BUOYANCY EFFECT ON MIXING FLOW (STABILITY, TURBULENCE, R-EPSILON MODEL, CURVATURE, SIMILARITY)

The physical problem of two parallel streams of a fluid coming in contact is considered here. A whole class of flows arising from the velocity ratio as the parameter has been identified. The physical mechanisms which come into play in low Reynolds number flow as it proceeds from a laminar to turbulent state via hydrodynamic instability have been studied. This work examines flow modification arising from buoyancy and streamline curvature. Numerical and experimental techniques have been employed in the analysis. Turbulence has been included by a kinetic energy-dissipation model. Experiments involve hot wire measurements of mean flow and turbulent fluctuations.; In unbounded flows, a mixing layer is initiated along the interface whenever the velocity ratio is different from unity. The rate of mixing layer growth and effect on buoyancy depends on whether the flow is laminar or turbulent. The physical mechanisms differ in these cases, having either a molecular origin or one involving the eddy structure in flow.; In internal flows, turbulence is predominantly produced in the wall region for even moderate velocity ratios (e.g., three). The mixing layer becomes apparent as the velocity ratio tends to large values. A value of infinity has been tested experimentally.; The effect of buoyancy is seen both inside and outside the mixing region in the experiments carried out here. This has implications in numerical computation. While mixing layers can be calculated with boundary layer solvers, buoyancy requires that wall boundary condition be imposed on the flow domain.; Experiments show that buoyancy can be included completely through their effect of mean flow rather than their direct effect on velocity fluctuations. This conclusion is important for turbulence modelling.; In mixed convection flow over a wall heater, the complexity of flow is insignificant and flow is dominated by transient bursts originating at the wall. The heat transfer law undergoes qualitative change as Reynolds number of superimposed flow increases from low to high values.