J051055 The Role of Tip Leakage Vortex Breakdown in Flow Fields and Aerodynamic Characteristics of Transonic Centrifugal Compressor Impellers

This paper describes the experimental and numerical investigations on unsteady three-dimensional flow fields in two types of transonic centrifugal compressor impellers with different aerodynamic characteristics. In the experimental results, the frequency spectra of the pressure fluctuations, which were measured with the high-response pressure transducers mounted on the casing wall just upstream of the impeller, turned out to be quite different between the compressor impellers at stall condition. The simulation results also showed different stall pattern for each compressor impeller. In the compressor impeller with a better performance at off-design condition, the stall cell was never formed despite decreasing flow rate and instead all the passages were covered with a reverse flow near the tip, where the vortex breakdown happened in the tip leakage vortex of full blade and led to the unsteadiness in the impeller. The vortex breakdown happened in all the passages prior to the stall and generated a blockage near the tip. This means that even with the advent of rotating stall the flow could not return to a normal undistorted condition in unstalled region, because all the passages are already occupied by the blockage due to the vortex breakdown. As a result, the rotating stall cell could not appear in the impeller. In the other compressor impeller, the rotating stall cell was formed at stall inception without the vortex breakdown in the tip leakage vortex of full blade, and developed with decreased flow rate.

Download Full-text

Influences of Tip Leakage Flows Discharged From Main and Splitter Blades on Flow Field in Transonic Centrifugal Compressor Stage

Volume 2B: Turbomachinery ◽

10.1115/gt2018-75345 ◽

2018 ◽

Cited By ~ 1

Author(s):

Masanao Kaneko ◽

Hoshio Tsujita

Keyword(s):

Flow Field ◽

Centrifugal Compressor ◽

Leading Edge ◽

Tip Clearance ◽

Blade Loading ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Leakage Flows ◽

Transonic Centrifugal Compressor ◽

Tip Leakage Flows

A transonic centrifugal compressor impeller is generally composed of the main and the splitter blades which are different in chord length. As a result, the tip leakage flows from the main and the splitter blades interact with each other and then complicate the flow field in the compressor. In this study, in order to clarify the individual influences of these leakage flows on the flow field in the transonic centrifugal compressor stage at near-choke to near-stall condition, the flows in the compressor at four conditions prescribed by the presence and the absence of the tip clearances were analyzed numerically. The computed results clarified the following noticeable phenomena. The tip clearance of the main blade induces the tip leakage vortex from the leading edge of the main blade. This vortex decreases the blade loading of the main blade to the negative value by the increase of the flow acceleration along the suction surface of the splitter blade, and consequently induces the tip leakage vortex caused by the negative blade loading of the main blade at any operating points. These phenomena decline the impeller efficiency. On the other hand, the tip clearance of the splitter blade decreases the afore mentioned acceleration by the formation of the tip leakage vortex from the leading edge of the splitter blade and the decrease of the incidence angle for the splitter blade caused by the suction of the flow into the tip clearance. These phenomena reduce the loss generated by the negative blade loading of the main blade and consequently reduce the decline of the impeller efficiency. Moreover, the tip clearances enlarge the flow separation around the diffuser inlet and then decline the diffuser performance independently of the operating points.

Download Full-text

Design and Off-Design Flow Fields of a Transonic Centrifugal Compressor Impeller

Volume 7: Turbomachinery, Parts A and B ◽

10.1115/gt2009-59986 ◽

2009 ◽

Cited By ~ 4

Author(s):

Seiichi Ibaraki ◽

Kunio Sumida ◽

Toru Suita

Keyword(s):

