Rapid calculation method for flow field prediction of compression system of variable cycle engine

Abstract

The invention discloses a rapid calculation method for flow field prediction of a compression system of a variable cycle engine, and the method comprises the steps: building a parameterized mapping model of valve opening and total pressure distribution based on a wall attachment turbulent jet theory; the fan state conversion process is dispersed into a plurality of quasi-steady-state working conditions according to the actuation angle range of a mode selection valve; constructing a total pressure distribution and recovery coefficient prediction module under each working condition by using the parameterized model; the prediction module is embedded into a fluid mechanics solver in the form of boundary conditions, numerical simulation of the state transition process is completed, and performance change data are obtained. According to the scheme, full-three-dimensional complex calculation is replaced by parameterized mapping, the efficiency and precision of variable circulating fan mode conversion performance analysis are remarkably improved, meanwhile, the calculation cost is reduced, and quick-response technical support is provided for compression system optimization design.

Description

Technical Field

[0001] The present application belongs to the technical field of variable cycle engines, and specifically relates to a fast calculation method for predicting the flow field of a compression system of a variable cycle engine. Background Art

[0002] The adaptive variable cycle engine innovatively combines the low-speed, high-fuel efficiency of a turbofan engine with the high-speed, high-thrust advantages of a turbojet engine, achieving optimal performance across the entire flight envelope. It is expected to power a new generation of fighter aircraft. The adaptive variable cycle engine exhibits significant structural complexity in the fan compression system design, primarily reflected in its multi-duct architecture and adjustable component structure.

[0003] Currently, the design phase of adaptive variable-circulation fans typically employs full 3D solid modeling and true-geometry meshing for the adjustable mechanism to simulate performance changes during operating state transitions. Changing the position of the mode selection valve requires remeshing the valve area, significantly increasing the complexity of the numerical calculations and reducing computational efficiency. Dynamic meshing techniques have also been employed to address this issue, but due to the wide range of valve opening variations, this can easily lead to computational instability.

[0004] In contrast, replacing the 3D solid modeling of mode-selective valves with a parameterized mathematical model of the total pressure distribution and total pressure recovery coefficient downstream of the valve avoids mesh reconstruction, simplifies the calculation process, and significantly improves solution efficiency. This eliminates the need for specialized meshing techniques, ensuring numerical stability. Currently, mathematical models for the total pressure distribution and total pressure recovery coefficient of mode-selective valves often use the local loss model for sudden expansion pipes. However, this model suffers from poor accuracy at small openings, making it difficult to conduct detailed studies of the coupling between upstream and downstream ducts.

[0005] In summary, at this stage, there is an urgent need for a fast calculation method to simplify the meshing process, improve the calculation efficiency, and ensure the calculation accuracy under different working conditions, so as to meet the needs of rapid performance analysis in the design stage of the adaptive circulation fan compression system.

[0006] Application Contents

[0007] In response to the problem that the existing mathematical model of local loss of sudden expansion pipes replaces three-dimensional solid modeling with poor accuracy at small openings, this application aims to provide a fast calculation method for predicting the flow field of the variable cycle engine compression system. The total pressure distribution and total pressure recovery coefficient model based on the wall-attached turbulent jet theory is used to replace the real three-dimensional geometric adjustable components, which can effectively simplify the calculation process, reduce the calculation time cost, ensure the calculation stability, improve the analysis efficiency, and provide guidance for the design of variable cycle impeller machinery.

[0008] In order to achieve the technical objectives of this application, the following technical solutions are adopted:

[0009] In one aspect of the present application, a fast calculation method for predicting the flow field of a variable cycle engine compression system is provided, comprising the following steps:

[0010] S1: Based on the wall-attached turbulent jet theory, a parameterized mapping model between valve opening and the actual total pressure distribution of the valve is constructed;

[0011] S2: Based on the division of the actuation angle intervals of the mode selection valve, the working state conversion process of the variable circulation fan is discretized into a plurality of mode selection valves, wherein the plurality of mode selection valves have a quasi-steady-state working condition with a clear position;

[0012] S3: Based on the parameterized mapping model, a prediction module for the valve actual total pressure distribution and the total pressure recovery coefficient under the quasi-steady-state working condition of the mode selection valve is constructed respectively, and the valve actual total pressure distribution and the total pressure recovery coefficient of all mode selection valves are obtained;

[0013] S4: The prediction module of the valve's actual total pressure distribution and total pressure recovery coefficient is embedded in the fluid dynamics solver in the form of boundary conditions to perform numerical simulation of the variable cycle fan's working state transition process;

[0014] S5: Obtain the performance evolution characteristics of the fan components of the adaptive variable cycle fan during the mode switching process.

