A tear-drop type root rounding structure, design method and application

Abstract

This invention discloses a teardrop-shaped root rounded structure, its design method, and its application, belonging to the field of flow control in turbomachinery. The cross-section of the rounded structure is controlled by two structural parameters: the rounding radius R and the chamfer angle θ. This rounded structure is distributed in a non-closed loop around the blade root circumference, with an outer edge profile that is teardrop-shaped, covering the portion of the blade root from the leading edge to the suction / pressure surface; that is, a teardrop-shaped profile is used for the transition between rounded sections. The method involves first controlling the cross-sectional shape of the blade root rounded section using the rounding radius and chamfer angle; then using a teardrop-shaped profile for the transition between blade root rounded sections, normalizing it to obtain a standardized teardrop-shaped thickness distribution curve; finally, multiplying the standardized teardrop-shaped thickness distribution curve by the rounding radius to obtain the actual thickness distribution of the teardrop-shaped rounded section on the blade root. This invention can reduce the driving and effect of lateral pressure difference and adverse pressure gradient on the low-velocity flow at the endwall, thereby suppressing corner separation under near-stall conditions of the stator blade.

Description

Technical Field

[0001] This invention belongs to the field of flow control in turbomachinery, specifically relating to a teardrop-shaped root rounded structure, its design method, and its application. Background Technology

[0002] With the development of high-load axial compressors, the single-stage load of compressors has increased, and the secondary flow caused by the reverse pressure gradient and lateral pressure difference has increased significantly, leading to an exacerbation of three-dimensional corner separation. Published experimental research "Axial Compressor Stator Aerodynamics" (Journal of Engineering for Gas Turbines and Power, 1985, 107(2)) shows that when a two-stage compressor is in near-stall condition, the airflow blockage caused by corner separation in the second-stage stator hub can cover up to 40% of the blade height. Published technical literature "A Criterion for Axial Compressor Hub-Corner Stall" (Journal of Turbomachinery, 2008, 130(3)) shows that the degree of corner separation is one of the key factors determining compressor performance and stability. Therefore, how to control stator corner separation and expand the operating range has become a current research hotspot.

[0003] The publicly available technical document, "Numerical Study on the Influence of Suction Surface Grooving on the Performance of Sector-Shaped Stator Blades in Transonic Compressors" (Journal of Dalian Maritime University, 2019, 45(04)), focuses on boundary layer suction for flow separation in the corner region of axial compressor stator blades. This involves creating suction grooves on the suction surface of the compressor stator blades to extract the low-energy fluid from the corner region, thereby suppressing further development of corner separation in the blade passage. However, this corner separation control technology requires additional air paths, controllers, and power supplies, and also requires external energy, which limits its application in practical engineering. Therefore, it is necessary to develop passive flow control technology for flow control in the corner region of compressor stator blades.

[0004] Passive flow control is flow control without auxiliary energy consumption. This control technology achieves the purpose of controlling the flow by changing the flow boundary conditions, pressure gradient, etc., and mainly adopts the adjustment and optimization of the geometric surface. The published technical literature "Mechanism of the influence of endwall rounding on the performance and flow field of high-load compressor blades" (Propulsion Technology, 2017, 38(12)) carried out a conventional blade root rounding study on the corner separation flow of the compressor. That is, a rounding with a constant radius is applied around the entire blade root region. The study shows that the rounding at the root of the stator blade can make the outlet flow more uniform and the secondary flow energy significantly reduced, thereby reducing the overall loss and improving the corner flow. However, conventional rounding requires applying rounding to the entire blade root region. When the rounding radius is small, the control of the secondary flow is not good. When the rounding radius is large, it is difficult to balance the flow capacity and efficiency of the compressor. Since the corner separation of the compressor generally occurs in a part of the suction surface of the stator blade, it is necessary to develop a rounding structure for the part of the blade root region. Summary of the Invention

[0005] The technical problem to be solved: To overcome the shortcomings of existing technologies, this invention provides a teardrop-shaped root rounded structure and its design method. This rounded structure is designed as a non-closed-loop distribution around the blade root circumferentially. The outer edge profile of the rounded structure is teardrop-shaped, covering the portion of the blade root from the leading edge to the suction surface / from the leading edge to the pressure surface, i.e., using a teardrop-shaped profile for the transition between rounded sections. Applying this rounded structure to the compressor stator root can reduce the driving and effect of lateral pressure differential and adverse pressure gradient on the low-velocity flow at the endwall, thereby suppressing corner separation under near-stall conditions.

