On the Relaxation of a Turbulent Boundary Layer After an Encounter with a Forward Facing Step


Book Description

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.




























Advances in Fluid Mechanics Measurements


Book Description

One cannot overemphasize the importance of studying fluids in motion or at rest for a variety of scientific and engineering endeavors. Fluid mechanics as an art reaches back into antiquity, but its rational formulation is a relatively recent undertaking. Much of the physics of a particular flow situation can be understood by conducting appropriate experiments. Flow visualization techniques offer a useful tool to establish an overall picture of a flow field and to delineate broadly its salient features before embarking on more detailed quantitative measurements. Among the single-point measurements that are particularly difficult are those in separated flows, non-Newtonian fluids, rotating flows, and nuclear aerosols. Pressure, shear stress, vorticity, and heat transfer coefficient are also difficult quantities to measure, particularly for time-dependent flows. These and other special situations are among the topics covered in this volume. Each article emphasizes the development of a particular measuring technique. The topics covered were chosen because of their importance to the field, recent appeal, and potential for future development. The articles are comprehensive and coverage is pedagogical with a bias towards recent developments.