Flow Instability at the Inlet of a Centrifugal Compressor

1981 ◽  
Vol 103 (2) ◽  
pp. 451-456
Author(s):  
G. Flueckiger ◽  
A. Melling
Keyword(s):  
Centrifugal Compressor ◽  
Flow Instability ◽  
Laser Doppler Anemometry ◽  
Suction Side ◽  
Operating Conditions ◽  
Gas Velocity ◽  
Unstable Flow ◽  
Flow Angle ◽  
Compressor Impeller ◽  
Service Conditions

Using laser Doppler anemometry, two components of the gas velocity have been measured at the inlet of a centrifugal compressor impeller, operated at speeds typical of service conditions for a medium-sized turbocharger. The flow was found to be unstable, especially adjacent to the suction side of the blades, such that two predominant conditions existed in the flow. The unstable flow is illustrated in the paper by distributions of relative velocity and relative flow angle, and the effects of different operating conditions on these distributions are examined. The instability is believed to be caused by a pre-stall condition as the compressor operating point approaches a fully stalled condition which occurs during surge.

Tip Leakage Flow Instability in a Centrifugal Compressor

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Teng Cao ◽  
Tadashi Kanzaka ◽  
Liping Xu ◽  
Tobias Brandvik
Keyword(s):  
Shear Layer ◽  
Centrifugal Compressor ◽  
Large Scale ◽  
Flow Instability ◽  
Leading Edge ◽  
Main Stream ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Unstable Flow ◽  
Tip Leakage

Abstract In this paper, an unsteady tip leakage flow phenomenon is identified and investigated in a centrifugal compressor with a vaneless diffuser at near-stall conditions. This phenomenon is associated with the inception of a rotating instability in the compressor. The study is based on numerical simulations that are supported by experimental measurements. The study confirms that the unstable flow is governed by a Kelvin–Helmholtz type instability of the shear layer formed between the main-stream flow and the tip leakage flow. The shear layer instability induces large-scale vortex roll-up and forms vortex tubes, which propagate circumferentially, resulting in measured pressure fluctuations with short wavelength and high amplitude which rotate at about half of the blade speed. The 3D vortex tube is also found to interact with the main blade leading edge, causing the reduction of the blade loading identified in the experiment. The paper also reveals that the downstream volute imposes a once-per-rev circumferential nonuniform back pressure at the impeller exit, inducing circumferential loading variation at the impeller inducer, and causing circumferential variation in the unsteady tip leakage flow.

Influence of Labyrinth Seal Leakage on Centrifugal Compressor Performance

2009 ◽  
Author(s):  
Bob Mischo ◽  
Beat Ribi ◽  
Christof Seebass-Linggi ◽  
Sebastiano Mauri
Keyword(s):  
Centrifugal Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Labyrinth Seal ◽  
Main Flow ◽  
Low Flow ◽  
Leakage Flow ◽  
Multi Stage ◽  
Compressor Impeller ◽  
Rotating Impeller

The focus of this paper lies on the leakage flow across the shroud of a centrifugal compressor impeller. It is common practice to use shrouded impellers in multi stage compressors featuring a single shaft. The rotating impeller then has to be sealed against the higher pressure in the downstream diffuser by means of labyrinths. The relative amount of leakage is higher for stages designed for low flow, meaning that the associated losses gain in relevance. In addition to this loss source, the injection of the leakage flow has a serious influence on the main flow in a region where it is prone to separation, i.e. at the suction side of the impeller blades close to the shroud, where the highest relative velocities are found. The present paper discusses the numerical results of several geometrical arrangements where the leakage flow was mixed with the main flow in different ways. The distance between the location of injection and the leading edge of the impeller as well as the orientation of the injected flow showed a distinct influence on the performance of the entire stage, mainly on stability.

scholarly journals Aerodynamic and Structural Characteristics of a Centrifugal Compressor Impeller

2019 ◽  
Vol 9 (16) ◽  
pp. 3416 ◽  
Author(s):  
T R Jebieshia ◽  
Senthil Kumar Raman ◽  
Heuy Dong Kim
Keyword(s):  
Centrifugal Compressor ◽  
Structural Characteristics ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
Von Mises Stress ◽  
Impeller Blade ◽  
Compressor Impeller ◽  
The One ◽  
Von Mises ◽  
Von Mises Stresses

