CN116467812A - A Non-linear Blade Tip Clearance Structure and Design Method of Centrifugal Compressor - Google Patents

Abstract

本发明公开了一种离心压缩机非线性叶顶间隙结构及设计方法，属于离心式叶轮机械技术领域，包括：非线性叶顶间隙分布规律：C＝15.71L ⁵ ‑53.058L ⁴ +61.664L ³ ‑26.422L ² +1.433L+1.667，其中C为无量纲间隙高度，C＝t/t _T ，t为叶顶间隙高度，t _T为叶片尾缘轴向间隙高度；L为叶轮叶顶无量纲叶片弦长，L＝l/l ₀ ，其中l为叶片叶顶任意点至前缘点弦线长度，l ₀为叶片叶顶弦线总长度，L∈[0,1]，0代表叶片前缘，1代表叶片尾缘；其特征在于叶顶间隙高度沿叶片弦长非线性变化，叶轮流道弯折处叶片中点间隙高度最小，且叶片尾缘轴向间隙高度小于叶片前缘径向间隙高度。 The non-linear blade tip clearance proposed by the present invention comprehensively considers the problems of blade tip leakage flow and impeller deformation, specifically suppresses backflow inside the gap and cross-blade lateral leakage flow, and at the same time ensures safe operation of the centrifugal impeller.

Description

A Non-linear Blade Tip Clearance Structure and Design Method of Centrifugal Compressor

technical field

The invention belongs to the technical field of centrifugal impeller machinery, and in particular relates to a nonlinear blade tip clearance structure and a design method of a centrifugal compressor.

Background technique

Centrifugal compressor is a common fluid pressurization equipment, which is generally composed of rotating elements (impeller) and fixed elements (diffuser and volute). Due to the different compressed fluid media, centrifugal compressors are widely used in refrigeration, petroleum, chemical and other fields.

The semi-open impeller with good strength and low manufacturing process is a common impeller form for centrifugal compressors, but there is a certain gap between the semi-open impeller and the wheel cover, which causes leakage inside the flow channel. The leakage loss caused by the blade tip clearance is the main source of the internal loss of the centrifugal compressor, which endangers the stability and boosting capacity of the compressor. A reasonable blade tip clearance structure design is conducive to suppressing the blade tip leakage and related flow loss, thereby improving the efficiency of the centrifugal compressor.

Conventional centrifugal compressor blade tip clearance design includes uniform constant blade tip clearance and linearly changing tip clearance from leading edge to trailing edge, which can only realize the control of clearance leakage by adjusting the size of the clearance. In addition, the existing solutions to the tip leakage phenomenon mainly include two types: one is to set wear coating or sealing structure on the surface of the impeller blade tip and the fixed element; the other is to design a tip clearance height adjustment mechanism to control the change of the tip clearance. However, the existing solutions require the use of high-cost materials or additional system structures, which not only poses challenges to the structural strength and manufacturing process of the compressor, but also creates higher requirements for the reliability of the overall machine operation.

Contents of the invention

Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a non-linear blade tip clearance structure and design method of a centrifugal compressor. The design method starts from the blade tip clearance structure itself, which is a nonlinear blade tip clearance, so as to suppress the leakage flow between the impeller of the centrifugal compressor and the fixed element, and reduce the influence of the blade tip leakage flow on the pressure ratio, efficiency and stability of the centrifugal compressor.

For solving the problems referred to above, technical scheme of the present invention is:

In the first aspect, the present invention provides a non-linear blade tip clearance structure of a centrifugal compressor. The meridian line of the volute wheel cover and the meridian line of the blade tip match each other to form a nonlinear tip clearance. The distribution of the nonlinear tip clearance satisfies the following formula:

C＝15.71L ⁵ -53.058L ⁴ +61.664L ³ -26.422L ² +1.433L+1.667

Among them, C is the dimensionless clearance height, C=t/t _T , t is the blade top clearance height, t _T is the axial clearance height of the blade trailing edge; L is the dimensionless blade chord length of the impeller blade top, L=l/l ₀ , where l is the length of the chord line from any point on the blade top to the leading edge point, l ₀ is the total length of the blade top chord line, L∈[0,1], 0 represents the blade leading edge, and 1 represents the blade trailing edge;

The blade tip clearance height at this time refers to the normal distance between the corresponding positions between the meridian line of the volute wheel cover and the meridian line of the blade top.

