Method for determining size of pulse wind tunnel test model

Abstract

The invention provides a method for determining the size of a pulse wind tunnel test model, and the method comprises the steps: determining the flow fields of a spray pipe and a test section through a numerical simulation method, and obtaining a wind tunnel flow field uniform region S1; calibrating the spray pipe and the uniform region S2 of the test section by adopting a cross-shaped bent frame, comparing the sizes of the two uniform regions S1 and S2, and selecting the uniform region with the smaller size as the uniform region S0 of the flow field; under the condition that the test angle is maximum, scaling is conducted on the selected model, and the maximum projection area M1 of the model in the vertical airflow direction accounts for 60%-65% of the cross-sectional area of the uniform area S0; carrying out integrated modeling on the scaled model, the spray pipe and the test section, carrying out numerical simulation on the whole flow process under the condition that the attack angle and / or sideslip angle test angle is maximum, re-determining the model scaling according to the model mounting position, the model front edge shock wave position and the uniform region coverage, and determining the flow field speed of the test section through the effective test time and the speed of the flow field of the test section. And determining a model length upper limit.

Description

Technical Field

[0001] The invention belongs to the field of wind tunnel model design, and in particular relates to a method for determining the size of a pulse wind tunnel test model. Background Art

[0002] Pulse wind tunnel scale models play an important role in aerodynamic research and design and development of aircraft. Compared with full-scale models or physical tests, scale models are less expensive, allowing more iterations and optimizations to be performed during the design and testing phases. Scale models can be quickly manufactured and tested, accelerating the process from concept to actual application of products. Using scale models in the early design phase can avoid potential damage to full-scale prototypes and reduce risks. Scale models are designed based on the principle of similarity to ensure that the model is similar to the actual object in terms of geometry and fluid dynamics. Wind tunnel tests can measure important data such as aerodynamic forces, pressure distribution, flow field characteristics, etc. on the model, providing a basis for design. With the advancement of technology, such as high-precision manufacturing and numerical simulation, the accuracy and practicality of scale models are constantly improving.

[0003] However, the scaled model cannot completely replicate the Reynolds number of the full-size model, which affects the viscous characteristics of the flow field and may lead to inconsistency with actual flight conditions. The reduction in model size may affect the simulation of certain details, such as surface roughness, local geometric features, etc. The limited size of the wind tunnel leads to the influence of the boundary layer on the model, which needs to be reduced through design and test techniques. Scaled models may have difficulty simulating certain complex dynamic effects, such as flutter, turbulence transition, etc.

[0004] Model ground testing is an important part of the aircraft design and testing process. The larger the model, the closer its proportion to the real aircraft, and the more representative and accurate the test results. However, the existing design method limits the model projection area to less than 20% of the nozzle uniform area, which results in a small model size and makes it difficult to accurately replicate the complex details of the real aircraft on the small model. The sensors and measuring equipment installed on the small model may be limited by size, resulting in reduced measurement accuracy. Summary of the invention

[0005] In view of the problem that the design method limits the model projection area to less than 20% of the nozzle uniform area, resulting in a small model size and difficulty in accurately replicating the complex details of the real aircraft on a small model, the inventor has conducted a keen study and provided a method for determining the size of a pulse wind tunnel test model. Based on the pulse wind tunnel, the maximum size of different typical shape models is determined by numerical simulation and theoretical analysis. The model projection area in the vertical airflow direction can reach 60% to 65% or even more of the nozzle uniform area. The present invention can not only expand the size of the pulse wind tunnel test model, but also more accurately simulate the structural details of the aircraft, while providing a larger operating space for test personnel, facilitating the installation and use of various test equipment.

