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Investigation of Bypass Transition in the Presence of a Separation Bubble With Tomographic PIV
Citation key 2016_lyko_asme
Author Lyko, C. and Michaelis, D. and Peitsch, D. and Dittmar, M.
Pages GT2016-57884
Year 2016
ISBN 978-0-7918-4972-9
DOI 10.1115/GT2016-57884
Location Seoul, South Korea
Journal ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition
Volume Volume 2D: Turbomachinery
Month 06
Note V02DT44A036,
Technische Universit├Ąt Berlin:
C. Lyko, D. Michaelis, D. Peitsch, M. Dittmar
Editor ASME
Series Turbo Expo: Power for Land, Sea, and Air
Abstract Low pressure turbines of small and medium sized engines may operate at very low Reynolds numbers. In consequence transition is delayed to an extend where laminar separation, detached transition and reattachment occur. The wakes from upstream blade rows lead to overall high turbulence levels which play a key role in the transition process. Freestream eddies buffeting the laminar boundary layer induce streamwise vortices known as Klebanoff Modes. To investigate this type of flow a flat plate was exposed to a pressure distribution. It is based on the PAK-B suction side and was created by a contoured wall facing the plate. The PAK-B is a Pratt \\& Whitney design and a Mach number scaled version of a highly aft loaded low pressure turbine airfoil. Due to the latter it suffers from a large separation bubble at low Reynolds numbers.The flow has been intensively investigated by hot-wire anemometry with a very high spatial resolution. This allows obtaining very precise information about the location of characteristic flow areas; for instance the separation and reattachment positions. Based on this information, Tomographic PIV was employed to expose detailed features in specific areas of the flow field. This technique provides the velocity vector information inside a flow volume. It complements hot-wire results, which give a time resolved information but only planar velocity magnitudes. Combining these techniques and comparing their results is therefore an excellent way to raise the physical understanding of the flow behaviour. This has been done using velocity profiles, skin friction coefficients and integral boundary layer parameters. As the 3D-PIV information allows calculation of derived quantities, like the vector field rotation, a picture of the coherent structures can be drawn.
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