Abstract
This paper is an extension of an experimental investigation by Alving & Fernholz
(1996). In the present experiments the effects of free-stream turbulence were investigated
on a boundary layer with an adverse pressure gradient and a closed reverse-flow
region. By adding free-stream turbulence the mean reverse-flow region was shortened
or completely eliminated and this was used to control the size of the separation
bubble. The turbulence intensity was varied between 0.2% and 6% using upstream
grids while the turbulence length scale was on the order of the boundary layer thickness.
Mean and fluctuating velocities as well as spectra were measured by means of
hot-wire and laser-Doppler anemometry and wall shear stress by wall pulsed-wire
and wall hot-wire probes.Free-stream turbulence had a small effect on the boundary layer in the mild
adverse-pressure-gradient region but in the vicinity of separation and along the
reverse-flow region mean velocity profiles, skin friction and turbulence structure were
strongly affected. Downstream of the mean or instantaneous reverse-flow regions
highly disturbed boundary layers developed in a nominally zero pressure gradient
and converged to a similar turbulence structure in all three cases at the end of the test
section. This state was, however, still very different from that in a canonical boundary
layer.
Publisher
Cambridge University Press (CUP)
Subject
Mechanical Engineering,Mechanics of Materials,Condensed Matter Physics
Cited by
24 articles.
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