Design method of aero-engine intake total pressure distortion generator based on porous media model

Abstract

The present invention discloses a method for designing an aero-engine intake total pressure distortion generator based on a porous medium model. First, the distortion generator is divided into a flow field calculation domain and a grid. The flow field calculation domain includes a common fluid calculation domain and a porous medium calculation domain. Then, the drag coefficient of each porous medium calculation domain subdomain is determined. Through experiments or porous plate flow field numerical simulation methods, the distortion plate design parameters with the same loss characteristics corresponding to the drag coefficient of each porous medium calculation domain subdomain are determined. Then, the distortion plate design parameters are substituted into the distortion generator to obtain the distortion generator body. Finally, the reliability of the distortion generator body is verified, and the design is completed if it meets the requirements. The present invention solves the high cost problem of obtaining a specific distortion spectrum only through repeated experiments. It has strong applicability and regularity and can be designed for any spectrum, greatly reducing the design cost.

Description

Technical Field

[0001] The present invention relates to the field of aero-engines, and in particular to a design method for an aero-engine intake total pressure distortion generator based on a porous medium model. Background Art

[0002] Under any flight condition, the inlet airflow at an aircraft's engine is often not uniform, but rather exhibits varying distortion patterns. These distortion patterns can lead to varying performance degradation and even potential accidents. Therefore, to study the impact of intake distortion on aircraft engines, experimental setups that simulate the distortion patterns and intensity under real-world operating conditions are essential in aircraft engine development. To generate a steady-state total pressure distortion pattern at the compressor / engine inlet that meets test requirements, the traditional approach is to place wire meshes of varying specifications at different locations. When airflow passes through these wire meshes, the total pressure loss at each location varies. Therefore, adjusting the wire mesh specifications can be used to adjust the total pressure distribution. Commonly used circumferential steady-state total pressure distortion generators generally employ this design approach. However, if the target distortion profile has a narrow range, high intensity, and includes both radial and circumferential distortion, employing the aforementioned conventional wire mesh distortion generator design inevitably requires placing wire meshes of varying specifications and shapes within a relatively small area. This method will face the following problems: 1) Currently, common metal meshes are all woven meshes, and it is very difficult to cut them into a toroidal form, especially when the toroidal width is small, it is easy to deform and fall apart, and the processing accuracy cannot be guaranteed. 2) In order to ensure that the metal mesh does not fall apart after cutting, it needs to be edged. However, the width of the edge is obviously large relative to the width of the metal mesh annulus. The flow loss caused by the edge will be significantly greater than the flow loss caused by the metal mesh. Moreover, the edges of adjacent toroidal metal meshes combined together will cause greater blockage to the airflow and generate greater flow loss, resulting in a large deviation between the total pressure value at the connection and the design target. 3) In order to ensure the structural strength of the distortion generator, the metal mesh distortion generator often requires the design of auxiliary brackets and base meshes. However, the existence of such accessories will inevitably have a corresponding impact on the flow field, thereby increasing the difficulty of the aerodynamic design of the distortion generator. 4) For this type of distortion generator, the only design method currently available is the trial and error method, and the CFD numerical simulation method cannot be used for preliminary design, which requires a lot of time and cost. Based on the above analysis, it is obviously inappropriate to use a distortion generator in the form of a wire mesh when time and cost are limited. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a design method of an aircraft engine intake total pressure distortion generator based on a porous medium model in view of the defects involved in the background technology.

[0004] The present invention adopts the following technical solutions to solve the above technical problems:

[0005] The design method of an aircraft engine intake total pressure distortion generator based on a porous media model includes the following steps:

[0006] Step 1) dividing the flow field calculation domain and the grid according to the axial position relationship between the distortion generator and the target section for generating the distortion map, and the position distribution of the total pressure measurement points on the target section;

[0007] The flow field calculation domain includes a common fluid calculation domain and a porous medium calculation domain. The porous medium calculation domain adds a source term to the momentum equation in the flow field control equation to simulate the obstruction of the distortion generator on the airflow, and its size is the same as the design size of the distortion generator. The common fluid calculation domain includes a target cross section, which is used to calculate the development of the airflow under different working conditions to obtain a calculation map of the target interface. The inlet of the common fluid calculation domain and the porous medium calculation domain, as well as the outlet of the common fluid calculation domain and the target cross section, are kept at a distance to ensure the full development of the flow field.

