Vortical Flow Structure and Loss Generation Process in a Transonic Centrifugal Compressor Impeller

2007 ◽  
Author(s):  
Seiichi Ibaraki ◽  
Masato Furukawa ◽  
Kenichiro Iwakiri ◽  
Kazuya Takahashi
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Centrifugal Compressor ◽  
Secondary Flows ◽  
Vortical Flow ◽  
Generation Process ◽  
Tip Leakage ◽  
Transonic Centrifugal Compressor ◽  
Compressor Impeller ◽  
Flow Phenomena

Transonic centrifugal compressors are used in turbochargers and turboshaft engines because of their small dimensions, relatively high efficiency and wide operating range. The flow field of the transonic centrifugal compressor impeller is highly three dimensional, and is complicated by shock waves, tip leakage vortices, secondary flows and the interactions among them. In order to improve the performance, it is indispensable to understand these complicated flow phenomena in the impeller. Although experimental and numerical research on transonic impeller flow has been reported, thus providing important flow physics, some undetected flow phenomena remain. The authors of the present report carried out detailed Navier-Stokes computations of a transonic impeller flow measured by Laser Doppler Velocimetry (LDV) in previous work. The highly complicated vortical flow structure and the mechanism of loss generation were revealed by a visual data mining technique, namely vortex identification based on the critical point theory and limiting streamline mapping by means of line integral convolution. As a result, it was found that the tip leakage vortices have a significant impact on the flow field and vortex breakdowns that increase the blockage of the flow passage, and that these were caused by shock wave interaction.

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

2009 ◽  
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.

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

2018 ◽  
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.

Suppression of Secondary Flows in a Transonic Centrifugal Compressor Impeller Using an Inverse Design Method Based on Meridional Viscous Flow Analysis

2019 ◽  
Author(s):  
Sasuga Ito ◽  
Shin Okada ◽  
Yuki Kawakami ◽  
Kaito Manabe ◽  
Masato Furukawa ◽  
...  
Keyword(s):  
Viscous Flow ◽  
Secondary Flow ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Aerodynamic Performance ◽  
Secondary Flows ◽  
Low Energy ◽  
Design Concept ◽  
Transonic Centrifugal Compressor ◽  
Compressor Impeller

Abstract Secondary flows in transonic centrifugal compressor impellers affect their aerodynamic performance. In open-type impellers, low energy fluids can accumulate on the suction surfaces near the trailing edge tip side since the secondary flows and tip leakage flows interfere each other and complex flow phenomena can be generated around the impellers. Therefore, designers must consider the effect of secondary flows to avoid the aerodynamic performance degradation while designing compressor impellers. In this paper, a novel design concept about suppression of secondary flows in centrifugal compressor impellers to improve their aerodynamic performance. A transonic centrifugal compressor impeller was redesigned with the present design concept by a two-dimensional inverse method based on a meridional viscous flow calculation in this study. A design concept was introduced in above calculation process. As the design concept, by bending vortex filaments with controlling peak positions of the blade loading distributions, induced velocity due to bound vortices at the blades was generated in radial opposite direction of the secondary flows on the suction surface. Due to investigate the effect of the design concept in this paper, three-dimensional Reynolds Averaged Navier-Stokes simulations were carried out, and the vortex cores were visualized by a critical point theory and colored by non-dimensional helicity. In the conventional transonic centrifugal compressor impeller, the secondary flow vortices were confirmed and one of the vortices was broken down. In the redesigned impeller, the breakdown of the secondary flow vortices was not observed and the accumulation of the low energy fluids was suppressed compared with the conventional impeller. The total pressure ratio and adiabatic efficiency of the redesign impeller were higher than that of the conventional impeller, and the secondary flows were successfully suppressed in this research.

Unsteady Effects of Blade Row Interaction on Flow Field and Aerodynamic Performance of a Transonic Centrifugal Compressor Impeller

2021 ◽  
Author(s):  
Kazutoyo Yamada ◽  
Kosuke Kubo ◽  
Kenichiro Iwakiri ◽  
Yoshihiro Ishikawa ◽  
Hirotaka Higashimori
Keyword(s):  
Steady State ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Aerodynamic Performance ◽  
Vaned Diffuser ◽  
Tip Leakage ◽  
Transonic Centrifugal Compressor ◽  
Compressor Performance ◽  
Unsteady Effects ◽  
Rans Analysis

