CN101173613A - Leakage Suppression Structure at the Top Clearance of Centripetal Turbine Wheel - Google Patents

Abstract

The invention discloses a leakage suppression structure at the top of a centripetal turbine impeller. The leakage suppression structure is a series of circumferential grooves or a series of axial grooves or a series of spiral grooves or a honeycomb sealing structure; It is on the inner wall surface of the solid wall wheel cover at the top of the impeller, and is located within the range of 30% to 120% of the meridian chord length at the top of the impeller. The leakage suppression structure at the top of the centripetal turbine impeller can effectively reduce the lateral leakage in the gap, increase the output power of the turbine, improve the efficiency of the turbine, and achieve the purpose of saving energy and reducing consumption. According to the current numerical simulation verification results, the output power of the centripetal turbine can be increased by about 2% while ensuring a slight increase in the efficiency of the centripetal turbine.

Description

Leakage Suppression Structure at the Top Clearance of Centripetal Turbine Wheel

technical field

The present invention relates to a leakage suppression structure at the top clearance of a centripetal turbine impeller, in particular to several sealing structures such as circumferential grooves, axial grooves, spiral grooves or honeycombs arranged on the inner wall of a conventional centripetal turbine solid-wall wheel cover, by reducing the clearance at the top of the impeller The lateral leakage of medium working fluid reduces the gap loss, increases the output power of the turbine, improves the efficiency of the turbine, and achieves the purpose of saving energy and reducing consumption.

Background technique

The existence of the gap at the top of the impeller makes the leakage flow through the gap and the resulting gap loss inevitable, whether it is for an axial flow or a centripetal turbine. When the turbine impeller is working, there is a certain pressure difference between the pressure surface and the suction surface of the blade. Under the action of this pressure difference, part of the working fluid on the pressure surface side of the blade will leak to the suction surface side of the blade through the gap at the top of the blade. On the one hand, the leaked working fluid does not push the blades to do work, causing a certain power loss to the turbine; on the other hand, this part of the leaked working fluid will be mixed with the mainstream, resulting in a leakage loss in the tip clearance and causing a flow through the turbine. Reduced efficiency.

The centripetal turbine impeller can be divided into three types: closed type, semi-open type and open type according to the structure of the flow channel. Due to the low allowable impeller inlet linear velocity, the application range of the closed impeller is severely limited. For semi-open and open impellers, since there is no wheel cover that rotates together with the blades on the top of the blades, their stress conditions have been improved, and the allowable linear speed at the impeller inlet can be very high. At present, the impellers cast by high-temperature alloy precision casting are used. The impeller inlet line speed is even as high as about 600m/s. It is well known that high impeller rotational speeds lead to increased power density and reduced size. Therefore, impellers with two flow channels, semi-open and open, are widely used in turbochargers, aero-engine auxiliary machines and micro gas turbines.

At present, the top of the semi-open and open impellers adopts the form of solid wall wheel cover, that is, without any structural treatment, and has a smooth inner surface. The gap between the inner surface of this wheel cover and the top of the impeller blade is generally About 1-3% of the local leaf height. Although the force condition of the impeller with this structure has been improved, it makes it possible for more working fluid to cross-flow in the gap at the top of the blade, which brings power loss and gap loss to the centripetal turbine.

Unlike the axial flow turbine impeller without a crown, which only has radial clearance at the top, the radial turbine impeller top clearance has both axial and radial clearances, as shown in Figure 1.

In view of the difference in clearance structure, the axial clearance and radial clearance of centripetal turbine impellers have inconsistent effects on the overall performance of the whole machine. Foreign scholars have obtained the results of the axial and radial clearances at the top of the impeller through test methods on the total-total efficiency and The test results of the influence degree of mass flow rate are shown in Table 1.

Table 1 The test results of the impact of the axial and radial clearances on the top of the impeller on the overall performance of the stage

- Total - Total Efficiency Traffic/% +1% axial play +1% radial clearance +1% axial play +1% radial clearance Futral and Holeski -0.15 -1.6 -0.1 +0.3 Ricardo -0.2 -0.5 -0.1 +0.5 Ishimo et al -0.2 -1.2 - +0.6 Krylov and Spunde -0.1 -0.6 -0.1 -0.2

The research results obtained by the applicant on the top clearance of a centripetal turbine impeller through numerical simulation method are shown in Table 2. Obviously, they are consistent with the results shown in Table 1: (1) The radial clearance at the top of the impeller is opposite to the axial clearance The influence of the stage efficiency of the centrifugal turbine is different. The radial clearance increases by 1% relative to the outlet blade height, and the stage efficiency decreases by 1.5%, while the axial clearance increases by 1% relative to the impeller inlet width, and the stage efficiency decreases by about 0.15%. (2) The impeller top diameter The radial gap and the axial gap have different effects on the flow capacity of the centripetal turbine. The radial gap increases by 1% relative to the outlet blade height, and the stage flow capacity increases by 0.24%, while the axial gap increases by 1% relative to the impeller inlet width, and the stage flow capacity increases. Ability reduced by 0.06%.

