阅读说明：本技术 离心式压气机的设计方法及其扩压器结构 (Design method of centrifugal compressor and diffuser structure thereof ) 是由 徐玉东 张心明 吕琼莹 熊恒 穆国振 于 2019-08-01 设计创作，主要内容包括：本发明公开了一种离心式压气机的设计方法及其扩压器结构,其中,所述离心式压气机包括：壳体、叶轮和扩压器,所述叶轮包括轮毂和叶轮叶片,所述扩压器包括扩压器叶片,所述设计方法包括：所述壳体和所述叶轮的轮毂中的曲线段均采用Bezier曲线设计,所述叶轮叶片中的曲线段采用3D自由曲线设计；所述扩压器叶片中的曲线段采用螺旋曲线设计。通过参数化设计方法,对气体入口进气角度和出口出气角度进行优化,改善气体流动状态,改善出口气流均匀程度,减少气体流动损失,实现较小尺寸条件下获得更高的压气能力和扩压能力。(The invention discloses a design method of a centrifugal compressor and a diffuser structure thereof, wherein the centrifugal compressor comprises the following components: the design method comprises the following steps of: the curved sections in the shell and the hub of the impeller are designed by Bezier curves, and the curved sections in the impeller blades are designed by 3D free curves; the curve section in the diffuser blade is designed by adopting a spiral curve. By a parametric design method, the gas inlet angle of a gas inlet and the gas outlet angle of an outlet are optimized, the gas flow state is improved, the uniformity degree of gas flow at the outlet is improved, the gas flow loss is reduced, and higher gas compression capacity and higher diffusion capacity are obtained under the condition of smaller size.)

1. A method of designing a centrifugal compressor, the centrifugal compressor comprising: casing, impeller and diffuser, the impeller includes wheel hub and impeller blade, the diffuser includes the diffuser blade, its characterized in that, the design method includes: the curved sections in the shell and the hub of the impeller are designed by Bezier curves, and the curved sections in the impeller blades are designed by 3D free curves; the curve section in the diffuser blade is designed by adopting a spiral curve.

2. The method of designing a centrifugal compressor as claimed in claim 1, wherein the Bezier curve is obtained by:

wherein p represents a point on the curve, n represents the order, i represents the index of the control point, i and n both take natural numbers, i is 0,1, … n, β_i,n(t) represents the Bernstein function, with 0 ≦ t ≦ 1.

3. The method of designing a centrifugal compressor according to claim 1, wherein the 3D free curve is a B-spline curve, as shown in the following equation:

wherein, B_k,n(t) represents a B-spline function, t is more than or equal to 0 and less than or equal to 1, n represents an order, i represents an index of a control point, i is 0,1, … n, i and n all take natural numbers, k represents a segment vertex of the B-spline, G represents a segment vertex of the B-spline, and_i,n(t) represents an n-1 th-order B-spline curve basis function.

4. The design method for a centrifugal compressor according to claim 3, further comprising:

adjusting the 3D free curve by adopting a plurality of times of B-spline curves;

setting the shape and thickness of the impeller blade;

constructing a blade model for forming the impeller according to the set shape and thickness and the 3D free curve;

and adjusting the blade inclination angle and the wrap angle of the blade model through the B-spline curve.

5. The method of designing a centrifugal compressor as recited in claim 1, wherein the impeller blades include an impeller main blade and an impeller splitter blade, and wherein the wrap angles of the impeller main blade and the impeller splitter blade are 72 degrees.

6. The design method of the centrifugal compressor according to claim 1, wherein the inlet angle of the impeller blade is 30 to 70 degrees, and the outlet angle is 20 to 60 degrees.

7. The method of claim 1, wherein the centrifugal compressor has a mass flow of 35g/s, a design pressure ratio of 3.5, and a maximum speed of 400000 r/min.

8. A diffuser structure comprises diffuser blades and is characterized in that the diffuser blades are designed by adopting spiral curves.

9. The diffuser structure of claim 8 wherein the diffuser vanes include diffuser main vanes and diffuser splitter vanes, the diffuser main vanes include radial main vanes and axial main vanes, the radial main vanes are uniformly distributed along a radial direction, a continuous inlet passage for the flow is formed between adjacent radial main vanes, the axial main vanes and the diffuser splitter vanes are uniformly distributed on the circumferential surface of the diffuser, and a continuous outlet passage for the flow is formed between the axial main vanes and the diffuser splitter vanes.