The nonlinear blade tip clearance structure of the centrifugal compressor includes the radial clearance height of the leading edge of the blade, the height of the blade tip clearance at the midpoint of the blade, and the axial clearance height of the trailing edge of the blade, wherein the blade tip clearance height of the midpoint of the blade at the bend of the impeller flow path is the smallest, and the axial clearance of the trailing edge of the blade is smaller than the radial clearance of the leading edge of the blade.

Based on the meridian line of the blade tip of the centrifugal compressor, and offset according to the distribution law of the nonlinear tip clearance to obtain the meridian line of the volute cover; or based on the meridian line of the volute cover of the centrifugal compressor, and offset according to the distribution law of the nonlinear tip clearance, the meridian line of the tip of the blade is obtained to realize the nonlinear tip clearance of the centrifugal compressor.

The centrifugal compressor is a semi-open impeller centrifugal compressor, preferably a centrifugal compressor.

In a second aspect, the present invention provides a method for designing a nonlinear blade tip clearance structure of a centrifugal compressor, the design method comprising the following steps:

Determine the type and working condition of the centrifugal compressor, the meridian line of the volute cover and the meridian line of the blade tip match each other to form a nonlinear tip clearance, and find the leading edge, trailing edge and midpoint of the blade;

According to the actual operating conditions of the centrifugal compressor, determine the respective normal offsets of the leading edge of the blade, the trailing edge of the blade and the midpoint of the blade;

Keep the meridian line of the volute wheel cover unchanged and change the meridian line of the blade top. At the three points of the leading edge of the blade, the trailing edge of the blade and the midpoint of the blade, perform an overall nonlinear offset on the meridian line of the volute wheel cover in the normal direction according to their respective normal offsets to obtain the offset curve; or keep the meridian line of the blade top of the blade unchanged and change the meridian line of the volute wheel cover, and perform an overall nonlinear offset on the meridian line of the blade top in the normal direction at the three points of the leading edge of the blade, the trailing edge of the blade and the midpoint of the blade according to their respective normal offsets. , get the offset curve;

Calculate the distance between the offset curve and the constant meridian line to obtain the blade tip clearance height, take 80-150 points between the leading edge and the trailing edge, and obtain the blade tip clearance height and the length of the meridian line of the centrifugal impeller blade tip at each point on the offset curve, respectively carry out dimensionless processing on the blade tip clearance height and the length of the centrifugal impeller blade tip meridian line, and then use the dimensionless blade chord length L of the impeller blade top as the abscissa, and use the dimensionless clearance height C as the ordinate to perform quintic polynomial nonlinear fitting, and obtain Non-linear blade tip clearance distribution law, according to the nonlinear blade tip clearance distribution law to determine the nonlinear blade tip clearance structure;

The non-dimensionalization processing process is: setting the blade trailing edge axial clearance height t _T , the axial direction being the axial direction of the rotating shaft, and dimensionless the blade tip clearance height t at different positions according to C=t/t _T to obtain the dimensionless clearance height C;

Obtain the meridian chord length of the blade top _of the centrifugal impeller from the leading edge to _the trailing edge of the blade. Dimensionless the meridian chord length of the blade top of the centrifugal impeller to obtain the dimensionless blade chord length L of the impeller blade.

The distribution law of the nonlinear tip clearance is C=15.71L ⁵ -53.058L ⁴ +61.664L ³ -26.422L ² +1.433L+1.667.

The blade tip clearance height at the blade midpoint at the bend of the impeller channel is the smallest, and the blade trailing edge axial clearance is slightly smaller than the blade leading edge radial clearance; the respective normal offsets of the blade leading edge, blade trailing edge, and blade midpoint are 0.5 unit, 0.3 unit, and 0.2 unit, respectively.

Determine the blade trailing edge axial clearance height t _T for the centrifugal compressor to be designed, use the nonlinear blade tip clearance distribution law to obtain the variation form of the leading edge to trailing edge blade tip clearance height t with L, and then obtain the nonlinear blade tip clearance structure of the centrifugal compressor.

Compared with the prior art, the beneficial effects of the present invention are as follows:

1. The design method of the present invention starts from the blade tip clearance structure itself, and the clearance form that varies nonlinearly from the leading edge to the trailing edge does not require additional complicated mechanisms and special materials, and can also achieve a better blade tip leakage control effect. The structure is simple, and the design and manufacturing process costs are low. It is suitable for clearance design of different types of centrifugal compressors and is easy to implement. At the same time, the present invention also considers the actual operating conditions of centrifugal compressors, and has high operational safety and reliability.

