A turbine endwall passage gap cooling structure design method

Abstract

The application discloses a turbine end wall passage gap cooling structure design method and belongs to the technical field of turbine end wall cooling. On the basis of traditional thermal expansion design indexes, the cooling effect of passage gap cold air on the end wall, end wall platform structure strength and cascade flow characteristics and other factors are introduced into the passage gap structure design indexes. According to the aerodynamic heat transfer performance parameters of the end wall, the passage gap width, cold air flow, installation angle and installation position and other parameters are determined; according to the blade profile and end wall structure strength parameters, the inclined type, multi-cold air chamber passage gap structure is selected, and the passage gap depth parameter is determined. The internal cold air flow control of the passage gap is realized, the problems of cold air accumulation and low utilization rate of the passage gap are overcome, the film cooling effect of the passage gap cold air on the end wall is improved, and the applicability of the passage gap structure design method in the actual application is enhanced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of gas turbines, and relates to a turbine end wall cooling structure design method, in particular to a turbine end wall passage gap cooling structure design method. BACKGROUND

[0002] Further improvement of the thermal efficiency of gas turbines depends on the continuous increase of turbine inlet temperature. In order to avoid failure of turbine hot end components in harsh environments, higher-order film cooling technology needs to be developed to ensure the safety of hot end components. Among them, the passage gap, as an inherent slot structure necessary for blade assembly process, can play a certain film cooling effect on the turbine end wall through internal cooling gas outflow. In the traditional end wall cooling layout design, the film cooling effect of discrete holes and upstream slots is the focus of researchers, while the film cooling effect of the passage gap is often ignored. Under the guidance of further improving the thermal efficiency of gas turbines, the cooling gas consumption of turbine hot end components needs to be further reduced, so the film cooling effect of the passage gap jet on the end wall is gradually valued in the field of turbine hot end component cooling layout design, and it has gradually become an important part of the end wall film cooling layout design.

[0003] In the design process of the traditional passage gap structure, only the thermal expansion rate is usually taken as a single design index, that is, to ensure that the end wall platforms on both sides of the passage gap have sufficient thermal expansion space under actual operating conditions, and the film cooling effect of the above-mentioned passage gap cooling gas outflow on the end wall is not included in the design index. Under the existing design method, the end wall passage gap is usually composed of a simple straight slot structure, which leads to uncontrolled internal cooling gas flow in the passage gap, and the cooling gas outflow accumulates in the passage gap trailing edge area, which does not have ideal cooling effect on the upstream and downstream areas of the end wall, causing significant cooling gas loss during turbine operation (Chowdhury N H K, Shiau C C, Han J C, et al. Turbine vane endwall film cooling with slashface leakage and discrete hole configuration [J]. Journal of Turbomachinery, 2017, 139(6): 061003.). SUMMARY

[0004] In order to overcome the shortcomings of the above-mentioned traditional end wall passage gap structure design method, the purpose of the present application is to provide a turbine end wall passage gap cooling structure design method, on the basis of the traditional thermal expansion design index, the factors such as the film cooling performance of the passage gap cold gas to the end wall and the end wall structure strength are included in the passage gap structure design index, and the passage gap geometry structure which effectively organizes the cold gas flow is designed by considering the turbine cascade end region flow characteristics, so as to solve the problems of uneven outflow of the passage gap cold gas and poor adhesion effect of the cold gas on the end wall.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0006] A turbine end wall passage gap cooling structure design method, comprising the following steps:

[0007] Step 1: import the blade and end wall modeling geometry parameters, and establish a turbine cascade and end wall platform three-dimensional geometric model;

[0008] Step 2: for the three-dimensional geometric model, the fluid domain of the cascade is meshed to obtain the cascade fluid domain grid; the solid domain of the blade and the end wall platform is meshed to obtain the blade and end wall solid domain grid;

[0009] Step 3: using the cascade fluid domain grid, the aerodynamic heat transfer performance parameters of the cascade and the end wall are numerically simulated to obtain the pressure side and suction side end wall heat transfer coefficient distribution, as well as the cascade flow field information and the development trajectory of the cold gas tracer variable;

[0010] Step 4: using the blade and end wall solid domain grid and the cascade and end wall aerodynamic heat transfer performance parameters in step 2, the end wall platform is calculated and analyzed by finite element software for centrifugal stress and structural stress to obtain the stress distribution of the end wall platform;

[0011] Step 5: determine the installation angle α and the installation position of the passage gap; the installation angle α of the passage gap refers to the included angle between the straight slot type passage gap and the center line of the cascade, and the straight slot type passage gap refers to the passage gap structure composed of a flat rectangular cavity;

[0012] Step 6: determine the width w of the passage gap;

[0013] Step 7: according to the installation angle α of the passage gap and the width w of the passage gap, the cold gas blowing ratio BR is adjusted by adjusting the passage gap cold gas flow MF;

