A Design and Modeling Method for a New Tube-Type Diffuser of a Micro Centrifugal Compressor

Abstract

The present invention discloses a novel design and shaping method for a tubular diffuser of a micro centrifugal compressor. First, the bottom surface A1 is determined, and then the suction surface A2, the pressure surface A3, the transition surface A4, and the casing surface A5 are sequentially obtained. The rho value of the center line of the bottom surface controls the curvature of the bottom surface. The bottom surface A1 controls the geometric angle at the bottom of the inlet, and the casing surface A5 controls the geometric angle at the top of the inlet. Moreover, the bottom surface A1 can also control the throat area. The middle part of the suction surface A2 can control the position of the suction surface to avoid the staggered intersection of the pressure surface and the suction surface. The groove opened at the outlet position guides the high-speed flow of the pressure surface to the low-speed area of the bottom surface, making the flow better. The present invention combines the advantages of the tubular diffuser and the conformal channel diffuser, improves the space utilization rate of the diffuser, better controls the flow process of the air flow in the diffuser, uses a method similar to the jet method of the axial flow compressor, and slots at the radial position of the diffuser outlet to eliminate the low-speed area of the suction surface.

Description

Technical Field

[0001] The present invention relates to the technical field of aero-engines, and particularly to a design modeling method for a new tubular diffuser of a micro centrifugal compressor. Background Art

[0002] In the field of micro aero-engines, due to a series of advantages such as high single-stage pressure ratio, few components, compact structure, high reliability, and strong foreign object impact resistance of centrifugal compressors, they have been widely used. With higher requirements for the performance of aero-engines, the pressure ratio of compressors is getting higher and higher. The consequence of the high pressure ratio is that the unevenness of the outlet air flow of the centrifugal compressor is greatly increased. And because the structure of the centrifugal compressor is very compact, the air flow needs to change from radial to axial within a very short distance, making it very difficult to organize the internal flow field of the centrifugal compressor. The traditional vane diffuser is divided into a radial section and an axial section, and there is a strong turning, even stagnation when the air flow turns. Previous studies have proposed tubular diffusers and conformal channel diffusers. For tubular diffusers, their design concept is to design according to the center line of the channel and the area distribution along the way, which is more suitable for centrifugal compressors with a larger degree of expansion. The design method of conformal diffuser blades is to directly design the channel. By determining the channel height distribution, channel cross-sectional area, number of blades, and the channel structure angle distribution of the hub and casing, a complete conformal channel can be constructed from the channel inlet to the channel outlet, and the blades are between adjacent channels.

[0003] However, for micro aero-engines, their geometric size is very small, the frontal area is small, and the compactness is very high. The "swallowtail" leading edge where the leading edges of the tubular diffuser are intersected no longer appears, replaced by a very irregular "notch". And because the tubular diffuser generally has a circular or elliptical cross-section, its space utilization rate is not high. For conformal channel diffusers, since the casings and hubs are rotating surfaces during their design, the rotating surface type of hub causes a large separation when the air flow turns from radial to axial. Therefore, this paper proposes a diffuser design modeling method for micro centrifugal compressors, which combines the advantages of tubular diffusers and conformal channel diffusers. The essential difference between tubular diffusers and conformal channel diffusers lies in the composition of the suction surface, pressure surface, casing, and hub. Tubular diffusers can be regarded as vane diffusers without casings and hubs, where the casing and hub surfaces are integrated into the suction and pressure surfaces and continuously twisted from radial to axial. The new tubular diffuser in this paper combines the advantages of the two diffusers. Compared with the hub surface, the casing surface has a considerable effect on the air flow turning. Therefore, the hub surface is integrated into the suction and pressure surfaces of the blade to form the main body of the new tubular diffuser. Since the new tubular diffuser turns quickly and has a compact size, air flow separation will occur at the turning position. Therefore, a slot is opened in the middle of the outlet radial direction to shoot the high-speed flow on the pressure surface towards the suction surface, driving the low-speed area of the suction surface, and finally completing the modeling of the new tubular diffuser. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a new tubular diffuser design and modeling method for a micro - centrifugal compressor to address the deficiencies in the background art. This method combines the design of tubular diffusers and conformal - channel diffusers, and performs parametric modeling of the diffuser, laying a foundation for parametric optimization. Slots are opened at the radial height at the outlet position to drive the separation vortex and improve the flow condition.

