This paper presents unsteady surface pressures measured on the suction surface of a LP turbine cascade that was subject to wake passing from a moving bar wake generator. The surface pressures measured under the laminar boundary layer upstream of the steady flow separation point were found to respond to the wake passing as expected from the kinematics of wake convection. In the region where a separation bubble formed in steady flow, the arrival of the convecting wake produced high frequency, short wavelength, fluctuations in the ensemble averaged blade surface pressure. The peak-to-peak magnitude was 30% of the exit dynamic head. The existence of fluctuations in the ensemble averaged pressure traces indicates that they are deterministic and that they are produced by coherent structures. The onset of the pressure fluctuations was found to lie beneath the convecting wake and the fluctuations were found to convect along the blade surface at half of the local freestream velocity. Measurements performed with the boundary layer tripped ahead of the separation point showed no oscillations in the ensemble average pressure traces indicating that a separating boundary layer is necessary for the generation of the pressure fluctuations. The coherent structures responsible for the large amplitude pressure fluctuations were identified using PIV to be vortices embedded in the boundary layer. It is proposed that these vortices form in the boundary layer as the wake passes over the inflexional velocity profiles of the separating boundary layer and that the rollup of the separated shear layer occurs by an inviscid Kelvin-Helmholtz mechanism.
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ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference
June 16–19, 2003
Atlanta, Georgia, USA
Conference Sponsors:
- International Gas Turbine Institute
ISBN:
0-7918-3689-4
PROCEEDINGS PAPER
Unsteady Surface Pressures Due to Wake Induced Transition in a Laminar Separation Bubble on a LP Turbine Cascade Available to Purchase
Rory Stieger,
Rory Stieger
Cambridge University, Cambridge, UK
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David Hollis,
David Hollis
Loughborough University, Loughborough, Leicestershire, UK
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Howard Hodson
Howard Hodson
Cambridge University, Cambridge, UK
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Rory Stieger
Cambridge University, Cambridge, UK
David Hollis
Loughborough University, Loughborough, Leicestershire, UK
Howard Hodson
Cambridge University, Cambridge, UK
Paper No:
GT2003-38303, pp. 927-935; 9 pages
Published Online:
February 4, 2009
Citation
Stieger, R, Hollis, D, & Hodson, H. "Unsteady Surface Pressures Due to Wake Induced Transition in a Laminar Separation Bubble on a LP Turbine Cascade." Proceedings of the ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. Volume 6: Turbo Expo 2003, Parts A and B. Atlanta, Georgia, USA. June 16–19, 2003. pp. 927-935. ASME. https://doi.org/10.1115/GT2003-38303
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