[0014] Step 8: according to the pressure side and suction side end wall heat transfer coefficient distribution, the inclined passage gap structure is designed to make the passage gap deflect to the side end wall with larger average heat transfer coefficient, and the exit angle β and the inclination direction of the passage gap are determined according to the difference value of the pressure side and suction side end wall heat transfer coefficient;

[0015] Step 9: According to the cascade flow field information and the cold gas tracer variable trajectory, the main region of the main flow invasion in the passage gap is obtained, and the double cold gas chamber passage gap structure is designed. The internal cold gas chamber is divided into two independent chambers near the tail end position of the main flow invasion region in the passage gap. For the case where the main flow does not invade in the passage gap, a single cold gas chamber passage gap structure is used.

[0016] Step 10: Check the aerodynamic heat transfer and structural strength performance of the passage gap design.

[0017] Step 11: Determine the passage gap depth h, which refers to the distance from the passage gap outlet to the sealing structure below the cold gas chamber.

[0018] Preferably, in step 3, different tracer variables are added to each cold gas inlet during numerical simulation to monitor the trajectory of cold gas flowing in the cascade at each uneven cold gas leakage point. The transport equation of the variable is:

[0019]

[0020] In the formula, Φ is the variable concentration, ρ is the fluid density, U j and u j is the fluid velocity, x j is the coordinate, t is the time, and S Φ is the source term.

[0021] Preferably, in step 5, the passage gap installation angle α is calculated by the following formula:

[0022] α = α s -(5°~10°)

[0023] The passage gap installation position is determined by the following formula:

[0024] y1 / y2 = 0.9~1.1

[0025] Where α s is the blade installation angle, y1 is the minimum distance between the pressure side edge of the passage gap and the pressure surface of the blade, and y2 is the minimum distance between the suction side edge of the passage gap and the suction surface of the blade.

[0026] For the case where the passage gap installation position intersects with the blade or its chamfer, or the blade installation angle is less than 30 degrees, a straight slot type passage gap structure cannot be used, and a two-section slot type passage gap structure is used. The two-section slot type refers to a passage gap composed of two straight slots with an included angle of 90°~180°.

[0027] Preferably, in step 5, the straight slot or two-segment passage gap structure is selected according to the blade pressure side and suction side profile and its deflection, the installation angle of the passage gap is determined according to the blade installation angle and the cold air flow trajectory of the passage gap, and the installation position of the passage gap is determined according to the blade profile parameters.

[0028] Preferably, in step 6, the passage gap width w is determined by the following formula:

[0029] w = (120% ~ 140%) · ε max

[0030] wherein ε max is the maximum value of the installation position deformation of the passage gap, which is obtained according to the stress distribution of the end wall platform.

[0031] Preferably, in step 7, the cold air blowing ratio of the passage gap outflow is 1.0-1.5; the cold air velocity V c and the blowing ratio are defined as follows:

[0032] V c = MF / (w · C ax / sin α)

[0033] BR = (p c · V c ) / (p ∞ · V ∞ )

[0034] wherein p ∞ and V ∞ are the average density and velocity of the main flow respectively; C ax is the axial chord length of the blade, and p c is the density of the cooling fluid.

[0035] Preferably, in step 8, the passage gap exit angle β is determined by the following formula:

[0036] β = 60° ~ 65°

[0037] Preferably, in step 9, the separation position of the two cold air chambers is located downstream of the boundary of the main flow intrusion area in the passage gap.

[0038] Preferably, in step 10, the passage gap structure obtained in step 9 and the three-dimensional geometric model of the turbine blade row and the end wall platform in step 1 are used to numerically simulate the aerodynamic heat transfer performance of the blade row and to perform finite element analysis on the structural strength of the end wall solid domain, and steps 5-9 are repeated and the parameters are adjusted until the following targets are met simultaneously:

[0039] 1) The difference between the peak and valley values of the circumferential average cooling efficiency η of the end wall along the axial direction is reduced by more than 30% compared with the result obtained in step 3;

[0040] 2) the average total pressure recovery coefficient at the cascade outlet ξ differs from the result obtained in step 3 by less than 2%;

[0041] 3) the maximum local blowing ratio BR of the cooling air is less than 2.5;

[0042] 4) the maximum structural stress differs from the result obtained in step 4 by less than 5% and is less than the material's endurance strength;

[0043] The circumferentially averaged cooling effectiveness η of the end wall and the average total pressure recovery coefficient ξ at the cascade outlet are defined as:

[0044] η = (T ∞ -T aw ) / (T ∞ -T c )

[0045] ξ = (P ∞ -P) / (0.5·ρ ∞ ·V ∞ 2

[0046] where P ∞ and P are the total pressures of the main flow and the local flow, respectively, and T ∞ , T aw , T c are the temperatures of the main flow, the adiabatic end wall and the cooling flow, respectively.

