Lee Angle Effects in Near Bed Turbulence: An Experimental Study on Low and Sharp Angle Dunes

Abstract

This research presents recent advances on morphodynamic modeling over gravel dunes. Boundary-layer separation over gravel fixed dunes is investigated by Acoustic Doppler Velocimetry (ADV). Using the measurements of flow over dunes at laboratory scale, examined the influence of dune lee sides on the separation of flow. Experiments were conducted in a horizontal flume. A train of 2D fixed dunes were installed on the bottom of the flume starting just downstream of the entrance on the flume. Experiments were carried out using 2 types of dunes with different lee slopes, (38 and 8 degree). The results of quadrant analyses base on the stress fraction SHf versus the hole size at two elevations near the bed and near water surface for two angles of lee side, ,at the central axis of the flume also investigated. Both experimental observations and quadrant results were in agreement about the influence of dune characteristics on the flow separation in different dune lee angles