CN112228401A

CN112228401A - Slotted vane diffuser

Info

Publication number: CN112228401A
Application number: CN202011065897.8A
Authority: CN
Inventors: 陈化; 赵亮; 马超; 张燕芳; 张晗; 郭峰; 刘海龙; 崔义强; 岳本壮; 李兆鑫
Original assignee: Dalian Maritime University
Current assignee: Dalian Maritime University
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2021-01-15

Abstract

The invention discloses a slotted vane diffuser which comprises a body and vanes arranged on the body, wherein the vanes comprise inner ends close to the center of the body and outer ends far away from the center of the body, and the vanes are inclined relative to a radius passing through the inner ends; the surface of the blade is provided with a slot communicated with two sides of the blade, and the slot is inclined relative to the blade. The slotted diffuser is arranged on the blade in an inclined mode, so that the working range of the compressor is enlarged, and the pneumatic efficiency is well guaranteed.

Description

Slotted vane diffuser

Technical Field

The invention relates to the field of diffusers, in particular to a slotted vaned diffuser.

Background

The diffuser is applied to a centrifugal compressor and is a device for converting fluid kinetic energy into static pressure energy. The diffuser mainly comprises a vaneless diffuser and a vaned (blade) diffuser, and compared with the vaneless diffuser, the vaned diffuser generally has better static pressure recovery coefficient near the designed mass flow, can realize higher peak efficiency of the compressor, and is widely applied to medium and large centrifugal compressors.

However, under low mass flow conditions, the positive angle of attack of the fluid ahead of the diffuser vanes and excessive diffusion of the gas flow in the diffuser cause separation of the flow in the diffuser, resulting in diffuser stall. When the mass flow is large, the diffuser blade can be blocked, namely the flow velocity of the throat of the diffuser blade reaches the local sound velocity, so that the flow capacity of the compressor is limited. These events limit the stable operating range of the compressor. Therefore, expanding the operating range of the vane diffuser while maintaining high aerodynamic efficiency of the vane diffuser has been an important requirement and research area for the development of centrifugal compressors.

Disclosure of Invention

The invention provides a slotted vane diffuser, which widens the working range of the vane diffuser and keeps the high pneumatic efficiency of the diffuser.

A slotted vane diffuser comprising a body and a vane disposed on the body, the vane comprising an inner end proximate a center of the body and an outer end distal the center of the body, the vane being canted relative to a radius passing through the inner end;

the surface of the blade is provided with a slot communicated with two sides of the blade, and the slot is inclined relative to the blade.

Further, the inclination direction of the slot and the inclination direction of the blade are the same, and the included angle between the center line of the slot and the blade is 5-20 degrees.

Further, the sectional area of the slit is gradually reduced from the air inlet to the air outlet.

Further, the blade is disposed on a hub side of the body, and a width of the slit is gradually reduced from the air inlet to the air outlet.

Further, the height of the slit is gradually reduced from the air inlet to the air outlet.

Further, the height of the slot is 4% -10% of the height of the blade.

Further, the width of the end part of the slot is 5% -20% of the arc length of the slot.

Further, the opening of the slot is arranged at the position of 25% -45% of the chord length of the blade.

Further, the slot is provided on a rim side of the body.

A compressor comprises a volute, an impeller and the diffuser.

The slotted vane diffuser disclosed by the invention has the advantages that the slots are formed in the vanes, so that fluid can flow from the pressure side near the inlet of the vanes to the suction side near the outlet of the vanes to generate boundary layer suction and add energy to the boundary layer, the separation of the boundary layer of the diffuser is delayed, and the problem of contradiction between stability expansion and efficiency in other slotting methods is solved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.

FIG. 1 is a schematic structural diagram of a compressor in an embodiment of the invention, wherein the compressor is a centrifugal compressor with a hub slot diffuser;

FIG. 2 is a schematic view of a diffuser in an embodiment of the invention, the diffuser being a slotted vaned diffuser;

FIG. 3 is an enlarged partial schematic view of a diffuser in an embodiment of the present invention;

FIG. 4 is a schematic top view of a diffuser vane in an embodiment of the present invention;

FIG. 5 is a perspective view of a diffuser vane in an embodiment of the present invention;

FIG. 6 is a flow chart of the surge point of an unslotted diffuser in accordance with an embodiment of the present invention;

FIG. 7 is a flow chart of the surge point of a slotted diffuser in accordance with an embodiment of the present invention;

FIG. 8 is an enlarged view of a portion of FIG. 6 in accordance with an embodiment of the present invention;

FIG. 9 is an enlarged view of a portion of FIG. 7 in accordance with an embodiment of the present invention;

FIG. 10 is a graph of the blade loading at the surge point of an unslotted diffuser in accordance with an embodiment of the present invention;