[0047] Preferably, the step 11 determines the cooling air chamber depth of the passage gap according to the lift height of the cooling air in the passage gap and the invasion depth of the main flow into the passage gap; the passage gap depth h is 0.8C ax position cooling air lift height to 110% of the maximum main flow invasion depth in the passage gap.

[0048] Compared with the prior art, the present application has the following beneficial technical effects:

[0049] 1) The passage gap cooling structure design method disclosed by the present application takes into account the factors of the film cooling effect of the passage gap cooling air on the end wall and the structural strength of the passage gap, and considers the cascade end wall flow characteristics, thereby overcoming the limitation of the prior passage gap structure design method which only considers the thermal expansion factor.

[0050] ​2) The channel gap cooling structure design method disclosed in the application overcomes the defects that the internal flow of the channel gap is difficult to control in the prior art, significantly improves the cold gas utilization rate, improves the cooling performance of the channel gap cold gas on the end wall, and enhances the applicability of the channel gap structure design method in actual application. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 It is a schematic diagram of a channel gap cooling structure design method.

[0052] Figure 2 It is a blade and end wall geometric model diagram of a gas turbine moving blade row.

[0053] Figure 3 It is a schematic diagram of the installation position of the channel gap on the end wall.

[0054] Figure 4 It is a schematic diagram of the inclined channel gap structure.

[0055] Figure 5 It is a schematic diagram of the double cold gas chamber channel gap structure.

[0056] Figure 6 It is a comparison diagram of the circumferential average cooling efficiency of the end wall along the axial distribution.

[0057] In the figure, 1-blade, 2-end wall platform suction side, 3-end wall platform pressure side, 4-channel gap, 5-blade root, 6-chamber partition, alpha s -blade installation angle, alpha-channel gap installation angle, beta-channel gap incidence angle, Cax-axial chord length, h-channel gap depth, w-channel gap width, z-axial coordinate. DETAILED DESCRIPTION

[0058] The embodiments of the application will be described in detail below with reference to the accompanying drawings and examples.

[0059] The design process of the turbine end wall channel gap described in the application is as Figure 1 shown, in order to more clearly illustrate the technical solutions of the application, the design method is applied to the first stage moving blade row of a gas turbine, and the blade and end wall geometry of the blade row is as Figure 2 shown.

[0060] The detailed process of the embodiment includes the following steps:

[0061] Step 1: Import the blade and end wall modeling geometric parameters into the commercial software Siemens NX to establish a three-dimensional geometric model of the fluid domain and solid domain of the turbine blade row and end wall platform.

[0062] In the present application, the blade and end wall modeling geometry parameters are the original basic data for the design of the passage gap, provided by the cascade designers. They include the inlet and outlet positions of the cascade, the blade profile, the blade leading edge and trailing edge line, the blade pitch, the blade height, the outer end wall surface modeling and the end wall platform thickness, etc.

[0063] In the present embodiment, the first stage rotor blade cascade of a gas turbine is taken as the research object, and the detailed blade and end wall geometry parameters are shown in Table 1, and the three-dimensional coordinates of the blade profile of the blade root section are shown in Table 2.

[0064] Table 1 Geometry parameters

[0065] Geometric parameter name Value Blade chord length (C) 89 mm blade axial chord (C ax )]]> 81 mm Blade height (S) 126 mm Pitch (P) 77 mm Blade mounting angle (a s )]]> 63.5° Inlet flow angle 50.5° Outlet flow angle 66.4° Number of blades 92

[0066] Table 2 Blade profile coordinates

[0067]

[0068]

[0069] Step 2: For the three-dimensional geometry model described in step 1, the fluid domain of the cascade is meshed to obtain the cascade fluid domain mesh; the solid domain of the blade and end wall platform is meshed to obtain the solid domain mesh.

[0070] In the present embodiment, the commercial software ICEM CFD 18.2 is used to perform structured hexahedral meshing on the fluid domain of the cascade, and the mesh is densified near the blade and end wall surface, and the total number of fluid domain mesh nodes is 5.69 million. The fluid domain includes the cascade flow passage and the passage gap.

[0071] The commercial software ANSYS-Mechanical is used to perform meshing on the solid domain, and the mesh type is tetrahedral unstructured mesh, and the mesh is densified at the vertices and edges of the end wall platform, and the total number of mesh nodes is 420,000. The solid domain includes the blade solid and the end wall platform.

[0072] Step 3: Calculation of the aerodynamic heat transfer performance of the cascade.

[0073] The cascade fluid domain mesh obtained in step 2 is used to perform numerical simulation calculation on the aerodynamic heat transfer performance parameters of the cascade and the end wall.

