Three-dimensional fan flutter prediction method and device, terminal and readable storage medium

Abstract

The present application proposes a three-dimensional fan flutter prediction method and device, terminal and readable storage medium, the method comprising: obtaining the no-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface when the acoustic liner in the fan duct is located above the rotor and overlaps with the rotor axially; determining the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field respectively based on the no-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface; on this basis, determining the unsteady aerodynamic work done by the fluid in the fan duct on the blade within a single vibration cycle; if the unsteady aerodynamic work is within the specified flutter range, determining that the fan blade flutters. The present application can meet the needs of extending the length of the acoustic liner for fan noise reduction, effectively deal with the situation where the acoustic liner overlaps with the rotor axially, and achieve the dual effects of blade tip sound processing on noise reduction and flutter control.

Description

[Technical field]

[0001] The present application relates to the field of aviation technology, and in particular to a three-dimensional fan flutter prediction method and device, a terminal and a readable storage medium. [Background technology]

[0002] For aircraft engines, acoustic reflections in a specific length of inlet duct can cause fan flutter under certain speed conditions without significant flow separation and viscous effects, which is called acoustic flutter. Currently, acoustic flutter can be suppressed by attenuating reflected waves through acoustic treatment.

[0003] Generally speaking, the acoustic liner in an aero-engine can be located at the front end of the fan rotor blade. For this case, first, the duct is divided into several segments by a given cross-sectional interface. Then, the response function of each segment is derived in a unified matrix form, which is called a transfer unit. The transfer units of the rotor and the acoustic liner are modeled separately using two methods of singularity. The three-dimensional lifting surface theory is then used to predict the rotor response, and the acoustic liner segment is regarded as a hard wall with equivalent surface mass source distribution. Next, the acoustic field is consistently represented as a rigid duct mode using the modal matching technique, and the matrix equation that controls the entire disturbance field is obtained. In the coefficient matrix of the matrix equation, each transfer unit is coupled by an interface matching condition. In addition, the boundary integral method is combined with the above steps to match the acoustic field at both ends of the duct opening with the radiated acoustic field. By solving the control equations, the coupled unsteady response of the rotor and the entire duct boundary can be solved simultaneously. Finally, the energy method is used to evaluate the possibility of flutter.

[0004] However, the interface matching solution strategy for the interference disturbance field in the above evaluation method requires that different acoustic elements in the pipeline be axially separated from each other. In the related art, in order to obtain a better noise reduction effect, an acoustic liner can be laid above the rotor, that is, the rotor and the acoustic liner overlap axially. Therefore, the above method cannot adapt to the situation where the rotor and the acoustic liner overlap axially.

[0005] Therefore, how to evaluate whether the fan is vibrating when the rotor and the acoustic liner overlap axially has become a technical problem that needs to be solved urgently. [Summary of the invention]

[0006] The embodiments of the present application provide a three-dimensional fan flutter prediction method and device, a terminal and a readable storage medium, aiming to solve the technical problem that the fan flutter evaluation method using the transfer unit method in the related art cannot be applied to the situation where the rotor and the acoustic liner overlap axially.

[0007] In a first aspect, an embodiment of the present application provides a three-dimensional fan flutter prediction method, comprising: when an acoustic liner is located above a rotor in a fan duct and overlaps axially with the rotor, obtaining a no-penetration boundary condition on a fan blade surface and an impedance boundary condition on an acoustic liner surface; determining a matching function of a rotor scattered sound field and a matching function of an acoustic liner scattered sound field based on the no-penetration boundary condition on the fan blade surface and the impedance boundary condition on the acoustic liner surface respectively; determining a first matrix equation of the no-penetration boundary condition on the fan blade surface and a second matrix equation of the impedance boundary condition on the acoustic liner surface respectively based on the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field; for any excitation disturbance source, determining an unsteady load on a blade based on the first matrix equation and the second matrix equation; determining an unsteady aerodynamic work performed by the fluid in the fan duct on the blade within a single vibration cycle based on the unsteady load on the blade; and determining that flutter occurs on the fan blade if the unsteady aerodynamic work is within a specified flutter range.

[0008] In an embodiment of the present application, optionally, the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field are determined respectively based on the no-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface, including: determining the matching function of the rotor scattered sound field based on the Green's function, the initial function of the rotor scattered sound field and the initial function of the blade unsteady load.

[0009] In an embodiment of the present application, optionally, determining the first matrix equation of the no-penetration boundary condition on the surface of the fan blade includes: obtaining the induced velocity on the blade surface based on a preset quantitative equation; determining a first transformation function of the no-penetration boundary condition on the surface of the fan blade based on a matching function of the rotor scattered sound field, the induced velocity on the blade surface and the no-penetration boundary condition; performing a series expansion on the dipole source distribution on the blade surface to obtain a blade unsteady load distribution in a series superposition form; determining the first matrix equation of the no-penetration boundary condition based on the blade unsteady load distribution in the series superposition form and the first transformation function.

