Stereoscopic TR-PIV measurements of mixed convection flow in a vertical channel with an open cavity with discrete heating

An experimental investigation of opposing mixed convection is carried out using stereoscopic time-resolved particle image velocimetry (TR-PIV) to assess the thermal effects on the flow structure over an open cubical cavity that lies at the midsection of a vertical water channel. The ratio between the channel and cavity depth is of 1, the wall facing the opening is isothermal and all other walls are adiabatic. The complex interaction between the induced incompressible forced flow at ambient temperature and buoyancy-induced flow from the heated wall of the cavity are studied experimentally for fixed Prandtl number of Pr=7, buoyancy strength or Richardson number in the range 0 ≤ Ri ≤ 20, and two Reynolds numbers defined with the channel hydraulic diameter and the mean velocity in the upstream channel of Re=1500 and 4500 that correspond to laminar and turbulent upstream boundary layers, respectively. The 3D flow features are presented in the form of mean statistics and instantaneous flow properties in planes normal to the cavity floor. It is found that the shear layer development is highly 3D due to the confinement effect induced by the lateral walls. We also show the modulation effect of opposing buoyancy on the flow distributions and the time-evolution of the shear layer. Also, the complex dynamics of the coherent structures in the region surrounding the cavity show that the entrainment rate is modified with increasing buoyancy. Root-mean-square contours of the fluctuating laminar velocity fields have been obtained, and Reynolds stress distribution and proper orthogonal decomposition analysis for the turbulent case show that an increase in the fractional energy of the characteristic POD modes takes place for increasing Ri numbers.