Design method of low-loss compact blade diffuser

Abstract

According to the design method of the low-loss compact blade diffuser, a radial blade diffuser and an axial blade diffuser are designed to be of an integrated structure, the surfaces of the two sides, from the radial direction to the axial direction, of the blade diffuser are not fused and shared with the rotation face of a hub, and a vaneless diffusion section is arranged between a centrifugal impeller and the integrated blade diffuser; a meridian flow channel is defined by a casing and a hub rotation face, absolute airflow at an outlet of the centrifugal impeller is deflected by 90 degrees from the radial direction to the axial direction through the meridian flow channel, and the molded line of the hub at the axial section is lifted; the three-dimensional large-turning diffuser blade is designed in a front edge stacking three-dimensional forming mode, and circumferential pre-rotation and circumferential differential velocity of absolute airflow at an outlet of a centrifugal impeller are eliminated. Compact structural layout can be achieved, the design and forming difficulty of the three-dimensional diffuser blades is simplified, the large-range angular separation phenomenon existing in the blade diffuser under the large blade profile turning condition can be remarkably restrained, and the low-loss and high-quality rectification effect of the blade diffuser on absolute airflow at an outlet of a centrifugal impeller is remarkably improved.

Description

Technical Field

[0001] The invention relates to a design method for a low-loss compact blade diffuser, which is applied to the technical fields of light turbine engines, auxiliary power units (APUs), ground micro gas turbines and the like. Background Art

[0002] The blade diffuser is an important component of a high-load centrifugal compressor. It is mainly responsible for efficiently rectifying the high-speed, large-angle absolute airflow flowing out of the centrifugal impeller, achieving the dual purpose of uniform exhaust along the axial (or radial) direction and deceleration and pressure increase. However, with the continuous increase in the load of the centrifugal impeller, the absolute velocity and absolute airflow angle of its outlet airflow also increase, which directly leads to the increasing difficulty of the blade diffuser design, and its internal flow becomes more complex, accompanied by greater flow losses. Even the flow instability of some centrifugal compressor stages is induced by the flow separation and blockage inside the blade diffuser.

[0003] At the same time, with the increasing demand for compact layout, small size, simple structure and easy processing of centrifugal compressors in engineering applications, scholars at home and abroad have also carried out design research on one-piece conformal blade diffuser that integrates radial blade diffuser and axial blade diffuser, and it has been applied to some small turbojet engines.

[0004] 1. The blade diffuser is mostly a split combination of a radial blade diffuser and an axial blade diffuser, and is combined with a 90° deflected meridian flow channel to achieve the purpose of rectifying the absolute airflow at the centrifugal impeller outlet, and the diffuser geometric blade shape adopts a wedge-shaped, airfoil-shaped or tubular type.

[0005] This split combined blade diffuser has a relatively small total pressure loss and can achieve efficient rectification of absolute airflow, but it requires a relatively large geometric space and has a large number of blade rows, which will result in a larger outer diameter and axial length of the centrifugal compressor. Once the outer diameter and axial length are reduced, the flow characteristics and outlet airflow quality of this combined blade diffuser will deteriorate sharply due to the excessive absolute velocity of the blade diffuser intake and the excessive change in the geometric curvature of the diffuser blade.

[0006] 2. The radial blade diffuser and axial blade diffuser of the conformal blade diffuser are integrated into an integrated blade, which reduces the number of blade rows of the blade diffuser and can significantly reduce the outer diameter and axial length of the blade diffuser, making its structure more compact than the split combined blade diffuser.

[0007] However, this type of conformal blade diffuser will have a large flow separation area near the hub angle area on the pressure side of the axial section, which significantly increases the total pressure loss and channel clogging effect of the blade diffuser, and thus significantly reduces the efficiency and compression ratio of the centrifugal compressor stage. At the same time, the geometric configuration method and process of this type of conformal blade diffuser are more complicated and complex than those of the conventional split-type combined blade diffuser. There is a phenomenon of fusion and sharing of the diffuser blade profile and the meridian flow channel rotation surface, and the blade geometry line changes very irregularly. For example, the suction side of the blade not only deflects and rectifies the absolute airflow, but also serves as the hub rotation surface in the axial flow section, which directly leads to the difficulty of geometric modeling and machining of this type of conformal blade diffuser and its complex structure.

