Design method for central line of meridian flow channel of tubular diffuser

Abstract

The invention relates to a method for designing a central line of a meridian flow channel of a tubular diffuser, which comprises the following steps of: dividing the central line of the meridian flow channel of the diffuser into three parts, namely an inlet straight line section, a bent pipe transition section and an outlet axial straight line section; and the dip angle distribution, changing along with normalization, of the central line of the meridian flow channel of the diffuser is defined, the total length of the central line of the meridian flow channel of the diffuser is calculated, finally, the coordinate distribution of the central line of the meridian flow channel of the diffuser obtained through design is calculated and output, and the configuration design of the central line of the meridian flow channel of the diffuser is completed. According to the method, the tubular diffuser structure meeting the engineering requirements can be rapidly constructed, meanwhile, the high geometrical configuration freedom degree is achieved, subsequent aerodynamic performance optimization design of the tubular diffuser is facilitated, and the engineering applicability and design space of the tubular diffuser are remarkably expanded.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of design of a tubular diffuser of a compressor in an aero-engine. BACKGROUND

[0002] With the rapid development of unmanned aerial vehicles, light aircraft and micro power systems, modern small aero-engines have higher requirements for the compactness and efficiency of compressors. The compactness of the compressor refers to further reducing the radial or axial size of the compressor components based on the original size to achieve compact space structure and weight reduction. How to achieve high pressure ratio and high efficiency in a limited space has become the core challenge of current compressor design. As a key component of the compressor, the geometric structure of the diffuser needs to ensure aerodynamic performance while meeting size requirements. Especially for the diffuser of a centrifugal or mixed flow compressor, how to efficiently guide airflow and achieve deceleration and pressure increase in a limited axial and radial space is the core of diffuser design.

[0003] In small aero-engines, the compressor often adopts a single-stage centrifugal or mixed flow configuration with high pressure ratio. The tubular diffuser has been applied to such single-stage high-pressure-ratio centrifugal / mixed flow compressors due to its flexible design and superior performance. Compared with traditional blade diffusers, tubular diffusers have the potential to further reduce radial size while ensuring the aerodynamic performance of the compressor.

[0004] Publication No. CN119026282A provides a tubular diffuser design method with a dovetail leading edge. Based on the given centerline coordinates of the centrifugal compressor diffuser meridian, the three-coordinate space coordinates are constructed through the spatial angle distribution of the centerline, and the cross-sectional shape along the centerline is determined by combining the area distribution, finally realizing the design and modeling of the tubular diffuser.

[0005] However, the application does not explicitly describe the design method of the diffuser meridian centerline, and the embodiment still uses the original diffuser meridian centerline of the prototype. This fixed form of diffuser meridian centerline cannot meet the urgent need for further reducing the radial size and achieving compact design of the tubular diffuser, and lacks design flexibility, which further limits the full play of the performance of the tubular diffuser. SUMMARY

[0006] The purpose of the present application is to avoid the shortcomings of the prior art and provide a tubular diffuser meridian centerline design method that realizes high design flexibility and low design complexity for centrifugal or mixed flow compressor tubular diffusers.

[0007] To achieve the above purpose, the technical solution adopted by the present application is as follows: a tubular diffuser meridian centerline design method, comprising the following steps: Step one, in the design coordinate system of the diffuser meridional flow passage center line, the impeller outlet radius, the axial coordinate corresponding to the impeller meridional flow passage center line outlet, and the radial and axial dimensions of the diffuser meridional flow passage center line inlet and the radial dimension of the diffuser meridional flow passage center line outlet are given, and the diffuser meridional flow passage center line is divided into three parts: an inlet straight section, a bend transition section and an outlet axial straight section; Further, the proportion of the inlet straight section and the outlet axial straight section in the diffuser meridional flow passage center line is determined; at the same time, the ratio of the radial dimension of the diffuser meridional flow passage center line inlet and the radial dimension of the diffuser meridional flow passage center line outlet to the impeller outlet radius is determined, and the angle between the diffuser meridional flow passage center line inlet and the horizontal plane and the angle between the diffuser meridional flow passage center line outlet and the horizontal plane are determined; Step two, based on the three parts of the diffuser meridional flow passage center line, the total length of the diffuser meridional flow passage center line is segmented and normalized, and then the inclination angle distribution of the diffuser meridional flow passage center line varying with the normalization is defined, which includes the inclination angle distribution of the inlet straight section, the inclination angle distribution of the outlet axial straight section and the inclination angle distribution of the bend transition section. The inclination angle distribution of the inlet straight section is constant and is the angle between the diffuser meridional flow passage center line inlet and the horizontal plane; the inclination angle distribution of the outlet axial straight section is constant and is the angle between the diffuser meridional flow passage center line outlet and the horizontal plane. The inclination angle distribution of the bend transition section is controlled by a first-order or second-order or third-order Bezier curve, which is used to realize the smooth transition from the inclination angle distribution of the inlet straight section to the inclination angle distribution of the outlet axial straight section, so that: The starting end horizontal and vertical coordinates of the Bezier curve are recorded as the proportion of the inlet straight section in the diffuser meridional flow passage center line and the angle between the diffuser meridional flow passage center line inlet and the horizontal plane, respectively. The terminal end horizontal and vertical coordinates of the Bezier curve are recorded as the proportion of the outlet axial straight section in the diffuser meridional flow passage center line and the angle between the diffuser meridional flow passage center line outlet and the horizontal plane, respectively. The intermediate control points of the Bezier curve are defined and controlled according to design requirements. Step three, calculate the total length of the diffuser meridional flow passage center line. Step four, based on the total length and the inclination angle distribution of the diffuser meridional flow passage center line, obtain the two-dimensional coordinate distribution of the diffuser meridional flow passage center line, that is, complete the geometric design of the diffuser meridional flow passage center line.