[0008] The porous medium calculation domain is divided into several subdomains, and parameters are set for each subdomain separately; the subdomain division method refers to the measurement point positions of the target section, and the number of subdomains is greater than or equal to the number of measurement points to ensure that the total pressure of each measurement point in the target section has an independent control method;

[0009] Step 2) Determine the resistance coefficient of each porous medium calculation domain subdomain so that the flow field conditions meet the design requirements and the calculated total pressure data of each measuring point falls within the allowable deviation band of its preset target value;

[0010] Step 3) By using experiments or numerical simulation of the porous plate flow field, combined with fast interpolation, the design parameters of the distortion plate with the same loss characteristics corresponding to the resistance coefficient of each porous medium calculation domain subdomain are determined;

[0011] Step 4) Substitute the design parameters of the distortion plate with the same loss characteristics corresponding to the resistance coefficient of each porous medium calculation domain subdomain into the distortion generator to obtain the distortion generator body;

[0012] In step 5), the reliability of the distortion generator body is verified using CFD numerical simulation or experimental measurement. If the reliability is not satisfied, the design parameters of the distortion plate with the same loss characteristics corresponding to the resistance coefficient of each porous medium calculation domain subdomain are fine-tuned, and the process is skipped to step 4). If the reliability is satisfied, the design is completed.

[0013] As a further optimization scheme of the design method of the aircraft engine intake total pressure distortion generator based on the porous medium model of the present invention, the model formula of the porous medium calculation domain in step 1) is:

[0014]

[0015] Where S i is the source term of the momentum equation of the porous medium (i=x,y,z), |u| is the fluid velocity, D u is the viscous drag coefficient, C u is the inertial resistance coefficient, μ is the fluid viscosity coefficient, ρ is the fluid density, and the negative momentum source term causes a pressure drop in the porous media calculation domain. The pressure difference between the outlet and the inlet is proportional to the fluid velocity or the square of the velocity.

[0016] As a further optimization scheme of the design method of the aircraft engine intake total pressure distortion generator based on the porous medium model of the present invention, the design parameters of the distortion plate in step 3) include the pore size and the pore spacing;

[0017] The total pressure drop after the fluid flows through the distortion plate is related to the air flow velocity after the distortion plate in a quadratic polynomial relationship: ΔP=a1u+a2u 2 , where ΔP is the total pressure drop of the fluid flowing through the porous medium, u is the fluid flow rate, and a1 and a2 are fitting coefficients; Δn is the thickness of the porous medium / distortion generator, then:

[0018] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0019] 1. Through the porous media model, the obstruction effect of the distortion generator on the incoming flow is simplified to a source term, eliminating the need to model and mesh the complex distortion generator. This greatly reduces the mesh size and calculation time, significantly lowering the iterative cost of the early design.

[0020] 2. Targeted testing, using CFD to determine the target loss characteristics, allows for targeted experimentation to identify the design parameters for the target distortion plate. This significantly reduces testing time and processing costs compared to trial-and-error iterations. Furthermore, when full-scale model testing is inconvenient, this method allows for the identification of specific distortion generator design parameters, which can then be arranged in a specific design. This further reduces costs and improves the accuracy of each test piece.

[0021] 3. Compared with splicing different distortion meshes together, this design method has higher strength and service life: it only needs to be processed on a whole piece of material, according to the designed porous medium domain partitioning method, and the distortion plate form with different design parameters in each area can be processed.

[0022] 4. This method has strong engineering applicability. It does not require excessive analysis of the flow field. It only needs to design the distortion generator based on the target map. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic flow diagram of the present invention;

[0024] Figure 2 is a schematic diagram of the porous medium model of the present invention;

[0025] Figure 3 is a schematic diagram of a distortion generator in the present invention;

[0026] Figure 4 It is a schematic diagram of the porosity-inertial resistance coefficient relationship curve in the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings:

[0028] The present invention can be implemented in many different forms and should not be considered to be limited to the embodiments described herein. On the contrary, these embodiments are provided to make this disclosure thorough and complete and will fully convey the scope of the invention to those skilled in the art. In the accompanying drawings, components are enlarged for clarity.

