Unsteady jet flow interference flow field numerical calculation method considering pulse jet flow pressure building process

Abstract

The invention provides an unsteady jet flow disturbing flow field numerical calculation method considering a pulse jet flow pressure building process, and relates to the technical field of computational fluid dynamics (CFD). The method comprises the following steps: designing and generating a jet flow control aircraft calculation grid with a jet pipe, switching boundary conditions at an inlet of the jet pipe according to whether the jet flow is started, selecting a physical time step length according to time scales of external flow and streaming and jet flow of the jet pipe, dispersing a jet flow pressure buildup curve according to the physical time step, and calculating the jet flow pressure buildup curve. And giving conditions at the inlet of the spray pipe according to a jet flow working time sequence and a pressure buildup discrete result, and carrying out unsteady iterative calculation according to a physical time step length. According to the invention, integrated calculation is carried out with the spray pipe, the jet switch is arranged at the inlet of the spray pipe, the actual working process of pulse jet is better met, the universality is good, and the program is relatively simple to realize; coupling simulation of various unsteady characteristics such as jet flow starting, jet flow interference flow field formation, jet flow closing and jet flow interference flow field recession in the pulse jet flow pressure building process can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of computational fluid dynamics (CFD), and in particular to a numerical calculation method for an unsteady jet interference flow field taking into account a pulse jet pressure building process. Background Art

[0002] The jet direct force control technology can supplement the control capability of aerodynamic control surfaces, quickly change the trajectory and attitude of the aircraft, and can be used to achieve a variety of different control purposes such as braking and separation of the aircraft. It is widely used in engineering practice. The engine jet and high-speed incoming flow are controlled to interact with each other, and the flow field around the nozzle and upstream and downstream forms a complex flow including flow separation and reattachment, shock wave and shock wave interference, shock wave and boundary layer interference, shear layer, and more complex high-order induced vortex and wave systems generated by the interaction between them.

[0003] The jet interference flow field wave / vortex instability has unsteady effects such as strong shock wave oscillation and large-scale vortex motion. In addition, the establishment and disappearance process of the interference flow field caused by the start-up and shutdown of the jet has significant unsteady characteristics. The reconstruction of the interference flow field and the changes in the interference range and intensity caused by the jet thrust adjustment are also significant unsteady processes. The superposition of these unsteady effects will have a great impact on the aerodynamic characteristics and stability of the aircraft, and is closely related to factors such as flight altitude, speed, and flight attitude.

[0004] In response to such complex problems, early studies mainly focused on steady jet interference problems. With the continuous improvement of aircraft design requirements, more and more attention has been paid to the study of the unsteady effects of jet interference. However, most studies usually impose jet conditions at the nozzle outlet and do not simulate the flow inside the nozzle. Therefore, they fail to fully reflect the unsteady characteristics of the jet interference flow field.

[0005] In view of the above reasons, the present invention proposes a numerical calculation method for an unsteady jet interference flow field taking into account a pulse jet pressure building process. Summary of the invention

[0006] The purpose of the present invention is to provide a numerical calculation method for the unsteady jet interference flow field taking into account the pulse jet pressure building process. The calculation method can realize the integrated simulation of various unsteady characteristics such as jet startup, jet interference flow field formation, jet shutdown, and jet interference flow field disappearance in the pulse jet pressure building process, and solve the problem of accurate prediction of the strong time-varying and strong unsteady flow caused by the pulse jet operation during the maneuvering flight of the jet-controlled aircraft.

[0007] The present invention provides a numerical calculation method for an unsteady jet interference flow field considering a pulse jet pressure building process, comprising the following steps:

[0008] S10: Computational grid division: The consistency design of computational grid is performed through the flow field with or without nozzles;

[0009] S30: Calculation boundary condition setting: when there is no spraying, the nozzle inlet is set to solid wall condition, and when there is spraying, the nozzle inlet is set to jet flow condition. The other boundary condition settings are consistent with those when there is spraying.

[0010] S40: Calculate the nozzle inlet velocity: Calculate the jet direction according to the nozzle installation position and the nozzle axis direction, and give the nozzle inlet velocity according to this direction. The nozzle inlet velocity remains unchanged during the pressure building process;

[0011] S40: Input of the jet pressure building process: discretize the jet total pressure according to the nozzle pressure building curve according to the physical time step, and give the jet total pressure at the nozzle inlet of each physical time step according to the discretized value. The jet total temperature remains unchanged during the pressure building process;

[0012] S50: Calculate the initial field: Calculate the flow field when there is no jet, take the converged flow field without jet as the initial field when the jet is calculated under the same incoming flow conditions, and perform unsteady calculation of the pulse jet interference flow field based on the initial field without jet;

[0013] S60: Jet condition switching: When the jet starts, the boundary condition at the nozzle inlet is switched from the solid wall condition to the jet condition. Under the jet condition, the total pressure, total temperature and inlet velocity of the jet are given in each physical time step.

