A numerical calculation method for unsteady jet interference flow field considering the pulse jet pressure building process

Abstract

The present invention provides a numerical calculation method for the unsteady jet interference flow field considering the pulse jet pressure building process, which relates to the field of computational fluid dynamics (CFD) technology. It generates a computational grid for a jet-controlled aircraft with a nozzle by design, and the boundary conditions at the nozzle inlet are switched according to whether the jet is started, and the physical time step is selected according to the external flow and the nozzle jet time scale. The jet pressure building curve is discretized according to the physical time step, and the nozzle inlet conditions are given according to the jet working sequence and the pressure building discrete results, and unsteady iterative calculations are performed according to the physical time step. The present invention has an integrated calculation with a nozzle, and sets the jet switch at the nozzle inlet, which is more in line with the actual working process of the pulse jet, has good versatility, and is relatively simple to implement. It can realize the coupled simulation of various unsteady characteristics such as jet start-up, jet interference flow field formation, jet closure, and jet interference flow field disappearance during the pulse jet pressure building process.

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 considering a pulse jet pressure building process. Background Art

[0002] Direct jet force control technology can complement aerodynamic control surfaces, rapidly change an aircraft's trajectory and attitude, and achieve a variety of control objectives, such as braking and separation. It is widely used in engineering practice. By controlling the interaction between the engine jet and the high-speed incoming flow, the flow field around the nozzle and upstream and downstream forms a complex flow pattern involving flow separation and reattachment, shock wave-shock wave interference, shock wave-boundary layer interference, and shear layer formation. These interactions generate even more complex high-order induced vortex and wave systems.

[0003] The jet interference flow field is wave / vortex unstable, with 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 brought about 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 research mainly focused on steady jet interference. 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 the unsteady jet interference flow field considering the 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. This 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: Design the consistency of the computational grid through the flow field with or without nozzle;

[0009] S20: Calculation boundary condition settings: When there is no spraying, the nozzle inlet is set to a solid wall condition; when there is spraying, the nozzle inlet is set to a jet flow condition. The other boundary condition settings are consistent with those with and without spraying.

[0010] S30: Calculate nozzle inlet velocity: Calculate the jet direction based on the nozzle installation position and nozzle axis direction, and give the nozzle inlet velocity according to this direction. The nozzle inlet velocity remains unchanged during the pressure buildup process.

[0011] S40: Input of the jet pressure building process: The total jet pressure is discretized according to the nozzle pressure building curve according to the physical time step. The total jet pressure at the nozzle inlet is given in each physical time step according to the discretized value. The total jet temperature remains unchanged during the pressure building process.

[0012] S50: Calculate the initial field: Calculate the flow field when there is no jet, and take the converged no-jet flow field as the initial field when the jet is calculated under the same incoming flow conditions. Based on the no-jet initial field, perform unsteady calculation of the pulse jet interference flow field.

[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 buildup process. From the moment the jet is closed, the nozzle inlet is switched to the solid wall condition and the unsteady calculation continues.

[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 for the jet to be ejected from the nozzle and the time for the incoming flow to flow 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 outlet velocity, L represents the length of the projectile, 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 based on a mathematically expressible pulse form, 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.

[0021] Preferably, the mathematically expressible pulse forms 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 the control equations and discretizes them through the finite volume method.

[0024] Preferably, the finite volume method is used for discretization in S40, 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 adopts the local time step method 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 consistent computational grid design for flow fields with and without nozzles, switching boundary conditions for calculations with and without nozzles at the nozzle inlet, selection of physical time steps adapting to various time scales, and discretization of the physical time steps for arbitrary jet pressure buildup curves, this system achieves integrated simulation of various unsteady characteristics during pulsed jet pressure buildup, including jet startup, formation of jet interference flow fields, jet shutdown, and disappearance of jet interference flow fields. This solves the problem of accurately predicting the highly time-varying and highly unsteady flows caused by pulsed jets during maneuvering flight of jet-controlled aircraft.

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

[0029] 3. Using a non-jet field with a nozzle as the initial field, the jet is turned on according to the jet operating sequence. The calculation process is more consistent with the actual pulse jet start-up and shut-off working conditions during flight.

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

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

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

[0033] Figure 2 Schematic diagram of a square jet pressure buildup curve in an embodiment of the present invention;

[0034] Figure 3 This 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 following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts 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 to indicate directions or positional relationships based on the directions 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 device or element referred to must have a specific direction, be constructed and operate in a specific direction, and therefore should not be understood as limiting the present invention.

