Method for evaluating air inlet distortion of engine in slow-running state

Abstract

The invention provides an engine slow state air inlet distortion evaluation method, and belongs to the technical field of aero-engine air inlet performance calculation, and the method comprises the steps: constructing an engine slow state numerical calculation model, the model comprises an air inlet channel outlet rear section and a throttling cone, the air inlet channel outlet rear section comprises a straight section and an expansion section, the throttling cone is arranged in the expansion section, and the rotating speed change of the engine is simulated by changing the axial position of the throttling cone, so that the throttling area is changed, the outlet flow of the air inlet channel is controlled, and the slow state simulation of the engine is realized; grid division and solver selection are carried out on the engine slow state numerical calculation model, boundary conditions are set, engine slow state steady flow field solving is carried out, and flow field parameters of an air inlet channel outlet simulation section are obtained; and discretizing an air inlet outlet simulation section which is the same as the real air inlet outlet section, and calculating an air inlet steady-state circumferential distortion index when the engine is in a slow state based on discrete point flow field parameters of the air inlet outlet simulation section.

Description

Technical Field

[0001] This application belongs to the field of aero-engine intake performance calculation technology, and specifically relates to a method for evaluating intake distortion in engine idle state. Background Technology

[0002] For certain subsonic aircraft with special configurations, their air intakes are typically designed as S-shaped internal ducts. For these aircraft, it is necessary to ensure not only the intake distortion at the engine takeoff matching point but also the intake distortion at engine idle to determine the engine's safe and stable operation. While numerical simulations at the engine takeoff matching point are relatively accurate in calculating engine intake performance, the total pressure recovery coefficient of the AIP section decreases significantly under high angles of attack and low flow rates. If traditional simulation methods are used to calculate intake distortion by changing back pressure conditions, the non-physical phenomenon of "overall backflow throughout the entire duct" can easily occur, which does not meet simulation requirements.

[0003] To achieve the assessment of air intake distortion in this type of special configuration aircraft under engine idle conditions, a method for assessing air intake distortion under engine idle conditions is needed. Summary of the Invention

[0004] The purpose of this application is to provide a method for evaluating intake distortion in an engine at idle state, in order to solve or mitigate at least one of the problems in the prior art.

[0005] The technical solution of this application is: a method for evaluating intake distortion in an engine at idle state, comprising:

[0006] A numerical calculation model for engine idle state is constructed. The model includes a rear section of the intake manifold outlet and a throttle cone. The rear section of the intake manifold outlet includes a straight section and an expansion section connected in sequence. The throttle cone is at least partially set in the expansion section. By changing the axial position of the throttle cone, the engine speed change is simulated, thereby changing the throttling area and controlling the intake manifold outlet flow rate to achieve engine idle state simulation.

[0007] The numerical calculation model of the engine idle state is meshed and the solver is selected. Boundary conditions are set, and the steady flow field of the engine idle state is solved to obtain the flow field parameters of the simulated section of the intake duct outlet.

[0008] The simulated intake duct outlet section, which is identical to the actual intake duct outlet section, is discretized. Based on the discrete point flow field parameters of the simulated intake duct outlet section, the steady-state circumferential distortion index of the intake air at engine idle state is calculated.

[0009] Preferably, when performing mesh generation on the numerical calculation model of the engine idle state, a hexahedral mesh structure is adopted, and local densification is performed in the area near the intake pipe and intake lip.

[0010] Preferably, the solver uses the finite volume method to solve the RANS equations, the turbulence model is selected as k-ω-SST, the inviscid pair flux is discretized using the Roe upwind scheme based on MUSCL difference, the viscous flux is discretized using the second-order upwind scheme, the discrete gradient uses the Green-Gauss grid basis, the turbulent kinetic energy and turbulent dissipation rate are differentially expressed using the first-order upwind scheme, and the time propagation uses an implicit method based on the density basis.

[0011] Preferably, the boundary conditions set when solving the steady flow field under engine idle conditions are as follows: the intake outlet boundary condition is set as the pressure outlet boundary, and the back pressure condition is not used for control. Its static pressure, total temperature and pressure far-field boundary are the same. The outlet flow rate is controlled by controlling the axial position of the throttle cone, thereby achieving matching with the engine idle state.