[0006] The technical solution of this invention is: a teardrop-shaped root rounded structure, wherein the cross-section of the rounded structure is determined by the rounding radius. R and chamfer θ Two structural parameters control the selection. R= 0.5 δ , θ =15°, where δ The thickness of the boundary layer at the entrance of the still leaf passage.

[0007] A further technical solution of the present invention is: the rounded structure is a non-closed-loop rounded structure arranged circumferentially along the blade root, with the leading edge as the starting point, and an axial length on the suction surface side of which is... L 1 = 0.7 C a The axial length located on the pressure surface side is L 2 = 0.3 C a ,in C a This indicates the axial chord length of the leaf shape at the leaf root.

[0008] A further technical solution of the present invention is: the outer edge distribution line of the rounded structure along the circumference is teardrop-shaped, the top arc of the teardrop shape is opposite to the leading edge of the leaf root, and the converging parts on both sides of the teardrop shape intersect with the root of the suction surface and the pressure surface, respectively, that is, the end point of the rounded structure is located on the suction surface and the pressure surface.

[0009] A design method for a teardrop-shaped root rounded structure, the specific steps of which are as follows: Step 1: Design the cross-sectional shape of the rounded structure and determine the rounding radius. R with chamfer θ ; Step 2: Use a teardrop-shaped profile to transition between the leaf root rounding, and normalize the profile to obtain a standardized teardrop-shaped thickness distribution; Step 3: Multiply the standardized teardrop-shaped thickness distribution by the rounding radius. R， The actual thickness distribution of the teardrop-shaped rounded structure on the leaf root was obtained.

[0010] A further technical solution of the present invention is: in step 1, a rounding radius is used. R with chamfer θ Two structural parameters control the cross-sectional shape of the blade root rounding; take R= 0.5 δ , θ =15°, where δ The thickness of the boundary layer at the entrance of the still leaf passage.

[0011] A further technical solution of the present invention is: the teardrop-shaped transition equation in step 2 is, (1) In the formula, t The dimensionless axial chord length of the leaf shape at the leaf base, 0 ≤ t ≤1.

[0012] A further technical solution of the present invention is: in step 2, the formula (1) is... x and t The relationship is transformed and normalized to obtain a standardized teardrop-shaped thickness distribution. X : (2)

[0013] A further technical solution of the present invention is: in step 3, let t = Z / L i The actual thickness distribution of the teardrop-shaped rounded structure at the leaf root T The formula is as follows: (3) In the formula, Z Indicates the axial coordinates of the leaf shape at the leaf base. L i It indicates the axial extension length, that is, the length of the rounding from the leading edge to a certain axial position.

[0014] A teardrop-shaped rounded root structure is applied to the root of the compressor stator blade.

[0015] A further technical solution of the present invention is: the axial extension length of the suction surface at the root of the compressor stator blade. L 1 = 0.7 C a axial extension length on the pressure surface L 2 = 0.3 C a ,in C a This indicates the axial chord length of the leaf shape at the leaf root.

[0016] Beneficial effects The beneficial effects of this invention are as follows: The rounded cross-section of this invention is controlled by two structural parameters: the rounding radius and the rounding angle. The overall design is a non-closed-loop distribution around the blade root, with a teardrop-shaped outer edge profile. Applying this rounded structure to the root of the compressor stator blades can weaken the driving and effect of the lateral pressure difference and adverse pressure gradient on the low-velocity flow at the endwall, thereby suppressing corner separation under near-stall conditions. Compared to conventional rounding, this invention can further reduce aerodynamic losses caused by corner separation under near-stall conditions. For axial compressors, applying this invention to the root of the stator blades where corner separation occurs can expand the compressor's stable operating range while maintaining both efficiency and flow capacity.

[0017] In the low-velocity flow region near the endwall, teardrop-shaped rounding can achieve a lower lateral pressure differential and redistribute the adverse pressure gradient, making its distribution more reasonable. This weakens the driving effect of the lateral pressure differential and adverse pressure gradient on the low-velocity flow near the endwall, thereby suppressing corner separation under near-stall conditions. Teardrop-shaped rounding significantly reduces aerodynamic losses caused by corner separation under near-stall conditions, reducing losses by approximately 12.83% compared to a stator without rounding. Compared to conventional rounding, teardrop-shaped rounding provides better control over corner separation, further reducing losses by approximately 2.37%.