[0014] S70: Iterative calculation: The unsteady iterative calculation is continued according to the pressure building process. From the moment the jet is closed, the nozzle inlet is switched to the solid wall condition and the unsteady calculation is continued.

[0015] Preferably, the consistency design of the computational grid in step S10 includes: using a partitioned docking structure grid to simulate the actual fixed connection state of the nozzle and the projectile body, and performing integrated grid division of the projectile body and the nozzle, wherein the nozzle adopts an O-type grid method, and the computational grids without and with the nozzle are consistent.

[0016] Preferably, in step S40, the physical time step Δt is determined according to the time when the jet flows out of the nozzle and the time when the incoming flow flows through the projectile, and the formula is:

[0017] Δt=0.1×min(L j / U j , L / U ∞ )

[0018] Where, L j represents the nozzle length, U j represents the jet exit velocity, L represents the projectile length, U ∞ Represents the incoming flow velocity.

[0019] Preferably, the nozzle length is the straight-line distance from the center of the nozzle inlet to the center of the nozzle outlet.

[0020] Preferably, step S40 specifically includes: directly constructing a nozzle total pressure curve equation according to a pulse form that can be mathematically expressed, and then discretizing the jet total pressure according to a physical time step, giving the jet total pressure at the nozzle inlet for each physical time step according to the discretized value, and the jet inlet velocity and the jet total temperature remain unchanged during the pressure building process.

[0021] Preferably, the pulse forms that can be expressed mathematically include square pulses, trapezoidal pulses and triangular pulses.

[0022] Preferably, for pulse forms that cannot be directly described mathematically, a given thrust curve is converted into a nozzle total pressure curve, and interpolation encryption is performed according to the physical time step.

[0023] Preferably, the unsteady calculation method in steps S50 and S70 uses the three-dimensional compressible Navier-Stokes equations as control equations and discretizes them through the finite volume method.

[0024] Preferably, in S40, the finite volume method is used for discretization, the convection term is discretized using the second-order accuracy Roe format, the viscosity term is discretized using the central difference format, the turbulence model uses the one-equation SA turbulence model, and the time term is discretized using the high computational efficiency dual time step method.

[0025] Preferably, the unsteady iterative calculation in step S70 adopts the LU-SGS implicit iterative method, and a local time step method is used to accelerate the convergence of the inner iterative process.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. Through the consistent design of the computational grid of the flow field with or without a jet with a nozzle, the switching of boundary conditions when calculating the flow field with or without a jet at the nozzle inlet, the selection of physical time steps that adapt to various time scales, and the discretization of the physical time steps of any form of jet pressure building curve, the integrated simulation of various unsteady characteristics such as jet startup, jet interference flow field formation, jet shutdown, and jet interference flow field disappearance during the pulse jet pressure building process is realized, and the problem of accurate prediction of the strong time-varying and strong unsteady flow caused by the pulse jet operation during the maneuvering flight of the jet-controlled aircraft is solved;

[0028] 2. Can adapt to any form of pressure building curve;

[0029] 3. Taking the non-jet field with nozzle as the initial field, the jet is turned on according to the jet working sequence. The calculation process is more consistent with the working states of pulse jet start-up and shutdown during actual flight;

[0030] 4. The flow field after the jet is turned on can be compared with the flow field without the jet at any grid unit to obtain a fine interference range and the unsteady process of the interference load. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 Schematic diagram of the appearance of a cone-column-skirt spiral body in an embodiment of the present invention;

[0033] Figure 2 It is a schematic diagram of a jet square pressure building curve in an embodiment of the present invention;

[0034] Figure 3 It is a cloud diagram of the interference flow field during the jet pressure building process in an embodiment of the present invention; DETAILED DESCRIPTION

[0035] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of 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.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0037] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] The present invention provides a numerical calculation method for an unsteady jet interference flow field considering a pulse jet pressure building process, comprising the following steps:

[0039] S10: Computational grid division: The consistency design of computational grid is performed through the flow field with or without nozzles;

