A Simulation Method for the Fan Flow Field in the State of a Windmill

Abstract

The present invention discloses a simulation method for the fan flow field under windmill conditions, which relates to the technical field of aeroengines. The method includes: obtaining the radial distributions of the velocity circulation and entropy increase passing through the fan blades and the blade geometric parameters under windmill conditions; constructing a three-dimensional body force model under windmill conditions according to the radial distributions of the velocity circulation and entropy increase passing through the fan blades and the blade geometric parameters; performing a full circumferential numerical simulation of the fan inlet through the three-dimensional body force model under windmill conditions, so as to obtain the windmill speed of the fan under different inlet and outlet conditions and the radial distributions of the inlet and outlet flow parameters. By using the proposed numerical simulation method for the fan windmill conditions, the present invention can accurately predict the fan windmill speed with very few computing resources, simulate the work addition and loss conditions in different radial ranges of the fan, and obtain the aerodynamic characteristics of the fan under windmill conditions and its influence on the upstream and downstream flows.

Description

Technical Field

[0001] The present invention relates to the technical field of aeroengines, and particularly relates to a method for simulating a fan flow field in a windmill state. Background Art

[0002] When an aeroengine experiences an in-flight shutdown or a combustion chamber flameout, the airflow passes through the unlit engine and drives the engine shaft to rotate under the combined action of aerodynamic force, rotor inertia, and drag torque, and the metastable rotation state that stabilizes at a certain rotational speed within a short time is called the "windmill state". During the design stage, it is very important to determine the key performance parameters of the fan in the windmill state. On the one hand, the drag characteristics of the engine in the windmill state affect the design of the vertical stabilizer of the aircraft; on the other hand, the engine flow rate, combustion chamber pressure, and temperature in the windmill state are directly related, and these three parameters are important parameters for determining the in-air ignition envelope of the engine.

[0003] With the continuous improvement of aviation technology, conventional fuel aircraft can no longer meet the requirements of lower fuel consumption, green cleanliness, and higher efficiency for aircraft, and distributed electric propulsion technology has become a viable solution. For a distributed electric propulsion system, predicting the inlet and outlet parameters of the fan in the windmill state has additional significance. When one or more fans fail, due to the very short lateral distance between the fans, the mutual influence between individual fans is significantly enhanced. The failure changes the distribution of aerodynamic parameters at the inlet and outlet sections, deepens the intake distortion degree of adjacent fans, and may cause a decrease in the surge margin or even stall of adjacent fans in severe cases, leading to secondary failures. Therefore, it is necessary to evaluate the fault propagation characteristics and influence modes in this new single-fan / multi-fan failure state. During the design stage, the computational resources consumed by performing full three-dimensional numerical simulation calculations on multiple fans and the external flow field under different working conditions are extremely large, making it difficult to meet the needs of engineering applications.

[0004] Therefore, some scholars have developed a numerical simulation method based on the volume force model. The principle is to simplify the force exerted by the blades on the airflow into a circumferentially uniform source term force field and add it to the control equation, and to model the actual flow inside the fan by solving the pipe flow with the volume force source term. However, this method can currently only simulate fans operating near the design state point. One of the main reasons is that in the windmill state, the rotational speed of the fan is an unknown quantity determined by the airflow parameters at the inlet and outlet of the fan, and the traditional numerical simulation method based on the volume force model requires the rotational speed as a known parameter and cannot be directly used to solve the windmill state.

[0005] At present, the following are proposed: (1) A numerical simulation method for fans / compressors based on the body force model, and a compressor stability calculation program CSTALL has been established. The body force modeling method is to decompose the force exerted by the blade on the airflow into an inviscid body force perpendicular to the relative velocity and a viscous body force parallel to the relative velocity. By derivation, a quantitative relationship between the velocity circulation change and entropy increase through the blade area and the body force is established to achieve the modeling of the blade force. This method can be used to simulate the fan working near the design state point more accurately, but because this method requires the fan speed as a known quantity, it cannot be used to solve the fan windmill state calculation; (2) A quantitative relationship between the blade body force and the local flow field parameters is established, and the prediction of the fan speed under the windmill state is achieved by introducing the "zero work" model of the fan shaft, thus realizing the numerical simulation calculation of the fan windmill state based on the body force model. However, this method requires that the aerodynamic parameters of the fan inlet flow are uniform, and the inlet converted flow rate at different speeds is required as input. In practical applications, this physical quantity is obviously unknown, so this method is difficult to use in engineering practice; (3) The torque is calculated using the flow parameters at the fan outlet in the literature https: / / doi.org / 10.3390 / aerospace10080724. Since the flow parameters at the fan outlet are non-uniform, this calculation method has a large error. Summary of the invention

