Passive Control of Rotating Stall in Vaneless Diffuser With Radial Grooves: Detailed Numerical Study

2009 ◽  
Author(s):  
Chuang Gao ◽  
Chuangang Gu ◽  
Tong Wang ◽  
Bo Yang
Keyword(s):  
Passive Control ◽  
Numerical Study ◽  
Design Procedure ◽  
Flow Distribution ◽  
Rotating Stall ◽  
Field Variation ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Diffuser Flow ◽  
Computational Fluid Dynamics Cfd

According to experiments described in the literature, radial grooves in vaneless diffuser walls are simple and powerful devices for suppressing rotating stall. To understand the mechanism behind the grooves and find some guidelines for diffuser designers, a detailed numerical study based on Computational Fluid Dynamics (CFD) was carried out. Not only the flow field variation caused by the grooves but also a simple model graphing the underlying nature was established. Also, the classic boundary layer integral method widely used in practical design procedure was adopted to calculate the diffuser flow distribution to verify the model. The CFD analysis indicated that the effectiveness of the grooves increases the flow angle thus delaying the diffuser wall flow reversals. The recommended placement of the grooves was in the region with reversed flow. Such locally fixed groove could effectively delay the stall without too much pressure loss. Also, a combined variable, representing the overall geometry of grooves was established and verified. The detailed study given in this paper gives guidelines for using grooves as a stall delay method.

An Analytical and Experimental Assessment of a Diffuser Flow Phenomenon as a Precursor to Stall

2012 ◽  
Author(s):  
James M. Sorokes ◽  
Jorge E. Pacheco ◽  
Clementine Vezier ◽  
Syed Fakhri
Keyword(s):  
Rotating Stall ◽  
Flow Coefficient ◽  
Centrifugal Impeller ◽  
Test Results ◽  
Vaneless Diffuser ◽  
Diffuser Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Analyses ◽  
Validation Testing ◽  
Lower Flow Rate

The paper describes an experimental and analytical study on the vaneless diffuser downstream of a high flow coefficient, high inlet relative Mach number centrifugal impeller. The diffuser flowfield exhibited a unique behavior in which the low momentum zone typically found along the shroud side of a centrifugal compressor diffuser suddenly shifted to the hub side of the diffuser just prior to the onset of diffuser rotating stall. The phenomenon was observed in the computational fluid dynamics (CFD) analyses conducted as well as in the experimental data obtained during stage validation testing. A review of the analytical and test results suggested that the phenomenon was at least partially attributable to the level of diffusion in the vaneless diffuser. Modifications made to reduce the diffusion rate were shown by CFD analysis to move the onset of the unusual shift of low momentum flow to a much lower flow rate. The modifications also increased the efficiency of the overall stage by 1.2%.

Passive Control of Rotating Stall in a Parallel-Wall Vaneless Diffuser by Radial Grooves

1999 ◽  
Vol 122 (1) ◽  
pp. 90-96 ◽  
Author(s):  
Junichi Kurokawa ◽  
Sankar L. Saha ◽  
Jun Matsui ◽  
Takaya Kitahora
Keyword(s):  
Passive Control ◽  
Reverse Flow ◽  
Tangential Velocity ◽  
Rotating Stall ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Remarkable Effect ◽  
Entire Flow ◽  
Parallel Wall ◽  
Theoretical Considerations

In order to control and suppress rotating stall in the diffuser of a centrifugal turbomachine, a passive method of utilizing radial shallow grooves is proposed and its effect is studied theoretically and experimentally. The results show that radial grooves of 3 mm depth on one wall or of only 1 mm depth on both walls can suppress rotating stall in a vaneless diffuser for the entire flow range. Theoretical considerations have revealed that this remarkable effect of radial grooves is caused by two mechanisms; one is a significant decrease in tangential velocity at the diffuser inlet due to mixing between the main flow and the groove flow, and the other is a remarkable increase in radial velocity due to the groove reverse flow. Both effects have the same contribution to increase the flow angle. [S0098-2202(00)02901-1]

Study of Vaneless Diffuser Rotating Stall Based on Two-Dimensional Inviscid Flow Analysis

