A method for determining the size of a test model for a pulse wind tunnel

Abstract

This invention provides a method for determining the size of a pulse wind tunnel test model, comprising: determining the flow field of the nozzle and test section using numerical simulation to obtain a uniform flow field region S1 in the wind tunnel; then calibrating the uniform flow field region S2 of the nozzle and test section using a cross-shaped frame, comparing the sizes of the two uniform flow fields S1 and S2, and selecting the smaller uniform flow field region S0 as the uniform flow field region S0; scaling down the selected model under the condition of maximum test angle, with the maximum projected area M1 of the model in the direction perpendicular to the airflow occupying 60% to 65% of the cross-sectional area of ​​the uniform flow field S0; integrating the scaled-down model with the nozzle and test section into a single model, numerically simulating the entire flow process under the condition of maximum angle of attack and / or sideslip angle test angle, redetermining the model scale based on the model installation position, the shock wave position at the leading edge of the model, and the coverage of the uniform flow field, and determining the upper limit of the model length through the effective test time and the velocity of the flow field in the test section.

Description

Technical Field

[0001] This invention belongs to the field of wind tunnel model design, and specifically relates to a method for determining the size of a pulse wind tunnel test model. Background Technology

[0002] Scaled-down models in pulsed wind tunnels play a crucial role in aerodynamic research and the design and development of aircraft. Compared to full-scale models or physical tests, scaled-down models are less expensive, allowing for more iterations and optimizations during the design and testing phases. Scaled-down models can be manufactured and tested rapidly, accelerating the process from concept to practical application. Using scaled-down models in the early design stages avoids potential damage to full-scale prototypes, reducing risk. Scaled-down models are designed based on similarity principles, ensuring similarity in geometric and hydrodynamic properties to the actual object. Wind tunnel testing can measure crucial data such as aerodynamic forces, pressure distribution, and flow field characteristics on the model, providing a basis for design. With advancements in technology, such as high-precision manufacturing and numerical simulation, the accuracy and practicality of scaled-down models continue to improve.

[0003] However, scaled-down models cannot fully replicate the Reynolds number of full-scale models, affecting the viscous properties of the flow field and potentially leading to discrepancies with actual flight conditions. Reducing the model size may affect the simulation of certain details, such as surface roughness and local geometric features. The finite size of wind tunnels leads to the influence of the boundary layer on the model, requiring design and experimental techniques to mitigate this effect. Scaled-down models may struggle to simulate certain complex dynamic effects, such as flutter and turbulent transitions.

[0004] Ground testing of models is a crucial step in the design and testing of aircraft. The larger the model, the closer its proportions are to the real aircraft, and the higher the representativeness and accuracy of the test results. However, existing design methods limit the projected area of ​​the model to less than 20% of the nozzle uniform area. This results in small model sizes, making it difficult to accurately replicate the complex details of the real aircraft on small models. Sensors and measuring equipment installed on small models may also be limited by size, leading to reduced measurement accuracy. Summary of the Invention

[0005] To address the problems of small model size and difficulty in accurately replicating the complex details of real aircraft on small models due to the limitation of the model's projected area to less than 20% of the nozzle's uniform area in design methods, the inventors have conducted in-depth research and provided a method for determining the size of pulse wind tunnel test models. Based on pulse wind tunnels, numerical simulation and theoretical analysis are used to determine the maximum size of models with different typical shapes. The projected area of ​​the model in the vertical airflow direction can reach 60% to 65% or even more of the nozzle's uniform area. This invention not only increases the size of pulse wind tunnel test models but also more accurately simulates the structural details of aircraft, while providing test personnel with greater operating space and facilitating the installation and use of various testing equipment.

[0006] The technical solution provided by this invention is as follows:

[0007] A method for determining the dimensions of a pulse wind tunnel test model, comprising:

[0008] The flow field of the nozzle and the test section was determined by numerical simulation to obtain the uniform region S1 of the wind tunnel flow field; then the uniform region S2 of the nozzle and the test section was calibrated by a cross frame, and the sizes of the two uniform regions S1 and S2 were compared. The smaller uniform region was selected as the uniform region S0 of the flow field.