[0008] Further, the diffuser is a centrifugal or mixed flow compressor; When the angle between the diffuser meridional flow passage center line inlet and the horizontal plane is 90 degrees, it is a centrifugal compressor, at this time, the inlet straight section is recorded as an inlet radial straight section. When the angle between the inlet of the diffuser meridional flow passage center line and the horizontal plane is less than 90 degrees and greater than 0 degrees, it is a mixed flow compressor, at this time, the inlet straight line segment is recorded as the inlet oblique straight line segment; At the same time, when the proportion of the inlet radial straight line segment or the inlet oblique straight line segment in the diffuser meridional flow passage center line is 0, the diffuser meridional flow passage center line is only composed of the elbow transition section and the outlet axial straight line segment.

[0009] Further, the step two is to segment and normalize the total length of the diffuser meridional flow passage center line, that is, to normalize the dimensionless form of the three parts corresponding to the diffuser meridional flow passage center line, respectively represented as: The inlet straight line segment is , the elbow transition section is , and the outlet axial straight line segment is ; Wherein, represents the proportion of the inlet straight line segment in the diffuser meridional flow passage center line, represents the proportion of the outlet axial straight line segment in the diffuser meridional flow passage center line. Further, in the inclination angle distribution of the diffuser meridional flow passage center line, the angle between the inlet of the diffuser meridional flow passage center line and the horizontal plane is recorded as ; the angle between the outlet of the diffuser meridional flow passage center line and the horizontal plane is recorded as ; In the inclination angle distribution of the elbow transition section, the starting end horizontal and vertical coordinates of the Bezier curve are recorded as and , respectively, and the terminal end horizontal and vertical coordinates of the Bezier curve are recorded as and ; At this time, the uniform distribution of the horizontal coordinate control point is used as the initial arrangement, that is: If it is a first-order Bezier curve, that is, the control point coordinates corresponding to the first-order Bezier curve are and ; If it is a second-order Bezier curve, that is, the control point coordinates corresponding to the second-order Bezier curve are , and ; And in the actual design, the adjustment range of the control point coordinates follows: The starting end to the terminal end horizontal coordinate satisfies , and the starting end to the terminal end vertical coordinate satisfies ; If it is a third-order Bezier curve, that is, the control point coordinates corresponding to the third-order Bezier curve are: , , and ; and in the actual design, the control point coordinate adjustment range follows: the starting end to the terminal end transverse coordinate satisfies , and the starting end to the terminal end longitudinal coordinate satisfies .

[0010] Further, in step three, the total length of the diffuser meridional flow passage center line is:

[0011] In the formula, is the impeller outlet radius, is the radial dimension of the diffuser meridional flow passage center line inlet, is the radial dimension of the diffuser meridional flow passage center line outlet, is the ratio of the radial dimension of the diffuser meridional flow passage center line inlet to the impeller outlet radius , is the ratio of the radial dimension of the diffuser meridional flow passage center line outlet to the impeller outlet radius , and the function represents the inclination angle distribution of the diffuser meridional flow passage center line; is the number of discrete division points of the inclination angle distribution, and , used to ensure the accuracy of the calculated value; when , represents the inclination angle at the th discrete point on the diffuser meridional flow passage center line, for example, represents the inclination angle at the 1st discrete point, represents the inclination angle at the last discrete point. At the same time, it also satisfies:

[0012] In the formula, is the angle between the diffuser meridional flow passage center line inlet and the horizontal plane, is the angle between the diffuser meridional flow passage center line outlet and the horizontal plane.

[0013] Further, the step four is specifically: By discretizing the inclination angle distribution of the diffuser meridional flow passage center line, the position changes of the diffuser meridional flow passage center line in the axial and radial directions are calculated in the form of integration, thereby obtaining the two-dimensional discrete point coordinate distribution of the diffuser meridional flow passage center line, which is expressed as:

[0014] wherein, , are the coordinates of each discrete point of the obtained diffuser meridional passage center line in axial and radial directions, respectively; is the total length of the diffuser meridional passage center line; the function represents the inclination angle distribution of the diffuser meridional passage center line; is the number of discrete division points of the inclination angle distribution, and is used to ensure the accuracy of the calculated value; when , represents the inclination angle at the discrete point on the diffuser meridional passage center line, such as represents the inclination angle at the first discrete point, represents the inclination angle at the last discrete point; At the same time, also satisfies:

[0015] wherein, is the included angle between the diffuser meridional passage center line inlet and the horizontal plane, is the included angle between the diffuser meridional passage center line outlet and the horizontal plane.

[0016] Further, it further includes a retrofit design step for an existing given diffuser meridional passage center line: In the design coordinate system of the diffuser meridional passage center line, according to the two-dimensional discrete point coordinate distribution of the given diffuser meridional passage center line, the total length of the given diffuser meridional passage center line is obtained; Then, based on the adjacent two-dimensional coordinate points, the inclination angle distribution of the given diffuser meridional passage center line is obtained, and then the given diffuser meridional passage center line is divided into an inlet straight section, a bend transition section and an outlet axial straight section, and the proportion of each section in the total length of the given diffuser meridional passage center line is determined respectively, to obtain the inclination angle distribution of the diffuser meridional passage center line with normalized changes; Further, for the inclination angle distribution of the bend transition section of the given diffuser meridional passage center line, the Levenberg-Marquardt algorithm is used for 3-order Bezier curve fitting, to realize the full-section parameterization characterization of the given diffuser meridional passage center line; Finally, by adjusting the Bezier curve control points of the bend transition section, the parameterization fitting and retrofit design of the bend transition section of the given diffuser meridional passage center line are completed.

