness of the expansion joint, ensuring the global optimal solution under multi-parameter collaboration and avoiding local optimization conflicts. Ensure that the maximum equivalent stress of the pipeline is lower than the allowable material values ​​of 234MPa for 316 stainless steel and 342MPa for S30408 ​​stainless steel. At the same time, verify that the axial deformation of the system and the force at the interface pipe fully meet the design requirements, and ensure that the pipeline has no risk of structural failure throughout the entire working envelope. The system achieves coordinated control of offline mixing uniformity, stress concentration suppression in the transition zone, and precise compensation of expansion joints throughout the entire work package, ensuring the structural safety of the test chamber's air intake system and realizing full-chain suppression of thermal stress and long-term stable operation of the system.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention relates to a method for coordinated control of thermal stress in the intake system of a wide-temperature-range aero-engine test compartment. By constructing a three-level progressive thermo-solid coupled finite element model and combining it with pipeline mechanics software for bidirectional calibration, the method eliminates the boundary condition deviation between the local refined model and the simplified model of the entire pipeline, thereby achieving high-precision prediction of pipeline system deformation and thermal stress distribution under extreme wide temperature ranges and providing an accurate simulation basis for coordinated control of thermal stress.

[0017] 2. This method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment establishes a three-dimensional unsteady flow thermal coupling numerical model to systematically analyze the quantitative influence of the ratio of cold and hot gas flow rates on the mixing uniformity under extreme temperature difference scenarios. Based on this, the mixing structure and flow guidance measures are optimized to effectively reduce the local temperature gradient and periodic thermal shock at the interface between cold and hot gases, thereby suppressing the concentration of thermal stress in the mixing section from the source.

[0018] 3. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment is to set a gradient temperature transition zone at locations with abrupt temperature changes, such as the inlet and outlet of the electric heater and the connection between the compartment and the air intake, and to combine the gradient insulation structure to force a linear and smooth transition of the pipe wall temperature, thereby completely eliminating the steep temperature drop or rise caused by a temperature difference of hundreds of degrees Celsius over a short distance, and controlling the maximum equivalent stress within the allowable range of the material.

