High-enthalpy boundary layer transition prediction method based on linear stability analysis

Abstract

The invention provides a high-enthalpy boundary layer transition prediction method based on linear stability analysis, and the method comprises the steps: S1, calculating a basic flow based on incoming flow data of an aircraft, and obtaining basic flow data; s2, generating an orthogonalized transition calculation grid by taking the shape of the aircraft as a reference, and interpolating the basic flow data to the transition calculation grid; s3, calculating basic flow data on the grid by using the orthogonal transition after interpolation, and calculating a space growth rate of small-disturbance unstable waves in a high-enthalpy boundary layer of the aircraft by adopting a linear stability analysis method; and S4, performing integration along the flow direction according to the calculated space growth rate of the small-disturbance unstable wave to obtain N value envelopes at different flow direction positions, and further judging the initial position of transition of the high-enthalpy boundary layer. By applying the technical scheme provided by the invention, the technical problem that a transition prediction method in the prior art cannot be suitable for transition prediction of a high-enthalpy boundary layer can be solved.

Description

Technical Field

[0001] The invention belongs to the field of aerospace technology, and in particular relates to a high enthalpy boundary layer transition prediction method based on linear stability analysis. Background Art

[0002] The process of flow changing to turbulence is called transition. Turbulent flow shows irregular pulsation over time and space, and the momentum and energy of fluid particles can be efficiently mixed. Compared with the boundary layer, the wall heat flux of the turbulent boundary layer will also increase by 3 to 5 times. Therefore, the boundary layer transition is an important factor that must be considered in the design of high-speed aircraft.

[0003] With the continuous increase of the Mach number of high-speed aircraft and the continuous expansion of airspace, the incoming flow of the aircraft will have the characteristics of high Mach number, high enthalpy and high Reynolds number at the same time, which makes the hypersonic high-enthalpy flow transition an emerging important scientific issue.

[0004] At present, a variety of transition prediction methods have been developed at home and abroad, such as N Methods, transition modes, transition criteria, direct numerical simulation and large eddy simulation, etc.

[0005] However, the widely used transition prediction model γ-Re θ The transition model is a completely localized transition model, and its empirical relationship is mainly calibrated by a low-speed plate, which is not suitable for high-enthalpy boundary layer flows with high-temperature real gas effects.

[0006] In summary, how to provide a transition prediction method suitable for high enthalpy boundary layers is a key issue that needs to be urgently solved in the field of boundary layer transition research. Summary of the invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art.

[0008] The present invention provides a high enthalpy boundary layer transition prediction method based on linear stability analysis, and the high enthalpy boundary layer transition prediction method based on linear stability analysis includes:

[0009] S1, calculating the basic flow based on the aircraft incoming flow data to obtain the basic flow data;

[0010] S2, generating an orthogonalized transition calculation grid based on the aircraft shape as a reference, and interpolating the basic flow data to the transition calculation grid;

[0011] S3, using the basic flow data on the interpolated orthogonal transition computational grid, the linear stability analysis method is used to calculate the spatial growth rate of small perturbation instability waves in the high enthalpy boundary layer of the aircraft;

[0012] S4, based on the calculated spatial growth rate of the small disturbance instability wave, the N value envelope at different flow positions is obtained by integrating along the flow direction, and then the starting position of the high enthalpy boundary layer transition is determined.

[0013] Furthermore, in S1, computational fluid dynamics simulation is performed on the calculation example based on the thermochemical non-equilibrium model and the thermal perfect mixed gas model, and the basic flow data obtained include: mass fractions of different chemical components, temperature, velocity, density, pressure and viscosity coefficient of the mixed gas.

[0014] Furthermore, in S1, when calculating the high enthalpy boundary layer basic flow, the high temperature real gas effect is added into the calculation process, including:

[0015] Calculate the thermophysical properties of mixed gas based on the multi-component mixed thermal complete gas model;

[0016] Calculate the spatial flux of different components based on their mass fractions;

[0017] The generation rates per unit time of different species are calculated based on the thermochemical nonequilibrium model and added to the mass equation source terms.

[0018] Furthermore, in S2, when performing interpolation, the calculated CGNS format basic flow data is first converted to the PLOT3D format, and the basic flow data stored on the multi-block structured grid nodes of the basic flow are linearly interpolated to the orthogonalized transition calculation grid used for linear stability analysis method calculation.

