A design method for a tubular diffuser with a dovetail leading edge

Abstract

The present invention relates to a design method of a tubular diffuser with a dovetail leading edge for a high-pressure ratio and high-load centrifugal compressor, including first determining the inlet throat area and outlet area of ​​the tubular diffuser, the circumferential angle distribution of the center line of the pure radial straight-cone tube section, and then determining the three-coordinate distribution of the center line and the metal angle of the tubular diffuser outlet and the three-coordinate distribution of the center line of the curved tube section in the radial rotation axis; then determining the coordinate points of each cross section along the center line of the tubular diffuser to complete the modeling of the tubular diffuser; finally, according to the modeling of the tubular diffuser and the number of tubular diffusers, the design of the tubular diffuser is completed. The method realizes the rapid modeling of the tubular diffuser by modeling the pure radial straight-cone tube section of the tubular diffuser, the curved tube section modeling in the radial rotation axis, and the dovetail leading edge modeling of the tubular diffuser, and can also write a corresponding modeling program to build a centrifugal compressor optimization platform with a tubular diffuser.

Description

Technical Field

[0001] The invention relates to the field of centrifugal compressor design, in particular to a design method for a tubular diffuser of a centrifugal compressor with high pressure ratio and high load. Background Art

[0002] Modern aircraft engines have increasingly higher requirements for thrust-to-weight ratio and reliability. The development of advanced centrifugal compressors with high pressure ratio, high load and wide operating margin is a technical challenge that must be overcome to promote the development of my country's small and medium-sized aircraft engines.

[0003] The performance of a high-pressure ratio centrifugal compressor is mainly limited by the centrifugal impeller and the diffuser. Among them, there are several main problems with the diffuser of a high-pressure ratio centrifugal compressor: after the airflow passes through the upstream high-load centrifugal impeller, it shows strong unevenness, which makes the radial distribution of the attack angle of the downstream diffuser inlet uneven; the incoming flow has a high absolute velocity, which makes the Mach number of the downstream diffuser inlet transonic or even supersonic; the distance between the impeller outlet and the diffuser inlet is small, and under the influence of the above-mentioned incoming flow, the unsteady interference between the diffuser and the impeller is aggravated, which is not conducive to the matching between the impeller and the diffuser; the strong adverse pressure gradient will further increase the boundary layer thickness in the diffuser channel, aggravating the internal flow separation and aerodynamic losses.

[0004] The research and development of tubular diffusers can be traced back to the 1960s. Its unique dovetail leading edge can better cope with the uneven supersonic flow at the outlet of the high-pressure ratio centrifugal impeller, and has played a remarkable role in improving the performance of high-pressure ratio centrifugal compressors. It is a compact and efficient diffuser suitable for high-pressure ratio centrifugal compressors.

[0005] At present, there are few public documents on the design methods of tubular diffusers. In the existing technology, the description of the theoretical method of centerline and cross-section modeling of tubular diffusers in the design process of tubular diffusers is relatively simple, and there is a lack of theoretical guidance for the modeling of dovetail leading edge. Therefore, when carrying out the design work of tubular diffusers, there is a possibility that the dovetail leading edge is not available, and there are many technical difficulties. Summary of the invention

[0006] The purpose of the present invention is to avoid the shortcomings of the prior art and provide a method for designing a tubular diffuser with a dovetail leading edge by combining the aerodynamic parameters of a high-pressure ratio centrifugal impeller and the meridional flow channel data of a compressor to carry out the design and modeling of a tubular diffuser, thereby realizing the rapid modeling of the tubular diffuser.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a design method of a tubular diffuser provided with a dovetail leading edge, comprising the following steps:

[0008] Step 1: Define the input parameters, including:

[0009] (1) The centerline coordinates of the hub and casing of the centrifugal compressor tubular diffuser are: and ,Require In the pure radial straight-cone pipe section, the When it changes, it is considered that the radial-to-axial bending pipe segment shaping stage has begun;

[0010] (2) Inclination angle of tubular diffuser , refers to the center line of the tubular diffuser inlet, which is also the angle between the center line of the pure radial straight-conical tube section and the horizontal X-axis. Combined with the outlet airflow angle of the centrifugal impeller;

[0011] (3) Metal angle of tubular diffuser outlet , refers to the outlet metal angle of the compressor. In order to achieve axial airflow, the airflow angle at the compressor outlet is Given, , Pick ;

[0012] (4) Geometric throat length coefficient of tubular diffuser , refers to the ratio of the length of the throat area of ​​the straight pipe section to the throat diameter in the pure radial straight-taper pipe section. The cross-sectional area of ​​the throat area of ​​the straight pipe section remains unchanged, which is a constant throat area;

[0013] (5) Cone expansion angle , refers to the unilateral expansion angle of the tapered tube section in a pure radial straight-tapered tube section, which is given as less than 4 degrees;

[0014] (6) Absolute Mach number at the inlet of tubular diffuser and the absolute exit Mach number , absolute Mach number at the inlet of tubular diffuser Given according to the absolute Mach number at the centrifugal impeller outlet; the absolute Mach number at the tubular diffuser outlet Given as 0.15-0.3;

[0015] (7) Total pressure loss coefficient of tubular diffuser , used to calculate the total outlet pressure of the tubular diffuser ;

[0016] (8) Inlet and outlet blockage coefficients of tubular diffusers and , inlet blocking coefficient Given the absolute inlet Mach number Determine; outlet blockage coefficient Given as 0.02-0.03;

[0017] (9) Centrifugal compressor mass flow , total pressure at centrifugal impeller outlet , total temperature at centrifugal impeller outlet , the total outlet pressure of the tubular diffuser , the total outlet temperature of the tubular diffuser Number of single channels of tubular diffuser ;

[0018] Step 2: According to the absolute Mach number of the tubular diffuser outlet , Centrifugal compressor mass flow , Total pressure at centrifugal impeller outlet and total temperature , Total outlet pressure of tubular diffuser and total temperature , Absolute Mach number at the inlet of tubular diffuser , Tubular diffuser inlet blockage coefficient and outlet blockage coefficient , determine the inlet throat area of ​​the tubular diffuser and outlet area ;

[0019] Step 3: Based on the centerline coordinates of the hub and casing of the centrifugal compressor tubular diffuser and and tubular diffuser inclination , determine the circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser distribution, and then determine the three-coordinate distribution of the center line of the pure radial straight-conical tube section of the tubular diffuser;

[0020] Step 4: According to the circumferential angle corresponding to the end point of the centerline of the pure radial straight-conical tube section of the tubular diffuser , determine the centerline inlet metal angle of the radial to axial bend section ; According to the outlet airflow angle of tubular diffuser , determine the tubular diffuser outlet metal angle ; According to the radial to axial bending section center line inlet metal angle and tubular diffuser outlet metal angle , determine the circumferential angle of the centerline of the radial-to-axial bend section of the tubular diffuser distribution, and then determine the three-coordinate distribution of the center line of the radial-axial bending section of the tubular diffuser;

