Spring 2001

ME/IE 8773-8774

Laminar-Turbulent Transition under Gas Turbine Airfoil Conditions

by

Ralph J. Volino, Ph.D.
Assistant Professor
Department of Mechanical Engineering

U.S. Naval Academy
Annapolis, MD 21402

Wednesday, April 11, 2001
3:30-4:30 p.m.
Room 108 ME
Broadcast on UNITE Channel A
Coffee and cookies will be available in 152 ME following the seminar

Modern gas turbine engines push the limits of existing technology. Turbine inlet temperatures, for example, may exceed 1700(C, requiring innovative cooling of the high pressure turbine airfoils. Providing sufficient local cooling, while avoiding overcooling, which would degrade overall efficiency, requires accurate prediction of the heat transfer in the engine. To decrease engine size and weight, modern airfoils are also subject to high loading. High loading results from strong pressure gradients through turbine passages, and can lead to boundary layer separation from airfoil surfaces. Separation, if it occurs, leads to a loss of power and a drop in efficiency. Designing for high loading while avoiding separation requires accurate prediction of the fluid mechanics. Key to the prediction of both the fluid mechanics and the heat transfer, and key to pushing the technology further, is an understanding of boundary layer transition. In spite of the high disturbance levels in engines, relatively low Reynolds numbers and regions of strong favorable pressure gradient result in extended regions of transitional flow on turbine airfoils. Heat transfer rates can increase significantly as a boundary layer undergoes transition, and boundary layers are more resistant to separation after transition to turbulence. Existing transition models are not always adequate, and it is believed that if a better understanding of the physics of transition were incorporated into the models, they might be improved. The transition is complex, and includes intermittent flow, switching between a badly disturbed non-turbulent state and a turbulent state. Recent experimental work involving conditional sampling has resulted in separate documentation of these two states within transition. The results, which include turbulence statistics and wavelet spectral analysis, improve our understanding of the flow and may prove useful in the development of intermittency based models. Results from this work, along with related work involving curvature effects and separated flow transition will be presented.

Ralph Volino is originally from Detroit, Michigan. He received his B.S. in Mechanical Engineering from Michigan State University in 1987, and his M.S.M.E. and Ph.D. from the University of Minnesota in 1990 and 1995. His recent work has included research into transition in separated boundary layers, separation control, transition under high disturbance conditions, modification of gas turbine endwall flows, and convection at air-water interfaces. He has spent recent summers with the Turbine Branch of the NASA Lewis/Glenn Research Center, the Remote Sensing Division of the Naval Research Laboratory, and the Turbine Engine Division of the Air Force Research Laboratory at Wright Patterson Air Force Base.

Informal Faculty Luncheon: Wednesday, April 11, 2001, 12:00 noon. A table is reserved at McCormick's Restaurant, Radisson Hotel Metrodome. Prof. Volino will be able to attend.