[0019] 4. This method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment establishes a refined stiffness model of a compound tie rod type and a bend-pipe pressure balance type expansion joint, decouples the nonlinear mapping law between the expansion joint stiffness and the pipe force and thermal displacement, and determines the optimal stiffness parameters accordingly, thereby achieving accurate compensation for the thermal displacement of the pipeline, ensuring that the pipe force at the equipment interface does not exceed the standard and that the coaxiality is controllable. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the workflow of a method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to the present invention. Figure 2 This is a schematic diagram of the method flow for the coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0022] Example 1, please refer to Figure 1 , Figure 2 This invention provides a technical solution: a method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment, comprising the following steps: Step 1: Construct a three-level progressive thermo-mechanical coupled finite element model of the air intake system. This involves sequentially building a simplified model without expansion joints, a model with expansion joints, and a complete model with expansion joints extending to the pipe fixing points. Pipeline mechanical analysis is combined to complete the pipe nodal force boundary calibration, achieving high-precision simulation of the entire system's deformation and stress. This ensures a high degree of consistency between the simulation boundaries and actual engineering conditions, improving the reliability of thermal stress prediction. For the simulation analysis of the air intake system of the aero-engine test compartment, ANSYS Workbench is selected as the thermo-mechanical coupled simulation platform. The model is defined as 316 stainless steel and S30408 ​​stainless steel. The density, elastic modulus, Poisson's ratio, thermal conductivity, and linear expansion coefficient of stainless steel and carbon steel in the full temperature range of -70℃ to 600℃ are calculated to ensure the simulation realism of material properties under extreme temperatures. A three-level progressive thermo-solid coupled finite element model of the intake system is constructed sequentially, including a simplified model without expansion joints, a model with expansion joints, and a complete model with expansion joints extending to the fixed point of the pipeline. Temperature and pressure boundary conditions are set for low temperature of -70℃, high temperature of 550℃, and electric heating conditions of 600℃, respectively, to achieve a progressively high-precision approximation of the deformation and stress of the entire system. A mechanical analysis model of the entire pipeline is established using CAESAR II software. The pipe force and torque data of the inlet and outlet of the local heater and the interface of the cabin are extracted and used to feed back and calibrate the boundary conditions of the three-level progressive thermo-solid coupled finite element model of the intake system, eliminating the bias of a single model and improving the accuracy of the boundary conditions. It should be noted that, based on the ANSYS Workbench thermo-mechanical coupling simulation platform, geometry cleanup, mesh generation, boundary condition application, and solution calculation were uniformly completed. For the three types of pipe materials used in the intake system—316 stainless steel, S30408 ​​stainless steel, and carbon steel—key thermophysical and mechanical property parameters were defined across the entire temperature range of -70℃ to 600℃, including density, elastic modulus, Poisson's ratio, thermal conductivity, and coefficient of linear expansion. All parameters were interpolated based on material handbooks and measured data to construct complete temperature dependence curves, ensuring that the simulation model accurately reflects the nonlinear thermodynamic behavior of the materials under extreme wide temperature conditions. Material parameters were entered into the simulation system in tabular form at each temperature point, and temperature interpolation calculations were automatically performed during the solution process. The first level is a simplified model without expansion joints, where each branch... The pipeline was cut off at the expansion joint interface, and only the main body of the front chamber was retained in the test chamber to obtain the basic deformation and thermal stress distribution. The second stage supplemented the simplified model with a compound tie rod type and a bend pressure balance type expansion joint structure. The equivalent stiffness method was used to complete the simplified modeling of the bellows, and core parameters such as bellows wall thickness, wave pitch, and wave number were set. The third stage extended each branch pipeline to the fixed point of the pipeline and set fully constrained boundary conditions at the terminal to restore the real constraint state. For each level of model, temperature and pressure boundary conditions of -70℃ low temperature, 550℃ high temperature, and 600℃ electric heating were applied respectively. Mesh refinement and thermo-structure coupling solution were completed in sequence to approximate the real response characteristics of the system step by step. In order to eliminate the boundary condition deviation of the single finite element model, CAESAR was used simultaneously. II. The software establishes a mechanical analysis model of the entire intake system pipeline, inputs the diameter, wall thickness, material, temperature and pressure parameters of the entire pipeline, completes the pipeline mechanical analysis under various working conditions, extracts the pipe force and torque data at the inlet and outlet of the local heater and the interface of the test chamber, and applies the extracted pipe force data as boundary conditions to the corresponding interface positions of the three-level finite element model. The calculation results of ANSYS and CAESAR II are compared to determine whether the deviation between the two meets the engineering accuracy requirements. Using the inlet pipe force of the electric heater as the calibration benchmark, the boundary condition settings of the finite element model are iteratively corrected to keep the calculation deviation within 5%. The three-level progressive model after calibration can be used for high-precision simulation and prediction of the deformation and thermal stress of the entire system. Furthermore, step 1 also includes: cutting off the branch pipeline to the expansion joint interface in the simplified model without expansion joints, retaining only the main body of the front compartment, completing the solution of the basic deformation and thermal stress distribution law, effectively reducing the model calculation scale, quickly obtaining the basic deformation and stress distribution law, using the equivalent stiffness method to simplify the bellows structure in the model with expansion joints, setting the wall thickness, wave pitch and wave number parameters, restoring the real force characteristics of the compound tie rod type and the pressure balance type expansion joint, accurately restoring the force behavior of the expansion joint, improving the simulation accuracy of thermal displacement compensation, and setting fully constrained boundary conditions at the end of each branch pipeline in the complete model with expansion joints and extending to the fixed point of the pipeline, comparing the pipe inlet force calculation results of ANSYS and CAESAR II, making the calculation deviation of the electric heater inlet pipe force less than 5%, ensuring the model boundary is real and reliable, and realizing high-precision prediction and calibration of pipe inlet force; It should be noted that in the simplified model construction stage without expansion joints, the geometric model of the intake system was first simplified by cutting each branch pipeline along the pipeline axis to the preset interface position of the expansion joint. The test chamber model only retained the main structure of the front chamber, discarding the rear chamber and auxiliary connecting parts. After completing the geometric cleanup, a hexahedral-dominated meshing strategy was adopted, setting at least three layers of mesh elements in the pipeline wall thickness direction to ensure the accuracy of the thermo-structure coupling solution. Four types of core working condition boundary conditions were applied to this simplified model, including a -70℃ low temperature condition, a 550℃ high temperature condition, and a 5 The 50℃ electric heating non-operating condition and the 600℃ electric heating operating condition were tested. Temperature boundaries were uniformly applied along the inner wall of the pipe for each condition, while pressure boundaries were set according to the design conditions. After solving, the axial deformation distribution, the location of the maximum equivalent stress, and the stress concentration factor of the pipe were extracted to obtain the distribution patterns of foundation deformation and thermal stress. In the construction of a refined model containing expansion joints, the equivalent stiffness method was used to simplify the bellows structure of the compound tie-rod type and the bend pressure balance type expansion joints. Specifically, the bellows was simplified into beam elements or beam elements