[0015] In one embodiment, constructing a parameterized mapping model of valve opening and valve actual total pressure distribution in step S1 includes the following steps:

[0016] S1-1: For different valve openings, the dimensionless total pressure distribution in the valve boundary layer is obtained using the velocity distribution law in the boundary layer, as follows:

[0017]

[0018] Among them, the y direction is defined as the duct height direction, p t is the total pressure distribution at the jet end interface, p tm is the maximum total pressure coefficient at the jet end interface, Specifically refers to 0.99 times p in the mixing layer of jet flow tm The corresponding y value;

[0019] S1-2: For different valve openings, the dimensionless total pressure distribution in the mixing layer is obtained using the wall-attached turbulent jet theory, as follows:

[0020]

[0021] The half-width value b is the total pressure 0.5 times p tmThe corresponding y value;

[0022] S1-3: Combine the dimensionless total pressure distribution in the boundary layer and the dimensionless total pressure distribution in the mixing layer to obtain the dimensionless total pressure distribution of different valve openings and valves;

[0023] S1-4: Through the test, the valve opening is different. b. Development patterns along the flow direction;

[0024] S1-5: Using the dimensionless parameter development law obtained in S1-4, the dimensionless total pressure distribution of the valve obtained in S1-3 is restored to the true total pressure distribution of the valve, and a parameterized mapping model of the valve opening and the true total pressure distribution of the valve is constructed.

[0025] In one embodiment, in step S2, the openings of different quasi-steady-state operating conditions are defined based on the ratio of the throat flow area of ​​the adjustable component to the duct flow area.

[0026] In one embodiment, step S3 includes the following steps:

[0027] S3-1: Based on the parameterized mapping model, the proportional interpolation method is used to obtain the actual total pressure distribution of the valve under the corresponding valve opening.

[0028] S3-2: Integrate the true total pressure distribution of the valve along the duct height direction to obtain the average total pressure of the cross section. Based on the average total pressure of the cross section, the total pressure recovery coefficient of the airflow before and after passing through the valve is obtained. A prediction module that includes the true total pressure distribution of the valve and the total pressure recovery coefficient is constructed.

[0029] S3-3: Obtain the actual total pressure distribution and total pressure recovery coefficient of the valve under quasi-steady-state working conditions of all mode-selected valves.

[0030] In one embodiment, in step S4, based on the prediction module of the valve's true total pressure distribution and total pressure recovery coefficient in S3, two user-defined function files are generated, namely: a user-defined function file applied to the upstream interface to characterize the valve's true total pressure loss; and a user-defined function file applied to the downstream interface to characterize the downstream valve's true total pressure distribution.

[0031] Furthermore, in step S4, a user-defined function file applicable to multiple solvers is generated for each quasi-steady-state operating condition to ensure compatibility and meet the interface specifications of different solvers.

[0032] The beneficial effects of this application are:

[0033] Using the theory of turbulent wall jets, we determine the total pressure distribution after the airflow passes through the valve and the total pressure recovery coefficient before and after the valve. This replaces the need for full 3D solid modeling and numerical simulation of adjustable components, enabling rapid calculation of the flow field of variable cycle engine fan components during mode transitions. This method is suitable for rapid design analysis during the design phase, demonstrating high computational efficiency and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flow chart of a method for quickly calculating the flow field during the working state conversion process of an adaptive variable cycle fan;

[0035] Figure 2 In the embodiment of this application Development patterns along the flow direction;

[0036] Figure 3 This is the development law of b along the flow direction in the embodiment of this application;

[0037] Figure 4 In the embodiment of this application Development patterns along the flow direction;

[0038] Figure 5 A method for using a user-defined function file in an embodiment of the present application;

[0039] Figure 6 For this application, a calculation model using a parametric mathematical model of the valve downstream was used;

[0040] Figure 7 A flow field calculation model for the working state conversion process of the traditional full three-dimensional solid modeling adaptive variable cycle fan. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0042] Exemplary embodiments

[0043] The following is combined with Figures 1 to 7 This application is further described in detail through specific implementation methods:

[0044] 2.5-level adaptive variable circulation fan, calculation altitude: sea level altitude, atmospheric temperature: 288K, apply the method described in this application, refer to Figure 1 As shown in the figure, the flow field of the fan working state conversion process under this condition is quickly calculated:

[0045] S1: Based on the wall-attached turbulent jet theory, a parameterized mapping model between valve opening and the actual total pressure distribution of the valve is established.

[0046] In this application, the total pressure distribution is the total pressure distribution downstream of the mean valve.

[0047] Step S1 specifically includes the following steps:

[0048] S1-1: For different valve openings, the dimensionless total pressure distribution in the boundary layer is obtained using the velocity distribution law in the boundary layer:

[0049]

[0050] The airflow direction is defined as the x direction, the y direction is defined as the duct height direction, and p t is the total pressure distribution at the jet end interface, p tm is the maximum total pressure coefficient at the jet end interface, Specifically refers to 0.99 times p in the mixing layer of jet flow tm The corresponding y value.