[0008] The existing disclosed patent technologies CN201410453415.4 and CN200810196137.3 integrate the radial section, turning section and axial section of the blade diffuser, which effectively reduces the radial and axial dimensions of the diffuser. However, the flow separation will inevitably occur at the turning point due to excessive local diffusion pressure, which will reduce the performance of the diffuser. At the same time, the diffuser has splitter blades, which increases the difficulty of processing and manufacturing to a certain extent. The existing disclosed patent technology CN108386389A integrates the radial diffuser and the axial diffuser into one and designs the leading edge as a sharp edge to reduce the loss, and integrates the blade geometric surface with the diffuser casing and the hub revolving surface to reduce the deflection angle and degree of the diffuser blade. However, this fusion method will cause the blade shape of the blade diffuser to be extremely complex, and its three-dimensional blade design process, geometric line distribution characteristics and processing technology will face great difficulties. At the same time, the uniformity of its outlet airflow and the total pressure loss along the way are greatly affected. Summary of the invention

[0009] Only by integrating the advantages and disadvantages of the above-mentioned different types of blade diffusers, developing a new design method for low-loss compact blade diffusers, and simplifying the geometric design difficulty and the three-dimensional geometric surface forming process of the diffuser blades, can the comprehensive aerodynamic performance of the blade diffuser and the entire centrifugal compressor and the quality of the airflow straightening at the blade diffuser outlet be effectively improved.

[0010] A design method for a low-loss compact blade diffuser comprises the following steps:

[0011] Step 1: The radial blade diffuser and the axial blade diffuser are designed as an integrated structure, the two side surfaces of the blade diffuser from radial to axial directions are not integrated and shared with the hub rotating surface, and a bladeless diffuser section is set between the centrifugal impeller and the integrated blade diffuser;

[0012] Step 2: The casing and the hub revolving surface form a meridian flow channel, which turns the absolute airflow at the centrifugal impeller outlet from radial deflection of 90° to axial, and the hub profile of the axial section is raised;

[0013] Step 3: Design the three-dimensional large-turn diffuser blades by adopting the three-dimensional forming method of leading edge stacking to eliminate the circumferential pre-swirl and circumferential velocity component of the absolute airflow at the centrifugal impeller outlet.

[0014] Furthermore, in step 1, the ratio of the outlet radius value to the inlet radius value of the bladeless diffuser section is 1.05 to 1.15, and the absolute airflow velocity at the inlet of the blade diffuser is ensured to be less than the speed of sound.

[0015] Furthermore, in step 2, the meridional flow channel of the blade diffuser includes a radial section, an axial section and a transition section between the first two. The axial length of the axial section is defined as the axial distance between the hub profile of the radial section of the diffuser and the outlet cross-section of the axial section. The axial length of the radial section of the blade diffuser is the blade height value at the outlet of the centrifugal impeller. The meridian profile of the transition section of the blade diffuser can adopt an arc profile or a high-order Bezier curve that approximates an arc.

[0016] Furthermore, the radial section blade height value of the meridional flow channel is constant and equal to the centrifugal impeller outlet blade height value, and the average blade height value of the transition section and the maximum blade height value of the axial section are both 1 to 1.2 times the radial section blade height value.

[0017] Furthermore, the radial section meridian profile of the blade diffuser includes a hub profile and a casing profile, and the hub profile and the casing profile have equal included angles with the radial direction; the geometric lift angle α1 of the hub profile of the axial section does not exceed 16°.

[0018] Furthermore, in step 3, the three-dimensional blade includes the design of two primitive-level blade profiles, namely the blade root and the blade tip. The maximum blade profile turning angle of each primitive level reaches more than 65 degrees. The number of primitive-level blade profiles is set to no more than 6 along the blade height direction according to actual needs, and all primitive-level blade profiles adopt a three-dimensional forming method with leading edge stacking to ensure a smooth transition of the curved surfaces of the suction surface and the pressure surface of the diffuser blade.

[0019] Furthermore, the calculation method of the inlet geometric angle β1 of each elementary level blade of the blade diffuser is as follows:

[0020] β1=α3+c1

[0021] Among them, α3 is the absolute airflow angle at the inlet radius of the blade diffuser corresponding to the centrifugal impeller outlet radial section, c1 is a constant, and the value range is 2 to 5°;

[0022] The calculation method of the blade installation angle ζ of each primitive blade profile is as follows:

[0023] ξ=β1-(β1-β2)·c2

[0024] Among them, c2 is a constant, with a value between 0.2 and 0.4. The c2 value corresponding to the primitive-level blade profile near the diffuser blade root is the smallest. As the blade height increases, the corresponding c2 value of the primitive-level blade profile also increases accordingly; β2 is the absolute airflow angle at the outlet of the primitive-level blade profile, with a value between 0 and 5°.

[0025] Furthermore, according to the total axial length △l, the inlet geometric angle β1, the outlet geometric angle β2 and the installation angle ζ of the blade diffuser, a three-point Bezier curve is used to obtain the distribution characteristics of the median camber line of the primitive stage blade profile.