[0021] Step 5: According to the geometric throat length coefficient of the tubular diffuser , cone expansion angle , tubular diffuser inlet throat area The centerline coordinates of the hub and casing of the tubular diffuser and , determine the area distribution of the pure radial straight-conical pipe section;

[0022] Step 6: Based on the centerline coordinates of the hub and casing of the tubular diffuser and , pure radial straight-cone pipe section outlet area and tubular diffuser outlet area , determine the area distribution of the radial to axial bend section of the tubular diffuser;

[0023] Step 7: According to Step 2 to Step 6, different cross sections along the center line of the tubular diffuser are determined, thereby completing the single-channel shape design of the tubular diffuser;

[0024] Step 8: According to the centerline radius of the tubular diffuser , tubular diffuser inclination 、Number of single channels of tubular diffuser and the inlet throat area of ​​the tubular diffuser , The value range of is 16~34, which determines the shape of the dovetail leading edge of the tubular diffuser;

[0025] Step 9: According to the single-channel shape design of the tubular diffuser and the number of single channels of the tubular diffuser , completing the full circumference design of the tubular diffuser.

[0026] Furthermore, in step 2, the inlet throat area of ​​the tubular diffuser is determined and outlet area , including the following steps:

[0027] (1) Based on the estimated total pressure loss coefficient of the tubular diffuser , Total pressure at centrifugal impeller outlet and total temperature , determine the total outlet pressure of the tubular diffuser and outlet total temperature They are , ;

[0028] According to the absolute Mach number of the tubular diffuser inlet , determine the velocity coefficient at the centrifugal impeller outlet or tubular diffuser inlet for:

[0029] ,

[0030] Determine the density flow function corresponding to the velocity coefficient at the centrifugal impeller outlet for:

[0031] ,

[0032] in, Represents the adiabatic index of gas, where the working fluid is air, is 1.4;

[0033] (2) Based on the mass flow rate of the input centrifugal compressor , total pressure at centrifugal impeller outlet , total temperature at centrifugal impeller outlet , Tubular diffuser inlet blockage coefficient And the comprehensive constant , determine the inlet throat area of ​​the tubular diffuser for:

[0034] ,

[0035] Determine the absolute Mach number at the tubular diffuser outlet Corresponding speed coefficient for:

[0036] ,

[0037] Determine the corresponding dense flow function at the outlet of the tubular diffuser for:

[0038] ,

[0039] Determine the outlet area of ​​the tubular diffuser for:

[0040] .

[0041] Furthermore, when determining the three-coordinate distribution of the center line of the pure radial straight-cone pipe section of the tubular diffuser in step 3, it is necessary to ensure that the coordinates of the pure radial straight-cone pipe section area If unchanged, then:

[0042] , ,

[0043] in, is the circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser, It is the radial coordinate of the starting point of the centerline of the centrifugal compressor meridian flow diffuser, which is also the inlet radius size of the tubular diffuser.

[0044] Furthermore, the step 4 is specifically as follows:

[0045] The circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser in step 3 is Distribution method to determine the circumferential angle of the centerline end point of the pure radial straight-conical tube section of the tubular diffuser ;

[0046] According to the circumferential angle of the end point of the center line Determine the centerline inlet metal angle of the radial to axial bending section for:

[0047] ,

[0048] According to the outlet airflow angle of tubular diffuser Requirements, determine the outlet metal angle of the tubular diffuser for:

[0049] , for ;

[0050] According to the center line inlet metal angle of the tubular diffuser radial to axial bending section and outlet metal angle , design the Bezier curve of the metal angle distribution of the radial to axial bending section, the ordinate of the control point is the angle, and the abscissa is the normalized meridian flow channel centerline length,

[0051] Then, according to the formula relationship of the circumferential angle:

[0052] ,

[0053] ,

[0054] Determine the circumferential angle of the centerline of the radially rotating axial bend of the tubular diffuser The distribution is:

[0055] ,

[0056] ,

[0057] Combined with the above and Distribution completes the design of the center line of the tubular diffuser.

[0058] Furthermore, the step five is specifically as follows:

[0059] The area of ​​the geometric throat section remains unchanged, which is the same as the inlet throat area. Equal, the length is the geometric throat length factor Multiply by the inlet throat diameter; the area of ​​the conical section is linearly distributed according to the conical expansion angle , inlet throat diameter and cone length, and the cross-sectional area of ​​the cone outlet is obtained. , the area distribution of the tapered tube section can be determined, and then the area distribution of the pure radial straight-tapered tube section of the tubular diffuser can be obtained.

[0060] Furthermore, the step six is ​​specifically as follows:

[0061] According to the centerline coordinates of the hub and casing of the tubular diffuser and , pure radial straight-cone pipe section outlet area and tubular diffuser outlet area , design the Bezier curve of the area distribution of the radial-to-axial bend section. The ordinate of the Bezier curve control point is the cross-sectional area of ​​the tubular diffuser, and the abscissa is the normalized meridian flow channel centerline length, which determines the area distribution of the radial-to-axial bend section of the tubular diffuser.

[0062] Furthermore, the step seven is specifically as follows:

[0063] The different cross-sections of the center line of the tubular diffuser include a pure radial straight-conical pipe section cross-section and a radial-rotating axial curved pipe section cross-section. The normal vector corresponding to the cross-section is determined according to the coordinates of the center line point of the tubular diffuser. for:

[0064] ,

[0065] According to the cross-sectional area distribution of the tubular diffuser, the centerline point coordinates of the tubular diffuser, the normal vector corresponding to the cross section and the cross-sectional equation , then the three coordinates of the cross section along the center line of the tubular diffuser are:

[0066] ,

[0067] in, , Indicates rounding to the nearest integer. It means to take the integer before the decimal point directly; and Represents two mutually perpendicular unit vectors on the cross section, and they are both perpendicular to the normal vector corresponding to the cross section In addition, in order to ensure that the output cross-section major axis endpoints and center points are on the circle of the corresponding radius, the two unit vectors selected and It is not arbitrary, one of them should be tangent to the corresponding radius torus, that is:

[0068] ,

[0069] ,

[0070] ,

[0071] Thus, the cross-sectional equation that meets the requirements is obtained. It should be noted that when m and n take different values, the corresponding cross-sectional shapes are also different; when m=n=1, the cross-section is rhombus, but considering that it is not conducive to the internal flow of the diffuser, the rhombus cross-section is not considered; when m=n=2, the cross-section is circular or elliptical, depending on whether the given a and b values ​​are the same; when m or n is greater than 2, the cross-section is elliptical, and the larger m and n are, the closer the cross-sectional shape is to a rectangle.