2. The non-linear blade tip clearance of the present invention realizes the control of the gap flow at different positions of the flow channel through the nonlinear change of the blade tip clearance height with the dimensionless blade chord length of the impeller tip, can effectively suppress the backflow phenomenon in the blade tip clearance, improve the operation stability of the centrifugal compressor, and simultaneously reduce the friction loss and flow loss of leakage flow near the blade tip at the bend of the impeller flow channel; effectively weaken the leakage flow intensity across the blade gap between adjacent flow channels in the rear section of the impeller flow channel, and reduce the impact of leakage flow on the secondary flow and vortex structure of the blade tip flow field. Increase the blade load, improve the supercharging capacity and overall efficiency of the centrifugal compressor. In particular, the effect on improving the circulation flow and the internal leakage flow of the low specific speed impeller centrifugal compressor with a small blade aspect ratio and a large proportion of blade tip clearance is more obvious.

3. The present invention changes the meridian line of the blade top by adjusting the structure of the impeller, or changes the meridian line of the volute wheel cover by only changing the structure of the volute, so as to realize the nonlinear distribution control of the tip clearance, and apply the optimal nonlinear tip clearance to various types of centrifugal compressors, especially low specific speed centrifugal compressors.

Description of drawings

Fig. 1 is a partial structural representation of a non-linear gap centrifugal compressor according to the design method of the present invention;

Figure 2 is a partial enlarged view of the nonlinear tip clearance structure and the distribution law of the nonlinear tip clearance. (a) is a partial enlarged view of the nonlinear tip clearance structure; (b) is a nonlinear tip clearance distribution diagram, which changes nonlinearly from the leading edge to the trailing edge.

Figure 3 is a performance comparison chart of a centrifugal compressor with a uniform constant blade tip clearance and a nonlinear blade tip clearance.

Marks in the figure: 10—volute, 11—volute channel, 12—vaneless diffuser channel, 13—volute wheel cover meridian, 20—back flange, 30—rotating shaft, 40—centrifugal impeller, 41—main blade of impeller, 42—splitter blade of impeller, 43—meridian line of blade top, 50 nonlinear blade tip clearance, t _L -radial clearance height of blade leading edge, t _M -blade tip clearance height of blade midpoint, t _T -blade trailing edge axial clearance height.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in detail. The present invention and its embodiments are described below, this description is not limiting, and the actual embodiments are not limited thereto. All in all, if a person of ordinary skill in the art is inspired by it, without departing from the inventive concept of the present invention, without creatively designing a structure and an embodiment similar to the technical solution, it shall fall within the scope of protection of the present invention.

The design method of the present invention is applicable to centrifugal compressors, and the centrifugal compressors are taken as an example below for description.

Considering the operation safety of the centrifugal compressor impeller, the deformation during operation, and the impact of the tip leakage at different positions of the impeller blades on the flow, by changing the meridian line of the centrifugal impeller blade tip or the volute cover meridian line, the control of the tip clearance structure is realized to achieve the purpose of nonlinear change of the tip clearance from the leading edge to the trailing edge, and the optimal nonlinear tip clearance distribution law for improving the performance of the compressor is obtained.

The non-linear tip clearance design of the centrifugal compressor in this embodiment is based on:

On the one hand, considering the complex three-dimensional distortion of the centrifugal impeller channel, under the action of the pressure difference in the impeller channel, the fluid will produce radial backflow along the gap from the blade trailing edge to the leading edge and cross-blade circumferential gap flow between adjacent flow channels, especially at the circumferential and axial bends of the runner in the middle of the blade, the gap leakage flow and the friction loss of the casing will increase. The structure generates disturbance, which intensifies the flow loss in the flow channel. Therefore, reducing the clearance height in the middle of the blade is beneficial to suppress the interaction of the clearance flow and its disturbance to the flow field on the blade tip;

On the other hand, during the actual operation of the centrifugal compressor, due to the centrifugal force, aerodynamic pressure and thermal load, the centrifugal impeller will be deformed to a certain extent. At the same time, the shafting will move when the impeller rotates, which will cause the tip clearance height to change. The research on the fluid-solid coupling of the centrifugal impeller found that the deformation of the leading and trailing edges of the centrifugal impeller blades is the largest in actual operation. Therefore, considering the safety margin and reliability of the impeller operation, the clearance height at the leading and trailing edges of the blades is relatively increased. In addition, the fluid downstream of the impeller flow channel has a large circumferential velocity, which intensifies the leakage flow of the blade tip and weakens the load and work ability of the blades in the rear section of the impeller. Therefore, the axial clearance height of the trailing edge of the blade should be set smaller than the radial clearance height of the leading edge.