[0029] Reference Figure 1 The present invention discloses a design method of an aero-engine intake total pressure distortion generator based on a porous medium model, comprising the following steps:

[0030] Step 1) dividing the flow field calculation domain and the grid according to the axial position relationship between the distortion generator and the target section for generating the distortion map, and the position distribution of the total pressure measurement points on the target section;

[0031] The flow field calculation domain includes a common fluid calculation domain and a porous medium calculation domain. The porous medium calculation domain adds a source term to the momentum equation in the flow field control equation to simulate the obstruction of the distortion generator on the airflow, and its size is the same as the design size of the distortion generator. The common fluid calculation domain includes a target cross section, which is used to calculate the development of the airflow under different working conditions to obtain a calculation map of the target interface. The inlet of the common fluid calculation domain and the porous medium calculation domain, as well as the outlet of the common fluid calculation domain and the target cross section, are kept at a distance to ensure the full development of the flow field.

[0032] The porous medium calculation domain is divided into several subdomains, and parameters are set for each subdomain separately; the subdomain division method refers to the measurement point position of the target section, and the number of subdomains is greater than or equal to the number of measurement points to ensure that the total pressure of each measurement point of the target section has an independent control method.

[0033] Figure 2 A porous medium model is proposed. The total pressure measurement plane is a torus, which is divided into five equal-area toruses along the radial direction. On the area bisector of each torus, a measuring point is arranged every 15° along the circumference, for a total of 120 measuring points. The distortion generator installation plane is also divided into 5*24 sectors, each corresponding to a total pressure measuring point, to ensure that the modification of the loss characteristic parameters of a sector can directly affect the corresponding total pressure measuring point data.

[0034] Step 2) Determine the resistance coefficient of each porous medium calculation domain subdomain so that the flow field conditions meet the design requirements and the calculated total pressure data of each measuring point falls within the allowable deviation band of its preset target value;

[0035] After completing the meshing and setting the initial values ​​of the flow field and porous media calculation domain subdomain parameters (to 0, i.e. no obstruction), it is necessary to find the resistance coefficient of each corresponding subdomain through two iterative processes: the target condition search process for changing the incoming flow condition and the loss characteristic search process for changing the resistance coefficient of each subdomain of the porous media calculation domain (see the appendix for details). Figure 1 ).

[0036] Since the task often requires the distortion under a certain working condition, it is necessary to first adjust the flow field to the target working condition, such as the Mach number, flow rate, speed, etc. at a certain location. Then compare the calculated value and target value of each total pressure measuring point. If the deviation is greater than the design requirement, the resistance coefficient of the porous medium calculation domain subdomain at the corresponding position can be modified according to the needs, and the calculation and iteration can continue. The result of the final iterative convergence should be: the flow field working condition meets the design requirements, and the calculated value of the total pressure data at each measuring point falls within the allowable deviation band of its preset target value. Under this result, the setting parameters of each porous medium calculation domain will be obtained as the search target for subsequent orifice plate characteristic tests.

[0037] Step 3) By using experiments or numerical simulation of the porous plate flow field, combined with fast interpolation, the design parameters of the distortion plate with the same loss characteristics corresponding to the resistance coefficient of each porous medium calculation domain subdomain are determined;

[0038] Due to the variety of designs of porous plates, it is necessary to find the relationship between design parameters and loss characteristics. By interpolating empirical relationships, we can find the design target of the distorted plate in a targeted manner. The loss characteristics of distorted plates with different design parameters are found through experiments as an example:

[0039] The test bench should be able to measure the total pressure and static pressure of the airflow after passing through the distortion plate (the distance between the measuring point and the test piece is at least twice the diameter of the test piece), and the distortion plate test piece is a uniform orifice plate with different design parameters. The design parameters of the orifice plate are the aperture (the size of the circular hole) and the hole spacing (the distance between the centers of adjacent circular holes). Its thickness is the same as the thickness of the calculation domain of the porous medium model. According to the previous experimental experience of the present invention, the loss characteristics of the distortion plate are strongly correlated with the porosity, but not with the specific design of the distortion plate. The porosity is defined as the ratio of the gas flow area of ​​the distortion plate to the area of ​​the entire distortion plate. That is, a porosity of 1 means there is no distortion plate, and a porosity of 0 means a solid plate without air flow. By adjusting the test bench operating conditions, the total pressure and static pressure after the orifice plate can be measured through the test bench, and then the velocity-total pressure loss characteristic line of each distortion plate can be obtained. This characteristic line is a quadratic function curve, and each uniform distortion plate with a porosity corresponds to a unique characteristic line. Ultimately, the loss characteristics that satisfy the resistance coefficients of each subdomain of the corresponding porous medium calculation domain can be found, and the design parameters of the distortion plate with these characteristics can be recorded for the final full-scale distortion generator design.