[0072] Furthermore, the pure radial straight-cone pipe section has a circular cross section; the curved pipe section in the radial rotation axis has an elliptical cross section, and m and n transition linearly from 2 to 6.

[0073] Furthermore, the step eight is specifically as follows:

[0074] The leading edge of the tubular diffuser is a dovetail leading edge formed by the intersection of adjacent pipes. However, if the given design parameters do not meet the conditions, the designed tubular diffuser will not have such a dovetail leading edge. Assuming that the center line of the tubular diffuser is parallel to the X-axis, its tangent circle radius is , the definition points B and G represent the starting point and end point of the dovetail leading edge of the tubular diffuser, respectively. satisfy When , a dovetail leading edge appears. The corresponding plane coordinates The formula is as follows:

[0075] ,

[0076] in, represents the single channel angle, that is , when the cross-sectional shape of the geometric throat is circular, Indicates the radius of the circle; when the cross-sectional shape of the geometric throat is an ellipse or a quasi-ellipse, represents the major axis or semi-major axis size, which is equivalent to half the width of the meridian flow channel, from which the Pythagorean theorem gives Dimensions to determine whether the designed tubular diffuser has a dovetail leading edge;

[0077] Similarly, the coordinates of the starting point B of the dovetail leading edge are obtained as follows:

[0078] ,

[0079] ,

[0080] Thus, a dovetail leading edge line of the tubular diffuser is obtained. After the pure radial straight-conical tube and the radial axial curved tube section are formed, the diffuser is stretched and cut according to the dovetail leading edge line to complete the shaping of the dovetail leading edge on one side. The coordinate point of the dovetail leading edge line on the other side of the tubular diffuser is and The coordinates of points B and G can be combined with , obtained by coordinate transformation, the formula is as follows:

[0081] ,

[0082] ,

[0083] Since the center line of the given tubular diffuser is not parallel to the X-axis, the coordinates of the two dovetail leading edge lines are transformed again by coordinate transformation. At this time, the angle between the two center lines is , so the coordinate point formulas of the two lines are as follows:

[0084] ,

[0085] ,

[0086] ,

[0087] ,

[0088] Inlet angle of attack of tubular diffuser The airflow angle calculated by combining the dovetail leading edge point G and numerical simulation OK, imported metal angle The formula is as follows:

[0089] ,

[0090] The inlet angle of attack of the tubular diffuser is obtained from this for:

[0091] ,

[0092] According to the above two dovetail leading edge lines, the dovetail leading edge is cut out. The starting point of the center line needs to be extended. The corresponding circle radius here , corresponding to the coordinates for:

[0093] ,

[0094] The dovetail leading edge and the extension line of the centerline starting point both belong to the pure radial straight-conical tube section of the tubular diffuser, so their z coordinates are all constants, and the cross-section at the centerline starting point is consistent with the cross-section at the geometric throat of the diffuser, thus completing the shaping of the dovetail leading edge of the tubular diffuser.

[0095] The beneficial effects of the present invention are as follows: the present invention provides a modeling method for a tubular diffuser with a dovetail leading edge for a high pressure ratio and high load centrifugal compressor. According to this method, in combination with the aerodynamic parameters of the designed high pressure ratio centrifugal impeller and the data of the compressor meridian flow channel, the four parts of the tubular diffuser can be modeled, including the modeling of a pure radial straight-conical pipe section, the modeling of a radial-rotating axial curved pipe section, the modeling of a diffuser dovetail leading edge and the modeling of a bladeless diffuser section, thereby realizing the rapid modeling of the tubular diffuser. A corresponding modeling program can also be written to build an optimization platform for a centrifugal compressor with a tubular diffuser. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Figure 1 is a flow chart of the process of the tubular diffuser design method of the present invention;

[0097] Figure 2 The centerline metal angle and circumferential angle distribution of the tubular diffuser of the test example of the present invention are divided into two parts: a pure radial straight-conical tube section and a radial-to-axial curved tube section;

[0098] Figure 3 It is the distribution of the area coefficient of the tubular diffuser from the inlet geometric throat to the outlet of the test example of the present invention, which is divided into two parts: a pure radial straight-conical pipe section and a radial-to-axial curved pipe section;

[0099] Figure 4 It is a plane sketch of a tubular diffuser of a test example of the present invention, which is used to explain the method of judging whether a dovetail leading edge exists and the calculation source of its inlet and outlet coordinate points;

[0100] Figure 5 The flat grass of the tubular diffuser of the test example of the present invention Figure 4 A partial enlarged view of

[0101] Figure 6 Schematic diagram of the center line and selected cross section of a tubular diffuser of a test example of the present invention;

[0102] Figure 7 It is a schematic diagram of the molding modeling of a single channel of a tubular diffuser of a test example of the present invention;

[0103] Figure 8 It is a schematic diagram of the molding modeling of the full channel of the tubular diffuser of the test example cited in the present invention. DETAILED DESCRIPTION

[0104] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0105] In order to achieve the above object, the present invention provides the following specific implementation methods:

[0106] Example 1: Figure 1 As shown, a design method of a tubular diffuser provided with a dovetail leading edge comprises the following steps:

[0107] Step 1: Define the input parameters, including:

[0108] (1) The centerline coordinates of the hub and casing of the centrifugal compressor tubular diffuser are: and ,Require In the pure radial straight-cone pipe section, the When it changes, it is considered that the radial-to-axial bending pipe segment shaping stage has begun;

[0109] (2) Inclination angle of tubular diffuser , refers to the center line of the tubular diffuser inlet, which is also the angle between the center line of the pure radial straight-conical tube section and the horizontal X-axis. Combined with the outlet airflow angle of the centrifugal impeller;

[0110] (3) Metal angle of tubular diffuser outlet , refers to the outlet metal angle of the compressor. In order to achieve axial airflow, the airflow angle at the compressor outlet is Given, , Pick ;

[0111] (4) Geometric throat length coefficient of tubular diffuser , refers to the ratio of the length of the throat area of ​​the straight pipe section to the throat diameter in the pure radial straight-taper pipe section. The cross-sectional area of ​​the throat area of ​​the straight pipe section remains unchanged, which is a constant throat area;

[0112] (5) Cone expansion angle , refers to the unilateral expansion angle of the tapered tube section in a pure radial straight-tapered tube section, which is given as less than 4 degrees;

[0113] (6) Absolute Mach number at the inlet of tubular diffuser and the absolute exit Mach number , absolute Mach number at the inlet of tubular diffuser Given according to the absolute Mach number at the centrifugal impeller outlet; the absolute Mach number at the tubular diffuser outlet Given as 0.15-0.3;