[0017] The application also provides a radial size-reduced tubular diffuser obtained by a meridional flow channel center line design method as described above, wherein the meridional flow channel center line of the tubular diffuser comprises: The proportion of the inlet straight line segment in the meridional flow channel center line of the diffuser is 0-0.15; The proportion of the outlet axial straight line segment in the meridional flow channel center line of the diffuser is 0.1-0.5; The radial size of the outlet of the meridional flow channel center line of the diffuser The ratio to the outlet radius of the impeller is 1.2-1.3, and the conventional design has a value of more than 1.4.

[0018] The application has the beneficial effects that the method can quickly construct a tubular diffuser structure meeting the engineering requirements, has a high degree of freedom of geometric configuration, and is convenient for subsequent development of aerodynamic performance optimization design, thereby significantly expanding the engineering applicability and design space of the tubular diffuser. On the other hand, the method can also parameterize and fit the existing diffuser meridional flow channel center line, and realize rapid reproduction and modification design of the existing diffuser flow channel.

[0019] Compared with the traditional “straight line-ellipse-straight line” design method, the method has the following advantages: on the one hand, the transition section of the bent pipe is controlled by the Bezier curve, has a higher degree of freedom of modeling, and can be flexibly adapted to the special mixed-flow compressor; on the other hand, the outlet radial size has flexibility and can realize the radial size reduction of the diffuser, and accurately meet the compact structure requirement of the compressor part of the small aero-engine.

[0020] In the engineering application level, the method has the following advantages: first, the meridional flow channel center line of the centrifugal or mixed-flow compressor tubular diffuser can be quickly designed; second, relying on the parameterized design logic, the method has a good programmatic implementation basis, is convenient for integration into the automatic modeling process and performance optimization platform, and effectively improves the design efficiency and performance level of the tubular diffuser. In addition, when the diffuser casing and hub profile of a certain type of diffuser are known, the discrete point coordinates of the meridional flow channel center line of the existing type of diffuser can be extracted; according to the segmentation logic and design parameter fitting strategy of the method, the existing diffuser meridional flow channel center line can be reproduced, and the diffuser modification and optimization design can be carried out based on this, thereby further improving the aerodynamic performance of the prototype compressor. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a schematic view of the diffuser meridional flow channel center line suitable for the centrifugal impeller of the application; Figure 2is a schematic diagram of the form of the diffuser meridional flow passage center line suitable for the inclined flow impeller of the present application; Figure 3 is a schematic diagram of the inclination distribution of the diffuser meridional flow passage center line with respect to the normalized change in an embodiment of the present application; Figure 4 is a verification diagram of the independence of the number of discrete points and the total length calculation result of the diffuser meridional flow passage center line in the calculation of the total length of the diffuser meridional flow passage center line in an embodiment of the present application; Figure 5 is a comparison diagram of the diffuser meridional flow passage center line obtained in an embodiment of the present application and the NASA HECC prototype diffuser meridional flow passage center line; Figure 6 is a comparison diagram of the radial size reduced tube diffuser model constructed based on the diffuser meridional flow passage center line obtained by the method in an embodiment of the present application and the tube diffuser model constructed using the NASA HECC prototype diffuser meridional flow passage center line; Figure 7 is a comparison diagram of the NASA HECC diffuser meridional flow passage center line obtained by parameter fitting based on the design method of the present application and the NASA HECC prototype diffuser meridional flow passage center line. DETAILED DESCRIPTION

[0022] The principles and characteristics of the present application are described below in conjunction with the accompanying drawings, and the examples are only used to explain the present application and are not intended to limit the scope of the present application.

[0023] The diffuser meridional flow passage center line obtained based on the present application can be used to ultimately realize the design and modeling of the tube diffuser according to the tube diffuser design method provided in the publication CN119026282A, which specifically includes: determining the inlet throat area and the outlet area of the tube diffuser according to the absolute Mach number at the outlet of the tube diffuser, the mass flow rate of the centrifugal compressor, the total pressure and total temperature at the outlet of the centrifugal impeller, the total pressure and total temperature at the outlet of the tube diffuser, the absolute Mach number at the inlet of the tube diffuser, the inlet blockage coefficient and the outlet blockage coefficient of the tube diffuser; determining the outlet metal angle of the radial-tapered tube segment of the tube diffuser and the three-coordinate distribution of the corresponding center line in space according to the inclination angle of the tube diffuser, the proportion of the inlet straight segment in the diffuser meridional flow passage center line and the two-dimensional discrete point coordinate distribution of the diffuser meridional flow passage center line; determining the three-coordinate distribution of the corresponding center line in space of the radial-tube segment of the tube diffuser according to the outlet metal angle of the radial-tube segment of the tube diffuser, the outlet metal angle of the tube diffuser and the two-dimensional discrete point coordinates of the diffuser meridional flow passage center line; According to the three-coordinate distribution of the radial-taper pipe section and the radial rotation shaft bending pipe section corresponding to the center line in space, the three-coordinate distribution of the center line corresponding to the tubular diffuser is obtained by merging; According to the two-dimensional discrete point coordinate distribution of the diffuser meridian flow passage center line, the geometric throat length coefficient of the tubular diffuser, the expansion angle of the taper pipe section, the inlet throat area of the tubular diffuser, the outlet area of the tubular diffuser, and the proportion of the inlet straight section in the diffuser meridian flow passage center line , the cross-sectional area distribution law of the tubular diffuser from the inlet to the outlet is determined; Further, the different cross-sectional distributions along the center line in space are determined, and the single-channel modeling design of the tubular diffuser is completed by sweeping; Finally, according to the radial dimension of the diffuser meridian flow passage center line inlet, the inclination angle of the tubular diffuser, the number of tubular diffuser circumferential channels, and the inlet throat area of the tubular diffuser, the swallow-tail front edge design is completed, and the overall modeling of the tubular diffuser is completed.