[0005] The present invention adopts the following technical solutions to solve the above - mentioned technical problems:

[0006] A new tubular diffuser design and modeling method for a micro - centrifugal compressor, comprising the following steps:

[0007] Step 1), calculate the inlet area and outlet area of the diffuser according to the rotor outlet air - flow parameters and diffuser size requirements, and obtain the inlet area and outlet area of each channel according to the preset number of channels;

[0008] Step 2), design the bottom - surface mid - line with the inlet air - flow vector and the outlet air - flow vector as the sketch plane according to the diffuser inlet area, outlet area and number of channels, and sweep according to the bottom - surface mid - line and the inlet and outlet cross - section lines to obtain the key - surface bottom;

[0009] Step 2.1), determine the cylindrical side - walls where the inlet cross - sections of each channel are located according to the diffuser inlet area, with circle O1 at the top and circle O2 at the bottom;

[0010] Step 2.2), divide the cylindrical side - wall between circle O1 and O2 into each channel according to the inlet area of the channel, and obtain the inlet cross - section S1 of one channel. The contour of S1 includes straight - edge L1, straight - edge L2, arc - edge C1 and arc - edge C2. Among them, straight - edge L1 and straight - edge L2 are both parallel to the diffuser axis, straight - edge L1 is on the suction side, straight - edge L2 is on the pressure side, arc - edge C1 is at the top, and arc - edge C2 is at the bottom;

[0011] Step 2.3), determine the ring where the outlet cross - sections of each channel of the diffuser are located, with inner - ring circle O3 and outer - ring circle O4. Determine circle O5 according to circle O3 and O4, so that circle O5 is concentric with circle O3 and O4, and the radius of circle O5 is equal to 1 / 2 of the sum of the radii of circle O3 and O4;

[0012] Step 2.4), draw a straight line L3 starting from the mid - point P1 of arc - edge C2 along the inlet air - flow velocity vector direction, and the projection of L3 on the outlet plane intersects circle O5 at point P2;

[0013] Step 2.5), according to P2 and the outlet area of the channel, intercept a sector cross-section S2 on the ring where each channel outlet cross-section is located as the outlet cross-section corresponding to the inlet cross-section S1. The contour of S2 includes straight edge L4, straight edge L5, arc edge C3, and arc edge C4. Among them, straight edge L4 is on the suction side, straight edge L5 is on the pressure side, arc edge C3 is on the inner side, and arc edge C4 is on the outer side. P2 is located at the midpoint of L4;

[0014] Step 2.5), stretch L3 along the diffuser axis as the sketch plane S3;

[0015] Step 2.6), take the intersection point of the line passing through P2 and parallel to the diffuser axis and L3 as the control point P3, P1 as the starting point, and P2 as the ending point to make a quadratic curve with a rho value of 0.6. This quadratic curve is the bottom center line L6;

[0016] Step 2.7), take the bottom endpoint P4 of L1 as the starting point of the perpendicular line L7, make a perpendicular line to L6, extend the ending point of the perpendicular line to P5, control the distance from P4 to P5 to control the diffuser width and thus control the throat area, and sweep C2, L4, and L7 with L6 as the guide line to obtain the bottom surface A1;

[0017] Step 3), on the suction side and pressure side of the bottom surface, form a suction surface and a pressure surface through ruled surfaces respectively, and form a transition surface with the casing surface on the side of the suction surface;

[0018] Step 3.1), let the curve on the suction side among the four curves enclosing the bottom surface A1 be L8, make a normal perpendicular line L9 to L8 at the mid-chord length of L8; the length of L9 forms a linear distribution with L1 and C3; sweep L1, L9, and C3 with L8 as the guide line to obtain the suction surface A2;

[0019] Step 3.2), design the casing line L10 in the form of straight line - arc - straight line based on the dimensions of the diffuser;

[0020] Step 3.3), the Z-axis of the rectangular coordinate system is the diffuser axis, the XOY plane of the rectangular coordinate system is perpendicular to the diffuser axis. Let the Z-axis of the cylindrical coordinate system be the Z-axis of the rectangular coordinate system, the cylindrical coordinate θ is the angle between the projection of the rectangular coordinate system and the X-axis, the cylindrical coordinate R is the distance from the projection of the rectangular coordinate system to the origin, m is the curve vector, and β is the curve angle; based on L10, d θ is used as the dependent variable, dm and R are determined by the coordinates of L10. Given the β angle and the variation law of tanβ, the following formula is used to obtain two curves L11 and L12 on the casing revolution surface:

[0021] dθ / dm = tanβ / R

[0022] Step 3.4), let L13 be the curve on the pressure side among the four curves enclosing the bottom surface A1, and L14 be the curve on the casing side among the four curves forming A2. A pressure surface A3 is obtained by performing ruled surface modeling on L11 and L13, and a suction surface transition surface A4 is obtained by performing ruled surface modeling on L12 and L14;

[0023] Step 4), trim the casing with the pressure surface A3 and the transition surface A4 to obtain a casing surface A5. A complete channel is formed by the bottom surface A1, the suction surface A2, the pressure surface A3, the transition surface A4, and the casing surface A5; Array the complete channels, that is, form a complete three-dimensional structure of the diffuser;

[0024] Step 5), after forming the complete channel, radially slot at the diffuser outlet position to convert the diffuser channel into blades.

