Effect of intake head wall and trash rack on vortices

The effect of the intake head wall slope and the installation of a trash rack on the type and strength of vortices are studied experimentally. The strength within each vortex was determined by measuring its tangential velocity utilizing an Acoustic Doppler Velocimeter (ADV). Experiments were carried out with a projected intake and an intake with various head wall slopes, discharges and submerged depths. The results from the projected intake tests indicated that Type 6 vortex was present. However, the vortex strength and type reduced as the intake head wall slope increased up to the vertical position. In addition, increasing the intake head wall slope increased the vortex instability. All tests were repeated with a trash rack. A relationship was developed for vortex strength and the intake critical submerged depth based on the intake Froude number and the head wall slope. Moreover, a relationship has been found between vortex strength and type.