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

[0007] A method for determining the size of a pulse wind tunnel test model comprises:

[0008] The flow field of the nozzle and the test section is determined by numerical simulation method, and the uniform area S1 of the wind tunnel flow field is obtained; then the nozzle and the uniform area S2 of the test section are calibrated by a cross rack, and the sizes of the two uniform areas S1 and S2 are compared, and the uniform area with a smaller size is selected as the uniform area S0 of the flow field;

[0009] Under the condition of maximum test angle, the selected model is scaled down, and the maximum projection area of ​​the model in the direction perpendicular to the airflow accounts for 60% to 65% of the cross-sectional area of ​​the uniform zone S0;

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

[0011] Furthermore, in the step of determining the flow field of the nozzle and the test section by using a numerical simulation method to obtain the uniform area of ​​the wind tunnel flow field, or in the step of integrating the scaled model with the nozzle and the test section to numerically simulate the entire flow process, the numerical simulation method uses the dimensionless three-dimensional non-equilibrium flow Navier-Stokes equation to solve, and the dimensionless three-dimensional non-equilibrium flow Navier-Stokes equation is:

[0012]

[0013] Where U is the conserved quantity vector, F, G, and E are the convection 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 chemical reaction and vibration energy source term vector, 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 the test section by a numerical simulation method to obtain the uniform area of ​​the wind tunnel flow field, or in the step of integrating the scaled model with the nozzle and the test section to numerically simulate the entire flow process, the nozzle inlet boundary layer thickness δ is considered, and the boundary layer thickness δ is determined by the following formula:

[0015]

[0016] Where Re x 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 the boundary condition for numerical simulation.

[0017] Furthermore, a pressure sensor and a heat flow sensor are installed on the cross arm of the cross frame, which are used to measure pressure and heat flow respectively; the cross arm of the cross frame is a two-section structure, and the two-section structure is connected by a hinge; the hinge is a hollow structure, and the sensor circuit is wired through the hollow part.

[0018] The length of 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 of the cross frame to the center of the frame is consistent with the radius of the nozzle outlet.

[0019] Furthermore, in the step of integrating the scaled model with the nozzle and the test section, priority is given to placing the model at the nozzle outlet, and the leading edge shock wave of the model is also located at the nozzle outlet; for the cone and waverider models, when the model is partially placed in 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 scale of the model according to the model installation position, the shock wave position at the leading edge of the model and the uniform area coverage, the method of determining the projection area of ​​the model in the direction perpendicular to the airflow includes:

[0021] If the leading edge of the model is located inside the nozzle, the projection area of ​​the model part located inside the nozzle in the direction perpendicular to the airflow does not exceed 20% of the cross-sectional area of ​​the uniform zone S0;

[0022] If the model is not in the nozzle, but the model leading edge shock wave is in the nozzle, its vertical airflow direction projection area does not exceed 40% of the cross-sectional area of ​​the uniform zone S0;

[0023] If the leading edge shock wave of the model is not in the nozzle, and if the uniform area S0 can effectively cover the model, the model size can continue to be increased at a rate of 1.05 times each time until the numerical simulation uniform area S0 cannot effectively cover the model; if the uniform area S0 cannot effectively cover the model, reduce the model size at a rate of 0.95 times each time until the uniform area S0 can effectively cover the model.

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

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

[0026]

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

[0028]

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

[0030] Furthermore, the effective test time is determined by taking the total pressure stable time t 1 and static pressure stabilization time t 2 The minimum value of the effective test time t 有效 , total pressure stabilization time t 1 The static pressure stabilization time t is the interval where the total pressure value fluctuates less than 10%. 2 This is the range where the static pressure value fluctuation is less than 8%.

[0031] A method for determining the size 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 order to solve the problems that the design method limits the model projection area to less than 20% of the nozzle uniform area, resulting in a small model size and difficulty in accurately replicating the complex details of a real aircraft on a small model, the inventors have conducted in-depth research and provided a method for determining the size of a pulse wind tunnel test model. Based on a pulse wind tunnel, numerical simulation and theoretical analysis methods are used to determine the maximum size of models with different typical shapes. The model projection area in the direction perpendicular to the airflow can reach 60% to 65% or even more of the nozzle uniform area.

[0033] (2) The present invention provides a method for determining the size of a pulse wind tunnel test model, which determines the initial scale of the model based on the uniform area of ​​the flow field; subsequently, the model scale is re-determined using the model installation position, the model leading edge shock wave position and the uniform area coverage; the model projection area in the vertical airflow direction determined by this method can reach 60% to 65% or even more of the nozzle uniform area, so that a large-scale model can be developed in a small-scale pulse wind tunnel, which can more accurately simulate the structural details of the aircraft; the large-scale model can reduce the deviation caused by the model scale effect and more realistically reflect the actual environment; the large-scale model provides a larger operating space, which is convenient for installing and using various test equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The following is a flow chart of the method for determining the size of the pulse wind tunnel test model;

[0035] Figure 2 Schematic diagram of the model placed in the wind tunnel;

[0036] Figure 3 This is a schematic diagram of the structure of the cross rack.