[0026] Furthermore, the leading edge radius values ​​Thic of different primitive-level blades LE Take 0.1~0.5mm, the trailing edge adopts blunt trailing edge structure characteristics, corresponding to the trailing edge radius value Thic TE Take 2~5mm; the maximum thickness value is at 60%~75% of the length of the arc line in the blade, and the maximum thickness value is 2·Thic max Take 1.4 to 2 times the width of the elementary blade trailing edge; the distribution characteristics of the elementary blade thickness along the corresponding mid-camber line are determined after the leading edge radius value, trailing edge radius value, maximum thickness point position and corresponding thickness value 2·Thic max Finally, the 9th-order Bezier curve is used to obtain the pressure surface profile and suction surface profile of the primitive-level blade symmetrically distributed along the mid-arc line by adjusting the corresponding thickness values ​​Thic1~Thic6 at other control points along the process to ensure the natural and smooth distribution of the thickness values ​​along the mid-arc line.

[0027] Furthermore, the design number of blades is equal to the total number of blades of the centrifugal impeller, which is an odd number, and a geometric chamfer is set at the intersection of the blade diffuser, the hub and the casing profile.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The blade diffuser design method and structure proposed in the present invention can not only greatly reduce the outer diameter and axial length of the centrifugal impeller outlet blade diffuser to achieve a compact structural layout, simplify the design and molding difficulty of the three-dimensional diffuser blade, but also significantly suppress the large-range angular separation phenomenon existing inside the blade diffuser under the condition of large blade folding, and significantly improve its low-loss and high-quality rectification effect on the absolute airflow at the centrifugal impeller outlet. The specific technical advantages are as follows: (1) The radial blade diffuser and the axial blade diffuser are integrated into an integrated blade diffuser, which greatly reduces the geometric space, outer diameter and number of blade rows occupied by the centrifugal impeller outlet diffuser section, and the structure is simpler and more compact, and avoids the problem of flow matching of multiple diffuser blade rows. (2) The three-dimensional blades of the integrated blade diffuser adopt a geometric line design method, and the blade geometric deflection angle is as high as 65° to 70° or more, which can effectively eliminate the circumferential pre-rotation and corresponding circumferential velocity component of the absolute airflow at the centrifugal impeller outlet, and achieve the purpose of efficient rectification of the absolute airflow at the centrifugal impeller outlet. (3) The relatively regular meridian flow channel surrounded by the casing and the hub revolving surface is responsible for converting the absolute airflow at the centrifugal impeller outlet from a radial deflection of 90° to an axial direction, while the three-dimensional large-turn blade is responsible for eliminating the circumferential pre-rotation and circumferential velocity distribution of the absolute airflow at the centrifugal impeller outlet. The two functions are strictly distinguished and the geometric line design is independent, which is convenient for realizing three-dimensional blade shaping and simplifying the processing technology and manufacturing cost of the blade diffuser. (4) The integrated blade diffuser combines the adjustment of the curvature distribution of the large-turn blade geometric profile and the tapered geometric shape design of the axial section of the meridian flow channel to effectively suppress the large separation of the hub angle area on the pressure surface side of the axial section of the diffuser blade, significantly reducing the flow separation loss inside the blade diffuser, and improving its flow capacity and the rectification effect on the absolute airflow.

[0030] The new blade diffuser design method proposed in the patent of this invention integrates the radial blade diffuser and the axial blade diffuser to form an integrated blade diffuser structure, which reduces the number of diffuser blade rows and makes the structure of the blade diffuser more compact and the outer diameter relatively smaller. At the same time, the new blade diffuser greatly reduces the difficulty of three-dimensional blade geometry forming. The design of its three-dimensional blades is independently separated from the forming process of the hub and the casing rotating surface, and the blades are only responsible for eliminating the circumferential pre-rotation and circumferential component velocity of the absolute airflow flowing out of the centrifugal impeller outlet through the large blade deflection angle to achieve its uniform axial outlet, while the hub and the casing rotating surface realize the absolute airflow at the centrifugal impeller outlet from radial to axial flow after a 90° deflection. The three-dimensional blade shape and the meridian flow channel have clear functional division of labor, which greatly reduces its design and machining difficulty. At the same time, the new integrated blade diffuser significantly reduces the flow separation range near the hub angle area of ​​the axial section of the diffuser by adjusting the geometric design features of the 90° deflection of the meridian flow channel and the three-dimensional curvature distribution law of the geometric profile of the pressure surface side of the diffuser blade, thereby achieving a significant reduction in the total pressure loss of the diffuser and uniformity of the axial outflow near the outlet. In addition, the new diffuser blade adopts a blunt trailing edge structural design feature, which is not only conducive to suppressing the separation of the hub angle area of ​​the axial section of the diffuser, but also facilitates the drilling, bolting, and setting of the concave line groove structure of the diffuser blade during the processing and assembly stages. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 (a) is a three-dimensional front view of a novel integrated blade diffuser designed using the method of the present invention;

[0032] Figure 1 (b) is a three-dimensional side view of a novel integrated blade diffuser designed using the patented method;

[0033] Figure 2 (a) is a schematic diagram of the overall structure of the blade diffuser meridian flow channel;

