Flow Structure Formation of Turbulent Mixed Convection in a Closed Rectangular Cavity

An experimental investigation of flow structure formation in turbulent mixed convection in a closed rectangular cavity with an aspect ratio of 1 : 1 : 5 and air as working fluid is presented. Mixed convection at Re = 1.1 · 10^4 and Ra = 3.0 · 10^8 is studied under well-defined conditions by combination of forced and thermal convection. The resulting flow structures strongly depend on the ratio of inertia and buoyancy forces. A 2D mean wind, which can be approximated by a solid body rotation, is found at pure forced convection. With increasing Archimedes number (Ar), realized by a temperature gradient between bottom and ceiling of the convection cell, this structure becomes instable. Leading to four convection rolls for Ar = 3.4, which are oriented in longitudinal direction of the cell, are observed