Low-frequency wake instability of an axisymmetric bluff body in pitch

Low-frequency wake instability of an axisymmetric bluff body in pitch

Gentile, V. (TU Delft Aerodynamics)
Schrijer, F.F.J. (TU Delft Aerodynamics)
van Oudheusden, B.W. (TU Delft Aerodynamics)
Scarano, F. (TU Delft Flow Physics and Technology)

Flow Physics and Technology

2016

The backflow instability in the wake past a cylindrical blunt-based body in pitch is investigated at a Reynolds number ReD = 6.7 · 104 based on the cylinder diameter. Time-resolved stereoscopic particle image velocimetry measurements have been performed in a cross-flow plane located 0.3 D downstream of the model base. An increasing displacement of the backflow region from the body centerline with increasing pitch angles is observed in the long-time average of the velocity field, with the emergence of a preferred orientation of the wake. The time history of the backflow centroid position shows a progressive reduction of both amplitude and time scales of the fluctuations, reflecting the transition from large-scale azimuthal meandering to a more stable confinement at an off-center position. Proper Orthogonal Decomposition of the velocity fluctuations reveals a reduction by approximately 80% in the contribution of the first two modes for angles increasing up to 1°, accompanied by a distortion of the dipolar distribution typically associated with backflow meandering, for misalignments from 0.3° and higher. The frequency spectra of the POD time-coefficients display a very-lowfrequency peak near StD ~ 10-3 only within 0.1° deviations from axisymmetric inflow conditions, thus endorsing the hypothesis that the long-term backflow instability only survives within small deviations from axisymmetric inflow conditions.

Turbulent axisymmetric wake
Azimuthal meandering
Stereoscopic PIV

http://resolver.tudelft.nl/uuid:fbc2431c-e817-4127-a584-2d7f30ed70d0

978-989-98777-8-8

Proceeedings of the 18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics: Lisbon, Portugal

18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics, 2016-07-04 → 2016-07-07, The Calouste Gulbenkian Foundation, Lisbon, Portugal

Institutional Repository

conference paper

© 2016 V. Gentile, F.F.J. Schrijer, B.W. van Oudheusden, F. Scarano