This paper describes numerical simulations of the instability mechanisms in a separation bubble subjected to a three-dimensional freestream pressure distribution. Two direct numerical simulations are performed of a separation bubble with laminar separation and turbulent reattachment under low freestream turbulence at flow Reynolds numbers and streamwise pressure distributions that approximate the conditions encountered on the suction side of typical low-pressure gas-turbine blades with blade sweep angles of 0° and 45°. The three-dimensional pressure field in the swept configuration produces a crossflow-velocity component in the laminar boundary layer upstream of the separation point that is unstable to a crossflow instability mode. The simulation results show that crossflow instability does not play a role in the development of the boundary layer upstream of separation. An increase in the amplification rate and most amplified disturbance frequency is observed in the separated-flow region of the swept configuration, and is attributed to boundary-layer conditions at the point of separation that are modified by the spanwise pressure gradient. This results in a slight upstream movement of the location where the shear layer breaks down to small-scale turbulence and modifies the turbulent mixing of the separated shear layer to yield a downstream shift in the time-averaged reattachment location. The results demonstrate that although crossflow instability does not appear to have a noticeable effect on the development of the transitional separation bubble, the 3D pressure field does indirectly alter the separation-bubble development by modifying the flow conditions at separation.
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ASME Turbo Expo 2012: Turbine Technical Conference and Exposition
June 11–15, 2012
Copenhagen, Denmark
Conference Sponsors:
- International Gas Turbine Institute
ISBN:
978-0-7918-4470-0
PROCEEDINGS PAPER
Direct Numerical Simulations of Transitional Separation–Bubble Development in Swept–Blade Flow Conditions
Joshua R. Brinkerhoff,
Joshua R. Brinkerhoff
Carleton University, Ottawa, ON, Canada
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Metin I. Yaras
Metin I. Yaras
Carleton University, Ottawa, ON, Canada
Search for other works by this author on:
Joshua R. Brinkerhoff
Carleton University, Ottawa, ON, Canada
Metin I. Yaras
Carleton University, Ottawa, ON, Canada
Paper No:
GT2012-68659, pp. 805-817; 13 pages
Published Online:
July 9, 2013
Citation
Brinkerhoff, JR, & Yaras, MI. "Direct Numerical Simulations of Transitional Separation–Bubble Development in Swept–Blade Flow Conditions." Proceedings of the ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. Volume 4: Heat Transfer, Parts A and B. Copenhagen, Denmark. June 11–15, 2012. pp. 805-817. ASME. https://doi.org/10.1115/GT2012-68659
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