A stepped contraction spiral groove air film sealing structure

Abstract

The present invention discloses a stepped contraction type spiral groove air film sealing structure, which includes an annular seal having a plurality of spiral grooves arranged on its end face, each spiral groove being divided into two parts along its geometric center line, namely a first spiral groove part and a second spiral groove part. The first spiral groove part forms a two-level stepped contraction shape from the outside to the inside along the geometric center line, and the second spiral groove part forms a three-level stepped contraction shape from the outside to the inside along the geometric center line. The open end of the spiral groove forms a two-level stepped contraction shape from the leeward side to the windward side along the circumferential direction. The structure utilizes the changes in groove depth and groove shape to increase the contact area between the airflow and the annular sealing end face, enhance the shear effect, blocking effect, pressure-boosting effect and compression effect, thereby reducing leakage, and improving the opening force and rigid-leakage ratio. The structure has a simple structure, low processing difficulty, high sealing performance and service life, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of sealing of bearing cavities of compressors of aero-engines, and relates to a spiral groove air film sealing structure, and specifically to a stepped contraction type spiral groove air film sealing structure. The invention utilizes the change of the spiral groove depth to improve the sealing performance, and utilizes the change of the spiral groove shape to optimize the air film sealing flow field, so as to achieve the purpose of reducing leakage and improving the air film sealing performance. Background Art

[0002] As one of the core components of an aircraft engine, the performance of the compressor directly affects the engine's thrust and efficiency. The higher speeds and higher thermodynamic cycle parameters of aircraft engines place higher demands on compressor performance. In addition to traditional flow-through design, the sealing flow needs to be redesigned to meet aircraft engine performance indicators. Studies have shown that a 1% reduction in sealing system leakage increases engine thrust by 1%. Furthermore, the compressor sealing system is a crucial means of ensuring a proper temperature and pressure distribution within the compressor bearing cavity. Its leakage directly affects the bearing cavity's thermal load and lubricating oil consumption. Furthermore, the compressor sealing system is a crucial safeguard for the safety and durability of the compressor structure. Its leakage directly affects the vibration and wear within the bearing cavity.

[0003] Compared with traditional sealing structures, such as grate seals and brush seals, air film seals are a technology that uses special structures (such as spiral grooves) set on the surface of a high-speed rotating rotor to generate a fluid dynamic pressure effect and form a stable air film between the rotor and the stator to achieve the sealing function. The air film seal itself has lower leakage and no friction loss, no vibration and noise, and is insensitive to rotor eccentricity. It has good application prospects in aircraft engines. The structural forms of air film seals include flat air films, radial air films, and spiral groove air films. The spiral groove air film seal uses spiral grooves to create a stable spiral air film on the rotor surface and is an important air film sealing structure. The structural parameters of the spiral groove (such as the shape, depth, width, spacing, inclination, etc. of the spiral groove) directly affect the formation process and stability of the air film, thereby affecting the performance of the air film seal. The performance of the air film seal mainly depends on the thickness, stiffness and leakage of the air film. The thickness of the air film determines the opening force of the air film seal (that is, the minimum rotation speed for the air film to be formed), the stiffness of the air film determines the bearing capacity of the air film seal (that is, the maximum eccentricity that allows the air film to remain stable), and the leakage of the air film determines the sealing efficiency of the air film seal (that is, the optimal design parameters for minimizing leakage).

[0004] To improve the performance of spiral groove air film seals, existing technologies primarily optimize the structure of the spiral grooves, such as by modifying parameters like the helix angle, depth, and pitch ratio, to create a more stable air film and enhance its load-bearing capacity. Despite numerous improvements to the spiral groove structure, the unique operating environment of aircraft engines presents challenges for their application. First, to better meet the higher performance requirements of aircraft engines, further optimization of the spiral groove structure is needed to further improve the sealing performance and reduce leakage. This also presents new challenges for the application of spiral groove air film seal technology in aircraft engines. Second, the high-altitude flight environment of aircraft engines results in lower inlet pressures at the film seal, reducing the seal's opening force. This, in turn, results in a lower stiffness-to-leakage ratio, reducing the seal's load-bearing capacity. The stiffness-to-leakage ratio, which measures the seal's stiffness relative to its leakage, reflects its performance. When the stiffness-to-leakage ratio is too low, the seal may be unable to withstand rotor eccentricity and vibration, leading to end-face contact or damage. In summary, the air film seal is a sealing structure with excellent performance and broad prospects, and has important application value in aircraft engines. However, the application of air film seal in aircraft engines also faces some technical difficulties that need to be solved urgently, and requires in-depth research and optimized design. Summary of the Invention