[0024] In order to achieve the overall modeling purpose of the tubular diffuser, the present application provides the following specific embodiments: Embodiment 1: A tubular diffuser meridian flow passage center line design method, comprising the following steps: S01, in the design coordinate system of the diffuser meridian flow passage center line, the impeller outlet radius, the axial coordinate corresponding to the impeller meridian flow passage center line outlet, and the radial and axial dimensions of the diffuser meridian flow passage center line inlet and the radial dimension of the diffuser meridian flow passage center line outlet are given, and the diffuser meridian flow passage center line is divided into three parts: an inlet straight section, a bending pipe transition section and an outlet axial straight section; Further, the proportion of the inlet straight section and the outlet axial straight section in the diffuser meridian flow passage center line is determined; at the same time, the ratio of the radial dimension of the diffuser meridian flow passage center line inlet and the radial dimension of the diffuser meridian flow passage center line outlet to the impeller outlet radius is determined, and the included angle of the diffuser meridian flow passage center line inlet and the diffuser meridian flow passage center line outlet with the horizontal plane.

[0025] S02, based on the three parts of the diffuser meridian flow passage center line, the total length of the diffuser meridian flow passage center line is segmented and normalized, that is, the normalized dimensionless form corresponding to the three parts of the diffuser meridian flow passage center line is respectively represented as: the inlet straight section is , the bending pipe transition section is , and the outlet axial straight section is ; wherein, represents the proportion of the inlet straight section in the diffuser meridian flow passage center line, represents the proportion of the outlet axial straight section in the diffuser meridian flow passage center line.

[0026] S03, further define the inclination distribution of the diffuser meridional flow passage center line with the normalization change, the inclination distribution specifically includes the inclination distribution of the inlet straight section, the inclination distribution of the outlet axial straight section and the inclination distribution of the elbow transition section; Wherein, the inclination distribution of the inlet straight section is the angle between the diffuser meridional flow passage center line inlet and the horizontal plane, denoted as ; The inclination distribution of the outlet axial straight section is the angle between the diffuser meridional flow passage center line outlet and the horizontal plane, denoted as ; The inclination distribution of the elbow transition section, the inclination distribution of the elbow transition section is controlled by a three-order Bezier curve, which is used to realize the smooth transition from the inclination distribution of the inlet straight section to the inclination distribution of the outlet axial straight section, and further, the starting end horizontal and vertical coordinates of the Bezier curve are denoted as the proportion of the inlet straight section in the diffuser meridional flow passage center line and the angle between the diffuser meridional flow passage center line inlet and the horizontal plane ; The terminal end horizontal and vertical coordinates of the Bezier curve are denoted as the proportion of the outlet axial straight section in the diffuser meridional flow passage center line and the angle between the diffuser meridional flow passage center line outlet and the horizontal plane ; At this time, the uniform distribution of the horizontal coordinate control point is used as the initial arrangement, then The three-order Bezier curve, that is, the control point coordinates corresponding to the three-order Bezier curve are: 、 、 and ; And in actual design, the control point coordinate adjustment range follows: The starting end to the terminal end horizontal coordinate satisfies , and the starting end to the terminal end vertical coordinate satisfies .

[0027] Thus, the middle control point of the Bezier curve is defined and controlled according to the design requirements.

[0028] S04, calculate the total length of the diffuser meridional flow passage center line :

[0029] Wherein, is the impeller outlet radius, is the radial dimension of the diffuser meridional flow passage center line inlet, is the radial dimension of the diffuser meridional flow passage center line outlet, The radial dimension of the diffuser meridional channel centerline inlet With impeller outlet radius The ratio, The radial dimension of the diffuser meridional channel centerline outlet With impeller outlet radius The ratio, function This indicates the angle distribution of the centerline of the diffuser meridional channel; The number of discrete division points for the tilt angle distribution, and This is used to ensure the calculated results The value is precise; when hour, Indicates the first [unit / item] on the center line of the diffuser meridional channel. The inclination angle at discrete points, such as This represents the inclination angle at the first discrete point. This represents the inclination angle at the last discrete point; At the same time, it also satisfies:

[0030] In the formula, The angle between the diffuser meridional channel centerline inlet and the horizontal plane. It is the angle between the centerline outlet of the diffuser meridional channel and the horizontal plane.