[0074] The grid of the cascade fluid domain obtained in step 2 is imported into the commercial software ANSYS CFX, and the method for solving the steady-state three-dimensional Reynolds time-averaged N-S equation in computational fluid dynamics is adopted to perform numerical simulation calculation on the aerodynamic and heat transfer performance parameters of the cascade and the end wall. In the numerical simulation process, different tracer variables are added at each cold gas inlet to monitor the flow trajectory of the cold gas at each uneven cold gas leakage point in the cascade. Specifically, the cold gas flow trajectory mainly includes the position coordinates of the cold gas flowing out of the cooling structure, the reattachment point coordinates of the cold gas on the end wall surface, and the height of the cold gas detaching from the end wall surface. Alternatively, the initial value of the inter-channel gap cold gas flow is 1.0% of the main flow. The transport equation of the variable in the numerical simulation calculation is as follows:

[0075]

[0076] In the formula, Φ is the concentration of the variable, U j and u j is the fluid velocity, x j is the coordinate, t is the time, ρ is the fluid density, S Φ is the source term.

[0077] Specifically, the commercial software ANSYS CFX 18.2 is used to set the flow boundary conditions, and the detailed boundary conditions are shown in Table 3. The fluid domain grid obtained in step 2 is subjected to numerical simulation calculation, and the turbulent flow model is selected as the SST k-ω model.

[0078] In this embodiment, the uneven cold gas leakage at the bottom of the inter-channel gap is simulated by 15 discrete holes, and a tracer variable is added at the inlet of each discrete hole during numerical calculation.

[0079] Table 3 Boundary conditions

[0080] Parameter name Value Cascade inlet pressure 109 kPa Cascade inlet temperature 350K Cascade outlet pressure 100 kPa Coolant temperature 250K Coolant initial flow rate 7.0 g / s Blade rotational speed 3000 rpm / min

[0081] The numerical simulation calculation is carried out on a workstation with 36 CPU cores, and the numerical calculation reaches a convergent state after 4000 steps of iteration.

[0082] The post-processing of the aerodynamic and heat transfer performance data of the cascade and the end wall is performed in the commercial software ANSYS CFX. Specifically, the following aerodynamic and heat transfer performance parameters are obtained: end wall static pressure and heat transfer coefficient distribution, cascade secondary flow vortex development trajectory coordinates, blade angle region heat transfer coefficient distribution, and three-dimensional coordinates of the development trajectory of the cold gas at each discrete hole in the cascade.

[0083] Step 4: End wall structure strength calculation.

[0084] Using the solid domain mesh of the blades and endwalls obtained in step 2 and the aerodynamic heat transfer performance parameters of the blades and endwalls obtained in step 3, the centrifugal stress and structural stress of the endwall platform were calculated and analyzed using the finite element software ANSYS–Mechanical.

[0085] Specifically, in this embodiment, the solid domain mesh of the blade entity and endwall platform generated in step 2 is imported into the commercial finite element software ANSYS–Mechanical. Simultaneously, the surface temperature distribution of the blade and endwall obtained in step 3 is assigned as boundary conditions to the surface nodes of the solid domain mesh in text file format. A rotational speed of 3000 rpm is applied to the blade and endwall entity, and a far-end displacement constraint is applied to the lower surface of the endwall platform. The solid domain material is selected as 20Cr13. Finite element analysis is performed on the imported solid domain mesh to obtain the distribution of centrifugal stress and structural stress of the endwall platform.

[0086] Step 5: Determine the installation angle α and installation position of the channel clearance. Select a straight-slot or two-section channel clearance structure based on the blade pressure side and suction side profiles and their deflection. Determine the installation angle of the channel clearance based on the blade installation angle and the cold air flow trajectory of the channel clearance. Determine the installation position of the channel clearance based on the blade profile parameters.

[0087] In this invention, the channel clearance installation angle α refers to the angle between the straight groove channel clearance and the blade cascade header line; the blade installation angle α s The angle between the blade chord and the header line is provided by the designer. A straight-slot channel clearance refers to a channel clearance structure consisting of a flat, rectangular chamber.

[0088] The channel gap installation angle of this invention is calculated by the following formula:

[0089] α = α s - (5° ~ 10°) (2)

[0090] That is, the channel clearance installation angle should be slightly smaller than the blade installation angle. The purpose is to facilitate the installation of the blade components in the hub while improving the axial redistribution of the cold air at the leading edge of the cooling structure.

[0091] Figure 3 A schematic diagram of the relative positions of the channel gaps is provided. Based on the blade mounting angle α described in step 1... s =63.5°, in this embodiment, the channel gap installation angle is selected as:

[0092] α=α s -6° = 57.5°

[0093] The installation angle of this channel gap can minimize the axial component of the cold air flow velocity, allowing the cold air to flow out from a position further upstream of the channel gap and enter the mainstream.

