TURBULENT FLOW OVER A FACING STEP AT SEVERAL REYNOLDS NUMBERS

摘要

An experimental study was performed over forward facing step (FFS). It was located within a transparent rectangular acrylic channel (1.4 m in length, 0.1 m in width and 0.02 m in height). The step is 0.01 m in height and 0.1 m in width, and was located 0.7 m downstream (fully developed region); a spanwise aspect ratio, w/h =10 was used. The experiments were carried out using particle image velocimetry (PIV), which is a non intrusive experimental technique. The experimental water flow conditions include three Reynolds numbers based on the step height, Re_h = 1124, 1404 and 1685. These flow conditions correspond to turbulent flow. Measurements were carried out in two zones; zone A begins at x = 8 cm (measured from the step base), and zone B starts at x = 0, y = 0, the visualization region corresponds to an area of 22.76 mm x 16.89 mm. 100 instantaneous velocity fields were obtained for each Re_h. A temporal and spatial average was performed to obtain a velocity profile in zone A; likewise, the corresponding turbulence intensity and shear stress distribution were evaluated. The average velocity profile was evaluated for each Re_h. Regarding the vortex center location, it was observed that as Re_h increases, the y-direction coordinate moves towards bottom of wall channel. For zone B, it was also observed a reduction of the shear stress as Re_h increases.