The present study focuses on the aerodynamic performance and structural analysis of the centrifugal compressor impeller. The performance characteristics of the impeller are analyzed with and without splitter blades by varying the total number of main and splitter blades. The operating conditions of the compressor under centrifugal force and pressure load from the aerodynamic analysis are applied to the impeller blade and hub to perform the one-way Fluid–Structure Interaction (FSI). For the stress assessment, maximum equivalent von Mises stresses in the impeller blades are compared with the maximum allowable stress of the impeller material. The effects of varying the pressure field on the deformation and stress of the impeller are also calculated. The aerodynamic and structural performance of the centrifugal compressor at 73,000 rpm are investigated in terms of the efficiency, pressure ratio, equivalent von Mises stress, and total deformation of the impeller.

Investigation of an Inversely Designed Centrifugal Compressor Stage: Part 1 — Design and Numerical Verification

2003 ◽  
Author(s):  
M. Zangeneh ◽  
M. Schleer ◽  
F. Plo̸ger ◽  
S. S. Hong ◽  
C. Roduner ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Design Method ◽  
Leading Edge ◽  
Inverse Design ◽  
Numerical Verification ◽  
Appreciable Effect ◽  
Tip Leakage Flow ◽  
Flow Angle ◽  
Compressor Impeller ◽  
Blade Geometry

In this paper the 3D inverse design code TURBOdesign-1 is applied to the design of the blade geometry of a centrifugal compressor impeller with splitter blades. In the design of conventional impellers the splitter blades normally have the same geometry as the full blades and are placed at mid-pitch location between the two full blades, which can usually result in a mis-match between the flow angle and blade angles at the splitter leading edge. In the inverse design method the splitter and full blade geometry is computed independently for a specified distribution of blade loading on the splitter and full blades. In this paper the basic design methodology is outlined and then the flow in the conventional and inverse designed impeller is compared in detail by using CFD code TASCflow. The CFD results confirm that the inverse design impeller has a more uniform exit flow, better control of tip leakage flow and higher efficiency than the conventional impeller. The results also show that the shape of the trailing edge geometry has a very appreciable effect on the impeller Euler head and this must be accurately modeled in all CFD computations to ensure closer match between CFD and experimental results. Detailed measurements are presented in part 2 of the paper.

Numerical Study on the Effect of a Volute on Surge Phenomena in a Centrifugal Compressor

2016 ◽  
Author(s):  
S. H. Jeon ◽  
D. H. Hwang ◽  
J. H. Park ◽  
C. H. Kim ◽  
J. H. Baek ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Stokes Equations ◽  
Flow Instability ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Unstable Flow ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Blade Passing Frequency

Numerical investigation of the effect of the volute on stall flow phenomenon is presented by solving three-dimensional Reynolds-averaged compressible Navier-Stokes equations. Two different configurations of a centrifugal compressor were used to compare their performance: One is an original centrifugal compressor which is composed of impeller, splitter, vaned diffuser and a volute and the other is the one without a volute. Steady calculations were performed to predict aerodynamic performance in terms of the pressure ratio, efficiency and mass flow rate. The results show that the operating range of the compressor with a volute is narrower than that of the compressor without a volute. This can be interpreted that flow instability is strongly influenced by the tongue of a volute which is highly asymmetric. Unsteady calculations were also performed with a time-step size of 38μs corresponding to a pitch angle of 5 degrees at the given rotational speed. The flow characteristics for two configurations are analyzed and compared at various instantaneous times showing unsteady dynamic features. Based on the unsteady flow simulation, fast Fourier transform at several discrete points in semi-vaneless space was performed at peak efficiency and near surge point in order to illustrate the unstable flow physics in both configurations. It is found that the blade passing frequency is dominant, indicating that diffuser passages have a periodicity of 40 degrees due to the rotational blades. Besides blade passing frequency, there were several noticeable frequencies which affect the instability of the whole system. Those frequencies in both configurations are compared and analyzed in various aspects.