Abstract This paper discusses the unsteady effects associated with the impeller/diffuser interaction on the internal flow field and aerodynamic performance of a centrifugal compressor. In centrifugal compressors with a vaned diffuser, the flow field is inherently unsteady due to the influence of interaction between the impeller and the diffuser, and the unsteadiness of the flow field can often have a great influence on the aerodynamic performance of the compressor. Especially in high-load compressors, it is considered that large unsteady effects are produced on the compressor performance with a strong flow unsteadiness. The unsteady effect on aerodynamic performance of the compressor has not been fully revealed yet, and sometimes the steady-state RANS simulation finds it difficult to predict the compressor performance. In this study, numerical simulations have been conducted for a transonic centrifugal compressor with a vaned diffuser. The unsteady effects were clarified by comparing the numerical results between a single-passage steady-state RANS analysis and a full-annulus unsteady RANS analysis. The comparison of simulation results showed the difference in entropy generation in the impeller. The impingement of diffuser shock wave with the impeller pressure surface brought about a cyclic increase in the blade loading near the impeller trailing edge. Accordingly, with increasing tip leakage flow rate, a second tip leakage vortex was newly generated in the aft part of the impeller, which resulted in additional unsteady loss generation inside the impeller.

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

2011 ◽  
Author(s):  
Kazutoyo Yamada ◽  
Masato Furukawa ◽  
Hisataka Fukushima ◽  
Seiichi Ibaraki ◽  
Isao Tomita
Keyword(s):  
Flow Rate ◽  
Centrifugal Compressor ◽  
Vortex Breakdown ◽  
Aerodynamic Characteristics ◽  
Flow Fields ◽  
Rotating Stall ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Transonic Centrifugal Compressor ◽  
Compressor Impeller

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.

Numerical Investigation on the Formation of Jet-Wake Flow Pattern in Centrifugal Compressor Impeller

2003 ◽  
Author(s):  
Qun Zheng ◽  
Shunlong Liu
Keyword(s):  
Pattern Formation ◽  
Flow Field ◽  
Numerical Investigation ◽  
Centrifugal Compressor ◽  
Internal Flow ◽  
Secondary Flows ◽  
Wake Flow ◽  
Centrifugal Impeller ◽  
Numerical Investigations ◽  
Compressor Impeller

Numerical investigations of internal flow field in centrifugal compressor impeller channel are carried out in this paper. Topological analyses of limit streamline pattern are used to interpret the Jet-Wake formation. With such a technique, it can give a clearly description of the wake. And the shape of the wake, the wake onset and wake developing process are depicted in detail. The numerical results also present the internal vortices, secondary flows and their effects on the Jet-Wake pattern formation. The influences of Coriolis force on flow field of the centrifugal impeller are also discussed.

On the Design Criteria for Suppression of Secondary Flows in Centrifugal and Mixed Flow Impellers

1997 ◽  
Author(s):  
M. Zangeneh ◽  
A. Goto ◽  
H. Harada
Keyword(s):  
Flow Field ◽  
Pressure Distribution ◽  
Centrifugal Compressor ◽  
Design Method ◽  
Secondary Flows ◽  
Mixed Flow ◽  
Optimum Pressure ◽  
Compressor Impeller ◽  
Specific Speed ◽  
Guide Lines

In this paper, for the first lime, a set of guide-lines are presented for the systematic design of mixed flow and centrifugal compressors and pumps with suppressed secondary flows and a uniform exit flow field. The paper describes the shape of the optimum pressure distribution for the suppression of secondary flows in the impeller with reference to classical secondary flow theory. The feasibility of achieving this pressure distribution is then demonstrated by deriving guide-lines for the design specifications of a 3D inverse design method, in which the blades are designed subject to a specified circulation distribution or 2πrV¯θ. The guide-lines will define the optimum choice of the blade loading or ∂rV¯θ/∂m and the stacking condition for the blades. These guide-lines are then used in the design of three different low specific speed centrifugal pump impellers and a high specific speed industrial centrifugal compressor impeller. The flow through all the designed impellers are computed numerically by a 3D viscous code and the resulting flow field is compared to that obtained in the corresponding conventional impeller. The results show consistent suppression of secondary flows in all cases. The design guide-lines are validated experimentally by comparing the performance of the inverse designed centrifugal compressor impeller with the corresponding conventional impeller. The overall performance of the stage with the inverse designed impeller with suppressed secondary flows was found to be 5% higher than the conventional impeller at the peak efficiency point. Exit flow traverse results at the impeller exit indicate a more uniform exit flow than that measured at the exit from the conventional impeller.

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