Self-circulation stability expansion mechanism for Flade fan

Abstract

The invention relates to the technical field of flow control of turbomachinery, in particular to a self-circulation stability extension mechanism for a Flade fan, which comprises a circulation pipeline assembly, a flow guide pipe assembly and a flow guide pipe assembly, an outlet of the circulating pipeline assembly is communicated with a fluid region of a guide vane in the fan casing through the nozzle, and an inlet of the suction nozzle is located at the 20%-40% axial chord length suction surface of a vane tip at the downstream of the front edge of the stator vane; and the outlet of the nozzle is positioned at 40-50% of the axial chord length of the blade tip at the upstream of the front edge of the moving blade and is positioned at the tail part of the guide blade. According to the self-circulation stability extension mechanism, the stall margin improvement amount of the Flade fan is effectively improved, so that the flow field of the Flade fan at a non-design point is effectively improved while the self-circulation stability extension mechanism ensures that the mechanism is simple, and the stable working margin of the fan is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flow control of turbomachinery, and particularly to a self-circulation stability augmentation mechanism for a Flade fan. Background Art

[0002] Modern variable cycle engines need to switch between two advantageous modes: high speed, low bypass ratio, and high specific thrust, and low speed, high bypass ratio, and low fuel consumption rate. This requires the Flade bypass duct blades to be rotatable to control the change in bypass duct flow rate. An important structure of variable cycle engines is the Flade (Fan on blade) form. The variable cycle engine with Flade can significantly adjust the engine inlet flow rate through its unique Flade component and improve the matching between the engine and the inlet duct.

[0003] However, in the existing design and preliminary research, high-load Flade fans have the problem of insufficient stable operating margin. Once the engine enters an unstable operating condition (such as rotating stall and surge), it will cause a decrease in efficiency at best and lead to blade damage or even complete destruction of the whole machine at worst. Therefore, it is necessary to adopt flow control technology to improve the stable operating margin of the Flade fan without affecting the normal rotation of the Flade component.

[0004] Currently, the internal flow control technology of aeroengines is divided into two types: active flow control and passive flow control according to the stability augmentation method. As a typical passive flow control technology, casing treatment has been widely used in the aviation industry. Traditional casing treatment methods, such as slot / slit casing treatment, have a large negative impact on efficiency at off-design conditions due to their irreversible geometric shape changes, and their application range is small, unable to meet the performance requirements of the Flade fan after variable speed and variable geometry. Self-circulation casing treatment usually bleeds air from the stage or the rear of the rotor and then jets it through a bridge circuit to a nozzle, which can have a smaller negative effect on efficiency while improving the stable operating margin of the Flade fan. It is an efficient casing treatment stability augmentation technology.

[0005] In the stability augmentation treatment device of the self-circulation casing disclosed in the prior art, the self-circulation mechanism is applied to the field of tip flow field control of a contra-rotating compressor, and this invention can inhibit the backward development of tip leakage flow, thereby broadening the stable operating margin of the compressor. There is also a self-circulation multi-stage axial flow compressor proposed in the prior art. This technology applies the self-circulation mechanism to the field of internal flow field control of a multi-stage axial flow compressor. This invention bleeds air from the rear of the rotor to blow away the vortices in the stator region, which can reduce the unsteady load on the downstream blade surface without affecting the aerodynamic performance of the compressor and broaden the stable operating margin of the compressor.

[0006] However, existing technologies are all designed for the compressor field with invariant geometry, but there is less research on the stability augmentation design of the self-recirculation casing in the Flade fan with variable guide / stator blade angles. In particular, the Flade fan has a unique variable geometry structure. In order to ensure that the Flade fan still has sufficient stable operating margin after the fan blades rotate and operate under variable conditions, and to reduce the negative impact on efficiency, there is an urgent need for a self-recirculation stability augmentation mechanism designed for the Flade fan. Summary of the Invention

[0007] The present invention provides a self-recirculation stability augmentation mechanism for a Flade fan to solve the problem of how to ensure that the Flade fan still has sufficient stable operating margin after the fan blades rotate and operate under variable conditions, and to reduce the negative impact on efficiency.