[0034] Figure 2 (b) is a schematic diagram of the main partitions of the blade diffuser meridian flow channel;

[0035] Figure 3 It is a schematic diagram of the mid-arc design of the primitive-stage blade profile of the new blade diffuser;

[0036] Figure 4 It is the thickness distribution diagram along the middle arc line of the primitive blade profile;

[0037] Figure 5 It is a two-dimensional schematic diagram of the blade element level designed by the present invention;

[0038] Figure 6 It is a schematic diagram of the three-dimensional structure of the blade diffuser designed by the present invention;

[0039] Figure 7 1. It is a schematic diagram comparing the meridian flow passage of the novel blade diffuser designed by the present invention and the prototype scheme;

[0040] Figure 8 This is a comparison chart of the total pressure recovery coefficient of the new blade diffuser designed by the present invention and the prototype scheme with the flow rate;

[0041] Fig. 9 (a) is a comparison chart of the speed isentropic efficiency of the new blade diffuser designed by the present invention and the prototype scheme with the flow rate;

[0042] Fig. 9 (b) is a comparison chart of the speed-to-total pressure ratio of the new blade diffuser designed by the present invention and the prototype scheme with the flow rate;

[0043] Fig.10 (a) The velocity near the leading edge of the new blade diffuser designed by the present invention is significantly reduced;

[0044] Fig.10 (b) The separation structure near the trailing edge of the new blade diffuser designed by the present invention is significantly suppressed;

[0045] Fig.11 The absolute airflow angle at the outlet of the novel blade diffuser designed by the present invention is distributed along the span direction.

[0046] Explanation of the reference numerals: 1 centrifugal impeller outlet; 2 blade diffuser inlet; 3 blade diffuser casing line; 4 blade diffuser outlet; 5 blade diffuser hub line; 6 axial section hub profile inclination angle α; 7 outer smooth arc radius R0; 8 inner smooth arc radius R1; 9 radial blade section; 10 transition blade section; 11 axial blade section; 12 leading edge point; 13 trailing edge point; 14 intersection point of two tangent lines; 15 leading edge point tangent; 16 trailing edge point tangent; 17 elementary stage mid-arc line; 18 elementary stage chord line; 19 elementary stage inlet geometric angle; 20 elementary stage installation angle; 21 elementary stage outlet geometric angle; 22 leading edge control point; 23 maximum thickness control point; 24 trailing edge control point; 28 diffuser blade suction surface; 29 diffuser blade pressure surface; 30 diffuser blade top surface; 31 blade diffuser hub surface; 32 elementary stage axial length. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0048] In the drawings of the specific embodiments of the present invention, in order to better and more clearly describe the working principles of the various components in the system, the connection relationship of the various parts in the device is shown, which only clearly distinguishes the relative position relationship between the various components, and cannot constitute a limitation on the signal transmission direction, connection sequence and structural size, size and shape of each part within the component or structure.

[0049] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0050] Example 1

[0051] This embodiment is a design method for a low-loss compact blade diffuser, comprising the following steps:

[0052] Step 1: Design the radial blade diffuser and the axial blade diffuser as one, and set a bladeless diffuser section between the centrifugal impeller and the integrated blade diffuser to ensure that the absolute airflow velocity at the inlet of the blade diffuser is less than the speed of sound.

[0053] Before this step, the corresponding centrifugal impeller outlet radius value, outlet blade height, and the corresponding centrifugal impeller outlet absolute airflow velocity (or absolute Mach number) and outlet absolute airflow angle must be determined. At the same time, the geometric constraints of the outer diameter size and axial length of the blade diffuser are given in combination with the actual application scenarios and requirements.

[0054] A radial bladeless diffuser section is designed between the inlet of the blade diffuser and the outlet of the centrifugal impeller to further reduce the absolute airflow velocity (or the corresponding absolute Mach number) at the outlet of the centrifugal impeller. The ratio of the outlet radius value of the bladeless diffuser section (corresponding to the inlet radius value of the blade diffuser) to the inlet radius value of the bladeless diffuser section (corresponding to the outlet radius value of the centrifugal impeller) is 1.05 to 1.15. The specific value of this ratio is based on ensuring that the absolute Mach number of the airflow at the inlet of the blade diffuser does not exceed 0.95 to 1.0, so as to effectively avoid the occurrence of shock waves in the blade diffuser channel and reduce its total pressure loss and flow separation. In addition, the value of this ratio must also take into account the outer diameter size constraints of the blade diffuser.

[0055] Step 2: The casing and the hub revolving surface enclose a meridian flow channel, which deflects the absolute airflow at the centrifugal impeller outlet by 90° from radial to axial.

[0056] The meridional flow passage of the blade diffuser includes a radial section, an axial section and a transition section between the first two.

