Axis-twisted seam type casing treatment structure and design method

Abstract

The invention discloses a processing structure and a design method for a seam type casing twisting along an axis, and belongs to the technical field of gas compressors. According to the number of rotors, a plurality of blade angular seams are formed in the compressor casing, the front ends of the seam pieces of the blade angular seams incline by 45 degrees in the radial direction in the direction opposite to the rotation direction of the rotors, the rear ends of the blade angular seams incline by 40 degrees in the rotation direction of the rotors, and the blade angular seams deflect by 55 degrees in the circumferential direction. The front end and the rear end of the structure are connected through a B spline curve to form a seam type structure which is gradually twisted in the axial direction. Compared with a traditional axial inclined seam, the suction amount and the jet flow amount are larger, on one hand, through the stronger suction effect of the axial seam, the strength of blade top leakage flow is weakened, transverse migration of the blade top leakage flow is restrained, and accumulation of low-energy fluid is delayed; on the other hand, the stronger high-speed jet flow at the front end of the seam enhances the kinetic energy of the main flow at the front edge and weakens the action of the radial secondary flow, so that the through-flow capacity of the rotor is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a casing treatment structure and a design method thereof, in particular to a twisted axial slot casing treatment structure and a design method thereof, and belongs to the technical field of compressors. BACKGROUND

[0002] With the evolution of modern warship power systems to full-fuel combined power plants, the stability of the compressor, as a core component of the gas turbine, is crucial. However, due to the multi-stage characteristics of the marine compressor, it leads to a mismatch under non-design conditions, and the performance of the gas turbine deteriorates. Casing treatment, as a widely used passive control system, can significantly improve the stable working margin of the compressor. So far, researchers have carried out research on casing treatment structures such as axial slots, circumferential grooves, and self-circulation, among which the axial slot casing treatment has been favored by many researchers due to its significant stability expansion effect.

[0003] For example, the invention patent application with publication number CN107524637A discloses a transonic axial flow fan blade angular slot machine case processing structure design, which has multiple narrow slots on the fan case along the axial direction and is uniformly arranged along the circumferential direction to form an axial slot machine case processing structure, and the width of the axial slot machine case processing structure covers the entire blade tip axial chord length. The opening surface of the axial slot machine case processing structure is rotated at a certain angle along the blade installation angle direction to form a blade angular slot machine case processing structure. The bleed air and jet direction of the blade angular slot machine case processing structure is adapted to the airflow direction in the blade tip passage, thereby improving the bleed air and jet quantity and reducing the airflow mixing loss; the stability enhancement capability of the blade angular slot machine case processing is enhanced, and the blade angular slot machine case processing structure further improves the comprehensive stall margin while reducing the efficiency loss. For example, the invention patent application with publication number CN107524637A discloses a transonic axial flow fan blade angular slot machine case processing structure design, which belongs to the technical field of turbomachinery: multiple narrow slots are opened on the fan case along the axial direction, and are uniformly arranged along the circumferential direction to form an axial slot machine case processing structure, and the width of the axial slot machine case processing structure covers the entire blade tip axial chord length. The opening surface of the axial slot machine case processing structure is rotated at a certain angle along the blade installation angle direction to form a blade angular slot machine case processing structure. The bleed air and jet direction of the blade angular slot machine case processing structure is adapted to the airflow direction in the blade tip passage, thereby improving the bleed air and jet quantity and reducing the airflow mixing loss; the stability enhancement capability of the blade angular slot machine case processing is enhanced, and the blade angular slot machine case processing structure further improves the comprehensive stall margin while reducing the efficiency loss. The above-mentioned technologies each have their own characteristics and are suitable for their respective adaptive use occasions and situations. However, the traditional axial inclined slot type machine case processing gradually exposes some limitations in actual application, especially when the marine axial flow compressor is in low operating conditions. First, the effect of widening the stability margin is not ideal, which is difficult to meet the increasing demand for stable operation of the compressor under complex operating conditions. Second, while improving the stability margin, there is often a large efficiency loss, which is not conducive to ships that pursue high-efficiency power systems. These deficiencies make it difficult for the traditional axial inclined slot type machine case processing to better adapt to the operating requirements of the marine axial flow compressor under diversified operating conditions, limiting its further popularization and application.