[0018] For the entire axial compressor, applying a teardrop-shaped rounding at the root of the stator vane where angular separation occurs can effectively control flow separation, expand the compressor's stable operating range, and balance efficiency and flow capacity. Verification through examples shows that the instability point flow rate decreased from 26.3568 kg / s to 25.7428 kg / s, with an overall stability margin improvement of approximately 3.03%. Simultaneously, the compressor's maximum efficiency decreased by only about 0.05%, while the maximum flow rate remained unchanged. Therefore, this invention can improve the compressor's stability expansion capability while balancing efficiency and flow capacity. Attached Figure Description

[0019] Figure 1 This is a three-dimensional schematic diagram of Example 1.

[0020] Figure 2 This is a schematic diagram of the rounded cross-section of the leaf root.

[0021] Figure 3 It is a teardrop-shaped line.

[0022] Figure 4 To standardize the teardrop-shaped thickness distribution curve.

[0023] Figure 5 This is a schematic diagram showing the distribution of teardrop-shaped rounded edges on the end wall.

[0024] Figure 6 A three-dimensional comparison diagram of the leaf cascade after applying conventional rounding and teardrop rounding to the leaf root.

[0025] Figure 7 A comparison of the blade grid flow limiting line and three-dimensional countercurrent range before and after applying teardrop-shaped rounding under near-stall conditions.

[0026] Figure 8 This is a comparison of the lateral pressure difference at 1% blade height before and after applying a teardrop-shaped rounding under near-stall conditions.

[0027] Figure 9 This is a comparison of the reverse pressure gradient at 1% blade height before and after applying teardrop-shaped rounding under near-stall conditions.

[0028] Figure 10 Comparison of flow-pressure ratio characteristics of a four-and-a-half-stage compressor before and after applying teardrop-shaped rounding to the root of the third and fourth stage stationary blades.

[0029] Figure 11 Comparison of flow-efficiency characteristics of a four-and-a-half-stage compressor before and after applying teardrop-shaped rounding to the root of the third and fourth stage stationary blades. Detailed Implementation

[0030] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0031] Currently, corner separation mainly originates from the driving effect of secondary flow on the low-energy fluid in the boundary layer at the endwall, which is closely related to the aerodynamic load of the compressor's primary stage. Most existing axial compressors are designed with primary loads varying along the spanwise direction, which affects the development of secondary flow within the channel, thus impacting corner separation in the compressor. This embodiment provides a teardrop-shaped root rounded structure for controlling compressor stator blade corner separation. This rounded structure is designed as a non-closed-loop distribution around the blade root circumferentially. The outer edge profile of the rounded structure is teardrop-shaped, covering the portion of the blade root from the leading edge to the suction surface / from the leading edge to the pressure surface, i.e., using a teardrop-shaped profile for the transition between rounding sections.

[0032] The design concept of this rounded structure is as follows: First, the cross-sectional shape of the blade root rounded section is controlled by two structural parameters: the rounded radius and the rounded chamfer. Then, a teardrop-shaped profile is used to transition between the blade root rounded sections, and the profile is normalized to obtain a standardized teardrop-shaped thickness distribution curve. Finally, the standardized teardrop-shaped thickness distribution curve is multiplied by the rounded radius to obtain the actual thickness distribution of the teardrop-shaped rounded section on the blade root.

[0033] The rounded structure of this invention can weaken the driving and effect of lateral pressure difference and adverse pressure gradient on the low-velocity flow at the endwall, thereby suppressing corner separation under near-stall conditions. Compared with conventional rounding, it can further reduce aerodynamic losses caused by corner separation under near-stall conditions. For axial compressors, applying this invention to the root of the stator vane where corner separation occurs can expand the stable operating range of the compressor while balancing efficiency and flow capacity.

[0034] Example 1: To specifically demonstrate the control mechanism and effect of the diagonal separation of the present invention, we first take a high-load, large-scale, low-speed axial compressor stator blade cascade (whose basic blade profile does not change along the blade height) as an example.