[0006] In view of the disadvantage that the torque is calculated by using the flow parameters at the fan outlet in the prior art, the calculation method has a large error due to the uneven flow parameters at the fan outlet and the uncertain fan speed. The present invention provides a method for simulating the fan flow field under a windmill state, thereby solving the problem of large errors in the calculation method in the prior art.

[0007] A method for simulating a fan flow field in a windmill state comprises the following steps:

[0008] Obtaining the flow field parameters and blade geometric parameters of the fan in the windmill state; the flow field parameters include the radial distribution of velocity circulation and entropy increase passing through the fan blades and the quantitative relationship between the fan resistance torque and the windmill speed;

[0009] A three-dimensional body force model under windmill state is constructed based on the radial distribution of velocity circulation and entropy increase passing through the fan blades, the geometric parameters of the fan blades, and the quantitative relationship between the fan resistance torque and the windmill speed.

[0010] By inputting the flow field parameters and blade geometric parameters of the fan under the windmill state to be tested into the three-dimensional body force model, the fan intake full-circle numerical simulation is carried out, and then the windmill speed of the fan under different inlet and outlet conditions and the radial distribution of the inlet and outlet flow parameters are obtained;

[0011] Among them, the construction process of the three-dimensional body force model in the windmill state specifically includes the following steps:

[0012] According to the geometric parameters of the fan blades, the force exerted by the fan blades on the air flow is equivalent to a circumferentially uniformly distributed body force field, and the body force field is added to the circumferentially averaged Euler equations in the form of a source term to determine the quantitative relationship between the three-dimensional body force and the change in velocity circulation and entropy increment passing through the fan blades;

[0013] According to the quantitative relationship between the fan drag torque and the windmill rotation speed, obtain the drag torque that the fan rotation needs to overcome;

[0014] According to the quantitative relationship between the three-dimensional body force and the change in velocity circulation and entropy increment passing through the fan blades, integrate the circumferential body force in the three-dimensional body force to obtain the torque output by the fan;

[0015] Calculate the error between the drag torque that the fan rotation needs to overcome and the torque output by the fan, and compare the error with the set threshold ε to determine whether to continue the update iteration of the rotation speed. If the error is smaller than ε, the iteration converges; otherwise, update the rotation speed.

[0016] Furthermore, the flow field parameters of the fan in the windmill state are obtained by performing single-channel steady Reynolds-averaged numerical simulations on the fan at different rotation speeds in the windmill state under uniform air intake.

[0017] Furthermore, the geometric parameters of the fan blades include the radius of the blades, the circumferential angular coordinates of the blades, the surface pressure of the blades, and the tangential velocity of the blades.

[0018] Furthermore, according to the geometric parameters of the fan blades, the force exerted by the fan blades on the air flow is equivalent to a circumferentially uniformly distributed body force field, and the body force field is added to the circumferentially averaged Euler equations in the form of a source term to determine the quantitative relationship between the three-dimensional body force and the change in velocity circulation and entropy increment passing through the fan blades. The specific steps are as follows:

[0019] The circumferentially averaged Euler equations are expressed as:

[0020]

[0021]

[0022]

[0023] where ρ is the density, is the velocity vector, t is the time, div represents taking the divergence, represents taking the gradient, e t is the total thermodynamic energy, h t is the total enthalpy, ω is the rotation speed, r is the radius, is the body force source term;

[0024] The source term Φ is expressed in the cylindrical coordinate system as:

[0025]

[0026] where Φ r , Φ θ and Φ x represent the components of the body force in the radial, circumferential, and axial directions, respectively;

