Numerical simulation method and computer program product for high back pressure inlet and outlet flow in the inlet

Abstract

The numerical simulation method and computer program product for high back pressure internal and external flow in an air intake can realize the numerical simulation of the high back pressure limit state inside a three-dimensional air intake of an aircraft. The method includes the following steps: (1) Derive the back pressure boundary conditions through the Riemann invariant characteristic theory. (2) Divide a suitable structural mesh for the actual air intake shape. (3) Set a certain number of flow field monitoring points inside the air intake. (4) Given the initial back pressure conditions, solve the three-dimensional Navier-Stokes equations, and increase the back pressure value according to a certain strategy during the calculation process so that it gradually reaches the limit back pressure value under the actual conditions. (5) Monitor the flow field monitoring points set inside the air intake and determine whether the convergence calculation results are obtained. (6) Output all flow field information. This invention has the characteristics of convenient operation, high calculation efficiency, stable convergence for complex shapes, and high robustness.

Description

Technical Field

[0001] This invention relates to the fields of computational fluid dynamics and flow visualization, specifically to a numerical simulation method and computer program product for high back pressure internal and external flow in an air intake based on a structured grid. Background Technology

[0002] With the development of computational fluid dynamics (CFD), numerical simulation has been used in the study of complex flow mechanisms and the analysis of aerodynamic characteristics.

[0003] For supersonic or hypersonic inlets, to ensure successful ignition and startup, the high-speed incoming flow is typically reduced to subsonic speed at the front of the combustion chamber. At this point, the pressure inside the combustion chamber is tens or even hundreds of times higher than the pressure at the inlet. In numerical simulations, it has been found that directly using commercial software with a given back pressure often fails to yield a convergent solution. Two main solutions exist: one is to initially obtain preliminary results with a lower back pressure, then gradually increase the back pressure to obtain convergent results under each back pressure condition. However, if the calculation results under any back pressure condition are incorrect, the entire process must be restarted, which is time-consuming and labor-intensive. Another alternative is to add an extension section at the inlet outlet and use a porous media model. This method modifies the friction coefficient of the porous media model and monitors the outlet pressure to obtain convergent results under a given back pressure condition. This method also relies on a given friction coefficient and requires repeated calculations and approximations to obtain convergent results under the given back pressure condition, making it equally cumbersome in engineering applications. Summary of the Invention

[0004] The technical problem solved by this application is to overcome the shortcomings of the prior art and provide a numerical simulation method for inlet and outlet flow under high back pressure based on structured grids, which can obtain the numerical simulation convergence results of this type of problem through a more convenient and efficient calculation method.

[0005] This application presents a numerical simulation method for high back pressure inlet and outlet flow in an air intake based on a structured grid. Based on the CFD method, a subsonic outflow back pressure boundary condition is developed on the basis of a general laboratory research program. At the same time, this simulation strategy can realize real-time monitoring during the calculation process, promptly detect whether the strategy for a given back pressure is appropriate, and make judgments and adjustments quickly.

[0006] The technical solution provided in this application is as follows:

[0007] A numerical simulation method for high back pressure inlet and outlet flow in an air intake includes:

[0008] S1: Establish a coordinate system and determine the computational domain based on the conditions and dimensions of the aircraft; create a structural mesh based on the actual shape of the aircraft and its air intake.

[0009] S2: The outer boundary of the computational domain includes the high back pressure far-field outer boundary; when calculating the high back pressure inlet flow problem, the additional high back pressure far-field outer boundary conditions are derived through the Riemann invariant characteristic theory. The additional high back pressure far-field outer boundary conditions are the back pressure or temperature of the far-field outer boundary.

[0010] Given additional high back pressure far-field outer boundary conditions, all flow field variables on the high back pressure far-field outer boundary are derived based on the additional high back pressure far-field outer boundary conditions.