FIG. 11 is a graph of slotted diffuser surge point blade loading in accordance with an embodiment of the present invention;

FIG. 12 is a flow chart of the point of maximum efficiency of an unslotted diffuser in accordance with an embodiment of the present invention;

FIG. 13 is a flow chart of a slotted diffuser point of maximum efficiency according to an embodiment of the present invention;

FIG. 14 is an enlarged view of a portion of FIG. 12 in accordance with an embodiment of the present invention;

FIG. 15 is an enlarged view of a portion of FIG. 13 in accordance with an embodiment of the present invention;

FIG. 16 is a graph of maximum efficiency point blade loading for an unslotted diffuser in accordance with an embodiment of the present invention;

FIG. 17 is a graph of slotted diffuser peak efficiency blade loading in accordance with an embodiment of the present invention;

FIG. 18 is a graph illustrating the effect of diffuser notching on compressor efficiency in an embodiment of the present invention;

FIG. 19 is a graph illustrating the effect of diffuser notching on compressor pressure ratio in an embodiment of the present invention;

FIG. 20 is a graph of the effect of diffuser notching depth on compressor performance in an embodiment of the present invention;

FIG. 21 is a graph of the effect of diffuser notching angle on compressor performance in an embodiment of the present invention;

FIG. 22 is a graph of the effect of diffuser slotted cross-sectional area on compressor performance in an embodiment of the present invention;

FIG. 23 is a graph of the effect of diffuser notch arc length on compressor performance in an embodiment of the present invention;

FIG. 24 is a graph of the effect of diffuser notching at different chord length locations on compressor performance in an embodiment of the present invention.

In the figure: 1. a compressor volute; 2. an air intake hood; 3. a diffuser; 4. an impeller housing; 5. an impeller; 6. A slot is formed; 7. a pressure surface; 8. a suction surface; 9. an air inlet; 10. an air outlet; s₁A gas inlet cross section; s₂The section of the air outlet; alpha, the included angle between the blade and the slot; h is₁Height of slot opening entrance; h is₂Height at the slot exit.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, a compressor includes a volute, an inlet shroud, an impeller shroud, and a diffuser. In the working process, the impeller 5 is driven by a turbine or other power devices to rotate, air is sucked into the air inlet flow channel through the air inlet of the air compressor shell and flows along the impeller flow channel under the action of centrifugal force, the air is compressed in the impeller flow channel, and the speed, the pressure and the temperature of the air are improved; then, the compressed air is output from the impeller flow passage and enters the flow passage of the diffuser 3, the speed is reduced, the kinetic energy is converted into pressure energy, and the pressure is further improved; and finally, the gas enters a flow channel of the compressor shell 1 and is discharged from a gas outlet of the compressor shell, so that the whole pressurizing process is completed.

The back shroud overlying the impeller and diffuser is not shown for clarity. The diffuser comprises a body and blades arranged on the body, the blades comprise inner ends or inlets close to the center of the body and outer ends or outlets far away from the center of the body, and the blades are inclined towards the rotating direction of the impeller relative to the radius passing through the inlets, as shown in figure 2; the surface of the blade is provided with a slot which is communicated with the two sides of the blade, the slot is further inclined relative to the blade towards the rotating direction of the impeller, the inclination angle is 5-20 degrees as shown in figure 3, and the angle alpha is 5-20 degrees.

Research and analysis show that diffuser flow separation mainly occurs in a wall surface boundary layer, the separation of the wall surface boundary layer reduces the diffusion capacity of the diffuser, and the diffuser stalls and the compressor is unstable under small flow. Separation also increases flow losses. In order to widen the working range of the compressor and increase the pneumatic efficiency of the compressor, the surface of the blade is provided with a slot, the height of the slot is 4-10% of the height of the blade, the slot communicates the two sides of the blade, namely a pressure surface and a suction surface, the width of the end part of the slot is 5-20% of the arc length of the slot, and fluid can flow from the pressure surface to the suction surface through the slot. Thus, at low flows, the diffuser is subjected to a positive angle of attack, and the suction surface boundary layer becomes thicker, risking separation. The fast fluid from the pressure surface adds forward kinetic energy to the boundary layer of the suction surface, thereby avoiding or delaying the separation of the boundary layer of the suction surface. And under large flow, the diffuser bears a negative attack angle, the boundary layer of the pressure surface becomes thick, and the danger of separation exists. At this time, the flow from the pressure surface to the suction surface through the slit plays a role of sucking the boundary layer of the pressure surface, so that the boundary layer becomes thin and the back pressure is reduced. Thereby avoiding or delaying separation of the boundary layer of the pressure face.

