Method for correcting interference length scale law under interaction of turbulent boundary layers of compression wave system

Abstract

The invention discloses a method for correcting an interference length scale law under interaction of turbulent boundary layers of a compression wave system, which comprises the following steps of: dispersing a curved surface into a plurality of infinitesimal straight-line segments, and calculating pressure rise of airflow passing through the compression wave system and a compression wave coverage range by combining an oblique shock wave relational expression; calculating the pressure rise generated by the separation shock wave; calculating the interference length caused by the shock waves generating the same airflow turning angle; and finally introducing a calculation formula to describe the influence of the dispersion degree of the compression wave system by using dimensionless parameters. According to the method, the influence of the pressure gradient is introduced, the problem that the separation scale is estimated by using the pressure ratio as a criterion in a traditional prediction method is solved, and the boundary layer interference length induced by the compression wave system can be effectively predicted.

Description

Technical Field

[0001] The invention belongs to the technical field of aerodynamics, and in particular relates to a method for correcting the interference length scaling law under the interaction of a compression wave system turbulent boundary layer. Background Art

[0002] Shock wave / boundary layer interference is common in the external and internal flows of supersonic and hypersonic aircraft. During the interference process, the adverse pressure gradient brought by the shock wave will make the boundary layer thicker or even separate. Once the boundary layer separates, it will increase the resistance, accompanied by severe unsteady aerodynamic forces and thermal loads.

[0003] Flow separation caused by shock wave / boundary layer interference is crucial to aerospace vehicles. The prediction of shock wave / boundary layer interference position and range can not only help the rapid iteration of supersonic and hypersonic aircraft aerodynamic design and avoid flow separation, but also can be used as a criterion for implementing flow control inside and outside the aircraft. In addition, the interference length Lint is an important characteristic scale that can be used as a characteristic scale to normalize the unsteady characteristics of the flow field.

[0004] However, the interference length scaling method proposed by existing studies is only applicable to shock wave / boundary layer interference. With the improvement of aircraft performance requirements, the total pressure loss caused by shock waves is too large. Therefore, curved surface design is adopted in many configuration designs. When supersonic airflow passes through the curved surface, a series of compression wave systems will be generated. For the same airflow turning angle or pressure rise, the total pressure loss caused by the compression wave system is smaller; at the same time, the scale of flow separation induced by the interference between the compression wave system and the boundary layer is also smaller than the scale of flow separation induced by the shock wave / boundary layer interference induced by the same airflow turning angle.

[0005] This also brings certain problems. Based on existing research, it is found that even for compression wave systems with the same turning angle and the same pressure rise, the flow separation scales caused by different dispersion degrees are also different. For the discrete form of compression wave system / boundary layer interference range, the traditional scaling law method needs to be further verified. Current research in this area mainly focuses on the form of shock waves and ignores the influence of different pressure gradients. For the same pressure rise, a smaller pressure gradient tends to induce a smaller flow separation. Therefore, the traditional method cannot effectively estimate the compression wave system / boundary layer interference length, which leads to misjudgment of the separation range. Summary of the invention

[0006] In order to overcome the shortcomings of the prior art, the present invention provides a correction method for the interference length scaling law under the interaction of the turbulent boundary layer of the compression wave system. First, the surface is discretized into a number of micro-element straight line segments, and then the pressure rise of the airflow passing through the compression wave system and the coverage of the compression wave are calculated in combination with the oblique shock wave relationship; next, the pressure rise generated by the separation shock wave is calculated; the interference length caused by the shock wave with the same airflow turning angle is calculated; finally, a calculation formula is introduced to use dimensionless parameters to describe the influence of the dispersion of the compression wave system. In the present invention, by introducing the influence of the pressure gradient, the problem of using the pressure ratio as a criterion for estimating the separation scale in the traditional prediction method is solved, and the boundary layer interference length induced by the compression wave system can be effectively predicted.

[0007] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0008] Step 1: Discretize the surface into several infinitesimal straight line segments;

[0009] Step 2: The supersonic airflow will generate several compression wave systems when passing through the micro-element straight line segment in step 1. Combined with the oblique shock wave relationship, calculate the pressure rise of the airflow passing through the compression wave system and the compression wave coverage range L com ;

[0010] Step 3: After the compression wave system interacts with the wall boundary layer, a separation shock wave will be generated. Calculate the pressure rise generated by the separation shock wave.

