Structure for prolonging service life of semi-open type centripetal impeller

Abstract

The invention relates to the technical field of turbines, and provides a centripetal impeller which is characterized in that a rim between two adjacent blades of the centripetal impeller is grooved to form corresponding lace grooves, the two sides of the inner side of each lace groove are a first straight line section and a second straight line section, and the bottom of the inner side of each lace groove is provided with a first arc section, a second arc section and a third arc section which are different in radius. The first arc section is connected with the first linear section, the third arc section is connected with the second linear section, the first arc section and the third arc section are sunken inwards, and the second arc section is located between the first arc section and the third arc section and protrudes outwards. Through the arrangement of the first arc section, the second arc section and the third arc section, stress can be released, so that stress concentration is avoided, the radius of each arc section is designed according to actual bearing force, so that arcs are different, different stresses of the groove bottom can be correspondingly reduced, cracking of the lace groove bottom is avoided, and the service life of the lace groove is prolonged. Therefore, the service life and reliability of the centripetal impeller are improved, and the influence on the performance of the centripetal impeller is small.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of turbines, and particularly relates to a structure for improving the service life of a semi-open centripetal impeller. BACKGROUND

[0002] In the field of aerospace and small power devices, the centripetal impeller, as the core rotor component of the centripetal turbine, is a key carrier for realizing the conversion of gas heat energy into mechanical energy. The working environment of the centripetal impeller is extremely harsh: during operation, the impeller needs to withstand the temperature load brought by high-temperature gas, the pressure load formed by gas pressure, and the centrifugal load generated by high-speed rotation, which puts extremely high requirements on the structural strength and fatigue resistance of the impeller. According to structural differences, the centripetal impeller can be divided into three types: closed type, semi-open type and open type. Among them, the semi-open centripetal impeller is particularly widely used in small gas turbine engines and aviation auxiliary power devices due to its consideration of both airflow flow efficiency and processing economy.

[0003] The rim lace structure is an important part of the semi-open centripetal impeller, mainly used for optimizing the airflow flow state at the rim of the impeller, suppressing airflow leakage, and assisting in supporting the impeller blades, and its structural design directly affects the overall performance and service life of the impeller. At present, the rim lace structure of the existing semi-open centripetal impeller in the industry has formed a relatively fixed design paradigm.

[0004] However, the traditional lace structure design has significant stress concentration defects under actual working conditions, which can easily lead to impeller failure. Specifically, the disc body of the semi-open centripetal impeller is usually designed as a thick structure to ensure structural rigidity and carrying capacity, and such thick disc body has a slow response speed to temperature changes (i.e. large thermal inertia under cold and hot impact); the lace groove forms a large stress, and the lace groove is an area where stress is easily concentrated. When the impeller operates under high temperature and high speed conditions, the thermal deformation of the thick disc body and the lace structure is not coordinated, and the superimposed centrifugal load and pressure load can form a local concentrated stress in the groove that exceeds the allowable value of the material. Under the long-term stress of this kind of high stress, small cracks will gradually appear at the bottom of the lace groove of the semi-open centripetal impeller; with the start-stop cycle and long-term operation of the impeller, the cracks will continuously expand and extend, eventually causing multiple penetrating cracks at the bottom of the lace groove, and in severe cases, even causing the rim lace to fall off. This kind of failure not only damages the aerodynamic performance of the impeller, leading to a sharp drop in turbine efficiency, but also can cause instability of the impeller dynamic balance, causing the rotor system to vibrate intensively, and then impacting the engine case, causing more serious safety accidents, which poses a major threat to the reliability and safety of small gas turbine engines and aviation auxiliary power devices.

