Estimation of Scour Hole Dimensions Due to Vertical Circular Submerged Jet

1. In the field of hydraulic research, bed erosion is of considerable importance because it is necessary to estimate and control erosion near hydraulic structures [1]. The cause of erosion in many conditions could be flow concentration as in a high velocity jet. The structures involved in hydraulic science are subjected to scour around their foundations. If the depth of scour becomes significant, the stability is endangered 2]. Therefore, study of maximum scour depth is required for the safe and economic design of hydraulic structures and their foundations. Research on erosion by jets has been mainly empirical because of the complex nature of the flow and its interaction with the sediment bed. Because of three dimensional intrinsic characteristics of turbulent flows in energy dissipation studies, and also problematic aspects of mathematic governing equations of the study, researchers have to focus on physical model. The model generally has an ability to respond the complexities of the subject. Not to mention that it needs expert people to be involved including its relative high costs. The effects of the variation of hydraulic condition on the scour hole in the plunge pool are investigated in present study using a physical model.2. The purpose of this study is the investigation of the variation of hydraulic condition and tailwater depth on the scour hole in the plunge pool by a submerged circular vertical jet. Therefore, a physical model was prepared. The model had an electromagnetic flow meter and pressure transducers. A slice gate was used for regulating tailwater depth. Experiments were conducted in a pool with 2m length, 1m width and m depth. Fig. 1 shows the experimental system of this research. Discharge was transported to the nozzle by a circular pipe with 4 inch diameter. For simulating a vertical jet, a roller for the nozzle was fixed at 90º. Tailwater depths were regulated at 0.325m, 0.385m and 0.435m [3]. The equilibrium time of scouring was determined for five times. For data acquisition of bed profile, a laser meter was used. Buckingham π theorem is used for determining effective parameters of scour hole as shown in Fig. 1. 3. Experimental: Results The experimental conditions were regulated to evaluate the effect of jet depth on the jet Froude number. After the equilibrium time, scouring dynamic depth was measured using a point gage. Scour profile was recorded using a laser meter after stopping the jet and filling the pool out. 4. The results of the experimental study on scour under submerged circular vertical jet were presented. It is noticeable that by variation of jet Froude number between 4 to 7, the relative scour hole length and depth are changed between 0.5 to 0.7, and 0.2 to 0.4, respectively. The present study extends the range of existing experimental data by involving jet diameters, different sediment size (gravel), and jet distance to bed resulting in much more complete conclusion than in all previous experimental studies.