[0012] Preferably, the method for calculating the intake steady-state circumferential distortion index is as follows:

[0013]

[0014] In the formula, The steady-state circumferential distortion index of the intake;

[0015] σ 0m The steady-state average total pressure recovery coefficient is used to measure the low-pressure area of ​​the surface.

[0016] σ m The steady-state average total pressure recovery coefficient of the measurement surface.

[0017] This application establishes a numerical calculation model of the engine idle state by setting a throttle cone downstream of the intake outlet. It adopts a hexahedral mesh structure and sets appropriate boundary conditions. Based on the steady method, it simulates the engine idle state and calculates the intake steady-state distortion index. It can analyze the changes in the intake flow field under the engine idle state, obtain high-precision intake steady-state distortion characteristics, and provide reliable data for the stability and safety assessment of aircraft engine idle state. Attached Figure Description

[0018] To more clearly illustrate the technical solutions provided in this application, the accompanying drawings will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application.

[0019] Figure 1 This is a schematic diagram of the engine idle state intake distortion assessment method of this application.

[0020] Figure 2 This is a schematic diagram of the intake duct outlet section in this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0022] To address the difficulty in assessing intake distortion under low-flow conditions, this application provides a method for assessing intake distortion at engine idle. By installing a throttling cone device downstream of the intake manifold and adjusting the axial position of the throttling throat to change the throttling area and the ratio of the throttling area to the throat area, the intake manifold outlet flow rate can be controlled, thereby achieving intake distortion assessment at engine idle.

[0023] like Figure 1 As shown, the engine idle state intake distortion assessment method provided in this application includes the following process:

[0024] Step S10: Construct a numerical calculation model of the engine idle state. The numerical calculation model of the engine idle state includes the rear section of the intake manifold outlet and a throttle cone. The rear section of the intake manifold outlet includes a straight section 1 and an expansion section 2 connected in sequence. The throttle cone 3 is at least partially set in the expansion section 2. By changing the axial position of the throttle cone 3, the engine speed change is simulated, thereby changing the throttling area, controlling the intake manifold outlet flow rate, and realizing the simulation of the engine idle state.

[0025] like Figure 2 The diagram shown is a schematic diagram of the intake manifold outlet section based on the numerical calculation model of the engine idle state in this embodiment of the present application. In this intake manifold outlet section, the straight section 1 and the expansion section 2 are connected in sequence. The throttle cone 3 is roughly set in the expansion section 2. The engine speed change is simulated by changing the axial position of the throttle cone 3. That is, by adjusting the axial position of the throttle throat, the throttle area can be changed. The ratio of the throttle area to the throat area is obtained with the throat area as a reference, thereby controlling the intake manifold outlet flow rate and realizing the simulation of the engine idle state.

[0026] In some embodiments of this application, the front end of the throttling cone 3 is a circular protrusion 33, and the side surface of the throttling cone 3 includes a first plane 31 and a second plane 32 that are bent but not coplanar, with a larger bending angle through the first plane 31. By providing the bent side surface, an adjustable-area throttling throat is formed between the bend of the first plane 31 and the second plane 32 and the expansion section 2.

[0027] Step S20: Mesh the numerical calculation model of the engine idle state and select the solver, set the boundary conditions, and solve the steady flow field of the engine idle state to obtain the flow field parameters of the simulated cross section of the intake duct outlet.

[0028] In this application, for the aircraft configuration, a hexahedral mesh is used to fill the computational domain, and local refinement is applied to the ducts inside the inlet and the area near the inlet lip. A high-precision three-dimensional steady solver uses the finite volume method to solve the RANS equations (i.e., Reynolds-averaged Navier-Stokes equations). The turbulence model is selected as k-ω-SST. Inviscid pair fluxes are discretized using the Roe upwind scheme based on MUSCL differences, viscous fluxes are discretized using a second-order upwind scheme, the discrete gradient uses a Green-Gauss grid basis, turbulent kinetic energy and turbulent dissipation rate are differentially expressed using a first-order upwind scheme, and time propagation uses an implicit method based on density basis.

[0029] In this application, the inlet outlet boundary condition is set as a pressure outlet boundary, but back pressure is not used for control. Its static pressure and total temperature are the same as those of the pressure far-field boundary to avoid unrealistic backflow and calculation divergence. By setting parameters such as flight altitude, Mach number, and aircraft attitude angle, the steady flow field solution of the engine idle state can be carried out, and the flow field parameters such as static pressure, total pressure, and velocity at the inlet outlet section can be obtained.

