Grate tooth sealing structure for enhancing sealing performance through shock wave effect

Abstract

The invention provides a labyrinth sealing structure for enhancing sealing performance through a shock wave effect, and relates to the technical field of aero-engine and gas turbine sealing. By designing a tooth tip molded line, a wall surface molded line or a combination of the tooth tip molded line and the wall surface molded line, a shrinkage-expansion type comb tooth slit channel which is gradually shrunk and then gradually expanded in the airflow direction is formed. The critical pressure ratio is adjusted by adjusting the area ratio of the throat section to the outlet section of the shrinkage-expansion type labyrinth slit channel, so that airflow reaches a sonic speed state in the throat section of the shrinkage-expansion type labyrinth slit channel and reaches a supersonic speed state in the expansion section, and therefore shock waves are generated. Extra total pressure loss and flow resistance effect generated by shock wave induction are superposed with total pressure loss and flow resistance effect generated by flow separation caused by geometric sudden expansion, so that the sealing performance of labyrinth seal is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of sealing for aeroengines and gas turbines. Specifically, it relates to a labyrinth seal structure that enhances the sealing performance through shock wave effects. Background Technique

[0002] Sealing technology is one of the key core technologies for improving the performance of aeroengines and gas turbines. Research shows that for an aeroengine, when the sealing leakage is reduced by 1%, the engine thrust increases by 1% and the fuel consumption rate decreases by 0.1%. Labyrinth sealing, graphite sealing, and brush sealing are the three widely used sealing technologies at present.

[0003] As one of the three sealing technologies, labyrinth sealing belongs to a non-contact sealing device. Due to its characteristics such as simple structure, easy processing, and flexible arrangement, it is widely used to block fluid leakage between high and low pressure cavities and regulate the leakage flow rate.

[0004] Taking the common labyrinth seal structure between a rotor and a stator as an example, as Figure 1 and Figure 2 shown. The labyrinth seal structure includes a stator 2 and a rotor 1. Labyrinth teeth 3 are arranged on the rotor 1, and the inner wall of the stator 2 and the labyrinth teeth form a sealing structure. The inlet air flow pressure of the labyrinth seal is relatively high. When the air flow passes through the slit formed by the first labyrinth teeth, the pressure decreases and the velocity increases. Then the air flow enters the cavity. Due to the sharp expansion of the channel contour, the air flow separates, forming separated flow and recirculation. The fluid velocity gradient inside the cavity is relatively large. Under the action of molecular viscosity and turbulent viscosity, the friction between fluid microgroups increases, thereby enhancing the loss of fluid mechanical energy. After passing through several labyrinth teeth, the loss of fluid mechanical energy accumulates continuously, and the total pressure drops. The pressure difference between the cavity before the last labyrinth teeth and the sealing outlet decreases, thereby reducing the air flow rate through the slit of the last labyrinth teeth. According to the conservation of flow rate, when the pressure difference on both sides of the seal remains unchanged, the flow rate through the seal is equal to the minimum flow rate of the air flow through the slits of each labyrinth tooth, thereby achieving the purpose of reducing the fluid leakage amount.

[0005] For labyrinth sealing, its main working principle is to set slits and cavities on the channel, and utilize the acceleration effect of the labyrinth tooth slits and the flow channel sudden expansion formed by the cavities to induce flow separation and recirculation at high speeds, thereby generating a large total pressure loss and an additional throttling effect, and then reducing the leakage amount of the air flow.

[0006] As Figure 3The Mach number distribution of the internal flow field of a traditional labyrinth seal is given when the total static pressure ratio of the inlet and outlet is 3.0. It can be observed that the Mach numbers of other labyrinth seal gaps do not exceed 1.0 except for the last labyrinth seal gap. This means that there is no total pressure loss induced by shock waves inside the traditional labyrinth seal. It can be seen that the traditional labyrinth seal mainly relies on the flow separation and recirculation induced by geometric sudden expansion to enhance the fluid mechanical energy loss and flow resistance effect, and does not involve various flow losses induced by shock waves. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a labyrinth seal structure that enhances the sealing performance through shock wave effects.