[0005] (1) Purpose of the invention

[0006] In order to solve the technical problems faced by existing traditional air film seals, such as large leakage at low inlet pressure, reduced opening force, and low rigid-leakage ratio, the purpose of the present invention is to propose a stepped contraction type spiral groove air film seal structure, which optimizes the traditional spiral groove structure into a stepped contraction type spiral groove structure, improves the sealing performance by utilizing the change in groove depth, and optimizes the air film seal flow field by utilizing the change in groove shape, thereby achieving the purpose of reducing leakage and improving the air film seal performance. The air film seal proposed in the present invention improves the traditional spiral groove structure, and the designed stepped contraction type spiral groove structure overcomes the above-mentioned shortcomings and deficiencies in the prior art. The overall structure is relatively simple, and the processing difficulty is no different from that of the traditional air film seal structure, but the sealing performance and life are greatly improved, and it has broad application prospects.

[0007] (2) Technical solution

[0008] To achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] A stepped contraction type spiral groove air film sealing structure includes at least one annular seal which is in a rotating state during operation, wherein the end face of the annular seal is smooth and flat and forms an annular sealing end face, wherein the radial outer side of the annular sealing end face is the high-pressure fluid side and the radial inner side is the low-pressure fluid side, and a plurality of spiral grooves are evenly spaced along the circumference of the annular sealing end face, wherein the end face between adjacent spiral grooves forms a sealing weir, and the end face between the spiral groove and the low-pressure fluid side forms a sealing dam, characterized in that:

[0010] Each of the spiral grooves is radially open at one end and closed at the other end, the open end extending radially outward to communicate with the high-pressure fluid side and forming an air inlet of the spiral groove, and the closed end extending radially inward to the sealing dam and forming a groove root of the spiral groove, and the two side walls in the circumferential direction of each of the spiral grooves forming a windward side and a leeward side thereof, respectively, wherein the windward side faces the incoming gas entering the spiral groove, and the leeward side is opposite to the windward side;

[0011] Each of the spiral grooves has a geometric centerline extending from the circumferential center of its open end to the circumferential center of its closed end, and the geometric centerline circumferentially divides each of the spiral grooves into a first spiral groove portion and a second spiral groove portion located on both sides thereof, wherein:

[0012] The first spiral groove portion is arranged adjacent to the windward side in the circumferential direction and is sequentially formed into a first step portion and a second step portion from the radially outer side to the radially inner side along the extension direction of the geometric center line. The first step portion has a constant groove depth h1 along the extension direction of the geometric center line, and the second step portion has a constant groove depth h2 along the extension direction of the geometric center line. The groove depth h1 is greater than the groove depth h2, so that the first spiral groove portion is formed as a whole into a two-stage stepped contraction shape from the outer side to the inner side along the extension direction of the geometric center line.

[0013] The second spiral groove portion is arranged adjacent to the leeward side in the circumferential direction and is sequentially formed as a step portion I, a step portion II, and a step portion III from the radially outer side to the radially inner side along the extension direction of the geometric center line. The step portion I has a constant groove depth H1 along the extension direction of the geometric center line, the step portion II has a constant groove depth H2 along the extension direction of the geometric center line, and the step portion III has a constant groove depth H3 along the extension direction of the geometric center line, wherein the groove depth H1>the groove depth H2>the groove depth H3, and the groove depth h1 is equal to the groove depth H2, and the groove depth h2 is equal to the groove depth H3, so that the second spiral groove portion is formed as a whole into a three-step stepped contraction shape from the outer side to the inner side along the extension direction of the geometric center line;

[0014] The open end of each spiral groove includes a first step portion located at the first spiral groove portion and a step portion I located at the second spiral groove portion, and the groove depth H1 of the step portion I is greater than the groove depth h1 of the first step portion, so that the open end of the spiral groove is formed as a whole in a two-stage stepped contraction shape from the leeward side to the windward side along the circumferential direction;

[0015] And wherein, the extension length of the first step portion along the geometric center line is equal to the sum of the extension lengths of the step portion I and the step portion II along the geometric center line, and the arc-shaped groove roots of the first step portion and the step portion II have the same second groove root radius R2 and are continuous in the circumferential direction, and the second groove root radius R2 is smaller than the first groove root radius R3 of the arc-shaped groove root of the step portion I; the second step portion has the same extension length along the geometric center line as the step portion III, and the arc-shaped groove roots of the two have the same third groove root radius R1 and are continuous in the circumferential direction, and the third groove root radius R1 is smaller than the second groove root radius R2.