[0004] Therefore, in order to improve the stability of the marine axial flow compressor under low operating conditions, there is an urgent need for a machine case processing structure that can further widen the stable operating margin of the compressor under low operating conditions with as little efficiency loss as possible to solve the above problems. SUMMARY

[0005] The application is to solve the problem of insufficient stability margin of the marine axial flow compressor under low working condition and to widen the stability margin without losing large adiabatic efficiency, and further proposes a twisted slit casing treatment structure along the axis and a design method on the basis of the traditional axial tilt slit casing treatment research, which can further widen the stable working margin of the compressor under low working condition with as little efficiency loss as possible.

[0006] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme: The design method of the twisted slit casing treatment structure along the axis is realized by the following steps: Step one: determining four end point coordinates of the slit bottom surface according to the position of the rotor blade tip leading edge, the axial length of the axial slit, the width of the front and rear ends of the axial slit, the axial superposition amount and the circumferentially deflected blade angular slit; and then determining the positions of another four top surface end points of the slit according to the radial tilt angle of the front end of the axial slit, the radial tilt angle of the rear end of the axial slit, the slit height and the four end point coordinates of the bottom surface; Step two: in order to realize the uniform twisting along the axis, the B-spline curve is used to connect the front end and the rear end of the slit, and the control point selection principle of the B-spline curve is that the intersection of the slit end point and the circumferentially deflected angle bisector and the midline of the axial length; by determining the eight end points of the slit and the eight additional control points connecting the end points, the B-spline curve is used to connect the end points and the control points, so as to form the gradually twisted slit structure along the axis.

[0007] Further, seven said twisted slit structures along the axis are uniformly distributed in the circumferential direction of each rotor passage.

[0008] Further, the axial length of the axial slit is 1.035 times the axial chord length of the rotor blade.

[0009] Further, the width of the front and rear ends of the axial slit is respectively: the front end width is 35 times the tip clearance, and the rear end width is 41 times the tip clearance.

[0010] Further, the axial superposition amount is 55%.

[0011] Further, the deflection angle of the circumferentially deflected blade angular slit is 55°.

[0012] Further, the front end of the axial slit is radially tilted by 45° in the opposite direction of the rotation of the rotor, and the rear end is radially tilted by 40° in the direction of the rotation of the rotor.

[0013] Further, the slit height is 25 times the tip clearance.

[0014] An axial torsion slit casing treatment structure obtained by a design method of the axial torsion slit casing treatment structure, comprising: a plurality of slit structures uniformly distributed in the circumference of the compressor casing, the front end of each slit structure is radially inclined by 45 degrees against the rotation direction of the rotor, the rear end is radially inclined by 40 degrees in the same direction as the rotation direction of the rotor, the blade angle of the circumferential deflection angle of the slit is 55 degrees, the slit height is 25 times of the tip clearance, the front end width is 35 times of the tip clearance, the rear end width is 41 times of the tip clearance, the slit length is 1.035 times of the axial chord length, the rear end is located at 55% of the axial length after the leading edge of the rotor, the front and rear ends of the slit are smoothly connected through a B-spline curve, and the control points of the B-spline curve include the intersection of the slit end points and the circumferential deflection angle bisector and the axial length center line.

[0015] Further, the curve equation of the B-spline curve is: Wherein, is a p-th B-spline basis function, is a control point.

[0016] The beneficial effects of the present application are: 1. The present application proposes a slit casing treatment structure which is gradually twisted along the axial direction and connected through a curved and twisted connection form different from the traditional straight line connection based on the traditional axial inclined slit structure, so as to enhance the stability of the marine axial flow compressor under low working conditions.