[0114] (7) Total pressure loss coefficient of tubular diffuser , used to calculate the total outlet pressure of the tubular diffuser ;

[0115] (8) Inlet and outlet blockage coefficients of tubular diffusers and , inlet blocking coefficient Given the absolute inlet Mach number Determine; outlet blockage coefficient Given as 0.02-0.03;

[0116] (9) Centrifugal compressor mass flow , total pressure at centrifugal impeller outlet , total temperature at centrifugal impeller outlet , the total outlet pressure of the tubular diffuser , the total outlet temperature of the tubular diffuser Number of single channels of tubular diffuser ;

[0117] Step 2: According to the absolute Mach number of the tubular diffuser outlet , Centrifugal compressor mass flow , Total pressure at centrifugal impeller outlet and total temperature , Total outlet pressure of tubular diffuser and total temperature , Absolute Mach number at the inlet of tubular diffuser , Tubular diffuser inlet blockage coefficient and outlet blockage coefficient , determine the inlet throat area of ​​the tubular diffuser and outlet area , including the following steps:

[0118] (1) Based on the estimated total pressure loss coefficient of the tubular diffuser , Total pressure at centrifugal impeller outlet and total temperature , determine the total outlet pressure of the tubular diffuser and outlet total temperature They are , ;

[0119] According to the absolute Mach number of the tubular diffuser inlet , determine the velocity coefficient at the centrifugal impeller outlet or tubular diffuser inlet for:

[0120] ,

[0121] Determine the density flow function corresponding to the velocity coefficient at the centrifugal impeller outlet for:

[0122] ,

[0123] in, Represents the adiabatic index of gas, where the working fluid is air, is 1.4;

[0124] (2) Based on the mass flow rate of the input centrifugal compressor , total pressure at centrifugal impeller outlet , total temperature at centrifugal impeller outlet , Tubular diffuser inlet blockage coefficient And the comprehensive constant , determine the inlet throat area of ​​the tubular diffuser for:

[0125] ,

[0126] Determine the absolute Mach number at the tubular diffuser outlet Corresponding speed coefficient for:

[0127] ,

[0128] Determine the corresponding dense flow function at the outlet of the tubular diffuser for:

[0129] ,

[0130] Determine the outlet area of ​​the tubular diffuser for:

[0131] .

[0132] Step 3: Based on the centerline coordinates of the hub and casing of the centrifugal compressor tubular diffuser and and tubular diffuser inclination , determine the circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser Distribution, and then determine the three-coordinate distribution of the center line of the pure radial straight-cone pipe section of the tubular diffuser. When determining the three-coordinate distribution of the center line of the pure radial straight-cone pipe section of the tubular diffuser, it is necessary to ensure that the coordinates in the pure radial straight-cone pipe section area If unchanged, then:

[0133] , ,

[0134] in, is the circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser, It is the radial coordinate of the starting point of the centerline of the centrifugal compressor meridian flow diffuser, which is also the inlet radius size of the tubular diffuser.

[0135] Step 4: According to the circumferential angle corresponding to the end point of the centerline of the pure radial straight-conical tube section of the tubular diffuser , determine the centerline inlet metal angle of the radial to axial bend section ; According to the outlet airflow angle of tubular diffuser , determine the tubular diffuser outlet metal angle ; According to the radial to axial bending section center line inlet metal angle and tubular diffuser outlet metal angle , determine the circumferential angle of the centerline of the radial-to-axial bend section of the tubular diffuser Distribution, and then determine the three-coordinate distribution of the center line of the radial-axial bending section of the tubular diffuser, specifically:

[0136] The circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser in step 3 is Distribution method to determine the circumferential angle of the centerline end point of the pure radial straight-conical tube section of the tubular diffuser ;

[0137] According to the circumferential angle of the end point of the center line Determine the centerline inlet metal angle of the radial to axial bending section for:

[0138] ,

[0139] According to the outlet airflow angle of tubular diffuser Requirements, determine the outlet metal angle of the tubular diffuser for:

[0140] , for ;

[0141] According to the center line inlet metal angle of the tubular diffuser radial to axial bending section and outlet metal angle , design the Bezier curve of the metal angle distribution of the radial to axial bending section, the ordinate of the control point is the angle, and the abscissa is the normalized meridian flow channel centerline length,

[0142] Then, according to the formula relationship of the circumferential angle:

[0143] ,

[0144] ,

[0145] Determine the circumferential angle of the centerline of the radially rotating axial bend of the tubular diffuser The distribution is:

[0146] ,

[0147] ,

[0148] Combined with the above and Distribution completes the design of the center line of the tubular diffuser.

[0149] Step 5: According to the geometric throat length coefficient of the tubular diffuser , cone expansion angle , tubular diffuser inlet throat area The centerline coordinates of the hub and casing of the tubular diffuser and , determine the area distribution of the pure radial straight-conical pipe section, specifically:

[0150] The area of ​​the geometric throat section remains unchanged, which is the same as the inlet throat area. Equal, the length is the geometric throat length factor Multiply by the inlet throat diameter; the area of ​​the conical section is linearly distributed according to the conical expansion angle , inlet throat diameter and cone length, and the cross-sectional area of ​​the cone outlet is obtained. , the area distribution of the tapered tube section can be determined, and then the area distribution of the pure radial straight-tapered tube section of the tubular diffuser can be obtained.

[0151] Step 6: Based on the centerline coordinates of the hub and casing of the tubular diffuser and , pure radial straight-cone pipe section outlet area and tubular diffuser outlet area , determine the area distribution of the radial to axial bend section of the tubular diffuser, specifically:

[0152] According to the centerline coordinates of the hub and casing of the tubular diffuser and , pure radial straight-cone pipe section outlet area and tubular diffuser outlet area , design the Bezier curve of the area distribution of the radial-to-axial bend section. The ordinate of the Bezier curve control point is the cross-sectional area of ​​the tubular diffuser, and the abscissa is the normalized meridian flow channel centerline length, which determines the area distribution of the radial-to-axial bend section of the tubular diffuser.

