Laboratory Study on the Impact of Collision Angle of Flow on Scour under the Submerged Pipe

Pipelines passing through the seas and rivers as a means for transferring fluids (oil, gas, water, sewage) have a great importance since the pipelines change flow pattern, increase turbulence and intensify the bed shear stress around submerged pipes, which create scour holes under the pipes. Development of scour hole under pipelines leads to instability and failure of pipelines, which may cause severe environmental and economic damages. In this paper, the results of laboratory research on the effect of different attack angle of the approaching flow on the maximum scour depth under submerged pipes have been provided. Experiments were conducted in two modes: 1) scour under pipe with 90° angle of attack, 2) scour under pipe with less than 90° angle of attack. The pipe was also placed in 2 positions, i.e. on the bed and at a distance of D/4 from the bed. Three (45°, 60° and 90°) angles of attack were employed in the experiments. The results showed that the angle of attack is an effective parameter on the location of the maximum scour depth and performance of vortices. For angles smaller than 90 degrees, maximum scour depth occurred in the right hand side of the flume.