[0005] At present, the prior art has not yet proposed an effective solution to the stress concentration problem of the semi-open centripetal impeller rim filigree structure. Therefore, how to improve the structure design of the rim filigree, eliminate the concentrated stress at the bottom of the filigree groove, avoid crack initiation and chunk failure, has become a key technical requirement for improving the service life of the semi-open centripetal impeller and ensuring the safe operation of small gas turbine engines and aviation auxiliary power units, and needs to be broken through. SUMMARY

[0006] In view of the above problems, the present application provides a structure for improving the service life of a semi-open centripetal impeller, comprising: grooves are formed in the rim between adjacent two blades of the centripetal impeller to form corresponding filigree grooves, the inner sides of each of the filigree grooves are first and second straight line segments, the inner bottom of each of the filigree grooves has first, second and third circular arc segments with different radii, the first circular arc segment is connected with the first straight line segment, the third circular arc segment is connected with the second straight line segment, the first and third circular arc segments are concave inward, and the second circular arc segment is located between the first and third circular arc segments and is convex outward.

[0007] Optionally, the radius of the first and third circular arc segments under greater stress is greater than the radius under smaller stress.

[0008] Optionally, the center of the second circular arc segment coincides with the center of the centripetal impeller, or the center of the second circular arc segment does not coincide with the center of the centripetal impeller.

[0009] Optionally, the radius of the centripetal impeller rim is R, the height of the filigree groove is h, and h / R is 0.25-0.40.

[0010] Optionally, h / R is 0.3.

[0011] Optionally, the width of the filigree groove gradually increases from the outside to the inside.

[0012] Optionally, a lug is provided on each of the blades.

[0013] Optionally, the surface of the filigree groove is polished to a roughness greater than or equal to 0.8 microns, and the polishing is performed along the circumferential direction of the filigree groove.

[0014] Optionally, the number of blades is the same as the number of filigree grooves, and the number is n.

[0015] Optionally, the angle between the reference lines of two adjacent filigree grooves is 360° / n.

[0016] The structure for improving the service life of a semi-open centripetal impeller provided by the present application has the following advantages compared with the prior art: The stress can be released through the setting of the first arc segment, the second arc segment and the third arc segment, so that stress concentration is avoided, the radius of each arc segment is designed according to actual bearing force, so that each arc is not the same, so that the different stress of the groove bottom can be correspondingly reduced, the lace groove bottom cracking is avoided, and the service life and reliability of the radial impeller are improved, and the performance of the radial impeller is little affected.

[0017] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and attained by the structure particularly pointed out in the description and the appended drawings. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0019] Figure 1 A front view of a structure for improving the service life of a semi-open radial impeller in an embodiment of the present application is shown. Figure 2 A partial three-dimensional schematic view of a structure for improving the service life of a semi-open radial impeller in an embodiment of the present application is shown. Figure 3 A lace groove circumferential stress schematic view of a structure for improving the service life of a semi-open radial impeller in an embodiment of the present application is shown. Figure 4 A lace groove polishing direction schematic view of a structure for improving the service life of a semi-open radial impeller in an embodiment of the present application is shown. Figure 5 A stress calculation result schematic view of a structure for improving the service life of a semi-open radial impeller in an embodiment of the present application is shown. Figure 6 A design flow schematic view of a structure for improving the service life of a semi-open radial impeller in an embodiment of the present application is shown.

[0020] In the drawings, 1, blade; 10, lace groove; 11, first straight line segment; 12, second straight line segment; 13, first arc segment; 14, second arc segment; 15, third arc segment. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely explain the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present application.

[0022] The structure for improving the service life of the semi-open centripetal impeller in the embodiment is mainly applied to an aviation auxiliary power device (APU) and a small gas turbine engine, and the design needs to adapt to the compact layout requirement of the power device and meet the strength and fatigue resistance requirements under high-temperature and high-speed working conditions.