[0019] Furthermore, in S3, the format used to calculate the spatial growth rate of small disturbance waves is the spatial format, and the method used is the fixed spanwise wavenumber method. The time frequency ω of the small disturbance wave is set as a constant, and the wavenumbers α and β are complex numbers. The real part represents the wavenumber of the disturbance wave in the flow direction and spanwise direction, and the positive and negative sign and size of the imaginary part represent the stability and instability of the disturbance wave. Then, by solving the small disturbance linear equation group at each flow direction station, the spatial growth rate of small disturbance unstable waves of different frequencies is obtained.

[0020] By applying the technical solution of the present invention, a high enthalpy boundary layer transition prediction method based on linear stability analysis is provided. The method obtains basic flow data based on aircraft incoming flow data, interpolates the basic flow data to the transition calculation grid, and uses a linear stability analysis method to calculate the spatial growth rate of small perturbation unstable waves in the aircraft high enthalpy boundary layer. The N value envelope at different flow direction positions is obtained by integrating along the flow direction, and then the starting position of the high enthalpy boundary layer transition is determined. The present invention can accurately simulate the development law of the basic flow of the high enthalpy boundary layer and the development law of the small perturbation unstable waves, and then more accurately predict the starting position of the transition. Compared with the prior art, the technical solution of the present invention can solve the technical problem that the transition prediction method in the prior art cannot be applied to the transition prediction of the high enthalpy boundary layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 A schematic flow chart of a high enthalpy boundary layer transition prediction method based on linear stability analysis provided according to a specific embodiment of the present invention is shown;

[0023] Figure 2 A schematic diagram showing a comparison between velocity data in a boundary layer provided according to a specific embodiment of the present invention and calculation results of an ideal gas model is shown;

[0024] Figure 3 A schematic diagram showing a comparison between temperature data in a boundary layer provided according to a specific embodiment of the present invention and calculation results of an ideal gas model is shown;

[0025] Figure 4 A schematic diagram of the xf characteristic plane of a small disturbance unstable wave provided according to a specific embodiment of the present invention is shown;

[0026] Figure 5 A flow direction N value distribution curve provided according to a specific embodiment of the present invention is shown. DETAILED DESCRIPTION

[0027] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to actual proportional relationships. The technology, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values.

[0030] like Figure 1 As shown, according to a specific embodiment of the present invention, a high enthalpy boundary layer transition prediction method based on linear stability analysis is provided, and the method includes:

[0031] S1, calculating the basic flow based on the aircraft incoming flow data to obtain the basic flow data;

[0032] S2, generating an orthogonalized transition calculation grid based on the aircraft shape as a reference, and interpolating the basic flow data to the transition calculation grid;

[0033] S3, using the basic flow data on the interpolated orthogonal transition computational grid, the linear stability analysis method is used to calculate the spatial growth rate of small perturbation instability waves in the high enthalpy boundary layer of the aircraft;

[0034] S4, based on the calculated spatial growth rate of the small disturbance instability wave, the N value envelope at different flow positions is obtained by integrating along the flow direction, and then the starting position of the high enthalpy boundary layer transition is determined.

[0035] By applying this configuration, a high enthalpy boundary layer transition prediction method based on linear stability analysis is provided, which obtains basic flow data based on aircraft incoming flow data, interpolates the basic flow data to the transition calculation grid, uses a linear stability analysis method to calculate the spatial growth rate of small perturbation unstable waves in the aircraft high enthalpy boundary layer, integrates along the flow direction to obtain the N value envelope at different flow direction positions, and then determines the starting position of the high enthalpy boundary layer transition. The present invention can accurately simulate the development law of the basic flow of the high enthalpy boundary layer and the development law of the small perturbation unstable waves, and then more accurately predict the starting position of the transition.

[0036] Firstly, in the present invention, the basic flow is calculated based on the aircraft flow data to obtain the basic flow data.

[0037] As a specific embodiment of the present invention, computational fluid dynamics (CFD) simulation is performed on the calculation example based on the thermochemical non-equilibrium model and the thermal perfect mixed gas model to obtain the aircraft flow field data (i.e., basic flow data) such as the mass fraction of different chemical components, the temperature, velocity, density, pressure and viscosity coefficient of the mixed gas.

[0038] Specifically, grid division is performed according to the shape of the aircraft; the wall temperature condition is given as an adiabatic wall condition based on the ballistic altitude, speed setting, incoming flow composition, density, pressure, temperature and velocity of the aircraft; the flow field is solved based on the thermochemical non-equilibrium model to obtain the flow field data, which includes the composition, density, velocity, temperature and laminar viscosity coefficient of the incoming flow, and the basic flow field is obtained by numerical simulation method.