The nonlinear blade tip clearance distribution law is the clearance height between the meridian line of the blade tip and the meridian line of the volute cover. Based on the non-dimensionalized axial clearance height of the trailing edge of the blade, the blade tip clearance height at the midpoint of the blade at the bend of the impeller channel is the smallest, while the radial clearance height of the leading edge of the blade and the axial clearance of the trailing edge of the blade increase, and the axial clearance height of the trailing edge of the blade is smaller than the radial clearance height of the leading edge of the blade.

In some designs, the volute and the back flange are included, and the volute and the back flange are assembled with the centrifugal impeller to form a booster space of the centrifugal compressor, wherein the meridian line of the volute wheel cover matches the meridian line of the impeller blade tip to form a non-linear tip clearance.

In a possible design scheme, the nonlinear blade tip clearance is based on the known centrifugal compressor impeller blade tip meridian line, and is shifted according to the nonlinear blade tip clearance distribution law to obtain the volute cover meridian line; or is based on the known centrifugal compressor volute wheel cover meridian line, and is shifted according to the nonlinear blade tip clearance distribution law to obtain the impeller blade tip meridian line, and finally assembled to obtain the nonlinear blade tip clearance.

The dimensionless clearance height C is obtained by dimensionless the blade tip clearance height at different positions based on the blade trailing edge axial clearance height t _T , which is expressed as C=t/t _T , where t is the blade tip clearance height, and t _T is the blade trailing edge axial clearance height;

The dimensionless blade chord length L of the impeller blade tip is obtained by dimensionless the length of the meridian chord line of the centrifugal impeller blade blade tip, L=l/l ₀ , wherein l is the length of the chord line from any point on the blade tip to the leading edge point, l ₀ is the total length of the blade tip chord line, L∈[0,1], 0 represents the leading edge of the blade, and 1 represents the trailing edge of the blade.

Determine the respective normal offsets of the blade leading edge, blade trailing edge, and blade midpoint according to the operating conditions and types of the centrifugal compressor, and the respective normal offsets of the blade leading edge, blade trailing edge, and blade midpoint are 0.5 units, 0.3 units, and 0.2 units;

Keep the meridian line 13 of the volute wheel cover unchanged and change the meridian line 43 of the blade tip, and carry out the overall nonlinear offset to the meridian line 13 of the volute wheel cover in the normal direction at the three points of the leading edge of the blade, the trailing edge of the blade and the midpoint of the blade according to the respective normal offsets to obtain the offset curve; The blade top meridian line 43 is overall nonlinearly offset to obtain an offset curve;

Calculate the distance between the offset curve and the constant meridian line to obtain the height of the blade tip clearance. Take 100 points between the leading edge and the trailing edge to obtain the blade tip clearance height and the length of the meridian line of the centrifugal impeller blade top at each point on the deviation curve. The blade tip clearance height and the length of the meridian line of the centrifugal impeller blade top meridian line are respectively used for dimensionless processing. After that, the dimensionless blade chord length L of the impeller blade top is used as the abscissa, and the dimensionless clearance height C is used as the ordinate to perform quintic polynomial nonlinear fitting to obtain a nonlinear blade tip Clearance distribution law, determine the nonlinear blade tip clearance structure according to the nonlinear blade tip clearance distribution law;

The distribution law of nonlinear blade tip clearance of centrifugal compressor is:

C=15.71L ⁵ -53.058L ⁴ +61.664L ³ -26.422L ² +1.433L+1.667.

For any centrifugal compressor, the size of the gap at the outlet has a significant impact on the working force and aerodynamic loss of the impeller. According to the design requirements for its safe operation, a reasonable blade trailing edge axial gap height t _T is determined for a certain centrifugal compressor. Using the above formula, the variation form of the leading edge to trailing edge blade tip clearance height t with L is obtained, that is, the nonlinear blade tip clearance structure of the centrifugal compressor is obtained.