[0017] 2. The present application proposes an axial slit casing treatment method which is gradually twisted along the axial line to solve the problem of insufficient stable operation range of the marine axial flow compressor under low working conditions. The method makes the two ends of the slit radially inclined in different directions according to the rotation characteristics of the rotor, and realizes the smooth transition of the radial inclination angle of the middle section of the slit by selecting specific control points and adopting a B-spline curve to realize the connection of the front and rear ends.

[0018] 3. The axial torsion slit casing treatment of the present application has larger suction and jet flow than the traditional axial inclined slit, on the one hand, the stronger axial suction weakens the strength of the tip leakage flow, suppresses its horizontal migration, and delays the accumulation of low-energy fluid; on the other hand, the stronger high-speed jet flow at the front end of the slit enhances the kinetic energy of the leading edge mainstream, and weakens the effect of the radial secondary flow, thereby improving the through-flow capacity of the rotor. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a parameterized design schematic diagram of the axial torsion slit casing treatment structure of the present application; Figure 2 is a structural schematic diagram of one embodiment of the axial torsion slit casing treatment structure of the present application; Figure 3It is a structural schematic diagram of an embodiment of a conventional axially inclined slotted casing structure of the present invention; Figure 4 This is a schematic diagram of the control point selection and connection of the B-spline curve in the present invention.

[0020] In the figure: 1. Blade tip; 2. Blade tip leading edge; 3. Blade tip trailing edge; 4. Blade tip axial length; 5. Axial overlap; 6. Slit axial length; 7. Rear end width; 8. Front end width; 9. Circumferential deflection angle; 10. Blade leading edge; 11. Blade trailing edge; 12. Rotor blade; 13. Slit twisted along the axis; 14. Traditional axially inclined slit. DETAILED DESCRIPTION

[0021] In the description of the present invention, it should be noted that all directional indications (such as front, rear, etc.) are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, they cannot be understood as limiting the present invention.

[0022] Specific implementation method 1: Combination Figures 1-4 This embodiment is described as follows. Figures 1-4 As shown, the design method of a slotted casing processing structure twisted along an axis in this embodiment is achieved by the following steps: Step 1: Determine the coordinates of the four endpoints of the bottom surface of the slit based on the position of the leading edge 2 of the rotor blade tip, the axial length of the axial slit, the front and rear width of the axial slit 7, the axial overlap 5, and the circumferentially deflected blade angular slit; then determine the positions of the other four top surface endpoints of the slit based on the radial inclination angle of the front and rear ends of the axial slit, the height of the slit, and the four bottom surface endpoints; Step 2: To achieve uniform axial twisting, a B-spline curve is used to connect the front and rear ends of the seam. The control points of the B-spline curve are selected based on the following principles: the endpoints of the seam and the intersection of the bisector of the circumferential deflection angle 9 and the midline of the axial length. By determining the eight endpoints of the seam and eight additional control points connecting these endpoints, a B-spline curve is used to connect each endpoint and the control points to form a seam structure that gradually twists along the axis. Seven of these axially twisting seam structures are evenly distributed circumferentially within each rotor channel. The special structure of the casing inner wall improves the airflow at the blade tips and expands the stable operating range of the compressor.

[0023] Preferably, the axial length of the axial slot is 1.035 times the axial chord length of the rotor blade 12. The front and rear end widths 7 of the axial slot are respectively 35 times and 41 times the tip 1 gap. The axial overlap 5 is 55%, that is, the rear end is located at 55% of the axial length behind the rotor leading edge. The deflection angle of the circumferentially deflected blade angular slot is 55°. The front end of the axial slot is radially inclined by 45° in the opposite direction of the rotor rotation, and the rear end is radially inclined by 40° in the direction of the rotor rotation. The slot height is 25 times the tip 1 gap. The stability of the operation of the compressor at low operating conditions can be further widened with as little efficiency reduction as possible, and the stability of the marine axial flow compressor at low operating conditions is improved.

