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Influence of suboptimally forced streamwise streaks on the turbulent boundary layer and shear layer

Waasdorp, W.P. (2018) Influence of suboptimally forced streamwise streaks on the turbulent boundary layer and shear layer.

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Abstract:A modified turbulent boundary layer and shear layer are studied. An experimental investigation is carried out where the base flow is modified by placing an array of cylinders upstream, resulting in the spanwise periodic disturbances, which is introduced to a backwards facing step. The design of the test section limits the spacing of the cylinders to be suboptimal. It is shown that this forcing results in spanwise periodic disturbances with elongated streamwise presence, streaks. The boundary layer velocity rms profiles show similar behaviour to previous results for streaks in a zero pressure gradient turbulent boundary layer, on a scale that is comparable to the cylinder height. A loudspeaker is used to force a single phase, single frequency disturbance. A linear stability analysis on the shear layer show eigenmodes that match the resulting Fourier modes of a phase averaging procedure. Comparison of the Fourier modes with a baseline case shows a stabilizing effect on the shear layer. The way in which streaks are studied can be greatly simplified by using an array of roughness elements to force streaks to desired specification. Due to changes of the shear layer, the resulting noise that is produced may be lower in amplitude and frequency.
Item Type:Essay (Master)
Clients:
ITA, São José dos Campos, Brazil
Faculty:ET: Engineering Technology
Subject:33 physics, 52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Link to this item:http://purl.utwente.nl/essays/75907
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