[0009] Under the condition of maximum experimental angle, the selected model is scaled down, and the maximum projected area of ​​the model in the vertical airflow direction accounts for 60% to 65% of the cross-sectional area of ​​the uniform region S0.

[0010] The scaled-down model, nozzle, and test section are integrated into a single model. The entire flow process is numerically simulated under the maximum test angle of attack and / or sideslip angle. The model scale is redefined based on the model installation location, the shock wave position at the model leading edge, and the coverage of the uniform region. The upper limit of the model length is determined by the effective test time and the velocity of the flow field in the test section.

[0011] Furthermore, in the step of determining the flow field of the nozzle and test section using numerical simulation methods to obtain the uniform region of the wind tunnel flow field, or in the step of integrating the scaled-down model with the nozzle and test section for integrated modeling and numerical simulation of the entire flow process, the numerical simulation method uses the dimensionless three-dimensional nonequilibrium flow Navier-Stokes equations for solution. The dimensionless three-dimensional nonequilibrium flow Navier-Stokes equations are:

[0012]

[0013] In the formula, U is the conserved quantity vector, F, G, and E are the convective flux vectors in each direction of the rectangular coordinate system, Fv, Gv, and Ev are the viscous flux terms in each direction, W is the vector of chemical reaction and vibrational energy source terms, t is time, x, y, and z are the coordinate values ​​of the three axes of the rectangular coordinate system, and Re is the Reynolds number.

[0014] Furthermore, in the step of determining the flow field of the nozzle and test section using numerical simulation methods to obtain the uniform region of the wind tunnel flow field, or in the step of integrating the scaled-down model with the nozzle and test section to numerically simulate the entire flow process, the nozzle inlet boundary layer thickness δ is considered. The boundary layer thickness δ is determined by the following formula:

[0015]

[0016] In the formula Re x δ is the Reynolds number at the nozzle inlet, x is the length of the shock tube upstream of the nozzle inlet, and the boundary layer thickness δ is used as a boundary condition for numerical simulation.

[0017] Furthermore, a pressure sensor and a heat flow sensor are installed on the cross arms of the cross frame to measure pressure and heat flow, respectively; the cross arms of the cross frame have a two-section structure, which is connected by a hinge; the hinge has a hollow structure, and the sensor wiring passes through the hollow part for wiring.

[0018] The outer arm of the hinge on the cross frame is 1 / 3 to 1 / 4 of the length of the cross arm; the distance from the outermost measuring point of the cross arm to the center of the frame is the same as the nozzle exit radius.

[0019] Furthermore, in the step of integrating the scaled-down model with the nozzle and test section into a single model, priority is given to placing the model at the nozzle exit position, with the model's leading edge shock wave also located at the nozzle exit; for cone and waverider models, when the model is partially placed inside the nozzle, the length of the placement is less than 1 / 4 of the nozzle inlet diameter.

[0020] Furthermore, in the step of re-determining the model scale based on the model installation location, the shock wave location at the model's leading edge, and the coverage of the uniform region, the method for determining the projected area of ​​the model in the vertical airflow direction includes:

[0021] If the leading edge of the model is located inside the nozzle, the projected area of ​​the part of the model located inside the nozzle in the direction perpendicular to the airflow direction shall not exceed 20% of the cross-sectional area of ​​the uniform region S0.

[0022] If the model is not inside the nozzle, but the leading edge shock wave of the model is inside the nozzle, its projected area in the direction perpendicular to the airflow does not exceed 40% of the cross-sectional area of ​​the uniform region S0.

[0023] If the model's leading edge shock wave is not inside the nozzle, and if the uniform region S0 can effectively cover the model, the model size can be increased by 1.05 times each time until the uniform region S0 can no longer effectively cover the model. If the uniform region S0 cannot effectively cover the model, the model size should be reduced by 0.95 times each time until the uniform region S0 can effectively cover the model.

[0024] Furthermore, the step of determining the upper limit of the model length through the effective test time and the velocity of the flow field in the test section includes:

[0025] If the wake flow of the model is not measured, the maximum value of the model length L1 satisfies the following condition:

[0026]

[0027] If the wake flow of the model is being measured, the maximum value of the model length L2 satisfies the following condition:

[0028]

[0029] Among them, t 有效 The effective test time is V, and the velocity of the flow field in the test section is V.