[0057] After determining the outlet radius value of the bladeless diffuser in step 1, the inlet radius value of the blade diffuser is also determined. The outlet section of the blade diffuser is located in the axial section, and the axial length of the axial section is defined as the axial distance between the hub profile of its radial section and the outlet section of the axial section, where the axial length of the radial section of the blade diffuser is the blade height value at the outlet of the centrifugal impeller.

[0058] The total axial length value △l of the blade diffuser is constrained by the total axial length of the centrifugal compressor stage. The total axial length of the centrifugal compressor stage minus the axial length of the centrifugal impeller (excluding the axial length occupied by the centrifugal impeller outlet height) can be obtained.

[0059] The casing profile of the axial section is designed with a straight profile of equal diameter, but the hub profile of the axial section is designed with an inclined profile with a certain lift angle, and the geometric lift angle α1 of the hub profile is preferably not more than 16°, but is not limited to this angle range, and the specific value depends on the internal flow field structure of the blade diffuser and the aerodynamic benefit.

[0060] The transition section meridian line of the blade diffuser adopts an arc line (such as Figure 2 The outer transition arc radius R on the casing profile side is shown o The inner transition arc radius R on the hub profile side i ) or a high-order Bezier curve that approximates a circular arc, but it is necessary to ensure that the meridian line of the transition section is naturally smoothly connected with the radial and axial line lines, and the geometric line distribution characteristics at the connection point must satisfy the geometric continuity and differentiability at the intersection.

[0061] The radial section blade height of the blade diffuser meridional flow channel is constant and equal to the centrifugal impeller outlet blade height; the average blade height of the transition section and the maximum blade height of the axial section are both 1 to 1.2 times the radial section blade height, but the outer diameter of the axial section must meet the geometric constraints of the application scenario and actual needs.

[0062] The radial section meridian profile of the blade diffuser (including the hub profile and the casing profile) can also be designed with an inclined structure with an angle with the radial direction, and the corresponding hub and casing profiles have equal angles with the radial direction, both controlled within the range of 0 to 5°.

[0063] Step 3, designing a three-dimensional large-fold blade by adopting a three-dimensional forming method of radially stacking the leading edge of the elementary-level blade profile, so as to eliminate the circumferential pre-swirl and circumferential velocity component of the absolute airflow at the outlet of the centrifugal impeller.

[0064] The design of the three-dimensional blade includes two basic blade levels, the blade root and the blade tip, and adopts a three-dimensional forming method with stacked leading edges. The number of basic blade levels is set along the blade height direction, and can also be appropriately increased according to the needs of actual refined design, but it is advisable not to exceed 6 to ensure the smoothness of the diffuser blade surface.

[0065] The inlet geometric angle β1 of each elementary blade of the blade diffuser is obtained by formula (1):

[0066] β1=α3+c1 (1)

[0067] Where α3 is the absolute airflow angle at the inlet radius of the blade diffuser corresponding to the centrifugal impeller outlet radial section, c1 is a constant, ranging from 2 to 5°. The outlet geometric angle β2 of the elementary blade profile is 0 to 5°, and the outlet geometric angle is opposite to the inlet geometric angle.

[0068] The blade installation angle ζ of each elementary blade profile is calculated using formula (2):

[0069] ξ=β1-(β1-β2)·c2 (2)

[0070] Among them, c2 is a constant term, with a value range of 0.2 to 0.4, and the c2 value corresponding to the primitive-level blade near the diffuser blade root is the smallest. As the blade height continues to increase, the c2 value of the corresponding primitive-level blade also increases accordingly. The specific values ​​of the above angles or constants need to be fine-tuned within the value range according to the flow field characteristics.

[0071] Each elementary blade profile of the blade diffuser is obtained by symmetrically loading thickness distribution on both sides of the blade profile centerline, wherein the blade profile centerline is designed by a simple Bezier curve.

[0072] Specifically, after determining the axial length △l, inlet geometric angle β1, outlet geometric angle β2 and installation angle ζ of the blade diffuser, the three-point Bezier curve can be used to obtain the corresponding camber distribution characteristics of the primitive level blade, such as Figure 3 shown.

[0073] like Figure 4 As shown, the leading edge radius value Thic of different primitive blade types LE Take 0.1~0.5mm; the trailing edge adopts the blunt trailing edge structure feature, corresponding to the trailing edge radius value Thic TE According to the process constraints of blade row diffuser processing and assembly, it is generally recommended to take the value in the range of 2 to 5 mm; the maximum thickness value is taken at 60% to 75% of the length of the blade arc, and the maximum thickness value is 2·Thic max It is recommended to take the element-level trailing edge width (i.e. 2·Thic TE ) is 1.4 to 2 times. The distribution characteristics of the thickness of the elementary blade along the corresponding mid-camber line are determined after the leading edge radius value, the trailing edge radius value, the maximum thickness point position and the corresponding thickness value 2·Thic maxFinally, the 9th-order Bezier curve is used to obtain the thickness value Thic1~Thic6 corresponding to other control points along the process to ensure the natural smooth distribution of the thickness value along the process.