[0040] In step 4), the division method of the computational domain of each porous medium at the installation location of the distortion generator is determined in step 1), the resistance coefficient of each porous medium computational domain subdomain is determined in step 2), and the design parameters of the distortion plate with the same loss characteristics corresponding to each resistance coefficient are found in step 3). The design parameters of the distortion plate with the same loss characteristics corresponding to the resistance coefficient of each porous medium computational domain subdomain are substituted into the distortion generator to obtain the distortion generator body, as shown in FIG. Figure 3 shown.

[0041] In step 5), the reliability of the distortion generator body is verified using CFD numerical simulation or experimental measurement. If the reliability is not satisfied, the design parameters of the distortion plate with the same loss characteristics corresponding to the resistance coefficient of each porous medium calculation domain subdomain are fine-tuned, and the process is skipped to step 4). If the reliability is satisfied, the design is completed.

[0042] The model of the porous media computational domain combines a flow resistance based on empirical assumptions in the region defined as the porous medium. The solid structure in the flow region is considered as a distributed resistance attached to the fluid. This resistance is added to the momentum governing equation in the form of a source term. The formula is:

[0043]

[0044] Where S iis the source term of the momentum equation of the porous medium (i = x, y, z), |u| is the fluid velocity, D is the coefficient matrix of the viscous resistance term, C is the coefficient matrix of the inertial loss term, μ is the fluid viscosity coefficient, ρ is the fluid density, and the negative momentum source term causes a pressure drop in the porous medium calculation domain. The pressure difference between the outlet and the inlet is proportional to the fluid velocity or the square of the velocity.

[0045] For porous media with simple internal structure and uniform structure distribution, substitute the diagonal items in the coefficient matrices D and C into D u and C u , and the other terms are zero, then:

[0046]

[0047] Where D u is the viscous drag coefficient, C u is the inertial drag coefficient. These two terms are the parameters input into the porous media model. In distortion generator design, the primary consideration is axial resistance, i.e., resistance in the direction of airflow. Therefore, only the drag coefficient in the direction of airflow needs to be adjusted. To reduce design variables, the viscous drag coefficient can be ignored, and only the inertial drag coefficient can be input. This is due to the fact that, during the application of this invention, it was found that distortion generators are generally thin, contributing little to frictional resistance; resistance is primarily generated by the collision and mixing of the airflow with the distortion generator. Furthermore, because the inertial drag coefficient is quadratically related to velocity, its contribution to flow resistance is more pronounced.

[0048] In step 3), the total pressure drop generated after the fluid flows through the distortion plate is in a quadratic polynomial relationship with the air flow velocity after the distortion plate:

[0049] ΔP=a1u+a2u 2 (1)

[0050] Where ΔP is the total pressure drop of the fluid flowing through the porous medium, u is the fluid flow rate, and a1 and a2 are the fitting coefficients of the quadratic polynomial equation.

[0051] The source term of the momentum equation is the total pressure drop per unit length of the porous medium, which has the following relationship:

[0052]

[0053] Where Δn is the thickness of the porous medium / distortion generator. Combining equations (1) and (2), the calculation formulas for the viscous drag coefficient and the inertial drag coefficient can be obtained:

[0054]

[0055]

[0056] Equations (3) and (4) link the resistance coefficient of the porous medium calculation domain subdomain with the total pressure loss characteristics of the distortion generator (first-order coefficient, second-order coefficient). Therefore, the core of step 3) is to find the total pressure loss characteristics corresponding to the resistance coefficient determined in step 2).

[0057] Since only the inertial drag coefficient was considered during the design phase of step 2), the quadratic coefficient in the distortion generator loss characteristics should also be emphasized in step 3). Previous experiments based on the present invention have shown that when the porosity of the test group is large, the quadratic coefficient and porosity have an exponential relationship; when the porosity of the test group is evenly distributed between 0 and 1, the overall relationship is a power relationship (the quadratic coefficient can also be converted into the inertial drag coefficient first, and the fitting rules are the same, see [1]). Figure 4 Therefore, during the test, we can first design test pieces with different porosities to obtain a fitting relationship, and then interpolate according to the target to find the target porosity and further clarify the target design parameters.

