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.

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 Experimental Investigation and Performance Analysis of Six Low Flow Coefficient Centrifugal Compressor Stages

1994 ◽  
Author(s):  
J. Paroubek ◽  
V. Cyrus ◽  
J. Kyncl
Keyword(s):  
Rotating Stall ◽  
Development Programme ◽  
Diameter Ratio ◽  
Flow Coefficient ◽  
Low Flow ◽  
Vaneless Diffuser ◽  
Test Rig ◽  
Return Channel ◽  
And Performance ◽  
Low Flow Coefficient

Some results of a research and development programme for centrifugal compressors are presented. Six stage configurations with low flow coefficient were tested. The stages had channel width parameter bo/D2=0.01 and 0.03. For each value of the width parameter three different impellers with inlet hub to outlet diameter ratio do/D2=0.3, 0.4 and 0.5 were designed. Test rig, instrumentation and data analysis are described. Special attention was devoted to probe calibrations and to evaluation of the leakage, bearing and disc friction losses. Aerodynamic performance of all tested stages is presented. Slip factors of impellers obtained experimentally and theoretically are compared. Losses in both vaneless diffuser and return channel with de-swirl vanes are discussed. Rotating stall was also investigated. Criteria for stall limit were tested.

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.

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%.

Control of Rotating Stall in the Diffuser of a Low Speed Centrifugal Compressor

2003 ◽  
Author(s):  
Saad A. Ahmed ◽  
Mohamed A. Gadalla
Keyword(s):  
Experimental Investigation ◽  
Centrifugal Compressor ◽  
Flow Instability ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Centrifugal Blower ◽  
Flow Area ◽  
Lower Flow ◽  
Preliminary Results ◽  
Control Delay

An experimental investigation to delay the onset of the rotating stall in the radial diffuser of a centrifugal blower was carried out. The method involved reducing the flow area by 50% at the diffuser exit using throttle rings attached to either diffuser shroud wall, or the diffuser hub wall. Simultaneous attachments of the throttle rings to both the diffuser’s shroud and the hub walls were also made. The following blockage ratios were used: 25% from both walls, 50% from the diffuser shroud and 0% from the diffuser hub and vice versa. The preliminary results suggest that the onset of the flow instability in the diffuser (stall) could be delayed (i.e., lower flow coefficient) when throttle rings were attached to the diffuser walls to reduce its exit flow area. The results also confirmed that the throttle rings could be an effective method to control/delay the stall in the vaneless radial diffuser.

Rotating Stall Induced in Vaneless Diffusers of Very Low Specific Speed Centrifugal Blowers

1985 ◽  
Vol 107 (2) ◽  
pp. 514-519 ◽  
Author(s):  
Y. Kinoshita ◽  
Y. Senoo
Keyword(s):  
Flow Analysis ◽  
Rotating Stall ◽  
Experimental Results ◽  
Flow Coefficient ◽  
Critical Flow ◽  
Flow Rates ◽  
Small Flow ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Vaneless Diffusers

The limit of rotating stall was experimentally determined for three very small specific speed centrifugal blowers. The impellers were specially designed for stall-free at very small flow rates, so that the cause of rotating stall could be attributed to the vaneless diffusers. Experimental results demonstrated that the blowers did not stall until the flow coefficient was reduced to very small values, which had never been reported in the literature. The critical flow coefficient for rotating stall agreed very well with the prediction based on a flow analysis and a criterion for rotating stall in vaneless diffusers developed by the authors.

Experimental Investigation and Performance Analysis of Six Low Flow Coefficient Centrifugal Compressor Stages

1995 ◽  
Vol 117 (4) ◽  
pp. 585-592 ◽  
Author(s):  
J. Paroubek ◽  
V. Cyrus ◽  
J. Kyncˇl
Keyword(s):  
Development Program ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Low Flow ◽  
Vaneless Diffuser ◽  
Test Rig ◽  
Disk Friction ◽  
Return Channel ◽  
And Performance ◽  
Low Flow Coefficient

Some results of a research and development program for centrifugal compressors are presented. Six-stage configurations with low flow coefficient were tested. The stages had channel width parameter b2/D2 = 0.01 and 0.03. For each value of the width parameter, three different impellers with inlet hub to outlet diameter ratio do/D2 = 0.3, 0.4, and 0.5 were designed. Test rig, instrumentation, and data analysis are described. Special attention was devoted to probe calibrations and to evaluation of the leakage, bearing, and disk friction losses. Aerodynamic performance of all tested stages is presented. Slip factors of impellers obtained experimentally and theoretically are compared. Losses in both vaneless diffuser and return channel with deswirl vanes are discussed. Rotating stall was also investigated. Criteria for stall limit were tested.