[0008] The present invention adopts the following solutions:

[0009] The present application provides a labyrinth seal structure that enhances the sealing performance through shock wave effects; a contraction-expansion type labyrinth seal slit channel that gradually narrows and then gradually expands along the air flow direction is formed by the labyrinth tooth tip profile, the wall profile, or a combination of both, so that shock waves are generated in the labyrinth seal slit, thereby enhancing the total pressure loss.

[0010] Further, the contraction-expansion type labyrinth seal slit channel includes a contraction section, a throat, and an expansion section.

[0011] Further, by adjusting the area ratio of the throat cross-section to the outlet cross-section of the contraction-expansion type labyrinth seal slit channel formed by the labyrinth tooth tip profile, the wall profile, or a combination of both, the air flow reaches the speed of sound at the throat cross-section of the contraction-expansion type labyrinth seal slit channel, continues to accelerate to supersonic speed in the expansion section, and then shock waves are generated in the expansion section, and the shock waves induce total pressure loss and flow resistance effects.

[0012] Further, by changing the labyrinth tooth tip profile, the wall profile, or a combination of both, the critical pressure ratio of the contraction-expansion type labyrinth seal slit channel can be adjusted.

[0013] Further, the profile of the contraction section adopts the Wyshinski curve or the bicubic curve; the expansion section adopts the inverted Wyshinski curve or the bicubic curve.

[0014] Further, the contraction-expansion type labyrinth seal slit channel can be used alone or in combination with the traditional labyrinth seal structure, and is located at the first stage or the intermediate stage.

[0015] By adopting the above technical solutions, the present invention can achieve the following technical effects:

[0016] The present invention provides a labyrinth seal structure that enhances the sealing performance through shock wave effects. By designing the labyrinth tip profile, the wall profile, or a combination of both, a convergent-divergent labyrinth slit channel that gradually narrows and then gradually expands along the airflow direction is formed. By adjusting the area ratio of the throat section to the outlet section of the convergent-divergent labyrinth slit channel, its critical pressure ratio is adjusted so that the airflow reaches the sonic state at the throat section of the convergent-divergent labyrinth slit channel and the supersonic state in the expansion section, thereby generating shock waves. The shock waves induce additional total pressure losses and flow resistance effects, which are superimposed on the total pressure losses and flow resistance effects caused by the flow separation due to geometric sudden expansion, thereby strengthening the sealing performance of the labyrinth seal. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0018] Figure 1 is a schematic diagram of the working principle of the labyrinth seal structure;

[0019] Figure 2 is a schematic diagram of the velocity field inside the labyrinth seal structure;

[0020] Figure 3 is the Mach number distribution near the traditional labyrinth seal slit when the total-static pressure ratio at the inlet and outlet is 3;

[0021] Figure 4 is a sectional view of a labyrinth seal structure that enhances the sealing performance through shock wave effects according to an embodiment of the present invention;

[0022] Figure 5 is a schematic diagram of the convergent-divergent labyrinth slit channel structure formed by the labyrinth tip profile and the wall surface of a labyrinth seal structure that enhances the sealing performance through shock wave effects according to an embodiment of the present invention;

[0023] Figure 6 is a schematic diagram of the convergent-divergent labyrinth slit channel structure formed by the wall profile and the labyrinth tip of a labyrinth seal structure that enhances the sealing performance through shock wave effects according to an embodiment of the present invention;

[0024] Figure 7 is a schematic diagram of the convergent-divergent labyrinth slit channel structure formed by the labyrinth tip profile and the wall profile of a labyrinth seal structure that enhances the sealing performance through shock wave effects according to an embodiment of the present invention;

[0025] Figure 8It is a schematic diagram of the flow field and Mach number distribution inside the labyrinth seal structure that enhances the sealing performance through the shock wave effect in the embodiment of the present invention when the total static pressure ratio at the inlet and outlet is 1.85;

[0026] Figure 9 It is a schematic diagram of the relationship between the area ratio of the throat section to the outlet section and the critical pressure ratio of the convergent-divergent labyrinth slit channel in the ideal state of the labyrinth seal structure that enhances the sealing performance through the shock wave effect in the embodiment of the present invention;