Table 2 Numerical simulation results of the impact of the axial and radial clearances on the top of the impeller on the overall performance of the stage

-   Axial clearance/% Radial clearance/% Total - Total Efficiency/% Efficiency change Flow/kg·s ^-1 Change in traffic/% Gap 1 1 1 92.721 - 1.0263 - Gap 2 twenty one 92.568 -0.153 1.0257 -0.058

gap 3 1 2 91.455 -1.266 1.0288 +0.244 gap 4 twenty two 91.166 -1.555 1.0284 +0.205

At present, scholars at home and abroad who study this issue generally believe that (1) in the impeller top clearance, the pressure difference between the pressure surface and the suction surface of the blade top and the "scraping" caused by the relative motion between the blade top and the wheel cover The flow plays a major role in affecting the gap flow field, and jointly controls the gap flow field at the top of the impeller; (2) In the top area of the working wheel, the working medium flows into the gap from the suction side of the gap under the action of "scraping", and from the pressure Compared with the pressure difference from the pressure side to the suction side, the "scraping" effect is absolutely dominant in this area; (3) In the middle area of the chord direction of the gap at the top of the impeller, due to the relative movement speed of the wheel cover decreases , the "scraping" effect weakens, the blade load gradually increases, and the pressure difference from the pressure side to the suction side increases, and the flow from the suction side to the pressure side caused by the "scraping" effect in the gap is also caused by the pressure difference (4) In the top area of the wind deflector, the pressure difference between the two sides of the impeller blades is relatively large, and the "scraping" effect becomes weaker, and almost all of the top gap is from the pressure side to the suction side. Airflow from face side leakage.

Figure 2 is the relationship curve of the gap leakage flow along the meridional chord direction under three gap sizes obtained by the inventor by studying the gap flow field at the top of a centripetal turbine impeller, where the leakage amount is at different chord positions on the arc surface in the gap Obtained by integration, it is stipulated that the leakage from the pressure surface to the suction surface is a positive value. It can be clearly seen from the figure that (1) the smaller the gap at the top of the impeller, the stronger the "scraping" effect on the top area of the impeller. When the gap is 1%, the gap from the pressure side to the suction side caused by the pressure difference in the gap The leakage flow at the chord direction of 45% is balanced with the leakage flow from the suction side to the pressure side caused by "scraping", and then the leakage basically increases linearly along the chord direction; and when the gap is 2%, The balance point for the leak is moved forward at 20% chordwise, and even further forward at 3% clearance. (2) The gap leakage mainly occurs in the middle and rear sections of the meridian chord length, and the leakage in this part increases almost linearly along the meridian chord length. (3) When the gap size is 2%, the gap leakage relative to the stage mass flow rate is 6.5%, which accounts for a considerable proportion.

Compared with the flow characteristics of the top clearance of the centripetal turbine impeller, if the top clearance of the axial flow turbine without crown increases by 1%, the stage efficiency will decrease by about 2%, which is greater than the influence of the radial clearance of the centripetal turbine on the performance of the stage. Moreover, the axial flow type is the main form adopted by large-scale prime mover machinery, and its tip clearance flow characteristics and leakage suppression structure have always been one of the research hotspots. However, for the centripetal turbine, which is generally an auxiliary prime mover, with the increasingly tense energy issues and the gradual wide application of micro gas turbines using the centripetal turbine as the core power component, the research on the aerodynamic performance of the related components of the centripetal turbine has been carried out in recent years. It has also gradually attracted the attention of scholars at home and abroad, and the research on the leakage suppression structure of the impeller top clearance is one of the hot research contents.

The difference between the radial turbine and the axial flow turbine in the top gap structure of the impeller makes the flow characteristics of the radial turbine impeller top gap completely different from that of the axial flow turbine, so it is necessary to construct the leakage suppression of the radial turbine impeller top gap according to its unique leakage characteristics structure.

Contents of the invention

Aiming at the problem of the output power loss and gap energy loss caused by the lateral flow of working medium in the top gap of the semi-open or open centripetal turbine impeller, the present invention proposes a leakage suppression structure at the top of the centripetal turbine impeller, which can effectively Suppress the leakage flow of the working fluid in the top gap of the semi-open or open impeller, reduce the gap loss, increase the output power of the centripetal turbine, improve its aerodynamic efficiency, and achieve energy saving and consumption reduction.