[0027] The body force is decomposed into the viscous force parallel to the flow direction and the inviscid force perpendicular to the flow direction The viscous force characterizes the flow loss in the fan blade passage, and its direction is opposite to the flow direction, obtaining:

[0028]

[0029]

[0030]

[0031] where, is the relative velocity. According to the momentum equation in the θ direction, the relationship between the actual circumferential body force and the velocity circulation is obtained;

[0032] From the first law of thermodynamics, the relationship between the entropy increase along the streamline and the viscous body force is obtained, that is:

[0033]

[0034]

[0035] where V m is the velocity along the meridian plane, m is the coordinate along the meridian plane, T s is the static temperature, s is the entropy, rV θ is the velocity circulation, and r represents the radius;

[0036] Thus, the relationship between the body force and the radial distributions of the change in velocity circulation and the entropy increment passing through the rotor blades and stator blades in the fan blades is obtained.

[0037] Furthermore, after obtaining the relationship between the body force and the radial distributions of the change in velocity circulation and the entropy increment passing through the rotor blades and stator blades in the fan blades, due to different operating conditions and have different values, the change in circulation and the entropy increment at non-reference points are calculated, and their calculation formulas are:

[0038]

[0039]

[0040] Among them, κ1 and κ2 are volume force correction coefficients, which characterize the circulation change and entropy increase change caused by the working point deviating from the reference point.

[0041] Furthermore, it also includes determining the volume force correction coefficient of the fan rotor blade, including the following steps:

[0042] Calibrate the volume force correction coefficient of the fan rotor blade by using the results of single-channel steady Reynolds-averaged numerical simulation;

[0043] Change the boundary conditions of the numerical simulation to obtain the and radial distributions under different working conditions;

[0044] Select one of the working conditions as the reference working point, then the calculation expression of the correction coefficient at the other working condition point is:

[0045]

[0046]

[0047] Complete the calibration of the volume force correction coefficient of the fan rotor blade by processing the single-channel steady Reynolds-averaged numerical simulation results under different working conditions.

[0048] Furthermore, when performing numerical simulation calculations based on the volume force model, the volume force correction coefficients κ 1,r and κ 2,r of the fan rotor blade are determined by the converted flow rate and converted rotational speed in the fan inlet sector, that is:

[0049] κ 1,r (κ 2,r ) = f(m cor,θ , n cor,θ )

[0050] where m cor,θ is the converted flow rate of the corresponding sector, n cor,θ is the converted rotational speed of the corresponding sector, which is obtained by extracting the flow parameters at the leading edge of the fan, and f indicates that κ is a binary function of m cor,θ and n cor,θ .

[0051] Furthermore, it also includes determining the circumferential coordinates of the rotor sector corresponding to the fan stator blade after completing the calibration of the volume force correction coefficient of the fan rotor blade, to obtain the m cor,θ and n cor,θ corresponding to the corresponding fan stator blade, which includes the following steps:

[0052] The circumferential coordinates of the sector are rotated by an angle θ in the opposite direction of the rotor rotation from the circumferential coordinates of the stator blades, i.e.: shift obtained as:

[0053]

[0054] θ = θ s -θ shift

[0055] where α 2,avg is the circumferential average gas flow angle at the outlet of the fan rotor blade, and L is the distance between the trailing edge of the rotor blade and the leading edge of the stator blade;

[0056] Determine the m cor,θ and n cor,θ values corresponding to the upstream rotor sector of the stator blade.

[0057] Furthermore, after obtaining the m cor,θ and n cor,θ corresponding to the fan stator blade, determine the volume force correction coefficients κ 1,s and κ 2,s of the fan stator blade, which includes the following steps:

[0058] First, perform single-channel steady Reynolds-averaged numerical simulations for different operating points, select one of the operating points as the reference operating point, and the correction coefficient is expressed as a function of the converted flow rate and converted rotational speed in the fan inlet sector, i.e.:

[0059] κ 1,s (κ 2,s ) = f(m cor,θ , n cor,θ )

[0060] According to the determined m cor,θ and n cor,θ values corresponding to the upstream rotor sector of the stator blade, obtain the volume force correction coefficient of the fan stator blade.