[0027] Figure 10 It is the relationship between the internal flow state of the fixed geometry convergent-divergent channel of the labyrinth seal structure that enhances the sealing performance through the shock wave effect in the embodiment of the present invention and the total static pressure ratio at the inlet and outlet;

[0028] Figure 11 It is a combined schematic diagram of the labyrinth seal of the convergent-divergent labyrinth slit channel of the labyrinth seal structure that enhances the sealing performance through the shock wave effect and the traditional labyrinth seal in the embodiment of the present invention;

[0029] Figure 12 It is a schematic diagram of the convergent-divergent channel constructed based on the Wyshinski curve and the bicubic curve of the labyrinth seal structure that enhances the sealing performance through the shock wave effect in the embodiment of the present invention;

[0030] Icon: Rotor 1, Stator 2, Labyrinth teeth 3, Labyrinth slit 4, Cavity 5, Converging section 6, Throat 7, Diverging section 8, Operating point 9. Detailed implementation manners

[0031] To make the purpose, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0032] Embodiment

[0033] Combined with Figures 4 to 12As shown in the figure, this embodiment provides a labyrinth seal structure that enhances the sealing performance through the shock wave effect. A labyrinth slit channel with a constriction-expansion form that gradually narrows and then gradually expands along the airflow direction is formed by the labyrinth tooth tip profile, the wall profile, or a combination of both, so that a shock wave is generated in the labyrinth slit 4, thereby enhancing the total pressure loss.

[0034] Specifically, in this embodiment, as Figure 4 shown, by setting the labyrinth tooth tip profile, the constriction-expansion form labyrinth slit channel is formed, which is similar to the constriction-expansion channel of a Laval nozzle. The constriction-expansion form labyrinth slit channel includes a contraction section 6, a throat 7, and an expansion section 8. The airflow accelerates in the contraction section 6, reaches the critical state at the throat 7 position, continues to accelerate in the expansion section 8, and the airflow reaches the supersonic state. Then, due to the over-expansion of the airflow, a shock wave is formed in the expansion section 8. On the one hand, the shock wave directly causes total pressure loss. On the other hand, the strong adverse pressure gradient induced by the shock wave causes the airflow to separate, forming local separated flow and recirculation, which in turn leads to secondary total pressure loss and enhances the flow resistance effect. The secondary total pressure loss caused by this airflow separation is formed by the adverse pressure gradient induced by the shock wave, which is different from the flow separation loss caused by the geometric expansion of the traditional labyrinth. This secondary total pressure loss is superimposed on the flow separation loss caused by geometric expansion.

[0035] Of course, in other embodiments, as Figures 5 to 7 shown, it can also be that the constriction-expansion form labyrinth slit channel is formed by setting the wall profile of the wall opposite to the labyrinth 3. Or the constriction-expansion form labyrinth slit channel is formed by simultaneously setting the labyrinth tooth tip profile and the wall profile of the wall opposite to the labyrinth 3.

[0036] As Figure 8As shown, the Mach number distribution and velocity distribution near the first narrow slit 4 of the current labyrinth seal are given when the total static pressure ratio of the inlet and outlet is 1.8. It can be observed that the air flow accelerates sharply in the contraction section 6, reaches the critical state (Ma = 1) at the throat 7, continues to accelerate to the supersonic state in the expansion section 8, and then due to over-expansion, an oblique shock wave with a wavefront Mach number of about 1.4 is formed in the expansion section 8. This shock wave directly causes the total pressure loss. At the same time, the adverse pressure gradient induced by the shock wave also causes flow separation, forming a separated flow in the expansion section 8. Due to the total pressure loss caused by the shock wave and the total pressure loss caused by the air flow separation, a local low-pressure area is formed in the expansion section 8, thus forming a backflow, enhancing the flow resistance effect. After that, due to the geometric sudden expansion of the channel, a large separated flow is formed. Therefore, the total pressure loss in the current labyrinth seal consists of three parts: shock loss, loss caused by shock-induced air flow separation, and loss caused by geometric sudden expansion. It can be seen that in the labyrinth seal structure with enhanced sealing performance through the shock wave effect of the present application, while maintaining the original total pressure loss and flow resistance effect induced by flow separation and backflow, more importantly, the total pressure loss caused by the shock wave, shock-induced flow separation and backflow, and the resulting additional flow resistance effect are introduced.

