FLOW PROFILE DEVELOPMENT IN THE UPSTREAM REGION FROM THE ENTRY PLANE OF A FLOW CONDUIT

The development of flow profiles in the upstream region of a leading edge of a flat plate during laminar free surface flow has been studied. Results obtained experimentally by Laser Doppler Anemometry were in good agreement with numerical flow simulations using FLUENT program. An upstream distortion of the velocity profiles occurs in the whole range of Reynolds numbers investigated for laminar flow. From the distortions an approach length can be defined where the upstream influence of the stagnation point at the tip of the plate is noticeable. On the basis of the source theory an analytical model can be developed for the upstream changes of velocity. For viscous flows the source strength consists of a superposition of the classical expression for inviscous flow and a term proportional to the square root of the viscous length. It can be concluded that the hydrodynamic boundary layer for laminar flow has a finite thickness at the leading edge of the wall of a flow conduit.