On the Relaxation of a Turbulent Boundary Layer after an Encounter with a Forward Facing Step,
COLLEGE OF AERONAUTICS CRANFIELD (ENGLAND) DEPT OF AERODYNAMICS
Pagination or Media Count:
An experiment was performed in a low-speed wind-tunnel to determine the mean flow relaxation characteristics for a zero pressure gradient turbulent boundary layer which encounters a small forward facing step. Of primary interest is the behavior of the local wall shear stress downstream of the step. This was determined by the use of a series of buried hot-wire gauges. The mean velocity profiles downstream of the step were measured using a traversing Pitot tube which indicated that a step produces very marked changes in the distribution for both the inner and outer regions of the flow. The results shed new light upon the variation of wall shear stress downstream of a severe perturbation and also indicate that the use of Preston tube or Clauser chart methods for the determination of wall shear may lead to very large errors. As a consistency check on the data, estimates of the step drag, based upon force-momentum conservation considerations, were compared with previously published drag balance measurements. The agreement between the data sets is very good.