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]

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 Vaned Diffuser by J-Grooves

2000 ◽  
Vol 123 (3) ◽  
pp. 507-515 ◽  
Author(s):  
Sankar L. Saha ◽  
Junichi Kurokawa ◽  
Jun Matsui ◽  
Hiroshi Imamura
Keyword(s):  
Passive Control ◽  
Swirl Flow ◽  
Rotating Stall ◽  
Positive Slope ◽  
Vaned Diffuser ◽  
Double Curvature ◽  
Entire Flow ◽  
Parallel Wall ◽  
Different Dimensions ◽  
Flow Pump

In order to control and suppress instabilities caused by swirl flow, the authors have proposed a very simple passive method utilizing shallow grooves mounted on a casing wall or diffuser wall(s) parallel to the pressure gradient. The groove is termed a “J-groove.” The method is theoretically analyzed and experimentally proved capable of suppressing rotating stall in a vaneless diffuser. The performance curve instability is characterized by the positive slope of the head-capacity curve of a mixed flow pump for the entire flow range. In continuation, this work is aimed at realizing experimentally the effect of J-grooves on suppressing rotating stall in the vaned diffuser of a centrifugal turbomachine. Thirteen double curvature vanes with various radial positions, various setting angles, and J-grooves of different dimensions are tested in a parallel wall vaned diffuser with a semi-open radial impeller with and without J-grooves. The results show that J-grooves can also suppress rotating stall in the vaned diffuser for the entire flow range.

Pressure and Velocity Fluctuations in the Diffuser for Rotating Stall Period

2012 ◽  
Author(s):  
Youhwan Shin ◽  
Ji-In Yoon ◽  
Yoon Pyo Lee
Keyword(s):  
Measurement Technique ◽  
Reverse Flow ◽  
Tangential Velocity ◽  
Ccd Camera ◽  
Rotating Stall ◽  
Vaneless Diffuser ◽  
Velocity Fluctuations ◽  
Pressure Transducers ◽  
Piv Measurement ◽  
Velocity Images

This study describes details on local reverse flow patterns in a vaneless diffuser by experiments through PIV measurement technique in the water bath during the unstable operation of a compressor with radial impeller. In order to do these measurements, the pressure transducers were installed on the hub wall with several diffuser radius ratios and they were synchronized with the velocity images of CCD camera. Especially we tried to make them synchronize with time during rotating stall period. For relatively high and low pressure instants, we observed and discussed how the radial and tangential velocity components fluctuated.

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.

The Features of Flow in a Parallel-Walled Radial Vaneless Diffuser

2000 ◽  
Author(s):  
K. B. Abidogun ◽  
S. A. Ahmed
Keyword(s):  
Tangential Velocity ◽  
Maximum Flow ◽  
Calculation Model ◽  
Angle Distribution ◽  
Limited Data ◽  
Vaneless Diffuser ◽  
Centrifugal Blower ◽  
Flow Angle ◽  
Flow Features ◽  
Measurement Path

Abstract Detailed experimental investigation of flow features in a parallel-walled radial vaneless diffuser of a centrifugal blower was carried out. Maximum flow rate through the blower, at a constant impeller speed of 1500 rpm, was maintained throughout the experiment to ensure that no self-exited flow oscillation occurs in the diffuser. The symmetrical flowfield in the diffuser was measured along a radial path using an X-wire probe. The radial and tangential velocity distributions and their statistics, as well as flow angle distribution, are reported. The results presented in this paper agree well with earlier work on this subject. For instance, the flow angle at half the diffuser width, which is the position at which critical flow angle (measured from the radial direction) have been generally reported to be about 78°, did not exceed 65° from the diffuser inlet to its outlet along the measurement path. The result also showed that the flow exiting the impeller is skewed as revealed by the triple velocity product correlations. This data is a useful tool for vaneless diffuser calculation model developers as there are very limited data that paralleled the current one as expounded in the text of this paper.

The Vortex-Filament Nature of Reverse Flow on the Verge of Rotating Stall

1989 ◽  
Vol 111 (4) ◽  
pp. 450-461 ◽  
Author(s):  
Y. N. Chen ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Reverse Flow ◽  
Research Work ◽  
Tangential Velocity ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Ring Vortex ◽  
Extensive Literature ◽  
Transition Range ◽  
Vortex Filaments ◽  
Spiral Vortex

On the verge of rotating stall, very orderly reverse flow forms from the outlet of the rotor/impeller along the casing/shroud toward the inlet in axial/centrifugal compressors (Koch, 1970; Haupt, et al., 1987). The experiment on a centrifugal compressor reveals furthermore that the reverse flow is composed of stable spiral vortex filaments. Their vorticity can be transferred to the inlet tip vortex, known as prerotation. The behavior of these vortex filaments is examined based on the fundamental research work on rotating bodies available in the literature. This result shows that the vortex filaments are composed of Taylor’s vortex pairs, but with unequal vortex strengths within the pair. They form the transition range from a laminar to a turbulent three-dimensional boundary layer with a very steep tangential velocity profile. This profile is associated with the appearance of a toroidal ring vortex in the rotor/impeller, acting as a recirculatig secondary flow. It can be further shown from the analysis of the extensive literature that the orderly path of the reverse flow is enabled by the cessation of the leakage flow of the rotor tip clearance. The reason for this is that the growing tangential flow field extends beyond the rotor tip up to the close proximity of the endwall, so that the tip clearance is blocked.

