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.

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]

Investigation of Internal Flow and Characteristic Instability of a Mixed Flow Pump

2009 ◽  
Author(s):  
Masahiro Miyabe ◽  
Akinori Furukawa ◽  
Hideaki Maeda ◽  
Isamu Umeki
Keyword(s):  
Flow Rate ◽  
Internal Flow ◽  
Rotating Stall ◽  
Leakage Flow ◽  
Suction Surface ◽  
Mixed Flow ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Pressure Surface ◽  
Flow Pump

The relationship between pump characteristic instabilities and internal flow was investigated in a mixed flow pump with specific speed of 700 (min−1 m3/min, m) or 1.72 (non-dimensional) by using a commercial CFD code and a dynamic PIV (DPIV) measurement. This pump has two positive slopes of a head-flow characteristic at the flow rates of about 60%Qopt and 82%Qopt. In the authors’ previous study, it was clarified that the characteristic instability at 82%Qopt is caused by the diffuser rotating stall (DRS) and the backflow near the hub of the vaned diffuser plays an important role on the onset of the diffuser rotating stall. In the present paper, the investigation is focused on the instability at about 60% Qopt. Based on both of experimental and numerical results, it was clarified that the characteristic instability at 60%Qopt is caused by the backflow at the inlet of the impeller tip and the leakage flow from the impeller pressure surface to the suction surface plays an important role on the onset of the backflow. The behaviors of backflow at the impeller inlet were visualized by the DPIV measurements and CFD simulation. Moreover, internal flow was investigated in detail and the occurrence of characteristic instability is assumed as follows: At the partial flow rate, the flow angle at the inlet of the impeller tip decreases and the flow hits the impeller pressure surface. Then, the blade loading at the inlet of impeller tip is increased and the recirculation at the leading edge and the leakage flow rate from pressure surface to suction surface increases. The leakage flow causes to generate vortices at the inlet of the suction surface of the impeller. As the flow rate is further decreased, the vortices develop to backflow with swirl. The leakage flow has peripheral component of absolute velocity and the swirling energy is continuously supplied by the backflow. Therefore, even the passage flow at the inlet of the impeller has been getting pre-swirling. The theoretical head, the Euler head is decreased due to the pre-swirling. Moreover, based on the CFD results, the pre-swirling and unsteady vortices near the suction surface of the impeller causes pump characteristic instability. When the flow rate is decreased further more, total head rises because the flow pattern in the impeller changes to centrifugal type due to the backflow from the vaned diffuser at the hub region.

scholarly journals Dynamic Characteristics of Rotating Stall in Mixed Flow Pump

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Xiaojun Li ◽  
Shouqi Yuan ◽  
Zhongyong Pan ◽  
Yi Li ◽  
Wei Liu
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Propagation Mechanism ◽  
Positive Slope ◽  
Mixed Flow ◽  
Outlet Flow ◽  
Research Gap ◽  
Flow Pump

Rotating stall, a phenomenon that causes flow instabilities and pressure hysteresis by propagating at some fraction of the impeller rotational speed, can occur in centrifugal impellers, mixed impellers, radial diffusers, or axial diffusers. Despite considerable efforts devoted to the study of rotating stall in pumps, the mechanics of this phenomenon are not sufficiently understood. The propagation mechanism and onset of rotating stall are not only affected by inlet flow but also by outlet flow as well as the pressure gradient in the flow passage. As such, the complexity of these concepts is not covered by the classical explanation. To bridge this research gap, the current study investigated prerotation generated at the upstream of the impeller, leakage flow at the tip clearance between the casing and the impeller, and strong reserve flow at the inlet of the diffuser. Understanding these areas will clarify the origin of the positive slope of the head-flow performance curve for a mixed flow pump. Nonuniform pressure distribution and adverse pressure gradient were also introduced to evaluate the onset and development of rotating stall within the diffuser.