[0030] Furthermore, the effective test time is determined as follows: the minimum value of the total pressure stabilization time t1 and the static pressure stabilization time t2 is taken as the effective test time t. 有效 The total pressure stabilization time t1 is the interval where the total pressure value fluctuates by less than 10%, and the static pressure stabilization time t2 is the interval where the static pressure value fluctuates by less than 8%.

[0031] The method for determining the dimensions of a pulse wind tunnel test model provided by the present invention has the following beneficial effects:

[0032] (1) The present invention provides a method for determining the size of a pulse wind tunnel test model. In response to the problem that the design method limits the model's projected area to less than 20% of the nozzle's uniform area, resulting in small model size and difficulty in accurately replicating the complex details of a real aircraft on a small model, the inventors have conducted intensive research and provided a method for determining the size of a pulse wind tunnel test model. Based on the pulse wind tunnel, the method uses numerical simulation and theoretical analysis to determine the maximum size of different typical shape models. The projected area of ​​the model in the vertical airflow direction can reach 60% to 65% or even more of the nozzle's uniform area.

[0033] (2) The present invention provides a method for determining the size of a pulse wind tunnel test model. The initial scale of the model is determined based on the uniform region of the flow field. Subsequently, the model scale is re-determined by utilizing the model installation position, the shock wave position at the leading edge of the model, and the coverage of the uniform region. The projected area of ​​the model in the vertical airflow direction determined by this method can reach 60% to 65% or even more of the area of ​​the uniform region of the nozzle, enabling large-size models to be carried out in small-size pulse wind tunnels, and more accurately simulating the structural details of the aircraft. Large-size models can reduce the deviation caused by the model scale effect and more realistically reflect the actual environment. Large-size models provide more operating space and facilitate the installation and use of various test equipment. Attached Figure Description

[0034] Figure 1 A flowchart illustrating the method for determining the dimensions of a pulse wind tunnel test model;

[0035] Figure 2 A schematic diagram showing the model placed in a wind tunnel;

[0036] Figure 3 This is a schematic diagram of the cross-shaped frame structure.

[0037] Explanation of icon numbers

[0038] 1- Nozzle; 2- Test section; 3- Model. Detailed Implementation

[0039] The features and advantages of the present invention will become clearer and more explicit from the following detailed description.

[0040] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0041] This invention provides a method for determining the dimensions of a pulse wind tunnel test model, such as... Figure 1 As shown, it includes the following steps:

[0042] Step 1: The flow field of the nozzle and test section is determined using numerical simulation to obtain the uniform flow field region S1 in the wind tunnel. Then, a crossbeam is used to calibrate the uniform flow field region S2 of the nozzle and test section. The sizes of the two uniform flow fields S1 and S2 are compared, and the smaller uniform flow field region is selected as the uniform flow field region S0. The wind tunnel nozzle and test section are shown below. Figure 2 As shown.

[0043] The numerical simulation method uses the dimensionless three-dimensional nonequilibrium flow Navier-Stokes equations for solution. The dimensionless three-dimensional nonequilibrium flow Navier-Stokes equations are as follows:

[0044]

[0045] In the formula, U is the conserved quantity vector, F, G, and E are the convective flux vectors in each direction of the rectangular coordinate system, Fv, Gv, and Ev are the viscous flux terms in each direction, W is the vector of chemical reaction and vibrational energy source terms, t is time, x, y, and z are the coordinate values ​​of the three axes of the rectangular coordinate system, and Re is the Reynolds number.

[0046] When calculating the flow field of the nozzle and test section using numerical simulation methods, the nozzle inlet boundary layer thickness δ needs to be considered. The boundary layer thickness δ is determined by the following formula:

[0047]

[0048] In the formula Re x Let be the Reynolds number at the nozzle inlet, and x be the length of the shock tube upstream of the nozzle inlet. The boundary layer thickness δ is used as a boundary condition in the numerical simulation.

[0049] like Figure 3 As shown, pressure sensors and heat flow sensors are installed on the cross arms of the cross-shaped frame to measure pressure and heat flow, respectively. The cross arms of the cross-shaped frame have a two-section structure connected by hinges to reduce the length of the cross arms. The length of the outer arm of the hinge is 1 / 3 to 1 / 4 of the total cross arm length. The distance from the outermost measuring point of the cross arm to the center of the frame is the same as the nozzle exit radius.

