A micro rib for improving endwall film cooling efficiency and a gas turbine

Abstract

A micro rib and a gas turbine for improving the endwall film cooling efficiency, belonging to the field of gas turbines; the micro rib is arranged on the endwall between the slot and the leading edge of the stator blade, and its trailing edge intersects with the stator blade; the separation of the leading edge horseshoe vortex to the pressure side and the suction side is inhibited by the micro rib, so that the horseshoe vortex migrates downstream. The micro rib is symmetrically distributed about the saddle point. The micro rib of the present invention limits the influence of the horseshoe vortex on the air flow to the leading edge part of the stator blade as much as possible, weakens its influence on the downstream endwall of the cascade passage, plays a protective role on the endwall, reduces the heat load of the endwall, and ensures the safe and efficient operation of the high-pressure gas turbine. The micro rib structure of the present invention has general applicability to reducing the endwall heat load at present.

Description

Technical Field

[0001] The present invention belongs to the field of gas turbines, and particularly relates to a micro rib for improving the endwall film cooling efficiency and a gas turbine. Background Art

[0002] As a main device for thermal power conversion, gas turbines are widely used in the fields of aviation propulsion, electric power, petrochemical industry, etc. With the increasing prominence of modern environmental problems and the adjustment of the energy structure, the necessity of improving the power and thermal efficiency of gas turbines has become increasingly prominent. In order to cope with the challenges in industrial applications, the working environment of the high-temperature and high-pressure components of gas turbines has deteriorated continuously. Among them, the turbine inlet temperature has increased to about 1800K or even higher, far exceeding the melting point of high-temperature materials. At the same time, the endwall surface bears half of the thermal load of the turbine wall. In order to enable the gas turbine to operate safely and stably, it is necessary to use high-temperature-resistant materials, thermal barrier coatings, cooling and other technical means to protect it, and among them, the cooling technology plays a very important role.

[0003] Since the gas turbine combustor and turbine are manufactured and processed separately and then assembled, there will inevitably be a gap between the combustor and the turbine. In order to prevent high-temperature gas from invading the disk cavity through this gap, in engineering applications, high-pressure air flow is led out from the rear-stage compressor through this gap. This part of the high-pressure air flow can cool and protect the endwall of the downstream turbine. This technical means is called slot cooling.

[0004] When the gas in the gas turbine flows through the stator blade in the cascade passage, stagnation will occur. Therefore, there is an adverse pressure gradient in the boundary layer at the leading edge of the stator blade; since the energy of the boundary layer fluid is lower than that of the mainstream fluid, there will also be a radial inward pressure gradient near the end face during the stagnation process. Under the action of the above pressure gradients, the boundary layer will separate at the leading edge of the stator blade to generate a horseshoe vortex. The leading edge of the stator blade is arc-shaped. When the air flow reaches stagnation at the leading edge point, the fluids on both sides of the leading edge point have not yet stagnated. Therefore, the horseshoe vortex separates into a pressure-side branch and a suction-side branch after encountering the stator blade. Under the action of the transverse pressure gradient in the downstream passage, the pressure-side branch of the horseshoe vortex will migrate towards the suction side. The slot cooling jet will separate from the wall surface under the entrainment action of the horseshoe vortex. Therefore, the coverage effect of the cooling jet on the leading edge endwall and the pressure-side endwall of the stator blade is poor. In engineering, in order to reduce the above influence, film holes jets are usually arranged at the positions where the coverage effect of the slot jet is poor for targeted cooling. However, under the background of the current demand for high thrust-to-weight ratio and high efficiency of gas turbines, the supply of cooling air flow is very limited. Increasing the amount of cold air for additional cooling of the endwall will be severely restricted. Therefore, during the continuous operation of the gas turbine, ablation phenomena often occur on the leading edge of the stator blade and the endwall near the pressure side, which has a serious impact on the safety and life of the gas turbine.

[0005] Therefore, the development of micro ribs that can improve the efficiency of endwall film cooling can reduce the risk of ablation of the leading edge of the stator blade and the endwall on the pressure side, improve the safety factor of the gas turbine, and have extremely important engineering application value. Summary of the Invention

[0006] Technical problems to be solved:

[0007] In order to avoid the deficiencies of the prior art, aiming at the shortcomings that the first-stage stator endwall of a gas turbine bears extremely high thermal loads and the conventional slot cooling technology cannot effectively reduce the thermal loads on the leading edge of the stator blade and the endwall on the pressure side, the present invention provides a micro rib for improving the efficiency of endwall film cooling, which improves the cooling effect of the cooling jet on the endwall by delaying the separation of the horseshoe vortex to both sides and weakening the intensity of the downstream horseshoe vortex, reduces the thermal load on the endwall surface, and ensures the safe and effective operation of the gas turbine.