[0011] Step 4: Calculate the interference length L caused by the shock wave with the same airflow turning angle int ;

[0012] Step 5: Introduce the calculation formula using the dimensionless parameter L int / L com Describe the effects of dispersion on compressional wave systems.

[0013] Furthermore, the step 1 is specifically as follows:

[0014] Discretize the known compression surface into n micro-element straight line segments and calculate the airflow deflection angle at each discrete position x(i)

[0015]

[0016] Furthermore, the step 2 is specifically as follows:

[0017] Using the oblique shock wave relationship, combined with the wavefront Mach number M(i), the weak compression wave angle β1(i), the waveback Mach number M(i+1), and the pressure ratio pr(i) of each compression wave are calculated, and the total pressure rise of the compression wave system is obtained as:

[0018]

[0019] Furthermore, the step 3 is specifically as follows:

[0020] Calculate the total airflow deflection angle on the curved compression surface

[0021]

[0022] Combined with the oblique shock wave relationship, the shock wave angle β2 and the pressure ratio pr2 of the reflected wave system are calculated using the downstream Mach number M2 of the compression wave system.

[0023] Furthermore, the step 4 is specifically as follows:

[0024] Using the oblique shock wave relationship, combined with the incoming flow Mach number M0, the airflow deflection angle Calculate the incident shock wave angle β, pressure ratio pr1, and reflected shock wave pressure ratio pr2, and further calculate the dimensionless interference length L of the shock wave / boundary layer interaction int *=L int / δ*:

[0025]

[0026] Where γ is the specific heat ratio, δ* represents the displacement thickness of the inflow boundary layer; when Re θ ≤10 4 When k=3.0, when Re θ ≥10 4 When k = 2.5, Re θ represents the Reynolds number based on the momentum thickness.

[0027] Furthermore, the step 5 is specifically as follows:

[0028] The compression wave coverage L is calculated using the compression wave angle β1(i) at each discrete position calculated in step 1. com , and further use the following formula to calculate the dimensionless length L of the compression wave system boundary layer interaction int *:

[0029]

[0030] When L com ≤L int When L com =L int .

[0031] The beneficial effects of the present invention are as follows:

[0032] The present invention introduces the influence of pressure gradient, thereby solving the problem of using pressure ratio as a criterion for estimating the separation scale in traditional prediction methods, and can effectively predict the boundary layer interference length induced by the compression wave system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the boundary layer interference of the compression wave system of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0035] like Figure 1 As shown, the purpose of the present invention is to solve the problem of interference length prediction under the interaction of compression wave system boundary layer. In order to make up for the influence of only considering the pressure ratio in the traditional scaling law, the present invention introduces the influence of pressure gradient, which can effectively predict the interference length under the influence of different dispersion degrees of compression wave system.

[0036] Step 1: Discretize a known surface into several infinitesimal straight line segments;

[0037] Step 2: When the supersonic airflow passes through these straight segments, it will generate several compression waves. Combined with the oblique shock wave relationship, the pressure rise of the airflow passing through the compression wave system and the compression wave coverage range L are calculated. com ;

[0038] Step 3: After these compression waves interact with the wall boundary layer, separation shock waves will be generated. Calculate the pressure rise generated by the separation shock waves.

[0039] Step 4: Calculate the interference length L caused by the shock wave with the same airflow turning angle int ;

[0040] Step 5: Using the dimensionless parameter L int / L com To describe the influence of the dispersion of the compression wave system and introduce the calculation formula.

[0041] Example:

[0042] Step 1: Discrete the compressed surface:

[0043] Discretize the known compression surface into a number (n) of infinitesimal straight line segments and calculate the airflow deflection angle at each discrete position x(i) (where i = 1, 2, 3…n),

[0044] Step 2: Calculation of compression wave pressure rise:

[0045] Using the oblique shock wave relationship, combined with the wavefront Mach number M(i), the weak compression wave angle β1(i), the waveback Mach number M(i+1), and the pressure ratio pr(i) of each compression wave are calculated, and the total pressure rise of the compression wave system is obtained as:

[0046]

[0047] Step 3: Calculation of pressure rise of reflected wave system:

[0048] Calculate the total airflow deflection angle on the curved compression surface

[0049]

[0050] Combined with the oblique shock wave relationship, the shock wave angle β2 and the pressure ratio pr2 of the reflected wave system are calculated using the downstream Mach number M2 of the compression wave system.