[0051] The details are as follows:

[0052]

[0053] S1-2: Using the wall-attached turbulent jet theory to obtain the dimensionless total pressure distribution in the mixing layer:

[0054]

[0055] The half-width value b is the total pressure 0.5 times p tm The corresponding y value.

[0056] The details are as follows:

[0057] <![CDATA[η m ]]> 0 0.3 0.6 0.9 1.2 1.5 1.76 <![CDATA[p t / p tm ]]> 1 0.92936 0.77139 0.56869 0.35647 0.15543 0

[0058] S1-3: Combine the dimensionless total pressure distribution in the boundary layer and the dimensionless total pressure distribution in the mixing layer to obtain the dimensionless total pressure distribution of different valve openings and valves.

[0059] S1-4: Through the test, the valve opening is different. b. The development law along the flow direction, taking the opening of 50% as an example, as shown in the attached Figures 2-4 shown.

[0060] S1-5: Using the dimensionless parameter development law obtained in S1-4, the dimensionless total pressure distribution of the valve obtained in S1-3 is restored to the true total pressure distribution of the valve, and a parameterized mapping model of the valve opening and the true total pressure distribution of the valve is constructed.

[0061] Taking the valve opening of 50% as an example, the specific details are as follows:

[0062] y(mm) 0 5 10 15 20 25 30 35 <![CDATA[p t (kPa)]]> 0 290.12 338.14 294.69 235.05 176.17 134.07 0

[0063] S2: Based on the division of the actuation angle intervals of the mode selection valve, the working state conversion process of the variable circulation fan is discretized into a plurality of mode selection valves, wherein the plurality of mode selection valves have quasi-steady-state working conditions with clear positions.

[0064] In this embodiment, the openings for different quasi-steady-state conditions are defined based on the ratio of the throat flow area of ​​the adjustable component to the duct flow area.

[0065] In this embodiment, the working state conversion process of the variable circulation fan is discretized into 8 mode selection valves as an example, where each mode selection valve has a quasi-steady-state working condition with a clear position, for example, the 8 mode selection valves are 6.7%, 20.0%, 33.3%, 46.7%, 60.0%, 73.3%, 86.7%, and 100.0%, respectively.

[0066] S3: Based on the parameterized mapping model, a prediction module for the valve's true total pressure distribution and total pressure recovery coefficient is constructed to obtain the valve's true total pressure distribution and total pressure recovery coefficient under different quasi-steady-state working conditions.

[0067] The specific steps include:

[0068] S3-1: Based on the parameterized mapping model, the proportional interpolation method is used to obtain the actual total pressure distribution of the valve under the corresponding valve opening. Taking 46.7% as an example, the following table is shown:

[0069] y(mm) 0 5 10 15 20 25 30 35 <![CDATA[p t (kPa)]]> 0 244.75 308.01 286.34 190.82 126.6 64.66 0

[0070] S3-2: Integrate the actual valve total pressure distribution along the duct height direction to obtain the average total pressure of the cross section. Based on the average total pressure of the cross section, obtain the total pressure recovery coefficient before and after the airflow passes through the valve, and construct a prediction module that includes the actual total pressure distribution of the valve and the total pressure recovery coefficient.

[0071] Among them, the total pressure recovery coefficient is the ratio of the average total pressure of the cross section to the total pressure after the air flow passes through the valve.

[0072] Specifically, taking a valve opening of 46.7% as an example, the total pressure recovery coefficient is 0.545.

[0073] S3-3: Obtain the true total pressure distribution and total pressure recovery coefficient of the valve under all quasi-steady-state conditions. Repeat steps S3-1 to S3-3 for each quasi-steady-state condition until the true total pressure distribution and total pressure recovery coefficient of the valve downstream under all quasi-steady-state conditions are obtained. The details are as follows:

[0074]

[0075] S4: The prediction module of the actual total pressure distribution and total pressure recovery coefficient of the valve is embedded in the fluid mechanics solver in the form of boundary conditions to perform numerical simulation of the variable cycle fan during the working state conversion process.

[0076] Specifically, refer to Figures 5-6 As shown, based on the prediction module for the valve's actual total pressure distribution and total pressure recovery coefficient in S3, two user-defined function files are generated: one for upstream interface 1, which characterizes the total pressure loss upstream of the valve; and one for downstream interface 2, which characterizes the total pressure distribution downstream of the valve. For example, for upstream interface 1, the upstream total pressure loss data is calculated using a parameterized mapping model and written to a UDF file; for downstream interface 2, the downstream total pressure distribution data is generated using a parameterized mapping model and written to a UDF file. The generated UDF files are then imported into a fluid mechanics solver (such as Fluent's UDF interface or OpenFOAM's boundary condition settings), and the boundary condition type for the upstream and downstream interfaces in the solver is set to "user-defined."