[0040] S30: Calculation boundary condition setting: when there is no spraying, the nozzle inlet is set to solid wall condition; when there is spraying, the nozzle inlet is set to jet flow condition; the other boundary condition settings are consistent with those with and without spraying;

[0041] S40: Calculate the nozzle inlet velocity: Calculate the jet direction according to the nozzle installation position and the nozzle axis direction, and give the nozzle inlet velocity according to this direction. The nozzle inlet velocity remains unchanged during the pressure building process;

[0042] S40: Input of the jet pressure building process: discretize the jet total pressure according to the nozzle pressure building curve according to the physical time step, and give the jet total pressure at the nozzle inlet of each physical time step according to the discretized value. The jet total temperature remains unchanged during the pressure building process;

[0043] S50: Calculate the initial field: Calculate the flow field when there is no jet, take the converged flow field without jet as the initial field when the jet is calculated under the same incoming flow conditions, and perform unsteady calculation of the pulse jet interference flow field based on the initial field without jet;

[0044] S60: Jet condition switching: When the jet starts, the boundary condition at the nozzle inlet is switched from the solid wall condition to the jet condition. Under the jet condition, the total pressure, total temperature and inlet velocity of the jet are given in each physical time step.

[0045] S70: Iterative calculation: Unsteady iterative calculation is continuously performed according to the pressure building process. From the moment the jet is closed, the nozzle inlet is switched to a solid wall condition and unsteady calculation is continued;

[0046] S80: If the jet is turned on again, repeat steps S60 and S70; if the jet is no longer turned on, continue iterative calculation until the jet-free field is restored.

[0047] The consistency design of the computational grid in step S10 includes: using a partitioned docking structure grid to simulate the actual fixed connection state of the nozzle and the projectile body, and performing integrated grid division of the projectile body and the nozzle, wherein the nozzle adopts an O-type grid method, and the computational grids without and with the nozzle are consistent, and only the boundary conditions at the nozzle inlet are set differently.

[0048] Although the selection of the physical time step of the dual time step method is not restricted by stability conditions, if the physical time step is too small, the calculation time will be unacceptable, and if the physical time step is too large, it will have a certain impact on the calculation accuracy, so it is necessary to determine a reasonable physical time step based on the physical problem itself. Since the pulse jet action time is generally short, in the millisecond level, and considering the existence of unsteady flows of different scales such as pulse jets and bypasses in the flow field, step S40 determines the physical time step Δt according to the time when the jet is ejected from the nozzle and the time when the incoming flow flows through the projectile. The formula is:

[0049] Δt=0.1×min(L j / U j , L / U ∞ )

[0050] Where, L j represents the nozzle length, U j represents the jet exit velocity, L represents the projectile length, U ∞ Represents the incoming flow velocity, and the above-mentioned nozzle length is the straight-line distance from the center of the nozzle inlet to the center of the nozzle outlet.

[0051] In this embodiment, step S40 specifically includes: directly constructing a nozzle total pressure curve equation according to a pulse form that can be mathematically expressed, and the pulse form that can be mathematically expressed includes a square pulse, a trapezoidal pulse, a triangular pulse, etc. For pulse forms that cannot be directly described mathematically, a given thrust curve is converted into a nozzle total pressure curve, and interpolation encryption is performed according to the physical time step, and then the jet total pressure is discretized according to the physical time step, and the jet total pressure at the nozzle inlet of each physical time step is given according to the discretized value, and the jet inlet velocity and the jet total temperature remain unchanged during the pressure building process.

[0052] In step S40, the finite volume method is used for discretization. The convection term is discretized using the second-order accuracy Roe format, the viscosity term is discretized using the central difference format, the turbulence model uses the one-equation SA turbulence model, and the time term is discretized using the high computational efficiency dual time step method.

[0053] In this embodiment, the unsteady calculation method of steps S50 and S70 adopts the three-dimensional compressible Navier-Stokes equations as the control equations and discretizes them through the finite volume method. The unsteady iterative calculation in step S70 adopts the LU-SGS implicit iterative method and adopts the local time step method to accelerate the convergence of the inner iterative process.

