investigation of dynamic pressure of vertical and circular free water jets on rough surfaces with variable angles

the security and stability of dams for flood passing through the spillway should be provided. so, kinetic energy of flow over large spillway must be dissipated. one of the energy dissipation structures at downstream dams, are plunging pools. the aim of this paper is to investigate dynamic pressure that is created by the impact of a series of rounded non-submerged jets on a flat plate with the roughness height of 0.8 cm in the angles of the impact of 30, 60 and 90 degrees. this research uses sensors to measure the instantaneous pressure (pressure transducer) with the ability to record and store the dynamic pressure oscillation of water jet. the results showed that increasing the drop height, average coefficient of dynamic pressure decreases. the extreme dynamic pressures coefficient increased with increase fall height. the mean coefficient of dynamic pressure increases with increasing discharge. as the angle of the impact jet decreases, the dynamic pressures reduce. also, the roughness increases the dynamic pressure up to 70% in the test interval.