Backflow device blade design method

Abstract

The invention discloses a design method of a backflow device blade. The efficiency of a gas compressor is improved. Theta i coordinates of all points on the middle-sized line are deduced according to the change rule of a known variable of the middle-sized line in a radial channel of the backflow device and are converted into Cartesian coordinates, the original airfoil thickness is overlaid on normal lines on the two sides of the middle-sized line, and data of a suction surface and a pressure surface of a blade of the backflow device are generated.

Description

Technical Field

[0001] The invention relates to the technical field of centrifugal compressors, and in particular to a method for designing return flow device blades. Background Art

[0002] The multi-stage centrifugal compressor is mainly composed of an impeller, a returner, a casing, and an inlet / outlet duct. The curved structure connecting the impeller and the returner is relatively simple, which causes the flow field of the airflow when it flows through the curve and enters the returner to be greatly affected by the airflow state at the impeller outlet. Due to the different airflow angles at different blade heights on the returner inlet section, when the compressor is operated under conditions that are partially higher than the design flow rate, a negative angle of attack will appear at the returner rear disk, which will deteriorate the flow field. Under conditions that are partially lower than the design flow rate, the positive angle of attack of the returner front disk will be too large, causing large impact losses. Both of the above situations will reduce the efficiency of the compressor.

[0003] In order to better match the airflow at the bend outlet and provide a more uniform flow field along the blade height direction for the inlet of the lower impeller, the efficiency of the compressor is improved. The present invention proposes a blade midline design method for a blade returner through experimental and numerical research on the geometric parameters of the returner and combined with an optimization algorithm. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for designing return flow blades to improve the efficiency of a compressor.

[0005] The object of the present invention is achieved in that:

[0006] A design method for return flow blades, given geometric parameters: inlet and outlet installation angle α 5A , α 6A , the return inlet and outlet radii r5, r6, the inlet and outlet widths b5, b6, and the z coordinate of the side profile of the disk cover, z s and z h ;

[0007] The radial coordinates from the inlet to the outlet of the recirculator are discretized into N equal parts, denoted as r5, r i , r i+1 ,…,r6,

[0008] The radial coordinate is converted into a dimensionless radial position calculation formula as follows:

[0009] R i =r i / r5 (1)

[0010] The coordinates θ of any point on the median line are obtained by formula (2): i ,

[0011]

[0012] Where P is the residual angular momentum coefficient of the return flow device, and

[0013] P=b5tanα 5A / (b6tanα 6A );

[0014] R6 is the ratio of the return flow inlet and outlet radii, and

[0015] R6=r6 / r5

[0016] Find θ i Then, according to equations (3) and (4), the coordinates (X i , Y i ), the conversion relationship between the two coordinates is as follows:

[0017] X i =r i cosθ i (3)

[0018] Y i =r i sinθ i (4)

[0019] The angle α between the perpendicular line connecting the coordinates of the median line and the origin and the tangent of the median line i , can be obtained by formula (5):

[0020]

[0021] According to α i Find any radius r i The normal angle γ i :

[0022] γ i =90°-arctan(Y i / X i )*180 / π-α i (6)

[0023] When generating the return flow blade, the original airfoil thickness is superimposed on the normals on both sides of the mid-line, that is, the data of the suction surface and pressure surface of the return flow blade are generated. The normal direction of each point on the mid-line is calculated and determined by formula (6).

[0024] Preferably, when the radial coordinates from the inlet to the outlet of the recirculator are discrete, the profile lines at the beginning and end of the recirculator blades are encrypted.

[0025] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0026] When generating the return flow blade, the original airfoil thickness is superimposed on the normals on both sides of the mid-line to generate the data of the suction and pressure surfaces of the return flow blade, and then the normal direction of each point on the mid-line is calculated. This can better match the airflow at the bend outlet, and at the same time provide a more uniform flow field along the blade height direction for the inlet of the lower-stage impeller, thereby improving the efficiency of the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the geometric parameters of the median line;

[0028] Figure 2 The generated blade profile of the return flow machine is shown in Figure 2.