[0016] Preferably, the first groove root radius R3 satisfies R3=2 / 3(R4-R1)+R1, and the second groove root radius R2 satisfies R2=1 / 3(R4-R1)+R1, wherein the radius R4 is the radius of the open end of the spiral groove 3.

[0017] Preferably, the arc length S2 at the entrance of the step portion I is the same as that of the first step portion and satisfies S2=0.5S1, and the arc length S1 is the arc length of the opening end of the spiral groove 3.

[0018] Preferably, the groove depth H1 of the step portion I is about 4 to 5 μm, the groove depth H2 of the step portion II is about 3 to 4 μm, and the groove depth H3 of the step portion III is about 2 to 3 μm.

[0019] Preferably, the ratio of the extension lengths of the first step portion and the second step portion in the first spiral groove portion along the geometric center line is about 2:1, and the ratio of the extension lengths of step portion I, step portion II, and step portion III in the second spiral groove portion along the geometric center line is about 1:1:1, so as to optimize the air film sealing flow field structure and improve the air film sealing performance.

[0020] Preferably, a plurality of micro grooves are provided on the annular sealing end face, and the micro grooves are distributed on the sealing weir and connected to the high-pressure fluid side to increase the circumferential contact area between the airflow and the sealing weir, thereby enhancing the shear effect and the pressure-boosting effect.

[0021] Preferably, a plurality of annular fine baffles are provided on the annular sealing end surface, and the annular fine baffles are distributed on the sealing dam and communicated with the low-pressure fluid side to reduce the circumferential contact area between the airflow and the sealing dam, thereby reducing the leakage amount and the rigid-leakage ratio.

[0022] Preferably, fine recesses are distributed on the first step portion, the second step portion in the first spiral groove portion, and the step portion I, step portion II, and step portion III in the second spiral groove portion to increase the contact area between the airflow and each step portion, thereby enhancing the shear effect and the pressure-boosting effect.

[0023] Preferably, the geometric center line of the spiral groove is a hyperbola, whose equation is r=a / b*θ, where r is the radial coordinate, θ is the circumferential coordinate, and a and b are constants, so as to improve the flow field distribution of the air film seal and increase the shear effect and pressure boosting effect of the airflow in the spiral groove.

[0024] Preferably, by flexibly adjusting the groove depths of the first step portion, the second step portion in the first spiral groove portion and the step portion I, step portion II, and step portion III in the second spiral groove portion, the pressure-boosting effect of the spiral groove and the distribution of the inlet low-pressure zone are adjusted, thereby reducing the leakage of the air film seal and improving the rigidity-leakage ratio of the air film seal.

[0025] (3) Technical effects

[0026] Compared with the prior art, the stepped contraction spiral groove air film sealing structure of the present invention has the following beneficial and significant technical effects:

[0027] (1) The stepped contraction type spiral groove air film sealing structure of the present invention forms three blocking areas in the radial direction by means of the three-stage contraction-like stepped structure of the second spiral groove portion arranged circumferentially adjacent to the leeward side, so that the airflow is continuously compressed when flowing from the radial outside to the radial inside in the second spiral groove portion, and the airflow is continuously blocked in each groove root area, promoting the conversion of fluid dynamic pressure into fluid static pressure effect. This can effectively reduce the radial outflow of the air film seal, thereby reducing the gas leakage on the radial inside of the annular sealing end face. Compared with the traditional spiral groove structure, the present invention can significantly reduce the leakage at low inlet pressure and improve the sealing efficiency. According to the results of numerical simulation, the present invention can reduce the leakage by an average of 1.5%.