[0054] like Figure 1 As shown, this embodiment provides an unsteady calculation test of the lateral pulse jet pressure building process for the cone-column-skirt spiral body shape according to the above method. When the incoming flow Mach number is 6, the flight altitude is 30km, the incoming flow attack angle and the sideslip angle are both 0°, the nozzle outlet Mach number is 2.65, the maximum total pressure of the jet is 2.87MPa, and the total temperature of the jet is 293.15K. The unsteady calculation of the jet interference is carried out with no jet field as the initial field. The jet condition is applied at the nozzle inlet. The jet working mode is input in the form of a square wave. The jet working time is 3ms. Figure 2 The flow field calculation results during the jet pressure buildup process are shown in Figure 3 As shown, the unsteady characteristics of the jet start-up, jet interference flow field formation, jet closure, and jet interference flow field disappearance during the pulse jet pressure building process are displayed.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A numerical calculation method for unsteady jet interference flow field considering the pulse jet pressure building process, characterized in that: The following steps are involved: S10: Computational grid division: The consistency design of computational grid is performed through the flow field with or without nozzles; S30: Calculation boundary condition setting: when there is no spraying, the nozzle inlet is set to solid wall condition; when there is spraying, the nozzle inlet is set to jet flow condition; the other boundary condition settings are consistent with those with and without spraying; S40: Calculate the nozzle inlet velocity: Calculate the jet direction according to the nozzle installation position and the nozzle axis direction, and give the nozzle inlet velocity according to this direction. The nozzle inlet velocity remains unchanged during the pressure building process; S40: Input of the jet pressure building process: discretize the jet total pressure according to the nozzle pressure building curve according to the physical time step, and give the jet total pressure at the nozzle inlet of each physical time step according to the discretized value. The jet total temperature remains unchanged during the pressure building process; S50: Calculate the initial field: Calculate the flow field when there is no jet, take the converged flow field without jet as the initial field when the jet is calculated under the same incoming flow conditions, and perform unsteady calculation of the pulse jet interference flow field based on the initial field without jet; S60: Jet condition switching: When the jet starts, the boundary condition at the nozzle inlet is switched from the solid wall condition to the jet condition. Under the jet condition, the total pressure, total temperature and inlet velocity of the jet are given in each physical time step. S70: Iterative calculation: The unsteady iterative calculation is continued according to the pressure building process. From the moment the jet is closed, the nozzle inlet is switched to the solid wall condition and the unsteady calculation is continued.

2. The numerical calculation method of the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 1 is characterized in that: The consistency design of the computational grid in step S10 includes: using a partitioned docking structure grid to simulate the actual fixed connection state of the nozzle and the projectile body, and performing integrated grid division of the projectile body and the nozzle, wherein the nozzle adopts an O-type grid method, and the computational grids without and with the nozzle are consistent.

3. The numerical calculation method of the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 1 is characterized in that: The step S40 determines the physical time step Δt according to the time when the jet flows out of the nozzle and the time when the incoming flow flows through the projectile, and the formula is: Δt=0.1×min(L j / U j L / U ∞ ) Where, L j represents the nozzle length, U j represents the jet exit velocity, L represents the projectile length, U ∞ Represents the incoming flow velocity.

4. The numerical calculation method for the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 3 is characterized in that: The nozzle length is the straight-line distance from the nozzle inlet center to the nozzle outlet center.

5. The numerical calculation method of the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 1 is characterized in that: The step S40 specifically includes: directly constructing a nozzle total pressure curve equation according to a pulse form that can be expressed mathematically, and then discretizing the jet total pressure according to a physical time step, and giving the jet total pressure at the nozzle inlet for each physical time step according to the discretized value, and the jet inlet velocity and the jet total temperature remain unchanged during the pressure building process.

6. The method for numerically calculating the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 5 is characterized in that: The pulse forms that can be expressed mathematically include square pulses, trapezoidal pulses and triangular pulses.

7. The method for numerically calculating the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 5 is characterized in that: For pulse forms that cannot be directly described mathematically, they are converted into nozzle total pressure curves according to the given thrust curves and interpolated and encrypted according to the physical time step.

8. The method for numerically calculating the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 1 is characterized in that: The unsteady calculation method of steps S50 and S70 adopts the three-dimensional compressible Navier-Stokes equation as the control equation and discretizes it through the finite volume method.

9. The method for numerically calculating the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 1 is characterized in that: In the S40, the finite volume method is used for discretization, the convection term is discretized using the second-order accuracy Roe format, the viscosity term is discretized using the central difference format, the turbulence model uses the one-equation SA turbulence model, and the time term is discretized using the high computational efficiency dual time step method.

10. The method for numerically calculating the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 1 is characterized in that: The unsteady iterative calculation in step S70 adopts the LU-SGS implicit iterative method, and adopts the local time step method to accelerate the convergence of the inner iterative process.

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