[0153] Step 7: According to Steps 2 to 6, determine the different cross-sections along the centerline of the tubular diffuser, thereby completing the single-channel shape design of the tubular diffuser, specifically:

[0154] The different cross-sections of the center line of the tubular diffuser include a pure radial straight-conical pipe section cross-section and a radial-rotating axial curved pipe section cross-section. The normal vector corresponding to the cross-section is determined according to the coordinates of the center line point of the tubular diffuser. for:

[0155] ,

[0156] According to the cross-sectional area distribution of the tubular diffuser, the centerline point coordinates of the tubular diffuser, the normal vector corresponding to the cross section and the cross-sectional equation , then the three coordinates of the cross section along the center line of the tubular diffuser are:

[0157] ,

[0158] in, , Indicates rounding to the nearest integer. It means to take the integer before the decimal point directly; and Represents two mutually perpendicular unit vectors on the cross section, and they are both perpendicular to the normal vector corresponding to the cross section In addition, in order to ensure that the output cross-section major axis endpoints and center points are on the circle of the corresponding radius, the two unit vectors selected and It is not arbitrary, one of them should be tangent to the corresponding radius torus, that is:

[0159] ,

[0160] ,

[0161] ,

[0162] Thus, the cross-sectional equation that meets the requirements is obtained. It should be noted that when m and n take different values, the corresponding cross-sectional shapes are also different; when m=n=1, the cross-section is rhombus, but considering that it is not conducive to the internal flow of the diffuser, the rhombus cross-section is not considered; when m=n=2, the cross-section is circular or elliptical, depending on whether the given a and b values ​​are the same; when m or n is greater than 2, the cross-section is elliptical, and the larger m and n are, the closer the cross-sectional shape is to a rectangle.

[0163] Step 8: According to the centerline radius of the tubular diffuser , tubular diffuser inclination 、Number of single channels of tubular diffuser and the inlet throat area of ​​the tubular diffuser , The value range of is 16~34, which determines the shape of the dovetail leading edge of the tubular diffuser, specifically:

[0164] The leading edge of the tubular diffuser is a dovetail leading edge formed by the intersection of adjacent pipes. However, if the given design parameters do not meet the conditions, the designed tubular diffuser will not have such a dovetail leading edge. Assuming that the center line of the tubular diffuser is parallel to the X-axis, its tangent circle radius is , the definition points B and G represent the starting point and end point of the dovetail leading edge of the tubular diffuser, respectively. satisfy When , a dovetail leading edge appears. The corresponding plane coordinates The formula is as follows:

[0165] ,

[0166] in, represents the single channel angle, that is , when the cross-sectional shape of the geometric throat is circular, Indicates the radius of the circle; when the cross-sectional shape of the geometric throat is an ellipse or a quasi-ellipse, represents the major axis or semi-major axis size, which is equivalent to half the width of the meridian flow channel, from which the Pythagorean theorem gives Dimensions to determine whether the designed tubular diffuser has a dovetail leading edge;

[0167] Similarly, the coordinates of the starting point B of the dovetail leading edge are obtained as follows:

[0168] ,

[0169] ,

[0170] Thus, a dovetail leading edge line of the tubular diffuser is obtained. After the pure radial straight-conical tube and the radial axial curved tube section are formed, the diffuser is stretched and cut according to the dovetail leading edge line to complete the shaping of the dovetail leading edge on one side. The coordinate point of the dovetail leading edge line on the other side of the tubular diffuser is and The coordinates of points B and G can be combined with , obtained by coordinate transformation, the formula is as follows:

[0171] ,

[0172] ,

[0173] Since the center line of the given tubular diffuser is not parallel to the X-axis, the coordinates of the two dovetail leading edge lines are transformed again by coordinate transformation. At this time, the angle between the two center lines is , so the coordinate point formulas of the two lines are as follows:

[0174] ,

[0175] ,

[0176] ,

[0177] ,

[0178] Inlet angle of attack of tubular diffuser The airflow angle calculated by combining the dovetail leading edge point G and numerical simulation OK, imported metal angle The formula is as follows:

[0179] ,

[0180] The inlet angle of attack of the tubular diffuser is obtained from this for:

[0181] ,

[0182] According to the above two dovetail leading edge lines, the dovetail leading edge is cut out. The starting point of the center line needs to be extended. The corresponding circle radius here , corresponding to the coordinates for:

[0183] ,

[0184] The dovetail leading edge and the extension line of the centerline starting point both belong to the pure radial straight-conical tube section of the tubular diffuser, so their z coordinates are all constants, and the cross-section at the centerline starting point is consistent with the cross-section at the geometric throat of the diffuser, thus completing the shaping of the dovetail leading edge of the tubular diffuser.

[0185] Example 2 is the same as Example 1, except that the pure radial straight-conical pipe section in step seven is a circular cross-section; the curved pipe section in the radial rotation axis is an elliptical cross-section, and m and n transition linearly from 2 to 6.

[0186] like Figure 2-8 To further illustrate the technical solution of the present invention, the following specific test examples are provided:

[0187] Determine the centerline shape of the tubular diffuser. Specifically, the tubular diffuser is mainly divided into two parts along the gas flow direction: a pure radial straight-conical tube section and a radial-rotating axial curved tube section. According to the provided centrifugal compressor tubular diffuser hub and casing meridian flow channel centerline coordinates and , diffuser inclination angle and tubular diffuser outlet metal angle , determine the metal angle and circumferential angle distribution of the tubular diffuser, such as Figure 2 As shown, the ordinate is the metal angle of the center line, the abscissa is the normalized meridian flow channel center line length, the unit is %, the dotted line represents the center line metal angle distribution of the pure radial straight-conical tube section of the tubular diffuser, the solid line represents the center line metal angle distribution of the radial rotation axis of the curved tube section of the tubular diffuser, which is controlled by a Bezier curve, and the designer adjusts it according to the needs to achieve different forms of radial rotation axis The center line distribution of the curved tube section; the dotted line represents the circumferential angle distribution of the center line of the tubular diffuser, which is converted from the metal angle distribution of the center line of the tubular diffuser, and then, according to the circumferential angle distribution of the center line, the three-coordinate distribution of the center line of the tubular diffuser is determined.

[0188] Determining the three-coordinate distribution of the center line of the tubular diffuser includes the following steps: according to the provided coordinates of the center line of the hub and the casing of the tubular diffuser, and Japanese diffuser inclination , determine the circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser The distribution is:

[0189] ,

[0190] According to the circumferential angle of the center line of the pure radial straight-conical tube section of the tubular diffuser Distribution, determine the three-coordinate distribution of the center line of the pure radial straight-conical tube section of the tubular diffuser as follows:

[0191] ;

[0192] According to the circumferential angle of the end point of the center line of the pure radial straight-taper pipe section and tubular diffuser outlet metal angle , design the metal angle distribution of the center line of the tubular diffuser in the radial-to-axial bending section, and then determine the circumferential angle distribution of the center line of the tubular diffuser in the radial-to-axial bending section.

[0193] According to the formula relationship of circumferential angle:

[0194] ,

[0195] ,

[0196] Determine the circumferential angle distribution of the center line of the curved pipe section of the tubular diffuser in the radial direction:

[0197] ,

[0198] According to the circumferential angle of the center line of the curved pipe section of the tubular diffuser Distribution, determine the three-coordinate distribution of the center line of the curved pipe section of the tubular diffuser in the radial direction:

[0199] .