[0028] (2) The stepped contraction type spiral groove air film sealing structure of the present invention forms two blocking areas at the groove root in the radial direction through the secondary contraction step structure of the first spiral groove part arranged near the windward side in the circumferential direction. The airflow in each groove root area will have a significant pressure-raising effect, thereby increasing the overall opening force of the air film seal. At the same time, thanks to the secondary contraction step structure arranged circumferentially at the inlet, the circumferential contact area between the airflow and the annular sealing end face can be increased, and the shear effect can be better utilized to increase the fluid dynamic pressure and increase the circumferential velocity of the fluid in the spiral groove area. This can effectively improve the support capacity of the air film seal for the high-pressure fluid side and improve the sealing stability. According to the results of numerical simulation, the present invention can increase the opening force by 19.94%.

[0029] (3) The stepped contraction type spiral groove air film sealing structure of the present invention is such that each spiral groove has a geometric center line extending from the circumferential center of its open end to the circumferential center of its closed end, and each spiral groove is divided into a first spiral groove part and a second spiral groove part located on both sides thereof. The first spiral groove part is designed to be designed as a two-stage stepped contraction shape from the radial outside to the radial inside along the extension direction of the geometric center line through a step-like structure design, and the second spiral groove part is designed as a three-stage stepped contraction shape from the radial outside to the radial inside along the extension direction of the geometric center line. As a result, the open end of the spiral groove is formed as a two-stage stepped contraction shape from the leeward side to the windward side along the circumferential direction. This can effectively change the flow field structure of the air film seal, so that the air film seal has a higher rigid-leakage ratio, that is, when the sealing gap changes, the rate of change of the leakage amount is smaller, thereby improving the sealing reliability. According to the numerical simulation results, the present invention can increase the rigid-leakage ratio by 6.47%.

[0030] (4) The stepped contraction type spiral groove air film sealing structure of the present invention is improved by the traditional spiral groove structure. Due to the improvement of the opening force and the rigidity-leakage ratio, the sealing structure can operate under lower inlet pressure conditions while still maintaining a good sealing effect, thereby broadening the scope of application. In addition, the reduction in leakage can reduce end face wear and slow down end face loss, thereby extending the service life of the air film seal.

[0031] (5) The stepped contraction type spiral groove air film sealing structure of the present invention is only a simple step adjustment based on the traditional spiral groove. The overall structure is relatively simple and the processing difficulty is no different from the traditional air film sealing structure. However, the sealing performance and life are greatly improved, and it has a broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The figure shows the overall schematic diagram of the stepped contraction type spiral groove air film sealing structure of the present invention;

[0033] Figure 2 Shown Figure 1 Schematic diagram of the cross-sectional structure at position 6-6;

[0034] Figure 3 Shown Figure 1 Schematic diagram of the cross-sectional structure at position 7-7;

[0035] Figure 4 The figure shows a partial structural diagram of a single groove of a stepped contraction type spiral groove air film seal according to the present invention;

[0036] Figure 5 Schematic diagram showing the radial pressure distribution comparison between the stepped contraction spiral groove air film seal structure of the present invention and the original structure (traditional spiral groove air film seal structure without steps);

[0037] Figure 6 The figure shows a comparison of the pressure nephograms of the stepped contraction spiral groove air film sealing structure of the present invention and the traditional spiral groove structure, wherein (a) is the pressure nephogram of the traditional spiral groove structure, and (b) is the pressure nephogram of the stepped contraction spiral groove air film sealing structure of the present invention.

[0038] Description of reference numerals:

[0039] 1-sealing dam, 2-sealing weir, 3-spiral groove, 4-air film sealing structure of a single spiral groove, 5-rotation direction, 6-second spiral groove portion, 61-step portion I, 62-step portion II, 63-step portion III, 7-first spiral groove portion, 71-first step portion, 72-second step portion, x-axis and y-axis are two orthogonal directions of the annular sealing end face, and z-axis is the axial direction of the annular sealing end face. DETAILED DESCRIPTION

[0040] In order to better understand the present invention, the contents of the present invention are further explained in conjunction with the embodiments below. In the accompanying drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be understood as limiting the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The structure and technical solution of the present invention are further described in detail below in conjunction with the accompanying drawings, and an embodiment of the present invention is given.