[0010] In an embodiment of the present application, optionally, before the step of determining the conversion function of the rotor scattered sound field, the method further includes: determining an initial function of the rotor scattered sound field based on a generalized acoustic analogy method.

[0011] In an embodiment of the present application, optionally, the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field are determined respectively based on the no-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface, including: determining the local normal velocity and the flow-following normal velocity of the particles on the acoustic liner surface based on the normal displacement and the target normal velocity of the particles on the acoustic liner surface; determining the matching function of the acoustic liner scattered sound field based on the local normal velocity and the flow-following normal velocity of the particles on the acoustic liner surface.

[0012] In an embodiment of the present application, optionally, a second matrix equation for determining the impedance boundary condition of the acoustic lining surface includes: determining a second transformation function for the impedance boundary condition of the acoustic lining surface based on a matching function of the acoustic lining scattered sound field; performing a sinusoidal expansion process on a target normal velocity based on a particle on the acoustic lining surface in the axial direction to obtain a normal velocity parameter; and determining a second matrix equation for the impedance boundary condition of the acoustic lining surface based on the second transformation function and the normal velocity parameter.

[0013] In an embodiment of the present application, optionally, before determining the unsteady load of the blade based on the first matrix equation and the second matrix equation for any excitation disturbance source, it also includes: obtaining the normal displacement of the blade in the fixed coordinate system of the rotor, and determining the normal motion velocity of the fluid particles on the blade surface based on the normal displacement; and determining the unsteady pressure corresponding to the normal motion velocity of the fluid particles on the blade surface based on a preset quantitative equation; then, for any excitation disturbance source, determining the unsteady load of the blade based on the first matrix equation and the second matrix equation includes: determining a target matrix equation group based on the first matrix equation and the second matrix equation, as well as the unsteady fluid particle normal motion velocity and the unsteady pressure caused by the excitation disturbance source, wherein the target matrix equation group is used to determine the unsteady load of the blade.

[0014] In a second aspect, an embodiment of the present application provides a three-dimensional fan flutter prediction device, including: a boundary condition acquisition unit, used to acquire the no-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface when the acoustic liner is located above the rotor in the fan duct and overlaps with the rotor axially; a matching function determination unit, used to determine the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field based on the no-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface; a matrix equation acquisition unit, used to determine the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field based on the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field. A matching function of the acoustic field is used to respectively determine a first matrix equation of the non-penetration boundary condition of the fan blade surface and a second matrix equation of the impedance boundary condition of the acoustic lining surface; an unsteady load determination unit is used to determine the unsteady load of the blade based on the first matrix equation and the second matrix equation for any excitation disturbance source; an unsteady aerodynamic work determination unit is used to determine the unsteady aerodynamic work done by the fluid in the fan duct on the blade within a single vibration cycle based on the unsteady load of the blade; and a flutter determination unit is used to determine that the fan blade flutters if the unsteady aerodynamic work is within a specified flutter range.

[0015] In an embodiment of the present application, optionally, the matching function determination unit is used to determine the matching function of the rotor scattered sound field based on the Green's function, the initial function of the rotor scattered sound field and the initial function of the blade unsteady load.

[0016] In an embodiment of the present application, optionally, the matrix equation acquisition unit is used to: obtain the induced velocity on the blade surface based on a preset quantitative equation; determine a first transformation function of the no-penetration boundary condition on the fan blade surface based on the matching function of the rotor scattered sound field, the induced velocity on the blade surface and the no-penetration boundary condition; perform a series expansion on the dipole source distribution on the blade surface to obtain a blade unsteady load distribution in a series superposition form; determine the first matrix equation of the no-penetration boundary condition based on the blade unsteady load distribution in the series superposition form and the first transformation function.

[0017] In an embodiment of the present application, optionally, it further includes: an initial function determination unit, which is used to determine the initial function of the rotor scattered sound field based on a generalized acoustic analogy method before the step of determining the conversion function of the rotor scattered sound field.

[0018] In an embodiment of the present application, optionally, the matching function determination unit is used to: determine the local normal velocity and the flow-following normal velocity of the particles on the surface of the sound lining based on the normal displacement and the target normal velocity of the particles on the surface of the sound lining; and determine the matching function of the scattered sound field of the sound lining based on the local normal velocity and the flow-following normal velocity of the particles on the surface of the sound lining.

[0019] In an embodiment of the present application, optionally, the matrix equation acquisition unit is used to: determine a second transformation function of the impedance boundary condition of the sound lining surface based on a matching function of the sound lining scattered sound field; perform axial sinusoidal expansion processing on a target normal velocity based on a particle on the sound lining surface to obtain a normal velocity parameter; and determine a second matrix equation of the impedance boundary condition of the sound lining surface based on the second transformation function and the normal velocity parameter.