[0037] Compared with the traditional labyrinth seal structure, the labyrinth seal structure with enhanced sealing performance through the shock wave effect of the present application introduces the total pressure loss induced by the shock wave and the additional resistance effect. The total pressure loss and flow resistance effect of the air flow passing through a single labyrinth slit 4 and a single cavity 5 are strengthened, so that the same pressure drop effect as that of the traditional labyrinth seal with more stages can be achieved with fewer labyrinth stages. Similarly, at the same number of labyrinth stages, due to the greater total pressure loss and flow resistance effect, the air flow leakage in the labyrinth seal structure with enhanced sealing performance by the shock wave effect of the present application is lower than that of the traditional labyrinth seal.

[0038] The introduction of the contraction-expansion type labyrinth slit channel of the present application has a lower critical pressure ratio than the traditional labyrinth seal. As Figure 9 shown, the relationship between the area ratio of the throat section and the outlet section of the contraction-expansion type labyrinth slit channel and the critical pressure ratio is given in the ideal state. It can be observed that by adjusting the above area ratio to adjust the critical pressure ratio, the labyrinth slit 4 can reach the critical state even at a small pressure ratio, thus reducing the influence of the outlet back pressure on the flow in the cavity in front of the labyrinth seal.

[0039] As Figure 10As shown, the flow inside the pipe is divided into different flow regimes. Among them, when the total static pressure ratio at the inlet and outlet is in the range of A - B, the flow throughout the channel is subsonic; when the total static pressure ratio at the inlet and outlet is at point B, the position of the throat 7 is critical, and the flow in the divergent section 8 is subsonic; when the total static pressure ratio at the inlet and outlet is in the range of B - C, the position of the throat 7 is critical, a part of the flow in the divergent section 8 is supersonic, and the shock wave is located inside the divergent section 8; when the total static pressure ratio at the inlet and outlet is at point C, the position of the throat 7 is critical, and the normal shock wave blocks the outlet; when the total static pressure ratio at the inlet and outlet is in the range of C - D, the position of the throat 7 is critical and the oblique shock wave blocks the outlet; when the total static pressure ratio at the inlet and outlet is at point D, the position of the throat 7 is critical for complete expansion; when the total static pressure ratio at the inlet and outlet is above point D, the position of the throat 7 is critical, the airflow is not fully expanded inside the channel, and expansion waves appear at the outlet.

[0040] Specifically, for the first characteristic pressure ratio, as shown at point D in Figure 10 , at this pressure ratio, the airflow expands fully inside the channel, and its static pressure is consistent with the back pressure at the outlet. The relationship between the total static pressure ratios at the inlet and outlet is as follows:

[0041]

[0042] where p out,1 is the outlet static pressure corresponding to the first characteristic pressure ratio, p t,in is the total inlet pressure, π(λ esup ) is the pressure ratio function, where λ esup is the supersonic solution of the flow rate function, obtained based on the conservation of the flow rate at the inlet and outlet, as follows:

[0043]

[0044] where A thr is the area of the cross - section of the throat 7, and A out is the area of the outlet cross - section. For the second characteristic pressure ratio, as shown at point C in Figure 10 , the airflow is over - expanded inside the channel, and the static pressure at the outlet position is less than the back pressure. The pressure is increased through the shock wave, and the critical state is that the normal shock wave blocks the outlet. According to the relationship between the static pressures before and after the normal shock wave, we can obtain:

[0045]

[0046] where p out,2 is the outlet static pressure corresponding to the second characteristic pressure ratio, Ma esup is the Mach number in front of the wave, which can be obtained from the velocity coefficient λ esupIt is calculated that k is the adiabatic index, which takes the value of 1.44 for air and 1.33 for gas. For the third characteristic pressure ratio, the air flow reaches the critical state at the throat 7 section and continues to accelerate to supersonic speed in the diverging section 8. Due to the insufficient total pressure, the shock wave moves into the pipe, and the critical state is when the shock wave moves to the position of the throat 7, as shown at point B in Figure 10 . According to the conservation of inlet and outlet flow rates and the total static pressure ratio function, the relationship is as follows:

[0047]

[0048] where λ esub is the subsonic solution of the flow rate function, and p out,3 is the outlet static pressure corresponding to the third characteristic pressure ratio. As shown at point A in Figure 10 , when the total static pressure ratio of the inlet and outlet is 1.0, there is no flow in the pipe.