In order to realize above-mentioned task, the present invention takes following technical solution:

A leakage suppression structure at the top of a centripetal turbine impeller, characterized in that the leakage suppression structure is a series of circumferential grooves or a series of axial grooves or a series of spiral grooves or a honeycomb seal; The inner wall surface of the solid wall wheel cover at the top of the impeller is located within the range of 30% to 120% of the meridian chord length at the top of the impeller.

The leakage suppression structure at the top of the centripetal turbine impeller can effectively reduce the lateral leakage in the gap, reduce the gap loss, increase the output power of the turbine, improve the efficiency of the turbine, and achieve the purpose of saving energy and reducing consumption.

At present, the numerical simulation verification of the effectiveness of the sealing structure has been basically completed, and it can increase the output power of the centripetal turbine by about 2% while ensuring a slight increase in the efficiency of the centripetal turbine.

Description of drawings

Figure 1 is a schematic diagram of the axial and radial clearance positions at the top of the centripetal turbine impeller;

Figure 2 shows the distribution of top clearance leakage along the meridian chord length under three clearance sizes for a centripetal turbine impeller design condition;

Fig. 3 is the sealing structure of the circumferential groove on the top of the centripetal turbine impeller;

Fig. 4 is the axial groove sealing structure at the top of the centripetal turbine impeller;

Fig. 5 is A-A sectional view among Fig. 4;

Fig. 6 is the spiral groove sealing structure at the top of the centripetal turbine impeller;

Fig. 7 is the honeycomb seal structure at the top of the centripetal turbine impeller;

Fig. 8 is the B direction view in Fig. 7;

The present invention will be further described in detail below in conjunction with the accompanying drawings and technical principles.

Detailed ways

Refer to accompanying drawings 3 to 8 for the specific structure of the present invention. The technical idea of the present invention is that a sealing structure is arranged on the inner wall of the solid wall wheel cover of a conventional semi-open or open centripetal turbine, and the transverse string in the gap at the top of the impeller blade The flow is suppressed, and under the premise of ensuring that the overall size of the gap at the top of the impeller does not change, the output power of the centripetal turbine is increased, the efficiency of the centripetal turbine is improved, and the purpose of energy saving and consumption reduction is achieved.

According to the inventor's research on the flow field in the top clearance of the centripetal turbine impeller, the transverse flow in the impeller clearance mainly occurs in the middle and rear of the meridian chord length, so the sealing structure arranged on the inner wall of the solid wall wheel cover must be located at the meridian chord length middle rear.

The middle and rear part of the meridian chord length refers to the chordwise position of 30%-120%.

There are two types of sealing structures, one is to obtain a certain sealing structure by directly removing part of the material on the inner wall of a conventional solid-wall wheel cover, and the other is to modify an existing solid-wall wheel cover and add a honeycomb structure.

There are three kinds of sealing structures obtained by removing part of the inner wall material of the conventional solid-wall wheel cover. One is to remove part of the material on the inner wall of the solid-wall wheel cover along the circumferential direction to form a series of circumferential channels. The inner wall of the solid wall wheel cover removes part of the material in the axial direction to form a series of axial grooves, and the third type is to remove part of the material on the inner wall of the solid wall wheel cover to form a series of spiral grooves.

Referring to Figure 1, when the centripetal turbine is in normal operation, after the working fluid passes through the guide (not shown in the drawings) and expands and accelerates, most of it expands again in the channel formed by the turbine impeller blades and converts the heat energy of the working fluid into mechanical energy A small part of the remaining working fluid leaks out of the centripetal turbine through the gap formed between the back of the impeller and the heat shield, and the other part "flows" through the gap at the top of the impeller formed between the impeller blades and the wheel cover. It does not participate in the conversion of thermal energy to mechanical energy and interacts with the working medium in the channel, resulting in a loss of power and a reduction in efficiency for the centripetal turbine. Transverse flow in the top gap, increasing the output power of the centripetal turbine.

According to the conclusions of domestic and foreign scholars on the influence of the axial clearance and radial clearance on the overall performance of the impeller top of the centripetal turbine, and the research results of the inventor on the leakage in the clearance at the top of the impeller, the leakage mainly occurs at the meridional chord length of the impeller. Therefore, it is most effective to arrange the sealing structure at the middle and rear part of the meridian chord length of the inner wall impeller of the conventional solid wall cover.

In the gap at the top of the centripetal turbine impeller, the flow is extremely complicated, while in the middle and rear region of the meridian chord length of the impeller, the pressure difference between the pressure side and the suction side of the gap plays a decisive role in the gap flow, that is, mainly from the gap pressure The leakage flow from the surface side to the suction surface side, under the influence of the main flow of the impeller channel, its flow direction forms a certain angle with the circumferential direction, and is biased towards the impeller outlet position.