[0008] The self-recirculation stability augmentation mechanism for a Flade fan of the present invention adopts the following technical solutions, including: A circulating pipeline assembly, whose inlet is connected to the fluid domain of the stationary blade in the fan casing through a suction nozzle, and whose outlet is connected to the fluid domain of the guide vane in the fan casing through a nozzle; wherein, the inlet of the suction nozzle is located at the suction surface of the tip axial chord length, 20%-40% downstream of the leading edge of the stationary blade; the outlet of the nozzle is located at the tip axial chord length, 40%-50% upstream of the leading edge of the moving blade, and is located at the tail of the guide vane.

[0009] Preferably, the circulating pipeline assembly includes: a plurality of circulating pipelines, wherein, the same ports of the plurality of circulating pipelines are commonly connected to a nozzle, and the outlet of the nozzle is connected to the fluid domain of the guide vane in the fan casing; the other ports of the plurality of circulating pipelines are each connected to a suction nozzle, and the port of the suction nozzle facing away from the nozzle is connected to the fluid domain of the stationary blade in the fan casing.

[0010] Preferably, the outlet of the nozzle is located at the tip axial chord length, 40% upstream of the leading edge of the moving blade, and is located at the tail of the guide vane.

[0011] Preferably, the inlet of the suction nozzle is located at the suction surface of the tip axial chord length, 20% downstream of the leading edge of the stationary blade.

[0012] Preferably, the gap between every two adjacent circulating pipelines among the plurality of circulating pipelines is a triangular gap.

[0013] Preferably, both the suction nozzle and the nozzle are Coanda nozzles.

[0014] Preferably, the throat height of the nozzle is 10 times the tip clearance of the moving blade, and the jet outlet angle of the nozzle is 12°.

[0015] Preferably, the circumferential coverage ratio of a single suction nozzle in the fan casing is 16%, and the width of the suction nozzle is 10% of the tip axial chord length of the stationary blade.

[0016] Preferably, the circumferential coverage ratio of the nozzle on the fan casing is 26%, and the nozzle width is 13% of the tip axial chord length of the moving blade.

[0017] Preferably, the aspect ratio of the outlet of the nozzle is 9:1; the aspect ratio of the inlet of the suction nozzle is 3:1.

[0018] The beneficial effects of the present invention are as follows: By providing a circulating pipeline assembly in the present invention, a suction nozzle is provided at the inlet of the circulating pipeline assembly, and a nozzle is provided at the outlet. The inlet of the suction nozzle is located at the suction surface of the tip axial chord length 20%-40% downstream of the leading edge of the stationary blade; the outlet of the nozzle is located at the tip axial chord length 40%-50% upstream of the leading edge of the moving blade. When the inlet of the suction nozzle is located at the suction surface of the tip axial chord length 20%-40% downstream of the leading edge of the stationary blade, the deflection of the stationary blade is not affected by the suction nozzle; when the outlet of the nozzle is located at the tip axial chord length 40%-50% upstream of the leading edge of the moving blade, the deflection of the guide vane is not affected by the nozzle; that is, through the setting of the suction nozzle and the nozzle, the flow field is not affected by the variable geometry of the Flade fan. Under the conditions of different guide / stator blade deflection angles and different rotational speeds, due to the pressure difference force, the low-energy fluid accumulated at the suction surface of the stator blade due to the adverse pressure gradient in the compressor passage can effectively enter the circulating pipeline assembly from the suction nozzle and eject high-energy fluid from the nozzle. By changing the flow direction of the air flow towards the leading edge of the moving blade with the high-energy fluid, the flow field of the rotor passage is improved, and the entry of the compressor into the unstable working condition is delayed. That is, under the dual regulation of the suction nozzle and the nozzle jet in the present invention, the self-circulation mechanism can effectively improve the improvement of the stall margin of the Flade fan, and can slightly improve the efficiency under certain working conditions, and has a lower negative effect on the efficiency. Therefore, while ensuring the simplicity of the mechanism, the self-circulation and stability improvement mechanism of the present invention can effectively improve the flow field of the Flade fan at off-design points, and improve the stable working margin of the fan. Under certain matching relationships, while stabilizing the flow, it can also effectively improve the efficiency of the compressor under extreme working conditions, verifying that the self-circulation mechanism has engineering application prospects, and providing a way to broaden the stable working margin without affecting the variable geometry of the Flade fan in the future. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 It is a three-dimensional structure diagram of a self-circulation and stability improvement mechanism for a Flade fan according to the present invention.