[0011] S3: Increase the given additional high back pressure far-field outer boundary conditions and proceed to step S3;

[0012] S4: Repeat step S3. Each time S3 is performed, the given additional high back pressure far-field outer boundary conditions are increased relative to the previous S4. It is then determined whether the flow field variables in the obtained computational domain have reached computational convergence. If the computation does not converge, it can be considered that the intake is in a non-starting state under the high back pressure far-field outer boundary conditions.

[0013] In S1, the steps for establishing the coordinate system are as follows: a three-dimensional Cartesian coordinate system is adopted, with the x-axis along the flow direction of the model, the y-axis along the normal direction, and the z-axis along the circumferential direction. The origin O is selected as the leading edge apex of the aircraft.

[0014] S1 further includes setting flow field monitoring points inside the air intake duct to record flow field information at the monitoring point locations in real time.

[0015] In S2, the outer boundary of the computational domain includes the high back pressure far-field outer boundary. When calculating the high back pressure inlet flow problem, the additional high back pressure far-field outer boundary conditions are derived using Riemann invariant characteristic theory. These additional high back pressure far-field outer boundary conditions are either back pressure values ​​or temperatures. Given these additional high back pressure far-field outer boundary conditions, all flow field variables on the high back pressure far-field outer boundaries are derived based on them, including:

[0016] S21. Define according to the coordinate system. The unit outward normal vector on the far-field outer boundary;

[0017] S22. The additional high back pressure far-field outer boundary condition that needs to be added is the back pressure P at the far-field outer boundary. b ;

[0018] Given back pressure value P0: P b =P0

[0019] S23. Solve the three-dimensional NS equations based on the back pressure value P0 to obtain the internal flow field variables;

[0020] S24. Riemannian invariants include the left-moving characteristic invariant R on the far-field outer boundary. b- Right-hand characteristic invariant R b+ Entropy characteristic invariant s b Supplementary tangential velocity characteristic invariant V bτ and the supplementary normal velocity characteristic invariant V bσ ;

[0021] Based on the Riemann invariant subsonic outflow case, calculate the Riemann invariant expression for the far-field outer boundary;

[0022] S25. Based on the Riemann invariant expression of the far-field outer boundary and the internal flow field variables, calculate R. b+ s b 、V bτ 、V bσ ;

[0023] S26, According to entropy s b Given the back pressure value P0, calculate R-.

[0024] S27, According to R b- R b+ s b 、V bτ 、V bσ The three-directional velocities on the far-field outer boundary are obtained from the unit outward normal vector on the far-field outer boundary.

[0025] S28. The temperature is obtained using the gas law.

[0026] In step S24, based on the Riemann invariant subsonic outflow condition, the Riemann invariant expression for the far-field outer boundary is calculated, including:

[0027] When the far-field outer boundary is under subsonic outflow conditions, 0 ≤ V n,e ≤c e V n,e For characteristic velocity, c e Since it is the speed of sound, V n,e -c e ≤0;

[0028] R - R is determined by the flow field variables of the external flow field. + ,s,V τ and V σ The Riemann invariants at the far-field outer boundary are determined by the flow field variables of the internal flow field, i.e.,

[0029]

[0030] V bτ =V τe V bσ =V σe ;

[0031] Among them, R b+ Corresponding to the characteristic velocity V bn +c b R b- Corresponding to the characteristic velocity V bn -c b s b Corresponding to the characteristic velocity V bn ;

[0032] Both are the speed of sound, p ∞ ,p e Both are pressure, ρ ∞ ,ρ e ρ is the density, γ is the specific heat ratio of the gas, and is a fixed value of 1.4; where subscripts are used. ∞ The subscript 'e' indicates the external flow field, and the subscript 'e' indicates the internal flow field.

[0033] R +e V represents the right-hand characteristic invariant of the internal flow field. n,e c is the velocity of the internal flow field along the outer normal; e The local sound velocity in the internal flow field;

[0034] R -∞ V is the left-hand characteristic invariant of the external flow field; n,∞ c is the velocity of the external flow field along the outer normal; ∞ The local sound velocity in the external flow field;

[0035] s be Determine the boundary entropy for the internal flow field; p e For internal flow field pressure; ρ e The internal flow field density;

[0036] V τe To supplement the tangential velocity of the internal flow field; V σe To supplement the normal velocity of the internal flow field.