[0041] like Figures 1 to 4 As shown, the stepped contraction type spiral groove air film sealing structure of the present invention comprises at least one annular sealing member which rotates during operation. The direction of rotation is as follows: Figure 1As shown in the accompanying drawings, reference numeral 5 shows that the end face of the annular seal is smooth and planar and forms an annular sealing end face. The radially outer side of the annular sealing end face serves as the high-pressure fluid side, and the radially inner side serves as the low-pressure fluid side. A number of spiral grooves 3 are evenly spaced along the circumference of the annular sealing end face. The end faces between adjacent spiral grooves form a sealing weir 2, and the end face between the spiral groove and the low-pressure fluid side forms a sealing dam 1. Each spiral groove 3 has an open end and a closed end in the radial direction. The open end extends radially outward to communicate with the high-pressure fluid side and forms the inlet of the spiral groove. The closed end extends radially inward to the sealing dam 1 and forms the root of the spiral groove. The two circumferential side walls of each spiral groove 3 respectively form its windward and leeward sides. The windward side faces the incoming gas entering the spiral groove 3, and the leeward side is opposite the windward side.

[0042] Each spiral groove 3 has a geometric center line extending from the circumferential center of its open end to the circumferential center of its closed end. The geometric center line divides each spiral groove 3 into a first spiral groove portion 7 and a second spiral groove portion 6 located on both sides thereof in the circumferential direction. The first spiral groove portion 7 is arranged adjacent to the windward side in the circumferential direction and is sequentially formed into a first step portion 71 and a second step portion 72 from the radial outer side to the radial inner side along the extension direction of the geometric center line. The first step portion 71 has a constant groove depth h1 along the extension direction of the geometric center line, and the second step portion 72 has a constant groove depth h2 along the extension direction of the geometric center line. , wherein the groove depth h1 is greater than the groove depth h2, so that the first spiral groove portion 7 is formed as a two-stage stepped contraction shape from the outside to the inside along the extension direction of the geometric center line; the second spiral groove portion 6 is arranged near the leeward side in the circumferential direction, and is formed into step portion I 61, step portion II 62, and step portion III 63 in sequence from the radial outside to the radial inside along the extension direction of the geometric center line. Step portion I 61 has a constant groove depth H1 along the extension direction of the geometric center line, step portion II 62 has a constant groove depth H2 along the extension direction of the geometric center line, and step portion III 63 has a constant groove depth H3 along the extension direction of the geometric center line, wherein, Groove depth H1>groove depth H2>groove depth H3, and the groove depth h1 is equal to the groove depth H2, and the groove depth h2 is equal to the groove depth H3, so that the second spiral groove portion 6 is formed as a three-step step contraction shape from the outside to the inside along the extension direction of the geometric center line; in addition, the open end of each spiral groove 3 includes a first step portion 71 located in the first spiral groove portion 7 and a step portion I61 located in the second spiral groove portion 6, and the groove depth H1 of the step portion I61 is greater than the groove depth h1 of the first step portion 71, so that the open end of the spiral groove 3 is formed as a two-step step contraction shape from the leeward side to the windward side along the circumferential direction; and wherein, the first step The extension length of step portion 71 along the geometric center line is equal to the sum of the extension lengths of step portion I 61 and step portion II 62 along the geometric center line, and the arc-shaped groove roots of the first step portion 71 and step portion II 62 have the same second groove root radius R2 and are continuous in the circumferential direction, and the second groove root radius R2 is smaller than the first groove root radius R3 of the arc-shaped groove root of step portion I 61; the second step portion 72 has the same extension length along the geometric center line as the step portion III 63, and the arc-shaped groove roots of the two have the same third groove root radius R1 and are continuous in the circumferential direction, and the third groove root radius R1 is smaller than the second groove root radius R2.

[0043] In a preferred embodiment of the present invention, the first groove root radius R3 satisfies R3=2 / 3(R4-R1)+R1, and the second groove root radius R2 satisfies R2=1 / 3(R4-R1)+R1, wherein the radius R4 is the radius of the open end of the spiral groove 3. The arc length S2 at the entrance of the step portion I 61 is the same as that of the first step portion 71 and satisfies S2=0.5S1, and the arc length S1 is the arc length of the open end of the spiral groove 3. The groove depth H1 of the step portion I 61 is about 4 to 5 μm, and the groove depths H2 and H3 of the step portion II 62 and the step portion III 63 are about 3 to 4 μm and about 2 to 3 μm respectively. The working principle of the stepped contraction type spiral groove air film sealing structure of the present invention is as follows:

[0044] The present invention divides the spiral groove 3 into a first spiral groove portion 7 and a second spiral groove portion 6 along its geometric centerline in the circumferential direction, and designs the first spiral groove portion 7 to be a two-stage stepped contraction shape from the radial outer side to the radial inner side along the extension direction of the geometric centerline through a stepped structure design, and designs the second spiral groove portion 6 to be a three-stage stepped contraction shape from the radial outer side to the radial inner side along the extension direction of the geometric centerline, thereby making the open end of the spiral groove 3 form a two-stage stepped contraction shape along the circumferential direction from the leeward side to the windward side. When the incoming gas flows into the spiral groove 3 of the air film seal from the inlet, the rotation of the annular seal end face will drive the airflow to rotate circumferentially. The two-stage contraction step structure set circumferentially at the inlet can increase the circumferential contact area between the airflow and the annular seal end face, and better utilize the shear effect to increase the fluid dynamic pressure, thereby increasing the circumferential velocity of the fluid in the spiral groove area. In addition, the two-stage contraction step structure set circumferentially at the inlet can form a good flow diversion effect on the inlet airflow and form a good constraint on the flowing fluid. At the same time, thanks to the three-step, contracting, stepped structure of the second spiral groove portion 6, located circumferentially near the leeward side, three stepped groove root areas, or three blocking areas, are formed in the radial direction. This causes continuous compression of the airflow as it flows from the radially outer side to the radially inner side of the second spiral groove portion 6, continuously blocking the airflow in each groove root area, promoting the conversion of fluid dynamic pressure into fluid static pressure. The two-step, contracting, stepped structure of the first spiral groove portion 7, located circumferentially near the windward side, forms blocking areas at two groove roots in the radial direction. The airflow in each groove root area experiences a significant pressure increase, thereby increasing the overall opening force of the air film seal. Furthermore, the dual-step contraction structure of the first and second spiral groove portions 7, 6, creates a strong blocking and shearing effect on the airflow, further reducing radial outflow from the air film seal and thereby reducing gas leakage from the radially inner side of the annular seal end face.

[0045] The structure has been verified by numerical simulation of air film sealing under different parameters, such as Figure 5 、 6 As shown, Figure 5Schematic diagram comparing radial pressure distribution of the stepped contraction spiral groove air film seal structure of the present invention with that of the original structure (traditional spiral groove air film seal structure without steps); Figure 6 The figure shows the pressure nephogram comparison of the stepped contraction spiral groove air film sealing structure of the present invention and the traditional spiral groove structure, wherein (a) is the pressure nephogram of the traditional spiral groove structure, and (b) is the pressure nephogram of the stepped contraction spiral groove air film sealing structure of the present invention. Figure 5 It can be seen from the numerical calculation results shown that compared with the traditional spiral groove sealing structure, the stepped contraction spiral groove air film sealing structure of the present invention has a significant improvement in radial pressure, which is increased by 40% and 49.5% respectively. Figure 6 The numerical calculation results show that the stepped spiral groove of the present invention significantly reduces leakage, significantly improves opening force, significantly increases the rigidity-to-leakage ratio, and significantly changes the distribution of the inlet low-pressure area. Analysis of typical operating conditions shows an average reduction of 1.5%, an increase in opening force by 19.94%, and a 6.47% improvement in the rigidity-to-leakage ratio.

[0046] The stepped contraction spiral groove air film seal structure of the present invention is an innovative design based on the traditional spiral groove air film seal structure. It adopts a structure with multiple steps and gradually contraction on the left and right sides of the geometric centerline of the spiral groove. Compared with the existing traditional spiral groove air film seal structure, it has several obvious advantages:

[0047] First, the structure of the stepped, contracting spiral groove of the present invention is achieved by designing the left and right sides of the spiral groove's geometric centerline into a multi-stage, gradually contracting structure, namely a two-stage first spiral groove portion 7 and a three-stage second spiral groove portion 6. This stepped contraction structure effectively enhances the shearing and blocking effects of the airflow, promoting the conversion of fluid dynamic pressure into fluid static pressure. This structural arrangement effectively reduces radial outflow from the air film seal, thereby reducing gas leakage from the annular seal end face. This reduced leakage reduces end face wear and tear, thereby extending the service life of the air film seal.