[0037] Description of Figure Numbers

[0038] 1-nozzle; 2-test section; 3-model. DETAILED DESCRIPTION

[0039] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0040] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0041] The present invention provides a method for determining the size of a pulse wind tunnel test model, such as Figure 1 As shown, the following steps are included:

[0042] Step 1: Use numerical simulation method to determine the flow field of the nozzle and the test section to obtain the uniform area S1 of the wind tunnel flow field; then use the cross rack to calibrate the nozzle and the uniform area S2 of the test section, compare the sizes of the two uniform areas S1 and S2, and select the uniform area with the smaller size as the uniform area S0 of the flow field. Figure 2 shown.

[0043] The numerical simulation method uses the dimensionless three-dimensional non-equilibrium flow Navier-Stokes equation to solve the dimensionless three-dimensional non-equilibrium flow Navier-Stokes equation:

[0044]

[0045] Where U is the conserved quantity vector, F, G, and E are the convective flux vectors in the respective directions of the Cartesian coordinate system, Fv, Gv, and Ev are the viscous flux terms in the respective directions, and W is the chemical reaction and vibrational energy source term vector; t is time, x, y, and z are the coordinate values of the three axes of the Cartesian coordinate system, and Re is the Reynolds number.

[0046] When calculating the flow field of the nozzle and the test section using the numerical simulation method, it is necessary to consider the boundary layer thickness δ at the nozzle inlet. The boundary layer thickness δ is determined by the following formula:

[0047]

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

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

[0050] The hinge is of a hollow structure, and the wires of the sensors can be routed through the hollow part without being interfered by the test air flow. At the same time, when bending the hinge, the existing wires do not need to be removed, which facilitates the rapid development of the test.

[0051] Step 2: Select models with configurations such as large blunt bodies, cones, and waveriders. Under the condition of the 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 direction perpendicular to the air flow accounts for 60% - 65% of the cross-sectional area of the uniform area S0. The cross-sectional size of the scaled-down model is determined by the model length and the model placement position.

[0052] Step 3: Integrate the scaled-down model with the nozzle and the test section for modeling. Under the condition of the maximum test angle (angle of attack and / or sideslip angle), numerically simulate the entire flow process. According to the model installation position, the position of the leading-edge shock wave of the model, and the coverage of the uniform area, re-determine the model scale; and determine the upper limit of the model length based on the effective test time and the flow velocity in the test section.

[0053] (1) If the leading edge of the model is located inside the nozzle, for the part of the model located inside the nozzle, its projected area in the direction perpendicular to the air flow does not exceed 20% of the cross-sectional area of the uniform area 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 zone S0.

[0055] (3) If the leading edge shock wave of the model is not in the nozzle, and if the uniform area S0 can effectively cover the model, the model size can be increased by a factor of 1.05 each time until the uniform area S0 of the numerical simulation cannot effectively cover the model; if the uniform area S0 cannot effectively cover the model, the model size can be reduced by a factor of 0.95 each time until the uniform area S0 can effectively cover the model.

[0056] Priority should be given to placing models such as large blunt bodies, cones and waveriders at the nozzle exit, 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 in the nozzle, with a length less than 1 / 4 of the nozzle inlet diameter.

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

[0058]

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

[0060]

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

[0062] Take the total pressure stable time t 1 And static pressure stabilization time t 2 The minimum value of the effective test time t 有效 , total pressure stabilization time t 1 The static pressure stabilization time t is the interval where the total pressure value fluctuates less than 10%. 2 The static pressure value fluctuation is less than 8%.

[0063] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0064] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for determining the size of a pulse wind tunnel test model, characterized in that: include: The flow field of the nozzle and the test section is determined by numerical simulation method, and the uniform area S1 of the wind tunnel flow field is obtained; then the nozzle and the uniform area S2 of the test section are calibrated by a cross rack, and the sizes of the two uniform areas S1 and S2 are compared, and the uniform area with a smaller size is selected as the uniform area S0 of the flow field; Under the condition of maximum test angle, the selected model is scaled down, and the maximum projection area of ​​the model in the direction perpendicular to the airflow accounts for 60% to 65% of the cross-sectional area of ​​the uniform zone S0; The scaled-down model, nozzle and test section are integrated into a model. The entire flow process is numerically simulated under the condition of maximum test angle. The model scale is re-determined according to the model installation position, the model leading edge shock wave position and the uniform area coverage. The upper limit of the model length is determined by the effective test time and the velocity of the test section flow field.