[0037] In step S25, R is calculated based on the Riemann invariant expression of the far-field outer boundary and the internal flow field variables. b+ s b 、V bτ 、V bσ ,include:

[0038] Internal flow field variables include p e ρ e 、S e c e 、Vτe 、V σe The internal flow field along the outer normal velocity V n,e and the velocity value V of the internal flow field e ;

[0039] Based on the above internal flow field variables, the following calculations are obtained:

[0040]

[0041] In S27, according to R b- R b+ s b 、V bτ 、V bσ The three-directional velocities on the far-field outer boundary are obtained from the unit outward normal vector on the far-field outer boundary, including:

[0042] According to S b And P0, to obtain the density on the far-field outer boundary.

[0043] According to ρ b Obtain the speed of sound at the far-field outer boundary.

[0044] After the flow field converges, C on the far-field outer boundary e =c b =c ∞ ,according to Combined with R b+ ,get

[0045] According to R b+ and R b- To obtain characteristic velocity

[0046] According to V bn The three-dimensional flow field velocities in the three directions on the far-field outer boundary are obtained as follows:

[0047]

[0048] Among them, u b u is the axial velocity on the boundary. e v is the axial velocity of the internal flow field. b v is the normal velocity on the boundary. e w represents the normal velocity of the internal flow field. b w represents the tangential velocity on the boundary. e The internal flow field tangential velocity; Let V be the boundary unit outward normal vector; define V e =(u e , v e w e) is the vector of internal flow field velocity.

[0049] In S4, the additional high back pressure far-field outer boundary condition is gradually increased from its initial value to the high back pressure far-field outer boundary condition under the actual condition; the initial value of the additional high back pressure far-field outer boundary condition = 1 / 3 × the high back pressure far-field outer boundary condition under the actual condition.

[0050] A computer program product includes a computer program / instructions that, when executed by a processor, implement the steps of any of the pulsed laser spot center positioning methods described above.

[0051] In summary, this application includes at least the following beneficial technical effects:

[0052] (1) This invention is completely independent and controllable.

[0053] (2) Structural mesh technology is used for complex shapes, which has good robustness.

[0054] (3) The entire calculation process can be monitored in real time. The intermediate process does not need to be fully converged to determine whether the calculation can be successful, which greatly improves the calculation efficiency.

[0055] (4) The pressure adjustment strategy in the calculation process is more convenient to adjust. Attached Figure Description

[0056] Figure 1 This is a flowchart of a numerical simulation method for high back pressure inlet and outlet flow in an air intake based on a structured grid, provided by an embodiment of the present invention.

[0057] Figure 2 This is a schematic diagram of the numerical simulation results for high back pressure internal flow in a two-dimensional air intake.

[0058] Figure 3 These are schematic diagrams of the simplified three-dimensional air intake numerical simulation results. Figure a shows the simplified three-dimensional shape of the aircraft; Figure b shows the pressure cloud map inside the air intake; and Figure c shows the Mach number cloud map inside the air intake. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments disclosed in the present invention will be described in further detail below with reference to the accompanying drawings.

[0060] This application discloses a numerical simulation method for high back pressure inlet and outlet flow in an air intake based on a structured grid, such as... Figure 1 As shown, the method includes the following steps:

[0061] Step 1: Derive the necessary back pressure boundary conditions, such as pressure, using the Riemann invariant characteristic theory. Based on the supplementary back pressure boundary conditions, derive all flow field variables on the far-field outer boundary. The flow field variables include temperature, pressure, and velocity.

