Experimental investigation of secondary flow in a heated channel using PIV and LIF simultaneously

Abstract

This paper describes an investigation of thermo-convective structures called Rayleigh-Bénard-Poiseuille (RBP) convection in a wide rectangular water channel formed above a heated bottom-wall. The phenomenon was investigated experimentally using planar Particle Image Velocimetry (PIV) for velocity vector field data and 2-color Laser-Induced Fluorescence (LIF) for temperature scalar field data. The PIV and LIF records were taken simultaneously on three cameras (one for PIV and two for LIF) in the central vertical plane of the channel in order to detect the secondary flow caused by the natural convection. The result is the combined temperature and velocity data used to evaluate the onset point of the secondary flow. The manifestation of this phenomenon on both velocity and temperature fields is described. The LIF method was confirmed to give more satisfactory results because the PIV method is generally less suitable for lower velocity measurement in boundary layers, both because of adverse reflections and because of the limitation for measuring very low velocities near walls. The measured data were compared with theoretical dependencies and with the literature data. Other limitations of the measurement were described, and steps for its improvement were suggested. In the present setup, temperature influence by the laser or wall accumulation was observed, which needs to be investigated more thoroughly and eliminated in future work.