Effect of lateral and longitudinal distance of baffled block on flow velocity for various tail water depth conditions

Abstract

One of the problems that cause damage to the stilling basin on the downstream of weir or dam is the tail water depth (TW depth) conditions which are not in accordance with the stilling basin’s boundary conditions. This conditions cause the hydraulic jump to jump off the stilling basin and higher flow velocity. Baffled blocks are blocks with a certain pattern installation that are installed on the stilling basin. These blocks have functions of generating hydraulic jumps and decreasing flow velocity. Therefore, this research was conducted to determine the effect of lateral and longitudinal distance of baffled block on flow velocity for various tail water depth conditions. Four models of stilling basin are made by changing the lateral and longitudinal distance of baffled block. The original pattern of baffled block is only effective for TW depth that matches boundary conditions (TW depth = 1.0 D2). Thus, the change in lateral baffled block distance so that it is located between chute blocks could reduce the TW depth to 0.9 D2. At 0.9 D2 TW depth conditions, this pattern could also reduce the flow velocity 0.35% more effectively than the 1.0 D2 TW depth condition. Due to, the change in longitudinal distance, the distance between baffled block and chute block is shorter, causing the flow velocity becomes unstable. It also causes the hydraulic jump to be higher so that the 1.0 D2 TW depth conditions are no longer effective. Thus, the change in longitudinal distance so that the distance between baffled block and chute block to be longer could stabilize the flow velocity at 0.9 D2 TW depth conditions. But, this pattern is able to reduce the flow velocity at 0.9D2 TW depth condition by 0.75%, which is lower than 1.0 D2 TW depth condition.