Natural Convection in Modulated Thermal Gradients and Gravity: Numerical Simulation and Experimental Measurements

This paper presents an investigation on natural convection in a cavity with an imposed modulated thermal gradient or modulated gravity forces. Numerical computations are presented, which are based on the finite element solution of transient Navier-Stokes and energy balance equations, along with appropriate boundary conditions or time-varying gravity forces. To verify the numerical predictions, an experimental system is setup where wall temperatures are oscillated to produce modulated temperature gradients and the velocity fields are measured by a laser-based Particle Image Velocimetry (PIV) system. Computed results compare well with experimental measurements for various conditions. With the mathematical model, so verified by experimental measurements, extensive numerical simulations are carried out to study the effects of modulation frequency and Prandtl numbers on the fluid flow. Results show the strong nonlinear interaction in the intermediate range of modulation frequency. It is also found that with a small Prandtl number typical of molten metals and semiconductor melts, modulated gravity and thermal gradients produce almost the same flow field both in structure and in magnitude.