[0024] Specifically, on the basis of the conventional axial inclined slot type casing processing research, the present application proposes a gradually twisted along the axis, that is, a casing processing method with a smooth change in the radial inclination angle of the middle section of the slot. The design method is as follows: Step one: first, determine the four end point coordinates of the slot bottom surface according to the rotor tip leading edge 2 position, the axial length of the axial slot, the front and rear end widths 7 of the axial slot, the 55% axial overlap 5, and the circumferentially 55° deflected blade angular slot. Then, determine the positions of the other four top surface end points of the axial slot according to the 45° radial inclination of the front end, the 40° radial inclination of the rear end, the slot height, and the four end point coordinates of the bottom surface.

[0025] Step two: in order to achieve uniform twisting along the axis, the front and rear ends of the structure are connected by a B-spline curve, which is different from the conventional straight line connection method. The control point selection principle is that the intersection of the circumferentially deflected angle 9 bisector and the axial length midline, so as to form a kind of slot structure gradually twisted along the axis. After determining the eight end points of the slot and the eight additional control points of the curve connecting these end points, the B-spline curve is used to connect these end points and control points, that is, the geometric structure of the slot type casing processing twisted along the axis is obtained, and seven slot structures twisted along the axis are uniformly distributed in the circumferential direction of each rotor passage. This method is based on the conventional axial inclined slot, and adopts the blade angular slot, the front end inclined in the opposite direction of the rotor rotation, the rear end inclined in the direction of the rotor rotation, and the B-spline curve connection in the middle to achieve the smooth transition of the radial inclination angle of the middle section of the slot.

[0026] As Figure 2As shown, the axial torsion slot casing treatment structure obtained by the design method of the axial torsion slot casing treatment structure comprises: a plurality of slot structures uniformly distributed in the circumference of the compressor casing, the front end of each slot structure is radially inclined by 45 degrees in the opposite direction of the rotation direction of the rotor, the rear end is radially inclined by 40 degrees in the same direction of the rotation direction of the rotor, the blade angle slot is circumferentially deflected by 55 degrees, the slot height is 25 times the blade tip 1 gap, the front end width is 35 times the blade tip 1 gap, the rear end width is 41 times the blade tip 1 gap, the slot length is 1.035 times the axial chord length, the rear end is located at 55% of the axial length after the leading edge of the rotor, the front and rear ends of the slot are smoothly connected through a B-spline curve, and the control points of the B-spline curve include the intersection of the slot end points and the circumferential deflection angle 9 bisector and the axial length center line.

[0027] The curve equation of the B-spline curve is: wherein, is a p-th B-spline basis function, is a control point.

[0028] Specifically, the structural parameters of the slot casing treatment are designed according to the geometric parameters and rotation characteristics of the compressor rotor. Through subsequent research, the geometric shape of the slot casing treatment is designed for gas dynamics to match the flow at the tip of the compressor rotor. On the compressor casing, a plurality of slot structures are arranged according to the number of the rotor, the front end of each slot structure is radially inclined by 45 degrees in the opposite direction of the rotation direction of the rotor, the rear end is radially inclined by 40 degrees in the same direction of the rotation direction of the rotor, and the blade angle slot is circumferentially deflected by 55 degrees. In order to realize uniform torsion along the axial direction, unlike the traditional straight connection method, the front and rear ends of the structure are connected through a B-spline curve. The control point selection principle is that the intersection of the slot end points and the circumferential deflection angle 9 bisector and the axial length center line, so as to connect through the B-spline curve to form a kind of slot structure which is gradually twisted along the axial direction. The axial torsion slot casing treatment structure of the application can further widen the stable working margin of the compressor under low working conditions with as little efficiency reduction as possible. The problem of weak effect of widening the stable margin and large efficiency reduction of the traditional axial inclined slot under low working conditions of the compressor is solved.