[0061] Furthermore, the resistance torque T resist is expressed as a function of the fan rotational speed ω, and its expression is:

[0062] T resist = f(ω)

[0063] The torque T output output by the fan is expressed as:

[0064]

[0065] where ω is the rotational speed of the local fan, and dv is the volume of the grid cell.

[0066] The present invention provides a method for simulating the fan flow field in the windmill state, which has the following beneficial effects:

[0067] The present invention uses the torque balance relationship of the fan rotor to predict the fan speed, obtains the torque output of the fan blade by integrating the circumferential body force source term, and realizes the coupled solution of the speed prediction and the flow field parameters; the present invention adopts the proposed fast numerical simulation method for the fan in the windmill state, which can use very few computing resources, accurately predict the fan speed in the windmill state, simulate the work addition and loss conditions in different radial ranges of the fan, and obtain the aerodynamic characteristics of the fan in the windmill state and its influence on the upstream and downstream flows. Since the torque output of the fan rotor is related to the local flow field parameters, it does not affect the accuracy of predicting the fan speed when the flow parameters are circumferentially non-uniform, and no other additional input parameters are required in the solution process, which better meets the requirements of engineering practical applications. Description of the Drawings

[0068] Figure 1 It is a schematic flow chart of the method for simulating the fan flow field in the windmill state according to the present invention;

[0069] Figure 2 It is a schematic flow chart of the prediction of the fan speed in the windmill state based on the body force model in the embodiment of the present invention;

[0070] Figure 3 It is a schematic diagram of the numerical simulation calculation grid based on the body force model in the embodiment of the present invention;

[0071] Figure 4 It is a schematic diagram of the comparison between the predicted result and the experimental result of the fan speed in the windmill state in the embodiment of the present invention. Detailed Embodiments

[0072] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0073] In order to quickly obtain the internal flow field characteristics and flow characteristics of the fan under different inlet and outlet conditions, the present invention proposes a method for simulating the fan flow field in the windmill state, which specifically includes the following steps:

[0074] S1: Under the condition of uniform intake air, perform a single-channel steady Reynolds-averaged numerical simulation on the fan at different speeds in the windmill state to obtain the radial distributions of the velocity circulation and entropy increase passing through the fan blades in the windmill state.

[0075] S2: According to the fan flow field parameters and blade geometric parameters described above, construct a three-dimensional body force model in the windmill state, including the following steps:

[0076] S21: Establish the quantitative relationship between the three-dimensional volume force source term in the windmill state, the change in the velocity circulation of the blade, and the entropy increment. Equivalent the force exerted by the blade on the air flow to a circumferentially uniformly distributed volume force field and add it to the circumferentially averaged Euler equations in the form of a source term. The equation has the following form:

[0077]

[0078]

[0079]

[0080] where ρ is the density, is the velocity vector, t is the time, div represents taking the divergence, represents taking the gradient, e t is the total thermodynamic energy, h t is the total enthalpy, ω is the rotational speed, r is the radius, is the volume force source term.

[0081] The source term Φ can be written in the following form in the cylindrical coordinate system:

[0082]

[0083] where Φ r 、Φ θ and Φ x represent the radial, circumferential, and axial components of the volume force respectively. The volume force can be decomposed into the viscous force parallel to the flow direction and the inviscid force perpendicular to the flow direction. The viscous force characterizes the flow loss in the blade passage and its direction is opposite to the flow direction, that is:

[0084]

[0085]

[0086]

[0087] where is the relative velocity. Analyzing the momentum equation in the θ direction, the relationship between the circumferential volume force and the velocity circulation can be obtained. Further, from the first law of thermodynamics, the relationship between the entropy increase along the streamline and the viscous volume force can be obtained, that is:

[0088]

[0089]

[0090] where V is the absolute velocity, m is the coordinate along the meridian plane, T sis the static temperature, s is the entropy, and rV θ is the velocity circulation. The meridian plane is the plane spanned by the circumferential angle θ = 0 and the (x, r) coordinates, where θ = 0 is along the circumferential direction.