[0062] Specifically, step one includes:

[0063] S11: Establish a coordinate system and determine the computational domain based on the conditions and dimensions of the aircraft;

[0064] The steps for establishing the coordinate system are as follows: a three-dimensional Cartesian rectangular coordinate system is adopted, with the x-axis along the flow direction of the model, the y-axis along the normal direction, and the z-axis along the circumferential direction. The origin O is selected as the leading edge apex of the aircraft.

[0065] S12: Divide the structural grid appropriately according to the actual shape of the aircraft and air intake.

[0066] Specifically, in step two, the process of drawing the structural mesh requires the use of external software such as POINTWISE or ICEM to generate meshes. Other mesh generation tools are also acceptable. This patent does not have a strict requirement for this step.

[0067] S13: The outer boundary of the computational domain includes the high backpressure far-field outer boundary, the supersonic inflow and outflow boundary, and the spacecraft wall boundary, etc.; according to the Riemann invariant principle, at the far-field outer boundary, the flow control equations contain three Riemann invariants, namely... Entropy Corresponding to characteristic velocities V n +c、V n -c and V n In the formula Let be the speed of sound, p be the pressure, ρ be the density, and γ be the specific heat ratio of the gas. Considering that the governing equations for actual three-dimensional flow consist of five equations, the tangential velocity V is added. τ and V σ Also as a Riemann invariant, V τ and V σ Corresponding to V n ;

[0068] The range of characteristic velocities is determined based on the actual flow characteristics within the intake manifold.

[0069] Based on the range of characteristic velocities: when calculating Riemann invariants, determine whether to use the values ​​of the internal or external flow fields to obtain the judgment result; and calculate R... + R - ,s,V τ V σ ;

[0070] Specifically, this includes: the Riemann invariants of the internal flow field are:

[0071]

[0072] The Riemann invariants of the external flow field are:

[0073]

[0074] When calculating high back pressure flow problems, the far-field outer boundary of the back pressure is usually under subsonic outflow conditions (0 ≤ V). n,e ≤c e ): At this time, the characteristic velocity V n,e -c e ≤0, the corresponding Riemann invariant (R - The characteristic velocities are determined by the external flow field; all other characteristic velocities are greater than zero, and the corresponding Riemann invariants (R...) are... + ,s,V τ 、V σ The internal flow field is still determined by the Riemann invariant, i.e.:

[0075] R + =R +,e R - =R -,∞ s = s e V τ =V τ,e V σ =V σ,e ;

[0076] For Riemann invariants that need to be calculated based on the values ​​of the external flow field, an additional flow parameter (i.e., c in R-) needs to be provided. ∞ (Calculations need to be performed based on an additional flow parameter); Based on the additional flow parameter, R- is calculated; based on R... b- R b+ s b 、V bτ 、V bσ The flow field variables on the far-field outer boundary (i.e., the flow field variables of the external flow field, including P, T, density and velocity) are calculated.

[0077] There are various ways to specify flow parameters, such as pressure, density, temperature, and mass flow rate. In this patent, the pressure is specified directly. Values ​​on other outer boundaries can be specified directly based on flight conditions, and the specification process will not be elaborated upon in this patent.

[0078] The following details the solution process for calculating the flow field variables (velocities in three directions) at the far-field outer boundary.

[0079] Based on the coordinate system, define Given the unit outward normal vector on the far-field outer boundary, the specific steps for solving the velocity parameters of the far-field outer boundary under high back pressure conditions are as follows:

[0080] Step 1: Given the back pressure value P0

[0081] P b =P0

[0082] Among them, P b P0 represents the back pressure at the far-field outer boundary, where P0 is a given back pressure value.

[0083] Based on the back pressure value P0, the internal flow field variables are obtained by solving the three-dimensional Navier-Stokes equations.

[0084] Step 2: Based on the Riemann invariant subsonic outflow situation:

[0085] R + =R +,e R - =R -,∞ s = s e V τ =V τe V σ =V σe

[0086] To calculate the Riemann invariants at the far-field outer boundary:

[0087] R b+ =R +e R b- =R -∞ s b =s be V bτ =V τe V bσ =V σe

[0088] The subscript b indicates the outer boundary of the far field.