[0029] The axial torsion slot casing treatment structure is designed taking the number of the axial flow compressor rotor blades as 17, the inlet hub ratio as 0.395, the aspect ratio of the first stage rotor as 1.78, the blade tip peripheral speed as 400 m / s, and the rotor blade tip gap as 0.5 mm.

[0030] As Figure 4As shown, firstly, according to the position of the blade leading edge 10, the slit front end width 8 is 17.5 mm, the slit axial length is 1.035 times the axial chord length, and the relative axial overlap of the blade 5 is 55%, the slit bottom surface front end two end points P1 and P2 positions can be obtained. Then according to the circumferential deflection of the slit piece 55°, the axial length and the slit piece rear end width 7 is 1.035 times the axial chord length, that is, the slit bottom surface rear end two end points P3 and P4 positions are obtained.

[0031] After the four-point position is determined, in order to smoothly transition the front and rear end connection, B-spline curve is used for connection. Taking one of the B-spline curves P1-P4 as an example, how to determine the control point selection and realize the B-spline curve connection is described.

[0032] P1, CP1, CP2 and P4 are selected in turn as the four control points of the B-spline curve, wherein P1 and P4 are the two end points of the B-spline curve. The selection principle of the additional two control points is that the circumferential deflection angle 9 and the bisector of the remaining angle are respectively the intersection points of the deflection circumferential and axial length midline, and then the curve equation is: Wherein the range of t is [0, 1].

[0033] Then according to the front end inclined 45° in the radial direction opposite to the rotor rotation direction and the rear end inclined 40° in the radial direction to the rotor rotation direction, the slit height is 12.5 mm. The axial slit top surface end points can be obtained, and the additional control point positions are calculated according to the above process, and then the front and rear ends are connected by B-spline curve using these control points.

[0034] In addition, as shown in Figure 3 , according to the above geometric parameters, a traditional axial inclined slit is constructed, the front end is inclined 45° to the rotor rotation direction and the middle is connected by a straight line, and other parameters are the same as the axial slit twisted along the axis used in the present application.

[0035] The present application is carried out on the marine axial flow compressor for constant value simulation, and the simulation process is as follows: S1: using the IGG / Autogrid5 module of the NUMECA software to generate the calculation grid of the compressor blade and the casing processing; S2: Numerical simulation of the flow characteristics of the compressor is carried out by using the Euranus solver of NUMECA-FINE / Turbo, based on three-dimensional steady Reynolds average Navier-Stokes (RANS) equation, and the Spalart-Allmaras turbulence model is selected for closure. Spatial discretization adopts finite volume method and central difference format, and time advancement adopts four-order Runge-Kutta method. At the same time, local time step and multi-grid acceleration technology are introduced to improve the convergence efficiency of calculation.

[0036] S3: The results obtained by numerical simulation are post-processed to obtain the improvement of the stable margin and the peak efficiency of the compressor by the twisted axial slot fairing treatment and the conventional axial inclined slot fairing treatment.

[0037] The results show that: the slot fairing treatment structure twisted along the axis adopted in the application can improve the stable margin from 19.64% to 40.2% under the premise of only losing 1.428% of the peak efficiency, which is obviously superior to the performance of the conventional axial inclined slot, which loses 1.596% of the peak efficiency to improve the stable margin to 22.2%. Flow field analysis shows that the suction and jet flow of the slot fairing treatment structure twisted along the axis adopted in the application is larger than that of the conventional axial inclined slot, on the one hand, the stronger suction effect of the axial slot weakens the strength of the blade tip 1 leakage flow, suppresses its transverse migration, and delays the accumulation of low-energy fluid; on the other hand, the stronger high-speed jet flow at the front end of the slot enhances the kinetic energy of the leading edge main flow, and weakens the effect of radial secondary flow, thereby improving the through-flow capacity of the rotor.