1996 ◽  
Vol 118 (1) ◽  
pp. 123-127 ◽  
Author(s):  
Yoshinobu Tsujimoto ◽  
Yoshiki Yoshida ◽  
Yasumasa Mori
Keyword(s):  
Propagation Velocity ◽  
Flow Instability ◽  
Present Report ◽  
Inviscid Flow ◽  
Rotating Stall ◽  
Critical Flow ◽  
Two Dimensional ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Pressure Disturbance

Rotating stalls in vaneless diffusers are studied from the viewpoint that they are basically two-dimensional inviscid flow instability under the boundary conditions of vanishing velocity disturbance at the diffuser inlet and of vanishing pressure disturbance at the diffuser outlet. The linear analysis in the present report shows that the critical flow angle and the propagation velocity are functions of only the diffuser radius ratio. It is shown that the present analysis can reproduce most of the general characteristics observed in experiments: critical flow angle, propagation velocity, velocity, and pressure disturbance fields. It is shown that the vanishing velocity disturbance at the diffuser inlet is caused by the nature of impellers as a “resistance” and an “inertial resistance,” which is generally strong enough to suppress the velocity disturbance at the diffuser inlet. This explains the general experimental observations that vaneless diffuser rotating stalls are not largely affected by the impeller.

Numerical Study of the Winter-Kennedy Method—A Sensitivity Analysis

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Binaya Baidar ◽  
Jonathan Nicolle ◽  
Chirag Trivedi ◽  
Michel J. Cervantes
Keyword(s):  
Boundary Conditions ◽  
Secondary Flow ◽  
Numerical Study ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Flow Distribution ◽  
Local Flow ◽  
Spiral Case ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Changes

The Winter-Kennedy (WK) method is commonly used in relative discharge measurement and to quantify efficiency step-up in hydropower refurbishment projects. The method utilizes the differential pressure between two taps located at a radial section of a spiral case, which is related to the discharge with the help of a coefficient and an exponent. Nearly a century old and widely used, the method has shown some discrepancies when the same coefficient is used after a plant upgrade. The reasons are often attributed to local flow changes. To study the change in flow behavior and its impact on the coefficient, a numerical model of a semi-spiral case (SC) has been developed and the numerical results are compared with experimental results. The simulations of the SC have been performed with different inlet boundary conditions. Comparison between an analytical formulation with the computational fluid dynamics (CFD) results shows that the flow inside an SC is highly three-dimensional (3D). The magnitude of the secondary flow is a function of the inlet boundary conditions. The secondary flow affects the vortex flow distribution and hence the coefficients. For the SC considered in this study, the most stable WK configurations are located toward the bottom from θ=30deg to 45deg after the curve of the SC begins, and on the top between two stay vanes.

Three-Dimensional Vaneless Diffuser Rotating Stall Numerical Study

2018 ◽  
Author(s):  
Filip Grapow ◽  
Grzegorz Liśkiewicz
Keyword(s):  
Mass Flow ◽  
High Efficiency ◽  
Numerical Study ◽  
Complex Structure ◽  
Sudden Change ◽  
Three Dimensional ◽  
Rotating Stall ◽  
Frequency Change ◽  
Vaneless Diffuser ◽  
Growth Pressure

Abstract Centrifugal compressor efficiency is the key to increasing incomes from its operation. There are several flow instabilities which can negatively affect a compressor, one of them being the rotating stall, as it decreases efficiency and mass flow while it can also lead to a surge. Among others, this can occur in the vaneless diffuser. A thorough understanding of this phenomenon and the ability to model its behaviour can lead to a robust protection system assuring high efficiency even at lower mass flow rates. In this paper, the simulated flow was viscous and compressible. Much attention was devoted to providing boundary conditions that would not affect flow conditions at the diffuser outlet. The transient simulation was conducted in order to observe sequential stages of the VDRS onset and growth. Pressure signals from different points in the diffuser have been analysed with the CWT method in the purpose of detecting oscillations frequency change in time. Results have shown that the complex structure and time evolution of the VDRS indeed require the application of three-dimensional methods. As the mass flowrate was continuously decreased a sudden change in number of the rotating stall cells was observed together with an appearance of new strong peak of the pressure oscillation.