10. The diffuser structure of claim 8 wherein the inlet width of the diffuser is 6.8mm, the outlet width of the diffuser is 4.2mm, the inlet angle of the diffuser vanes is 65 degrees, and the outlet angle of the diffuser vanes is 72 degrees.

Technical Field

The invention relates to the field of turbojet engine equipment, in particular to a design method of a centrifugal compressor and a diffuser structure of the centrifugal compressor.

Background

Micro Turbine Engine (MTE) has the advantages of small volume, light weight, high energy density and the like and is widely applied to the field of energy sources. The centrifugal compressor is a core component of the micro turbojet engine, and the design level of the centrifugal compressor directly influences the overall performance of the micro turbojet engine. Compared with an axial-flow compressor, the centrifugal compressor has the characteristics of light weight, small volume and high single-stage pressure ratio, so that the centrifugal compressor is widely applied to a micro turbojet engine.

At present, the conventional centrifugal compressor has large structural size, long axial size and heavy weight. The existing diffuser structure is a segmented blade diffuser, the size of the diffuser is large, the gas viscosity action in a diffusion channel is enhanced, and the friction loss is large; or the wedge-shaped blade passage type diffuser is mixed at the turning position from the axial direction to the radial direction and turns from the radial direction to the axial direction on the meridian plane, and meanwhile, a boundary layer and secondary flow occur, so that the loss is large.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a design method of a centrifugal compressor and a diffuser structure thereof, so as to overcome the defects of the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme:

one aspect of the present invention is to provide a method of designing a centrifugal compressor including: the design method comprises the following steps of: the curved sections in the shell and the hub of the impeller are designed by Bezier curves, and the curved sections in the impeller blades are designed by 3D free curves; the curve section in the diffuser blade is designed by adopting a spiral curve.

Preferably, the Bezier curve is obtained by:

where p represents a point on the curve, n represents the order, i represents the index of the control point, i and n each take a natural number, i ═ 0, 1.. n, β_i，n(t) represents the Bemstein function, 0 ≦ t ≦ 1.

Preferably, the 3D free curve is a B-spline curve, as shown in the following formula:

wherein, B_k，n(t) represents a B-spline curve function, t is more than or equal to 0 and less than or equal to 1, n represents an order, i represents an index of a control point, i is 0,1_i，n(t) represents an n-1 th-order B-spline curve basis function.

Preferably, the design method further comprises: adjusting the 3D free curve by adopting a plurality of times of B-spline curves; setting the shape and thickness of the impeller blade; constructing a blade model for forming the impeller according to the set shape and thickness and the 3D free curve; and adjusting the blade inclination angle and the wrap angle of the blade model through the B-spline curve.

Preferably, the impeller blades comprise an impeller main blade and an impeller splitter blade, and wrap angles of the impeller main blade and the impeller splitter blade are both 72 degrees.

Preferably, the inlet angle of the impeller blade is 30-70 degrees, and the outlet angle is 20-60 degrees.

Preferably, the mass flow rate of the centrifugal compressor is 35g/s, the designed pressure ratio is 3.5, and the maximum value of the rotating speed is 400000 r/min.

It is another aspect of the present invention to provide a diffuser structure that includes diffuser vanes that are designed with a spiral curve.

Preferably, the diffuser blade includes diffuser main blade and diffuser splitter blade, diffuser main blade includes radial section main blade and axial segment main blade, radial section main blade is along radial evenly distributed, constitutes the continuous inlet channel of air current between the adjacent radial section main blade, axial section main blade with diffuser splitter blade evenly distributed on the circumferential surface of diffuser, axial section main blade with constitute the continuous exit passage of air current between the diffuser splitter blade.

Preferably, the inlet width of the diffuser is 6.8mm, the outlet width of the diffuser is 4.2mm, the air inlet angle of the diffuser blade is 65 degrees, and the air outlet angle of the diffuser blade is 72 degrees.