Shock Wave ◽

Flow Field ◽

Flow Structure ◽

Centrifugal Compressor ◽

Flow Fields ◽

Design Flow ◽

Centrifugal Impeller ◽

Tip Leakage ◽

Operating Range ◽

Transonic Centrifugal Compressor

For reasons of their small dimensions, relatively higher efficiency and wider operating range transonic centrifugal compressors are usually applied to turbochargers and turboshaft engines. The flow field of a transonic centrifugal impeller is completely three dimensional and accompanied by shock waves, tip leakage vortices, secondary flows and interactions of them. Especially the operating range of a transonic centrifugal compressor decreases rapidly with increased pressure ratio. The expansion of the compressor operating range is one of the important issues. Also the higher off-design performance is strongly required for the applications like as turbochargers which have to operate from near surge limit to choke limit. The authors carried out the detailed flow measurement of a transonic centrifugal impeller with an inlet Mach number of 1.3 at design and off-design conditions by using Laser Doppler Velocimeter (LDV) and high frequency pressure transducers. The flow fields of design and off-design conditions were compared and discussed in this paper. As a result authors found out the difference and the similarity of the flow structure between design and off-design conditions. The location of the shock wave differs with the flow rate and influences the flow field of the inducer. The interaction of the shock wave and tip leakage vortex shows the same manner. Also detailed Navier-Stokes computations were conducted to elucidate the complicated vortical flow structure with the experimental results.

Download Full-text

J051054 Effects of Tip Leakage Vortex Breakdown on Unsteady Flow Fields in an Axial Flow Compressor Rotor at Near-Stall Condition

The Proceedings of Mechanical Engineering Congress Japan ◽

10.1299/jsmemecj.2011._j051054-1 ◽

2011 ◽

Vol 2011 (0) ◽

pp. _J051054-1-_J051054-5

Author(s):

Hiroaki KIKUTA ◽

Kazutoyo YAMADA ◽

Satoshi Gunjishima ◽

Goki OKADA ◽

Yasunori HARA ◽

...

Keyword(s):

Unsteady Flow ◽

Vortex Breakdown ◽

Axial Flow ◽

Flow Fields ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Axial Flow Compressor ◽

Compressor Rotor ◽

Flow Compressor

Download Full-text

Effects of Stream Surface Inclination on Tip Leakage Flow Fields in Compressor Rotors

Journal of Turbomachinery ◽

10.1115/1.2841777 ◽

1998 ◽

Vol 120 (4) ◽

pp. 683-692 ◽

Cited By ~ 22

Author(s):

M. Furukawa ◽

K. Saiki ◽

K. Nagayoshi ◽

M. Kuroumaru ◽

M. Inoue

Keyword(s):

Boundary Layer ◽

Vortex Breakdown ◽

Axial Flow ◽

Flow Fields ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Wall Boundary Layer ◽

Wall Boundary

Experimental and computational results of tip leakage flow fields in a diagonal flow rotor at the design flow rate are compared with those in an axial flow rotor. In the diagonal flow rotor, the casing and hub walls are inclined at 25 deg and 45 deg, respectively, to the axis of rotation, and the blade has airfoil sections with almost the same tip solidity as that of the axial flow rotor. It is found out that “breakdown” of the tip leakage vortex occurs at the aft part of the passage in the diagonal flow rotor. The “vortex breakdown” causes significant changes in the nature of the tip leakage vortex: disappearance of the vortex core, large expansion of the vortex, and appearance of low relative velocity region in the vortex. These changes result in a behavior of the tip leakage flow that is substantially different from that in the axial flow rotor: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing pressure trough at the aft part of the rotor passage, large spread of the low-energy fluid due to the leakage flow, much larger growth of the casing wall boundary layer, and considerable increase in the absolute tangential velocity in the casing wall boundary layer. The vortex breakdown influences the overall performance, also: large reduction of efficiency with the tip clearance, and low level of noise.