[0038] The above is only a preferred embodiment of the application, and does not limit the application in any form, although the application has been disclosed as above, however, it is not intended to limit the application, any skilled person in the art, without departing from the technical solution of the application, can make some changes or modifications to the above disclosed technical content to make equivalent embodiments, but as long as it does not deviate from the technical solution of the application, according to the technical essence of the application, within the spirit and principles of the application, any simple modification, equivalent replacement and improvement of the above embodiments, all still belong to the protection scope of the technical solution of the application.

Claims

1. A design method for a slotted casing processing structure twisted along an axis, characterized by: The design method is implemented by the following steps: Step 1: Determine the coordinates of the four endpoints of the bottom surface of the slit according to the position of the leading edge of the rotor blade tip (2), the axial length of the axial slit, the width of the front and rear ends of the axial slit (7), the axial overlap (5), and the angular slit of the circumferential deflection of the blade; and then determine the positions of the other four endpoints of the top surface of the slit according to the radial inclination angle of the front end of the axial slit, the radial inclination angle of the rear end of the axial slit, the height of the slit, and the four endpoints of the bottom surface; Step 2: To achieve uniform torsion along the axial direction, a B-spline curve is used to connect the front and rear ends of the seam. The control points of the B-spline curve are selected based on the following principles: the end points of the seam and the intersection of the bisector of the circumferential deflection angle (9) and the midline of the axial length; By determining the eight endpoints of the seam and eight additional control points connecting these endpoints, and using B-spline curves to connect the endpoints and the control points, a seam structure that gradually twists along the axis is formed.

2. The design method of the slotted casing processing structure with axial twisting according to claim 1 is characterized in that: Seven slot-type structures twisted along the axis are evenly distributed in the circumferential direction in each rotor channel.

3. The design method of the slotted casing processing structure with axial twisting according to claim 2 is characterized in that: The axial length of the axial slot is 1.035 times the axial chord length of the rotor blade (12).

4. The design method of the slotted casing processing structure with axial twisting according to claim 3 is characterized in that: The front and rear end widths (7) of the axial slit are respectively: the front end width (8) is 35 times the gap of the blade tip (1), and the rear end width (7) is 41 times the gap of the blade tip (1).

5. The design method of the slotted casing processing structure with axial twisting according to claim 4 is characterized in that: The axial overlap (5) is 55%.

6. The design method of the slotted casing processing structure with axial twisting according to claim 5, characterized in that: The deflection angle of the circumferentially deflected blade angular slot is 55°.

7. The method for designing a slotted casing processing structure with axial twisting according to claim 6, characterized in that: The front end of the axial slot is radially inclined by 45 degrees in the opposite direction of the rotor's rotation, and the rear end is radially inclined by 40 degrees in the direction of the rotor's rotation.

8. The method for designing a slotted casing processing structure twisted along an axis according to claim 7, characterized in that: The height of the slit is 25 times the gap of the blade tip (1).

9. A slotted casing processing structure twisted along the axis obtained by the design method of claim 8, characterized in that: include: A plurality of slot structures are evenly distributed along the circumference of the compressor casing, wherein the front end of each slot structure is radially inclined 45° in the opposite direction of the rotor rotation direction and the rear end is radially inclined 40° in the same direction as the rotor rotation direction, and the blade angle slot is 55° circumferentially deflected. The slot height is 25 times the blade tip (1) gap, the front end width is 35 times the blade tip (1) gap, the rear end width is 41 times the blade tip (1) gap, the slot length is 1.035 times the axial chord length, and the rear end is located at 55% of the axial length behind the rotor leading edge. The front and rear ends of the slot are smoothly connected by a B-spline curve, and the control points of the B-spline curve include the slot end points and the intersection of the bisector of the circumferential deflection angle (9) and the midline of the axial length.

10. The slotted casing processing structure twisted along the axis according to claim 9, characterized in that: The curve equation of the B-spline curve is: ,in, is the p-order B-spline basis function, For the control point.

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