Turbulence Amplitude Amplification in an Externally Forced, Subsonic Turbulent Boundary Layer
Experimental studies of the changes in turbulence characteristics inside a boundary layer due to external forcing were performed using hot-wire anemometry. The forcing was created by a periodically forced shear layer that was external to a compressible subsonic turbulent boundary layer. The convecting coherent structures in the shear layer create a concomitant unsteady pressure and velocity field and provide an external disturbance for the turbulent boundary layer on the wall of the tunnel close to the forced shear layer. Both the pressure and velocity fluctuations inside the boundary layer were simultaneously measured along with the forcing signal, and a phase-locked analysis was performed. Regions of amplified turbulence inside the boundary layer were observed. Near the wall, the region of amplified turbulence was slightly upstream or lagging of the external forcing and away from the wall it was downstream or leading the forcing signal. Analysis of the convective speeds in the region of amplified turbulence supported the existence of the critical layer inside the wake region of the boundary layer, and the critical layer is believed to be responsible for the amplified levels of the turbulence in the wake region. Various modulation and amplification correlation coefficients were computed and analyzed, and the results also indicated the presence of the critical layer. Examination of the phase-locked turbulence revealed similarities between the turbulence amplitude amplification results due to these externally forced experiments and modulation response of an internally forced, subsonic boundary layer in the literature.
© 2019 by Ranade, Duvvuri, McKeon, Gordeyev, Christensen, and Jumper. Published by the American Institute of Aeronautics and Astronautics, Inc. Received 31 August 2018; revision received 26 April 2019; accepted for publication 21 May 2019; published online 25 June 2019. Presented as Paper 2016-1120 at the 54th AIAA Aerospace Sciences Meeting, San Diego, CA, 4–8 January 2016. This effort was funded in part by the High Energy Laser–Joint Technology Office (HEL-JTO) and administered through the Air Force Office for Scientific Research (AFOSR) under Grant Number FA9550-13-1-0001. The U.S. Government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright notation thereon.
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