[0048] Furthermore, the stepped, contracting spiral groove air film seal structure of the present invention, due to the arrangement of the first spiral groove portion 7 and the third-stage second spiral groove portion 6, forms a two-stage contracting stepped structure along the circumferential direction at the spiral groove inlet. This increases the circumferential contact area between the airflow and the annular seal end face, better utilizing the shear effect to increase the fluid dynamic pressure and the circumferential velocity of the fluid in the spiral groove area. Furthermore, the two-stage contracting stepped structure circumferentially arranged at the inlet effectively guides the inlet airflow and effectively constrains the flowing fluid.

[0049] At the same time, in the structure of the stepped contraction spiral groove of the present invention, the two contraction spiral grooves will have a significant pressure-boosting effect at the groove root, thereby increasing the opening force of the air film seal. From the definition of the rigidity-to-leakage ratio of the air film seal, it can be seen that it is equal to the ratio of leakage to rigidity. When the leakage of the air film seal decreases and the opening force increases, it is bound to lead to an increase in the rigidity-to-leakage ratio, thereby increasing the bearing capacity of the air film seal. Due to the increase in opening force and rigidity-to-leakage ratio, the sealing structure can operate under lower inlet pressure conditions while still maintaining a good sealing effect, broadening the scope of application, so that the structure can be used for aircraft engine compressor bearing cavity sealing and interstage sealing, achieving high-efficiency sealing for different needs.

[0050] The above embodiments fully and effectively achieve the objectives of the present invention. Those skilled in the art will appreciate that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the above specific embodiments. Although the present invention has been described with reference to the embodiments currently considered to be the most practical and preferred, it should be understood that the present invention is not limited to the disclosed embodiments, and any modifications that do not deviate from the functional and structural principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A stepped contraction type spiral groove air film sealing structure, comprising at least one annular seal member which is in a rotating state during operation, wherein the end surface of the annular seal member is smooth and planar and forms an annular sealing end surface, wherein the radial outer side of the annular sealing end surface is a high-pressure fluid side and the radial inner side is a low-pressure fluid side, and the annular sealing end surface is provided with a plurality of spiral grooves uniformly spaced along its circumference, the end surface between adjacent spiral grooves forms a sealing weir, and the end surface between the spiral groove and the low-pressure fluid side forms a sealing dam, characterized in that: Each of the spiral grooves is radially open at one end and closed at the other end, the open end extending radially outward to communicate with the high-pressure fluid side and forming an air inlet of the spiral groove, and the closed end extending radially inward to the sealing dam and forming a groove root of the spiral groove, and the two side walls in the circumferential direction of each of the spiral grooves forming a windward side and a leeward side thereof, respectively, wherein the windward side faces the incoming gas entering the spiral groove, and the leeward side is opposite to the windward side; Each of the spiral grooves has a geometric centerline extending from the circumferential center of its open end to the circumferential center of its closed end, and the geometric centerline circumferentially divides each of the spiral grooves into a first spiral groove portion and a second spiral groove portion located on both sides thereof, wherein: The first spiral groove portion is arranged adjacent to the windward side in the circumferential direction and is sequentially formed into a first step portion and a second step portion from the radially outer side to the radially inner side along the extension direction of the geometric center line. The first step portion has a constant groove depth h1 along the extension direction of the geometric center line, and the second step portion has a constant groove depth h2 along the extension direction of the geometric center line. The groove depth h1 is greater than the groove depth h2, so that the first spiral groove portion is formed as a whole into a two-stage stepped contraction shape from the outer side to the inner side along the extension direction of the geometric center line. The second spiral groove portion is arranged adjacent to the leeward side in the circumferential direction and is sequentially formed as a step portion I, a step portion II, and a step portion III from the radially outer side to the radially inner side along the extension direction of the geometric center line. The step portion I has a constant groove depth H1 along the extension direction of the geometric center line, the step portion II has a constant groove depth H2 along the extension direction of the geometric center line, and the step portion III has a constant groove depth H3 along the extension direction of the geometric center line, wherein the groove depth H1>the groove depth H2>the groove depth H3, and the groove depth h1 is equal to the groove depth H2, and the groove depth h2 is equal to the groove depth H3, so that the second spiral groove portion is formed as a whole into a three-step stepped contraction shape from the outer side to the inner side along the extension direction of the geometric center line; The open end of each spiral groove includes a first step portion located at the first spiral groove portion and a step portion I located at the second spiral groove portion, and the groove depth H1 of the step portion I is greater than the groove depth h1 of the first step portion, so that the open end of the spiral groove is formed as a whole in a two-stage stepped contraction shape from the leeward side to the windward side along the circumferential direction; And wherein, the extension length of the first step portion along the geometric center line is equal to the sum of the extension lengths of the step portion I and the step portion II along the geometric center line, and the arc-shaped groove roots of the first step portion and the step portion II have the same second groove root radius R2 and are continuous in the circumferential direction, and the second groove root radius R2 is smaller than the first groove root radius R3 of the arc-shaped groove root of the step portion I; the second step portion has the same extension length along the geometric center line as the step portion III, and the arc-shaped groove roots of the two have the same third groove root radius R1 and are continuous in the circumferential direction, and the third groove root radius R1 is smaller than the second groove root radius R2.

