Experimental Investigation of Mixed Convection in Horizontal Channel Flow in Combination with Cylindrical Roughness Elements

Abstract

The flow features of mixed convection flow in the presence of a cylindrical roughness element are investigated in a horizontal laminar flat-plate flow inside a water channel by means of Temperature-Sensitive Paint (TSP). The buoyancy forces are generated by partially heating the flat plate, however, the beginning of the flat plate is adiabatic. A cylindrical roughness element is positioned at the start of the heated part of the test section. Different ratios of forced and free convection, which form the mixed convection flow, are investigated by adjusting the free stream velocity and the heating power. Thereby, the Reynolds number is varied in the range of 398≤Rek≤1195, while the Grashof number reaches values between 3.97⋅108≤Gr≤1.46⋅109. This leads to Richardson numbers of 0.53≤Ri≤7.72. For an increasing Reynolds number and a decreasing Grashof number, the onset of longitudinal vortices is shifted downstream while their spanwise wavelength is increased. The wake of the element changes from a well-organized, laminar flow into a turbulent flow which is accompanied with a broadening of the wake. An interaction between the wake and the vortices is observed for some conditions. In addition, this study reveals that the Richardson number is not a suitable measure for predicting the flow features of the investigated configurations.