scholarly journals Two-Dimensional Rotating Stall Analysis in a Wide Vaneless Diffuser

2006 ◽  
Vol 2006 ◽  
pp. 1-11 ◽  
Author(s):  
S. Ljevar ◽  
H. C. de Lange ◽  
A. A. van Steenhoven
Keyword(s):  
Flow Instability ◽  
Numerical Study ◽  
Rotating Stall ◽  
Parameter Analysis ◽  
Two Dimensional ◽  
Vaneless Diffuser ◽  
Core Flow ◽  
Flow Solver ◽  
Incompressible Viscous Flow ◽  
Commercial Code

We report a numerical study on the vaneless diffuser core flow instability in centrifugal compressors. The analysis is performed for the purpose of better understanding of the rotating stall flow mechanism in radial vaneless diffusers. Since the analysis is restricted to the two-dimensional core flow, the effect of the wall boundary layers is neglected. A commercial code with the standard incompressible viscous flow solver is applied to model the vaneless diffuser core flow in the plane parallel to the diffuser walls. At the diffuser inlet, rotating jet-wake velocity pattern is prescribed and at the diffuser outlet constant static pressure is assumed. Under these circumstances, two-dimensional rotating flow instability similar to rotating stall is found to exist. Performed parameter analysis reveals that this instability is strongly influenced by the diffuser geometry and the inlet and outlet flow conditions.

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.

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.

Experimental Investigation of Rotating Stall Characteristics in a Radial Vaneless Diffuser

2000 ◽  
Author(s):  
K. B. Abidogun ◽  
S. A. Ahmed
Keyword(s):  
Flow Instability ◽  
Cell Structure ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Critical Flow ◽  
Vaneless Diffuser ◽  
Pressure Transducers ◽  
Mass Flowrate ◽  
Hot Wires ◽  
Good Agreement

Rotating stall characteristics in a radial vaneless diffuser model was investigated experimentally. Measurements were made using hot-wires and pressure transducers (static and dynamic). The mass flowrate through the blower, at constant impeller speed, was gradually reduced until flow instability occurred in the diffuser. This enabled the onset and propagation of rotating stall to be fully described. The blower was operated without the vaneless diffuser in order to ascertain the cause of the flow instability. It was discovered that the impeller did not stall at the flow rates at which the blower was operated with the diffuser. The critical flow angles measured at the diffuser inlet, and midway between the diffuser walls, were in good agreement with earlier reported values in the open literature. The maximum number of rotating stall cells found in this study was two. The single-stall cell structure was found to be dominant over the two-stall cell structure at flow coefficients much lower than the critical flow coefficient.

Numerical Study of Rotating Stall in a Pump Vaned Diffuser

2002 ◽  
Vol 124 (2) ◽  
pp. 363-370 ◽  
Author(s):  
Takeshi Sano ◽  
Yoshiki Yoshida ◽  
Yoshinobu Tsujimoto ◽  
Yuki Nakamura ◽  
Tatsuhito Matsushima
Keyword(s):  
Turbulence Model ◽  
Flow Rate ◽  
Numerical Study ◽  
Rotating Stall ◽  
Flow Instabilities ◽  
Negative Slope ◽  
Performance Curve ◽  
Vaned Diffuser ◽  
Commercial Code

This paper treats the flow instabilities in a vaned diffuser by using CFD. A commercial code with the standard κ-ε turbulence model was used for the present work. It was found that the flow instabilities in the vaned diffuser: i.e., rotating stall, alternate blade stall, and asymmetric stall, could be simulated by the present calculations. These instabilities were observed in a range with negative slope of the pressure performance curve of the diffuser. The rotating stall onset flow rate is larger for the case with larger clearance between the impeller and diffuser 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.

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.

Advanced Experimental and Numerical Analysis of the Pressurized Air Wave Bearings

2007 ◽  
Author(s):  
Adrian Sescu ◽  
Florin Dimofte ◽  
Carmen Sescu ◽  
Abdollah A. Afjeh ◽  
Robert Handschuh
Keyword(s):  
Finite Difference ◽  
Reynolds Equation ◽  
Numerical Study ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Two Dimensional ◽  
Commercial Code ◽  
Type Boundary ◽  
Experimental Rig ◽  
Good Agreement

Experimental, analytical, and numerical investigations have been done in the field of gas lubrication, but few people focused on details of fluid flow between the sliding surfaces. In this work the entire pressurized wave bearing is analyzed in detail. The numerical study using a three-dimensional commercial code and a two-dimensional finite difference code gives information about the flow at many levels. The numerically computed flow rates using the commercial code are compared with experimental results determined at NASA Glenn Research Center on an experimental rig. The calculated discharge coefficient is used in the finite difference code which solves the Reynolds equation. The holes effect is considered as a source term, instead of applying hybrid type boundary conditions on the holes contours. Data from experimental tests, commercial three-dimensional code, and two-dimensional code are reported and compared to each other. Good agreement was found between numerical study and experiment.

scholarly journals Numerical Study on the Temporal Discretization Schemes in Two-Phase Wave Simulation

2019 ◽  
Author(s):  
Young Jun Kim ◽  
Benjamin Bouscasse ◽  
Sopheak Seng ◽  
David Le Touze
Keyword(s):  
Viscous Flow ◽  
Numerical Study ◽  
Second Order ◽  
Linear Wave ◽  
Two Dimensional ◽  
Discretization Scheme ◽  
Two Phase ◽  
Flow Solver ◽  
Temporal Discretization ◽  
Discretization Schemes

Abstract The generation and propagation of waves in a viscous flow solver are indispensable part of naval computational fluid dynamic (CFD) applications. This paper presents numerical simulations of two-dimensional wave propagation in the framework of two-phase finite volume method (FVM) with different temporal discretization schemes. Implicit Euler, Crank-Nicolson (CN) and second-order backward temporal discretization schemes are compared by using viscous flow solver based on the open source library OpenFOAM. The combinations of each temporal discretization scheme and explicit limiter are used for the formulation of the Volume Of Fluid (VOF) field convection equation. A new formulation using the second-order backward temporal discretization scheme with explicit limiter are investigated. Two-dimensional periodic domains are considered to compare different time-stepping methods. Also, five different refinement levels of meshes are used to study the convergence properties of each method. The non-linear wave is generated with stream function wave theory using ‘foamStar’, which is a specialized OpenFOAM library package developed by Bureau Veritas in collaboration with École Centrale de Nantes.

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