[0020] In an embodiment of the present application, optionally, it also includes: a preprocessing unit, which is used to obtain the normal displacement of the blade in the fixed coordinate system of the rotor before determining the unsteady load of the blade based on the first matrix equation and the second matrix equation for any excitation disturbance source, and determine the normal motion velocity of the fluid particles on the blade surface based on the normal displacement; and determine the unsteady pressure corresponding to the unsteady fluid velocity based on a preset quantitative equation; then the unsteady load determination unit is used to: determine the target matrix equation group based on the first matrix equation and the second matrix equation, as well as the normal motion velocity of the unsteady fluid particles and the unsteady pressure caused by the excitation disturbance source, wherein the target matrix equation group is used to determine the unsteady load of the blade.

[0021] In a third aspect, an embodiment of the present application provides a terminal, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are configured to execute any of the methods described in the first aspect above.

[0022] In a fourth aspect, an embodiment of the present application provides a readable storage medium storing computer-executable instructions, wherein the computer-executable instructions are used to execute the method flow described in any one of the first aspects above.

[0023] The above technical scheme addresses the technical problem that the fan flutter evaluation method using the transfer unit method in the related art cannot be applied to the situation where the rotor and the acoustic liner overlap axially. It can adapt to the need to extend the length of the acoustic liner for fan noise reduction and effectively deal with the situation where the acoustic liner overlaps axially with the rotor. That is, the interaction between rotor scattering and acoustic liner scattering can be considered, thereby predicting the influence of the blade tip acoustic liner on the rotor flutter stability, and achieving the dual effects of blade tip acoustic processing on noise reduction and flutter control.

Brief Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A flow chart of a three-dimensional fan flutter prediction method according to an embodiment of the present application is shown;

[0026] Figure 2 A schematic diagram showing axially overlapped rotor and acoustic liner parts in a fan duct model with rotor blade tip acoustic treatment according to an embodiment of the present application is shown;

[0027] Figure 3 A schematic diagram showing a non-local acoustic liner portion in a fan duct model with rotor blade tip acoustic processing according to an embodiment of the present application is shown;

[0028] Figure 4 A schematic diagram of a blade force triangle and a velocity triangle in a rotor fixed coordinate system according to an embodiment of the present application is shown;

[0029] Figure 5 A schematic diagram showing the sound scattering effect of a non-local reactive sound liner according to an embodiment of the present application is shown;

[0030] Figure 6 A block diagram of a three-dimensional fan flutter prediction device according to an embodiment of the present application is shown;

[0031] Figure 7 A block diagram of a terminal according to an embodiment of the present application is shown. [Specific implementation method]

[0032] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0033] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0034] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0035] Figure 1 A flow chart of a three-dimensional fan flutter prediction method according to an embodiment of the present application is shown.

[0036] like Figure 1 As shown, a three-dimensional fan flutter prediction method according to an embodiment of the present application includes:

[0037] Step 102 : When the acoustic liner in the fan duct is located above the rotor and overlaps with the rotor axially, obtain a no-penetration boundary condition of the fan blade surface and an impedance boundary condition of the acoustic liner surface.

[0038] As the cabin length of modern high bypass ratio turbofan engines becomes shorter and the fan diameter becomes larger, the demand for noise reduction is increasing. In this regard, the length of the acoustic liner originally located on the front wall of the fan can be increased to extend it to the tip of the fan rotor blade to effectively reduce the noise level. In this way, the acoustic liner will be located above the rotor and overlap with the rotor axially.

[0039] like Figure 2 As shown in the figure, the fan duct is simplified into an infinitely long straight duct with uniform cross-section containing uniform axial flow, and its inner and outer radii are R h and R d Inside the pipe is a subsonic annular rotor rotating at an angular velocity Ω and an axially overlapped finite length wall acoustic liner. is the cylindrical coordinate fixed on the pipe, n x 、n r , is the corresponding unit vector, specifying the circumferential coordinates The reverse direction of the rotation of the vortex increases. The flow field in the tube is regarded as the superposition of small amplitude isentropic disturbances and the inclusion of density ρ 0 , pressure p 0 , speed of sound c 0 , Mach number M a The axial time-averaged flow field. The average flow velocity relative to the pipe is U = Ma*c 0 , the average flow velocity relative to the moving blade is The rotor consists of B equally spaced blades with an axial chord length of is constant along the span direction. and Represent the axial coordinates of the leading and trailing edges of the blades respectively. Combined with Figure 3 As shown, the tube wall has a limited axial length. Except for the sound lining part, the rest of the wall is hard wall. are the axial coordinates of the front and rear ends of the acoustic liner respectively. The non-local reaction acoustic liner consists of a radial depth of h cav The model is composed of a cavity and a perforated plate, and the average flow velocity in the cavity is assumed to be zero.

[0040] In order to reduce the complexity of solving and processing the characteristic solution of the flow duct in the acoustic liner, the infinite hard-walled duct Green's function G(x',τ|x,t) can be used to construct the solution of the disturbance field in the fan duct, that is, the unsteady disturbance generated in the fan duct is still consistently expressed as a series superposition form of orthogonal hard-walled duct modes. Where x and x' are the vector coordinates of the observation point and the source point, respectively, and t and τ represent time.