[0023] As shown in Figure 1 The present application provides a structure for improving the service life of a semi-open centripetal impeller, which comprises: a corresponding lace groove 10 is formed by grooving the rim between two adjacent blades 1 of the centripetal impeller, the inner sides of each lace groove 10 are two first straight line segments 11 and two second straight line segments 12, the inner bottom of each lace groove 10 has three first, second and third circular arc segments 13, 14 and 15 with different radii, the first circular arc segment 13 is connected with the first straight line segment 11, the third circular arc segment 15 is connected with the second straight line segment 12, the first and third circular arc segments 13 and 15 are concave inward, and the second circular arc segment 14 is located between the first and third circular arc segments 13 and 15 and is convex outward. The first, second and third circular arc segments 13, 14 and 15 are arranged to release stress, thereby avoiding stress concentration. The radii of each circular arc segment are designed according to the actual bearing force, so that each circular arc is not the same, thereby corresponding to reduce the different stresses of the groove bottom, avoid the lace groove 10 bottom cracking, improve the service life and reliability of the centripetal impeller, and have little effect on the performance of the centripetal impeller.

[0024] It should be noted that the first circular arc segment 13 is connected with the end of the first straight line segment 11, the first circular arc segment 13 is in a concave inward form (concave to the center of the impeller), and if the area corresponding to the position "close to the center of gravity" when the impeller rotates (the stress in this area is larger due to the additional bending moment), the radius R1 is larger; The third arc segment 15 is connected with the end of the second straight line segment 12 and also has an inwardly concave shape. If the corresponding area is far from the center of gravity (the stress is small), the radius R2 is small. Due to the influence of the center of gravity of the outer impeller and the blade 1, an additional bending moment is generated when the rotor rotates. The stress on the rounded position close to the center of gravity is large, and the stress on the rounded position far from the center of gravity is small. That is, the radius of the first arc segment 13 and the third arc segment 15 under large stress is larger than the radius under small stress, that is, R1>R2, so as to adapt to the stress difference of different areas and avoid local stress concentration caused by a single radius. The second arc segment 14 is located between the first arc segment 13 and the third arc segment 15 and has an outwardly convex shape (convex to the outer side of the rim). The center of the second arc segment 14 coincides with the center of the radial impeller. The center of the second arc segment 14 coincides with the center of the impeller, which can simplify the machining positioning. The radius R3 can be larger than the radius R1, which can smoothly transition the first arc segment 13 and the third arc segment 15 and further disperse the stress at the bottom of the groove. Alternatively, the center of the second arc segment 14 does not coincide with the center of the radial impeller. By flexibly adjusting the center position of the second arc segment 14, different specifications of impellers can be quickly adapted without changing the core structure of the "double straight line segment and three arc segment". The overall profile of the lace groove 10 does not need to be redesigned for each specification, which shortens the product development cycle.

[0025] In an embodiment, the radial impeller rim radius is R, and the lace groove 10 height is h. h / R is 0.25-0.40. It should be noted that if the radial impeller rim radius is R=80mm (millimeter) (adapted to the rim size of a small APU), the lace groove 10 groove height h (the distance from the rim top to the groove bottom) is set to 24mm, then h / R=24 / 80=0.3, which is within the range of 0.25-0.40. This ratio can ensure that the rotor back gas leakage is ≤5% (aerodynamic performance loss is within an acceptable range), while avoiding excessive groove depth that causes insufficient disc strength.

[0026] In an embodiment, the reference line of the lace groove 10 forms corresponding angles α1 and α2 with the first straight line segment 11 and the second straight line segment 12, respectively. It should be noted that the first straight line segment 11 and the second straight line segment 12 are located on both sides of the lace groove 10 and gradually shrink towards the center of the impeller (wheel center) along the blade 1 contour, avoiding damage to the root of the blade 1. Optionally, the angles α1 and α2 are within the range of 20°-45°.

[0027] In one embodiment, the baseline of the lace groove 10 is L1 and L2 distances from the starting points of the first straight segment 11 and the second straight segment 12, respectively. It should be noted that the above-mentioned parameters α1, α2, L1, and L2 are determined in coordination with the root size of the blade 1 to ensure that the remaining thickness of the root of the blade 1 after grooving is ≥5mm, which meets the strength requirements.