[0029] Figure 3 It is a schematic diagram of the meridian view of the return flow device;

[0030] Figure 4 It is a schematic diagram of the medium-sized line geometry;

[0031] Figure 4 Medium θ i Represents the angle between any point on the median line and the coordinate origin and the X-axis, r i represents the radius of any point on the median line, α i represents the angle between the perpendicular line connecting any point on the median line and the origin and the tangent direction of the median line, γ i Represents the radius r i The normal angle at the mid-line. DETAILED DESCRIPTION

[0032] Different from the conventional single arc midline, the midline of the present invention is known to have a variable (tangential velocity / angular momentum) in the radial channel of the returner. Based on this variation law, the θ of each point on the midline is deduced. i Coordinates are converted into Cartesian coordinates, and the original airfoil thickness is superimposed on the normals on both sides of the mid-line to generate the data of the suction and pressure surfaces of the return flow blade. The specific steps are as follows:

[0033] When designing a mid-size line, the geometric parameters that need to be given include the inlet and outlet installation angle α 5A and α 6A , the return inlet and outlet radii r5 and r6, the inlet and outlet widths b5, b6 and the z coordinate of the side profile of the disk cover s and z h The radial coordinates from the inlet to the outlet of the reflux device are discretized into N equal parts, denoted as r5, r i , r i+1 ,…,r6, when the radial coordinates are discretized, the density can also be increased at the beginning and end of the center line of the return flow device blade.

[0034] The dimensionless radial position calculation formula is:

[0035] R i =r i / r5 (1)

[0036] The coordinates θ of any point on the median line are obtained by formula (2): i See Figure 4 As shown,

[0037]

[0038] Where P is the residual angular momentum coefficient of the return flow device, and

[0039] P=b5tanα 5A / (b6tanα 6A );

[0040] R6 is the ratio of the return flow inlet and outlet radii, and

[0041] R6=r6 / r5

[0042] Find θ i Then, according to equations (3) and (4), the coordinates (X i , Y i ), the conversion relationship between the two coordinates is as follows:

[0043] X i =r i cosθ i (3)

[0044] Y i =r i sinθ i (4)

[0045] The angle α between the perpendicular line connecting the coordinates of the median line and the origin and the tangent of the median line i , can be obtained by formula (5):

[0046]

[0047] According to α i Find any radius r i The normal angle γ i :

[0048] γ i =90°-arctan(Y i / X i )*180 / π-α i (6)

[0049] When generating the return flow blade, the original airfoil thickness is superimposed on the normals on both sides of the mid-line to generate the suction and pressure surface data of the return flow blade. The normal direction of each point on the mid-line is determined by formula (6). The return flow blade generated by this method is shown in Figure 2 shown.

[0050] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for designing return flow blades, characterized in that: Given geometric parameters: inlet and outlet installation angle α 5A , α 6A , the return inlet and outlet radii r5, r6, the inlet and outlet widths b5, b6, and the z coordinate of the side profile of the disk cover, z s and z h ; The radial coordinates from the inlet to the outlet of the recirculator are discretized into N equal parts, denoted as r5, r i , r i+1 ,…,r6, The radial coordinate is converted into a dimensionless radial position calculation formula as follows: R i ＝r i / r5 (1) The coordinates θ of any point on the median line are obtained by formula (2): i , Where P is the residual angular momentum coefficient of the return flow device, and P=b5tanα 5A / (b6tanα 6A ); R6 is the ratio of the return flow inlet and outlet radii, and R6＝r6 / r5 Find θ i Then, according to equations (3) and (4), the coordinates (X i , Y i ), the conversion relationship between the two coordinates is as follows: X i =r i cosθ i (3) Y i =r i sinθ i (4) The included angle α between the perpendicular line connecting the coordinates of the median line and the origin and the tangent of the median line i , can be obtained by formula (5): According to α i Find any radius r i The normal angle γ i : c i =90°-arctan(Y i / X i )*180 / π-a i (6) When generating the return flow blade, the original airfoil thickness is superimposed on the normals on both sides of the mid-line, that is, the data of the suction surface and pressure surface of the return flow blade are generated. The normal direction of each point on the mid-line is calculated and determined by formula (6).

2. A method for designing return flow blades according to claim 1, characterized in that: When the radial coordinates from the inlet to the outlet of the return flow device are discrete, the center line at the beginning and end of the return flow device blade is encrypted.

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