[0021] Figure 2 This is a meridional plane schematic diagram of a self-circulation stability augmentation mechanism for a Flade fan according to the present invention.

[0022] Figure 3 This is a schematic diagram of the jet structure of a self-circulation stability augmentation mechanism for a Flade fan according to the present invention.

[0023] Figure 4 This is a schematic diagram of a self-circulation stability augmentation mechanism for a Flade fan on a certain transonic Flade fan according to the present invention.

[0024] Figure 5 This is a schematic diagram for comparing the flow field and limit streamlines of the local moving blades corresponding to the original Flade fan of the present invention and a 1.5-stage Flade fan after adopting the self-circulation stability augmentation mechanism at 99% blade height near the stall point.

[0025] Figure 6 This is the spanwise distribution of the inlet flow angle of the moving blades of a 1.5-stage Flade fan near the stall point before and after adopting the self-circulation stability augmentation mechanism according to the present invention.

[0026] Figure 7 This is a schematic diagram for comparing the flow field and limit streamlines of the stator blades corresponding to the original Flade fan of the present invention and a 1.5-stage Flade fan after adopting the self-circulation stability augmentation mechanism at 99% blade height near the stall point.

[0027] Figure 8 This is a schematic diagram of the static pressure distribution of the stator blades of a 1.5-stage Flade fan at 99% blade height cross-section near the stall point before and after adopting the self-circulation stability augmentation mechanism according to the present invention.

[0028] Figure 9 This is a schematic diagram of different inlet positions of the suction nozzle in the embodiment of the present invention.

[0029] Figure 10 This is a schematic diagram of the improvement amount of the stall margin of the Flade fan corresponding to different inlet positions of the suction nozzle and the circumferential coverage ratio of the nozzle on the fan casing according to the present invention.

[0030] Figure 11 This is a schematic diagram of the improvement amount of the stall margin of the Flade fan corresponding to different guide vane deflection angles, stator vane deflection angles and rotational speeds according to the present invention.

[0031] In the figure: 1. Suction component; 2. Circulation pipeline; 3. Nozzle; 4. Moving blade; 5. Guide vane; 6. Stator blade. Detailed implementation mode

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to 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 the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] An embodiment of a self-circulating stability-enhancing mechanism for a Flade fan according to the present invention. The self-circulating stability-enhancing mechanism of this embodiment is applied to a high-load variable-speed, variable-guide, and variable-stator-blade-angle transonic 1.5-stage Flade fan, and includes: a circulating pipeline assembly. Among them, as Figure 1 and Figure 2 shown, the circulating pipeline assembly includes: a plurality of circulating pipelines 2. The shape of the circulating pipeline 2 is strip-shaped. Among them, the same ports of the plurality of circulating pipelines 2 are commonly connected to a nozzle 3. The outlet of the nozzle 3 is communicated with the fluid domain of the guide vane 5 in the fan casing; the other ports of the plurality of circulating pipelines 2 are each connected to a suction nozzle 1, and the port of the suction nozzle 1 facing away from the nozzle 3 is communicated with the fluid domain of the stator blade 6 in the fan casing. Among them, the inlet of the suction nozzle 1 is located at the suction surface of the tip axial chord length 20%-40% downstream of the leading edge of the stator blade; the outlet of the nozzle 3 is located at the tip axial chord length 40%-50% upstream of the moving blade 4 and at the tail of the guide vane 5. It should be noted that when the inlet of the suction nozzle is located at the suction surface of the tip axial chord length 20%-40% downstream of the leading edge of the stator blade, the deflection of the stator blade is not affected by the suction nozzle; when the outlet of the nozzle is located at the tip axial chord length 40%-50% upstream of the leading edge of the moving blade, the deflection of the guide vane is not affected by the nozzle.