[0058] Since the design process only considers the inertial drag coefficient and the quadratic coefficient, the design parameters should be back-substituted into the porous media model after the design is completed, and a full-scale CFD simulation should be performed to verify the deviation from the porous media model design results. Based on the previous design experience of this invention, the deviation between the two is small, so this design method is suitable. However, based on the preliminary design model, the design parameters can still be fine-tuned according to CFD or test results.

[0059] This invention is applicable to the design of any total pressure distortion generator, not just for aircraft engine inlet flow distortion or cylindrical internal flow pipe design. However, attention should be paid to the degree of correlation between the porous medium calculation domain and each measuring point. That is, each change in the porous medium calculation domain parameters should significantly affect the degree of total pressure loss at a specific measuring point. Therefore, it is only necessary to focus on the porous medium calculation domain parameter settings at the distortion plate installation location and the total pressure data at the measuring point of the target cross section, eliminating the need for excessive analysis of the distortion development in the flow field, greatly reducing the number of dimensions that need to be considered in the design.

[0060] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such, will not be interpreted in an idealized or overly formal sense.

[0061] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A design method for an aircraft engine intake total pressure distortion generator based on a porous media model, characterized in that: The following steps are involved: Step 1) dividing the flow field calculation domain and the grid according to the axial position relationship between the distortion generator and the target section for generating the distortion map, and the position distribution of the total pressure measurement points on the target section; The flow field calculation domain includes a common fluid calculation domain and a porous medium calculation domain. The porous medium calculation domain adds a source term to the momentum equation in the flow field control equation to simulate the obstruction of the distortion generator on the airflow, and its size is the same as the design size of the distortion generator. The common fluid calculation domain includes a target cross section, which is used to calculate the development of the airflow under different working conditions to obtain a calculation map of the target interface. The inlet of the common fluid calculation domain and the porous medium calculation domain, as well as the outlet of the common fluid calculation domain and the target cross section, are kept at a distance to ensure the full development of the flow field. The porous medium calculation domain is divided into several subdomains, and parameters are set for each subdomain separately; the subdomain division method refers to the measurement point positions of the target section, and the number of subdomains is greater than or equal to the number of measurement points to ensure that the total pressure of each measurement point in the target section has an independent control method; The model formula of the porous medium calculation domain is: Where S i is the source term of the porous medium momentum equation, i=x,y,z; |u| is the fluid velocity, D u is the viscous drag coefficient, C u is the inertial resistance coefficient, μ is the fluid viscosity coefficient, ρ is the fluid density, the negative momentum source term causes a pressure drop in the porous media calculation domain, and the pressure difference between the outlet and the inlet is proportional to the fluid velocity or the square of the velocity; Step 2) Determine the resistance coefficient of each porous medium calculation domain subdomain so that the flow field conditions meet the design requirements and the calculated total pressure data of each measuring point falls within the allowable deviation band of its preset target value; Step 3) By using experiments or numerical simulation of the porous plate flow field, combined with fast interpolation, the design parameters of the distortion plate with the same loss characteristics corresponding to the resistance coefficient of each porous medium calculation domain subdomain are determined; Step 4) Substitute the design parameters of the distortion plate with the same loss characteristics corresponding to the resistance coefficient of each porous medium calculation domain subdomain into the distortion generator to obtain the distortion generator body; In step 5), the reliability of the distortion generator body is verified using CFD numerical simulation or experimental measurement. If the reliability is not satisfied, the design parameters of the distortion plate with the same loss characteristics corresponding to the resistance coefficient of each porous medium calculation domain subdomain are fine-tuned, and the process is skipped to step 4). If the reliability is satisfied, the design is completed.

2. The method for designing an aircraft engine intake total pressure distortion generator based on a porous media model according to claim 1, characterized in that: The design parameters of the distortion plate in step 3) include the aperture and the hole spacing; The total pressure drop after the fluid flows through the distortion plate is related to the air flow velocity after the distortion plate in a quadratic polynomial relationship: ΔP=a1u+a2u 2 , where ΔP is the total pressure drop of the fluid flowing through the porous medium, u is the fluid flow rate, and a1 and a2 are fitting coefficients; Δn is the thickness of the porous medium / distortion generator, then:

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