[0008] The technical solution of the present invention is: a micro rib for improving the efficiency of endwall film cooling, the micro rib is arranged on the endwall between the slot and the leading edge of the stator blade, and its trailing edge intersects with the stator blade; the separation of the leading-edge horseshoe vortex to the pressure side and the suction side is inhibited by the micro rib, so that the horseshoe vortex migrates downstream.

[0009] A further technical solution of the present invention is: the micro rib is symmetrically distributed about the saddle point.

[0010] A further technical solution of the present invention is: the micro rib includes 2 to 5 micro rib plates arranged side by side, and the trailing edges of each micro rib plate intersect with the stator blade.

[0011] A further technical solution of the present invention is: the middle micro rib plate of the micro rib passes through the saddle point, and the remaining micro rib plates are symmetrically distributed about the saddle point.

[0012] A further technical solution of the present invention is: the height H of the micro rib r and the local boundary layer thickness H b The relationship is: 1.0H b <H r <2.0H b .

[0013] A further technical solution of the present invention is: the width W of the micro rib plate r and the height H of the micro rib r The relationship is: 0.1H r <W r <0.2H r .

[0014] A further technical solution of the present invention is: the distance L between the leading edge of the micro rib and the slot exit r , the distance L between the leading edge of the stator blade and the slot exit bThe relationship is: 0.3L b <L r <0.5L b 。

[0015] A further technical solution of the present invention is that the distance between adjacent micro rib plates, that is, the pitch Y of the micro rib plates, and the width W of the micro rib plates r The relationship is: 2W r <Y<3W r 。

[0016] A further technical solution of the present invention is that the micro rib plate is a flat plate structure perpendicular to the end wall and perpendicular to the slot.

[0017] A gas turbine includes a stator blade; micro ribs for improving the film cooling efficiency of the end wall are arranged on the end wall between the stator blade and its upstream slot; the micro ribs include a plurality of mutually parallel micro rib plates, the micro rib plates are perpendicular to the end wall and the slot, and the trailing edge intersects with the leading edge of the stator blade; the micro ribs are symmetrically distributed about the saddle point.

[0018] Working principle: Since the leading edge of the stator blade is arc-shaped, when the air flow reaches stagnation at the leading edge point, the fluid on both sides of the leading edge point has not yet stagnated. Therefore, the horseshoe vortex separates into a pressure surface side branch and a suction surface side branch after encountering the stator blade. Under the action of the transverse pressure gradient in the downstream channel, the pressure surface side branch of the horseshoe vortex will migrate towards the suction surface side. The slot cooling jet will break away from the wall under the entrainment action of the horseshoe vortex. Therefore, the coverage effect of the cooling jet on the leading edge end wall and the pressure surface side end wall of the stator blade is poor. In order to overcome the separation of the horseshoe vortex caused by the pressure difference on both sides when the air flow reaches stagnation at the leading edge point of the stator blade, the present invention proposes to arrange five micro ribs in parallel at the leading edge of the stator blade. When the air flow reaches stagnation at the leading edge point of the stator blade, the air flows on both sides of the leading edge point of the stator blade are also stagnated due to the obstruction of the micro ribs, weakening the separation of the horseshoe vortex to both sides, and limiting the influence of the horseshoe vortex on the air flow as much as possible to the leading edge part of the stator blade, weakening its influence on the downstream end wall of the cascade channel, and playing a protective role on the end wall.

[0019] In order to achieve the above object, the technical solution adopted by the present invention is to arrange micro ribs approximately axially near the saddle point of the leading edge of the stator blade to inhibit the migration of the horseshoe vortex at the leading edge of the stator blade to both sides downstream. The specific analysis is as follows:

[0020] (1) The position of the middle micro rib plate at the leading edge of the stator blade. During the stagnation process of the air flow, the static pressure reaches the highest at a certain circumferential position at the leading edge of the stator blade. The upstream boundary layer separates at this point to form a horseshoe vortex, and the left and right branches of the horseshoe vortex are formed on both sides of the saddle point. Arranging the middle micro rib plate at the saddle point can make the micro rib limit the separation tendency of the horseshoe vortex to both sides to the greatest extent.

[0021] (2) Design method of micro ribs. In order to weaken the separation of the horseshoe vortex to both sides to the greatest extent and reduce the increase in the endwall surface heat load caused by the entrainment of the horseshoe vortex, micro ribs are arranged at the leading edge of the stator blade to inhibit the separation of the horseshoe vortex to both sides. By using the numerical simulation method, the specific arrangement angle and geometric parameters of the micro ribs are determined according to the specific operating conditions and blade profile geometric conditions.