[0041] Based on the linear superposition principle, the disturbance field in the fan duct can be divided into three parts. The first part is the unsteady pressure The unsteady fluid velocity is The second part is the excitation disturbance source, and the second part is the rotor scattered field The third part is the acoustic lining scattering field And the scattered sound field in the back cavity The tilde sign indicates the amount by which the harmonic changes over time. iwt , where ω is the disturbance angular frequency in the pipeline fixed coordinate system.

[0042] like Figure 4 As shown in the figure, the rotor scattered acoustic field can be equivalent to the disturbance field excited by the dipole source, which corresponds to the unsteady aerodynamic load exerted by the blade on the fluid. where q∈[1,B] refers to the number of leaves as The positive direction of increasing, is perpendicular to the blade surface S q The unit vector of the acoustic liner is: the scattering field of the acoustic liner can be equivalent to the scattered acoustic field excited by the monopole source. The equivalent monopole source intensity is related to the normal vibration velocity of the acoustic liner surface. Directly proportional.

[0043] On this basis, the disturbance field in the fan duct including the rotor and blade tip acoustic liner must simultaneously satisfy the no-penetration boundary condition of the blade surface and the impedance boundary condition of the acoustic liner surface.

[0044] The no-penetration boundary condition on the blade surface satisfies:

[0045]

[0046] The above formula is applicable to the blade surface and

[0047] The impedance boundary condition of the acoustic lining surface satisfies:

[0048]

[0049] The above formula is applicable to the surface of the sound lining Among them, Figure 3 As shown, the unit vector n r Perpendicular to the surface of the acoustic liner, Z p is the impedance of the perforated plate, which can be given by the impedance model. Its size is determined by the diameter of the small holes on the perforated plate, the plate thickness, and the perforation rate.

[0050] Step 104 : Based on the non-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface, a matching function of the rotor scattered sound field and a matching function of the acoustic liner scattered sound field are determined respectively.

[0051] Step 106, based on the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field, respectively determine a first matrix equation of the no-penetration boundary condition of the fan blade surface and a second matrix equation of the impedance boundary condition of the acoustic liner surface.

[0052] Step 108: For any excitation disturbance source, determine the blade unsteady load based on the first matrix equation and the second matrix equation.

[0053] Step 110 , determining the unsteady aerodynamic work performed by the fluid in the fan duct on the blade within a single vibration cycle based on the unsteady load on the blade.

[0054] Step 112: If the unsteady aerodynamic work is within a specified flutter range, it is determined that the fan blades are fluttering.

[0055] Combined with the non-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface, the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field are derived, and the first matrix equation of the non-penetration boundary condition of the fan blade surface and the second matrix equation of the impedance boundary condition of the acoustic liner surface are further derived, and the blade unsteady load is solved by the first matrix equation and the second matrix equation. Finally, the unsteady aerodynamic work done by the fluid in the fan duct on the blade in a single vibration cycle is solved based on the blade unsteady load.

[0056] Based on the conservative assumptions commonly used in aeroelastic stability analysis, the mechanical damping and structural damping of the fan rotor are considered to be zero. According to the energy method, the unsteady aerodynamic work W aero <0 means the blades do work on the fluid, the vibration is reduced, and the rotor remains stable. aero >0 means that the fluid does work on the blades, the initial blade cascade oscillation will be rapidly amplified, the rotor will become unstable, and flutter will occur.

[0057] In general, for any given flutter excitation source and The above equations (1) and (2) are about the distribution of dipole sources on the blade surface. Distribution of monopole sources on the surface of the harmonic lining It is extremely difficult to directly solve the simultaneous equations of . Therefore, we can use the three-dimensional lifting surface theory and the singular point distribution expansion idea of ​​the equivalent distribution source method to convert and They are written as their own finite series expansion forms, and the positive definite algebraic equations about the corresponding singular expansion coefficients are derived to achieve the simultaneous solution of the unsteady response of the rotor acoustic liner. The following is an explanation of the derivation of the rotor scattered sound field, the acoustic liner scattered sound field and the excitation disturbance source involved in the above derivation process.

[0058] For the rotor scattered sound field, based on the generalized acoustic analogy method, the initial function of the rotor scattered sound field is determined, that is, based on the generalized acoustic analogy theory, the initial function expression of the rotor scattered sound field is determined as:

[0059]

[0060] where G is the Green's function for an infinitely long annular hard-walled pipe with uniform axial flow, and the blade unsteady load It can be written as follows:

[0061]

[0062] Here, Δp represents the unsteady pressure difference between the upper and lower surfaces of the first blade (reference blade), and λ is the angular frequency of the incoming flow disturbance felt on the rotating blade. Using equation (4) as the initial function of the blade unsteady load, based on the Green function G, the initial function of the rotor scattered sound field and the initial function of the blade unsteady load, the matching function of the rotor scattered sound field is determined, that is, the above equation (4) and the Green function G are substituted into equation (3) to obtain:

[0063]

[0064] Next, the induced velocity on the blade surface can be obtained based on a preset quantitative equation; based on the matching function of the rotor scattered sound field, the induced velocity on the blade surface and the no-penetration boundary condition, a first transformation function of the no-penetration boundary condition on the fan blade surface is determined; the dipole source distribution on the blade surface is expanded in series to obtain a blade unsteady load distribution in a series superposition form; based on the blade unsteady load distribution in the series superposition form and the first transformation function, a first matrix equation of the no-penetration boundary condition is determined.