Referring to Fig. 1 to Fig. 3, the centrifugal compressor according to the embodiment of the present invention is a centrifugal compressor, and the centrifugal compressor includes several parts such as a volute, a centrifugal impeller and a diffuser. As shown in Figure 1, the centrifugal compressor partial assembly includes a volute 10, a back flange 20, a rotating shaft 30, and a centrifugal impeller 40, wherein the volute partially has a volute flow channel 11, a vaneless diffuser flow channel 12, and a volute wheel cover meridian line 13;

After the centrifugal compressor of this example is assembled as shown in Figure 1, the meridian line 13 of the volute wheel cover and the meridian line 43 of the blade tip match each other to form a nonlinear tip clearance 50, which is a non-linear tip clearance centrifugal compressor. The gas kinetic energy is converted into pressure energy, and finally discharged from the right volute outlet.

In this example, the blade trailing edge axial clearance height t _T =0.3 mm, the specific centrifugal compressor impeller is selected according to its geometric parameters, and can be any other value. The non-linear tip clearance 50 distribution of the centrifugal compressor in this example satisfies the law: t=4.713L ⁵ -15.917L ⁴ +18.499L ³ -7.927L ³ +0.43L+0.5, the blade leading edge radial clearance height t _L =0.5mm, and the blade tip clearance height t _M at the blade midpoint =0.2mm. The meridian line 43 of the blade tip of the known centrifugal impeller 40 is shifted according to the above-mentioned non-linear blade tip clearance distribution law to obtain the volute cover meridian line 13. It is also possible to obtain the blade tip meridian line 43 based on the offset of the volute cover meridian line 13 of the known centrifugal impeller 40 according to the above-mentioned non-linear blade tip clearance distribution law. Therefore, after assembly, the volute cover meridian line 13 and the blade tip meridian line 43 match each other to form a nonlinear tip clearance 50.

Compared with the existing centrifugal compressor with uniform constant tip clearance, the non-linear tip clearance centrifugal compressor mentioned above in this example realizes the nonlinear change of the tip clearance from the leading edge to the trailing edge, better optimizes the leakage flow in the tip clearance of the centrifugal impeller, effectively suppresses the backflow in the tip clearance and the lateral leakage flow across the blades, reduces the underflow loss in the flow channel and the flow loss related to the tip leakage, and improves the operation stability of the centrifugal compressor. As shown in Figure 3, this figure is a performance comparison of the entire stage of centrifugal compressors using uniform constant blade tip clearance and nonlinear blade tip clearance respectively. At different speeds, correction efficiency = isentropic efficiency/maximum isentropic efficiency. In Figure 3, the upper three sets of speed data represent the comparison data of the total pressure ratio under different clearance structures, and the lower three sets of speed data represent the comparison data of the correction efficiency under different clearance structures. It can be seen that the efficiency and total pressure ratio of the centrifugal compressor with nonlinear blade tip clearance are significantly improved at three speeds.

The non-linear blade tip clearance proposed by the present invention comprehensively considers the problems of blade tip leakage flow and impeller deformation, specifically suppresses backflow inside the gap and cross-blade lateral leakage flow, and at the same time ensures safe operation of the centrifugal impeller.

What is not mentioned in the present invention is applicable to the prior art.

Claims (8)

1. A centrifugal compressor nonlinear blade tip clearance structure which is characterized in that: the volute wheel cover meridian line and the blade top meridian line are mutually matched to form a nonlinear blade top gap, and the nonlinear blade top gap distribution meets the following formula:

C＝15.71L ⁵ -53.058L ⁴ +61.664L ³ -26.422L ² +1.433L+1.667

wherein C is the dimensionless gap height, c=t/t _T T is the height of the clearance between the blade tips, t _T The axial clearance height of the tail edge of the blade; l is the chord length of the impeller blade top dimensionless blade, and l=l/L ₀ Wherein l is the chord line length from any point of the blade top to the front edge point, l ₀ For the total length of the chord line of the blade top, L is E [0,1]0 represents the leading edge of the blade, and 1 represents the trailing edge of the blade;

the height of the blade tip clearance at the moment refers to the normal distance of the corresponding positions between the meridian line of the volute casing wheel cover and the meridian line of the blade tip.

2. The centrifugal compressor nonlinear tip clearance structure of claim 1, wherein the centrifugal compressor nonlinear tip clearance structure comprises a blade leading edge radial clearance height, a blade tip clearance height at a blade midpoint, a blade trailing edge axial clearance height, wherein the blade tip clearance height at the blade midpoint at the impeller flowpath bend is minimal and the blade trailing edge axial clearance is less than the blade leading edge radial clearance.