[0031] S05. By discretizing the inclination angle distribution of the diffuser meridional channel centerline, and calculating the positional changes of the diffuser meridional channel centerline in the axial and radial directions by accumulating the results in an integral form, the two-dimensional discrete point coordinate distribution of the diffuser meridional channel centerline is obtained as follows:

[0032] In the formula, , These are the coordinates of each discrete point on the centerline of the obtained diffuser meridional channel in the axial and radial directions, respectively. The total length of the diffuser meridional channel centerline; function This indicates the angle distribution of the centerline of the diffuser meridional channel; The number of discrete division points for the tilt angle distribution, and This is used to ensure the calculated results The value is accurate; when hour, Indicates the first [unit / item] on the center line of the diffuser meridional channel. The inclination angle at discrete points, such as This represents the inclination angle at the first discrete point. This represents the inclination angle at the last discrete point; at the same time, Also satisfied: , In the formula, is the angle between the inlet of the diffuser meridional flow passage center line and the horizontal plane, is the angle between the outlet of the diffuser meridional flow passage center line and the horizontal plane, that is, the geometric design of the diffuser meridional flow passage center line is completed.

[0033] Example 2: as shown in Figure 1 the same as example 1, except that the diffuser is a centrifugal compressor, so that the angle between the inlet of the diffuser meridional flow passage center line and the horizontal plane is 90 degrees, at this time, the inlet straight line segment is recorded as the inlet radial straight line segment; As shown in Figure 1 in the figure is the proportion of the inlet radial straight line segment in the diffuser meridional flow passage center line, is the proportion of the outlet axial straight line segment in the diffuser meridional flow passage center line, is the outlet radius of the centrifugal impeller, is the radial size of the inlet of the diffuser meridional flow passage center line, is the radial size of the outlet of the diffuser meridional flow passage center line; At the same time, when the proportion of the inlet radial straight line segment in the diffuser meridional flow passage center line is 0, the diffuser meridional flow passage center line is composed of only the elbow transition section and the outlet axial straight line segment.

[0034] At this point, the final obtained pipe diffuser meridional flow passage center line of the pipe diffuser is: the proportion of the inlet radial straight line segment in the diffuser meridional flow passage center line is 0~0.15; the proportion of the outlet axial straight line segment in the diffuser meridional flow passage center line is 0.1~0.5; the ratio of the radial size of the outlet of the diffuser meridional flow passage center line to the outlet radius of the impeller is 1.2~1.3, and the value of the conventional design is above 1.4; by reducing to achieve the design purpose of reducing the radial size of the pipe diffuser.

[0035] Example 3: as shown in Figure 2 the same as example 1, except that the diffuser is a mixed flow compressor, so that the angle between the inlet of the diffuser meridional flow passage center line and the horizontal plane is less than 90 degrees and greater than 0 degrees, at this time, the inlet straight line segment is recorded as the inlet oblique straight line segment; As shown in Figure 2As shown in the figure is the ratio of the inlet oblique straight line segment in the diffuser meridional passage center line, is the ratio of the outlet axial straight line segment in the diffuser meridional passage center line, is the outlet radius of the axial flow impeller, is the radial dimension of the inlet of the diffuser meridional passage center line, is the radial dimension of the outlet of the diffuser meridional passage center line; At the same time, when the ratio of the inlet oblique straight line segment in the diffuser meridional passage center line is 0, then the diffuser meridional passage center line is only composed of the elbow transition section and the outlet axial straight line segment.

[0036] At this point, the final obtained in the tubular diffuser of the tubular diffuser meridional passage center line is: the ratio of the inlet oblique straight line segment in the diffuser meridional passage center line is 0~0.15; the ratio of the outlet axial straight line segment in the diffuser meridional passage center line is 0.1~0.5; the ratio of the radial dimension of the outlet of the diffuser meridional passage center line to the outlet radius of the axial flow impeller is 1.2~1.3, and the value of the conventional design is above 1.4; by reducing to achieve the design purpose of reducing the radial dimension of the tubular diffuser.

[0037] Example 4: the same as example 1, except that the inclination distribution of the elbow transition section is controlled by a first-order Bezier curve, which is used to realize the smooth transition from the inclination distribution of the inlet straight line segment to the inclination distribution of the outlet axial straight line segment. In the inclination distribution of the elbow transition section, the horizontal and vertical coordinates of the starting end of the Bezier curve are respectively denoted as and , and the horizontal and vertical coordinates of the terminal end of the Bezier curve are respectively denoted as and ; at this time, the uniform distribution of the horizontal coordinate control point is used as the initial arrangement, then the first-order Bezier curve, that is, the control point coordinates corresponding to the first-order Bezier curve are and .

[0038] Example 5: the inclination distribution of the elbow transition section is controlled by a second-order Bezier curve, which is used to realize the smooth transition from the inclination distribution of the inlet straight line segment to the inclination distribution of the outlet axial straight line segment. In the inclination distribution of the elbow transition section, the horizontal and vertical coordinates of the starting end of the Bezier curve are respectively denoted as and , the terminal end of the Bezier curve is recorded as and ; At this time, the initial arrangement is in the form of uniform distribution of the abscissa control points, and then The inclination distribution of the elbow transition section of the curve is recorded as and , the terminal end of the Bezier curve is recorded as and ; at this time, the initial arrangement is in the form of uniform distribution of the abscissa control points, and then the second-order Bezier curve, that is, the control point coordinates corresponding to the second-order Bezier curve are , and ; and in actual design, the adjustment range of the control point coordinates complies with: , the abscissa of the starting end to the terminal end complies with .