[0065] According to the quantitative equation, the normal component of the induced velocity on the corresponding blade surface can be written as:

[0066]

[0067] in, is the kernel function of the acoustic pressure and induced velocity.

[0068] Then, the no-penetration boundary condition (1) on the blade surface can be rewritten as:

[0069]

[0070] in, Includes the effects of excitation disturbance sources and acoustic lining scattering.

[0071] In order to obtain the physically meaningful solution for Δp ​​satisfying the Kutta condition at the trailing edge of the blade, the unsteady load distribution Δp can be solved based on the Glauert solution of the thin airfoil problem and the finite radial mode expansion method.

[0072] Δp is written as a series superposition form:

[0073]

[0074] Finally, equation (7) is written as the first matrix equation:

[0075]

[0076] in, is the corresponding kernel function, F i′j′ is the blade force coefficient, N x 、N r are the number of axial and radial observation points, respectively.

[0077] For the acoustic liner scattering sound field, the unsteady response equation of the finite-length wall acoustic liner in the annular fan duct can be derived by the equivalent distributed source method. The acoustic scattering diagram of the non-local response acoustic liner is shown in Figure 5 As shown. Specifically, the local normal velocity and the flow-following normal velocity of the particles on the surface of the acoustic lining can be determined based on the normal displacement of the particles on the surface of the acoustic lining and the target normal velocity; the matching function of the acoustic lining scattered sound field can be determined based on the local normal velocity and the flow-following normal velocity of the particles on the surface of the acoustic lining. Then, based on the matching function of the acoustic lining scattered sound field, the second transformation function of the impedance boundary condition of the acoustic lining surface is determined; the target normal velocity based on the particles on the surface of the acoustic lining is subjected to sine expansion processing in the axial direction to obtain the normal velocity parameters; based on the second transformation function and the normal velocity parameters, the second matrix equation of the impedance boundary condition of the acoustic lining surface is determined.

[0078] The normal displacement of the particle on the surface of the acoustic liner should have exactly the same frequency ω as the incident sound field. i and the circumferential periodicity m i , specifically:

[0079]

[0080] The local normal velocity of the corresponding particle on the acoustic liner surface is:

[0081]

[0082] On the side facing the main pipe, the normal velocity of the particle on the surface of the acoustic liner is:

[0083]

[0084] in,

[0085] V r ψ(x) = iω i η L,r ψ(x) (13)

[0086] Based on the generalized acoustic analogy theory, the matching function of the acoustic lining scattering sound field is:

[0087]

[0088] Furthermore, the second transformation function of the impedance boundary condition on the acoustic lining surface is obtained as:

[0089]

[0090] where includes the effects of the excitation perturbation source and the rotor scattering.

[0091] Similarly, expanding V r ψ(x) sinusoidally in the axial direction, we have

[0092]

[0093] where the normal velocity parameter is:

[0094]

[0095] Furthermore, taking the inverse sine transform of both sides of the impedance equation (15):

[0096]

[0097] where can be obtained by substituting the Green's function G of the infinitely long rigid-walled annular duct into formula (14). Finally, the second matrix equation of the impedance boundary condition on the acoustic lining surface is obtained as:

[0098]

[0099] where the kernel function N m is the circumferential mode number, and N l is the number of finite terms truncated from the sine expansion of the normal acoustic particle velocity V r ψ(x) on the acoustic lining surface.

[0100] For the excitation perturbation source, the normal displacement of the blade in the rotor-fixed coordinate system can be obtained, and based on the normal displacement, the unsteady fluid velocity on the blade surface can be determined; and based on a preset quantitative equation, the unsteady pressure corresponding to the unsteady fluid velocity can be determined; then for any excitation perturbation source, based on the first matrix equation and the second matrix equation, the unsteady blade load is determined, including: based on the first matrix equation, the second matrix equation, the unsteady fluid velocity and the unsteady pressure, a target matrix equation set is determined, where the target matrix equation set is used to determine the unsteady blade load.

[0101] At the initial stage of flutter instability, it is assumed that the rotor blade undergoes small-amplitude vibrations with a fixed frequency and a fixed vibration mode. The normal displacement of the blade in the rotor-fixed coordinate system is:

[0102]

[0103] where the first term in represents the α-order bending vibration with an amplitude of H, and its normalized radial distribution function is the second term represents the β-order torsional vibration with an amplitude of Θ, and its normalized spanwise distribution function is θ β (r), Ω s is the vibration frequency.