[0091] The relationship between the body force and the radial distributions of the change in velocity circulation and the entropy increment passing through the fan rotor blades and the stator blades is thus obtained. Considering that under different operating conditions and values are different, but their radial distribution profiles are similar. The change in circulation and the entropy increase at non-reference points can be calculated using the following formula:

[0092]

[0093]

[0094] where κ1 and κ2 are correction coefficients, representing the changes in circulation and entropy increase caused by the operating point deviating from the reference point.

[0095] For the fan rotor and stator blades, they are determined respectively in the following ways:

[0096] (1) Fan rotor blades:

[0097] First, the correction coefficients are calibrated using the results of single-channel steady Reynolds-averaged numerical simulations. By changing the boundary conditions of the numerical simulation in step S1, the and radial distributions under different operating conditions can be obtained. Selecting one of the typical operating conditions as the reference operating point, the correction coefficient for another operating point can be calculated according to the following formula:

[0098]

[0099]

[0100] Processing the results of single-channel steady Reynolds-averaged numerical simulations under different operating conditions can complete the calibration of the correction coefficients for the fan rotor blades. When performing numerical simulation calculations based on the body force model, the correction coefficients κ 1,r and κ 2,r can be determined by the corrected flow rate and the corrected rotational speed in the fan inlet sector, that is:

[0101] κ 1,r (κ 2,r ) = f(m cor,θ , n cor,θ ) (11)

[0102] where m cor,θ is the corrected flow rate of the corresponding sector, and n cor,θ is the corrected rotational speed of the corresponding sector, which are obtained by extracting the flow parameters at the leading edge of the fan.

[0103] (2) Fan stator blades:

[0104] For the fan stator blades, first calibrate the correction factor according to the method of the rotor blades. When using the body force model for calculation, considering that its working state is mainly determined by the upstream rotor blades, it is necessary to determine the circumferential coordinates of the rotor sector corresponding to the stator blades to obtain the corresponding m cor,θ and n cor,θ . The circumferential coordinates of the sector can be obtained by rotating the circumferential coordinates of the guide vane by a certain angle θ shift in the opposite direction of the rotor rotation, that is:

[0105]

[0106] θ = θ s -θ shift (13)

[0107] where α 2,avg is the circumferential average gas flow angle at the outlet of the fan rotor blade, and L is the distance between the trailing edge of the rotor blade and the leading edge of the stator blade. After obtaining the m cor,θ and n cor,θ values corresponding to the upstream rotor sector of the stator blade, the κ 1,s and κ 2,s can be obtained by interpolation, thus completing the calculation of the body force source term.

[0108] S22: Construct a fan windmill speed prediction model.

[0109] In the windmill state, the fan operates under the ram pressure of the air flow, and its speed is determined by the fan inlet and outlet conditions and the characteristics of the engine. The torque output by the fan blades is mainly used to overcome the resistance of the rotor rotation, and the resistance usually increases with the increase of the speed. Therefore, use the relationship of torque balance to establish a speed prediction model. The resistance torque T resist can be expressed as a function of the fan speed ω:

[0110] T resist = f(ω) (14)

[0111] When using the body force model for calculation, the torque T output output by the fan can be obtained by integrating the circumferential blade force, that is:

[0112]

[0113] where ω is the local fan rotation speed, and dv is the volume of the grid unit. When T output < T resistWhen the output torque of the fan is less than the resistance work required to maintain this rotational speed, the fan will decelerate; conversely, the fan will accelerate. To ensure the stability of the iterative solution process, the idea of a PID control system is adopted for the update iteration of the rotational speed. When initializing the flow field, first a guessed initial rotational speed ω is given, and the control equations are solved to obtain the flow field parameters at the first step, and the output torque and resistance torque of the fan blades at the current rotational speed are calculated. ε is an artificially set error criterion, and different values will be taken for different working conditions and objects; it can be known from the momentum equation of the fan blades that when the error between the two is small enough, it can be considered that the rotational speed reaches stability and the iteration converges. If the error between the two does not meet the requirements, then the rotational speed is updated, that is:

[0114]

[0115] Substitute the updated rotational speed into the iteration of the next time step until the calculation converges.