[0074] Figure 5 The distribution characteristics of the diffuser elementary blade profile are obtained by symmetrically loading the thickness value along the mid-arc line.

[0075] After completing the blade design of the primitive stages of different blade heights of the blade diffuser, the primitive stages can be projected onto the rotating surface at the corresponding blade height position, and the primitive stages of different blade heights can be stacked by the leading edge stacking method to form a three-dimensional blade structure, such as Figure 6 shown.

[0076] In a preferred embodiment, considering that the blades of the blade diffuser designed by the present invention are relatively thick, preferably, the number of blades should be close to the total number of blades of the centrifugal impeller (if the centrifugal impeller adopts a splitter blade structure, the total number of blades is the sum of large and small blades), and the number of blades should be an odd number. A geometric chamfer should be set at the intersection of the blade diffuser, the hub and the casing profile, and the chamfer radius value is recommended to be 1 to 4 mm. After the design is completed, the three-dimensional blade outlet section can be flush cut to ensure that it is a flat end face perpendicular to the axis.

[0077] In a preferred embodiment, a low-loss compact blade diffuser design method and structure proposed in this embodiment can also be applied to the design of a blade diffuser with a sharp trailing edge according to the application scenario and actual needs, and its axial section can also be used alone as an axial diffuser.

[0078] Example 2

[0079] Taking the improved design of the diffuser of NASA's CC3 centrifugal compressor as an example, the present invention is further described in detail in conjunction with the accompanying drawings:

[0080] NASA's CC3 centrifugal compressor was selected as the research object. The key geometric parameters are shown in Table 1. The centrifugal compressor adopts a centrifugal impeller + radial blade diffuser layout. In order to verify the design method and structure of a low-loss compact blade diffuser proposed in this patent application. Taking NASA's CC3 centrifugal compressor as an example, on the basis of its centrifugal impeller, the modified design of its radial blade diffuser is completed, and the design method of the present invention is used to design a new integrated blade diffuser (not only including the rectifying function of the radial blade diffuser, but also further adding the rectifying function of the axial diffuser) to replace the original radial blade diffuser, and verify the performance of the modified blade diffuser.

[0081] Table 1 Technical indicators of CC3 centrifugal compressor

[0082]

[0083] A new blade diffuser was modified and designed for NASA's CC3 centrifugal compressor. After clarifying the basic parameters of the centrifugal impeller, the outlet outer diameter of the blade diffuser was given as 280.16mm and the inlet radius was given as 230mm, that is, the ratio of the outlet radius value of the bladeless diffuser section to its inlet radius value was about 1.067. Then the axial length of the radial section of the blade diffuser was determined to be 17mm, and the total axial length of the blade diffuser was 47.35mm. The blade diffuser casing profile was bent 90° with a diameter of 20mm starting from the radial section radius of 253.12mm, thereby obtaining the axial section of the blade diffuser casing profile. The hub profile of the axial section was designed with an inclined profile that was lifted by 14°.

[0084] The design of the new diffuser blade includes two primitive blades, the blade root and the blade tip, and adopts a three-dimensional forming method with stacked leading edges. Combined with the flow parameters of the centrifugal impeller and the bladeless diffuser section, the inlet geometry angle of the blade diffuser blade root primitive is determined to be -70°, and the outlet geometry angle is 3°. The installation angle of the blade root primitive is calculated to be -54°; the inlet geometry angle of the blade tip primitive is -68°, and the outlet geometry angle is 2°. The installation angle of the blade tip primitive is calculated to be -48°.

[0085] Each element-level blade of the blade diffuser is obtained by symmetrically loading the thickness distribution on both sides of the blade centerline. The blade centerline is designed by a simple Bezier curve. The leading edge radius of the root element level is 0.44mm, and the leading edge radius of the tip element level is 0.43mm. The trailing edge adopts a blunt trailing edge structure, with a trailing edge radius of 3mm for the root element level and a trailing edge radius of 3.14mm for the tip element level. The maximum thickness value of the blade diffuser is located at 70% of the length of the blade center arc line, and the maximum thickness value is 1.7 times the width of the element-level trailing edge. Then, the 9th-order Bezier curve is used to obtain the distribution characteristics of the thickness of the element-level blade along the corresponding center arc line, and then the corresponding thickness values ​​at other control points along the way are adjusted to ensure the natural and smooth distribution of the thickness value along the way. Finally, after completing the blade profile design of the primitive stage of different blade heights of the blade diffuser, the primitive stage can be projected onto the rotating surface at the corresponding blade height position, and the primitive stages of different blade heights can be stacked by using the leading edge stacking method to form a three-dimensional blade structure.

[0086] In this case, by comprehensively considering the diffuser blade parameters, the total number of blade diffusers was finally selected to be 23, and a geometric chamfer structure with a radius of 1.2 mm was set at the intersection of the blade diffuser, the hub and the casing surface.