Slotted vanes can be arranged on the hub side or the rim side to improve the performance of the diffuser. Because the invention grasps the key of controlling the boundary layer separation of the end wall surface, the height of the slot of the invention can achieve the purpose of flow control only by a few percent of the height of the blade. Because the mass of the fluid passing through the slot is less, the loss possibly brought by the flow of the slot is reduced, thereby being beneficial to the efficiency of the compressor.

The slot is arranged at one end of the pressure surface and is an air inlet, the other end of the suction surface is an air outlet, and the cross sections of the air inlet and the air outlet can be equal or unequal. As shown in FIG. 4, the air flow enters from the air inlet 9 and exits from the air outlet 10 with an outlet cross section S₂Area ratio of (S) inlet section S₁The slot is equivalent to a nozzle, the outlet flow speed can be improved, and the better boundary layer control effect is realized. In order to realize the purpose that the sectional area of the outlet is smaller than that of the inlet, the width of the slot is gradually reduced from the inlet to the outlet; or keeping the width of the slot constant, and gradually reducing the height of the slot from the inlet to the outlet, as shown in fig. 5, h₁Greater than h₂。

Obviously, the invention is applicable to both volute-containing and volute-free compressors. The invention will be further explained and illustrated below by taking a conventional compressor with a volute as an example. The presence of the compressor volute creates a circumferentially asymmetric exit boundary for the diffuser. As shown in fig. 6, 8 and 10, when the compressor operates under low mass flow conditions, the back pressure of the vane diffuser increases as the gas flow moves circumferentially in the volute. In a conventional compressor, this leaves the vane diffuser in a high back pressure condition in several passages near the exit of the volute, causing the flow there to separate from the suction surfaces of the vanes, creating a backflow. In the case of a hub side open groove, as shown in fig. 7, 9 and 11, under the driving of the pressure gradient at the two ends of the groove, some fluid flows from the pressure surface to the suction surface, and the flow increases the energy of the boundary layer at the suction surface side, and at the same time, sucks away the stagnant boundary layer which may be separated, thereby avoiding the flow separation between the suction surface and the hub end wall, eliminating the backflow and widening the small flow operation boundary.

When the centrifugal compressor is in a high flow condition, a negative angle of attack occurs at the diffuser inlet, causing flow separation to occur at the pressure face of the vane, causing backflow at the diffuser outlet region, as shown in fig. 12, 14 and 16. Unlike small flows, each diffuser vane passage has backflow except for the two diffusers under the volute tongue because the volute applies a lower and more uniform outlet pressure to the diffuser than at low mass flows. Because the negative incidence angle of the leading edge of the blade is not large, the vortex generated by separation is weak, and the generated backflow area is smaller than that in surging. However, the channels are separated due to more diffusion. The amount of negative load (pressure on the pressure side lower than the suction side) is greater in fig. 16. In the case of hub notching, as shown in fig. 13, 15 and 17, the blade load is lost and the flow in the diffuser is more uniform. The elimination of flow separation reduces the losses within the diffuser, improves static pressure recovery, and also improves flow in the downstream volute. These all contribute to reducing losses and achieving higher compressor peak efficiency.

Hub side blade grooving and rim side blade grooving, both of which have a positive impact on improving compressor surge and blockage.

When the groove is formed in the hub end, the surge boundary of the compressor can be effectively increased compared with the groove formed in the blade on the side of the wheel rim. As shown in the calculation results of fig. 8. This is because the hub end notch can delay the separation and backflow of the boundary layer on the end wall surface at the outlet hub of the diffuser, thereby more effectively improving the stability of the diffuser. Moreover, the surge end efficiency and peak efficiency of the hub side slot is better than the rim side slot. When the rim side is grooved, the plugged end is more efficient than the hub side grooved as shown in fig. 8. Therefore, it can be considered that the hub-side blade grooving is better than the rim-side blade grooving at medium and small flow rates.

As shown in fig. 4, the section 1 is a plane where the air inlet is perpendicular to the slit, and the section 2 is a plane where the air outlet is perpendicular to the slit, and as shown in fig. 4, if a certain groove height h is fixed, the shape (width) of the groove is changed so that the cross-sectional area of the section 2 is larger than that of the section 1, so that the groove shape becomes a gradually expanding shape from the inlet to the outlet, and the performance of the surge end of the compressor is improved.

Furthermore, if a certain height h is fixed, the shape of the groove is changed, so that the cross section area of the section 2 is equal to that of the section 1, and the surge and blockage range of the diffuser is expanded to a certain extent.