Study of a Highly Loaded Centrifugal Compressor With Pipe Diffuser at Design and Off-Design Operating Conditions

2015 ◽  
Author(s):  
Ge Han ◽  
Xingen Lu ◽  
Yanfeng Zhang ◽  
Shengfeng Zhao ◽  
Junqiang Zhu
Keyword(s):  
Centrifugal Compressor ◽  
Flow Separation ◽  
Incidence Angle ◽  
Leading Edge ◽  
Performance Comparison ◽  
Operating Conditions ◽  
Flow Distortion ◽  
Flow Angle ◽  
Rotating Speed ◽  
Highly Loaded

This present work is aimed at providing detailed understanding of the flow mechanisms in a highly loaded centrifugal compressor with different diffusers. Performance comparison between compressor stages with pipe diffuser and its original wedge diffuser was conducted by a validated state-of-the-art multi-block flow solver at different rotating speeds. Stage with pipe diffuser achieved a better performance above 80% rotating speed but a worse performance at lower rotating speeds near surge, than that of stage with wedge diffuser. Four operating points including the design point were analyzed in detail. The inherent diffuser leading edge of pipe diffuser could alleviate the flow distortion upstream diffuser throat and created a better operating condition for the downstream diffusion, which reduced the possibility of flow separation in discrete passages at design rotating speed. At 60% rotating speed operating point, there was a misalignment between the leading edge absolute flow angle and the metal angle of diffuser, resulted in an acceleration near diffuser leading edge due to the large negative incidence angle. The sharp leading edge of pipe diffuser could largely accommodate this negative incidence as comparison of the round leading edge of wedge diffuser. As a result, the flow separation was depressed and a better performance was achieved in the pipe diffuser. At 60% rotating speed near surge, performance of the pipe diffuser dropped below wedge diffuser. Total pressure loss of pipe diffuser exceeded that of the wedge diffuser due to the larger friction loss near wall at throat and cone, meanwhile ineffective static pressure recovery for pipe diffuser was triggered by the strong boundary layer blockage in the front of pipe diffuser cone.

Experimental and Numerical Analysis of the Secondary Flow Across the Interphase Balance Drum of a High Pressure Back-to-Back Centrifugal Compressor

2017 ◽  
Author(s):  
Carmine Carmicino ◽  
Francesco Maiuolo ◽  
Emanuele Rizzo
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Numerical Analysis ◽  
Pressure Distribution ◽  
Centrifugal Compressor ◽  
Operating Conditions ◽  
Local Pressure ◽  
Flow Angle ◽  
One Dimensional ◽  
Honeycomb Seal

With the major aim of gathering information on the machine lateral stability in high pressure-high density conditions, and of assessing the prediction capabilities of the in-house design tools and overall process, a back-to-back centrifugal compressor has been instrumented and tested in several operating conditions. The present paper focuses on the secondary flows across the interphase balance drum of the back-to-back compressor, where the sealing is accomplished with a honeycomb seal. The compressor interphase section has been instrumented with dedicated special probes for the clearance measurement associated to pressure and flow angle probes in order to characterize pressure distributions and swirl variations depending on the specific operating range. The experimental data acquired over the machine operation have been compared with a three-dimensional steady-state numerical analysis results obtained from the simulation, carried out with a Reynolds averaged Navier-Stokes (RANS) approach, of the flowfield in the complex interphase secondary system composed by the impeller cavities and the honeycomb seal. This paper addresses the comparison between numerical results and experimental data, which allowed the matching of models with experiments in terms of pressure distribution and the complex flowfield. Finally, all the data have been used to validate an in-house one-dimensional flow network solver for pressure distribution and leakage flow calculations along cavities and seals. Results have shown a general good agreement between measured data and calculation output. In particular, computational fluid dynamic analysis provided detailed pressure and velocity distributions that allowed gaining insight in the physics of such a complex region. The one-dimensional model has been demonstrated to be a fast and reliable tool to well predict local pressure variations inside cavities and seals and, consequently, the residual axial thrust.