[0087] Example 3

[0088] Performance evaluation of the designed low-loss compact integrated vane diffuser

[0089] Figure 7 The meridian view of the new diffuser scheme is compared with the prototype scheme. The new diffuser has a 30.48% smaller outer diameter than the prototype diffuser. The total pressure recovery coefficient of the diffuser is an important parameter for evaluating the performance of the blade diffuser. The total pressure recovery coefficient of the blade diffuser can be obtained through numerical simulation calculation, such as Figure 8 As shown. Figure 8 It can be seen that the new blade diffuser designed using this patent has a significantly reduced outer diameter and a total pressure recovery coefficient after completing the 90° airflow deflection from radial to axial, which is generally higher than that of the prototype radial blade diffuser, and is increased by at least 2%, which has significant technical advantages.

[0090] Fig. 9 This is a performance comparison chart of NASA's CC3 centrifugal compressor using the new diffuser solution and the prototype solution at the design speed. As can be seen from the figure, after adopting the new blade diffuser solution, the pressure ratio and efficiency values ​​at all operating points are significantly better than the prototype solution. Table 2 gives a comparison of the key aerodynamic performance indicators of the new diffuser solution and the prototype solution. The total pressure of the centrifugal compressor of the new solution at the design point is increased by about 5% compared with the prototype solution, and the isentropic efficiency is increased by about 1.08% compared with the prototype solution.

[0091] Table 2 Comparison of key aerodynamic performance of the new diffuser scheme and the prototype scheme at the design speed

[0092]

[0093] Fig.10 The following is a comparison of the three-dimensional streamlines of the new blade diffuser designed using the patented method and the prototype scheme. As can be seen from the figure, the inlet velocity of the new blade diffuser is significantly reduced, and the flow separation area on the pressure side is significantly reduced, which is also the main reason for the improvement of its comprehensive aerodynamic performance. In addition, Fig.11 It can be seen that the new blade diffuser has a good rectifying ability for the centrifugal impeller outlet airflow, and can control the angle between the axial outlet airflow and the axial direction within ±18°.

[0094] The present invention provides a low-loss compact blade diffuser design method and structure, which focuses on solving the technical problem that existing conventional blade diffusers are difficult to effectively take into account multiple requirements such as small-size, simple and compact layout structure, simple and efficient geometric shape, and low-loss, high-quality rectification effect. The blade diffuser design method and structure proposed in the present invention patent can not only effectively reduce the outer diameter size of the centrifugal impeller outlet blade diffuser to achieve a compact structural layout and simplify the difficulty of three-dimensional diffuser blade design, but also significantly suppress the large-range angular separation phenomenon existing inside the blade diffuser under large blade folding conditions, and significantly improve its low-loss, high-quality rectification effect on the absolute airflow at the centrifugal impeller outlet. The present invention integrates the radial blade diffuser and the axial blade diffuser into an integrated blade diffuser, which greatly reduces the geometric space, outer diameter and number of blade rows occupied by the centrifugal impeller outlet diffuser section, and the structure is simpler and more compact, and avoids the problem of flow matching of multiple diffuser blade rows. The three-dimensional blades of the integrated blade diffuser of the present invention adopt the design method of arbitrary geometric profiles, and the geometric deflection angle of the blades is as high as 65° to 70° or more, which can effectively eliminate the circumferential pre-swirl and corresponding circumferential velocity component of the absolute airflow at the outlet of the centrifugal impeller, and achieve the purpose of efficient rectification of the absolute airflow at the outlet of the centrifugal impeller. The relatively regular meridian flow channel surrounded by the casing and the hub revolving surface of the present invention is responsible for converting the absolute airflow at the outlet of the centrifugal impeller from a radial deflection of 90° to an axial direction, while the three-dimensional large folding blades are responsible for eliminating the circumferential pre-swirl and circumferential velocity component of the absolute airflow at the outlet of the centrifugal impeller. The functions of the two are strictly distinguished, and the geometric profile design is independent, which is convenient for realizing three-dimensional blade shaping and simplifying the processing technology and manufacturing cost of the blade diffuser. The integrated blade diffuser of the present invention combines the curvature distribution adjustment of the large-turn blade geometry and the tapered geometry design of the axial section of the meridian flow channel to effectively suppress the large separation of the hub angle area on the pressure surface side of the axial section of the diffuser blade, significantly reduce the flow separation loss inside the blade diffuser, and improve its flow capacity and the rectification effect on the absolute airflow.