[0089] R+ and S are obtained from the internal flow field variables. b 、V τ 、V σ ;

[0090] Entropy S on the boundary b Given the back pressure value P0, the density at the far-field outer boundary can be calculated:

[0091]

[0092] Where, ρ b The density is located at the outer boundary of the far field.

[0093] Step 3: Based on the density, obtain the speed of sound at the far-field outer boundary:

[0094]

[0095] Among them, C b The speed of sound at the outer boundary of the far field.

[0096] Step 4

[0097] After the flow field converges, C on the far-field outer boundary e =c b =C∞, therefore we can utilize Combined with R b+ We can find that:

[0098]

[0099] Further utilization It can be calculated

[0100]

[0101] Among them, V bn Characteristic velocity;

[0102] After determining the characteristic velocity, use the following formula:

[0103] u b =u e +(V bn ·nV e ·n)n x

[0104] v b =v e +(V bn ·nV e ·n)n y

[0105] w b =w e +(V bn ·nV e ·n)n z

[0106] Obtain the three-dimensional flow field velocity u in three directions on the far-field outer boundary. b ,v b ,w b Of which V e The velocity values ​​of the internal flow field are given; the internal flow field variables include the velocity values ​​of the internal flow field, which are known variables during the calculation process.

[0107] Step 5: The temperature can be obtained through the gas law. At this point, the flow field parameters on all back pressure boundaries (i.e., the far-field outer boundary under high back pressure conditions) have been obtained.

[0108] Step 2: Set a certain number of flow field monitoring points inside the air intake.

[0109] Specifically, in this step, flow field monitoring points are set at locations within the flow field that reflect the key flow characteristics of the intake duct, such as the intake duct inlet, throat, and intake duct outlet. The three-dimensional coordinate information of the monitoring points is recorded to monitor the flow field information of the monitoring points during the calculation process.

[0110] Step 3: Given an initial value of the back pressure at the far-field outer boundary, increase the back pressure at the far-field outer boundary according to a certain strategy during the calculation process, so that the back pressure at the far-field outer boundary gradually reaches the back pressure value under real conditions.

[0111] Specifically, in step four, when given the initial back pressure condition, one-third of the actual back pressure condition is usually chosen as the initial back pressure. This avoids non-physical solutions during the initial iterative calculation. The numerical simulation method used is to solve the three-dimensional compressible Navier-Stokes equations using the finite volume method.

[0112] The three-dimensional compressible Navier-Stokes equations are

[0113]

[0114] in, As a conserved variable, Let x, y, and z be the inviscid flux vectors in the three directions, respectively. t represents the viscous flux vectors in the x, y, and z directions, respectively; t represents time, x represents the flow direction in the Cartesian coordinate system, y represents the normal direction in the Cartesian coordinate system, and z represents the circumferential direction in the Cartesian coordinate system.

[0115] In solving the three-dimensional compressible Navier-Stokes equations, the back pressure at the far-field outer boundary is gradually increased from the initial value of 1 / 3×P0 to the back pressure value P0 under actual conditions. The solution with the back pressure at the far-field outer boundary as the back pressure value P0 under actual conditions is taken as the final result. The calculation method for the variables on the high back pressure outer boundary of the computational domain has been obtained in step 1. By additionally giving other boundary conditions of the computational domain (such as supersonic inflow and outflow boundary conditions, solid wall boundary, etc.), the specific values ​​of flow field variables such as pressure, temperature, and velocity inside the entire computational domain can be obtained by iteratively solving the Navier-Stokes equations.

[0116] Step 4: Monitor the flow field monitoring points set inside the air intake duct to determine whether the calculation has converged.

[0117] Specifically, in step four, the flow field at the monitoring point is monitored in real time. This patent mainly monitors the pressure value at the monitoring point and uses the pressure fluctuation curve to determine whether the convergence state has been reached or whether there may be non-physical calculation errors.

