Tomographic-PIV measurement of the flow around a zigzag boundary layer trip |
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Authors: | Email author" target="_blank">G?E?ElsingaEmail author J?Westerweel |
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Institution: | (1) Laboratory for Aero and Hydrodynamics, Delft University of Technology, Delft, The Netherlands |
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Abstract: | Tomographic-PIV was used to measure the boundary layer transition forced by a zigzag trip. The resulting instantaneous three-dimensional
velocity distributions are used to quantitatively visualize the flow structures. They reveal undulating spanwise vortices
directly behind the trip, which break up into individual arches and then develop into the hairpin-like structures typical
of wall-bounded turbulence. Compared to the instantaneous flow structure, the structure of the average velocity field is very
different showing streamwise vortices. Such streamwise vortices are often associated with the low-speed streaks occurring
in bypass transition flows, but in this case clearly are an artifact of the averaging. Rather, the present streaks in the
separated flow region directly behind the trip are resulting from the waviness in the spanwise vortices as introduced by the
zigzag trip. Furthermore, these streaks and the separated flow region are observed to be related to a large-scale, spanwise
uniform unsteadiness in the flow that contributes significantly to the velocity fluctuations over large downstream distances
(up to at least the edge of the present measurement domain). |
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Keywords: | |
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