Suppression of Performance Curve Instability of a Mixed Flow Pump by Use of J-groove

2000 ◽  
Vol 122 (3) ◽  
pp. 592-597 ◽  
Author(s):  
Sankar L. Saha ◽  
Junichi Kurokawa ◽  
Jun Matsui ◽  
Hiroshi Imamura
Keyword(s):  
Angular Momentum ◽  
Pressure Gradient ◽  
Reverse Flow ◽  
Swirl Flow ◽  
Maximum Efficiency ◽  
Performance Curve ◽  
Positive Slope ◽  
Mixed Flow ◽  
Remarkable Effect ◽  
Flow Pump

In order to control and suppress performance curve instability characterized by the positive slope of head-capacity curve of a mixed flow pump, a very simple passive method utilizing shallow grooves mounted on a casing wall parallel to the pressure gradient (J-groove) is proposed. The optimum groove dimension and location for suppressing such an instability are determined experimentally. Results show that shallow grooves of adequate dimension and proper location can suppress such instability perfectly without decreasing the pump maximum efficiency. The remarkable effect of shallow grooves is to decrease both the swirl strength and the propagation of reverse flow at the impeller inlet region, through angular momentum absorption owing to mixing of groove reverse flow and swirl flow, yielding recovery of impeller theoretical head. [S0098-2202(00)02603-1]

scholarly journals The Vortex Behaviour of the Rotating-Stall Cell of a Centrifugal Compressor With Vaned Diffuser

1992 ◽  
Author(s):  
Y. N. Chen ◽  
U. Seidel ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Centrifugal Compressor ◽  
Tangential Velocity ◽  
Vortex Pair ◽  
Swirl Flow ◽  
Rotating Stall ◽  
Longitudinal Vortex ◽  
Vortex Loop ◽  
Vaned Diffuser ◽  
Pressure Transducers ◽  
Longitudinal Vortices

The aerodynamic behaviour of the rotating-stall cell of a centrifugal compressor with radial blading and vaned diffuser is investigated experimentally using two stagnation pressure transducers located parallel to each other on the opposing walls of the semi-vaneless annular space between the impeller and the diffuser. The transducers are turned simultaneously step by step through an angle of 360° during the measurement, so that the flow field of both the forward and reverse flows and the swirl flow components can be detected in the stalled and the unstalled regions. It was shown in the previous papers of the authors (1991 b) that the jet and wake in the flow of the blade channel in the normal operating range are cores of longitudinal vortices with opposite rotational sense. During rotating stall, the jet of a blade channel bends over the outlet edge of the blade and is converted into the wake of the neighbouring one to form a vortex loop around the blade in question. The swirling speed of this vortex loop (the vorticity) is measured to be about twice impeller speed for the present case. The vortex loops of the adjacent blades then join together to form a bubble, the stall cell, embodying the region of the stalled blades. The outer reach of the vortex bubble forms the border of the outer lobe of the Rossby waves associated with the vortex pair “high” (H) and “low” (L) guiding the stall cell. The longitudinal-vortex-nature of the jet stream along the flank of the Rossby wave, as determined recently in a vaneless diffuser by the authors (1991a), is confirmed in the present investigation. Its intensity reaches a velocity of about 20% u2 when measured in the absolute frame, or 120% u2 when measured in the rotating impeller frame, superimposed by a swirling component of (1 to 4) x ωimp (u2 = tangential velocity of the impeller outlet. ωimp = angular velocity of the impeller).

Rotating Stall Behavior in a Diffuser of Mixed Flow Pump and Its Suppression

2008 ◽  
Author(s):  
Masahiro Miyabe ◽  
Akinori Furukawa ◽  
Hideaki Maeda ◽  
Isamu Umeki
Keyword(s):  
Flow Rate ◽  
Internal Flow ◽  
Rotating Stall ◽  
Low Energy ◽  
Suction Surface ◽  
Mixed Flow ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Pump Design ◽  
Flow Pump