[0034] Exemplarily, in a specific embodiment, the outlet of the nozzle 3 is located at the tip axial chord length 40% upstream of the moving blade 4.

[0035] Exemplarily, in a specific embodiment, the inlet of the suction nozzle 1 is located at the suction surface of the tip axial chord length 20% downstream of the leading edge of the stator blade.

[0036] Exemplarily, in a specific embodiment, the gap between every two adjacent circulating pipelines 2 among the plurality of circulating pipelines 2 is a triangular gap.

[0037] Exemplarily, in a specific embodiment, both the suction nozzle 1 and the nozzle 3 are Coanda nozzles.

[0038] Exemplarily, in a specific embodiment, as Figure 3 shown, the throat height of the nozzle 3 is 10 times the tip clearance of the moving blade, and the jet outlet angle of the nozzle 3 is 12°. Exemplarily, in a specific embodiment, the circumferential coverage ratio of a single suction nozzle 1 on the fan casing is 16%, the width of the suction nozzle 1 is 10% of the tip axial chord length of the stator blade, the inlet aspect ratio of the suction nozzle 1 is 3:1, the circumferential coverage ratio of the nozzle 3 on the fan casing is 26%, the width of the nozzle 3 is 13% of the tip axial chord length of the rotor blade, and the outlet aspect ratio of the nozzle 3 is 9:1. It should be noted that, as Figure 9 and Figure 10 shown, Figure 9 a schematic diagram of the specific axial position selection of the suction nozzle is given, where positions A, B, C, and D represent the inlets of four suction nozzles located at different axial positions. Specifically, position A is the axial position on the pressure surface of the leading edge of the stator blade; B is the axial position on the suction surface of the leading edge of the stator blade, position C is the axial position on the pressure surface at 0.4 times the tip axial chord length of the stator blade from the leading edge of the stator blade; D is the axial position on the suction surface at 0.4 times the tip axial chord length of the stator blade from the leading edge of the stator blade. Through comparative experiments on different suction port positions, using the control method and keeping other variables consistent, the optimal position of the suction port is D. The stall margin improvement amount (SMI) at each position is as Figure 10 shown. Finally, when the optimal position of the suction port is determined to be D, the stall margin improvement amount is the largest. The selection of the axial position of the nozzle also adopted multiple groups of control experiments, and finally the aforementioned axial position was determined. It should be noted that three groups of experiments with circumferential coverage ratios of 16%, 26%, and 36% were respectively carried out for the nozzle. It was found that as the circumferential coverage ratio increases, the stall margin improvement amount first increases and then decreases with the increase of the circumferential coverage ratio. As Figure 10 shown, finally, when the circumferential coverage ratio of the nozzle 3 on the fan casing is determined to be 26%, the stall margin improvement amount is the largest.

[0039] Hereinafter, the self-circulation stability augmentation mechanism of the present invention will be applied to a high-load variable-speed, variable-guide, and variable-stator-blade-angle transonic 1.5-stage Flade fan for numerical simulation experiments to illustrate the self-circulation stability augmentation mechanism of the present invention: Step 1, as Figure 4As shown, the number of self-circulating stability augmentation mechanisms is 1, the number of suction nozzles 1 and circulating pipelines 2 is 5 each, and the number of nozzles 3 is 1. The two-dimensional profile of nozzle 3 is fitted by a Coanda curve. To ensure that the jet flows closely along the wall surface and reduce mixing losses at the outlet of nozzle 3, the jet orifice is designed based on the wall attachment effect. The throat height of nozzle 3 is 10 times the tip clearance of the moving blade, the jet outlet angle of nozzle 3 is 12°, the shape of the jet orifice of the nozzle is rectangular, and the aspect ratio is 9:1. The suction nozzles 1 and the nozzle 3 are connected using the circulating pipeline 2. The inlet of nozzle 3, the outlet of the suction nozzle, and the connecting bridge path 2 are smoothly transitionally connected, aiming to ensure the minimum loss of air flow during the flow process. Since nozzle 3 is located at 40%-50% of the tip axial chord length upstream of the leading edge of the moving blade, the regulation effect of the jet orifice of nozzle 3 is not affected by the change in the guide vane angle, and the inlet of the suction nozzle 1 is not affected by the change in the stator vane angle.