Performance Analysis of the Impeller of a Centrifugal Air Compressor

2019 ◽  
Author(s):  
T. R. Jebieshia ◽  
S. K. Raman ◽  
H. D. Kim
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
Von Mises Stress ◽  
Structural Performance ◽  
Impeller Blade ◽  
Compressor Impeller ◽  
The One ◽  
Von Mises ◽  
Von Mises Stresses

Abstract The present study focuses on the aerodynamic performance and structural analysis of the centrifugal compressor impeller. Performance characteristics of the impeller are analyzed with and without splitter blades by varying the total number of main and splitter blades. The operating conditions of the compressor under centrifugal force and pressure load from the aerodynamic analysis were applied to the impeller blade and hub to perform the one-way Fluid-Structure Interaction (FSI). For the stress assessment, maximum equivalent von-Mises stresses in the impeller blades are compared with the maximum allowable stress of the impeller material. The effects of varying pressure field on the deformation and stress of the impeller is also calculated. The aerodynamic and structural performance of the centrifugal compressor at 73000 rpm are investigated in terms of the efficiency, pressure ratio, equivalent von-Mises stress, and total deformation of the impeller.

Study of a Surge-Free Centrifugal Compressor With Automatically Variable Inlet and Diffuser Vanes

1996 ◽  
Author(s):  
Hideomi Harada
Keyword(s):  
Centrifugal Compressor ◽  
Guide Vane ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Low Flow ◽  
Inlet Guide Vane ◽  
Analysis Method ◽  
Unstable Flow ◽  
Flow Angle ◽  
Operating Range

In order to improve the operating range of a centrifugal compressor, computer-controlled variable inlet and diffuser vanes were attached to a compressor with a pressure ratio of 2.5. Low-solidity cascade vanes capable of controlling the vane angle up to 0 degrees from the tangential direction were used for the vaned diffuser. The compressor’s overall performance was then tested using a closed-loop test stand. By automatically adjusting the diffuser vanes to the most suitable flow angle, pressure fluctuations caused by the unstable flow in the diffuser during low-flow operation of the centrifugal compressor could be suppressed, and the compressor could be operated nearly up to the shut-off flow rate without any surge. The author experimentally confirmed the critical operating range of both the impeller and diffuser at two different tip speeds and five inlet guide vane angles. Furthermore, a three-dimensional viscous flow-analysis method was applied to the impeller, and a three-dimensional momentum integral analysis method was applied to the diffuser. Then the critical operating ranges obtained in the experiments were qualitatively validated. The operating range of a centrifugal compressor under low-flow conditions, which has until now been limited because of surge, dramatically improved in this study, thereby demonstrating that it may be possible to develop a surge-free centrifugal compressor.

Numerical Investigation of Diffuser Flow Field and Rotating Stall in a Centrifugal Compressor With Vaned Diffuser

2017 ◽  
Author(s):  
Yang Zhao ◽  
Jiayi Zhao ◽  
Zhiheng Wang ◽  
Guang Xi
Keyword(s):  
Centrifugal Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Rotating Stall ◽  
Tip Leakage Flow ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Diffuser Flow ◽  
Flow Phenomena ◽  
Reversal Flow

The diffuser rotating stall in a centrifugal compressor with vaned diffuser is one of important unsteady flow phenomena, which limits the operating range of the compressor. In this paper, the unsteady CFD analysis on a low-speed centrifugal compressor has been performed to investigate the flow characteristic in the diffuser and the propagation of the diffuser rotating stall. The flow behaviors at the outlet of the impeller at design and off-design conditions are firstly investigated. It is found that a reversal flow, induced by the tip leakage flow, exists near the shroud at the impeller outlet and becomes serious with the mass flow rate reduced. Due to the span-wise variation of the flow angle at the diffuser inlet and the inversed pressure gradient in the passage, the leading-edge vortex (LEV) generates on the diffuser leading edge. The LEV then induces the secondary flow in the diffuser passage and then causes the hub-corner separation. Furthermore, the propagation of the diffuser rotating stall is presented in details. The suction-side separation near the hub induces the blockage in the passage. And the shedding vortex from the suction side moves toward the leading edge of the adjacent blade. When the vortex reaches to the leading edge of the adjacent blade, the incidence increase and a new separation occurs on the suction side. With the development of the new separation, the passage becomes blocked gradually and the upstream stalled passage recovers to a normal condition. The rotating stall propagates along the direction of the impeller rotation at about 4.5% of the impeller rotational speed.

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