[0094] For the determined channel gap installation angle a, define the minimum distance between the channel gap pressure side edge and the blade pressure surface as y1, and the minimum distance between the channel gap suction side edge and the blade suction surface as y2. Then the channel gap installation position is determined by the following formula:

[0095] y1 / y2 = 0.9 ~ 1.1 (3)

[0096] Further, for the case where the channel gap installation position intersects with the blade or its chamfer, or the blade installation angle is less than 30 degrees, the straight slot type channel gap structure cannot be used, and a two-section slot type channel gap design channel gap structure should be used to weaken the accumulation of cold air at the channel gap trailing edge and facilitate the installation of the blade on the disc. The two-section slot type channel gap of the present application refers to a channel gap composed of two straight slots with an included angle of 90° ~ 180°.

[0097] In this embodiment, the deflection angle of the blade profile from the leading edge to the trailing edge is small, and the space between two adjacent blade rows is sufficient, so in the straight slot type channel gap and the two-section slot type channel gap structure, the straight slot type channel gap is selected.

[0098] The coordinates of the blade leading edge point and the trailing edge point in step 1 are z / C ax = 0 and z / C ax = 1.0, respectively, and according to the blade pressure side and suction side profile geometry coordinates in step 1, it is determined that the intersection point between the channel gap installation position and z / C ax = 0 in this embodiment is located at y / P = 0.87.

[0099] Step 6: Determine the channel gap width w.

[0100] According to the end wall platform stress distribution obtained in step 4, the maximum deformation of the channel gap installation position obtained in step 5, i.e. the maximum value of the deformation ε max , is obtained. The gap width w is determined by the following formula:

[0101] w = (120% ~ 140%) · ε max (4)

[0102] In this embodiment, the maximum deformation of the channel gap installation position is ε max = 1.31 mm, so the gap width is determined as w = 130% · ε max = 1.7 mm

[0103] Step 7: Determine the channel gap cold air flow MF.

[0104] According to the channel gap installation angle obtained in step 5 and the channel gap width w obtained in step 6, the cold air blowing ratio BR is adjusted by adjusting the cold air flow rate MF of the channel gap. Preferably, the cold air blowing ratio of the channel gap outflow is 1.0-1.5 to reduce the cold air consumption and weaken the tendency of the cold air to separate from the end wall, while ensuring that the end wall cooling performance changes less with the fluctuation of the cold air flow rate. The cold air velocity and the blowing ratio are defined as follows:

[0105] V c = MF / (w · C ax / sinα) (5)

[0106] BR = (ρ c · V c ) / (ρ ∞ · V ∞ ) (6)

[0107] wherein ρ ∞ and V ∞ are the average density and velocity of the main flow, respectively.

[0108] In this embodiment, the cold air blowing ratio of the channel gap is set to 1.0, and the channel gap installation angle α = 57.5° obtained in step 5 and the channel gap width w = 1.7 mm obtained in step 6 are combined to calculate MF = 7.7 g / s.

[0109] Step 8: Determine the channel gap exit angle β.

[0110] Referring to Figure 4 , the present application adopts an inclined channel gap structure design, and the exit angle and the inclination direction of the channel gap are determined according to the difference between the heat transfer coefficients of the pressure side and the suction side end walls: when the average heat transfer coefficient of the pressure side end wall is greater than that of the suction side end wall, an inclined channel gap structure towards the pressure side is used; when the average heat transfer coefficient of the pressure side end wall is less than that of the suction side end wall, an inclined channel gap structure towards the suction side is used. Specifically, according to the heat transfer coefficient distribution of the pressure side and the suction side end walls obtained in step 3, an inclined channel gap structure design is adopted, so that the channel gap is deflected towards the end wall with a larger average heat transfer coefficient. The channel gap exit angle β is determined by the following formula:

[0111] β = 60° ~ 65° (7)

[0112] The pressure side end wall refers to the end wall surface between the passage gap and the pressure surface of the blade, and the suction side end wall refers to the end wall surface between the passage gap and the suction surface of the blade. The reason for using the inclined passage gap to change the cold air ejection angle β is that the traditional passage gap is designed to be perpendicular to the end wall, that is, the airflow ejection angle is 90°, which leads to too large a radial velocity component of the cold air in the passage gap. Changing the ejection angle of the passage gap can significantly improve the reattachment performance of the cold air on the end wall surface. The preferred ejection angle range of the passage gap can enhance the cold air reattachment performance while ensuring the structural strength of the end wall platform edge under high-temperature mainstream ablation.

[0113] In this embodiment, the average heat transfer coefficients of the pressure side and suction side end walls are 2653 W·m 2 ·K and 3125 W·m 2 ·K, respectively. The average heat transfer coefficient of the suction side end wall is greater than that of the pressure side end wall, and there is a high heat transfer area near the throat position of the suction side end wall cascade. Therefore, an inclined passage gap structure towards the suction side is adopted, with a deflection angle of 30°, so β = 90°-30° = 60°.