The relationship between pump characteristic instability and internal flow was investigated on a mixed flow pump with specific speed ωs = 1.72 (dimensionless) or 700 (m3/min, m, min−1) by using a commercial CFD code and a dynamic PIV (DPIV) measurement. As a result, it was clarified that the diffuser rotating stalls causes the positive slope of a head-flow characteristic and the backflow at hub-side of the vaned diffuser plays an important role on the onset of the diffuser rotating stall. The complex behaviors of diffuser rotating stall were visualized by the DPIV measurements and CFD simulation. Moreover, the internal flow was investigated in detail and the inception of characteristic instability was presumed as follows: At the partial flow rate, low energy fluids are accumulated in the corner between the hub surface and the suction surface of the diffuser vane. As the flow rate is further decreased, the low energy fluids region at the corner axi-symmetrically expands along the hub and become unstable due to adverse pressure gradient. Then, strong backflow occurs and impinges against passage flow from the impeller at the inlet of the vaned diffuser. In addition, the backflow blocks the passage flow from impeller and the inlet flow angle at the leading edge of adjacent diffuser vane is reduced. Therefore, flow separation occurs near the inlet of suction surface of the vaned diffuser, and a strong vortex is generated there. After that, the vortex develops and becomes a stall core. Based on above considerations, pump design parameter studies were numerically carried out and diffuser rotating stall was suppressed and pump characteristic instability was controlled by enlarging the inlet diameter of diffuser hub.

Effect of Blade Thickness on Rotating Stall of Mixed-Flow Pump Using Entropy Generation Analysis

Energy ◽  
2021 ◽  
pp. 121381
Author(s):  
Leilei Ji ◽  
Wei Li ◽  
Weidong Shi ◽  
Fei Tian ◽  
Ramesh Agarwal
Keyword(s):  
Entropy Generation ◽  
Rotating Stall ◽  
Mixed Flow ◽  
Blade Thickness ◽  
Flow Pump

Performance Study of a Mixed Flow Impeller Covering an Unsteady Flow Field

1992 ◽  
Vol 206 (2) ◽  
pp. 83-93 ◽  
Author(s):  
S Sarkar
Keyword(s):  
Axial Flow ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Performance Study ◽  
Mixed Flow ◽  
Pump Impeller ◽  
Wide Range ◽  
Reversal Flow ◽  
Flow Through ◽  
Flow Pump

The results presented here are part of a detailed programme measuring the aerodynamics of a high specific speed mixed flow pump impeller over a wide range of operating conditions, including its behaviour in the unsteady stalled regime. The aim is to elucidate the physics of the flow through such an impeller. The noticeable features are the formation of part-span rotating stall cells having no periodicity and organized structure at reduced flow and also the shifting positions of reversal flow pockets as the flowrate changes. Measurements of loss and its variation with span-wise positions and flowrates enable the variation of local efficiency to be determined. The overall flow picture is similar to that expected in an axial flow impeller, though the present impeller displays a narrow stall hysteresis loop almost right through its operating range.

scholarly journals Suppression of Mixed-Flow Pump Instability and Surge by the Active Alteration of Impeller Secondary Flows

1993 ◽  
Author(s):  
Akira Goto
Keyword(s):  
Flow Characteristic ◽  
Secondary Flows ◽  
Wake Flow ◽  
Streamwise Vorticity ◽  
Jet Injection ◽  
Positive Slope ◽  
Suction Surface ◽  
Mixed Flow ◽  
Pump System ◽  
Flow Pump

An active method for enhancing pump stability, featuring water jet injection at impeller inlet, was applied to a mixed-flow pump. The stall margin, between the design point and the positive slope region of the head-flow characteristic, was most effectively enlarged by injecting the jet in the counter-rotating direction of the impeller. The counter-rotating streamwise vorticity along the casing, generated by the velocity discontinuity due to the jet injection, altered the secondary flow pattern in the impeller by opposing the passage vortex and assisting the tip leakage vortex motion. The location of the wake flow was displaced away from the casing-suction surface corner of the impeller, thus avoiding the onset of the extensive corner separation, the cause of positive slope region of the head-flow characteristic. This method was also confirmed to be effective for stabilizing a pump system already in a state of surge.

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