[0035] like Figure 1 As shown, the basic blade profile of the stator blade cascade is a double circular arc blade profile, with designed inlet and outlet airflow angles of 52° and 12° respectively, an installation angle of 20.5°, a designed diffusion coefficient of 0.5, a chord length of 114.3 mm, a blade span of 200 mm, and a cascade pitch of 53.4 mm.

[0036] like Figure 2 As shown, the rounding radius is used. R with chamfer θ Two structural parameters control the cross-sectional shape of the blade root rounding. (Take...) R= 0.5 δ , θ =15°, where δ The boundary layer thickness at the inlet of the stationary blade channel.

[0037] A teardrop-shaped profile is used for the transition between the rounded leaf base and the leaf tip. The teardrop-shaped profile is as follows: Figure 3 As shown, its equation is: (1) In the formula, the parameter t The dimensionless axial chord length representing the leaf shape at the leaf base. , 0≤ t ≤1. In equation (1) x and t The relationship is transformed and normalized to obtain... Figure 4 The standardized teardrop-shaped thickness distribution shown X : (2) Multiply equation (2) by the radius of the rounding R and order t = Z / L i ,get Figure 5 The actual thickness distribution of the teardrop-shaped rounded edge at the leaf root is shown. T : (3) In the formula, Z Indicates the axial coordinates of the leaf shape at the leaf base. L i Indicates the axial extension length, i.e. L i Defined as the length of the rounded edge extending from its leading edge to a certain axial position. Axial extension length on the suction surface. L 1 = 0.7 C a axial extension length on the pressure surface L 2 = 0.3 C a ,in C a This indicates the axial chord length of the leaf shape at the leaf root.

[0038] like Figure 6 As shown, this compares the application of a conventional rounding at the leaf root ( R= 0.5 δ , θ =15°) and teardrop-shaped rounding ( R= 0.5 δ , θ =15°, L 1 = 0.7 C a , L 2 = 0.3 C a The three-dimensional structure diagram after ().

[0039] like Figure 7 As shown, the flow in the prototype blade cascade begins to separate at the leading edge of the blade root suction surface, and this separation persists almost continuously downstream. Flow separation exists to varying degrees throughout the entire blade height. The region where the three-dimensional counterflow begins to separate from the leading edge of the blade root occupies a considerable portion of the blade height, and the entire counterflow range is relatively close to the upstream. After introducing the teardrop-shaped rounded endwall, the limiting streamlines on the endwall show almost no separation in the blade passage, and the separation line on the blade suction surface shifts significantly backward. Although it is slightly forward in the middle of the blade compared to the prototype, the overall effect is good. Especially near the blade root, the counterflow region can be observed to move downstream and towards the middle of the blade, and a considerable area near the root shows no counterflow.

[0040] like Figures 8-9 As shown, near the leading edge of the prototype blade cascade, the transverse pressure difference and adverse pressure gradient on the near-endwall first reach a maximum value, and then gradually decrease. Therefore, the huge transverse pressure difference and high adverse pressure gradient on the suction surface near the leading edge of the prototype blade cascade are an important reason why flow separation occurs on the endwall from the leading edge. Because separation already occurs at the leading edge, the effects of separation continue in the downstream flow due to the persistent adverse pressure gradient.

[0041] The teardrop-shaped, rounded blade cascade does not have a particularly high lateral pressure differential and adverse pressure gradient at its leading edge. Therefore, the local suction surface pressure differential and adverse pressure gradient at the leading edge of the teardrop-shaped, rounded blade cascade are insufficient to drive flow separation from the outset. Continuing downstream along the axial direction, although the adverse pressure gradient is higher than that of the prototype blade cascade between approximately 10% and 40% of the axial chord length, the endwall flow does not separate at this point, making it sufficient to withstand the adverse pressure gradient. Beyond 40% of the axial chord length, as the flow continues downstream, the adverse pressure gradient consistently decreases, resulting in a lower overall degree of flow separation downstream compared to the prototype blade cascade.

[0042] comprehensive Figures 7-9 It can be seen that in the low-velocity flow region near the endwall, the teardrop-shaped rounding can achieve a lower lateral pressure difference and redistribute the adverse pressure gradient to make its distribution more reasonable, thereby weakening the driving and effect of the lateral pressure difference and adverse pressure gradient on the low-velocity flow at the endwall, and thus suppressing corner separation under near-stall conditions.

