Investigations on Large-Scale Geometric Roughness Elements in Open Channels with Different Heights

Abstract

Large-scale geometric roughness elements is one of the solutions that is used to protect open
channels from erosion. It is use to change the hydraulic characteristics of the flow. It may be concrete blocks
or large stone placed at the bed of the channel to impose more resistance in the bed. The height of these
roughness elements is an important parameter that can affect the hydraulic characteristics of the flow. Using
a series of tests of T-shape roughness elements at three different heights, 3, 4.5, and 6cm, arranged in the
fully rough configuration in order to investigate the velocity distributions along the flume. ANSYS
Parametric Design Language, APDL, and Computational Fluid Dynamics, CFD, were used to simulate the
flow in an open channel with roughness elements. This simulation helps to find the best height of roughness
elements that can be used to change the hydraulic characteristics of the flow. The results showed that the
velocity values are decreased near the bed by about 61%, 58%, and 64% in case of 3cm, 4.5cm, and 6cm
roughness heights consequently compared with the velocity of the control case. The velocity values are
increased near the free surface by about 32% and 19% in case of roughness elements height 6cm compared
with 3cm and 4.5cm roughness heights respectively. The case of 6cm roughness height is considered to be
the effective case for decreasing the velocity values near the bed of the flume.