[0200] Determining the cross-sectional area distribution of the tubular diffuser along the center line includes the following steps: according to the geometric throat length coefficient of the tubular diffuser , cone expansion angle , tubular diffuser inlet throat area The centerline coordinates of the hub and casing of the tubular diffuser and , determine the area distribution of the pure radial straight-conical pipe section; the area of ​​the geometric throat section remains unchanged, which is the same as the inlet throat area Equal, the length is the geometric throat length factor Multiply by the inlet throat diameter;

[0201] The area of ​​the cone section is distributed linearly according to the cone expansion angle. , inlet throat diameter and cone length, and the cross-sectional area of ​​the cone outlet is obtained. , the area distribution of the tapered tube section can be determined, and then the area distribution of the pure radial straight-tapered tube section of the tubular diffuser can be obtained.

[0202] According to the centerline coordinates of the hub and casing of the tubular diffuser, and , pure radial straight-cone pipe section outlet area and tubular diffuser outlet area , determine the area distribution of the radial to axial bend section of the tubular diffuser; Figure 3 As shown, the ordinate is the cross-sectional area coefficient of the tubular diffuser, which is obtained by dividing the actual cross-sectional area by the inlet throat area of ​​the tubular diffuser. It is obtained that the horizontal axis is the normalized length of the centerline of the meridian flow channel, and the unit is %. The dotted line represents the geometric throat area distribution of the pure radial straight-conical section of the tubular diffuser, the dotted line represents the cone section area distribution of the pure radial straight-conical section of the tubular diffuser, and the solid line represents the area distribution of the curved section in the radial rotation axis of the tubular diffuser, which is controlled by a Bezier curve, and the designer can adjust it according to the needs.

[0203] like Figure 6 As shown, determining the three-coordinate distribution coordinate point distribution of the cross section of the tubular diffuser along the center line includes the following steps: according to the center line point coordinates of the tubular diffuser, the cross-sectional area distribution of the tubular diffuser, and the normal vector corresponding to the cross section and the cross-sectional equation , determine the three coordinates of the cross section along the center line of the tubular diffuser:

[0204] ,

[0205] in, , Indicates rounding to the nearest integer. It means to take the integer before the decimal point directly; and Represents two mutually perpendicular unit vectors on the cross section, and they are both perpendicular to the normal vector corresponding to the cross section In addition, in order to ensure that the output cross-section major axis endpoints and center points are on the circle of the corresponding radius, the two unit vectors selected and It is not arbitrary, one of them should be tangent to the corresponding radius torus, that is:

[0206] , ,

[0207] When m and n take different values, the corresponding cross-sectional shapes are also different.

[0208] The pure radial straight-taper pipe section of this test example uses a circular cross section; the curved pipe section in the radial rotation axis uses a quasi-elliptical cross section, and m and n can be linearly transitioned from 2 to 6. Because the quasi-ellipse equation is relatively complex, it is not easy to obtain the area formula for m and n by integrating, but its area is the same as the area formula of the ellipse is proportional to In this way, the elliptical cross-sectional area for different m and n can be obtained.

[0209] The coefficients corresponding to different m and n As shown in Table 1, when m and n are non-integers between 2 and 9, the corresponding coefficients are It can be obtained by interpolation.

[0210] Table 1

[0211]

[0212] like Figure 4 , Figure 5 and Figure 6As shown, determining the shape of the dovetail leading edge of the tubular diffuser includes the following steps: An important feature of the tubular diffuser is its large forward-swept dovetail leading edge, which is formed by the intersection of adjacent pipes. However, if the given design parameters do not meet the conditions, the designed tubular diffuser will not have such a dovetail leading edge.

[0213] For ease of understanding, assume that the center line of the tubular diffuser is parallel to the X-axis and its tangent circle radius is Points B and G in the figure represent the starting point and end point of the dovetail leading edge of the tubular diffuser. satisfy When the dovetail leading edge appears. Figure 5 and three According to the principle of angular similarity, The corresponding plane coordinates The formula is as follows:

[0214] ,

[0215] in, represents the single channel angle, that is , when the cross-sectional shape of the geometric throat is circular, Indicates the radius of the circle; when the cross-sectional shape of the geometric throat is an ellipse or a quasi-ellipse, represents the major axis or semi-major axis size, which is equivalent to half the width of the meridian flow channel, from which the Pythagorean theorem gives size to determine whether the designed tubular diffuser has a dovetail leading edge.

[0216] Similarly, the coordinates of the starting point B of the dovetail leading edge can be obtained as follows:

[0217] ,

[0218] ,

[0219] Thus, a dovetail leading edge line of the tubular diffuser is obtained. After the pure radial straight-conical tube and the radial axial curved tube section are formed, the diffuser is stretched and cut according to the dovetail leading edge line to complete the shaping of the dovetail leading edge on one side. The coordinate point of the dovetail leading edge line on the other side of the tubular diffuser is and The coordinates of points B and G can be combined with , obtained by coordinate transformation, the formula is as follows:

[0220] ,

[0221] ,

[0222] Since the center line of the given tubular diffuser is not parallel to the X-axis, the coordinates of the two dovetail leading edge lines can be transformed again by coordinate transformation. Note that the angle between the two center lines is , so the coordinate point formulas of the two lines are as follows:

[0223] ,

[0224] ,

[0225] ,

[0226] ,

[0227] The inlet angle of attack of the tubular diffuser can be obtained by combining the dovetail leading edge point G and the airflow angle calculated by numerical simulation. OK, imported metal angle The formula is as follows:

[0228] ,

[0229] From this we can know the inlet angle of attack of the tubular diffuser for:

[0230] ,

[0231] pass Figure 5 It can be found that according to the above two dovetail leading edge lines, the dovetail leading edge is cut out, and the starting point of the center line needs to be extended. The corresponding circle radius here is , corresponding to the coordinates for:

[0232] ,

[0233] The dovetail leading edge and the extension line of the centerline starting point belong to the pure radial straight-conical tube section of the tubular diffuser, so their z coordinates are fixed values. The cross section at the centerline starting point must be consistent with the cross section at the diffuser geometric throat; the dovetail leading edge cut out by the dovetail leading edge line is as follows: Figure 7 As shown. The single-channel design of the tubular diffuser is completed;

[0234] In order to facilitate numerical calculation, the tubular diffuser is connected to the upstream centrifugal impeller, and the bladeless diffuser section is added, including the following steps: and single channel angle Determine the annular surface where the tubular diffuser connects to the impeller outlet. The corresponding annular surface is cut off from the tubular diffuser to obtain the diffuser inlet annular surface. By lofting these two annular surfaces, the bladeless diffuser section is modeled, and then the single-channel design of the tubular diffuser is completed.