[0116] S3: Based on S2, construct a three-dimensional body force model of the windmill state and perform a full-circumference numerical simulation of the fan intake. Divide the entire pipe flow channel area with stator blades added to the fan into a circumferentially symmetric hexahedral structured grid, and use the leading and trailing edge profiles of the fan and stator blades to divide the entire channel into a blade area and a non-blade area, so as to add a body force source term in the blade area. When calculating, given the boundary conditions according to the actual working conditions, including the total temperature, total pressure and the distribution of the velocity direction at the inlet, and the average static pressure at the outlet, and the remaining walls are set as non-slip boundary conditions.

[0117] S4: Through the three-dimensional body force model of the windmill state simulation, obtain the radial distributions of the windmill rotational speed of the fan and the inlet and outlet flow parameters under different inlet and outlet conditions.

[0118] As described above, only the preferred specific embodiments of the present invention are given, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A simulation method for the fan flow field in the windmill state, characterized in that, It includes the following steps: Obtain the flow field parameters and blade geometric parameters of the fan under the windmill state; The flow field parameters include the radial distributions of the velocity circulation and entropy increase passing through the fan blades, as well as the quantitative relationship between the fan resistance moment and the windmill rotation speed; Construct a three-dimensional body force model under the windmill state based on the radial distributions of the velocity circulation and entropy increase passing through the fan blades, the fan blade geometric parameters, and the quantitative relationship between the fan resistance moment and the windmill rotation speed; By inputting the flow field parameters and blade geometric parameters of the fan under the windmill state to be measured into the three-dimensional body force model, simulate the full circumferential numerical value of the fan intake, and then obtain the windmill rotation speed of the fan under different inlet and outlet conditions and the radial distributions of the inlet and outlet flow parameters; Among them, the construction process of the three-dimensional body force model under the windmill state specifically includes the following steps: According to the fan blade geometric parameters, equivalently convert the force exerted by the fan blades on the airflow into a circumferentially uniformly distributed body force field, and add the body force field to the circumferentially averaged Euler equations in the form of a source term to determine the quantitative relationship between the three-dimensional body force and the change in velocity circulation and entropy increment passing through the fan blades; According to the quantitative relationship between the fan resistance moment and the windmill rotation speed, obtain the resistance moment that the fan rotation needs to overcome; According to the quantitative relationship between the three-dimensional body force and the change in velocity circulation and entropy increment passing through the fan blades, integrate the circumferential body force in the three-dimensional body force to obtain the torque output by the fan; Calculate the error between the resistance moment that the fan rotation needs to overcome and the torque output by the fan, and compare the error with the set threshold ε to determine whether to continue the update iteration of the rotation speed. If the error is smaller than ε, the iteration converges; otherwise, update the rotation speed.

2. The simulation method for the fan flow field in the windmill state according to claim 1, characterized in that, The acquisition of the flow field parameters of the fan under the windmill state is obtained by performing single-channel steady Reynolds-averaged numerical simulations on the fan at different rotation speeds under the windmill state with uniform intake.

3. The simulation method for the fan flow field in the windmill state according to claim 1, characterized in that, The fan blade geometric parameters include the radius of the blade, the circumferential angular coordinates of the blade, the surface pressure of the blade, and the tangential velocity of the blade.

4. The simulation method for the fan flow field in the windmill state according to claim 1, characterized in that, According to the fan blade geometric parameters, equivalently convert the force exerted by the fan blades on the airflow into a circumferentially uniformly distributed body force field, and add the body force field to the circumferentially averaged Euler equations in the form of a source term to determine the quantitative relationship between the three-dimensional body force and the change in velocity circulation and entropy increment passing through the fan blades. It specifically includes the following steps: The circumferentially averaged Euler equations are expressed as: where ρ is the density, is the velocity vector, t is the time, div represents taking the divergence, represents taking the gradient, e t is the total thermodynamic energy, h t is the total enthalpy, ω is the rotational speed, r is the radius, is the body force source term; Source term It is expressed in the cylindrical coordinate system as: where Φ r , Φ θ and Φ x represent the components of the body force in the radial, circumferential, and axial directions, respectively; The body force is decomposed into a viscous force parallel to the flow direction and an inviscid force perpendicular to the flow direction The viscous force characterizes the flow loss in the fan blade passage, and its direction is opposite to the flow direction, resulting in: Among them, is the relative velocity. According to the momentum equation in the θ direction, the relationship between the actual circumferential body force and the velocity circulation is obtained. From the first law of thermodynamics, obtain the relationship between the entropy increase along the streamline and the viscous body force, that is: where V m is the velocity along the meridian plane, m is the coordinate along the meridian plane, T s is the static temperature, s is the entropy, rV θ is the circulation of velocity, r represents the radius; From this, obtain the relationship between the body force and the radial distributions of the change in velocity circulation and entropy increment passing through the rotor blades and stator blades in the fan blades.