[0022] Beneficial effects

[0023] The beneficial effects of the present invention are as follows: The micro ribs of the present invention for improving the endwall film cooling efficiency can overcome the separation of the horseshoe vortex caused by the pressure difference on both sides when the air flow reaches stagnation at the leading edge point of the stator blade. When the air flow reaches stagnation at the leading edge point of the stator blade, the air flows on both sides of the leading edge point of the stator blade are also stagnated due to the obstruction of the micro ribs, weakening the separation of the horseshoe vortex to both sides, limiting the influence of the horseshoe vortex on the air flow as much as possible to the leading edge part of the stator blade, weakening its influence on the downstream endwall of the cascade passage, playing a protective role on the endwall, reducing the heat load of the endwall, and ensuring the safe and efficient operation of the high-pressure gas turbine. The micro rib structure of the present invention has general applicability to reducing the endwall heat load at present.

[0024] Under the flow condition that the mass flow ratio of the slot jet is 0.75%, comparing the structure of the present invention with the traditional structure, we obtain Figure 6 the cooling efficiency distribution contour map shown. The dimensionless effective cooling area (i.e., the ratio of the area where the cooling efficiency is greater than 0.1 to the total area of the endwall) of the embodiment of the present invention is increased by 117.46%, as shown in Table 1. The micro rib structure of the present invention has general applicability to reducing the endwall heat load at present.

[0025] Table 1 Comparison of cooling efficiency between the structure of the present application and the traditional structure

[0026] Description of the drawings

[0027] Figure 1 is the meridional plane cross-sectional view of the high-pressure turbine stator of the conventional endwall;

[0028] Figure 2 is the top view of the high-pressure turbine stator of the conventional endwall;

[0029] Figure 3 is the schematic diagram of the horseshoe vortex branch and the saddle point in the flow field of the conventional endwall;

[0030] Figure 4 is the meridional plane cross-sectional view of the turbine stator with micro ribs at the leading edge of the stator blade;

[0031] Figure 5 is the top view of the turbine stator with micro ribs at the leading edge of the stator blade.

[0032] Figure 6 It is a comparison chart of the cooling efficiency between the structure of the present invention and the traditional structure; (a) traditional end wall, (b) end wall of the present invention.

[0033] Explanation of reference numerals: 1 - stator end wall, 2 - slot, 3 - stator blade, 4 - micro rib, 5 - pressure surface side branch of horseshoe vortex, 6 - suction surface side branch of horseshoe vortex, 7 - saddle point, 8 - distance L between the leading edge of the micro rib and the outlet of the slot r , 9 - width W of the micro rib plate r , 10 - height H of the micro rib r , 11 - pitch Y of the micro rib plate. Specific embodiments

[0034] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0035] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.

[0036] The specific structure of the present invention is shown in the attached Figures 4 - 5 , and the design idea is as follows:

[0037] See Figure 4 And Figure 5 , and Figure 1 Compared with the conventional cascade in , a micro rib 4 is arranged on the end wall between the slot and the leading edge of the stator blade in the present invention. The micro rib 4 includes 5 micro rib plates arranged in parallel, and their trailing edges all intersect with the stator blade. When the air flow reaches stagnation at the leading edge point of the stator blade 3, the air flows on both sides of the leading edge point of the stator blade 3 are also stagnated due to the obstruction of the micro rib 4, and the separation of the horseshoe vortex to both sides is inhibited, and the influence of the horseshoe vortex on the air flow is limited as much as possible to the leading edge part of the stator blade 3, weakening its influence on the downstream end wall 1 of the cascade passage and playing a protective role for the end wall 1. (The horseshoe vortex separates into pressure surface and suction surface branches at the saddle point, and is determined according to the simulation results and the flow structure near the end wall)

[0038] See Figure 5 , a micro rib 4 is introduced at the leading edge of the stator blade 3, and its specific arrangement angle and geometric parameters are determined according to the specific operating conditions and blade profile geometric conditions, and are processed together with the stator blade 3.

[0039] In the implementation of the present invention, first, modeling and simulation are carried out through the given cascade geometry and flow conditions, and then the position of the micro rib 4 of the present invention is determined according to the characteristics of the conventional end wall surface flow structure obtained. Its specific arrangement angle and geometric parameters are determined according to the specific operating conditions and blade profile geometric conditions.