[0049] For a given total static pressure ratio of the inlet and outlet, according to the above relationship, the flow state in the convergent-divergent channel is determined by the area ratio of the throat section to the outlet section. Therefore, the flow state in the channel can be changed by adjusting the above area ratio.

[0050] The convergent-divergent type labyrinth slot channel of the labyrinth seal structure for enhancing the sealing performance through the shock wave effect described in this application can adjust the area ratio of the throat section to the outlet section by setting the labyrinth tooth tip profile, the wall profile, or a combination of both, and then adjust the operating point 9 to the B-C interval, as close as possible to point C to increase the Mach number before the shock wave. The operating state is that the throat 7 is at the critical position, part of the diverging section 8 is supersonic, and the shock wave is located in the diverging section 8. This shock wave causes total pressure loss and induces flow separation and additional resistance effects, thereby enhancing the sealing performance of the seal.

[0051] Preferably, as shown in Figure 11 , the convergent-divergent type labyrinth slot channel is arranged on the first labyrinth slot 4 or the middle labyrinth slot 4; or it is combined with the traditional labyrinth seal. As shown in Figure 12 , the profile of the convergent section 6 adopts the Witzensky curve or the bicubic curve; the diverging section 8 adopts the inverted Witzensky curve or the bicubic curve.

[0052] The above is only the preferred implementation mode of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention.

[0053] 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 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 therefore should not be construed as a limitation on the present invention.

[0054] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more, unless otherwise specifically defined.

[0055] In the present invention, unless otherwise clearly defined and limited, the terms "mounted", "connected", "coupled", "fixed", etc. should be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0056] In the present invention, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

Claims

1. A comb tooth sealing structure that enhances sealing performance through shock wave effect; characterized in that: A contraction-expansion type of grate slit channel is formed by the grate tooth tip profile, the wall profile or a combination of the two, which gradually contracts and then expands along the airflow direction, so that the airflow generates shock waves in the grate tooth slits, thereby enhancing the total pressure loss.

2. The comb teeth sealing structure with enhanced sealing performance through shock wave effect according to claim 1, characterized in that: The contraction-expansion type comb tooth slit channel comprises a contraction section, a throat and an expansion section.

3. The comb teeth sealing structure with enhanced sealing performance through shock wave effect according to claim 2, characterized in that: By adjusting the area ratio of the throat section and the outlet section of the contraction-expansion type comb tooth slit channel formed by the comb tooth tip profile, the wall profile or a combination of the two, the airflow reaches the speed of sound in the throat section of the contraction-expansion type comb tooth slit channel, continues to accelerate to supersonic speed in the expansion section, and then generates a shock wave in the expansion section, which induces total pressure loss and flow resistance effect.

4. The comb teeth sealing structure with enhanced sealing performance through shock wave effect according to claim 3, characterized in that: By changing the comb tooth tip profile, the wall profile or a combination of the two, the critical pressure ratio of the contraction-expansion type comb tooth slit channel can be adjusted.

5. The comb teeth sealing structure with enhanced sealing performance through shock wave effect according to claim 2, characterized in that: The profile of the contraction section adopts a Vyshinsky curve or a bicubic curve; the expansion section adopts an inverted Vyshinsky curve or a bicubic curve.

6. The comb teeth sealing structure with enhanced sealing performance through shock wave effect according to any one of claims 1 to 5, characterized in that: The contraction-expansion type comb teeth slit channel can be used alone or in combination with a traditional comb teeth sealing structure, and is located at the first stage or the middle stage.

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