Experimental Study of the Effect of the Location of a Continuous Porous Obstacle on the Bottom of a Stepped Spillway on the Characteristics of the Flow

Abstract Introduction: In the present study, we investigated the effect of the location and height of a three-dimensional porous obstacle (with porosity in all three dimensions) which is located on the bottom of the steps in the width of the flume and the number of steps with this type of obstacle has been investigated on a stepped spillway. Methods: The slope of the spillway was 1: 2 and had 8 steps, the total height was 87 cm and the width of the flume was 1.2 m. The measuring instruments in the present study were point gage, image processing technique and observations of the experiment. Findings: In a continuous three-dimensional porous obstacle, according to the relative height, location and number of steps with an obstacle, the starting flow boundaries of the placement change compared to the flat step, so that by increasing the relative distance of the obstacle from the edge of the steps and decreasing the number of steps with continuous porous obstacle. The tendency of the flow to expand in the upper range of the transition flow (neighborhood with the skimming flow regime) increases. Conclusion: In the nappe flow regime, the placement of a three-dimensional porous obstacle for the variables of the present study increases the energy dissipation by up to 5% more than in the flat step (control). For transitional and skimming flow regimes, in most cases, continuous porous obstacle placement has no positive depreciation effect. In addition, according to the size of the areas formed by BIV, it can be said that in conditions where the mixing area measured in two consecutive steps was more than the flat step, energy dissipation has also increased.