[0039] Example 6: the same as example 1, except that it further includes the modification design steps of the existing given diffuser meridional flow passage center line: In the design coordinate system of the diffuser meridional flow passage center line, according to the two-dimensional discrete point coordinate distribution of the given diffuser meridional flow passage center line, the total length of the given diffuser meridional flow passage center line is obtained; Then, based on the adjacent two-dimensional coordinate points, the inclination distribution of the given diffuser meridional flow passage center line is obtained, and then the given diffuser meridional flow passage center line is divided into an inlet straight section, an elbow transition section and an outlet axial straight section, and the proportion of each section in the total length of the given diffuser meridional flow passage center line is determined, to obtain the inclination distribution of the diffuser meridional flow passage center line with normalized change; Further, for the inclination distribution of the elbow transition section of the given diffuser meridional flow passage center line, the Levenberg-Marquardt algorithm is used for third-order Bezier curve fitting to realize the parameterization characterization of the full section of the given diffuser meridional flow passage center line; Finally, by adjusting the Bezier curve control points of the elbow transition section, the parameterization fitting and modification design of the elbow transition section of the given diffuser meridional flow passage center line are completed.

[0040] As Figure 1 and Figures 3-7 , in order to further illustrate the technical scheme and technical effects of the present application, the following specific design examples are provided.

[0041] Specific design example 1: This example uses the diffuser meridional centerline design of the NASA HECC high-ratio centrifugal compressor (model information from the NASA public report "NASA-High Efficiency Centrifugal Compressor") as an example to implement a radially reduced tubular diffuser meridional centerline design. Finally, a model of a radially reduced tubular diffuser is constructed, applicable to the meridional centerline form of the NASA HECC centrifugal impeller, as shown below. Figure 1 As shown, it includes the following steps: Step 1: Determine the design input parameters: Based on the one-dimensional outlet parameters of the centrifugal impeller, determine the required input variables, mainly including: the outer diameter of the centrifugal impeller outlet. Axial coordinates corresponding to the outlet of the impeller meridional channel centerline Diffuser meridional channel centerline inlet radial dimension outer diameter of centrifugal impeller outlet ratio Diffuser meridional channel centerline outlet radial dimension outer diameter of centrifugal impeller ratio It should be noted that the NASA HECC prototype diffuser This example aims to significantly reduce This method reduces the radial dimension of the tubular diffuser, achieving a compact design for the tubular diffuser. Angle between the diffuser meridional channel centerline inlet and the horizontal plane The angle is 90 degrees, the angle between the diffuser meridional channel centerline outlet and the horizontal plane. The percentage of the radial straight section at 0 degrees within the diffuser meridional channel centerline. The proportion of the straight section of the outlet axis in the centerline of the diffuser meridional channel ; Step 2: Obtain the normalized diffuser meridional channel centerline length, and determine its corresponding zones in the inlet radial straight section, the bend transition section, and the outlet axial straight section, as follows: Inlet radial straight section ,Right now ; bend transition section ,Right now ; Export axial straight section ,Right now ; Step 3: Construct the inclination angle distribution of the diffuser meridional channel centerline, as shown in the attached figure. Figure 3 As shown, the specific situation is as follows: The inclination angle distribution of the inlet radial straight section is constant at 90 degrees, and the corresponding horizontal coordinate interval is ; The inclination angle distribution of the elbow transition section is controlled by a second-order Bezier curve, and the coordinates of the middle control point are , and the corresponding horizontal coordinate interval of the elbow transition section is ; The inclination angle distribution of the outlet axial straight section is constant at 0 degrees, and the corresponding horizontal coordinate interval is ; Step four, according to the inclination angle distribution of the diffuser meridional passage center line constructed in step three, the total length of the diffuser meridional passage center line is determined by numerical integration : To verify the correlation between the calculation accuracy and the discrete division point number , the convergence test is performed on different discrete division point numbers in this example, as shown in Figure 4 . The horizontal coordinate ( is the discrete division point number), and the vertical coordinate is the corresponding calculated value. From the figure, it can be seen that when the discrete division point number , the calculated value tends to be stable, and it is considered that when , the calculation accuracy of can be guaranteed. Based on this, the discrete division point number is selected in this embodiment, and the total length of the diffuser meridional passage center line is finally calculated Step five, output the two-dimensional discrete point coordinate distribution of the diffuser meridional passage center line : Based on the inclination angle distribution of the diffuser meridional passage center line and the total length of the diffuser meridional passage center line , the two-dimensional discrete point coordinate distribution on the diffuser meridional passage center line is calculated in sequence , and this example outputs 60 points, as shown in Table 1, Table 1 is the two-dimensional discrete point coordinates of the diffuser meridional passage center line with reduced radial dimension, and the data in the table is in mm, which will be used for subsequent design and modeling of the tubular diffuser.

[0042] Table 1

[0043] Figure 5A comparison diagram of the meridional flow passage center line of the radial size-reduced diffuser obtained in the specific design example 1 (radial size-reduced_R42 = 1.2 marked in the figure) and the meridional flow passage center line of the prototype diffuser of the NASA HECC centrifugal compressor (NASA HECC prototype_R42 = 1.409).

[0044] As can be clearly seen from the figure, the size of the meridional flow passage center line of the radial size-reduced diffuser in the radial direction is much smaller than that of the prototype design, verifying the effectiveness of the design method proposed in the application; Figure 6 In order to keep the design parameters consistent, the three-dimensional models of the pipe diffusers based on the meridional flow passage center lines of the two diffusers in the Figure 5 application are compared, and the comparison diagram is shown. The results show that the model of the pipe diffuser constructed by using the design method of the application is significantly reduced in radial size, further verifying the potential of the method in realizing the radial size reduction of the diffuser and achieving the purpose of compact design of the diffuser.