[0104] Correspondingly, the normal motion velocity of the fluid particles on the blade surface can be expressed as:

[0105]

[0106] where

[0107] Next, based on a preset quantitative equation, the unsteady pressure corresponding to the unsteady fluid velocity is determined

[0108] So far, equations (1) and (2) are written as:

[0109]

[0110] For the convenience of calculation, we write in the form of equation (19), and write in the form of equation (9):

[0111]

[0112] Finally, the target matrix equation set is obtained:

[0113]

[0114] Obviously, for the given excitation source term and The above formula is about the singular point expansion coefficient F i′j′ and V ml The positive definite algebraic equations are used to reflect the coupled unsteady response of the rotor and the acoustic liner.

[0115] Finally, based on the energy method, the rotor flutter stability is judged. By solving the target matrix equation group, the blade unsteady load Δp can be obtained, and then the unsteady aerodynamic work done by the fluid on the blade in one vibration cycle can be calculated based on the blade unsteady load. Among them, the unsteady aerodynamic work is:

[0116]

[0117] According to the energy method, the unsteady aerodynamic work W aero <0 means the blades do work on the fluid, the vibration is reduced, and the rotor remains stable. aero >0 means that the fluid does work on the blades, the initial blade cascade oscillation will be rapidly amplified, the rotor will become unstable, and flutter will occur.

[0118] The above technical scheme is different from the interface mode matching of the transfer unit method. Instead, it directly establishes the matching equations of the rotor scattered sound field and the acoustic liner scattered sound field based on the non-penetration boundary conditions of the rotating blade surface and the impedance boundary conditions of the acoustic liner surface, and by performing series expansion on the dipole source distribution on the rotor blade surface and the monopole source distribution on the acoustic liner surface, the combined integral equations are rewritten as a positive definite algebraic equation group about the singular expansion coefficient, so that the unsteady response of the rotor acoustic liner can be solved simultaneously, and finally the flutter possibility is evaluated by the energy method. Through the above technical scheme, the rotor blade tip sound treatment can be realized to control the fan flutter. By deriving the combined solution equations of the rotor scattered sound field and the acoustic liner scattered sound field, a three-dimensional fan prediction model considering the blade tip sound treatment is established. Compared with the relevant technology, it can meet the needs of extending the length of the acoustic liner for fan noise reduction, and effectively deal with the situation where the acoustic liner overlaps with the rotor axial direction, that is, the interaction between the rotor scattering and the acoustic liner scattering can be considered, so as to predict the influence of the blade tip acoustic liner on the rotor flutter stability, and achieve the dual effect of blade tip sound treatment on noise reduction and flutter control.

[0119] Figure 6 A block diagram of a three-dimensional fan flutter prediction device according to an embodiment of the present application is shown.

[0120] like Figure 6As shown, the embodiment of the present application provides a three-dimensional fan flutter prediction device 600, including: a boundary condition acquisition unit 602, which is used to acquire the no-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface when the acoustic liner is located above the rotor in the fan duct and overlaps with the rotor axially; a matching function determination unit 604, which is used to determine the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field based on the no-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface; a matrix equation acquisition unit 606, which is used to determine the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field based on the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field. A matching function of the acoustic field is used to respectively determine a first matrix equation of the non-penetration boundary condition of the fan blade surface and a second matrix equation of the impedance boundary condition of the acoustic lining surface; an unsteady load determination unit 608 is used to determine the unsteady load of the blade based on the first matrix equation and the second matrix equation for any excitation disturbance source; an unsteady aerodynamic work determination unit 610 is used to determine the unsteady aerodynamic work done by the fluid in the fan duct on the blade within a single vibration cycle based on the unsteady load of the blade; and a flutter determination unit 612 is used to determine that the fan blade is fluttering if the unsteady aerodynamic work is within a specified flutter range.

[0121] In an embodiment of the present application, optionally, the matching function determination unit 604 is used to determine the matching function of the rotor scattered sound field based on the Green's function, the initial function of the rotor scattered sound field and the initial function of the blade unsteady load.

[0122] In an embodiment of the present application, optionally, the matrix equation acquisition unit 606 is used to: obtain the induced velocity on the blade surface based on a preset quantitative equation; determine a first transformation function of the no-penetration boundary condition on the fan blade surface based on the matching function of the rotor scattered sound field, the induced velocity on the blade surface and the no-penetration boundary condition; perform a series expansion on the dipole source distribution on the blade surface to obtain a blade unsteady load distribution in a series superposition form; determine the first matrix equation of the no-penetration boundary condition based on the blade unsteady load distribution in the series superposition form and the first transformation function.

[0123] In an embodiment of the present application, optionally, it further includes: an initial function determination unit, which is used to determine the initial function of the rotor scattered sound field based on a generalized acoustic analogy method before the step of determining the conversion function of the rotor scattered sound field.