[0030] Step S30: Discretize the simulated intake duct outlet section, which is the same as the actual intake duct outlet section, and calculate the intake steady-state distortion index when the engine is at idle based on the discrete point flow field parameters of the simulated intake duct outlet section.

[0031] This application simulates engine idle state by setting a throttle cone 3 downstream of the intake manifold outlet. When calculating the steady-state distortion index, an intake manifold outlet section at the same location as the actual intake manifold outlet section is selected for discretization. Based on the flow field parameters of the discrete points of this intake manifold outlet section, the steady-state circumferential distortion index of the engine intake under idle state is calculated. The calculation method is as follows:

[0032] In the formula, σ 0m The steady-state average total pressure recovery coefficient of the low-pressure area is measured (when there are multiple low-pressure areas, the minimum value among the low-pressure areas is taken). ;

[0033] θ2 is the starting angle of the low-pressure zone where the steady-state average total pressure recovery coefficient of the cross section is the smallest;

[0034] θ1 is the end angle of the low-pressure zone where the steady-state average total pressure recovery coefficient of the cross section is the smallest;

[0035] σ rm Let σrj be the ordinate and θ be the abscissa.

[0036] σ rj The average value of the steady-state total pressure recovery coefficient of the j-th rake arm;

[0037] σm It is the steady-state average total pressure recovery coefficient of the measurement surface (usually the AIP section).

[0038] This application establishes a numerical calculation model of the engine idle state by setting a throttle cone downstream of the intake outlet. It adopts a hexahedral mesh structure and sets appropriate boundary conditions. Based on the steady method, it simulates the engine idle state and calculates the intake steady-state distortion index. It can analyze the changes in the intake flow field under the engine idle state, obtain high-precision intake steady-state distortion characteristics, and provide reliable data for the stability and safety assessment of aircraft engine idle state.

[0039] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for evaluating intake distortion in an engine at idle state, characterized in that, include: A numerical calculation model for engine idle state is constructed. The model includes a rear section of the intake manifold outlet and a throttle cone. The rear section of the intake manifold outlet includes a straight section and an expansion section connected in sequence. The throttle cone is at least partially set in the expansion section. By changing the axial position of the throttle cone, the engine speed change is simulated, thereby changing the throttling area and controlling the intake manifold outlet flow rate to achieve engine idle state simulation. The numerical calculation model of the engine idle state is meshed and the solver is selected. Boundary conditions are set, and the steady flow field of the engine idle state is solved to obtain the flow field parameters of the simulated section of the intake duct outlet. The simulated intake duct outlet section, which is identical to the actual intake duct outlet section, is discretized. Based on the discrete point flow field parameters of the simulated intake duct outlet section, the steady-state circumferential distortion index of the intake air at engine idle state is calculated.

2. The method for evaluating intake distortion in engine idle state as described in claim 1, characterized in that, When meshing the numerical calculation model of the engine idle state, a hexahedral mesh structure is used, and local densification is performed in the area near the intake pipe and intake lip.

3. The method for evaluating intake distortion in engine idle state as described in claim 2, characterized in that, The solver uses the finite volume method to solve the RANS equations. The turbulence model is k-ω-SST. Inviscid fluxes are discretized using the Roe upwind scheme based on MUSCL differences, and viscous fluxes are discretized using a second-order upwind scheme. The discrete gradient uses a Green-Gauss grid basis, and the turbulent kinetic energy and turbulent dissipation rate are differentially expressed using a first-order upwind scheme. The time propagation uses an implicit method based on density basis.

4. The method for evaluating intake distortion in engine idle state as described in claim 3, characterized in that, When solving the steady flow field under engine idle conditions, the boundary conditions are set as follows: the intake outlet boundary condition is set as the pressure outlet boundary, and the back pressure condition is not used for control. Its static pressure, total temperature and pressure far-field boundary are the same. The outlet flow rate is controlled by controlling the axial position of the throttle cone, thereby achieving matching with the engine idle state.

5. The method for evaluating intake distortion in engine idle state as described in claim 4, characterized in that, The method for calculating the steady-state circumferential distortion index of the intake is as follows: In the formula, The steady-state circumferential distortion index of the intake; σ 0m The steady-state average total pressure recovery coefficient is used to measure the low-pressure area of ​​the surface. σ m The steady-state average total pressure recovery coefficient of the measurement surface.

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