Theoretical Analysis of Fluid Forces on an Open-Type Centrifugal Impeller in Whirling Motion

For turbomachines operating at supercritical shaft speed, it is important to understand the characteristics of unsteady fluid forces on the impeller that occur due to shaft vibration. The present paper treats the forces on an open-type centrifugal impeller in whirling motion using unsteady potential flow theory. The whirling forces obtained agree reasonably with experimental results and show a destabilizing region at small positive whirl. It was found that the destabilizing force is due to the forces on the hub caused by temporal change in the thickness of the flow channel, with minor contribution of tip leakage on the destabilization.

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Theoretical Analysis of Fluid Forces on an Open-Type Centrifugal Impeller in Whirling Motion.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.66.651_2920 ◽

2000 ◽

Vol 66 (651) ◽

pp. 2920-2926

Author(s):

Akira HIWATA ◽

Yoshinobu TSUJIMOTO

Keyword(s):

Theoretical Analysis ◽

Centrifugal Impeller ◽

Open Type ◽

Fluid Forces ◽

Whirling Motion

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Lateral Fluid Forces on Whirling Centrifugal Impeller (2nd Report: Experiment in Vaneless Diffuser)

Journal of Fluids Engineering ◽

10.1115/1.3242628 ◽

1987 ◽

Vol 109 (2) ◽

pp. 100-106 ◽

Cited By ~ 11

Author(s):

H. Ohashi ◽

H. Shoji

Keyword(s):

Orbital Motion ◽

Operating Conditions ◽

Centrifugal Impeller ◽

Test Results ◽

Vaneless Diffuser ◽

Fluid Forces ◽

Damping Effect ◽

Whirling Motion ◽

Stiffness Matrices ◽

Whirl Speed

Fluid forces acting on a rotating centrifugal impeller in whirling motion are studied experimentally. A two-dimensional impeller installed in a parallel walled vaneless diffuser was forced on a circular orbital motion at various positive and negative whirl speeds. The measurements show that the fluid forces exert a damping effect on the rotor at most operating conditions, but excite positive whirl when the impeller operates at a partial discharge and rotates at speeds more than twice the whirl speed. The test results were compared with those calculated by the theory described in the 1st Report. The characteristics of whirling fluid forces are examined from both the measurements and calculations. The measured fluid forces are expressed in terms of mass, damping, and stiffness matrices.

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Effects of Seal Geometry on Dynamic Impeller Fluid Forces and Moments

Journal of Fluids Engineering ◽

10.1115/1.1598988 ◽

2003 ◽

Vol 125 (5) ◽

pp. 786-795 ◽

Cited By ~ 8

Author(s):

Yoshiki Yoshida ◽

Yoshinobu Tsujimoto ◽

Goh Morimoto ◽

Hiroki Nishida ◽

Shigeki Morii

Keyword(s):

Force Sensor ◽

Rotating Stall ◽

Low Flow ◽

Centrifugal Impeller ◽

Face Seal ◽

Vaneless Diffuser ◽

Fluid Force ◽

Fluid Forces ◽

Whirling Motion ◽

Force Moment

This paper reports an experimental investigation of the rotordynamic fluid force and moment on a centrifugal impeller with three types of wear-ring seals; i.e., a face seal and two types of toothed seals. The impeller is equipped with a vaneless diffuser. Rotordynamic fluid forces and moments on the impeller in whirling motion were measured directly by using four-axis force sensor. Unsteady pressures were measured at several locations in the diffuser. It was found that, (1) at low flow rate, the fluid force and fluid force moment become maximum at a certain whirling speed caused by a coupling between the whirl motion and vaneless diffuser rotating stall and (2) the seal geometry with axial seal affects the direction of the coupled fluid force relative to the direction of eccentricity through the change in the unsteady leakage flow due to the whirl.

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A Theoretical Analysis of Unsteady Fluid Forces and Pressure Distributions on a Blade of Cavitating Cascades. 2nd Report, Sinusoidal Gust Flow.

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.68.1458 ◽

2002 ◽

Vol 68 (669) ◽

pp. 1458-1465

Author(s):

Hironori HORIGUCHI ◽

Makoto MIKAMI ◽

Stephane LAFFITE ◽

Yoshinobu TSUJIMOTO

Keyword(s):

Theoretical Analysis ◽

Fluid Forces ◽

Pressure Distributions ◽

Unsteady Fluid

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Lateral Fluid Forces on Whirling Centrifugal Impeller (1st Report: Theory)

Journal of Fluids Engineering ◽

10.1115/1.3242647 ◽

1987 ◽

Vol 109 (2) ◽

pp. 94-99 ◽

Cited By ~ 9

Author(s):

H. Shoji ◽

H. Ohashi

Keyword(s):

Potential Flow ◽

Guide Vane ◽

Flow Theory ◽

Operating Conditions ◽

Centrifugal Impeller ◽

Flow Rates ◽

Guide Vanes ◽

Fluid Forces ◽

Damping Effect ◽

Whirling Motion

Lateral fluid forces acting on a rotating centrifugal impeller in whirling motion are analyzed using unsteady potential flow theory. Impellers operating in diffusers with and without vanes are modeled and the fluid forces calculated for different whirl speeds and flow rates. The influences of these parameters are clarified by parametric calculations. The results for whirling impellers operating in vaneless diffusers show that the fluid forces exert a damping effect on the rotor whirling motion at all operating conditions. The results for impellers operating in vaned diffusers or guide vanes show that the time averaged values of fluid forces remain almost unchanged, while there are significant instantaneous fluctuations due to the impeller/guide vane interactions.

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