[0040] The numerical simulation results show that when the jet mass flow ratio of the slot 2 is 0.5%, the micro rib 4 can significantly increase the cooling efficiency at the leading edge of the stator blade 3 and make the cooling more uniform when the following conditions are met, that is, the number of the micro ribs 4 is 2 - 5, and they are arranged side by side on the leading edge end wall of the stator blade 3. The middle micro rib 4 passes through the saddle point 7, and the remaining micro ribs 4 are symmetrically distributed about it.

[0041] The height H of the micro rib r 10 and the local boundary layer thickness H b The relationship is: 1.0H b <H r <2.0H b . (The local boundary layer thickness H b refers to the height perpendicular to the wall surface from the boundary layer wall surface to the position where the tangential flow velocity along the wall surface reaches 99% of the free stream velocity, which is confirmed according to the numerical simulation results).

[0042] The width W of the micro rib plate r 9 and the micro rib height H r 10 The relationship is: 0.1H r <W r <0.2H r .

[0043] The trailing edge of the micro rib 4 intersects with the stator blade 3.

[0044] The distance L between the leading edge of the micro rib 4 and the outlet of the slot 2 r 8. The distance L between the leading edge of the stator blade and the outlet of the slot b The relationship is: 0.3L b <L r <0.5L b .

[0045] The distance between each micro rib plate, that is, the pitch Y11 of the micro rib plate, and the micro rib width W r The relationship is: 2W r <Y<3W r . The micro rib 4 is symmetrically distributed about the saddle point 7.

[0046] The technical principle of the present invention is as follows:

[0047] See Figure 3, since the leading edge of the stator vane 3 is arc-shaped, when the air flow reaches stagnation at the leading edge point, the fluid on both sides of the leading edge point has not yet stagnated. Therefore, the horseshoe vortex separates into the pressure surface side branch 5 and the suction surface side branch 6 on both sides of the saddle point 7. The cooling jet flow in the slot 2 will separate from the end wall surface 1 under the entrainment action of the horseshoe vortex. Therefore, the coverage effect of the cooling jet flow on the leading edge end wall and the pressure surface side end wall of the stator vane 3 is poor.

[0048] See Figure 4 And Figure 5 , in order to overcome the separation of the horseshoe vortex caused by the pressure difference from the saddle point 7 to both sides when the air flow reaches stagnation at the leading edge point of the stator vane 3, the present invention proposes to arrange five micro ribs 4 in parallel at the leading edge of the stator vane 3. When the air flow reaches stagnation at the leading edge point of the stator vane 3, the air flows on both sides of the leading edge point of the stator vane 3 are also stagnated due to the obstruction of the micro ribs 4, weakening the separation of the horseshoe vortex to both sides, limiting the influence of the horseshoe vortex on the air flow to the leading edge part of the stator vane 3 as much as possible, weakening its influence on the downstream end wall 1 of the cascade passage, and playing a protective role for the end wall.

[0049] The numerical simulation results have preliminarily proved that the micro ribs 4 of the present invention can significantly inhibit the separation of the horseshoe vortex.

[0050] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill 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 purposes of the present invention.

Claims

1. A micro rib for improving the efficiency of endwall film cooling, characterized in that: the micro rib is arranged on the endwall between the slot and the leading edge of the stator blade, and its trailing edge intersects with the leading edge of the stator blade; the separation of the leading-edge horseshoe vortex to the pressure side and the suction side is inhibited by the micro rib, so that the horseshoe vortex migrates downstream. The micro rib includes 5 micro rib plates arranged side by side, and the trailing edges of the micro rib plates all intersect with the leading edge of the stator blade; the middle micro rib plate of the micro rib passes through the saddle point, and the remaining micro rib plates are symmetrically distributed with respect to the saddle point. The height of the micro rib H r has the following relationship with the local boundary layer thickness H b as follows: 1.0 H b ＜ H r ＜2.0 H b ； The width of the micro rib W r and the height of the micro rib H r are related as: 0.1 H r < W r <0.2 H r ; The distance between the leading edge of the micro rib and the slot exit L r , and the distance between the leading edge of the stator blade and the slot exit L b are in the relationship of: 0.3 L b < L r <0.5 L b ; The distance between adjacent micro-ribs, i.e., the pitch of the micro-ribs Y , and the width of the micro-ribs W r are related as: 2 W r < Y <3 W r .

2. The micro rib for improving the endwall film cooling efficiency according to claim 1, wherein: The micro rib is a flat plate structure perpendicular to the end wall and perpendicular to the slot.

3. A gas turbine, comprising stator blades; characterized in that: A micro rib for improving the end wall film cooling efficiency according to claim 1 or 2 is provided on the end wall between the stator blade and its upstream slot.

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