[0114] Step 9: Determine the cold air chamber structure inside the passage gap.

[0115] Reference Figure 5 According to the cascade end wall aerodynamic heat transfer performance parameters and the development trajectory of the cold air tracer variable obtained in step 3, the main area of mainstream invasion in the passage gap is obtained. A double-cold-air-chamber passage gap structure is adopted, and the separation position of the cold air chamber in the passage gap is determined according to the mainstream invasion trajectory and its start and end positions. The internal cold air chamber is divided into two independent chambers near the tail end position of the mainstream invasion area in the passage gap. The separation position of the two cold air chambers is located downstream of the boundary position of the mainstream invasion area in the passage gap. The main area of mainstream invasion refers to the area where the velocity component of the fluid in the passage gap in the opposite direction of the blade height is the largest.

[0116] When there is no mainstream invasion in the passage gap, a single-cold-air-chamber passage gap structure is adopted; when there is mainstream invasion in the passage gap, a double-cold-air-chamber passage gap structure is adopted. In this embodiment, according to the cascade end wall aerodynamic heat transfer performance parameters obtained in step 3, the attachment area of the cold air in the passage gap on the end wall is mainly concentrated near the trailing edge of the passage gap, and the cooling efficiency of the cold air in the passage gap for the upstream end wall is poor. The mainstream invasion in the passage gap starts at z / C ax = 0.04 and ends at z / C ax = 0.35. Therefore, in this embodiment, a double-cold-air-chamber passage gap structure is adopted, and the chamber is divided into two independent cold air chambers at the downstream boundary z / C ax = 0.35 position of the mainstream invasion area.

[0117] The reason why the two independent cold air chamber passage gap structure design is adopted to establish two independent cold air chambers in the passage gap is that the traditional passage gap generally adopts a single cold air chamber, which causes uneven distribution of cold air outflow, and cannot play a role in overcoming the main flow invasion of the passage gap. The passage gap design with two independent cold air chambers can improve the cold air outflow intensity of the upstream region of the passage gap and enhance the film cooling performance of the upstream end wall.

[0118] Step 10: Check the aerodynamic heat transfer and structural strength performance of the passage gap design. The calculation process includes:

[0119] a. Apply the passage gap structure obtained in step 9 to the blade and end wall geometry model described in step 1 to re-establish the cascade fluid domain and solid domain geometry model and mesh. In this embodiment, the determined passage gap structure parameters and flow parameters are summarized in Table 4.

[0120] Table 4 Passage gap structure parameters

[0121] Parameter name Value Installation angle of the passage gap (a) 57.5° Passage gap type Straight slot type Installation position intersection with z = 0 y / P = 0.87 Passage gap width (w) 1.7 mm Blowing ratio of the passage gap (BR) 1.0 Coolant flow rate of the passage gap (MF) 7.7 g / s Ejection angle of the passage gap (b) 60° Coolant chamber partition position z / C ax = 0.35

[0122] b. Re-calculate the aerodynamic heat transfer performance of the cascade and the structural strength of the end wall by using the computational fluid dynamics and finite element calculation methods described in steps 3 and 4, respectively, that is, numerical simulation of the cascade aerodynamic heat transfer performance and finite element analysis of the end wall solid domain structural strength.

[0123] c. Compare and analyze the calculation results obtained in steps 3, 4 and 10. Repeat steps 5-9 and adjust the size of the structure design parameters until the following targets are met simultaneously, then proceed to the next step:

[0124] 1) The difference between the peak and valley of the end wall circumferential average cooling efficiency η along the axial distribution is reduced by more than 30% compared with the result obtained in step 3;

[0125] 2) The difference between the cascade outlet average total pressure recovery coefficient ξ and the result obtained in step 3 is less than 2%;

[0126] 3) The maximum value of the local blowing ratio BR of the cold air is less than 2.5;

[0127] 4) The maximum structural stress is less than 5% different from the result obtained in step 4, and less than the material's endurance strength.

[0128] Wherein the end wall circumferential average efficiency η and the total pressure recovery coefficient ξ are defined as:

[0129] η = (T ∞ -T aw ) / (T ∞ -T c(8)

[0130] ξ=(P ∞ -P) / (0.5·ρ ∞ ·V ∞ 2 (9)

[0131] In the formula, P ∞ P and P are the total pressures of the mainstream and local fluids, respectively.