[0077] S5: Obtain the performance evolution characteristics of the fan components during the mode switching process of the adaptive variable cycle fan. The performance change of the total boost ratio of the whole machine is as follows:

[0078]

[0079]

[0080] The bypass ratio changes are shown in the following table:

[0081] Opening 6.70％ 20.0％ 33.3％ 46.7％ 60.0％ 73.3％ 86.7％ 100％ Bypass ratio of traditional full 3D method 0.024 0.078 0.139 0.212 0.286 0.346 0.378 0.398 Fast calculation method for bypass ratio 0.023 0.083 0.144 0.228 0.295 0.343 0.375 0.392

[0082] By comparison, reference Figure 6 and 7 Compared with traditional full three-dimensional numerical simulation, the computing efficiency is improved by about 20 times, and the computing error is less than 3.5%.

[0083] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fast calculation method for predicting the flow field of a variable cycle engine compression system, characterized in that: The following steps are involved: S1: Based on the wall-attached turbulent jet theory, a parameterized mapping model between valve opening and the actual total pressure distribution of the valve is constructed; S2: Based on the division of the actuation angle interval of the mode selection valve, the working state conversion process of the variable circulation fan is discretized into several mode selection valves, and some mode selection valves have quasi-steady-state working conditions with clear positions; S3: Based on the parameterized mapping model, a prediction module for the valve actual total pressure distribution and total pressure recovery coefficient under the quasi-steady-state working condition of the mode selection valve is constructed to obtain the valve actual total pressure distribution and total pressure recovery coefficient of all mode selection valves; S4: The prediction module of the valve's actual total pressure distribution and total pressure recovery coefficient is embedded in the fluid dynamics solver in the form of boundary conditions to perform numerical simulation of the variable cycle fan's working state transition process; S5: Obtain the performance evolution characteristics of the fan components of the adaptive variable cycle fan during the mode switching process.

2. The calculation method according to claim 1, characterized in that Constructing a parameterized mapping model between valve opening and the actual total pressure distribution of the valve includes the following steps: S1-1: For different valve openings, the dimensionless total pressure distribution in the valve boundary layer is obtained using the velocity distribution law in the boundary layer, as follows: Among them, the y direction is defined as the duct height direction, p t is the total pressure distribution at the jet end interface, p tm is the maximum total pressure coefficient at the jet end interface, Specifically refers to 0.99 times p in the mixing layer of jet flow tm The corresponding y value; S1-2: For different valve openings, the dimensionless total pressure distribution in the mixing layer is obtained using the wall-attached turbulent jet theory, as follows: The half-width value b is the total pressure 0.5 times p tm The corresponding y value; S1-3: Combine the dimensionless total pressure distribution in the boundary layer and the dimensionless total pressure distribution in the mixing layer to obtain the dimensionless total pressure distribution of different valve openings and valves; S1-4: Through the test, the valve opening is different. b. Dimensionless development law along the flow direction; S1-5: Using the obtained dimensionless parameter development law, the obtained dimensionless total pressure distribution of the valve is restored to the true total pressure distribution of the valve, and a parameterized mapping model of the valve opening and the true total pressure distribution of the valve is constructed.

3. The calculation method according to claim 1, characterized in that The openings under different quasi-steady-state conditions are defined based on the ratio of the throat flow area of ​​the adjustable component to the duct flow area.

4. The calculation method according to claim 1, characterized in that Step S3 includes the following steps: S3-1: Based on the parameterized mapping model, the actual total pressure distribution of the valve under the corresponding valve opening is obtained through the proportional interpolation method. S3-2: Integrate the true total pressure distribution of the valve along the duct height direction to obtain the average total pressure of the cross section. Based on the average total pressure of the cross section, the total pressure recovery coefficient of the airflow before and after passing through the valve is obtained. A prediction module that includes the true total pressure distribution of the valve and the total pressure recovery coefficient is constructed. S3-3: Obtain the actual total pressure distribution and total pressure recovery coefficient of the valve under quasi-steady-state working conditions of all mode-selected valves.

5. The calculation method according to claim 1, characterized in that Step S4 includes: generating a user-defined function file of total pressure loss at the upstream interface and a user-defined function file of total pressure distribution at the downstream interface based on a prediction module of the actual total pressure distribution of the valve and the total pressure recovery coefficient.

6. The calculation method according to claim 5, characterized in that Each quasi-steady-state load case generates a user-defined function file suitable for multiple solvers.

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