11 (1983) 107--119 107 Elsevier Science Publishe~ B.V., Amsterdam -- Printed in The Netherlands SURFACE FLOW PATTERNS ON RECTANGULAR BODIES IN THICK BOUNDARY LAYERS I P Castro Dept of Mechanical Engineering, Unlverslty of Surrey and M Dianat Dept of Civil Engineering, University of Surrey i. INTRODUCTION In recent years there have been a number of experimental studies of the complex turbulent flow around three-dlmenslonal surface mounted bodies in thick boundary layers. Whilst many of these studies have of necessity concentrated on either the surface pressure fleld on the body Itself or the flow fleld downstream of the highly turbulent reversed flow region in the near wake, it is generally recognlsed that a proper understanding of such flows requires a much more detailed understanding of the dynamics of the flow near the body than is currently available. However although mean and fluctuating surface pressure measurements can be, and often are, made it is much mere difficult to make measurements in the flow itself, where local mean velocitles may be reversed and turbulence intensities are very high. Flow visualisatlon can be effective, but it is difficult to obtain quantitative results. In particular, o11 flow vlsuallsatlon can be used with great effect to determine the mean characteristics of surface flows, but only in highlighting mean surface flow directions and the location of critical points. Hunt et al (Ref i) have demonstrated how such work can be combined with simple topological ideas to delineate overall flow patterns with some measure of confidence, but there is no doubt that knowledge of the magnitude of surface skin friction and, further, of how the instantaneous surface flow is linked with the external flow, would be of great help in understanding the various flow phenomena that occur. The present work was motivated inltially by the need to understand how body geometry and/or upstream flow characteristics promote or prevent reattachment onto the body itself of the shear layers which separate from the leading eges. Clearly the dispersion of pollutants from sources in the near wake of a body could be slgnlflcantly affected by reattachment of the shear layers onto the body surface and it is well known that such reattachment is always accompanied by strong pressur e recovery on the surface (often giving a base pressure much closer to ambient than would otherwise be the case) so that mean aerodynamic n~04-3908/83/$03.00 © 1983 E~e~erSc~ncePu~ishe~ B.V.