[0050] The hinge has a hollow structure, allowing the sensor's wiring to pass through the hollow portion without being interfered with by the test airflow. Furthermore, bending the hinge does not require dismantling existing wiring, facilitating rapid testing.

[0051] Step 2: Select a model with a large blunt head, cone, or waverider configuration. Under the condition of maximum test angle (angle of attack or sideslip angle), scale down the model size to ensure that the maximum projected area M1 of the model in the vertical airflow direction occupies 60% to 65% of the cross-sectional area of ​​the uniform zone S0. The size of the scaled-down model cross-section is determined by the model length and the model placement position.

[0052] Step 3: Integrate the scaled-down model, nozzle, and test section into a single model. Under the maximum test angle (angle of attack and / or sideslip angle), numerically simulate the entire flow process. Based on the model installation location, the shock wave position at the model leading edge, and the coverage of the uniform region, redetermine the model scale. And determine the upper limit of the model length by using the effective test time and the velocity of the flow field in the test section.

[0053] (1) If the leading edge of the model is located inside the nozzle, the projected area of ​​the model part located inside the nozzle in the vertical airflow direction shall not exceed 20% of the cross-sectional area of ​​the uniform region S0.

[0054] (2) If the model is not inside the nozzle, but the model leading edge shock wave is inside the nozzle, its projected area in the direction perpendicular to the airflow does not exceed 40% of the cross-sectional area of ​​the uniform region S0.

[0055] (3) If the model's leading edge shock wave is not inside the nozzle, and if the uniform region S0 can effectively cover the model, the model size can be increased by 1.05 times each time until the uniform region S0 can no longer effectively cover the model. If the uniform region S0 cannot effectively cover the model, the model size should be reduced by 0.95 times each time until the uniform region S0 can effectively cover the model.

[0056] Priority should be given to placing models such as blunt-nosed bodies, cones, and waveriders at the nozzle exit position, with their leading-edge shock waves also located at the nozzle exit. For cones and waveriders, if the model length is long, part of the model can be placed inside the nozzle, with the length being less than 1 / 4 of the nozzle inlet diameter.

[0057] If the wake flow of the model is not measured, the maximum value of the model length L1 satisfies the following condition:

[0058]

[0059] If the wake flow of the model is being measured, the maximum value of the model length L2 satisfies the following condition:

[0060]

[0061] Among them, t 有效 The effective test time is V, and the velocity of the flow field in the test section is V.

[0062] The minimum value of the total pressure stabilization time t1 and the static pressure stabilization time t2 is taken as the effective test time t. 有效 The total pressure stabilization time t1 is the interval where the total pressure value fluctuates by less than 10%, and the static pressure stabilization time t2 is the interval where the static pressure value fluctuates by less than 8%.

[0063] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0064] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for determining the dimensions of a pulse wind tunnel test model, characterized in that, include: The flow field of the nozzle and the test section was determined by numerical simulation to obtain the uniform region S1 of the wind tunnel flow field; then the uniform region S2 of the nozzle and the test section was calibrated by a cross frame, and the sizes of the two uniform regions S1 and S2 were compared. The smaller uniform region was selected as the uniform region S0 of the flow field. Under the condition of maximum experimental angle, the selected model is scaled down, and the maximum projected area of ​​the model in the vertical airflow direction accounts for 60% to 65% of the cross-sectional area of ​​the uniform region S0; The scaled-down model, nozzle, and test section are integrated into a single model. The entire flow process is numerically simulated under the maximum test angle. The model scale is redefined based on the model installation location, the shock wave position at the model leading edge, and the coverage of the uniform region. The upper limit of the model length is determined by the effective test time and the velocity of the flow field in the test section. In the step of re-determining the model scale based on the model installation location, the shock wave position at the model's leading edge, and the coverage of the uniform region, the method for determining the projected area of ​​the model in the vertical airflow direction includes: If the leading edge of the model is located inside the nozzle, the projected area of ​​the part of the model located inside the nozzle in the direction perpendicular to the airflow direction shall not exceed 20% of the cross-sectional area of ​​the uniform region S0; If the model is not inside the nozzle, but the leading edge shock wave of the model is inside the nozzle, its projected area in the direction perpendicular to the airflow does not exceed 40% of the cross-sectional area of ​​the uniform region S0; If the model's leading edge shock wave is not inside the nozzle, and if the uniform region S0 can effectively cover the model, continue to increase the model size by a factor of 1.05 each time, until the uniform region S0 in the numerical simulation can no longer effectively cover the model; if the uniform region S0 cannot effectively cover the model, decrease the model size by a factor of 0.95 each time, until the uniform region S0 can effectively cover the model.