[0235] According to the shape of the tubular diffuser and the number of single channels of the tubular diffuser , completing the full channel design of the tubular diffuser.

[0236] like Figure 8 As shown, the tubular diffuser of the selected example of the present invention is designed by the design method of the tubular diffuser described above. A major feature of the tubular diffuser is the presence of a large forward-swept dovetail leading edge structure formed by the intersection of adjacent diffuser pipes. This type of leading edge enables the tubular diffuser to better cope with the high Mach number non-uniform incoming flow at transonic speed, reduce the shock wave intensity in the channel, and the weak rotation component brought by the leading edge can redistribute the low-energy fluid inside the diffuser, reduce the aerodynamic load of the diffuser, and thus improve the performance of the high-pressure ratio centrifugal compressor.

[0237] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for designing a tubular diffuser with a dovetail leading edge, characterized in that: The following steps are involved: Step 1: Define the input parameters, including: (1) The centerline coordinates of the hub and casing of the centrifugal compressor tubular diffuser are: and ,Require In the pure radial straight-cone pipe section, the When it changes, it is considered that the radial-to-axial bending pipe segment shaping stage has begun; (2) Inclination angle of tubular diffuser , refers to the center line of the tubular diffuser inlet, which is also the angle between the center line of the pure radial straight-conical tube section and the horizontal X-axis. Combined with the outlet airflow angle of the centrifugal impeller; (3) Metal angle of tubular diffuser outlet , refers to the outlet metal angle of the compressor. In order to achieve axial airflow, the airflow angle at the compressor outlet is Given, , Pick ; (4) Geometric throat length coefficient of tubular diffuser , refers to the ratio of the length of the throat area of ​​the straight pipe section to the throat diameter in the pure radial straight-taper pipe section. The cross-sectional area of ​​the throat area of ​​the straight pipe section remains unchanged, which is a constant throat area; (5) Cone expansion angle , refers to the unilateral expansion angle of the tapered tube section in a pure radial straight-tapered tube section, which is given as less than 4 degrees; (6) Absolute Mach number at the inlet of tubular diffuser and the absolute exit Mach number , absolute Mach number at the inlet of tubular diffuser Given according to the absolute Mach number at the centrifugal impeller outlet; the absolute Mach number at the tubular diffuser outlet Given as 0.15-0.3; (7) Total pressure loss coefficient of tubular diffuser , used to calculate the total outlet pressure of the tubular diffuser ; (8) Inlet and outlet blockage coefficients of tubular diffusers and , inlet blocking coefficient Given the absolute inlet Mach number Determine; outlet blockage coefficient Given as 0.02-0.03; (9) Centrifugal compressor mass flow , total pressure at centrifugal impeller outlet , total temperature at centrifugal impeller outlet , the total outlet pressure of the tubular diffuser , the total outlet temperature of the tubular diffuser Number of single channels of tubular diffuser ; Step 2: According to the absolute Mach number of the tubular diffuser outlet , Centrifugal compressor mass flow , Total pressure at centrifugal impeller outlet and total temperature , Total outlet pressure of tubular diffuser and total temperature , Absolute Mach number at the inlet of tubular diffuser , Tubular diffuser inlet blockage coefficient and outlet blockage coefficient , determine the inlet throat area of ​​the tubular diffuser and outlet area ; Step 3: Based on the centrifugal compressor tubular diffuser hub and casing meridian flow channel centerline coordinates and and tubular diffuser inclination , determine the circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser Distribution, and then determine the three-coordinate distribution of the center line of the pure radial straight-conical tube section of the tubular diffuser; Step 4: According to the circumferential angle corresponding to the end point of the centerline of the pure radial straight-conical tube section of the tubular diffuser , determine the centerline inlet metal angle of the radial to axial bend section ; According to the outlet airflow angle of tubular diffuser , determine the tubular diffuser outlet metal angle ; According to the radial to axial bending section center line inlet metal angle and tubular diffuser outlet metal angle , determine the circumferential angle of the centerline of the radial-to-axial bend section of the tubular diffuser distribution, and then determine the three-coordinate distribution of the center line of the radial-axial bending section of the tubular diffuser; Step 5: According to the geometric throat length coefficient of the tubular diffuser , cone expansion angle , Tubular diffuser inlet throat area The centerline coordinates of the hub and casing of the tubular diffuser and , determine the area distribution of the pure radial straight-conical pipe section; Step 6: Based on the centerline coordinates of the hub and casing of the tubular diffuser and , pure radial straight-cone pipe section outlet area and tubular diffuser outlet area , determine the area distribution of the radial to axial bend section of the tubular diffuser; Step 7: According to Step 2 to Step 6, different cross sections along the center line of the tubular diffuser are determined, thereby completing the single-channel shape design of the tubular diffuser; Step 8: According to the centerline radius of the tubular diffuser , tubular diffuser inclination 、Number of single channels of tubular diffuser and the inlet throat area of ​​the tubular diffuser , The value range of is 16 to 34, which determines the shape of the dovetail leading edge of the tubular diffuser, specifically: The leading edge of the tubular diffuser is a dovetail leading edge formed by the intersection of adjacent pipes. However, if the given design parameters do not meet the conditions, the designed tubular diffuser will not have such a dovetail leading edge. Assuming that the center line of the tubular diffuser is parallel to the X-axis, its tangent circle radius is , the definition points B and G represent the starting point and end point of the dovetail leading edge of the tubular diffuser, respectively. satisfy When , a dovetail leading edge appears. The corresponding plane coordinates The formula is as follows: ， in, represents the single channel angle, that is , when the cross-sectional shape of the geometric throat is circular, Indicates the radius of the circle; when the cross-sectional shape of the geometric throat is an ellipse or a quasi-ellipse, represents the major axis or semi-major axis size, which is equivalent to half the width of the meridian flow channel, from which the Pythagorean theorem gives Dimensions to determine whether the designed tubular diffuser has a dovetail leading edge; Similarly, the coordinates of the starting point B of the dovetail leading edge are obtained as follows: ， ， Thus, a dovetail leading edge line of the tubular diffuser is obtained. After the pure radial straight-conical tube and the radial axial curved tube section are formed, the diffuser is stretched and cut according to the dovetail leading edge line to complete the shaping of the dovetail leading edge on one side. The coordinate point of the dovetail leading edge line on the other side of the tubular diffuser is and The coordinates of points B and G can be combined with , obtained by coordinate transformation, the formula is as follows: ， ， Since the center line of the given tubular diffuser is not parallel to the X-axis, the coordinates of the two dovetail leading edge lines are transformed again by coordinate transformation. At this time, the angle between the two center lines is , so the coordinate point formulas of the two lines are as follows: ， ， ， ， Inlet angle of attack of tubular diffuser The airflow angle calculated by combining the dovetail leading edge point G and numerical simulation OK, imported metal angle The formula is as follows: ， The inlet angle of attack of the tubular diffuser is obtained from this for: ， According to the above two dovetail leading edge lines, the dovetail leading edge is cut out. The starting point of the center line needs to be extended. The corresponding circle radius here , corresponding to the coordinates for: ， The dovetail leading edge and the extension line of the centerline starting point both belong to the pure radial straight-conical tube section of the tubular diffuser, so their z coordinates are all constant values, and the cross section at the centerline starting point is consistent with the cross section at the diffuser geometric throat, thus completing the shaping of the dovetail leading edge of the tubular diffuser; Step 9: According to the single-channel shape design of the tubular diffuser and the number of single channels of the tubular diffuser , completing the full circumference design of the tubular diffuser.