Incipient Rotating Stall Characteristics Measured by Semiconductor L2F and Pressure Transducer in Vaneless Diffusers of Centrifugal Blowers

2000 ◽  
Author(s):  
Masahiro Ishida ◽  
Daisaku Sakaguchi ◽  
Hironobu Ueki
Keyword(s):  
Correlation Coefficient ◽  
Pressure Transducer ◽  
Large Scale ◽  
Reverse Flow ◽  
Transient Behavior ◽  
Rotating Stall ◽  
Vaneless Diffuser ◽  
Centrifugal Blower ◽  
Auto Correlation ◽  
Flow Fluctuation

In order to clarify the transient behavior from the non-stall condition to the developed rotating stall in vaneless diffuser of a centrifugal blower, blade-to-blade variations of velocity and wait pressure were measured immediately upstream and downstream of the impeller exit as well as in the vaneless diffuser by means of the semiconductor laser 2-focus velocimeter and the pressure sensor respectively. The specified auto-correlation coefficient of large scale disturbances with the wavelength larger than twice of the blade spacing show that the intermittent stall occurs prior to the developed rotating stall. By analyzing the flow-fluctuation-ellipse and the correlation coefficient with respect to the radial and tangential components of velocity fluctuation, it is found that the intermittent stall as well as the developed rotating stall are triggered by the interaction between the reverse flow in the diffuser entry region and the jet-wake like flow discharged from the impeller.

scholarly journals Comparison Between Complete Hilbert Transform and Simplified Solutions of the Moore Rotating Stall Model

1996 ◽  
Author(s):  
Gianmario L. Arnulfi ◽  
Fabio L. Ghiglino ◽  
Aristide F. Massardo
Keyword(s):  
Hilbert Transform ◽  
Complete Solution ◽  
Axial Compressor ◽  
Axial Flow ◽  
Detailed Comparison ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Flow Perturbation ◽  
Wide Range ◽  
The Hilbert Transform

The main objective of this work is the analysis and the comparison between different methods utilised to solve the Moore rotating stall model. To date only simplified relations between the axial flow perturbation g and the transverse one h have been utilised and presented in literature, such as h′ = −g or the truncated Fourier series. On the contrary, in this paper the accurate relation given by the Hilbert Transform is utilised, and to improve the numerical stability of the method a new expression of the first derivative of transverse flow coefficient perturbation is proposed and utilised. A complete and detailed comparison between the results of the simplified methods and the solution proposed here is presented. This comparison is extended to a wide range of geometrical and physical compressor parameters, and it allows the accuracy of simplified approaches to be tested. Finally, a correlative approach estimating overall rotating stall effects based on the complete solution proposed here is presented. It allows rotating stall influence to be quickly and easily taken into account in several axial compressor areas (design, optimisation, active control, etc.).

Comparison Between Complete Hilbert Transform and Simplified Solutions of the Moore Rotating Stall Model

1998 ◽  
Vol 120 (3) ◽  
pp. 446-453
Author(s):  
G. L. Arnulfi ◽  
F. L. Ghiglino ◽  
A. F. Massardo
Keyword(s):  
Hilbert Transform ◽  
Complete Solution ◽  
Axial Compressor ◽  
Axial Flow ◽  
Detailed Comparison ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Flow Perturbation ◽  
Wide Range ◽  
The Hilbert Transform

The main objective of this work is the analysis and the comparison between different methods utilized to solve the Moore rotating stall model. To date only simplified relations between the axial flow perturbation g and the transverse one h have been utilized and presented in literature, such as h′ = −g or the truncated Fourier series. On the contrary, in this paper the accurate relation given by the Hilbert Transform is utilized, and to improve the numerical stability of the method, a new expression of the first derivative of transverse flow coefficient perturbation is proposed and utilized. A complete and detailed comparison between the results of the simplified methods and the solution proposed here is presented. This comparison is extended to a wide range of geometric and physical compressor parameters, and it allows the accuracy of simplified approaches to be tested. Finally, a correlative approach estimating overall rotating stall effects based on the complete solution proposed here is presented. It allows rotating stall influence to be quickly and easily taken into account in several axial compressor areas (design, optimization, active control, etc.).

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