2. The method for determining the dimensions of a pulse wind tunnel test model according to claim 1, characterized in that, In the step of determining the flow field of the nozzle and test section using numerical simulation methods to obtain the uniform region of the wind tunnel flow field, or in the step of integrating the scaled-down model with the nozzle and test section for integrated modeling and numerical simulation of the entire flow process, the numerical simulation method uses the dimensionless three-dimensional nonequilibrium flow Navier-Stokes equations for solving. The dimensionless three-dimensional nonequilibrium flow Navier-Stokes equations are as follows: In the formula, U is the conserved quantity vector, F, G, and E are the convective flux vectors in each direction of the rectangular coordinate system, Fv, Gv, and Ev are the viscous flux terms in each direction, and W is the vector of chemical reaction and vibrational energy source terms. t For time, x , y , z These are the coordinate values ​​of the three axes in a rectangular coordinate system. Re It is the Reynolds number.

3. The method for determining the dimensions of a pulse wind tunnel test model according to claim 1, characterized in that, The step of determining the flow field of the nozzle and test section using numerical simulation methods to obtain the uniform flow field region in the wind tunnel, or the step of integrating the scaled-down model with the nozzle and test section into a single model and numerically simulating the entire flow process, takes into account the nozzle inlet boundary layer thickness. δ Boundary layer thickness δ Determined by the following formula: In the formula Re x The Reynolds number at the nozzle inlet. x The length of the shock tube upstream of the nozzle inlet and the boundary layer thickness are given. δ Used as boundary conditions in numerical simulations.

4. The method for determining the dimensions of a pulse wind tunnel test model according to claim 1, characterized in that, Pressure sensors and heat flow sensors are installed on the cross arms of the cross frame, which are used to measure pressure and heat flow, respectively. The cross arms of the cross frame have a two-section structure, which is connected by a hinge. The hinge has a hollow structure, and the sensor wiring passes through the hollow part.

5. The method for determining the dimensions of a pulse wind tunnel test model according to claim 1, characterized in that, The outer arm of the hinge on the cross-shaped frame is 1 / 3 to 1 / 4 of the length of the cross arm; and / or The distance from the outermost measuring point of the cross arm of the cross-shaped frame to the center of the frame is the same as the nozzle exit radius.

6. The method for determining the dimensions of a pulse wind tunnel test model according to claim 1, characterized in that, The model is a large blunt-nosed body, a cone, or a waverider configuration.

7. The method for determining the dimensions of a pulse wind tunnel test model according to claim 1, characterized in that, In the step of integrating the scaled-down model with the nozzle and test section into a single model, priority is given to placing the model at the nozzle exit position, with the model's leading edge shock wave also located at the nozzle exit. For cone and waverider models, when the model is partially placed inside the nozzle, the length of the placement is less than 1 / 4 of the nozzle inlet diameter.

8. The method for determining the dimensions of a pulse wind tunnel test model according to claim 1, characterized in that, The step of determining the upper limit of the model length by using the effective test time and the velocity of the flow field in the test section includes: If the wake flow of the model is not measured, the maximum value of the model length L1 satisfies the following condition: If the wake flow of the model is being measured, the maximum value of the model length L2 satisfies the following condition: in, t 有效 For effective test time, V The velocity of the flow field in the test section.

9. The method for determining the dimensions of a pulse wind tunnel test model according to claim 8, characterized in that, The effective test time is determined in the following manner: Take the total pressure stabilization time t 1 and static pressure settling time t The minimum value of 2 is taken as the effective test time. t 有效 Total pressure stabilization time t 1 represents the range where the total pressure fluctuation is less than 10%, and the static pressure stabilization time. t 2 represents the range where the static pressure fluctuation is less than 8%.

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