[0132] In this embodiment, the difference between the peak and valley values ​​of the axial distribution of the average film cooling efficiency of the endwall circumferential direction obtained in step 10 is reduced by 31.5% compared to the result obtained in step 3; the average total pressure recovery coefficient ξ at the blade outlet obtained in step 10 is reduced by 0.7% compared to the result obtained in step 3; the maximum value of the local blowing ratio of the cold air obtained in step 10 is 2.1; and the maximum structural stress obtained in step 10 is increased by 3.6% compared to the result obtained in step 4, but is less than the material's creep strength. All of the above indicators meet the design objectives.

[0133] Step 11: Determine the cold air chamber depth h of the channel gap based on the rising height of the cold air in the channel gap and the intrusion depth of the mainstream into the channel gap. The channel gap depth refers to the distance between the channel gap outlet and the bottom sealing structure of the cold air chamber.

[0134] Specifically, in this step, based on the cold air tracer variable trajectory within the channel gap obtained in step 10, the preferred channel gap depth is 0.8°C. ax The location is 90% to 110% of the height of the cold air rise, and at the same time, it is 150% to 200% of the maximum mainstream intrusion depth within the channel gap.

[0135] In this embodiment, based on the three-dimensional trajectory coordinates of the cold gas tracer variable in the channel gap obtained in step 10, the channel gap is 0.8°C. ax The cold air rises to a height of 4.1 mm at the location, and the maximum mainstream intrusion depth within the channel gap is 2.3 mm. Therefore, the channel gap depth is determined to be h = 3.9 mm.

[0136] Based on this, the final design of the end-wall channel gap cooling structure is shown to have a axial distribution value that differs from the initial design's average circumferential cooling efficiency. Figure 6 A comparison was made to illustrate the effectiveness of the design.

[0137] To sum up, on the basis of the traditional thermal expansion design index, the cooling effect of the channel gap cold air on the end wall, the end wall platform structure strength and the cascade flow characteristics and other factors are included in the channel gap structure design index. According to the aerodynamic heat transfer performance parameters of the end wall, the channel gap width, the cold air flow, the installation angle and the installation position and other parameters are determined; according to the blade profile and the end wall structure strength parameters, the inclined type, the multi-cold air chamber channel gap structure is selected, and the channel gap depth parameter is determined. The internal cold air flow control of the channel gap is realized, the problems of cold air accumulation and low utilization rate of the channel gap are overcome, the film cooling effect of the channel gap cold air on the end wall is improved, and the applicability of the channel gap structure design method in practical application is enhanced.

Claims

1. A design method for a turbine end-wall channel gap cooling structure, characterized in that, Includes the following steps: Step 1: Import the geometric parameters of the blade and endwall shape, and establish a three-dimensional geometric model of the turbine blade cascade and endwall platform; Step 2: For the three-dimensional geometric model, mesh the fluid domain of the blade cascade to obtain the blade cascade fluid domain mesh; mesh the solid domain of the blade and endwall platform to obtain the blade and endwall solid domain mesh. Step 3: Using the aforementioned blade cascade fluid domain grid, perform numerical simulation calculations on the aerodynamic heat transfer performance parameters of the blade cascade and endwalls to obtain the heat transfer coefficient distributions on the pressure side and suction side endwalls, as well as the flow field information of the blade cascade and the development trajectory of the cold gas tracer variables. Step 4: Using the solid domain mesh of the blades and endwalls described in Step 2, as well as the aerodynamic heat transfer performance parameters of the blade cascade and endwalls, the centrifugal stress and structural stress of the endwall platform are calculated and analyzed using finite element software to obtain the stress distribution of the endwall platform. Step 5: Determine the installation angle α and installation position of the channel gap; the channel gap installation angle α refers to the angle between the straight groove channel gap and the blade header line, and the straight groove channel gap refers to the channel gap structure composed of a straight rectangular cavity; Step 6: Determine the channel gap width w; Step 7: Adjust the airflow ratio BR by adjusting the airflow rate MF in the channel gap according to the channel gap installation angle α and the channel gap width w; Step 8: Based on the heat transfer coefficient distribution of the pressure side and suction side end walls, an inclined channel gap structure design is adopted, so that the channel gap deflects towards the end wall with a larger average heat transfer coefficient. The exit angle β and the tilting direction of the channel gap are determined based on the difference in heat transfer coefficient between the pressure side and suction side end walls. Step 9: Based on the cascade flow field information and the development trajectory of the cold gas tracer variable, the main area where the mainstream intrusion occurs in the channel gap is obtained. A dual-cold gas chamber channel gap structure design is adopted. Near the tail end of the mainstream intrusion area in the channel gap, the internal cold gas chamber is divided into two independent chambers. For cases where no mainstream intrusion occurs in the channel gap, a single-cold gas chamber channel gap structure is adopted. Step 10: Verify the aerodynamic heat transfer and structural strength performance of the channel gap design; Step 11: Determine the channel gap depth h, where the channel gap depth h refers to the distance between the channel gap outlet and the sealing structure below the cold air chamber.