[0043] Table 1 Comparison of total pressure loss of the cascade before and after applying conventional rounding and teardrop rounding under near-stall conditions.

[0044] The simulation results in Table 1 show that the teardrop-shaped rounding can significantly reduce the aerodynamic losses caused by corner separation under near-stall conditions, reducing the losses by about 12.83% compared to the prototype blade cascade; compared to the conventional rounding, the teardrop-shaped rounding has a better control effect on corner separation, and can further reduce the losses by about 2.37%.

[0045] Example 2: To further illustrate the control effect of this invention on the separation of the stator vane angle region in a real axial compressor, a four-and-a-half-stage compressor is used as an example. Under near-stall conditions at 97.5% of the design speed, large-scale low-energy fluids appeared successively at the roots of the third and fourth stage stator vanes.

[0046] like Figures 9-10 As shown, in this embodiment, a numerical simulation study was conducted on applying the teardrop-shaped rounding of the present invention to the root of the third and fourth stage stator blades, and data on the changes in compressor performance before and after applying the present invention were obtained.

[0047] Table 2 Comparison of the performance of the fourth-stage semi-compressor before and after applying teardrop-shaped rounding at the root of the third and fourth stage stationary blades.

[0048] Simulation results show that applying a teardrop-shaped rounding at the root of the stator vane bank where angular separation occurs in an axial compressor can effectively control flow separation and expand the compressor's stable operating range. The instability point flow rate decreased from 26.3568 kg / s to 25.7428 kg / s, with an overall stability margin improvement of approximately 3.03%. Simultaneously, the compressor's maximum efficiency decreased by only about 0.05%, while the maximum flow rate remained unchanged. Therefore, this invention can improve the compressor's stability expansion capability while balancing efficiency and flow capacity.

[0049] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A compressor stator blade comprising a teardrop-shaped, rounded root structure, characterized in that: The cross-section of the rounded structure is determined by the rounding radius. R and chamfer θ Two structural parameters control the selection. R= 0.5 δ , θ =15°, where δ The thickness of the boundary layer at the entrance of the still leaf passage; The rounded structure is a non-closed-loop rounded structure arranged circumferentially along the blade root, starting from the leading edge, with an axial length of [missing information] on the suction surface side. L 1 = 0.7 C a The axial length located on the pressure surface side is L 2 = 0.3 C a ,in C a Indicates the axial chord length of the leaf shape at the leaf base; The outer edge of the rounded structure is shaped like a teardrop, with the top arc of the teardrop facing the leading edge of the leaf root. The converging parts on both sides of the teardrop intersect with the roots of the suction and pressure surfaces, respectively, thus positioning the end points of the rounded structure on the suction and pressure surfaces.

2. A design method for the compressor stator vanes as described in claim 1, characterized in that... The specific steps are as follows: Step 1: Design the cross-sectional shape of the rounded structure and determine the rounding radius. R with chamfer θ ; Step 2: Use a teardrop-shaped profile to transition between the leaf root rounding, and normalize the profile to obtain a standardized teardrop-shaped thickness distribution; Step 3: Multiply the standardized teardrop-shaped thickness distribution by the rounding radius. R， The actual thickness distribution of the teardrop-shaped rounded structure on the leaf root was obtained.

3. The compressor stator vane design method according to claim 2, characterized in that: In step 1, the rounding radius is used. R with chamfer θ Two structural parameters control the cross-sectional shape of the blade root rounding; take R= 0.5 δ , θ =15°, where δ The thickness of the boundary layer in the blade inlet channel.

4. The compressor stator vane design method according to claim 3, characterized in that: The teardrop-shaped transition equation in step 2 is as follows: (1) In the formula, t The dimensionless axial chord length of the leaf shape at the leaf base, 0 ≤ t ≤1.

5. The compressor stator vane design method according to claim 4, characterized in that: In step 2, the equation (1) is... x and t The relationship is transformed and normalized to obtain a standardized teardrop-shaped thickness distribution. X : (2) 6. The compressor stator vane design method according to claim 5, characterized in that: In step 3, let t = Z / L i The actual thickness distribution of the teardrop-shaped rounded structure at the leaf root T The formula is as follows: (3) In the formula, Z Indicates the axial coordinates of the leaf shape at the leaf base. L i It indicates the axial extension length, that is, the length of the rounding from the leading edge to a certain axial position.

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