[0118] Step 5: Output all flow field information.

[0119] Specifically, in step six, the converged calculated flow field is output in a certain order. This method uses the Tecplot output format for output, which can be displayed using Tecplot post-processing software.

[0120] Example:

[0121] This example uses simplified two-dimensional and simplified three-dimensional air intakes as embodiments to demonstrate the effectiveness of the present invention.

[0122] (1) For a simplified two-dimensional air inlet, a numerical simulation of the flow field density gradient along the flow direction inside the air inlet is presented, such as... Figure 2 As shown

[0123] (2) Regarding the simplified three-dimensional air intake, simplified three-dimensional aircraft and air intake shape, as well as pressure cloud maps and Mach number cloud maps of the flow field inside the air intake are shown, such as... Figure 3 As shown

[0124] The contents not described in detail in this application specification are common knowledge to those skilled in the art.

[0125] The present application has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present application. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and implementation methods of the present application without departing from the spirit and scope of the present application, and all such modifications and improvements fall within the scope of the present application. The scope of protection of the present application is determined by the appended claims.

Claims

1. A numerical simulation method for high back pressure inlet and outlet flow in an air intake, characterized in that, include: S1: Establish a coordinate system and determine the computational domain based on the conditions and dimensions of the aircraft; create a structural mesh based on the actual shape of the aircraft and its air intake. S2: The outer boundary of the computational domain includes the high back pressure far-field outer boundary; when calculating the high back pressure inlet flow problem, the additional high back pressure far-field outer boundary conditions are derived through the Riemann invariant characteristic theory. The additional high back pressure far-field outer boundary conditions are the back pressure or temperature of the far-field outer boundary. Given additional high back pressure far-field outer boundary conditions, all flow field variables on the high back pressure far-field outer boundary are derived based on the additional high back pressure far-field outer boundary conditions. S3: Increase the given additional high back pressure far-field outer boundary conditions and proceed to step S3; S4: Repeat step S3. Each time S3 is performed, the given additional high back pressure far-field outer boundary conditions are increased relative to the previous one, and it is determined whether the flow field variables in the obtained computational domain have reached computational convergence. If the computation does not converge, it can be considered that the intake is in a non-starting state under the high back pressure far-field outer boundary conditions.

2. The numerical simulation method for high back pressure inlet and outlet flow in an intake duct according to claim 1, characterized in that: In S1, the steps for establishing the coordinate system are as follows: a three-dimensional Cartesian coordinate system is adopted, with the x-axis along the flow direction of the model, the y-axis along the normal direction, and the z-axis along the circumferential direction. The origin O is selected as the leading edge apex of the aircraft.

3. The numerical simulation method for high back pressure inlet and outlet flow in an intake duct according to claim 1, characterized in that: S1 further includes setting flow field monitoring points inside the air intake duct to record flow field information at the monitoring point locations in real time.

4. The numerical simulation method for high back pressure inlet and outlet flow in an intake duct according to claim 1, characterized in that, In S2, the outer boundary of the computational domain includes the high back pressure far-field outer boundary. When calculating the high back pressure inlet flow problem, the additional high back pressure far-field outer boundary conditions are derived using Riemann invariant characteristic theory. These additional high back pressure far-field outer boundary conditions are either back pressure values ​​or temperatures. Given these additional high back pressure far-field outer boundary conditions, all flow field variables on the high back pressure far-field outer boundaries are derived based on them, including: S21. Define according to the coordinate system. The unit outward normal vector on the far-field outer boundary; S22. The additional high back pressure far-field outer boundary condition that needs to be added is the back pressure P at the far-field outer boundary. b ; Given back pressure value P0: P b =P0 S23. Solve the three-dimensional NS equations based on the back pressure value P0 to obtain the internal flow field variables; S24. Riemannian invariants include the left-moving characteristic invariant R on the far-field outer boundary. b- Right-hand characteristic invariant R b+ Entropy characteristic invariant S b Supplementary tangential velocity characteristic invariant V bτ and the supplementary normal velocity characteristic invariant V bσ ; Based on the Riemann invariant subsonic outflow case, calculate the Riemann invariant expression for the far-field outer boundary; S25. Based on the Riemann invariant expression of the far-field outer boundary and the internal flow field variables, calculate R. b+ 、S b 、V bτ 、V bσ ; S26, According to entropy S b And the back pressure value P0, calculate R b- ; S27, According to R b- R b+ 、S b 、V bτ 、V bσ The three-directional velocities on the far-field outer boundary are obtained from the unit outward normal vector on the far-field outer boundary. S28. The temperature is obtained using the gas law.