Compared with the prior art, the invention has the following advantages and beneficial effects:

the invention optimizes the gas inlet angle of the gas inlet and the gas outlet angle of the gas outlet by adopting a parametric design method for the centrifugal compressor, improves the gas flow state, improves the uniformity degree of the gas flow at the gas outlet, reduces the gas flow loss, and realizes higher gas compression capacity and diffusion capacity under the condition of smaller size.

The invention reduces the size and the weight of the compressor, improves the working rotating speed of the compressor and improves the air compression capability of the miniature centrifugal compressor.

The invention can make the air and the fuel in the combustion chamber of the turbojet engine fully mixed by adjusting and optimizing the air flow angle at the outlet of the diffuser.

Drawings

FIG. 1 is a schematic three-dimensional structure of a centrifugal compressor according to the present invention;

FIG. 2 is a schematic cross-sectional view of a three-dimensional structure of a centrifugal compressor according to the present invention;

FIG. 3 is a schematic view of the housing and impeller hub profile of the present invention;

FIG. 4 is a front view of a centrifugal compressor according to the present invention;

FIG. 5 is a rear view of the centrifugal compressor of the present invention;

FIG. 6 is a left side view of the centrifugal compressor of the present invention;

fig. 7 is a schematic view of a diffuser configuration according to the present invention.

Reference numerals:

1-a shell; 2-an impeller; 3-a diffuser; 4-impeller main blades; 5-impeller splitter blades; 6-diffuser main blade; 7-diffuser splitter blades; 8-a gas stream inlet; 9-diffuser outlet.

Detailed Description

The embodiments of the present invention will be described below with reference to the accompanying drawings. Those of ordinary skill in the art will recognize that the described embodiments can be modified in various different ways, or combinations thereof, without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are illustrative in nature and not intended to limit the scope of the claims. Furthermore, in the present description, the drawings are not to scale and like reference numerals refer to like parts.

Abbreviations and Key term definitions

Centrifugal impeller: the energy between the flowing medium and the shaft power is converted by the blades rotating at high speed, and the centrifugal force is generated by the rotation of the impeller to increase the pressure of the medium.

A diffuser: the high-speed airflow at the outlet of the impeller is subjected to speed reduction and pressure expansion, so that the kinetic energy of the gas obtained in the impeller is converted into pressure energy as far as possible.

Fig. 1 is a schematic three-dimensional structure of a centrifugal compressor according to the present invention, and fig. 2 is a schematic cross-sectional three-dimensional structure of a centrifugal compressor according to the present invention, as shown in fig. 1 and fig. 2, the centrifugal compressor according to the present invention includes a casing 1, an impeller 2, and a diffuser 3, the impeller 2 includes a hub and impeller blades, and the diffuser 3 includes diffuser blades. The centrifugal impeller is rotated at a high speed to apply work to an air medium to perform air compression, meanwhile, the flow velocity of the gas outlet is increased, the gas enters the diffuser 3 from the gas outlet of the centrifugal impeller, the diffuser 3 is used for diffusing and decelerating the gas flow to reduce the gas flow velocity, and the gas uniformly enters the combustion chamber through the diffuser outlet 9 to be fully mixed with the fuel in the combustion chamber.

The gas pressure in the centrifugal compressor is increased because the gas is subjected to the action of centrifugal force to generate pressure due to the rotation of the impeller 2 when the gas flows through the impeller 2, and meanwhile, the gas obtains velocity, and the flowing velocity of the gas is gradually reduced when the gas flows through an expansion channel such as a diffuser 3, so that the gas pressure is increased.

The design of a centrifugal compressor has a significant impact on its performance. The design method of the centrifugal compressor comprises the following steps: the curve sections in the hubs of the shell 1 and the impeller 2 are designed by adopting a Bezier curve, and the curve sections in the impeller blades are designed by adopting a 3D free curve; the curve section in the diffuser blade is designed by adopting a spiral curve. By adopting a parametric design method, the size of the centrifugal compressor is reduced, the working speed of the compressor is increased, and the air compression capacity of the centrifugal compressor is improved.

It should be noted that the hub, the impeller blades, and the diffuser blades of the casing 1 and the impeller 2 all include straight-line segments, and the straight-line segments are designed according to the size and shape requirements of the compressor.