[0025] Compared with the prior art, the present invention adopts the above technical solutions and has the following technical effects:

[0026] 1. Combining the advantages of tubular diffusers and conformal channel diffusers, improving the space utilization rate of the diffuser, better controlling the airflow flow process in the diffuser, using a method similar to the jet of an axial compressor, slotting radially at the diffuser outlet position to eliminate the low-speed area on the suction surface.

[0027] 2. The diffuser can be parametrically optimized, such as the center line of the bottom surface, the throat area, the installation angles at the bottom and top of the pressure surface and the suction surface, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram for generating the bottom surface;

[0029] Figure 2 It is a schematic diagram for generating the pressure surface;

[0030] Figure 3 It is a schematic diagram for generating the suction surface and the transition surface;

[0031] Figure 4 It is a schematic diagram for generating the casing surface;

[0032] Figure 5 (a), Figure 5 (b) are respectively the top view and the three-dimensional schematic diagram of the three-dimensional channel periodic array;

[0033] Figure 6 a), Figure 6 (b) are respectively the schematic diagrams of the blade and the slotted blade. EMBODIMENT

[0034] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings:

[0035] The present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, components are enlarged for clarity.

[0036] It should be understood that although the terms first, second, third, etc. may be used herein to describe various elements, components, and / or parts, these elements, components, and / or parts are not limited by these terms. These terms are only used to distinguish one element, component, and / or part from another. Thus, the first element, component, and / or part discussed below may become the second element, component, or part without departing from the teachings of the present invention.

[0037] A novel tubular diffuser design and modeling method for a micro centrifugal compressor of the present invention includes the following steps:

[0038] A novel tubular diffuser design and modeling method for a micro centrifugal compressor includes the following steps:

[0039] Step 1), calculate the inlet area and outlet area of the diffuser according to the rotor outlet air flow parameters and the diffuser size requirements, and obtain the inlet area and outlet area of each channel according to the preset number of channels;

[0040] Step 2), based on the diffuser inlet area, outlet area, and number of channels, design the bottom center line with the inlet air flow vector and the outlet air flow vector as the sketch plane, and sweep according to the bottom center line and the inlet and outlet section lines to obtain the key surface bottom;

[0041] Step 2.1), determine the cylindrical side walls where the inlet sections of each channel are located according to the diffuser inlet area, with the top being circle O1 and the bottom being circle O2;

[0042] Step 2.2), divide the cylindrical side wall between circle O1 and O2 into each channel according to the inlet area of the channel, and obtain the inlet section S1 of one of the channels. The contour of S1 includes straight edge L1, straight edge L2, arc edge C1, and arc edge C2. Among them, straight edge L1 and straight edge L2 are both parallel to the diffuser axis, straight edge L1 is on the suction side, straight edge L2 is on the pressure side, arc edge C1 is at the top, and arc edge C2 is at the bottom;

[0043] Step 2.3), determine the ring where the outlet sections of each diffuser channel are located, with the inner ring being circle O3 and the outer ring being circle O4. Determine circle O5 according to circle O3 and O4 such that circle O5 is concentric with circle O3 and O4, and the radius of circle O5 is equal to 1 / 2 of the sum of the radii of circle O3 and O4;

[0044] Step 2.4), draw a straight line L3 starting from the midpoint P1 of the arc edge C2 along the direction of the inlet air flow velocity vector. The projection of L3 on the outlet plane intersects the circle O5 at point P2;

[0045] Step 2.5), intercept a sector cross-section S2 on the ring where each channel outlet cross-section is located as the outlet cross-section corresponding to the inlet cross-section S1 according to P2 and the outlet area of the channel. The contour of S2 includes a straight edge L4, a straight edge L5, an arc edge C3, and an arc edge C4. Among them, the straight edge L4 is located on the suction side, the straight edge L5 is located on the pressure side, the arc edge C3 is located on the inner side, the arc edge C4 is located on the outer side, and P2 is located at the midpoint of L4;

[0046] Step 2.5), stretch L3 along the diffuser axis as the sketch plane S3;