[0124] In an embodiment of the present application, optionally, the matching function determination unit 604 is used to: determine the local normal velocity and the flow-following normal velocity of the particles on the surface of the acoustic liner based on the normal displacement and the target normal velocity of the particles on the surface of the acoustic liner; and determine the matching function of the scattered sound field of the acoustic liner based on the local normal velocity and the flow-following normal velocity of the particles on the surface of the acoustic liner.

[0125] In an embodiment of the present application, optionally, the matrix equation acquisition unit 606 is used to: determine a second transformation function of the impedance boundary condition of the sound lining surface based on a matching function of the sound lining scattered sound field; perform axial sinusoidal expansion processing on a target normal velocity based on a particle on the sound lining surface to obtain a normal velocity parameter; and determine a second matrix equation of the impedance boundary condition of the sound lining surface based on the second transformation function and the normal velocity parameter.

[0126] In an embodiment of the present application, optionally, it also includes: a preprocessing unit, which is used to obtain the normal displacement of the blade in the fixed coordinate system of the rotor before determining the unsteady load of the blade based on the first matrix equation and the second matrix equation for any excitation disturbance source, and determine the normal motion velocity of the fluid particles on the blade surface based on the normal displacement; and determine the unsteady pressure corresponding to the unsteady fluid velocity based on a preset quantitative equation; then the unsteady load determination unit 608 is used to: determine the target matrix equation group based on the first matrix equation and the second matrix equation, as well as the normal motion velocity of the unsteady fluid particles and the unsteady pressure caused by the excitation disturbance source, wherein the target matrix equation group is used to determine the unsteady load of the blade.

[0127] The three-dimensional fan flutter prediction device 600 uses any of the solutions described in the above embodiments, and therefore has all the above technical effects, which will not be repeated here.

[0128] Figure 7 A block diagram of a terminal according to an embodiment of the present application is shown.

[0129] like Figure 7 As shown, a terminal 700 of an embodiment of the present application includes at least one memory 702; and a processor 704 in communication with the at least one memory 702; wherein the memory stores instructions executable by the at least one processor 704, and the instructions are configured to execute the solution described in any of the above embodiments. Therefore, the terminal 700 has the same technical effects as any of the above embodiments, which will not be described in detail.

[0130] The terminal in the embodiment of the present application exists in various forms, including but not limited to:

[0131] (1) Mobile communication devices: These devices are characterized by their mobile communication functions and their main purpose is to provide voice and data communications. These terminals include: smart phones (such as iPhone), multimedia phones, functional phones, and low-end phones.

[0132] (2) Ultra-mobile personal computer devices: These devices fall into the category of personal computers, have computing and processing capabilities, and generally also have mobile Internet access features. These terminals include: PDA, MID and UMPC devices, such as iPad.

[0133] (3) Portable entertainment devices: These devices can display and play multimedia content. They include audio and video players (such as iPods), handheld game consoles, e-books, smart toys, and portable car navigation devices.

[0134] (4) Server: A device that provides computing services. The server consists of a processor, hard disk, memory, system bus, etc. The server is similar to a general computer architecture, but because it needs to provide highly reliable services, it has higher requirements in terms of processing power, stability, reliability, security, scalability, and manageability.

[0135] (5) Other electronic devices with data interaction functions.

[0136] In addition, an embodiment of the present application provides a readable storage medium storing computer executable instructions, wherein the computer executable instructions are used to execute the method flow described in any of the above embodiments.

[0137] The technical solution of the present application is described in detail above in combination with the accompanying drawings. Through the technical solution of the present application, the demand for extending the length of the acoustic liner for fan noise reduction can be met, and the situation of axial overlap between the acoustic liner and the rotor can be effectively dealt with. That is, the interaction between rotor scattering and acoustic liner scattering can be considered, thereby predicting the influence of the blade tip acoustic liner on the rotor flutter stability, and achieving the dual effects of blade tip acoustic processing on noise reduction and flutter control.

[0138] It should be understood that although the terms first, second, etc. may be used to describe matrix equations in the embodiments of the present application, these matrix equations should not be limited to these terms. These terms are only used to distinguish matrix equations from each other. For example, without departing from the scope of the embodiments of the present application, the first matrix equation may also be referred to as the second matrix equation, and similarly, the second matrix equation may also be referred to as the first matrix equation.

[0139] The word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0140] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0141] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of hardware plus software functional units.

[0142] The above-mentioned integrated unit implemented in the form of a software functional unit can be stored in a readable storage medium. The above-mentioned software functional unit is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor (Processor) to perform some steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), disk or optical disk and other media that can store program codes.

[0143] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A three-dimensional fan flutter prediction method, It is characterized in that include: In the case where the acoustic liner is located above the rotor in the fan duct and overlaps with the rotor axially, obtaining a no-penetration boundary condition on the surface of the fan blade and an impedance boundary condition on the surface of the acoustic liner; Based on the non-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface, respectively determining the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field; Based on the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field, respectively determine a first matrix equation of the no-penetration boundary condition of the fan blade surface and a second matrix equation of the impedance boundary condition of the acoustic liner surface; For any excitation disturbance source, determining the blade unsteady load based on the first matrix equation and the second matrix equation; determining the unsteady aerodynamic work performed by the fluid in the fan duct on the blade during a single vibration cycle based on the unsteady load on the blade; If the unsteady aerodynamic work is within a specified flutter range, it is determined that the fan blade flutters.