[0028] like Figure 2 As shown, in one embodiment, the width of the lace groove 10 gradually increases from the outside to the inside. The sharp edges formed by the lace groove and the two sides need to be designed with smooth transitions. A rounded edge that changes from the outside to the inside is better than a fixed rounded edge. That is, the rounded radius near the outer rim of the lace groove 10 is R4, and the rounded radius at the bottom corner of the lace groove 10 is R5. It should be noted that the sharp edges formed by the lace groove 10 and the two end faces of the impeller (axial end faces of the disc body) need to be smoothly transitioned to avoid stress concentration at the sharp edges. The rounded radius of the sharp edge near the outer rim is R4 = 0.5mm (small rounded edge, suitable for the narrow space at the rim); the rounded radius of the sharp edge at the bottom of the lace groove 10 and the end face is R5 = 2.2mm (large rounded edge, further reducing the stress at the bottom of the groove). The above rounding can be achieved by machining with a ball end mill of a CNC milling cutter to ensure a smooth transition without burrs.

[0029] In one embodiment, a protrusion is provided on each blade 1. The protrusion disperses the stress on the blade, thereby increasing the structural strength of the blade. It should be noted that the protrusion is arranged perpendicular to the blade 1.

[0030] like Figure 4 As shown, in one embodiment, the surface of the lace groove 10 is polished to a roughness greater than or equal to 0.8 micrometers, and polishing is performed along the circumference of the lace groove 10. It should be noted that the radial impeller disc is thick and its response to heat and cold is slow. The lace groove 10, flow channel, and blade 1 are in contact with the combustion gas and respond quickly to the gas temperature, thus forming circumferential stress in the lace groove 10, i.e., generating tensile and compressive cyclic loads in the circumferential direction, such as... Figure 3 As shown, cracks perpendicular to the direction of force will appear at the bottom of the groove, i.e., axial cracks. To improve the fatigue resistance of the lace groove 10, the processing and polishing processes must meet the following requirements: Machining method: The decorative groove 10 is machined using a CNC milling machine. Carbide end mills are used as the cutting tools. The cutting tool rotates in the circumferential direction of the impeller (rather than the axial direction) to avoid forming axial tool marks on the groove surface. Axial tool marks are prone to forming a perpendicular direction with the circumferential tensile and compressive cyclic load (caused by the difference in thermal response), which can induce axial cracks. Polishing: After processing, use a wool wheel with diamond polishing compound (W1.5 grit) to circumferentially polish the surface of the lace groove (e.g., Figure 4As shown, polishing along the axial direction (in order to improve crack resistance) is not allowed in the direction of the arrow (i.e., the impeller circumference). The surface roughness after polishing must reach Ra0.8 (by testing with a surface roughness tester) to reduce the risk of crack initiation caused by surface defects and improve the fatigue resistance of the groove surface.

[0031] In one embodiment, the number of blades 1 is the same as the number of lace grooves 10, which is n. It should be noted that the blades 1 are evenly distributed along the circumference of the disc rim, and the number is set to n=12-14 (to adapt to the aerodynamic requirements of small APUs). The blades 1 are made of high-temperature resistant materials, and the root is integrally forged with the disc to ensure resistance to centrifugal loads.

[0032] In one embodiment, the angle between the reference lines of two adjacent lace grooves 10 is 360° / n. It should be noted that the lace grooves 10 are formed by CNC milling at the rim between two adjacent blades 1, and the number of grooves is the same as the number of blades 1 (i.e., 12). The included angle α = 360° / n = 30° between the reference lines (virtual reference lines along the impeller radial direction) of two adjacent lace grooves 10 ensures uniform force distribution in the circumferential direction and avoids localized load concentration.