5. The numerical simulation method for high back pressure inlet and outlet flow in an intake duct according to claim 4, characterized in that, In step S24, based on the Riemann invariant subsonic outflow condition, the Riemann invariant expression for the far-field outer boundary is calculated, including: When the far-field outer boundary is under subsonic outflow conditions, 0 ≤ V n,e ≤c e V n,e Since V is the characteristic velocity, n,e -c e ≤0; The Riemann invariant at the far-field outer boundary is, V bτ =V τe ,V bσ =V σe ; Among them, R b+ Corresponding to the characteristic velocity V bn +c b c b R represents the speed of sound at the outer boundary of the far field. b- Corresponding to the characteristic velocity V bn -c b s b Corresponding to the characteristic velocity V bn ; Both are the speed of sound, p ∞ Both are pressure, ρ ∞ ρ is the density, γ is the specific heat ratio of the gas, and is a fixed value of 1.4; where subscripts are used. ∞ The subscript 'e' indicates the external flow field, and the subscript 'e' indicates the internal flow field. R +e V represents the right-hand characteristic invariant of the internal flow field. n,e c is the velocity of the internal flow field along the outer normal; e The local sound velocity in the internal flow field; R -∞ V is the left-hand characteristic invariant of the external flow field; n,∞ c is the velocity of the external flow field along the outer normal; ∞ The local sound velocity in the external flow field; S be Determine the boundary entropy for the internal flow field; p e For internal flow field pressure; ρ e The internal flow field density; V τe To supplement the tangential velocity of the internal flow field; V σe To supplement the normal velocity of the internal flow field.

6. The numerical simulation method for high back pressure inlet and outlet flow in an intake duct according to claim 5, characterized in that, In S27, according to R b- R b+ 、S b 、V bτ 、V bσ The three-directional velocities on the far-field outer boundary are obtained from the unit outward normal vector on the far-field outer boundary, including: According to S b And P0, to obtain the density on the far-field outer boundary. S e For entropy characteristic invariants in the internal flow field; According to ρ b Obtain the speed of sound at the far-field outer boundary. After the flow field converges, c at the far-field outer boundary e =c b =c ∞ ,according to Combined with R b+ ,get According to R b+ and R b- To obtain characteristic velocity According to V bn The three-dimensional flow field velocities in the three directions on the far-field outer boundary are obtained as follows: Among them, u b u is the axial velocity on the boundary. e v is the axial velocity of the internal flow field. b v is the normal velocity on the boundary. e w represents the normal velocity of the internal flow field. b w represents the tangential velocity on the boundary. e The internal flow field tangential velocity; Let V be the boundary unit outward normal vector; define V e =(u e , v e w e ) is the vector of internal flow field velocity.

7. The numerical simulation method for high back pressure inlet and outlet flow in an intake duct according to claim 1, characterized in that: In S4, the additional high back pressure far-field outer boundary condition is gradually increased from its initial value to the high back pressure far-field outer boundary condition under the actual condition; the initial value of the additional high back pressure far-field outer boundary condition = 1 / 3 × the high back pressure far-field outer boundary condition under the actual condition.

8. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instruction is executed by the processor, it implements the steps of the numerical simulation method for high back pressure inlet and outlet flow of an intake duct as described in any one of claims 1-7.

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