[0051] Step 4: Calculation of interference length caused by shock waves with the same turning angle:

[0052] Using the oblique shock wave relationship, combined with the incoming flow Mach number M0, the airflow deflection angle Calculate the incident shock wave angle β, pressure ratio pr1, and reflected shock wave pressure ratio pr2, and further calculate the dimensionless interference length L of the shock wave / boundary layer interaction int *=L int / δ*:

[0053]

[0054] Where γ is the specific heat ratio, when Re θ ≤10 4 When k=3.0, when Re θ ≥10 4 When k=2.5.

[0055] Step 5: Calculation of the interference length of the compression wave system:

[0056] The compression wave coverage L is calculated using the compression wave angle β1(i) at each discrete position calculated in step 1. com , and further use the following formula to calculate the dimensionless interference length L under the interaction of the compression wave system boundary layer int *:

[0057]

[0058] When L com ≤L int When L com =L int .

Claims

1. A method for correcting the interference length scaling law under the interaction of compression wave system turbulent boundary layer, characterized in that: The steps include: Step 1: Discretize the surface into several infinitesimal straight line segments; Step 2: The supersonic airflow will generate several compression wave systems when passing through the micro-element straight line segment in step 1. Combined with the oblique shock wave relationship, calculate the pressure rise of the airflow passing through the compression wave system and the compression wave coverage range L com ; Step 3: After the compression wave system interacts with the wall boundary layer, a separation shock wave will be generated. Calculate the pressure rise generated by the separation shock wave. Step 4: Calculate the interference length L caused by the shock wave with the same airflow turning angle int ; Step 5: Introduce the calculation formula using the dimensionless parameter L int / L com Describe the effects of dispersion on compressional wave systems.

2. The method for correcting the interference length scaling law under the interaction of compression wave system turbulent boundary layer according to claim 1 is characterized in that: The step 1 is specifically as follows: Discretize the known compression surface into n micro-element straight line segments and calculate the airflow deflection angle at each discrete position x(i) 3. The method for correcting the interference length scaling law under the interaction of compression wave system turbulent boundary layer according to claim 2 is characterized in that: The step 2 is specifically as follows: Using the oblique shock wave relationship, combined with the wavefront Mach number M(i), the weak compression wave angle β1(i), the waveback Mach number M(i+1), and the pressure ratio pr(i) of each compression wave are calculated, and the total pressure rise of the compression wave system is obtained as:

4. The method for correcting the interference length scaling law under the interaction of compression wave system turbulent boundary layer according to claim 3 is characterized in that: The step 3 is specifically as follows: Calculate the total airflow deflection angle on the curved compression surface Combined with the oblique shock wave relationship, the shock wave angle β2 and the pressure ratio pr2 of the reflected wave system are calculated using the downstream Mach number M2 of the compression wave system.

5. The method for correcting the interference length scaling law under the interaction of compression wave system turbulent boundary layer according to claim 4 is characterized in that: The step 4 is specifically as follows: Using the oblique shock wave relationship, combined with the incoming flow Mach number M0, the airflow deflection angle Calculate the incident shock wave angle β, pressure ratio pr1, and reflected shock wave pressure ratio pr2, and further calculate the dimensionless interference length L of the shock wave / boundary layer interaction int *=L int / δ*: Where γ is the specific heat ratio, δ* represents the displacement thickness of the inflow boundary layer; when Re θ ≤10 4 When k=3.0, when Re θ ≥10 4 When k = 2.5, Re θ represents the Reynolds number based on the momentum thickness.

6. The method for correcting the interference length scaling law under the interaction of compression wave system turbulent boundary layer according to claim 5 is characterized in that: The step 5 is specifically as follows: The compression wave coverage L is calculated using the compression wave angle β1(i) at each discrete position calculated in step 1. com , and further use the following formula to calculate the dimensionless length L of the compression wave system boundary layer interaction int *: When L com ≤L int When L com =L int .

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