[0045] Specific design example 2: This example takes the NASA HECC high-pressure-ratio centrifugal compressor as an example to realize the parametric fitting of the given meridional flow passage center line of the diffuser, and compares the fitted meridional flow passage center line of the diffuser with the given meridional flow passage center line of the diffuser, including the following steps: Step one, according to the two-dimensional discrete point coordinate distribution of the given meridional flow passage center line of the diffuser, the total length of the meridional flow passage center line of the diffuser is calculated ; Step two, based on the two-dimensional discrete point coordinate distribution, the inclination distribution of the meridional flow passage center line of the diffuser is obtained, and the proportion of the inlet radial straight line segment in the meridional flow passage center line of the diffuser , the proportion of the outlet axial straight line segment in the meridional flow passage center line of the diffuser , the angle between the inlet of the meridional flow passage center line of the diffuser and the horizontal plane is 90 degrees, and the angle between the outlet of the meridional flow passage center line of the diffuser and the horizontal plane is 0 degrees; Step three, for the inclination distribution of the elbow transition section, this example adopts Levenberg-Marquardt algorithm for 3-order Bezier curve fitting, and the coordinates of the four points corresponding to the Bezier curve are respectively 、 、 and ; Step four, based on the inclination distribution of the meridional flow passage center line of the diffuser obtained after parametric fitting, the total length of the meridional flow passage center line of the diffuser is recalculated and output the two-dimensional discrete point coordinate distribution of the diffuser meridional flow passage center line.

[0046] Figure 7 The figure shows the comparison between the diffuser meridional flow passage center line obtained in the specific design example 2 (HECC diffuser center line (fitting)) and the given diffuser meridional flow passage center line (HECC diffuser center line (prototype)). As can be seen from the figure, the two diffuser meridional flow passage center lines are basically consistent, and at the elbow transition section, the diffuser meridional flow passage center line obtained by the method has a slight deviation from the given diffuser meridional flow passage center line. This difference is mainly caused by the insufficient order of the Bezier curve used, thereby verifying the feasibility of the design method for parameterizing the given diffuser meridional flow passage center line.

[0047] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for designing a meridional flow passage centerline of a vaneless diffuser, characterized by, The method comprises the following steps: Step one, in the design coordinate system of the diffuser meridian flow passage center line, the impeller outlet radius, the axial coordinate corresponding to the impeller meridian flow passage center line outlet, the radial and axial dimensions of the diffuser meridian flow passage center line inlet and the radial dimension of the diffuser meridian flow passage center line outlet are given, and the diffuser meridian flow passage center line is divided into three parts, namely, an inlet straight section, a bend transition section and an outlet axial straight section; Further, the proportion of the inlet straight section and the outlet axial straight section in the diffuser meridian flow passage center line is determined; meanwhile, the ratio of the radial dimension of the diffuser meridian flow passage center line inlet and the radial dimension of the diffuser meridian flow passage center line outlet to the impeller outlet radius is determined, and the included angle of the diffuser meridian flow passage center line inlet and the diffuser meridian flow passage center line outlet with the horizontal plane is determined; Step two, based on the three parts of the diffuser meridian flow passage center line, the total length of the diffuser meridian flow passage center line is segmented and normalized, and then the inclination angle distribution of the diffuser meridian flow passage center line varying with the normalization is defined, which specifically includes the inclination angle distribution of the inlet straight section, the inclination angle distribution of the outlet axial straight section and the inclination angle distribution of the bend transition section; The inclination angle distribution of the inlet straight section is always the included angle of the diffuser meridian flow passage center line inlet with the horizontal plane; the inclination angle distribution of the outlet axial straight section is always the included angle of the diffuser meridian flow passage center line outlet with the horizontal plane; The inclination angle distribution of the bend transition section is controlled by a first-order or second-order or third-order Bezier curve, which is used to realize the smooth transition from the inclination angle distribution of the inlet straight section to the inclination angle distribution of the outlet axial straight section, so that: The horizontal and vertical coordinates of the starting end of the Bezier curve are respectively recorded as the proportion of the inlet straight section in the diffuser meridian flow passage center line and the included angle of the diffuser meridian flow passage center line inlet with the horizontal plane; The horizontal and vertical coordinates of the terminal end of the Bezier curve are respectively recorded as the proportion of the outlet axial straight section in the diffuser meridian flow passage center line and the included angle of the diffuser meridian flow passage center line outlet with the horizontal plane; The intermediate control point of the Bezier curve is defined and controlled according to design requirements; Step three, the total length of the diffuser meridian flow passage center line is calculated; Step four, based on the total length and the inclination angle distribution of the diffuser meridian flow passage center line, the two-dimensional coordinate distribution of the diffuser meridian flow passage center line is obtained, that is, the geometric design of the diffuser meridian flow passage center line is completed.

2. The tubular diffuser meridional passage centerline design method of claim 1 wherein, The diffuser is a centrifugal or mixed flow compressor; When the included angle of the diffuser meridian flow passage center line inlet with the horizontal plane is 90 degrees, it is a centrifugal compressor, at this time, the inlet straight section is recorded as an inlet radial straight section; When the included angle of the diffuser meridian flow passage center line inlet with the horizontal plane is less than 90 degrees and greater than 0 degree, it is a mixed flow compressor, at this time, the inlet straight section is recorded as an inlet oblique straight section; At the same time, when the proportion of the inlet radial straight section or the inlet oblique straight section in the diffuser meridian flow passage center line is 0, the diffuser meridian flow passage center line is only composed of the bend transition section and the outlet axial straight section.