Blade Excitation by Broad-Band Pressure Fluctuations in a Centrifugal Compressor

1988 ◽  
Vol 110 (1) ◽  
pp. 129-137 ◽  
Author(s):  
U. Haupt ◽  
M. Rautenberg ◽  
A. N. Abdel-Hamid
Keyword(s):  
Centrifugal Compressor ◽  
Reverse Flow ◽  
Pressure Ratio ◽  
Pressure Fluctuations ◽  
Broad Band ◽  
Rotating Stall ◽  
High Mass ◽  
Blade Vibration ◽  
Flow Angle ◽  
Unsteady Pressure

The mechanism of blade excitation during the operation of a high-mass-flow, high-pressure-ratio centrifugal compressor has been investigated. This was carried out in the compressor operating range below 60 percent of design speed and in the zone of unsteady flow occurrence, where considerable blade vibration has been measured but no periodic unsteady pressure pattern such as rotating stall could be identified. Experiments conducted to study the mechanism of interactions between flow and blades were accomplished using several measuring methods simultaneously, such as measurements of blade vibration, flow angle at impeller inlet, unsteady pressure at different meridional and peripheral locations, as well as flow visualization by means of oil pattern. Analysis of the measurements showed typical broad-band characteristics of the unsteady pressure field and also for the blade vibration behavior. Results of flow angle investigations at the impeller inlet together with the analysis of oil pattern show that the broad-band pressure fluctuations and blade excitation can be attributed to a strong reverse flow near the suction side of the radial blade in the shroud zone. This reverse flow has its source downstream of the impeller and is extending back up to a location ahead of the impeller inlet. Similar results were obtained when the compressor was operated with vaneless and vaned diffuser configurations.

Rotating Mechanism of Diffuser Stall in a Centrifugal Compressor With Vaneless Diffuser

2021 ◽  
Author(s):  
Nobumichi Fujisawa ◽  
Yuki Agari ◽  
Yoshifumi Yamao ◽  
Yutaka Ohta
Keyword(s):  
Boundary Layer ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Reverse Flow ◽  
Boundary Layer Separation ◽  
Vaneless Diffuser ◽  
Low Velocity ◽  
Flow Angle ◽  
Discharge Flow ◽  
Layer Separation

Abstract The rotating mechanism of diffuser stall in a centrifugal compressor with a vaneless diffuser is investigated via experimental and computational analyses. Diffuser stall is generated as the mass flow rate decreases, and it rotates at 25%–30% of the impeller rotational speed. First, a diffuser stall cell emerges at 180° from the cutoff by the hub-side boundary layer separation. Subsequently, the diffuser stall cell develops further owing to boundary layer separation accumulation and an induced low-velocity area. The low-velocity region forms a blockage across the diffuser passage span. The diffuser stall cell expands owing to the boundary layer separations that occurred on the shroud and hub wall by turns. Finally, the diffuser stall cell vanishes when it passes the cutoff because mass flow recovery occurred. Furthermore, the static pressure ahead of the rotating stall decreases because of the merging of the impeller discharge flow and the reverse flow from the casing. Accordingly, a reverse flow occurred owing to the evolution of the separation vortex at the diffuser exit. In addition, the flow angle decreases by the merging of the impeller discharge flow and reverse flow from the casing. Therefore, boundary layer separations start occurring on the shroud and hub wall ahead of the stall cell. The rotating mechanism of the diffuser stall is induced by the reverse flow development and a decrease in the flow angle ahead of the stall cell.

Transient Process of Rotating Stall in Radial Vaneless Diffusers

1994 ◽  
Author(s):  
H. Watanabe ◽  
S. Konomi ◽  
I. Ariga
Keyword(s):  
Flow Rate ◽  
Reverse Flow ◽  
Flow Region ◽  
Rotating Stall ◽  
Lower Side ◽  
Hot Wire ◽  
Vaneless Diffuser ◽  
Reversed Flow ◽  
Stall Inception ◽  
Wire Probe

This paper describes the process of rotating stall inception in a radial vaneless diffuser. Unsteady flow and rotating stall were investigated by measuring the wall static pressures and velocity distributions using X hot-wire probe. From the measurements of the velocity fluctuation, it is confirmed that the periodical disturbance in the reverse flow region as the prestall symptom occurs prior to the onset of stall and then the growth of that periodical disturbance leads to the rotating stall with fully developed non axisymmetric reversed flow. On the process of the rotating stall inception, reverse flow regions in the diffuser grow from the diffuser exit toward the inlet along the shroud and hub wall, and the rotating stall occurs when the reverse flow region on the shroud wall reaches to the impeller exit. In this paper, the effects of the diffuser exit blockage on the process of stall inception were also described. The flow rate of stall onset is moved to the lower side by the restriction of the diffuser exit width, however, this restriction does not affect the distribution of the reverse flow regions. That restriction suppresses the prestall disturbance in the reverse flow regions and then stabilize the flow in the diffuser.

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.

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