with equivalent axial stiffness and lateral stiffness. The spring unit inputs core geometric parameters such as bellows wall thickness, single-wave pitch, total number of waves, and effective diameter based on the expansion joint design drawings. For compound tie-rod type expansion joints, an intermediate connecting pipe is set to connect two sets of bellows, and the tie rod structure is set as a rigid body with pre-tight displacement constraints applied. For bend-type pressure-balanced expansion joints, working bellows and balancing bellows are set on both sides of the bend, and spherical washers are installed at the ends of the tie rods for non-separating contact. By adjusting the equivalent elastic modulus of the bellows material, the deviation between the deformation of the simulation model under unit axial force and the theoretical calculation value is controlled within a certain range. Within 10%, the true stress characteristics and compensation behavior of the two types of expansion joints under thermal displacement are restored. In the complete model containing expansion joints and extending to the fixed point of the pipeline, each branch pipeline is extended along the actual laying path to the fixed support position of the pipeline. Fully constrained boundary conditions are set at the terminal nodes of each branch pipeline to restrict all degrees of freedom in six directions, restoring the true constraint state of the pipeline system at the ground anchor point. After completing the thermo-mechanical coupling solution of the complete model, the pipe force and torque components at the inlet and outlet flange positions of the electric heater are extracted. At the same time, the CAESAR II software is used to establish a full pipeline mechanical analysis model. The same pipe diameter, wall thickness, material temperature dependence curve and constraint point position are entered to complete the solution of each working condition. The pipe force calculated by ANSYS is compared with the CAESAR II results for each working condition. The vector deviation of the inlet pipe force of the electric heater is used as the calibration index. The expansion joint stiffness parameters and boundary layer mesh density in the finite element model are adjusted iteratively until the deviation between the two converges to within 5%, thus completing the model accuracy verification. Step 2: For the high / low temperature gas mixing section, optimize the cold / hot gas flow ratio and mixing structure based on fluid-thermal coupling simulation, quantify the mixing uniformity index, reduce the local temperature gradient and thermal shock in the pipeline, effectively suppress the thermal shock in the mixing section, and improve the downstream temperature uniformity. Extract the core area of ​​the high / low temperature gas mixing section where the main pipeline and branch pipelines intersect, extract the internal fluid domain through geometric filling, and construct a three-dimensional unsteady fluid-thermal coupling numerical model. This effectively captures the transient temperature changes during the mixing process, provides accurate boundaries for thermal stress analysis, initiates the fluid energy equation, and selects Realizable... Using the k-epsilon turbulence model and standard wall function, we set the inlet and pressure outlet boundaries of the gas mass flow at -70℃, 40℃, and 550℃ to accurately simulate strong shear and backflow flow, improving the reliability of the mixing temperature field calculation. For two extreme temperature difference scenarios of 40℃ / -70℃ and 40℃ / 550℃, we set five sets of hot and cold gas flow ratio conditions to quantify the mixing uniformity of temperature standard deviation, optimize the flow guide structure and pipe intersection angle, systematically reveal the influence of ratio on uniformity, and effectively reduce local temperature gradient and thermal shock. It should be noted that the core region of the high- and low-temperature gas mixing section at the junction of the main pipeline and the branch pipeline is selected as the analysis object. This region encompasses the fluid domain from the junction of the hot and cold gas inlets to the fully developed downstream section. The internal fluid space of the pipeline is extracted through geometric filling operations, and a three-dimensional unsteady flow-thermal coupling numerical model is constructed. The mesh generation adopts a mixture of polyhedral and hexahedral elements, with local refinement near the hot and cold gas interface and pipe wall to ensure the solution accuracy within the temperature boundary layer. The fluid domain model retains all geometric features inside the mixing section, including the branch pipeline connection angle, the inner wall of the main pipeline, and any possible flow guiding structures. The fluid energy equation is enabled during the simulation solution, and the Realizable turbulence model, suitable for strong shear flow and recirculation flow, is selected. The k-epsilon model employs standard wall functions for near-wall treatment. The gas medium is set as a compressible fluid following the ideal gas law, with density varying with temperature and pressure. Boundary conditions are specifically set as follows: the outlet is a pressure outlet boundary with a relative pressure of zero; each inlet is set as a mass flow inlet boundary. Mass flow rate and temperature parameters are defined for -70℃ cryogenic gas, 40℃ ambient gas, and 550℃ high-temperature gas, respectively. The time step for transient solutions is adaptively adjusted based on the Coulomb number to ensure accurate capture of the unsteady characteristics of the mixing process. Systematic simulation analyses are conducted for two extreme temperature difference mixing scenarios faced by the aero-engine test chamber air intake system: the first scenario involves the mixing of 40℃ ambient gas and -70℃ cryogenic gas, and the second scenario involves the mixing of 40℃ ambient gas and 550℃ high-temperature gas. Five different cold and hot gas flow ratios are set for each scenario, covering the complete ratio range from pure cold gas inflow to pure hot gas inflow. The total cold and hot gas flow rate remains constant across all scenarios. To ensure that the downstream transport capacity remains unchanged, each set of working conditions is iteratively solved until the residual curve converges and the inlet and outlet mass flow rate deviation is less than one-thousandth. Temperature field distribution data, velocity vector distribution, and turbulent kinetic energy distribution of different cross sections within the mixing section are extracted. The temperature standard deviation is used as a quantitative evaluation index for mixing uniformity, that is, the root mean square value of the difference between the temperature of each node on the target cross section and the average temperature of the cross section is calculated. The quantitative influence of the difference in flow rates of hot and cold gases on the temperature uniformity of the mixed gas downstream of the pipeline is analyzed and summarized. Unfavorable mixing ratio intervals that lead to excessive local temperature gradients or frequent thermal shocks are identified, providing data support for the structural optimization of the mixing section. Based on the temperature field and flow field distribution obtained from the simulation of the mixing characteristics under multiple working conditions, the structural optimization design of the mixing section is carried out in a targeted manner. The core objective of the optimization work is to reduce the local temperature gradient at the interface between hot and cold gases and suppress the periodic thermal shocks caused by turbulent mixing. Specific optimization measures include: adjusting the intersection angle of the branch pipeline and the main pipeline from a right angle to an obtuse angle downstream to reduce the momentum difference between hot and cold gases.A porous flow equalization plate or guide vane structure is added at an appropriate position downstream of the branch pipe inlet to guide the low temperature gas or high temperature gas to diffuse evenly towards the central area of ​​the main pipe. After the structural modification is completed, the fluid domain model is re-established and the flow-heat coupling simulation under the same boundary conditions is performed. The temperature standard deviation index before and after optimization under the same working condition is compared. It is verified that the optimized blending structure can reduce the temperature standard deviation of the downstream key section of the blending section by more than 70% while keeping the total pressure loss from increasing significantly. Finally, the optimal cold and hot gas flow ratio range under each extreme temperature difference scenario is determined to ensure that the temperature uniformity of the gas outlet of the blending section meets the temperature distribution requirements of the downstream pipeline and the test chamber inlet, thus eliminating the hidden danger of pipeline thermal stress concentration caused by local overcooling or overheating areas from the source. Step 3: A gradient transition zone of 100mm to 1000mm is established at locations of sudden temperature changes, such as the inlet and outlet of the local heater and the connection between the pipes and the test chamber. This determines the optimal range to suppress stress concentration caused by sudden temperature changes in