[0095] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0096] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A design method for a low-loss compact blade diffuser, characterized in that: The steps include: Step 1: The radial blade diffuser and the axial blade diffuser are designed as an integrated structure, the two side surfaces of the blade diffuser from radial to axial directions are not integrated and shared with the hub rotating surface, and a bladeless diffuser section is set between the centrifugal impeller and the integrated blade diffuser; Step 2: The casing and the hub revolving surface form a meridian flow channel, which turns the absolute airflow at the centrifugal impeller outlet from radial deflection of 90° to axial, and the hub profile of the axial section is raised; Step 3: Design the three-dimensional large-turn diffuser blades by adopting the three-dimensional forming method of leading edge stacking to eliminate the circumferential pre-swirl and circumferential velocity component of the absolute airflow at the centrifugal impeller outlet.

2. The method for designing a low-loss compact blade diffuser according to claim 1, characterized in that: In step 1, the ratio of the outlet radius value to the inlet radius value of the bladeless diffuser section is 1.05-1.15, and the absolute airflow velocity at the inlet of the blade diffuser is ensured to be less than the speed of sound.

3. The low-loss compact blade diffuser design method according to claim 1, characterized in that: In step 2, the meridional flow channel of the blade diffuser includes a radial section, an axial section and a transition section between the first two. The axial length of the axial section is defined as the axial distance between the hub profile of the radial section of the diffuser and the outlet cross section of the axial section. The axial length of the radial section of the blade diffuser is the blade height value at the outlet of the centrifugal impeller. The meridian profile of the transition section of the blade diffuser adopts an arc profile or a high-order Bezier curve that approximates an arc.

4. The method for designing a low-loss compact blade diffuser according to claim 3, characterized in that: The radial section blade height of the meridional flow channel is constant and equal to the centrifugal impeller outlet blade height. The average blade height of the transition section and the maximum blade height of the axial section are both 1 to 1.2 times the radial section blade height.

5. The method for designing a low-loss compact blade diffuser according to claim 3, characterized in that: The radial section meridian profile of the blade diffuser includes a hub profile and a casing profile, and the angles between the hub profile and the casing profile and the radial direction are equal; the geometric lift angle α1 of the hub profile of the axial section does not exceed 16°.

6. The method for designing a low-loss compact blade diffuser according to claim 3, characterized in that: In step 3, the three-dimensional blade includes the design of two primitive-level blade shapes, namely the blade root and the blade tip. The maximum blade shape turning angle of each primitive level reaches more than 65°. The number of primitive-level blade shapes is set to no more than 6 along the blade height direction according to actual needs, and all primitive-level blade shapes adopt a three-dimensional forming method with leading edge stacking to ensure a smooth transition between the suction surface and the pressure surface of the diffuser blade.

7. The method for designing a low-loss compact blade diffuser according to claim 6, characterized in that: The calculation method of the inlet geometric angle β1 of each elementary stage blade of the blade diffuser is as follows: β1＝α3+c1 Among them, α3 is the absolute airflow angle at the inlet radius of the blade diffuser corresponding to the centrifugal impeller outlet radial section, c1 is a constant, and the value range is 2 to 5°; The calculation method of the blade installation angle ζ of each primitive blade profile is as follows: ξ=β1-(β1-β2)·c2 Among them, c2 is a constant, with a value between 0.2 and 0.

4. The c2 value corresponding to the primitive-level blade profile near the diffuser blade root is the smallest. As the blade height increases, the corresponding c2 value of the primitive-level blade profile also increases accordingly; β2 is the absolute airflow angle at the outlet of the primitive-level blade profile, with a value between 0 and 5°.

8. The method for designing a low-loss compact blade diffuser according to claim 7, characterized in that: According to the total axial length △l, inlet geometric angle β1, outlet geometric angle β2 and installation angle ζ of the blade diffuser, the distribution characteristics of the camber line of the primitive stage blade are obtained by using a three-point Bezier curve.

9. The method for designing a low-loss compact blade diffuser according to claim 6, characterized in that: Leading edge radius Thic of different primitive blade types LE Take 0.1~0.5mm, the trailing edge adopts blunt trailing edge structure characteristics, corresponding to the trailing edge radius value Thic TE Take 2~5mm; the maximum thickness value is at 60%~75% of the length of the arc line in the blade, and the maximum thickness value is 2·Thic max Take 1.4 to 2 times the width of the elementary blade trailing edge; the distribution characteristics of the elementary blade thickness along the corresponding mid-camber line are determined after the leading edge radius value, trailing edge radius value, maximum thickness point position and corresponding thickness value 2·Thic max Finally, the 9th-order Bezier curve is used to obtain the pressure surface profile and suction surface profile of the primitive-level blade symmetrically distributed along the mid-arc line by adjusting the corresponding thickness values ​​Thic1~Thic6 at other control points along the process to ensure the natural and smooth distribution of the thickness values ​​along the mid-arc line.

10. The method for designing a low-loss compact blade diffuser according to claim 1, characterized in that: The design number of blades is equal to the total number of blades of the centrifugal impeller, which is an odd number. A geometric chamfer is set at the intersection of the blade diffuser, the hub and the casing surface.

Images