Coherent structures around isolated spur dikes at various approach flow angles

摘要

The turbulent flow structures around an isolated spur dike located at three different approach flow angles are investigated. Detached eddy simulation is used at a channel Reynolds number of 45,000. Experimental velocity measurements were also conducted using acoustic Doppler velocimetry for validating the simulations. It is found that the size and orientation of the horseshoe vortex system change considerably with the approach flow angle. The main necklace vortex is largest in size and most coherent for 90°. Within this orientation it has larger amplitude bimodal oscillations compared to the 60° and 120° cases. A new scour mechanism is defined for the 60° case which is expected to generate more scour upstream of the spur dike. The possible scour area around the spur dike is found to be the maximum in the 90° case which is roughly by 15% larger than that of the 120° case.