3. The centrifugal compressor nonlinear tip clearance structure of claim 1, wherein the volute cap meridian line is obtained based on the centrifugal compressor blade tip meridian line and shifted according to the nonlinear tip clearance distribution rule; or based on the radial line of the volute wheel cover of the centrifugal compressor, and the radial line of the blade top is obtained by shifting according to the distribution rule of the nonlinear blade top gap, so that the nonlinear blade top gap of the centrifugal compressor is realized.

4. The centrifugal compressor nonlinear tip clearance structure of claim 1, wherein the centrifugal compressor is a semi-open impeller centrifugal compressor, preferably a centrifugal compressor.

5. The design method of the nonlinear blade tip clearance structure of the centrifugal compressor is characterized by comprising the following steps of:

determining the type and working condition of a centrifugal compressor, wherein the meridian line of the volute casing wheel cover and the meridian line of the blade top of the blade are matched with each other to form a nonlinear blade top gap, and finding the front edge, the tail edge and the middle point of the blade;

determining respective normal offset values of the blade leading edge, the blade trailing edge and the blade midpoint according to actual operation conditions of the centrifugal compressor;

the radial line of the volute wheel cover is kept unchanged, the radial line of the blade top of the blade is changed, and the three points of the front edge of the blade, the tail edge of the blade and the midpoint of the blade are subjected to integral nonlinear offset according to respective normal offset in the normal direction to obtain an offset curve; or the radial line of the blade top of the blade is kept unchanged, the radial line of the volute wheel cover is changed, and the radial line of the blade top of the blade is subjected to integral nonlinear offset in the normal direction at three points of the front edge of the blade, the tail edge of the blade and the midpoint of the blade according to respective normal offset values, so that an offset curve is obtained;

calculating the distance between an offset curve and a constant meridian line to obtain a blade top clearance height, taking 80-150 points between a leading edge and a trailing edge, obtaining the blade top clearance height of each point on the offset curve and the radial length of the blade top of the centrifugal impeller blade, carrying out dimensionless treatment on the blade top clearance height and the radial length of the blade top of the centrifugal impeller respectively, and then carrying out five-time polynomial nonlinear fitting by taking the chord length L of the blade top dimensionless blade of the impeller as an abscissa and taking the dimensionless clearance height C as an ordinate to obtain a nonlinear blade top clearance distribution rule, and determining a nonlinear blade top clearance structure according to the nonlinear blade top clearance distribution rule;

the dimensionless treatment process comprises the following steps: setting the axial clearance height t of the trailing edge of the blade _T The axial direction is the axial direction of the rotating shaft, according to C=t/t _T The blade tip clearance height t at different positions is dimensionless, and the dimensionless clearance height C is obtained;

obtaining the radial chord length of the blade top of the centrifugal impeller from the front edge to the tail edge of the blade, and obtaining the chord length L of the blade top non-dimensional blade of the impeller by non-dimensionalization of the radial chord length of the blade top of the centrifugal impeller, wherein L=l/L ₀ Wherein l is the chord line length from any point of the blade top to the front edge point, l ₀ For the total length of the chord line of the blade top, L is E [0,1]0 represents the leading edge of the blade and 1 represents the trailing edge of the blade.

6. The method for designing a non-linear tip clearance structure of a centrifugal compressor according to claim 5, wherein the distribution rule of the non-linear tip clearance is c=15.71L ⁵ -53.058L ⁴ +61.664L ³ -26.422L ² +1.433L+1.667。

7. The method of claim 5, wherein the tip clearance height at the midpoint of the vane at the bend of the impeller flowpath is minimal and the vane trailing edge axial clearance is slightly less than the vane leading edge radial clearance; the respective normal offsets for the blade leading edge, the blade trailing edge, and the blade midpoint are 0.5 units, 0.3 units, 0.2 units, respectively.

8. The method for designing a nonlinear tip clearance structure of a centrifugal compressor according to claim 5, wherein the axial clearance height t of the trailing edge of the blade is determined for the centrifugal compressor to be designed _T And obtaining a variation form of the clearance height t of the blade tip from the leading edge to the trailing edge along with L by utilizing a nonlinear blade tip clearance distribution rule, so as to obtain a nonlinear blade tip clearance structure of the centrifugal compressor.