[0047] Step 2.6), use the intersection point of the straight line passing through P2 and parallel to the diffuser axis and L3 as the control point P3, P1 as the starting point, and P2 as the ending point to make a quadratic curve with a rho value of 0.6. This quadratic curve is the bottom center line L6;

[0048] Step 2.7), use the bottom end point P4 of L1 as the starting point of the perpendicular line L7, make a perpendicular line to L6, extend the ending point of the perpendicular line to P5, control the distance from P4 to P5 to control the diffuser width and thus control the throat area, and sweep C2, L4, and L7 with L6 as the guide line to obtain the bottom surface A1, as Figure 1 shown;

[0049] Step 3), form a suction surface and a pressure surface on the suction side and the pressure side of the bottom surface respectively through ruled surfaces, and form a transition surface with the casing surface on the side of the suction surface;

[0050] Step 3.1), let the curve located on the suction side among the four curves enclosing the bottom surface A1 be L8, and make a normal perpendicular line L9 at the half-chord length of L8; the length of L9 forms a linear distribution with L1 and C3; sweep L1, L9, and C3 with L8 as the guide line to obtain the suction surface A2, as Figure 2 shown;

[0051] Step 3.2), design the casing line L10 in the form of a straight line - arc - straight line based on the dimensions of the diffuser;

[0052] Step 3.3), the Z-axis of the rectangular coordinate system is the diffuser axis, the XOY plane of the rectangular coordinate system is perpendicular to the diffuser axis, let the Z-axis of the cylindrical coordinate system be the Z-axis of the rectangular coordinate system, the θ angle between the cylindrical coordinate system and the X-axis in the projection of the rectangular coordinate system, the R of the cylindrical coordinate system is the distance to the origin in the projection of the rectangular coordinate system, m is the curve vector, and β is the curve angle; based on L10, d θAs dependent variables, dm and R are determined by the L10 coordinates. Given the β angle and the variation law of tanβ, two curves L11 and L12 on the casing revolution surface are obtained according to the following formula:

[0053] dθ / dm = tanβ / R

[0054] In step 3.4), let L13 be the curve on the pressure side among the four curves enclosing the bottom surface A1, and L14 be the curve on the casing side among the four curves forming A2. A ruled surface A3 is formed by performing ruled surface modeling on L11 and L13, and a suction surface transition surface A4 is formed by performing ruled surface modeling on L12 and L14, as Figure 3 shown;

[0055] In step 4), the casing is trimmed by the pressure surface A3 and the transition surface A4 to obtain the casing surface A5. A complete channel is formed by the bottom surface A1, the suction surface A2, the pressure surface A3, the transition surface A4, and the casing surface A5, as Figure 4 shown; The complete channel is arrayed, that is, a complete three-dimensional structure of the diffuser is formed, as Figure 5 shown in (a), Figure 5 shown in (b);

[0056] In step 5), after the complete channel is formed, a radial slot is opened at the diffuser outlet position to convert the diffuser channel into blades. A slot is opened at the middle of the bottom surface outlet and the middle of the transition surface outlet. The width and axial height of the slot can be freely selected, as Figure 6 shown in (a), Figure 6 shown in (b).

[0057] The modeling method of the present invention mainly lies in the determination of the bottom surface A1. Once the bottom surface is determined, the suction surface A2, the pressure surface A3, the transition surface A4, and the casing surface A5 can be sequentially obtained according to the steps. The rho value of the bottom surface center line controls the bottom surface curvature. The bottom surface A1 can control the geometric angle at the bottom of the inlet. The casing surface A5 can control the geometric angle at the top of the inlet. And the bottom surface A1 can also control the throat area. The middle part of the suction surface A2 can control the position of the suction surface, avoiding the intersection of the pressure surface and the suction surface. The slot opened at the outlet position guides the high-speed flow on the pressure surface to the low-speed area of the bottom surface, making the flow better.

[0058] The functions of each curved surface are as follows:

[0059] Bottom surface A1: Suction surface, hub;

[0060] Suction surface A2: Suction surface, hub;

[0061] Pressure surface A3: Pressure surface, casing;

[0062] Transition surface A4: Pressure surface;

[0063] Casing surface A5: Casing.

[0064] Those skilled in the art can understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as the general understanding of those of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with their meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless defined as such here.

