Abstract
In the present study, the distributions of time-average and fluctuated wall shear stresses were measured using a flow vector sensor of MEMS and velocity downstream from an orifice using laser Doppler velocimetry. The air flow was supplied to a circular pipe from a blow-down wind tunnel. The diameter of the pipe were D = 51 mm, 100 mm and 194 mm. The diameter ratio were β (= d/D; d, diameter of orifice) = 0.41, 0.50 and 0.62. Near the wall in the recirculating region downstream from the orifice, the minimum mean skin friction coefficient was located at approximately x/h = 5, and the maximum RMS intensity skin friction coefficient at approximately x/h = 7. The absolute value of the minimum mean skin friction coefficient and the maximum RMS intensity skin friction coefficient decreased with increasing in Reynolds number. The similarity between skin friction coefficients of RMS and the FAC rate was confirmed.
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