Fig. 3 is a schematic diagram of the profiles of the casing and the impeller hub of the present invention, as shown in fig. 3, in an embodiment of the present invention, a design method of a casing 1 and a hub of an impeller 2 of a centrifugal compressor adopts a straight line segment + a Bezier curve segment + a straight line segment, wherein only a curve segment portion is shown in fig. 3, d0 in fig. 3 represents a hub inlet diameter, d1 represents an impeller inlet diameter, d2 represents a diffuser outlet diameter, and the Bezier curve adopts a 4-step spline curve, and is controlled by 5 control points, as shown in fig. 3, the control points of the casing Bezier curve are P1 to P5, and the control points of the hub Bezier curve are P1 'to P5'.

The Bezier curve is obtained by:

where p represents a point on the curve, n represents the order, i represents the index of the control point, i and n each take a natural number, i ═ 0, 1.. n, β_i，n(t) represents the Bernstein function, 0. ltoreq. t.ltoreq.1,

when the order is 4, then n is 4, i is (0, 1, 2, 3, 4), and the 4 th spline curve is represented by the following formula:

the shape of the Bezier curve can be changed by changing the positions of the control points, the geometric shapes of the shell 1 and the hub can be intuitively and flexibly changed, the curve is smooth and continuous, and therefore the formed flow passage area is smooth and continuous.

It should be noted that the Bezier curve is not limited to a 4 th-order spline curve, and may have other orders such as 3 th order (including four control points), 5 th order (including six control points), 6 th order (including seven control points), and the like. As the order increases, the number of control points increases. The selected order is proper, and if the order is too high, the control is accurate but the adjustment is not easy; if the order is too low, control is not accurate.

In an embodiment of the present invention, the 3D free curve is a B-spline curve, as shown in the following formula:

wherein, B_k，n(t) represents a B-spline curve function, t is more than or equal to 0 and less than or equal to 1, n represents an order, i represents an index of a control point, i is 0,1_i，n(t) represents an n-1 th-order B-spline curve basis function,0≤j≤n-i。

preferably, the 3D free curve is a fifth-order B-spline curve, as shown in the following equation:

it should be noted that the order of the B-spline curve is not limited to five orders, and may be other orders such as 3 orders, 4 orders, 6 orders, etc., and the higher the order is, the more the number of control points is, the more complicated the curve shape is, and the more accurate the control is; the lower the order number, the fewer the number of control points, the simpler the curve shape, and the lower the control accuracy.

By adopting the B-spline curve, the local position of the B-spline curve is controllable in the variation range of the number of the control points (for example, the value range of i is 0-5), and only one section of the curve is influenced when one vertex is moved, but the whole curve is not influenced, so that the B-spline curve can be flexibly and locally adjusted.

In an optional embodiment of the present invention, the method for designing a centrifugal compressor further includes:

adjusting the 3D free curve by using a plurality of times of B-spline curves, wherein the adjustment can be five times, and the adjustment is equally divided into 5 sections from the hub to the rim;

and setting the shape and the thickness of the impeller blade, wherein the shape of the impeller blade is adjusted and controlled according to a B-spline curve, and modeling. Specifically, the shape of the impeller blade is preliminarily designed according to design parameters including inlet gas density, temperature, pressure, outlet gas temperature, pressure, compressor efficiency and the like, and then the shape of a meridian flow channel, the shape of the blade, the installation angle of the blade and the thickness of the blade are directly given according to experience;

constructing a blade model for forming the impeller according to the set shape and thickness and the 3D free curve, and then repeatedly adjusting the blade model according to the three-dimensional calculation simulation structure so as to finally obtain the impeller meeting the requirements;

and on two sections of the hub and the rim, adjusting the blade inclination angle and the wrap angle of the blade model through B-spline curves, wherein the inclination angle is controlled and modified by curve control points, and the adjustment is the size of the inclination angle. The wrap angle is determined according to the number of the main blades, and the size of the wrap angle is adjusted.