[0065] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only for the specific embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A novel design and modeling method for a tubular diffuser of a micro centrifugal compressor, characterized in that, It includes the following steps: Step 1), calculate the inlet area and outlet area of the diffuser according to the rotor outlet air flow parameters and the diffuser size requirements, and obtain the inlet area and outlet area of each channel according to the preset number of channels; Step 2), design the bottom center line with the inlet air flow vector and the outlet air flow vector as the sketch plane according to the diffuser inlet area, outlet area and the number of channels, and sweep according to the bottom center line and the inlet and outlet section lines to obtain the key surface bottom; Step 2.1), determine the cylindrical side walls where the inlet sections of each channel are located according to the diffuser inlet area, the top of which is circle O1 and the bottom is circle O2; Step 2.2), divide the cylindrical side wall between circle O1 and O2 into each channel according to the inlet area of the channel, and obtain the inlet section S1 of one of the channels. The contour of S1 includes straight edge L1, straight edge L2, arc edge C1, and arc edge C2. Among them, straight edge L1 and straight edge L2 are both parallel to the diffuser axis, straight edge L1 is located on the suction side, straight edge L2 is located on the pressure side, arc edge C1 is located on the top, and arc edge C2 is located on the bottom; Step 2.3), determine the ring where the outlet sections of each diffuser channel are located, the inner ring of which is circle O3 and the outer ring is circle O4. Determine circle O5 according to circle O3 and O4, so that circle O5 is concentric with circle O3 and O4, and the radius of circle O5 is equal to 1 / 2 of the sum of the radii of circle O3 and O4; Step 2.4), draw a straight line L3 from the midpoint P1 of arc edge C2 along the inlet air flow velocity vector direction. The projection of L3 on the outlet plane intersects circle O5 at point P2; Step 2.5), intercept a sector section S2 on the ring where the outlet sections of each channel are located as the outlet section corresponding to the inlet section S1 according to P2 and the outlet area of the channel. The contour of S2 includes straight edge L4, straight edge L5, arc edge C3, and arc edge C4. Among them, straight edge L4 is located on the suction side, straight edge L5 is located on the pressure side, arc edge C3 is located on the inner side, arc edge C4 is located on the outer side, and P2 is located at the midpoint of L4; Step 2.5), stretch L3 along the diffuser axis as the sketch plane S3; Step 2.6), make a quadratic curve with a rho value of 0.6 with the intersection point of the straight line passing through P2 and parallel to the diffuser axis and L3 as the control point P3, P1 as the starting point, and P2 as the ending point. This quadratic curve is the bottom center line L6; Step 2.7), use the bottom end point P4 of L1 as the starting point of the perpendicular line L7, make a perpendicular line to L6, and extend the ending point of the perpendicular line to P5. Control the distance from P4 to P5 to control the diffuser width and thus control the throat area. Sweep C2, L4, and L7 with L6 as the guide line to obtain the bottom surface A1; Step 3), form a suction surface and a pressure surface on the suction side and pressure side of the bottom surface respectively through ruled surfaces, and form a transition surface with the casing surface on the side of the suction surface; Step 3.1), let the curve located on the suction side among the four curves enclosing the bottom surface A1 be L8, and make a normal perpendicular line L9 to L8 at the half chord length of L8; The length of L9 forms a linear distribution with L1 and C3; Sweep L1, L9, and C3 with L8 as the guide line to obtain the suction surface A2; Step 3.2), the casing line L10 is designed in the form of straight line - arc - straight line based on the size of the diffuser; Step 3.3), the Z-axis of the rectangular coordinate system is the axis of the diffuser, the XOY plane of the rectangular coordinate system is perpendicular to the axis of the diffuser, let the Z-axis of the cylindrical coordinate system be the Z-axis of the rectangular coordinate system, and the cylindrical coordinate system θ is the angle between the projection of the rectangular coordinate system and the X-axis, the cylindrical coordinate R is the distance from the projection of the rectangular coordinate system to the origin, m is the curve vector, and β is the curve angle; based on L10, d θ is used as the dependent variable, dm and R are determined by the coordinates of L10. Given the β angle and the variation law of tanβ, two curves L11 and L12 on the casing revolution surface are obtained according to the following formula: dθ / dm = tanβ / R Step 3.4), let L13 be the curve on the pressure side among the four curves enclosing the bottom surface A1, and L14 be the curve on the casing side among the four curves forming A2. A ruled surface is formed between L11 and L13 to obtain the pressure surface A3, and a ruled surface is formed between L12 and L14 to obtain the suction surface transition surface A4; Step 4), the casing is trimmed by the pressure surface A3 and the transition surface A4 to obtain the casing surface A5. A complete channel is formed by the bottom surface A1, the suction surface A2, the pressure surface A3, the transition surface A4, and the casing surface A5. The complete channels are arrayed to form a complete three - dimensional structure of the diffuser; Step 5), after the complete channel is formed, radial slots are opened at the diffuser outlet to convert the diffuser channel into blades.

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