[0040] Step 2: The numerical simulation experiment uses the NUMECA commercial software package in the field of turbomachinery. The fan computational domain grid is generated by the AutoGrid5 / IGG module, the grid topology of the self-circulating mechanism is generated by the IGG module, the fan grid topology adopts the O4H grid topology structure, the inlet and outlet grid topologies of the computational domain are of the H type, and the computational domain surrounding the blade adopts the O type grid. The tip clearance adopts the butterfly grid topology structure, with an inner O type grid and an outer H type grid, and the near-wall grid is encrypted to ensure that the Yplus value < 2, aiming to capture the flow field details. Five different fan grids under the deflection of the guide / stator vane angles are divided in AutoGrid5, and then the self-circulating mechanism is spliced to form a numerical simulation model. Because the number of grid nodes and grid density of the self-circulating mechanism cannot be the same as those of the main channel grid nodes and grid density in the casing domain, the self-circulating mechanism and the fan tip domain adopt a completely non-matching connection.

[0041] Step 3: Use the NUMECA / FINE module to conduct steady-state numerical simulation experiments on the Flade fan at different guide / stator vane angles and different rotational speeds. The three-dimensional Reynolds-averaged Navier-Stokes equations in the cylindrical coordinate system are solved using the finite volume method. The Spalart-Allmaras model is selected for the turbulence model, the spatial terms are discretized using the central difference scheme, and the fourth-order Runge-Kutta method is used for the solution of the time terms. In addition, the implicit residual smoothing method and the multigrid technique are used to accelerate the convergence process, and the Courant-Friedrichs-Lewy (CFL) number is taken as 3.0. The rotating-stator interface adopts circumferential conservation, and the circumferential averaging method is used for data transfer. The total pressure (101325 Pa) and total temperature (288.15 K) are given at the inlet boundary condition, with uniform axial air intake; the average static pressure is given at the outlet, the wall surface adopts the adiabatic wall no-slip boundary condition, and each channel is set as a periodic boundary condition.

[0042] Step 4: AsFigures 5 to 8 The numerical simulation results shown, where Figure 5 a is a schematic diagram of the flow field and limit streamlines at 99% blade height near the stall point of the local moving blades corresponding to the original Flade fan, Figure 5 b is a schematic diagram of the flow field and limit streamlines at 99% blade height near the stall point of the local moving blades corresponding to a 1.5-stage Flade fan with a self-circulation stability augmentation mechanism, Figure 7 a is a schematic diagram of the flow field and limit streamlines at 99% blade height near the stall point of the stationary blades corresponding to the original Flade fan, Figure 7 b is a schematic diagram of the flow field and limit streamlines at 99% blade height near the stall point of the stationary blades corresponding to a 1.5-stage Flade fan with a self-circulation stability augmentation mechanism; the 1.5-stage Flade fan under different guide vane and stationary blade angles and different rotational speed matches is regulated by the self-circulation stability augmentation mechanism, and good stability augmentation effects can be obtained. As Figure 7 and Figure 8 shown, when the guide / stationary blade angle deflects, the position of the self-circulation mechanism remains unchanged, and it does not affect the rotation of the guide / stationary blade. The suction port of the suction component can significantly suck away the low-energy fluid accumulated at the suction surface of the stationary blade due to the channel adverse pressure gradient, eliminate the reverse flow area, slow down the blockage of the stationary blade channel, and the recirculation phenomenon in the channel disappears significantly. After the suction port is regulated, the static pressure on the suction surface of the stationary blade is significantly increased; as Figure 5 and Figure 6 shown, the high-energy fluid ejected from the nozzle can significantly regulate the inlet air angle of the moving blade inlet air flow, thereby reducing the air flow attack angle at the moving blade tip inlet, the overflow phenomenon at the rotor leading edge disappears, and the leading edge load is significantly reduced.