Download Full-text

Operating Range Enhancement by Tip Leakage Vortex Breakdown Control of a Centrifugal Compressor

International Journal of Gas Turbine, Propulsion and Power Systems ◽

10.38036/jgpp.11.2_38 ◽

2020 ◽

Vol 11 (2) ◽

pp. 38-43

Author(s):

Isao Tomita ◽

Masato Furukawa

Keyword(s):

Centrifugal Compressor ◽

Vortex Breakdown ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Operating Range

Download Full-text

Mechanism of Blockage Generation in Transonic Centrifugal Compressor at Design and Off-Design Conditions

Volume 2C: Turbomachinery ◽

10.1115/gt2015-43126 ◽

2015 ◽

Cited By ~ 1

Author(s):

Masanao Kaneko ◽

Hoshio Tsujita

Keyword(s):

Shock Wave ◽

Flow Rate ◽

Centrifugal Compressor ◽

Leading Edge ◽

Suction Surface ◽

Tip Leakage Vortex ◽

Stall Inception ◽

Aerodynamic Loss ◽

Tip Leakage ◽

Transonic Centrifugal Compressor

In a transonic centrifugal compressor, the loss generation is intensified by the formation of the shock wave and consequently the blockage is expected to increase. The blockage is considered to influence not only the flow rate and the increase of the static pressure but also the stall inception. However, the detailed mechanism of the blockage generation in the transonic centrifugal compressor has not been fully clarified. In this study, in order to clarify the mechanisms of loss and blockage generations in the transonic centrifugal compressor which are expected to be strongly influenced by the operating condition, the flows in the compressor at the off-design condition as well as at the design condition were analyzed numerically. The verifications of the computed results were carried out by comparing with available experimental results. The computed result clarified that the loss generation near the impeller inlet at design condition was mainly caused by the interactions of the shock wave with the tip leakage vortex appearing from the leading edge of the main blade as well as the boundary layer on the suction surface of the main blade. Moreover, these interactions were intensified by the decrease of the flow rate, and consequently enhanced the blockage effects by the tip leakage vortex from the leading edge of the main blade and resulted in the increase of the aerodynamic loss especially along the shroud surface in the impeller passage. On the other hand, the decrease of the blockage effects by the tip leakage vortex from the main blade with the increase of the flow rate formed the shock wave on the suction surface of the splitter blade at near-choke condition. This shock wave interacted with the tip leakage vortex from the splitter blade and consequently increased the aerodynamic loss.

Download Full-text

Effects of Stream Surface Inclination on Tip Leakage Flow Fields in Compressor Rotors

Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery ◽

10.1115/97-gt-043 ◽

1997 ◽

Author(s):

Masato Furukawa ◽

Kazuhisa Saiki ◽

Kenya Nagayoshi ◽

Motoo Kuroumaru ◽

Masahiro Inoue

Keyword(s):

Boundary Layer ◽

Vortex Breakdown ◽

Axial Flow ◽

Flow Fields ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Wall Boundary Layer ◽

Wall Boundary

Experimental and computational results of tip leakage flow fields in a diagonal flow rotor at the design flow rate are compared with those in an axial flow rotor. In the diagonal flow rotor, the casing and hub walls are inclined at 25 degrees and 45 degrees, respectively, to the axis of rotation, and the blade has airfoil sections with almost the same tip solidity as that of the axial flow rotor. It is found out that “breakdown” of the tip leakage vortex occurs at the aft part of the passage in the diagonal flow rotor. The “vortex breakdown” causes significant changes in the nature of the tip leakage vortex: disappearance of the vortex core, large expansion of the vortex, and appearance of low relative velocity region in the vortex. These changes result in the behavior of the tip leakage flow substantially different from that in the axial flow rotor: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing pressure trough at the aft part of the rotor passage, large spread of the low-energy fluid due to the leakage flow, much larger growth of the casing wall boundary layer, and considerable increase in the absolute tangential velocity in the casing wall boundary layer. The vortex breakdown influences the overall performance, also: large reduction of efficiency with the tip clearance, and low level of noise.

