Experimental Probing of the Turbulent Non-Turbulent Interface in Wall Jets

Abstract

Turbulent flows past a solid surface exhibit region close to the surface where the presence of the surface is felt. In external flows such as boundary layers, the turbulence is confined to a region close to the surface and separated from the outer non-turbulent freestream by a sharp interface. This interface is known as the turbulent non-turbulent interface (TNTI). Several aspects of the TNTI have been studied earlier such as its statistical location, it spread and structure. However, the TNTI in wall jets (jets blown along a solid surface) has not been studied in the literature. The study is important since the outer region of a wall jet is considered to behave similarly to a free jet. However, if there is an influence of the wall seen on the characteristics of the TNTI, this will be an evidence of the fact that the wall does not allow the outer part to behave like a free jet, i.e., there is inner-outer interaction. The project investigated the TNTI in wall jets using the wall jet setup existing in the Fluid Dynamics Laboratory (FDL) at IITM, Pune. Particle Image Velocimetry (PIV) has been used to perform high speed measurements of the flow and capture the interface.