[0039] In a specific calculation scenario, computational fluid dynamics simulation requires given control equations, numerical discretization methods, and boundary conditions. The gas model used in this embodiment is Park's five-component air reaction model and a single-temperature thermodynamic model. The spatial discretization uses the LDFSS format and the Minmod limiter, and the time discretization uses the DAF format. The incoming flow components are set to 77% nitrogen and 23% oxygen, and the wall boundary conditions use completely non-catalytic adiabatic wall boundary conditions. Numerical solutions are performed based on the control equations, chemical reaction kinetics and thermodynamic models, numerical discretization methods, and boundary conditions to obtain basic flow data.

[0040] In addition, when calculating the basic flow in the high enthalpy boundary layer, the high temperature real gas effect needs to be added into the calculation process, including:

[0041] Calculate the thermophysical properties of mixed gas based on the multi-component mixed thermal complete gas model;

[0042] Calculate the spatial flux of different components based on their mass fractions;

[0043] The generation rates per unit time of different species are calculated based on the thermochemical nonequilibrium model and added to the mass equation source terms.

[0044] Furthermore, after obtaining the basic flow data, an orthogonalized transition calculation grid is generated based on the aircraft shape, and the basic flow calculation results are interpolated to the transition calculation grid.

[0045] As a specific embodiment of the present invention, when performing interpolation, the calculated CGNS format flow field data is first converted to the PLOT3D format, and the basic flow data stored on the multi-block structured grid nodes of the basic flow are linearly interpolated to the orthogonal grid used for LST (Linear Stability Theory) calculation.

[0046] Furthermore, after the basic flow calculation results are interpolated to the transition calculation grid, the basic flow data on the interpolated orthogonal transition calculation grid are used to calculate the spatial growth rate of small perturbation instability waves in the high enthalpy boundary layer of the aircraft using the linear stability analysis method.

[0047] As a specific embodiment of the present invention, the format used in calculating the spatial growth rate of small disturbance waves is a spatial format. It is assumed that the time frequency ω of the small disturbance wave is a constant, and the wave numbers α and β are complex numbers. The real part represents the wave number of the disturbance wave in the flow direction and the span direction, and the positive and negative and size of the imaginary part represent the stability and instability of the disturbance wave. Then, by solving the small disturbance linear equation group at each flow direction station, the spatial growth rates of small disturbance unstable waves of different frequencies are obtained.

[0048] Furthermore, after obtaining the spatial growth rate of the small perturbation instability wave in the high enthalpy boundary layer of the aircraft, the N value envelope at different flow direction positions is obtained by integrating the calculated spatial growth rate of the small perturbation instability wave along the flow direction, and then the starting position of the boundary layer transition is determined.

[0049] As a specific embodiment of the present invention, the method used to calculate the streamwise growth rate of the small disturbance wave is the fixed spanwise wave number method, by taking the imaginary part β of the spanwise wave number i = 0, only the real part of the spanwise wave number is circulated to obtain the maximum growth rate of the disturbance in the direction of the fixed group velocity, and then the N value envelope curve at different positions is obtained by integrating along the group velocity direction, and then N is taken according to the actual flow law. T The boundary layer transition starting position is determined by the criterion.

[0050] Compared with the prior art, the advantages of the present invention are: it realizes a high enthalpy boundary layer transition prediction method based on linear stability analysis, adds the influence of high-temperature real gas effect in the basic flow calculation and linear stability analysis, can accurately simulate the development law of the high enthalpy boundary layer basic flow and the development law of small disturbance instability waves, and then predicts the starting position of the transition.

[0051] In order to further understand the present invention, the following Figures 1 to 5 The high enthalpy boundary layer transition prediction method based on linear stability analysis of the present invention is described in detail.

[0052] Step 1: Calculate the basic flow based on the aircraft flow data to obtain the basic flow data.

[0053] Computational fluid dynamics simulation of the calculation example was carried out based on the thermochemical non-equilibrium model and the thermal perfect mixed gas model to obtain the aircraft flow field data such as the mass fraction of different chemical components, temperature, velocity, density, pressure and viscosity coefficient of the mixed gas.

[0054] When calculating the basic flow in high enthalpy boundary layers, high temperature real gas effects are added into the calculation process, including:

[0055] Calculate the thermophysical properties of mixed gas based on the multi-component mixed thermal complete gas model;

[0056] Calculate the spatial flux of different components based on their mass fractions;

[0057] The generation rates per unit time of different species are calculated based on the thermochemical nonequilibrium model and added to the mass equation source terms.