In order to suppress the occurrence of the above leakage flow, the kinetic energy of the leakage flow needs to be dissipated, so some novel sealing structures are proposed to dissipate the kinetic energy of the leakage airflow, turning it into heat energy, reducing the amount of leakage, and increasing the output power of the centripetal turbine , to improve the efficiency of the centripetal turbine.

Based on the above research results, one solution is to arrange a certain number of circumferential grooves, axial grooves, spiral grooves or honeycombs in the middle and rear of the meridian chord length of the impeller inner wall of the conventional solid-wall wheel cover, and for the Leakage airflow is suppressed. The circumferential groove sealing structure is shown in Figure 3, the axial groove sealing results are shown in Figures 4 and 5, the spiral groove sealing structure is shown in Figure 6, and the honeycomb sealing structure is shown in Figures 7 and 8.

Technical principle of the present invention is as follows:

When the centripetal turbine works, the working fluid flowing out of the stator part flows into the impeller channel, most of the working fluid expands and does work and is discharged axially, and another small part of the working fluid leaks from the top area of the impeller blade through the top gap to the adjacent In the blade channel of the blade, it does not participate in the conversion of heat and power, and this part of the working fluid leaked from the top gap meets the main flow of the channel, forming a gap leakage loss.

Utilizing the characteristic that the leakage flow direction forms a certain angle with the circumferential direction, a series of circumferential grooves, axial grooves or spiral grooves are arranged according to certain rules on the inner wall of the solid wall wheel cover, so that a large part of the leakage air flow is in the gap. The cavity formed by the inflow channel near the pressure surface side, on the one hand, the leakage airflow decelerates due to the sudden expansion of the flow area, on the other hand, it collides with the wall of the circumferential channel, the flow direction changes and a vortex is formed in the cavity The structure dissipates the kinetic energy of the leakage airflow into heat energy, suppresses the occurrence of leakage, reduces the leakage, increases the output power of the centripetal turbine, reduces the leakage loss, and improves the efficiency of the centripetal turbine.

Honeycomb seal is a sealing structure with a series of regular hexagonal honeycomb holes evenly distributed in both axial and circumferential directions. The sealing structure, its technical principle is the same as the above channel sealing principle, so it will not be repeated here.

The search results of the applicant's patents on the leakage suppression structure at the top of the centripetal turbine at home and abroad show that no sealing device with similar structural features to the present invention has been found.

Claims (8)

1. a top clearance leakage restraint structure of centripetal turbine wheel impeller is characterized in that, described leak suppressing structure is a series of peripheral grooves or a series of axial groove or a series of spiral chute or honeycomb seal; This leakage internal face of structural configuration real wall wheel cap of drawing up at the impeller top, and be positioned at impeller top meridian chord length 30%～120% scope.

2. top clearance leakage restraint structure of centripetal turbine wheel impeller as claimed in claim 1 is characterized in that, the groove depth of described peripheral groove and groove width ratio are 1.0～6.0, and pitch of grooves and groove width ratio are 1.0～6.0;

3. top clearance leakage restraint structure of centripetal turbine wheel impeller as claimed in claim 1 is characterized in that, the groove depth of described axial groove is 1.0～5.0 with the ratio of groove width, and pitch of grooves is 1.0～5.0 with the ratio of groove width;

4. top clearance leakage restraint structure of centripetal turbine wheel impeller as claimed in claim 1, it is characterized in that described spiral fluted quantity is 1～8, rotation direction is identical with the impeller sense of rotation or opposite, groove depth and groove width ratio are 0.5～5.0, and pitch of grooves and groove width ratio are 0.5～5.0;

5. top clearance leakage restraint structure of centripetal turbine wheel impeller as claimed in claim 1 is characterized in that, the honeycomb degree of depth of described honeycomb seal and regular hexagon honeycomb opposite side distance ratio are 0.5～5.0;

6. top clearance leakage restraint structure of centripetal turbine wheel impeller as claimed in claim 2 is characterized in that, the conduit cross section of described peripheral groove is semicircle, and triangle is trapezoidal, zigzag fashion or rectangle.

7. top clearance leakage restraint structure of centripetal turbine wheel impeller as claimed in claim 3 is characterized in that, the conduit cross section of described axial groove is semicircle, and triangle is trapezoidal, zigzag fashion or rectangle.

8. top clearance leakage restraint structure of centripetal turbine wheel impeller as claimed in claim 4 is characterized in that, described spiral fluted conduit cross section is semicircle, and triangle is trapezoidal, zigzag fashion or rectangle.

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