Upstream condition effects on favorable pressure gradient turbulent boundary layers

Paper i proceeding, 2005

The effects of upstream conditions in favorable pressure gradient boundary layers has been studied by carrying out an experiment using laser-doppler anemometry (LDA) and applying the already developed similarity analysis of the equations of motion for a pressure gradient flow [1]. The technique allows for near the wall measurements over multiple traverses along the plate. A complete set of upstream conditions comprised of upstream wind-tunnel speed, trip wire location and strength of pressure gradient has been analyzed and carefully controlled in order to isolate these conditions on the outer flow, which in general they are disregarded in experiments. Furthermore, the scalings obtained through the similarity analysis for the velocity, Reynolds normal and Reynolds shear stress profiles have been used to normalize the data acquired. Five intrinsic results were found: First, for favorable pressure gradient (FPG) boundary layers, the mean deficit profiles almost collapse with the free stream velocity, U∞; thus showing the effects of the strength of pressure gradient. Second, the upstream conditions do not show up in the velocity deficit profiles when normalized using the Zagarola and Smits [2]. The Reynolds stress profiles indisputably show the effects of upstream conditions. The boundary layer parameter such as the shape factor has been found to show the effects of the upstream conditions. Finally, the recognition of a developing or non-equilibrium flow is observed through the pressure parameter, ∧, which previously was found to be a constant by Castillo and George [1] in equilibrium flows. © 2005 by the American Institute of Aeronautics and Astronautics, Inc.