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	Volume 4, Issue 2 Pg 117 - 228 (October 2008)
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Advances and Applications in Fluid Mechanics

-plane downstream the porous strip. Three blowing rates are used with a magnitude less than 6% of the mean centreline velocity

m/s corresponding to the Reynolds number

The results obtained from ensemble averaging of the instantaneous velocity vector fields of PIV images reveal that blowing significantly decreases the magnitude of the streamwise velocity in the inner layer immediately behind the porous strip, whereas the outer layer characterized by

is not affected. The downward shift of streamwise mean velocity significantly increases with increasing of wall blowing velocity

Note that the increase in

removes the appearance of the log-layer far the wall up to about 100 viscous wall units for

delaying the extent of the inner region. The data of streamwise mean velocity extracted from the PIV images exhibit a similar behavior to that measured by hot-wire anemometry at same station. The magnitude of the streamwise velocity fluctuations significantly increases in the inner region downstream of the porous strip. Immediately behind this strip, the turbulent plane channel flow quickly responds to the wall condition with the streamwise mean velocity and fluctuation distributions which highly depend of the blowing rate in the inner layer. Using the basic Reynolds decomposition of the turbulent flow fields, the issues of visualization in the wall region

show structures located above the wall and lifted up by wall blowing. The PIV instantaneous field of spanwise vorticity

shows that these vortices are more titled and aligned in form of the packets in the streamwise direction downstream the blowing strip. Using the Willmarth and Lu [28] decomposition, these vortices packets are located above a region of strong second-quadrant fluctuations

generating a shear layer inclined up to

to the wall for the highest wall blowing velocity

For the no-blowing case, the individual vortices packets grow upwards in the streamwise direction at a mean angle from

to the wall. This result agrees well with those of literature.

Advances and Applications in Fluid Mechanics
Volume 4, Issue 2, Pages 157 - 176 (October 2008)

PIV MEASUREMENTS OF THE FULLY TURBULENT CHANNEL FLOW WITH WALL LOCALIZED BLOWING AT LOW REYNOLDS NUMBER
M. Haddad (France), A. Mazouz (France), L. Labraga (France) and L. Keirsbulck (France)

Abstract:
The present paper reports the results of the Particle Image Velocimetry (PIV) visualization in a fully developed turbulent plane channel flow subjected to a localized wall blowing applied through a spanwise porous strip. The PIV visualization is used to measure the total two dimensional velocity fields in a streamwise-wall-normal

-plane downstream the porous strip. Three blowing rates are used with a magnitude less than 6% of the mean centreline velocity

m/s corresponding to the Reynolds number

is not affected. The downward shift of streamwise mean velocity significantly increases with increasing of wall blowing velocity

Note that the increase in

removes the appearance of the log-layer far the wall up to about 100 viscous wall units for

show structures located above the wall and lifted up by wall blowing. The PIV instantaneous field of spanwise vorticity

generating a shear layer inclined up to

to the wall for the highest wall blowing velocity

For the no-blowing case, the individual vortices packets grow upwards in the streamwise direction at a mean angle from

to the wall. This result agrees well with those of literature.

Keywords and phrases: channel flow, blowing, coherent structures, HWA, PIV.

Communicated by Jyh-Chen Chen

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