Refractive Index Matched Experiments in Transient Phenomena: from Airfoils to Pipes

Abstract. Transient behavior of flow around different geometries has profound effect on the various industrial and natural processes. Time-resolved PIV using high speed cameras are the most commonly used experimental tool transient phenomena research. Refractive index matching of the fluid and the geometry/bodies facilitates unobstructed optical access, further enabling simultaneous velocity measurements on both the sides of the object. The first section, discusses the flow and pressure fields around an airfoil undergoing dynamic stall. The airfoil is index matched and the time – resolved stereo PIV is used to estimate velocity fields on both the sides of the airfoil. The pressure is then estimated from the velocity using omni-directional integration of the velocity data. The data shows the evolution, development and fragmentation of a huge dynamic stall vortex, as well as a scaling factor associated with the airfoil loading. The second section talks about flow in a round pipe, with sudden change in cross sectional area. This study uses time resolved tomographic PIV as well as stereo PIV. The effect of transients is evident in the separation and recirculation bubbles formed near the vicinity of the cross-sectional area change. We then add acrylic spheres in the pipe flow to study the effect of the transients on the motion of the spheres. Lastly, as an ongoing experiment, the 3D flow fields around a buoyancy driven sphere rising in a quiescent tank are studied using time – resolved tomographic PIV.