Download Full-text

Numerical Investigation Into the Mechanism of Tip Flow Unsteadiness in a Transonic Compressor

Volume 2D: Turbomachinery ◽

10.1115/gt2017-64065 ◽

2017 ◽

Author(s):

Guangyao An ◽

Yanhui Wu ◽

Jinhua Lang ◽

Zhiyang Chen ◽

Bo Wang ◽

...

Keyword(s):

Vortex Breakdown ◽

Pressure Oscillation ◽

Operating Point ◽

Recirculation Region ◽

Leakage Flow ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Flow Unsteadiness ◽

Transonic Compressor ◽

Evolution And Development

It is well known that tip flow unsteadiness has profound effects on both performance and stability of axial compressors. A number of numerical simulations have been performed in transonic compressors to uncover the nature of tip flow unsteadiness. From this research, tip flow unsteadiness can be attributed to many factors, such as the movement of the primary and secondary leakage flow, the interaction between shock and vortex, and the tip leakage vortex breakdown. However, no final conclusion has yet been reached on this matter. The current investigation is carried out to explore the origin of tip flow unsteadiness from the perspective of the evolution and development of tip leakage vortex breakdown. In this paper, unsteady RANS simulations have been performed to investigate the fluid dynamic processes in a tip-critical transonic compressor, NASA Rotor 35. A vortex core visualization method based on an eigenvector method is introduced as an important tool to identify the vortex arising from tip leakage flow. As the flow rate varies, three critical operating points with distinctive features of flow unsteadiness are observed. At the first critical operating point, bubble-type breakdown occurs, and gives rise to a weak unsteadiness with high frequency in the rotor passage due to the oscillation of the recirculation region induced by the tip leakage vortex breakdown. At the second critical operating point, the vortex breakdown has transformed from bubble-type to spiral-type, which leads to the frequency of the pressure oscillation reduced almost by half and the amplitude increased significantly. At the third critical operating point, a new vortex that is perpendicular to the pressure surface comes into being in the tip region, which leads to a prominent pressure oscillation of the tip flow and another jump in amplitude. As a result, the evolution and development of tip leakage vortex breakdown are closely related to the tip flow unsteadiness of the investigated rotor.

Download Full-text

Numerical Investigation of Relation Between Unsteady Behavior of Tip Leakage Vortex and Rotating Disturbance in a Transonic Axial Compressor Rotor

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-50779 ◽

2008 ◽

Cited By ~ 5

Author(s):

K. Yamada ◽

K. Funazaki ◽

H. Sasaki

Keyword(s):

Vortex Breakdown ◽

Axial Compressor ◽

Tip Clearance ◽

Tip Leakage Vortex ◽

Tip Clearance Flow ◽

Tip Leakage ◽

Compressor Rotor ◽

Clearance Flow ◽

Transonic Axial Compressor ◽

Rotating Instability

The purpose of this study is to have a better understanding of the unsteady behavior of tip clearance flow at near-stall condition from a multi-passage simulation and to clarify the relation between such unsteadiness and rotating disturbance. This study is motivated by the following concern. A single passage simulation has revealed the occurrence of the tip leakage vortex breakdown at near-stall condition in a transonic axial compressor rotor, leading to the unsteadiness of the tip clearance flow field in the rotor passage. These unsteady flow phenomena were similar to those in the rotating instability, which is classified in one of the rotating disturbances. In other words it is possible that the tip leakage vortex breakdown produces a rotating disturbance such as the rotating instability. Three-dimensional unsteady RANS calculation was conducted to simulate the rotating disturbance in a transonic axial compressor rotor (NASA Rotor 37). The four-passage simulation was performed so as to capture a short length scale disturbance like the rotating instability and the spike-type stall inception. The simulation demonstrated that the unsteadiness of tip leakage vortex, which was derived from the vortex breakdown at near-stall condition, invoked the rotating disturbance in the rotor, which is similar to the rotating instability.

Download Full-text