5. The simulation method for the fan flow field in the windmill state according to claim 4, characterized in that, After obtaining the relationship between the body force and the radial distributions of the change in velocity circulation and the entropy increment passing through the rotor blades and stator blades in the fan blades, due to different operating conditions and having different values, the circulation change and entropy increment at non-reference points are calculated, and their calculation formulas are as follows: Among them, κ1 and κ2 are body force correction coefficients, characterizing the changes in circulation and entropy increase caused by the operating point deviating from the reference point.

6. A method for simulating the fan flow field in the windmill state according to claim 5, characterized in that, It also includes determining the body force correction coefficient of the fan rotor blades, including the following steps: Calibrate the body force correction coefficient of the fan rotor blades using the results of single-channel steady Reynolds-averaged numerical simulations; Change the boundary conditions of the numerical simulation to obtain the and radial distributions; Select one of the working conditions as the reference operating point, then the calculation expression for the body force correction coefficient of the other working condition is: Calibration of the volume force correction coefficient of the fan rotor blade is completed by processing the single-channel steady Reynolds-averaged numerical simulation results under different working conditions.

7. A method for simulating the fan flow field in the windmill state according to claim 6, characterized in that, When performing numerical simulation calculations based on the body force model, the body force correction coefficient κ of the fan rotor blade 1,r and κ 2,r are determined by the converted flow rate and converted rotational speed in the fan inlet sector, i.e.: κ 1,r (κ 2,r ) = f(m cor,θ , n cor,θ ) where m cor,θ is the converted flow rate of the corresponding sector, n cor,θ is the converted rotational speed of the corresponding sector, obtained by extracting the flow parameters at the leading edge of the fan, and f indicates that κ is a binary function of m cor,θ and n cor,θ .

8. A method for simulating the fan flow field in the windmill state according to claim 7, characterized in that, It also includes determining the circumferential coordinates of the rotor sector corresponding to the stator blade after calibrating the volume force correction coefficient of the fan rotor blade, and obtaining m cor,θ and n cor,θ , which includes the following steps: The circumferential coordinates of the sector are obtained by rotating the circumferential coordinates of the stator blades by an angle θ in the opposite direction of the rotor rotation, i.e.: shift That is: θ = θ s -θ shift Among them, α 2,avg is the circumferential average gas flow angle at the outlet of the fan rotor blade, and L is the distance between the trailing edge of the rotor blade and the leading edge of the stator blade; Determine the m cor,θ and n cor,θ values corresponding to the upstream rotor sector of the stator vane.

9. A method for simulating the fan flow field in the windmill state according to claim 8, characterized in that, After obtaining m cor,θ and n cor,θ corresponding to the fan stator vane, the volume force correction coefficients κ 1,s and κ 2,s are determined, which includes the following steps: First, single-channel steady Reynolds-averaged numerical simulations are carried out for different operating points. One of the operating points is selected as the reference working point. The correction coefficient is expressed as a function of the corrected flow rate and corrected rotational speed in the fan inlet sector, i.e.: κ 1,s (κ 2,s ) = f(m cor,θ , n cor,θ ) Based on the determined values of m cor,θ and n cor,θ corresponding to the upstream rotor sector of the stator vane, the volume force correction factor of the fan stator vane is obtained.

10. A method for simulating the fan flow field in the windmill state according to claim 4, characterized in that, The resistance torque T resist is expressed as a function of the fan speed ω, and its expression is: T resist = f(ω) The torque T output by its fan output is expressed as: where ω is the rotational speed of the local fan and dv is the volume of the grid cell.

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