the pipe wall, significantly alleviating localized stress concentration and enhancing structural safety. Based on the full-system thermo-mechanical coupling simulation results, the inlet and outlet of the electric heater, the connection between the main pipe and the test chamber, and the junction of hot and cold pipes are identified as high-risk areas for sudden temperature changes. This effectively identifies the sources of thermal stress concentration, providing precise target locations for the transition zone design. At the abrupt change location, ten gradient transition zone length schemes of 100mm, 200mm, 300mm, 400mm, 500mm, 600mm, 700mm, 800mm, 900mm and 1000mm were set to construct a complete length gradient sequence. The system revealed the continuous influence of transition zone size on stress suppression. Thermo-structure interaction simulation was completed under each scheme in sequence, and the maximum deformation of the pipeline, the pipe nodal force and the maximum equivalent stress data were extracted. The quantitative correlation law between transition zone length and thermal stress was established, providing data support for the selection of the optimal interval. It should be noted that, based on the three-level progressive thermo-solid coupled finite element model of the intake system after the nozzle force calibration was completed, the temperature and stress field distribution data of the entire system under the following conditions were extracted: -70℃ low temperature, 550℃ high temperature, and 600℃ electric heating. The inlet and outlet of the electric heater, the connection between the main pipeline and the test chamber, and the junction of the hot and cold pipelines were identified as the three core high-risk areas for temperature abrupt changes. For each location of temperature abrupt change, a gradient temperature transition zone was set from the temperature abrupt change section along the pipeline axis downstream. The length of the transition zone was designed according to a 1... Geometric models were established for ten gradient levels: 00mm, 200mm, 300mm, 400mm, 500mm, 600mm, 700mm, 800mm, 900mm, and 1000mm. Within each transition zone, the nominal pipe diameter and wall thickness remained constant. The pipe wall temperature boundary conditions between the start and end points of the transition zone were applied using linear interpolation based on the difference between the upstream abrupt temperature change and the downstream stable temperature. This ensured that only the transition zone length parameter changed between different length schemes, while other boundary conditions and mesh strategies remained consistent to eliminate other variables. To mitigate interference with simulation results, the thermo-mechanical coupling solution calculations were performed sequentially for ten transition zone length schemes. For each scheme, four types of core boundary conditions were applied: -70℃ low-temperature condition, 550℃ high-temperature condition, 550℃ electric heating non-operation condition, and 600℃ electric heating operation condition. After convergence, the maximum global deformation of the pipeline, the triaxial nozzle force components and resultant force at each temperature abrupt change interface, and the maximum equivalent stress value within the pipeline wall and its location were extracted from the post-processing results. The transition zone length was plotted as the abscissa, and the maximum equivalent stress value under the corresponding scheme was plotted as the ordinate. The vertical axis is used to establish a quantitative correlation curve between the transition zone length and thermal stress. Simulation results show that when the transition zone length is less than 400 mm, the pipe wall experiences a temperature jump of several hundred degrees Celsius over a short distance, and the maximum equivalent stress decreases significantly with the increase of the transition zone length. When the transition zone length increases to the range of 600 mm to 700 mm, the stress decrease trend gradually flattens out. When the transition zone length exceeds 700 mm, the marginal benefit of further increasing the length for stress reduction decreases significantly, while the increase in the total pipe length will bring greater axial thermal deformation and the risk of increased pipe nodal force. Furthermore, step 3 also includes: using the equivalent stress strength of 316 stainless steel (234 MPa) and S30408 ​​stainless steel (342 MPa) as allowable material thresholds, screening the optimal transition zone length range at each temperature abrupt change location to ensure that the selected transition zone length can reliably meet the material strength safety margin requirements. Combining engineering installation space constraints and simulation data, the optimal transition zone length range of 600 mm to 700 mm is determined to ensure that the pipe wall temperature transitions smoothly and linearly within the transition zone, achieving the optimal balance between stable temperature transition and compact installation space. Based on the optimal transition zone length, the wall thickness, material grade, and gradient insulation structure of the temperature transition section are designed to eliminate stress concentration caused by steep temperature drops and rises, thus preventing thermal shock from damaging the integrity of the pipeline from the structural root. It should be noted that the maximum equivalent stress under different transition zone length schemes at each temperature abrupt change location was compared item by item. The difference analysis between the maximum equivalent stress value calculated by each scheme and the allowable threshold of the corresponding material was performed to screen out all transition zone length schemes that met the stress compliance requirements. After excluding unfavorable length intervals with excessive stress, the edge length schemes that would cause a significant increase in nozzle force or excessive deformation were further eliminated by combining the nozzle force distribution and axial deformation data under each scheme. The candidate range of transition zone lengths that met the three constraints of stress, nozzle force, and deformation was initially determined. Taking into account the physical constraints of the actual engineering installation space of the intake system, including the actual distance from the electric heater outlet to the first downstream support, the on-site welding operation space at the connection between the pipe and the cabin, and the safety distance requirements between adjacent pipelines, the simulation data was matched and analyzed with the installation space constraints within the above candidate ranges, and finally, 600mm to 700mm is the optimal transition zone length range shared by all temperature abrupt change locations. This length range can achieve a smooth and linear transition of pipe wall temperature within the transition zone, control the maximum equivalent stress below the allowable threshold of the material, and meet the compactness requirements of on-site installation, avoiding interference with surrounding equipment due to excessively long transition zones. Based on the determined optimal transition zone length range, the engineering matching design of the temperature transition section is carried out. The pipe in the transition section maintains the same nominal diameter and wall thickness grade as the upstream main pipe. The material grade is selected as 316 stainless steel or S30408 ​​stainless steel, which is consistent with the main pipe, to avoid the introduction of additional stress by welding dissimilar steels. A gradient insulation structure is set on the outer wall of the transition section, and a multi-layer composite insulation material with a gradually changing thermal conductivity along the axial direction is used to make the equivalent thermal resistance of the insulation layer change linearly from the beginning to the end of the transition section, forcing the pipe wall temperature to transition linearly and smoothly along the axial direction, and completely eliminating local stress concentration caused by steep temperature drops or rises. Step 4: Establish stiffness models for compound tie rod type and bend pressure balance type expansion joints, decouple the nonlinear mapping between expansion joint stiffness and pipe force and thermal displacement, clarify the nonlinear coupling law of stiffness-pipe force-thermal displacement, achieve precise matching between expansion joint stiffness and thermal displacement, and improve compensation efficiency. Step 5: Based on the deformation distribution of the entire pipeline, optimize the installation position and number of expansion joints, and achieve complete thermal displacement compensation and precise control of pipe force through stiffness gradient adjustment, thereby eliminating the pipeline thermal displacement blind zone and reducing the risk of equipment interface load. Step 6: Integrate multi-physics simulation verification under full working conditions, coordinate and control the mixing uniformity, transition zone design, and expansion joint parameters to ensure that the maximum equivalent stress is lower than the allowable value of the material, so that the system deformation and pipe force fully meet the standards, and ensure that the system stress and deformation under the entire working package are fully controllable, thus guaranteeing operational reliability.