2. The three-dimensional fan flutter prediction method according to claim 1, It is characterized in that The method of determining the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field based on the non-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface respectively includes: A matching function of the rotor scattered sound field is determined based on the Green's function, the initial function of the rotor scattered sound field and the initial function of the blade unsteady load.

3. The three-dimensional fan flutter prediction method according to claim 2, It is characterized in that The first matrix equation for determining the no-penetration boundary condition of the fan blade surface includes: Based on the preset quantitative equation, the induced velocity on the blade surface is obtained; Determining a first transformation function of the no-penetration boundary condition of the fan blade surface based on the matching function of the rotor scattered acoustic field, the induced velocity of the blade surface, and the no-penetration boundary condition; Performing series expansion on the dipole source distribution on the blade surface to obtain a blade unsteady load distribution in a series superposition form; Based on the series superposition form of the blade unsteady load distribution and the first transformation function, a first matrix equation of the no-penetration boundary condition is determined.

4. The three-dimensional fan flutter prediction method according to claim 2, It is characterized in that Before the step of determining the conversion function of the rotor scattered sound field, the method further comprises: Based on a generalized acoustic analogy approach, an initial function of the rotor scattered acoustic field is determined.

5. The three-dimensional fan flutter prediction method according to claim 1, It is characterized in that The method of determining the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field based on the non-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface respectively includes: Determining the local normal velocity and the flow-following normal velocity of the particle point on the surface of the acoustic liner based on the normal displacement of the particle point on the surface of the acoustic liner and the target normal velocity; Based on the local normal velocity and the flow-following normal velocity of the particle point on the surface of the acoustic liner, a matching function of the acoustic liner scattered sound field is determined.

6. The three-dimensional fan flutter prediction method according to claim 5, It is characterized in that The second matrix equation for determining the impedance boundary condition of the acoustic lining surface includes: Determine a second transformation function of the impedance boundary condition of the surface of the acoustic liner based on the matching function of the acoustic field scattered by the acoustic liner; Perform sine expansion processing on the target normal velocity of the particle point on the surface of the acoustic liner in the axial direction to obtain the normal velocity parameter; A second matrix equation of the impedance boundary condition of the acoustic liner surface is determined based on the second transformation function and the normal velocity parameter.

7. The three-dimensional fan flutter prediction method according to claim 1, It is characterized in that Before determining the blade unsteady load based on the first matrix equation and the second matrix equation for any excitation disturbance source, the method further includes: Obtaining the normal displacement of the blade in the rotor fixed coordinate system, and determining the normal motion velocity of the fluid particles on the blade surface based on the normal displacement; and Based on a preset quantitative equation, determine the unsteady pressure corresponding to the unsteady fluid velocity; Then, for any excitation disturbance source, determining the blade unsteady load based on the first matrix equation and the second matrix equation includes: Based on the first matrix equation and the second matrix equation, as well as the normal motion velocity of the unsteady fluid particles and the unsteady pressure caused by the excitation disturbance source, a target matrix equation group is determined, wherein the target matrix equation group is used to determine the unsteady load on the blade.

8. A three-dimensional fan flutter prediction device, It is characterized in that include: A boundary condition acquisition unit, for acquiring a non-penetration boundary condition of a fan blade surface and an impedance boundary condition of an acoustic liner surface when the acoustic liner in the fan duct is located above the rotor and overlaps with the rotor axially; A matching function determination unit, used to determine the matching function of the rotor scattered sound field and the matching function of the acoustic liner scattered sound field respectively based on the non-penetration boundary condition of the fan blade surface and the impedance boundary condition of the acoustic liner surface; A matrix equation acquisition unit, used to determine a first matrix equation of a non-penetration boundary condition of a surface of the fan blade and a second matrix equation of an impedance boundary condition of a surface of the acoustic liner, respectively, based on a matching function of the rotor scattered acoustic field and a matching function of the acoustic liner scattered acoustic field; An unsteady load determination unit, configured to determine the unsteady load of the blade based on the first matrix equation and the second matrix equation for any excitation disturbance source; an unsteady aerodynamic work determination unit, configured to determine the unsteady aerodynamic work performed by the fluid in the fan duct on the blade within a single vibration cycle based on the unsteady load on the blade; The flutter determination unit is used to determine that the fan blades are fluttering if the unsteady aerodynamic work is within a specified flutter range.

9. A terminal, It is characterized in that include: at least one processor; and, a memory communicatively coupled to the at least one processor; The memory stores instructions executable by the at least one processor, wherein the instructions are configured to execute the method according to any one of claims 1 to 7.

10. A readable storage medium, It is characterized in that Computer executable instructions are stored, and the computer executable instructions are used to execute the method process according to any one of claims 1 to 7.

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