Further, if a certain height h is fixed, the shape of the groove is changed to make the cross-sectional area of the section 2 smaller than that of the section 1, so that the groove shape becomes a tapered shape from the inlet to the outlet, the surge boundary and the blockage boundary are both expanded, the improvement of the blockage (large flow rate) end is more obvious, and the high pneumatic efficiency is maintained. As shown in fig. 22, in the case of the same mass flow rate, the aerodynamic efficiency is highest when the cross-sectional area is gradually reduced from the inlet to the outlet, and therefore, the shape in which the groove shape is tapered from the inlet to the outlet is the optimum shape.

As shown in fig. 23, the mass flow starting points corresponding to different arc lengths are different, that is, the working ranges are different, wherein when the width of the groove is 5% to 20% of the circumferential arc length of the inlet, the aerodynamic efficiency is high, and the working range is significantly wider, that is, the mass flow corresponding to the starting point is smaller, so that the optimum width of the groove is 5% to 20% of the circumferential arc length of the inlet.

Further, if the groove depth is changed by fixing the width of the groove so that the cross-sectional area of the section 2 is smaller than that of the section 1, as shown in fig. 5, an effect similar to the change of the width of the groove can be produced, but the effect is slightly inferior.

Furthermore, when the groove depth is at a shallow height, the effect of expanding the surging and blocking boundary of the centrifugal compressor is small; with the proper increase of the height, the method has obvious effect on expanding the surge and blockage of the centrifugal compressor; if the groove depth continues to increase, the effect on expanding the surge and blockage boundaries of the compressor is reduced and the efficiency is reduced, as shown in FIG. 20, with increasing mass flow, yielding an optimum groove depth of 4-10% of the blade height.

The optimal inlet position of the slotting is determined according to the method, the respective influences of the angle and the width are determined, and then all factors are superposed, so that the ideal slotting effect is achieved.

The slot in this embodiment is suitable for use with blades of various shapes, such as airfoil, wedge, linear, or other types.

The diffuser disclosed by the invention can be used for directly processing the existing diffuser, namely processing the blades of the existing diffuser and removing part of materials of the blades to form a slot structure, and the number of parts and the installation mode of the existing centrifugal compressor are not changed.

The slot 6 may be provided at either the hub end or the rim end, and for ease of illustration, the slot 6 is provided at one end of the hub in one embodiment provided herein. In addition, when the slot 6 is formed, the slot 6 can be arranged on each blade, and the mode that the slot 6 is arranged on only part of the blades can still have the stabilizing effect of the centrifugal compressor. The specific position and number of the slots are based on the actual requirement. The pneumatic efficiency of the grooves at the hub end and at the rim side is compared as shown in fig. 18, and in both cases the pressure ratio is compared as shown in fig. 19.

The diffuser disclosed by the invention is characterized in that the surface of the diffuser blade is provided with a slot for connecting the pressure surface and the suction surface of the blade. The grooves at the hub end and the rim end obviously reduce the surge flow of the compressor and widen the operating range; the grooving of the hub end also improves the efficiency of the compressor.

In the embodiment, the inclination directions of the slot and the blade are the same, and the included angle between the central line of the slot and the blade is 5-20 degrees. As shown in fig. 21, the efficiency is significantly higher in this range of included angles, and the efficiency drops significantly faster for the included angles of 3 ° and 30 ° especially at higher mass flow rates. Therefore, an angle of 5 to 20 degrees between the centerline of the slot and the vane is preferred.

The opening of the slot is arranged at 25% -45% of the chord length of the blade, as shown in figure 24, the opening is arranged between 25% -45% of the chord length, and the compressor efficiency is higher.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A slotted vane diffuser comprising a body and vanes disposed on said body, said vanes including inner ends proximate a center of said body and outer ends distal from said center of said body, said vanes being canted relative to a radius passing through said inner ends;

2. The slotted vane diffuser of claim 1 wherein the slot is angled in the same direction as the vane, and the slot centerline is angled between 5 ° and 20 ° with respect to the vane.

3. The slotted vane diffuser of claim 1 wherein the slot has a cross-sectional area that decreases from the inlet to the outlet.

4. The slotted vane diffuser of claim 3 wherein the vanes are disposed on the hub side of the body and the slot tapers in width from the inlet port to the outlet port.

5. The slotted bladed diffuser of claim 3, wherein the slot has a height that decreases from the inlet to the outlet.

6. The slotted bladed diffuser of claim 1, wherein the slot has a height of between 4% and 10% of the blade height.

7. The slotted bladed diffuser of claim 1, wherein the slot ends have a width that is between 5% and 20% of the arc length over which they are positioned.

8. The slotted diffuser of claim 1, wherein the slot opening is located at 25% -45% of the chord length of the vane.

9. The slotted vane diffuser of claim 1 wherein the slot is disposed on a rim side of the body.

10. A compressor comprising a volute, an impeller and a diffuser according to any one of claims 1 to 9.