2. The design method for the turbine end-wall channel gap cooling structure according to claim 1, characterized in that, In step 3, during the numerical simulation, different tracer variables are added at each cold air inlet to monitor the trajectory of the cold air flowing within the blade cascade at each non-uniform cold air leakage point. The transport equations for the variables are as follows: In the formula, Φ represents the variable concentration, and ρ represents the fluid density. U j and u j x is the fluid velocity. j Let S be the coordinate, t be the time, and S be the time. Φ For source terms.

3. The design method for the turbine end-wall channel gap cooling structure according to claim 1, characterized in that, In step 5, the channel gap installation angle α is calculated by the following formula: α＝α s -(5°～10°) The installation position of the channel gap is determined by the following formula: y1 / y2 = 0.9 to 1.1 Where α s y1 is the blade mounting angle, y2 is the minimum distance between the pressure side edge of the channel gap and the pressure surface of the blade, and y3 is the minimum distance between the suction side edge of the channel gap and the suction surface of the blade. In cases where the channel gap installation position intersects with the blade or its chamfer, or where the blade installation angle is less than 30 degrees, a straight groove channel gap structure cannot be used. In such cases, a two-section groove design channel gap structure is adopted. The two-section groove refers to a channel gap composed of two straight grooves connected by an included angle of 90° to 180°.

4. The design method for the turbine endwall channel gap cooling structure according to claim 1 or 3, characterized in that, In step 5, a straight groove or two-section channel gap structure is selected based on the blade pressure side and suction side profile and their deflection. The installation angle of the channel gap is determined based on the blade installation angle and the cold air flow trajectory of the channel gap. The installation position of the channel gap is determined based on the blade profile parameters.

5. The design method for the turbine end-wall channel gap cooling structure according to claim 3, characterized in that, In step 6, the channel gap width w is determined by the following formula: w=(120%~140%)·e max Where ε max It is the maximum value of the deformation at the installation position of the channel gap, obtained based on the stress distribution of the end wall platform.

6. The design method for the turbine end-wall channel gap cooling structure according to claim 1, characterized in that, In step 7, the cold air blowing ratio at the channel gap is 1.0-1.5; the cold air velocity V c The air-blowing ratio is defined as follows: V c =MF / (w·C ax / sinα) BR=(ρ c ·V c ) / (ρ ∞ ·V ∞ ) In the formula, ρ ∞ and V ∞ These represent the mainstream average density and velocity, respectively; C ax ρ is the axial chord length of the blade. c This refers to the density of the cooling fluid.

7. The design method for the turbine end-wall channel gap cooling structure according to claim 1, characterized in that, In step 8, the channel gap exit angle β is determined by the following formula: β＝60°～65°。 8. The design method for the turbine end-wall channel gap cooling structure according to claim 1, characterized in that, In step 9, the separation position of the two cold air chambers is located at the downstream boundary of the mainstream intrusion area within the channel gap.

9. The design method for the turbine end-wall channel gap cooling structure according to claim 1, characterized in that, In step 10, using the channel gap structure obtained in step 9 and the three-dimensional geometric model of the turbine blade cascade and endwall platform described in step 1, numerical simulation of the aerodynamic heat transfer performance of the blade cascade is performed, and finite element analysis of the structural strength of the endwall solid domain is conducted. Steps 5-9 are repeated and their parameters are adjusted until the following objectives are simultaneously met: 1) The difference between the peak and valley values ​​of the average circumferential cooling efficiency η of the end wall along the axial direction is reduced by more than 30% compared with the result obtained in step 3; 2) The average total pressure recovery coefficient ξ at the blade outlet differs from the result obtained in step 3 by less than 2%; 3) The maximum value of the local airflow ratio (BR) of the air conditioner is less than 2.5; 4) The maximum structural stress differs from the result obtained in step 4 by less than 5%, and is less than the material's endurance strength; The definitions of the endwall circumferential average cooling efficiency η and the blade outlet average total pressure recovery coefficient ξ are as follows: η=(T ∞ -T aw ) / (T ∞ -T c ) ξ=(P ∞ -P) / (0.5·ρ ∞ ·V ∞ 2 ) In the formula, P ∞ P and T represent the total pressure of the mainstream and local fluids, respectively. ∞ T aw T c These are the mainstream temperature, the adiabatic end wall temperature, and the cooling fluid temperature, respectively.

10. The design method for the turbine endwall channel gap cooling structure according to claim 1, characterized in that, In step 11, the depth of the cold air chamber in the channel gap is determined based on the rising height of the cold air in the channel gap and the intrusion depth of the mainstream into the channel gap; based on the cold air tracer variable trajectory obtained in step 10, the channel gap depth h is 0.8°C. ax The location is 90% to 110% of the height of the cold air rise, and at the same time, it is 150% to 200% of the maximum mainstream intrusion depth within the channel gap.

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