[0023] Example 2, as Figure 1 , Figure 2 As shown, based on Embodiment 1, the present invention provides a technical solution: Step 4 specifically includes: establishing theoretical calculation models for the axial stiffness and lateral stiffness of the bellows wall thickness, wave number, wave pitch, and tie rod structure for the compound tie rod type expansion joint and the bend pressure balance type expansion joint, respectively, to ensure that the stiffness calculation is based on evidence and to provide an accurate theoretical benchmark for subsequent simulation; completing the fine modeling of the expansion joint in ANSYS, setting non-separation contact at the spherical washer, setting the tie rod as a rigid body, restoring the real force characteristics of bellows expansion and contraction and tie rod constraint, and realistically restoring the force behavior of the expansion joint to improve the accuracy of thermal displacement simulation; completing the stiffness adjustment of the expansion joint by adjusting the elastic modulus, wall thickness, and wave number parameters of the bellows material to make the simulated stiffness consistent with the design target stiffness; calibrating the benchmark stiffness of the five core expansion joints to ensure that the simulated stiffness is accurate and reliable, laying the foundation for the thermal stress control of the entire system; It should be noted that for a compound tie-rod type expansion joint, its axial stiffness is composed of the equivalent stiffness of the two sets of tandem bellows and the bending stiffness of the intermediate pipe. The lateral stiffness depends on the bellows' wave number, effective diameter, and the constraint method of the tie rod. The theoretical model introduces a balance equation between the tie rod's preload displacement and the bellows' elastic restoring force to describe the tie rod's limiting effect on the bellows' axial elongation. For a bend-type pressure-balanced expansion joint, a pressure-thrust self-balancing equation is established between the working bellows and the balancing bellows. The product relationship between the effective area difference of the two bellows and the system's internal pressure is clarified, thereby determining the key geometric parameters of the balancing bellows. The bellows wall thickness directly affects the bellows' flexibility. The total compensation is determined by the wave number and the bearing capacity, while the wave pitch is negatively correlated with the single-wave stiffness. All the above geometric parameters are entered into the theoretical model based on the nominal values ​​in the design drawings. A shell element discrete bellows structure is used to accurately describe the bending and expansion deformation behavior of the expansion joint. A non-separating contact is set at the spherical gasket, allowing relative rotation but restricting normal separation to simulate the gasket's self-alignment and uniform load transfer function under thermal displacement. The tie rod is set as a rigid body, ignoring its own elastic deformation, and only participates in force transmission as a displacement constraint element, restoring the true force characteristics of bellows expansion and contraction and tie rod constraint. For the compound tie rod type expansion joint, a rigid intermediate pipe connection is established between the two sets of bellows, with the tie rods connected at both ends. The spherical washer is coupled to the bellows end plate, and a preload displacement is applied to simulate the initial compression during installation. For the bend pressure-balanced expansion joint, a working bellows is installed on the outside of the bend, and a balancing bellows is installed on the inside or opposite side. The tie rod passes through the two sets of bellows end plates and a preload is applied, so that the thrust generated by the balancing bellows cancels out the internal pressure thrust of the working bellows, thereby eliminating the additional load of the internal pressure on the fixed support. The deviation between the deformation of the simulation model under a unit axial force or a unit lateral force and the theoretical calculation value is controlled within 10%, ensuring that the simulation stiffness is consistent with the design target stiffness. During the debugging process, the geometric parameters of the bellows are kept unchanged, and the elastic modulus of the material is adjusted. As the main tuning variable, the bisection method is used to iteratively approximate the target stiffness value. If the single variable adjustment cannot converge, the wall thickness parameter is adjusted in a coordinated manner. For every 0.1 mm increase in wall thickness, the axial stiffness increases by about 8% to 12%. The adjustment of the wave number takes priority on the increase or decrease of the whole wave. Each increase or decrease of one wave corresponds to a stiffness change of about 5% to 10% of the original value. After the stiffness of a single expansion joint is debugged, the stiffness parameters after the debugging convergence are solidified into the simulation model. Following this process, the reference stiffness of the five core expansion joints in the intake system is calibrated in sequence, including three sets of compound tie rod type expansion joints and two sets of bend pressure balance type expansion joints, to ensure that the stiffness response of each expansion joint under independent loading conditions meets the design requirements. Furthermore, step 4 also includes: setting six sets of gradient stiffness parameter schemes with stiffness lower than and higher than the reference stiffness respectively, conducting full-condition expansion joint stiffness simulation, ensuring that the simulation results cover extreme thermal displacement response, avoiding the risk of stiffness boundary extrapolation, extracting the pipe force and thermal displacement data of the test chamber interface, electric heater inlet and outlet and each branch pipeline under different stiffnesses, establishing a quantitative nonlinear mapping relationship between expansion joint stiffness and pipe force and thermal displacement, realizing accurate quantitative characterization of the influence law of stiffness change on pipe force and thermal displacement, determining the optimal stiffness parameters of each expansion joint with the goal of pipe force meeting the standard and thermal displacement being fully compensated, decoupling the nonlinear coupling law of stiffness-pipe force-thermal displacement, and ensuring that the expansion joint takes into account both flexible compensation and controllable interface load under wide temperature range conditions; It should be noted that, based on the calibration of the five sets of core expansion joint reference stiffness, six sets of gradient stiffness parameter schemes, both lower and higher than the reference stiffness, were set up. The stiffness adjustment range was applied to each expansion joint simulation model in six gradient levels: 70%, 85%, 100%, 115%, 130%, and 145% of the reference stiffness. For each stiffness scheme, four types of core boundary conditions were applied: -70℃ low temperature condition, 550℃ high temperature condition, 550℃ electric heating non-operating condition, and 600℃ electric heating operating condition. The full-condition expansion joint stiffness simulation solution was completed sequentially to ensure that the simulation results cover the extreme thermal displacement response of the intake system within the entire operating envelope. The three-dimensional nozzle force components and resultant force at the test chamber interface, electric heater inlet and outlet, and each branch pipeline position under different stiffness schemes, as well as the axial and lateral thermal displacement data at each interface, were extracted. The expansion joint stiffness was used as the x-axis, and the corresponding nozzle force was used as the y-axis. Using thermal displacement as the ordinate, quantitative nonlinear mapping curves between expansion joint stiffness and nozzle force, and between expansion joint stiffness and thermal displacement, were established. Simulation results show that the nozzle force increases monotonically with the increase of expansion joint stiffness, while the thermal displacement compensation decreases monotonically with the increase of stiffness, indicating a clear nonlinear coupling relationship between the two. With the dual optimization objectives of ensuring that the nozzle force does not exceed the allowable load of the equipment interface and that the thermal displacement is fully compensated to the allowable deformation range of the pipe fixing point, stiffness parameter ranges that simultaneously satisfy both constraints were selected from various expansion joint stiffness gradient schemes. By cross-comparing the nozzle force compliance rate and residual thermal displacement under different stiffness schemes, the optimal stiffness parameters of each expansion joint were determined, enabling the expansion joint to absorb 8 to 15 mm of axial thermal deformation under extreme wide temperature range conditions while controlling the nozzle force within the design allowable range. Finally, the nonlinear coupling law of stiffness-nozzle force-thermal displacement was decoupled and clarified. Step 5 specifically includes: based on the deformation distribution pattern of the entire pipeline, identifying high-risk pipe sections with excessive pipe force and axial deformation, optimizing the installation position and number of expansion joints, accurately locating weak links, avoiding blind additions and waste, and adding duplex tie rod type or bend pressure balance type expansion joints as needed in areas with concentrated deformation to form an expansion joint thermal displacement compensation system covering the entire pipeline, achieving coordinated absorption of thermal displacement of the entire pipeline without compensation blind spots. Through expansion joint stiffness gradient adjustment and layout optimization, complete compensation of axial thermal displacement of 8 to 15 mm is achieved, the joint pipe force is reduced by more than 40%, the coaxiality deviation is less than 0.1 mm, ensuring reliable alignment of pipeline and equipment interfaces and stable operation. It should be noted that, firstly, the axial deformation cloud map and pipe force distribution data of the three-level progressive thermo-solid coupling model after step 4 calibration under the conditions of -70℃ low temperature, 550℃ high temperature, and 600℃ electric heating are extracted. High-risk pipe sections with excessive pipe force (exceeding the allowable load of the equipment by more than 15%) and excessive axial deformation (exceeding 20mm) are identified at the inlet and outlet flanges of the electric heater, the connection interface of the test chamber, and the first elbow downstream of the junction of the hot and cold pipes. For these high-risk locations, the coverage blind spots of the existing expansion joint layout are evaluated point by point, and pipe sections with deformation gradients exceeding 5mm / m are marked as candidate areas for adding expansion joints. For straight pipe sections with concentrated axial deformation and limited space, double-rod type expansion joints are preferred. Their two sets of tandem bellows, combined with a rigid intermediate connecting pipe, can absorb axial displacement within 15mm within a compact length of 200mm to 300mm. For pipe sections with lateral sway or angular rotation, bend pressure balance type expansion joints are selected, utilizing… The self-balancing structure of the working bellows and the balancing bellows eliminates the internal pressure thrust. By adding 1 to 2 sets of expansion joints to each high-risk pipe section, a thermal displacement compensation system covering the key nodes of the entire pipeline is formed, so that the thermal displacement of each pipe section falls within the effective compensation range of the expansion joints. After the expansion joints are added, the stiffness parameters of each expansion joint are uniformly adjusted according to the optimal stiffness range determined in step 4. For the double tie rod type expansion joint, the axial stiffness is controlled within the range of 2000N / mm to 3500N / mm, and for the bend pressure balancing type expansion joint, the lateral stiffness is controlled within the range of 800N / mm to 1500N / mm. Through the coordinated optimization of layout and stiffness, the axial thermal displacement of the entire pipeline under the four core working conditions is fully compensated to the range of 8 to 15mm. The pipe force of each equipment interface is reduced by more than 40% compared with that before optimization. At the same time, a laser alignment instrument is used to detect the coaxiality deviation of the test chamber interface flange to ensure that the deviation value is less than 0.1mm, which meets the requirements of equipment installation and operation. Step 6 specifically includes: integrating a multi-physics simulation environment covering all operating conditions from -70℃ to 600℃, conducting collaborative iterative simulation verification of parameters such as temperature uniformity of the mixing section, length of the temperature transition zone, and stiffness of the expansion joint, ensuring the global optimal solution under multi-parameter collaboration, avoiding local optimization conflicts, ensuring that the maximum equivalent stress of the pipeline is lower than the material allowable values ​​of 234MPa for 316 stainless steel and 342MPa for S30408 ​​stainless steel, verifying that the axial deformation of the system and the force at the interface pipe fully meet the design requirements, ensuring that the pipeline has no structural failure risk within the entire working envelope, completing the collaborative control of mixing uniformity, stress concentration suppression in the transition zone, and precise compensation of the expansion joint within the entire working envelope, ensuring the structural safety of the air intake system of the test chamber, and achieving full-chain suppression of thermal stress and long-term stable operation of the system; It should be noted that, firstly, the optimal hot and cold gas flow ratio range for the blending section and the optimized flow guiding structure parameters determined in step 2 are imported into the fluid-thermal coupling model to verify the uniformity index of reducing the downstream temperature standard deviation of the blending section by more than 70%. Simultaneously, the optimal transition zone length of 600mm to 700mm and the gradient insulation structure parameters determined in step 3, the optimal stiffness range of the expansion joints determined in step 5 (2000N / mm to 3500N / mm for the duplex tie rod type and 800N / mm to 1500N / mm for the bend pressure balance type), and the layout scheme of the added expansion joints are also introduced. The system was incorporated into a three-level progressive thermo-solid coupling model for comprehensive solution under all operating conditions. During the simulation, four core boundary conditions were applied sequentially: -70°C, 550°C, 550°C with electric heating off, and 600°C with electric heating on. This ensured that the calculation results covered the extreme thermodynamic responses within the entire operating envelope of the intake system. The comprehensive simulation results were extracted, and the maximum equivalent stress value within the pipe wall was checked item by item. Using the equivalent stress strength of 234 MPa for 316 stainless steel and 342 MPa for S30408 ​​stainless steel as the allowable material thresholds, the locations of each temperature abrupt change were confirmed. The maximum equivalent stress at the downstream key section of the mixing section is lower than the allowable limit of the corresponding material, with no risk of excessive local stress concentration. Simultaneously, the three-dimensional pipe force components and resultant force at the inlet and outlet flanges of the electric heater, the connection interface of the test chamber, and the downstream elbow position of the hot and cold pipe junction were extracted to verify that the pipe force at each interface meets the allowable load requirements of the equipment, and that the axial thermal displacement is fully compensated to the range of 8mm to 15mm. A laser alignment instrument was used to detect the coaxiality deviation of the test chamber interface flanges, confirming that the deviation value is less than 0.1mm, meeting the alignment accuracy requirements for equipment installation and operation; the optimized... The subsequent blending structure can reduce the temperature standard deviation of the downstream critical section of the blending section by more than 70%, eliminating the local overcooling or overheating areas caused by the mixing of hot and cold gases from the source; the 600mm to 700mm gradient transition zone makes the pipe wall temperature transition linearly and smoothly along the axial direction, completely suppressing the stress concentration caused by a sharp drop or rise in temperature; the coordinated optimization of the expansion joint layout and stiffness reduces the interface pipe force by more than 40%, and the axial thermal displacement is fully compensated. The above three measures have been verified by multi-physics field collaborative simulation under full working conditions, jointly ensuring the structural safety and operational reliability of the test chamber air intake system within the entire working envelope.

