Flow field investigation in rotating rib-roughened channel by means of particle image velocimetry |
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Authors: | Email author" target="_blank">Filippo?ColettiEmail author Thomas?Maurer Tony?Arts Alberto?Di Sante |
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Institution: | 1.Turbomachinery and Propulsion Department,von Karman Institute for Fluid Dynamics,Rhode-Saint-Genèse,Belgium;2.Mechanical Engineering Department,Stanford University,Stanford,USA;3.Institute of Aerospace Thermodynamics,Stuttgart University,Stuttgart,Germany;4.General Electric,Florence,Italy |
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Abstract: | The turbulent velocity field over the rib-roughened wall of an orthogonally rotating channel is investigated by means of two-dimensional
particle image velocimetry (PIV). The flow direction is outward, with a bulk Reynolds number of 1.5 × 104 and a rotation number ranging from 0.3 to 0.38. The measurements are obtained along the wall-normal/streamwise plane at mid-span.
The PIV system rotates with the channel, allowing to measure directly the relative flow velocity with high spatial resolution.
Coriolis forces affect the stability of the boundary layer and free shear layer. Due to the different levels of shear layer
entrainment, the reattachment point is moved downstream (upstream) under stabilizing (destabilizing) rotation, with respect
to the stationary case. Further increase in rotation number pushes further the reattachment point in stabilizing rotation,
but does not change the recirculation length in destabilizing rotation. Turbulent activity is inhibited along the leading
wall, both in the boundary layer and in the separated shear layer; the opposite is true along the trailing wall. Coriolis
forces affect indirectly the production of turbulent kinetic energy via the Reynolds shear stresses and the mean shear. Two-point
correlation is used to characterize the coherent motion of the separated shear layer. Destabilizing rotation is found to promote
large-scale coherent motions and accordingly leads to larger integral length scales; on the other hand, the spanwise vortices
created in the separating shear layer downstream of the rib are less organized and tend to be disrupted by the three-dimensional
turbulence promoted by the rotation. The latter observation is consistent with the distributions of span-wise vortices detected
in instantaneous flow realizations. |
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