2. The stepped contraction type spiral groove air film sealing structure according to claim 1, characterized in that: The first groove root radius R3 satisfies R3=2 / 3(R4-R1)+R1, and the second groove root radius R2 satisfies R2=1 / 3(R4-R1)+R1, wherein the radius R4 is the radius of the open end of the spiral groove 3.

3. The stepped contraction type spiral groove air film sealing structure according to claim 1, characterized in that: The arc length S2 at the entrance of the step portion I is the same as that of the first step portion and satisfies S2=0.5S1. The arc length S1 is the arc length of the opening end of the spiral groove 3.

4. The stepped contraction type spiral groove air film sealing structure according to claim 1, characterized in that: The groove depth H1 of the step portion I is about 4 to 5 μm, the groove depth H2 of the step portion II is about 3 to 4 μm, and the groove depth H3 of the step portion III is about 2 to 3 μm.

5. The stepped contraction spiral groove air film sealing structure according to claim 1, characterized in that: The ratio of the extension lengths of the first step portion and the second step portion along the geometric center line in the first spiral groove portion is approximately 2:1, and the ratio of the extension lengths of step portion I, step portion II, and step portion III along the geometric center line in the second spiral groove portion is approximately 1:1:1, so as to optimize the air film sealing flow field structure and improve the air film sealing performance.

6. The stepped contraction type spiral groove air film sealing structure according to claim 1, characterized in that: A plurality of fine grooves are provided on the annular sealing end surface. The fine grooves are distributed on the sealing weir and communicated with the high-pressure fluid side to increase the circumferential contact area between the airflow and the sealing weir, thereby enhancing the shear effect and the pressure-boosting effect.

7. The stepped contraction type spiral groove air film sealing structure according to claim 1, characterized in that: A plurality of annular fine baffles are provided on the annular sealing end surface. The annular fine baffles are distributed on the sealing dam and communicated with the low-pressure fluid side to reduce the circumferential contact area between the airflow and the sealing dam, thereby reducing the leakage amount and the rigid-to-leakage ratio.

8. The stepped contraction type spiral groove air film sealing structure according to claim 1, characterized in that: The first step portion, the second step portion in the first spiral groove portion, and the step portion I, step portion II, and step portion III in the second spiral groove portion are all distributed with fine recesses to increase the contact area between the airflow and each step portion, thereby enhancing the shear effect, the pressure-boosting effect, and the blocking effect.

9. The stepped contraction type spiral groove air film sealing structure according to claim 1, characterized in that: The geometric center line of the spiral groove is a hyperbola, and its equation is r=a / b*θ, where r is the radial coordinate, θ is the circumferential coordinate, and a and b are constants, so as to improve the flow field distribution of the air film seal and increase the shear effect and pressure boosting effect of the airflow in the spiral groove.

10. The stepped contraction type spiral groove air film sealing structure according to claim 1, characterized in that: By flexibly adjusting the groove depths of the first step portion, the second step portion in the first spiral groove portion and the step portion I, step portion II, and step portion III in the second spiral groove portion, the pressure-boosting effect of the spiral groove and the distribution of the inlet low-pressure zone are adjusted, thereby reducing the leakage of the air film seal and improving the rigidity-leakage ratio of the air film seal.

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