Rotating Stall Characteristics in a Wide Vaneless Diffuser

2005 ◽  
Author(s):  
S. Ljevar ◽  
H. C. de Lange ◽  
A. A. van Steenhoven
Keyword(s):  
Boundary Layers ◽  
Flow Instability ◽  
Stability Limit ◽  
Rotating Stall ◽  
Two Dimensional ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Wall Boundary ◽  
The Stability ◽  
Rotating Instability

Paper reports a numerical study on vaneless diffuser flow instability performed for the purpose of better understanding of rotating stall mechanism in radial vaneless diffusers. This analysis is restricted to the two-dimensional flow where effect of wall boundary layers is neglected. Numerical results reveal that a two-dimensional rotating flow instability similar to rotating stall occurs when critical flow angle is exceeded. They also show that the stability limit and the structure of a two dimensional rotating instability are influenced by the configuration geometry and inlet and outlet flow conditions. Good agreement with data from the literature is found for the stability limit and number and speed of propagating cells. Number of cells and their speed is somewhat higher than observed in experiments from literature. This might imply that inception point is caused by the core flow instability and that wall boundary layers are more determinative for the structure of rotating instability.

scholarly journals Rotating Stall Measurements in the Vaneless Diffuser of a Radial Flow Compressor

1982 ◽  
Author(s):  
P. M. Ligrani ◽  
R. Van Den Braembussche ◽  
M. Roustan
Keyword(s):  
Flow Behavior ◽  
Reynolds Numbers ◽  
Rotating Stall ◽  
Hot Wire ◽  
Vaneless Diffuser ◽  
Inlet Flow ◽  
Flow Angle ◽  
Measurement Results ◽  
Flow Compressor ◽  
Hot Film

Results from an experimental study of flow behavior at the inlet of a vaneless diffuser of a centrifugal compressor are presented. Hot-film measurements and measurement results from a crossed hot-wire probe are discussed for operating points having inlet flow coefficients ranging from 0.006 to 0.019 at different Reynolds numbers. Instantaneous, time-averaged, and phase-averaged absolute velocity and flow angle at the diffuser inlet are deduced from the hot-wire signals after correction for mean density variations. These results show how flow behavior varies in stable, rotating stall and surge regimes of compressor operation. The critical flow angle at the onset of rotating stall shows agreement with other measurements confirming the importance of diffuser inlet width and diffuser inlet flow angle on the onset of rotating stall in vaneless diffusers.

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.

Numerical Study of Rotating Stall in a Vaneless Diffuser

2002 ◽  
Vol 2002.77 (0) ◽  
pp. _6-41_-_6-42_
Author(s):  
Mamoru ABE ◽  
Takeshi SANO ◽  
Tatsuhito Matsushima ◽  
Yoshiki YOSHIDA ◽  
Yoshinobu TSUJIMOTO
Keyword(s):  
Numerical Study ◽  
Rotating Stall ◽  
Vaneless Diffuser

scholarly journals Numerical Study on Rotating Stall in Finite Pitch Cascades

1994 ◽  
Author(s):  
Toshio Nishizawa ◽  
Hiroyuki Takata
Keyword(s):  
Numerical Study ◽  
Flow Behavior ◽  
Vortex Method ◽  
Rotating Stall ◽  
Axial Distance ◽  
Flow Angle ◽  
Guide Vanes ◽  
Stall Inception ◽  
Stall Cells ◽  
Inception Point

Flow behavior of rotating stall in finite pitch cascades is discussed through numerical analyses by means of a vortex method, which is particularly developed to solve unsteady flows through stalled cascades. It is shown that stall vortex and unstall vortex are, shed from each stalled blade periodically, and the behavior of these vortices has considerable effects on various properties of rotating stall, such as magnitude of flow fluctuation, propagation velocity, the number of stall cells, and so on. When a rotating stall is initiated and developed in an isolated cascade at smaller inlet flow angles around the stall inception point, a plural number of stall cells tend to propagate on the growing process, although only one stall cell survives eventually in a fully developed rotating stall. At larger flow angles, a single stall cell splits into two separate cells as it propagates. These processes are found for the first time through the analyses of finite pitch cascades. With the inlet guide vanes upstream, a plural number of stall cells can grow in a fully developed rotating stall, and the number of stall cells depends on the exit flow angle of the guide vanes and the axial distance between the two cascades. The numerical results agree well with experiments.

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