[0037] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said 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 an indirect connection through an intermediate medium, or it can be a communication between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the 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: Design the consistency of the computational grid through the flow field with or without nozzle;

[0040] S20: Calculation boundary condition settings: When there is no spraying, the nozzle inlet is set to a solid wall condition; when there is spraying, the nozzle inlet is set to a jet flow condition. The other boundary condition settings are consistent with those with and without spraying.

[0041] S30: Calculate nozzle inlet velocity: Calculate the jet direction based on the nozzle installation position and nozzle axis direction, and give the nozzle inlet velocity according to this direction. The nozzle inlet velocity remains unchanged during the pressure buildup process.

[0042] S40: Input of the jet pressure building process: The total jet pressure is discretized according to the nozzle pressure building curve according to the physical time step. The total jet pressure at the nozzle inlet is given in each physical time step according to the discretized value. The total jet temperature remains unchanged during the pressure building process.

[0043] S50: Calculate the initial field: Calculate the flow field when there is no jet, and take the converged no-jet flow field as the initial field when the jet is calculated under the same incoming flow conditions. Based on the no-jet initial field, perform unsteady calculation of the pulse jet interference flow field.

[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: The unsteady iterative calculation is continued according to the pressure buildup process. From the moment the jet is closed, the nozzle inlet is switched to the solid wall condition and the unsteady calculation continues.

[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 no-jet 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 nozzle. Among them, the nozzle adopts an O-type grid method. The computational grids without and with nozzles 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, the calculation accuracy will be affected to a certain extent. Therefore, 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, on the order of milliseconds, and considering the presence of unsteady flows of different scales such as pulse jets and bypass flows in the flow field, step S40 determines the physical time step Δt based on the time the jet is ejected from the nozzle and the time the incoming flow passes 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 outlet velocity, L represents the length of the projectile, 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 based on a mathematically expressible pulse form, where the mathematically expressible pulse form 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, interpolation and encryption are performed according to the physical time step, and then the jet total pressure is discretized according to the physical time step. The jet total pressure at the nozzle inlet for each physical time step is given according to the discretized value. 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 iteration method, and adopts the local time step method to accelerate the convergence of the inner iteration 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-cylinder-skirt spiral body according to the above method. When the incoming flow Mach number is 6, the flight altitude is 30km, the incoming flow angle of attack and sideslip angle are both 0 degrees, 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 a non-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, and 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 shutdown, 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 by: The following steps are involved: S10: Computational grid division: Design the consistency of the computational grid through the flow field with or without nozzle; S20: Calculation boundary condition settings: When there is no spraying, the nozzle inlet is set to a solid wall condition; when there is spraying, the nozzle inlet is set to a jet flow condition. The other boundary condition settings are consistent with those with and without spraying. S30: Calculate nozzle inlet velocity: Calculate the jet direction based on the nozzle installation position and nozzle axis direction, and give the nozzle inlet velocity according to this direction. The nozzle inlet velocity remains unchanged during the pressure buildup process. S40: Input of the jet pressure building process: The total jet pressure is discretized according to the nozzle pressure building curve according to the physical time step. The total jet pressure at the nozzle inlet is given in each physical time step according to the discretized value. The total jet temperature remains unchanged during the pressure building process. S50: Calculate the initial field: Calculate the flow field when there is no jet, and take the converged no-jet flow field as the initial field when the jet is calculated under the same incoming flow conditions. Based on the no-jet initial field, perform unsteady calculation of the pulse jet interference flow field. 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 buildup process. From the moment the jet is closed, the nozzle inlet is switched to the solid wall condition and the unsteady calculation continues.

2. The numerical calculation method for 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 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 for the unsteady jet interference flow field considering the pulse jet pressure building process according to claim 1 is characterized in that: In step S40, the physical time step Δt is determined based on the time it takes for the jet to exit the nozzle and the time it takes for the incoming flow to flow through the projectile. 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 outlet velocity, L represents the length of the projectile, 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 for 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 based on a mathematically expressible pulse form, 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. The jet inlet velocity and the jet total temperature remain unchanged during the pressure building process.

6. The numerical calculation method for 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 numerical calculation method for 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 numerical calculation method for unsteady jet interference flow field considering the pulse jet pressure building process according to claim 1 is characterized in that: 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.

9. The numerical calculation method for 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 numerical calculation method for 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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