[0033] Through the above design, the stress distribution of the lace groove 10 is significantly improved: The maximum stress at the bottom of the existing tank is approximately 450 MPa, while in this embodiment, by dispersing stress with three circular arc segments and adapting the stress gradient with differentiated radii, the maximum stress at the bottom of the tank is reduced to 363 MPa (e.g., ...). Figure 5 As shown in the finite element analysis results, the stress reduction is about 20%; circumferential machining and polishing further eliminate surface stress concentration sources, increasing the fatigue life of the lace groove 10 to more than 1.5 times that of the original structure, effectively preventing cracking at the bottom of the groove.

[0034] like Figure 6 As shown, the design process of this invention is as follows: Original centripetal impeller modeling (including impeller disk body and blade profile modeling); Parametric modeling of the centrifugal impeller groove (defining key parameters such as groove size and angle, as well as the relationships between parameters, and creating the groove model). Define materials (set the properties of the initial materials); Define the 10 parameters of the lace groove (set the specific values ​​of the lace groove parameters); Apply loads such as temperature, pressure, and rotational speed (set the boundary conditions for the operation of the centripetal impeller, including temperature gradient, pressure load, and rotational speed). Finite element analysis (using professional software such as ANSYS); whether the lace groove 10 lower stress level requirements are met, met, end the whole process, not satisfied redefined lace groove 10 parameters, until the defined lace groove 10 parameters are met.

[0035] In summary, the core design of the embodiment of the present application is to disperse the stress of the groove bottom through multiple circular arc segments (or spline curves), to adapt the stress gradient by differentiating the radius, to balance the aerodynamic performance and strength by reasonably controlling the h / R ratio, and to eliminate crack initiation sources through circumferential machining and high roughness polishing; thereby avoiding stress concentration, designing the radius of each circular arc segment according to the actual bearing force, so that each circular arc is not the same, thereby being able to correspondingly reduce the different stresses of the groove bottom, avoiding cracking of the lace groove 10 bottom, thereby improving the service life and reliability of the radial turbine, and having little effect on the performance of the radial turbine.

[0036] Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A semi-open centripetal impeller life improvement structure, characterized by, The application relates to a radial impeller. Each of the lace grooves (10) has a first linear section (11) and a second linear section (12) on the inner side, and a first circular arc section (13), a second circular arc section (14) and a third circular arc section (15) on the inner bottom, the first circular arc section (13) is connected with the first linear section (11), the third circular arc section (15) is connected with the second linear section (12), the first circular arc section (13) and the third circular arc section (15) are concave, and the second circular arc section (14) is located between the first circular arc section (13) and the third circular arc section (15) and is convex.

2. The semi-open centripetal impeller life enhancement structure according to claim 1, characterized in that, The radius of the first circular arc section (13) and the third circular arc section (15) is greater than that of the second circular arc section (14).

3. The semi-open centripetal impeller life enhancement structure according to claim 1, wherein, The center of the second circular arc section (14) is coincident with the center of the radial impeller, or the center of the second circular arc section (14) is not coincident with the center of the radial impeller.

4. The semi-open centripetal impeller life enhancement structure according to claim 1, wherein The radius of the radial impeller is R, the height of the lace groove (10) is h, and h / R is 0.25-0.

40.

5. The semi-open centripetal impeller life enhancement structure according to claim 4, wherein, h / R is 0.

3.

6. The improved semi-open centripetal impeller life enhancing structure as claimed in claim 1 wherein, The width of the lace groove (10) gradually increases from outside to inside.

7. The improved semi-open centripetal impeller life enhancing structure as claimed in claim 1 wherein, A convex plate is arranged on each of the blades (1).

8. The improved semi-open centripetal impeller life enhancing structure according to claim 1, wherein, The surface roughness of the lace groove (10) is greater than or equal to 0.8 microns, and the surface is polished along the circumference of the lace groove (10).

9. The improved semi-open centripetal impeller life enhancing structure as claimed in claim 1 wherein, The number of the blades (1) is equal to that of the lace grooves (10), and the number is n.

10. The semi-open centripetal impeller life enhancement structure according to claim 9, wherein, The angle between the reference lines of two adjacent lace grooves (10) is 360 degrees / n.

Images