3. The tubular diffuser meridional passage centerline design method of claim 1 wherein, The step two is to segment and normalize the total length of the diffuser meridional flow passage center line, that is, to normalize the three parts of the diffuser meridional flow passage center line into dimensionless forms, respectively denoted as: The inlet straight section is , the elbow transition section is , and the outlet axial straight section is ; wherein, represents the proportion of the inlet straight line segment in the diffuser meridian flow passage center line, represents the proportion of the outlet axial straight line segment in the diffuser meridian flow passage center line; Further, in the distribution of the inclination angle of the meridian flow passage center line of the diffuser, the included angle between the inlet of the meridian flow passage center line of the diffuser and the horizontal plane is denoted as ; and the included angle between the outlet of the meridian flow passage center line of the diffuser and the horizontal plane is denoted as . In the inclination distribution of the elbow transition section, the initial end of the Bezier curve is denoted as and respectively, and the terminal end of the Bezier curve is denoted as and respectively. At this time, the initial arrangement is in the form of uniform distribution of the abscissa control points, and then: If it is a first order Bezier curve, there are control point coordinates corresponding to the first order Bezier curve and ; If it is a second order Bezier curve, that is, there are control point coordinates corresponding to the second order Bezier curve , and ; And in the actual design, the adjustment range of the control point coordinates complies with: The starting end to the terminal end horizontal coordinate satisfies The starting end to the terminal end vertical coordinate satisfies ; If it is a third order Bezier curve, there are three control points corresponding to the third order Bezier curve, and the coordinates of the control points are: , , and ; And in the actual design, the adjustment range of the control point coordinates complies with: The starting end to the terminal end horizontal coordinate satisfies The starting end to the terminal end vertical coordinate satisfies .

4. The tubular diffuser meridional passage centerline design method of claim 1 wherein, In step three, the total length of the centerline of the diffuser meridional passage is: Ldiffuser = Ldiffuser,1 + Ldiffuser,2 + Ldiffuser,3 ， wherein is the outlet radius of the impeller, is the radial dimension of the inlet of the meridional flow passage of the diffuser, is the radial dimension of the outlet of the meridional flow passage of the diffuser, is the radial dimension of the inlet of the meridional flow passage of the diffuser is the ratio of the outlet radius of the impeller to the radial dimension of the inlet of the meridional flow passage of the diffuser, is the ratio of the radial dimension of the outlet of the meridional flow passage of the diffuser to the outlet radius of the impeller , the function represents the distribution of the inclination angle of the meridional flow passage of the diffuser; is the number of discrete division points of the distribution of the inclination angle, and , for ensuring the accuracy of the calculated value of ; when , represents the inclination angle at the discrete point on the meridional flow passage of the diffuser, such as represents the inclination angle at the 1st discrete point, represents the inclination angle at the last discrete point; Meanwhile, it also satisfies: ， wherein is the angle between the inlet of the diffuser meridional flow passage center line and the horizontal plane, is the angle between the outlet of the diffuser meridional flow passage center line and the horizontal plane.

5. The tubular diffuser meridional passage centerline design method of claim 1 wherein, The step four is specifically: By discretizing the inclination distribution of the diffuser meridional flow passage center line, the position changes of the diffuser meridional flow passage center line in the axial and radial directions are calculated in the integral form, so as to obtain the two-dimensional discrete point coordinate distribution of the diffuser meridional flow passage center line, denoted as: ， wherein, , are the coordinates of each discrete point of the obtained diffuser meridional passage center line in axial and radial directions, respectively; is the total length of the diffuser meridional passage center line; the function represents the inclination angle distribution of the diffuser meridional passage center line; is the number of discrete division points of the inclination angle distribution, and is used to ensure the accuracy of the calculated value; when , represents the inclination angle at the discrete point on the diffuser meridional passage center line, such as represents the inclination angle at the 1st discrete point, represents the inclination angle at the last discrete point; At the same time, Also satisfied: ， In the formula, is the angle between the inlet of the meridian flow passage center line of the diffuser and the horizontal plane, is the angle between the outlet of the meridian flow passage center line of the diffuser and the horizontal plane.

6. The tubular diffuser meridional passage centerline design method of any of claims 1-5, wherein, It also includes the retrofit design steps of the existing given diffuser meridional flow passage center line: In the design coordinate system of the diffuser meridional flow passage center line, according to the two-dimensional discrete point coordinate distribution of the given diffuser meridional flow passage center line, the total length of the given diffuser meridional flow passage center line is obtained; Then, based on the adjacent two-dimensional coordinate points, the inclination distribution of the given diffuser meridional flow passage center line is obtained, and then the given diffuser meridional flow passage center line is divided into an inlet straight section, a bend transition section and an outlet axial straight section, and the proportions of each section in the total length of the given diffuser meridional flow passage center line are determined, so as to obtain the inclination distribution of the diffuser meridional flow passage center line varying with the normalization; Further, for the inclination distribution of the bend transition section of the given diffuser meridional flow passage center line, the Levenberg-Marquardt algorithm is used for third-order Bezier curve fitting, so as to realize the parameterization representation of the whole given diffuser meridional flow passage center line. Finally, by adjusting the Bezier curve control points of the bend transition section, the parameterization fitting and retrofit design of the bend transition section of the given diffuser meridional flow passage center line are completed.

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