[0024] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment, characterized in that, Includes the following steps: Step 1: Construct a three-level progressive thermo-solid coupled finite element model of the intake system. Sequentially establish a simplified model without expansion joints, a model with expansion joints, and a complete model with expansion joints extending to the fixed point of the pipe. Combine pipe mechanical analysis to complete the pipe force boundary calibration. Step 2: For the high and low temperature gas mixing section, optimize the cold / hot gas flow ratio and mixing structure based on fluid-thermal coupling simulation, quantify the mixing uniformity index, and reduce the local temperature gradient and thermal shock in the pipeline. Step 3: Set a gradient transition zone of 100mm to 1000mm at the location of temperature abrupt change to determine the optimal range to suppress stress concentration caused by the sudden temperature change of the pipe wall. Step 4: Establish stiffness models for compound tie rod type and bend pressure balance type expansion joints, decouple the nonlinear mapping between expansion joint stiffness and pipe force and thermal displacement, and clarify the nonlinear coupling law of stiffness-pipe force-thermal displacement. Step 5: Based on the deformation distribution of the entire pipeline, optimize the installation position and number of expansion joints, and achieve complete thermal displacement compensation and precise control of pipe force through stiffness gradient adjustment; Step 6: Integrate multi-physics simulation verification under full working conditions to ensure that the maximum equivalent stress is lower than the allowable value of the material, so that the system deformation and nozzle force fully meet the standards.

2. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to claim 1, characterized in that: Step 1 specifically includes: For the simulation analysis of the air intake system of the aero-engine test compartment, ANSYS Workbench was selected as the thermo-mechanical coupling simulation platform. The density, elastic modulus, Poisson's ratio, thermal conductivity and linear expansion coefficient of 316 stainless steel, S30408 ​​stainless steel and carbon steel in the full temperature range of -70℃ to 600℃ were defined. A three-level progressive thermo-solid coupled finite element model of the intake system was constructed sequentially, including a simplified model without expansion joints, a model with expansion joints, and a complete model with expansion joints extending to the fixed point of the pipeline. Temperature and pressure boundary conditions were set for low temperature of -70℃, high temperature of 550℃, and electric heating conditions of 600℃, respectively. A full pipeline mechanical analysis model was established using CAESAR II software. The force and torque data of the inlet and outlet of the local heater and the interface of the cabin were extracted and used to feed back into the boundary conditions of the three-stage progressive thermo-solid coupled finite element model of the air intake system.

3. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to claim 2, characterized in that: Step 1 further includes: For the simplified model without expansion joints, the branch pipelines are cut off to the expansion joint interface, and only the main body of the front compartment is retained to complete the solution of the basic deformation and thermal stress distribution law. In the model containing expansion joints, the equivalent stiffness method is used to simplify the bellows structure. The wall thickness, wave pitch and wave number parameters are set to restore the real force characteristics of the compound tie rod type and the pressure balance type of the bend pipe expansion joint. In the complete model including expansion joints and extending to the fixed point of the pipeline, fully constrained boundary conditions are set at the end of each branch pipeline. The pipe inlet force calculation results of ANSYS and CAESAR II are compared to ensure that the calculation deviation of the electric heater inlet force is less than 5%.

4. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to claim 1, characterized in that: Step 2 specifically includes: The core area of ​​the high and low temperature gas mixing section at the intersection of the main pipeline and the branch pipeline is extracted, and the internal fluid domain is extracted by geometric filling to construct a three-dimensional unsteady flow thermal coupling numerical model. The fluid energy equation is activated, and the Realizable k-epsilon turbulence model and standard wall function are selected. The mass flow inlet and pressure outlet boundaries of the gas at -70℃, 40℃, and 550℃ are set. For two extreme temperature difference scenarios of 40℃ / -70℃ and 40℃ / 550℃, five sets of hot and cold gas flow ratio conditions were set up to quantify the mixing uniformity of temperature standard deviation and optimize the intersection angle of the flow guide structure and the pipeline.

5. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to claim 1, characterized in that: Step 3 specifically includes: Based on the full-system thermo-mechanical coupling simulation results, the air inlet and outlet of the electric heater, the connection between the main pipeline and the test chamber, and the junction of the hot and cold pipelines are identified as high-risk areas for temperature sudden changes. For each location of a temperature abrupt change, ten gradient transition zone length schemes of 100mm, 200mm, 300mm, 400mm, 500mm, 600mm, 700mm, 800mm, 900mm and 1000mm are set respectively. Thermo-structure interaction simulations were performed sequentially for each scheme, and the data of maximum pipe deformation, pipe nodal force and maximum equivalent stress were extracted to establish a quantitative correlation between transition zone length and thermal stress.

6. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to claim 5, characterized in that: Step 3 also includes: Using the equivalent mechanical strength of 316 stainless steel (234 MPa) and S30408 ​​stainless steel (342 MPa) as the allowable thresholds for materials, the optimal transition zone length range at each temperature abrupt change location was screened. Based on the engineering installation space constraints and simulation data, 600mm to 700mm was determined as the optimal transition zone length range to ensure a smooth and linear transition of pipe wall temperature within the transition zone. Based on the optimal transition zone length, the wall thickness, material grade, and gradient insulation structure of the temperature transition section are designed to eliminate stress concentration caused by steep temperature drops and rises.

7. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to claim 1, characterized in that: Step 4 specifically includes: For compound tie rod type expansion joints and bend pressure balance type expansion joints, theoretical calculation models for the axial stiffness and lateral stiffness of bellows wall thickness, wave number, wave pitch and tie rod structure are established respectively. In ANSYS, a detailed model of the expansion joint was completed. The spherical washer was set to be in non-separation contact, and the tie rod was set as a rigid body to restore the real force characteristics of the bellows expansion and contraction and the tie rod constraint. By adjusting the elastic modulus, wall thickness, and wave number parameters of the bellows material, the stiffness of the expansion joint was adjusted to ensure that the simulated stiffness was consistent with the design target stiffness, and the reference stiffness of the five sets of core expansion joints was calibrated.

8. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to claim 7, characterized in that: Step 4 also includes: Six sets of gradient stiffness parameter schemes, one below the reference stiffness and the other above the reference stiffness, were set up to conduct full-condition expansion joint stiffness simulation. Extract the force and thermal displacement data of the test chamber interface, electric heater inlet and outlet and each branch pipeline under different stiffnesses, and establish a quantitative nonlinear mapping relationship between expansion joint stiffness and inlet force and thermal displacement. With the goal of achieving the required pipe force and complete thermal displacement compensation, the optimal stiffness parameters of each expansion joint are determined, and the nonlinear coupling law of stiffness-pipe force-thermal displacement is decoupled.

9. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to claim 1, characterized in that: Step 5 specifically includes: Based on the deformation distribution pattern of the entire pipeline, identify high-risk pipe sections with excessive pipe inlet force and excessive axial deformation, and optimize the installation position and number of expansion joints. In areas of concentrated deformation, additional double-strut or bend-type pressure-balanced expansion joints are installed as needed to form an expansion joint thermal displacement compensation system covering the entire pipeline.

10. The method for coordinated control of thermal stress in the air intake system of a wide-temperature-range aero-engine test compartment according to claim 1, characterized in that: Step 6 specifically includes: An integrated multiphysics simulation environment covering all working conditions from -70℃ to 600℃ was used to conduct collaborative iterative simulation verification of the temperature uniformity of the mixing section, the length of the temperature transition zone, and the stiffness parameters of the expansion joint. Ensure that the maximum equivalent stress of the pipeline is lower than the allowable material values ​​of 234MPa for 316 stainless steel and 342MPa for S30408 ​​stainless steel, and at the same time verify that the axial deformation of the system and the force at the interface pipe fully meet the design requirements. The system achieves coordinated control of offline mixing uniformity, stress concentration suppression in the transition zone, and precise compensation of expansion joints throughout the entire work package, ensuring the structural safety of the test chamber's air intake system.

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