Conical diffusers are often installed downstream of a turbomachine with a central hub. Previous studies showed that nonstreamlined hubs had extended separated wakes that reduced the adverse pressure gradient in the diffuser. Active flow control techniques can rapidly close the central separation bubble, but this restores the adverse pressure gradient, which can cause the outer wall boundary layer to separate. The present study focuses on the use of a step-wall diffuser to stabilize the wall boundary layer separation in the presence of core flow control. Three-component mean velocity data for a set of conical diffusers were acquired using magnetic resonance velocimetry. The results showed the step-wall diffuser stabilized the wall boundary layer separation by fixing its location. An axisymmetric step separation bubble was formed. A step with a periodically varying height reduced the reattachment length of the step separation and allowed the diffuser to be shortened. The step-wall diffuser was found to be robust in a range of core flow velocity profiles. The minimum distance between the core flow control mechanism and the step-wall diffuser as well as the minimum length of the step were determined.
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April 2013
Research-Article
Flow Separation Control in an Annular to Conical Diffuser Using Two-Dimensional and Three-Dimensional Wall Steps
Christopher J. Elkins,
John K. Eaton
John K. Eaton
e-mail: eatonj@stanford.edu
Department of Mechanical Engineering
,Stanford University
,488 Escondido Mall
,Building 500
,Stanford, CA 94305
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Kin Pong Lo
e-mail: kinpong.lo@gmail.com
Christopher J. Elkins
e-mail: celkins@stanford.edu
John K. Eaton
e-mail: eatonj@stanford.edu
Department of Mechanical Engineering
,Stanford University
,488 Escondido Mall
,Building 500
,Stanford, CA 94305
Manuscript received June 4, 2012; final manuscript received January 9, 2013; published online March 21, 2013. Assoc. Editor: Michael G. Olsen.
J. Fluids Eng. Apr 2013, 135(4): 041102 (11 pages)
Published Online: March 21, 2013
Article history
Received:
June 4, 2012
Revision Received:
January 9, 2013
Citation
Lo, K. P., Elkins, C. J., and Eaton, J. K. (March 21, 2013). "Flow Separation Control in an Annular to Conical Diffuser Using Two-Dimensional and Three-Dimensional Wall Steps." ASME. J. Fluids Eng. April 2013; 135(4): 041102. https://doi.org/10.1115/1.4023648
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