Fig. 4 is a front view of a centrifugal compressor according to the present invention, fig. 5 is a rear view of the centrifugal compressor according to the present invention, and fig. 6 is a left view of the centrifugal compressor according to the present invention, and as shown in fig. 4 to 6, the impeller blades include an impeller main blade 4 and an impeller splitter blade 5, for example, including 5 impeller main blades 4 and 5 impeller splitter blades 5, so as to ensure a mass flow rate of intake air. As shown in fig. 4, the impeller main blades 4 and the impeller splitter blades 5 are uniformly distributed and are staggered with each other, that is, one impeller splitter blade 5 is disposed between every two impeller main blades 4.

The blade meridian is determined according to the gas flow characteristics, the non-uniformity of the blade meridian can cause the risk of gas flow separation, and continuous and smooth flow direction change is obtained when the design is carried out. Wrap angleThe degree of the circumferential surrounding of the impeller blades is obtained by the following formula:

preferably, the wrap angles of the impeller main blades 4 and the impeller splitter blades 5 are 72 degrees, so as to ensure that the cross-sectional area of the flow channel is uniformly changed.

The inlet angle and the outlet angle of the centrifugal impeller blade obviously influence the performance of the centrifugal compressor, and in one embodiment of the invention, the inlet angle alpha of the impeller blade₁Is 30-70 degrees, preferably 40 degrees, and has an outlet angle alpha₂The angle is 20-60 degrees, preferably 30 degrees, and when the inlet angle of the blade is 40 degrees and the outlet angle is 30 degrees, the pressure ratio of the centrifugal compressor reaches the maximum.

In one embodiment of the invention, the mass flow rate of the centrifugal compressor is 35g/s, the designed pressure ratio is 3.5, the maximum value of the rotating speed is 400000r/min, and the efficiency is more than 80%. The maximum diameter of the centrifugal compressor is not more than 39mm, the diameter of the impeller is 25mm, and the diameter of the diffuser is 35 mm.

Fig. 7 is a schematic view of the diffuser structure of the present invention, and as shown in fig. 7, the diffuser structure of the present invention includes diffuser blades, and preferably, the diffuser blades are designed in a spiral curve, and have a spiral structure and a smooth transition surface, so that wind can smoothly pass through the blades in the process of obtaining the maximum wind resistance, thereby preventing the wind from staying on the diffuser blades, reducing the kinetic energy loss of the air, and improving the efficiency of the diffuser. The design of the spiral line type of the diffuser blade refers to that the arc of the center line of the blade is designed into the spiral line type, the transition fillet adopted by the inner arc and the outer arc of the blade can meet the requirement by automatically chamfering according to the thickness of the diffuser blade, and the chamfering is not particularly limited. In an embodiment of the present invention, the diffuser blades include diffuser main blades 6 and diffuser splitter blades 7, the diffuser main blades 6 include radial main blades and axial main blades, the radial main blades are uniformly distributed along a radial direction, a continuous inlet channel of an airflow is formed between adjacent radial main blades, the axial main blades and the diffuser splitter blades 7 are uniformly distributed on a circumferential surface of the diffuser, and a continuous outlet channel of the airflow is formed between the axial main blades and the diffuser splitter blades 7. As shown in fig. 4, a diffuser splitter blade is disposed between each two main blades of the axial section. The distribution mode of the diffuser blades changes the sectional structure of the existing blade diffuser, and ensures that the passage of the airflow from the radial inlet to the axial outlet is kept continuous. The diffuser blade structure adopts the cross section shape of pneumatic optimization, effectively inhibits the secondary flow of the diffuser passage cross section corner area, reduces the accumulation of low-energy fluid in the corner area, and the cross section shape of the passage can be continuously changed from an inlet to an outlet and is in smooth transition. The diffuser inlet channel has secondary flow, transverse flow and even separation flow phenomena, and the diffuser splitter vane 7 is arranged at the axial section of the diffuser to reduce the secondary flow, the transverse flow and the separation flow of the airflow and ensure that the airflow uniformly flows to the combustion chamber.

In one embodiment of the invention, the inlet width of the diffuser 3 is 6.8mm, the outlet width of the diffuser 3 is 4.2mm, and the air inlet angle beta of the diffuser blades is₁Is 65 degrees, and the air outlet angle beta of the diffuser blade₂Is 72 degrees.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.