2. A method for designing a tubular diffuser with a dovetail leading edge according to claim 1, characterized in that: In the step 2, the inlet throat area of ​​the tubular diffuser is determined and outlet area , including the following steps: (1) Based on the estimated total pressure loss coefficient of the tubular diffuser , Total pressure at centrifugal impeller outlet and total temperature , determine the total outlet pressure of the tubular diffuser and outlet total temperature They are , ; According to the absolute Mach number of the tubular diffuser inlet , determine the velocity coefficient at the centrifugal impeller outlet or tubular diffuser inlet for: ， Determine the density flow function corresponding to the velocity coefficient at the centrifugal impeller outlet for: ， in, Represents the adiabatic index of gas, where the working fluid is air, is 1.4; (2) Based on the mass flow rate of the input centrifugal compressor , total pressure at centrifugal impeller outlet , total temperature at centrifugal impeller outlet , Tubular diffuser inlet blockage coefficient And the comprehensive constant , determine the inlet throat area of ​​the tubular diffuser for: ， Determine the absolute Mach number at the tubular diffuser outlet Corresponding speed coefficient for: ， Determine the corresponding dense flow function at the outlet of the tubular diffuser for: ， Determine the outlet area of ​​the tubular diffuser for: 。 3. A method for designing a tubular diffuser with a dovetail leading edge as claimed in claim 1, characterized in that: When determining the three-coordinate distribution of the center line of the pure radial straight-cone pipe section of the tubular diffuser in step 3, it is necessary to ensure that the coordinates of the pure radial straight-cone pipe section area are If unchanged, then: ， ， in, is the circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser, It is the radial coordinate of the starting point of the centerline of the centrifugal compressor meridian flow diffuser, which is also the inlet radius size of the tubular diffuser.

4. A method for designing a tubular diffuser with a dovetail leading edge according to claim 1, characterized in that: The step 4 is specifically as follows: The circumferential angle of the centerline of the pure radial straight-conical tube section of the tubular diffuser in step 3 is Distribution method to determine the circumferential angle of the centerline end point of the pure radial straight-conical tube section of the tubular diffuser ; According to the circumferential angle of the end point of the center line Determine the centerline inlet metal angle of the radial to axial bending section for: ， According to the outlet airflow angle of tubular diffuser Requirements, determine the outlet metal angle of the tubular diffuser for: , for ; According to the center line inlet metal angle of the tubular diffuser radial to axial bending section and outlet metal angle , design the Bezier curve of the metal angle distribution of the radial to axial bending section, the ordinate of the control point is the angle, and the abscissa is the normalized meridian flow channel centerline length, Then, according to the formula relationship of the circumferential angle: ， ， Determine the circumferential angle of the centerline of the radially rotating axial bend of the tubular diffuser The distribution is: ， ， Combined with the above and Distribution completes the design of the center line of the tubular diffuser.

5. A method for designing a tubular diffuser with a dovetail leading edge according to claim 1, characterized in that: The step five is specifically as follows: The area of ​​the geometric throat section remains unchanged, which is the same as the inlet throat area. Equal, the length is the geometric throat length factor Multiply by the inlet throat diameter; the area of ​​the conical section is linearly distributed according to the conical expansion angle , inlet throat diameter and cone length, and the cross-sectional area of ​​the cone outlet is obtained. , the area distribution of the tapered tube section can be determined, and then the area distribution of the pure radial straight-tapered tube section of the tubular diffuser can be obtained.

6. A method for designing a tubular diffuser with a dovetail leading edge according to claim 1, characterized in that: The step six is ​​specifically as follows: According to the centerline coordinates of the hub and casing of the tubular diffuser and , pure radial straight-cone pipe section outlet area and tubular diffuser outlet area , design the Bezier curve of the area distribution of the radial-to-axial bend section. The ordinate of the Bezier curve control point is the cross-sectional area of ​​the tubular diffuser, and the abscissa is the normalized meridian flow channel centerline length, which determines the area distribution of the radial-to-axial bend section of the tubular diffuser.

7. A method for designing a tubular diffuser with a dovetail leading edge as claimed in claim 1, characterized in that: The step seven is specifically as follows: The different cross-sections of the center line of the tubular diffuser include a pure radial straight-conical pipe section cross-section and a radial-rotating axial curved pipe section cross-section. The normal vector corresponding to the cross-section is determined according to the coordinates of the center line point of the tubular diffuser. for: ， According to the cross-sectional area distribution of the tubular diffuser, the centerline point coordinates of the tubular diffuser, the normal vector corresponding to the cross section and the cross-sectional equation , then the three coordinates of the cross section along the center line of the tubular diffuser are: ， in, , Indicates rounding to the nearest integer. It means to take the integer before the decimal point directly; and Represents two mutually perpendicular unit vectors on the cross section, and they are both perpendicular to the normal vector corresponding to the cross section In addition, in order to ensure that the output cross-section major axis endpoints and center points are on the circle of the corresponding radius, the two unit vectors selected and It is not arbitrary, one of them should be tangent to the corresponding radius torus, that is: ， ， ， Thus, the cross-sectional equation that meets the requirements is obtained. It should be noted that when m and n take different values, the corresponding cross-sectional shapes are also different; when m=n=1, the cross-section is rhombus, but considering that it is not conducive to the internal flow of the diffuser, the rhombus cross-section is not considered; when m=n=2, the cross-section is circular or elliptical, depending on whether the given a and b values ​​are the same; when m or n is greater than 2, the cross-section is elliptical, and the larger m and n are, the closer the cross-sectional shape is to a rectangle.

8. A method for designing a tubular diffuser with a dovetail leading edge according to claim 7, characterized in that: The pure radial straight-cone pipe section is a circular cross section; the curved pipe section in the radial rotation axis is an elliptical cross section, and m and n transition linearly from 2 to 6.

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