[0043] In addition, the numerical simulation results of a 1.5-stage high-load transonic Flade fan verify that the self-circulation mechanism can effectively improve the stable operating margin of the Flade fan under different guide vane angles (0 - 40°), different stationary blade angles (0 - 20°), and different rotational speeds (0.8 - 1.0 times the design rotational speed) matches. As Figure 11 shown, Figure 11 the horizontal axis of the bar chart represents different guide vane deflection angles, stationary blade deflection angles, and rotational speeds. From Figure 11 it can be seen that in the numerical simulation, the average stall margin improvement of a certain type of transonic fan can reach 4.5%, and the stall margin improvement can reach more than 5.3% under certain matching relationships. And at 0.8 times the design rotational speed and the design operating condition point, the adiabatic efficiency of this fan is increased by 0.9%. It can be seen that the self-circulation mechanism can improve a large stable operating margin and has a low negative effect on efficiency.

[0044] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A self-circulating stabilization mechanism for a Flade fan, characterized in that: include: a circulation pipeline assembly, the inlet of which is connected to the fluid domain of the stationary blades in the fan casing through a suction nozzle, and the outlet of which is connected to the fluid domain of the guide blades in the fan casing through a nozzle; Among them, the inlet of the suction nozzle is located at the suction surface of 20%-40% of the axial chord length of the blade tip downstream of the leading edge of the static blade; the outlet of the nozzle is located at 40%-50% of the axial chord length of the blade tip upstream of the leading edge of the moving blade, and is located at the tail of the guide vane.

2. A self-circulating stabilization mechanism for a Flade fan according to claim 1, characterized in that: The circulation pipeline assembly includes: multiple circulation pipelines, wherein the same port of the multiple circulation pipelines is commonly connected to a nozzle, and the outlet of the nozzle is connected to the fluid domain of the guide vane in the fan casing; the other ports of the multiple circulation pipelines are respectively connected to a suction nozzle, and the port of the suction nozzle facing away from the nozzle is connected to the fluid domain of the stationary blade in the fan casing.

3. A self-circulating stabilization mechanism for Flade fans according to claim 1, characterized in that: The nozzle outlet is located at 40% of the axial chord length of the blade tip upstream of the leading edge of the moving blade and at the tail of the guide vane.

4. A self-circulating stabilization mechanism for a Flade fan according to claim 1, characterized in that: The inlet of the suction nozzle is located at the suction surface of the blade tip 20% of the axial chord length downstream of the leading edge of the stationary blade.

5. A self-circulating stabilization mechanism for Flade fans according to claim 2, characterized in that: There is a triangular gap between every two adjacent circulation pipelines in the plurality of circulation pipelines.

6. A self-circulating stabilization mechanism for Flade fans according to claim 1, characterized in that: Both the suction nozzle and the nozzle are Coanda nozzles.

7. A self-circulating stabilization mechanism for a Flade fan according to claim 1, characterized in that: The throat height of the nozzle is 10-15 times the tip clearance of the moving blades, and the jet outlet angle of the nozzle is 10-15°.

8. A self-circulating stabilization mechanism for a Flade fan according to claim 2, characterized in that: The circumferential coverage ratio of a single suction nozzle on the fan casing is 15%-20%, and the width of the suction nozzle is 10% of the axial chord length of the tip of the stationary blade.

9. A self-circulating stabilization mechanism for a Flade fan according to claim 2, characterized in that: The nozzle has a circumferential coverage ratio of 25%-30% on the fan casing, and the nozzle width is 13% of the axial chord length of the blade tip.

10. A self-circulating stabilization mechanism for a Flade fan according to claim 2, characterized in that: The outlet length-to-width ratio of the nozzle is 7:1 to 9:1; the inlet length-to-width ratio of the suction nozzle is 1:1 to 3:1.

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