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.

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.

A Theoretical Model for Rotating Stall in the Vaneless Diffuser of a Centrifugal Compressor

1985 ◽  
Vol 107 (2) ◽  
pp. 507-513 ◽  
Author(s):  
P. Frigne ◽  
R. Van den Braembussche
Keyword(s):  
Theoretical Model ◽  
Centrifugal Compressor ◽  
Static Pressure ◽  
Inviscid Flow ◽  
Rotating Stall ◽  
Vaneless Diffuser ◽  
Flow Core ◽  
Flow Angle ◽  
Unsteady Boundary Layers ◽  
Number Of Cells

A theoretical model for rotating stall in the vaneless diffuser of a centrifugal compressor is presented. It consists of a time-evolutive calculation of the strong interaction between the inviscid flow core and the unsteady boundary layers along the walls. It is shown that, depending on the diffuser geometry and the diffuser inlet flow angle, a transient perturbation of the outlet static pressure will generate a rotating flow pattern, if the periodicity of this perturbation corresponds to the experimentally observed number of cells. The relative rotational speed and the phase relation between the velocity and the flow angle variations are also in agreement with experimental data.

Effects of Vaneless Diffuser Geometries on Rotating Stall

2002 ◽  
Author(s):  
K. B. Abidogun
Keyword(s):  
Angular Speed ◽  
Current Data ◽  
Rotating Stall ◽  
Diameter Ratio ◽  
Flow Coefficient ◽  
Critical Flow ◽  
Appreciable Effect ◽  
Vaneless Diffuser ◽  
Centrifugal Blower ◽  
Flow Perturbation

Detailed experimental investigation was carried out to document the effects of vaneless diffuser diameter and width ratios on the fundamental characteristics of flow perturbation in the vaneless diffuser of a centrifugal blower. In addition, a benchmark set of experimental data will be provided to aid numerical investigation of instabilities in the vaneless diffuser flowfield in particular and the entire compression system in general. The current data showed that a decrease of the diffuser width, at constant impeller angular speed, resulted in a decrease of the critical flow coefficient. The data further revealed that a decrease in the diffuser diameter ratio, resulted in an increase in the frequency of rotating stall. Variation of the diffuser width does not have any appreciable effect on the frequency of rotating stall. The effects of flow coefficient on stall characteristics are also reported.

Effects of Vaneiess Diffuser Geometry on Flow Instability in Centrifugal Compression Systems

1981 ◽  
Author(s):  
A. N. Abdelhamid
Keyword(s):  
Critical Angle ◽  
Previous Investigation ◽  
System Analysis ◽  
Flow Instability ◽  
Rate Of Change ◽  
Radius Ratio ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Flow Oscillations ◽  
Initial Pattern

Experiments were conducted to determine the effects of vaneless diffuser radius ratio on the occurrence of self-excited flow oscillations in a centrifugal compression system. Analysis of the results indicated the successive occurrence of two types of diffuser rotating pressure patterns as the flow rate in the system was gradually decreased. The rotational speed of the latter pattern was higher than that of the initial pattern and both speeds varied inversely with diffuser radius ratio. The critical flow angle at which each pattern was first observed increased with diffuser radius ratio. However, for diffuser radius ratio equal to and larger than 1.75 the rate of change of the critical angle with radius ratio decreased significantly. The results also showed that the minimum diffuser radius ratio necessary for self excitation of each pattern were different. Occurrence of two rotating pressure patterns confirms analytical results presented in a previous investigation.

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.

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]

Sign in / Sign up

Export Citation Format

Share Document