Experimental and Numerical Studies of Velocity and Turbulence Intensities for Mid-Channel Bar

Turbulent phenomenon in braided rivers is much more complex compared to the straight and meandering rivers. The turbulent flow structure at locations upstream and downstream of the mid-channel are analysed experimentally and numerically by plotting the vertical profiles of velocity and turbulent parameters. Fluent Computational Fluid Dynamics (CFD) code is used to satisfactorily validating the experimental measurements. Reynolds stress model (RSM) is used in the numerical simulation as a turbulence model. The observation of the vertical profile of turbulent parameters found the submergence ratio greatly influences the flow structure in the vicinity of bar. The effect of submergence ratio (ratio of bar height to flow depth) on the flow structure is analysed by using the depth-wise profile of velocity and turbulent parameters. The studies concluded that: (1) For region upstream of bar, the low value of longitudinal velocity and negative value of vertical velocity leads to the region susceptible to scouring; (2) The bar height has a significant effect on the flow turbulence in its vicinity. The value of total turbulent intensity at points downstream of mid-channel bar is much more as compared to upstream points. This is mainly due to the vortex shedding in the downstream region of bar; (3) RSM CFD code is satisfactorily validating the depth-wise profile of turbulent and velocity distributions yielded from experimental results. 4) The sweep event is dominant in the near bed region ( z / h < 0.1) for sections upstream of bar. For region near ( z / h = 0.1), there is canceling effect (sweep vs ejection) which leads to the value of S u and S w tends to zero in that region; 5) For points downstream of bar at region ( z / h < 0.1), the positive value of S u and S w indicate the dominance of outward interaction event.