[0058] In this embodiment, the XCFD numerical calculation platform is used to solve the high enthalpy boundary layer laminar basic flow.

[0059] The comparison between the velocity and temperature data in the boundary layer calculated in this embodiment and the calculation results of the ideal gas model is as follows: Figure 2 and Figure 3 shown.

[0060] Step 2: Generate an orthogonalized transition calculation grid based on the aircraft shape and interpolate the basic flow data to the transition calculation grid.

[0061] The flow parameters in the boundary layer obtained by the basic flow calculation are interpolated from the CFD calculation grid to the orthogonal grid as the basic flow field for LST calculation.

[0062] Step 3: Use the basic flow data on the interpolated orthogonal transition calculation grid and the linear stability analysis method to calculate the spatial growth rate of small perturbation instability waves in the high enthalpy boundary layer of the aircraft.

[0063] After obtaining the basic flow field after interpolation to the orthogonal grid, the finite difference method is used to solve the small perturbation linear equations considering the high-temperature real gas effect, and the spatial growth rates of small perturbation instability waves with different frequencies are obtained.

[0064] In this example, linear stability analysis was performed using fit_transition software.

[0065] The xf characteristic plane of the small perturbation unstable wave calculated in this embodiment is as follows: Figure 4 shown.

[0066] Step 4: According to the calculated spatial growth rate of the small disturbance unstable wave, the N value envelope at different flow positions is obtained by integrating along the flow direction, and then the starting position of the high enthalpy boundary layer transition is determined.

[0067] The spatial growth rate of the small disturbance unstable waves of different frequencies calculated in step 3 is numerically integrated along the flow direction to obtain the N value envelope of the disturbance amplification factor of the small disturbance waves of different frequencies. Take the appropriate N T The criterion value determines the starting position of the boundary layer transition.

[0068] The flow direction N value distribution curve obtained by integration in this embodiment is as follows: Figure 5 shown.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high enthalpy boundary layer transition prediction method based on linear stability analysis, characterized in that: The high enthalpy boundary layer transition prediction method based on linear stability analysis includes: S1, calculating the basic flow based on the aircraft incoming flow data to obtain the basic flow data; S2, generating an orthogonalized transition calculation grid based on the aircraft shape as a reference, and interpolating the basic flow data to the transition calculation grid; S3, using the basic flow data on the interpolated orthogonal transition computational grid, the linear stability analysis method is used to calculate the spatial growth rate of small perturbation instability waves in the high enthalpy boundary layer of the aircraft; S4, based on the calculated spatial growth rate of the small disturbance instability wave, the N value envelope at different flow positions is obtained by integrating along the flow direction, and then the starting position of the high enthalpy boundary layer transition is determined.

2. The high enthalpy boundary layer transition prediction method based on linear stability analysis according to claim 1, characterized in that: In S1, computational fluid dynamics simulations were performed on the calculation example based on the thermochemical nonequilibrium model and the thermal perfect mixture gas model. The basic flow data obtained included: mass fractions of different chemical components, temperature, velocity, density, pressure and viscosity coefficient of the mixed gas.

3. The high enthalpy boundary layer transition prediction method based on linear stability analysis according to claim 1, characterized in that: In S1, when calculating the basic flow in the high enthalpy boundary layer, the high temperature real gas effect is added into the calculation process, including: Calculate the thermophysical properties of mixed gas based on the multi-component mixed thermal complete gas model; Calculate the spatial flux of different components based on their mass fractions; The generation rates per unit time of different species are calculated based on the thermochemical nonequilibrium model and added to the mass equation source terms.

4. The high enthalpy boundary layer transition prediction method based on linear stability analysis according to claim 3, characterized in that: In S2, when interpolating, the calculated CGNS format basic flow data is first converted to the PLOT3D format, and the basic flow data stored on the multi-block structured grid nodes of the basic flow are linearly interpolated to the orthogonal transition calculation grid used for linear stability analysis method calculation.

5. The high enthalpy boundary layer transition prediction method based on linear stability analysis according to claim 4, characterized in that: In S3, the format used to calculate the spatial growth rate of small perturbation waves is the spatial format, the method used is the fixed spanwise wave number method, and the time frequency of the small perturbation waves is set ω is a constant, wave number α and β are complex numbers. The real part represents the wave number of the disturbance wave in the stream and span directions. The positive and negative sign and size of the imaginary part represent the stability and instability of the disturbance wave. Then, by solving the small disturbance linear equations at each stream station, the spatial growth rate of small disturbance unstable waves of different frequencies is obtained.

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