2. The method for determining the size 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 the test section by a numerical simulation method to obtain the uniform area of ​​the wind tunnel flow field, or in the step of integrating the scaled model with the nozzle and the test section to numerically simulate the entire flow process, the numerical simulation method uses the dimensionless three-dimensional non-equilibrium flow Navier-Stokes equation for solution, and the dimensionless three-dimensional non-equilibrium flow Navier-Stokes equation is: Where U is the conserved quantity vector, F, G, and E are the convection 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 chemical reaction and vibration energy source term vector, 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.

3. The method for determining the size 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 the test section by a numerical simulation method to obtain the uniform area of ​​the wind tunnel flow field, or in the step of integrating the scaled model with the nozzle and the test section to numerically simulate the entire flow process, the nozzle inlet boundary layer thickness δ is considered, and the boundary layer thickness δ is determined by the following formula: Where Re x 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 the boundary condition for numerical simulation.

4. The method for determining the size of a pulse wind tunnel test model according to claim 1, characterized in that: A pressure sensor and a heat flow sensor are installed on the cross arm of the cross frame, which are used to measure pressure and heat flow respectively; the cross arm of the cross frame is a two-section structure, and the two-section structure is connected by a hinge; the hinge is a hollow structure, and the sensor line is wired through the hollow part.

5. The method for determining the size of a pulse wind tunnel test model according to claim 1, characterized in that: The length of the outer arm of the hinge on the cross frame is 1 / 3 to 1 / 4 of the length of the cross arm; and / or The distance between the outermost measuring point of the cross arm of the cross frame and the center of the frame is consistent with the radius of the nozzle outlet.

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

7. The method for determining the size of a pulse wind tunnel test model according to claim 1, characterized in that: In the step of integrating the scaled model with the nozzle and the test section, priority is given to placing the model at the nozzle outlet, and the model leading edge shock wave is also located at the nozzle outlet; for the cone and waverider models, when the model is partially placed in the nozzle, the length of the placement is less than 1 / 4 of the nozzle inlet diameter.

8. The method for determining the size of a pulse wind tunnel test model according to claim 1, characterized in that: In the step of re-determining the scale of the model according to the model installation position, the shock wave position at the leading edge of the model and the uniform area coverage, the method for determining the projection area of ​​the model in the direction perpendicular to the airflow includes: If the leading edge of the model is located inside the nozzle, the projection area of ​​the model part located inside the nozzle in the direction perpendicular to the airflow does not exceed 20% of the cross-sectional area of ​​the uniform zone S0; If the model is not in the nozzle, but the model leading edge shock wave is in the nozzle, its vertical airflow direction projection area does not exceed 40% of the cross-sectional area of ​​the uniform zone S0; If the leading edge shock wave of the model is not in the nozzle, and if the uniform area S0 can effectively cover the model, the model size can continue to be increased at a rate of 1.05 times each time until the numerical simulation uniform area S0 cannot effectively cover the model; if the uniform area S0 cannot effectively cover the model, reduce the model size at a rate of 0.95 times each time until the uniform area S0 can effectively cover the model.

9. The method for determining the size 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 the effective test time and the velocity of the flow field in the test section comprises: If the model wake flow is not measured, the maximum value of the model length L1 satisfies the following conditions: If the model wake flow is measured, the maximum value of the model length L2 satisfies the following condition: Among them, t 有效 is the effective test time, and V is the velocity of the flow field in the test section.

10. The method for determining the size of a pulse wind tunnel test model according to claim 9, characterized in that: The effective test time is determined as follows: Take the minimum value of total pressure stabilization time t1 and static pressure stabilization time t2 as the effective test time t 有效 The total pressure stabilization time t1 is the interval in which the total pressure value fluctuates less than 10%, and the static pressure stabilization time t2 is the interval in which the static pressure value fluctuates less than 8%.

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