Simulation and visualization of the refraction effects in the thermal boundary layer near a heated horizontal down-facing disk

The simulation and optical visualization of the refraction effects in an axisymmetric temperature field was undertaken in the case of free convection from a heated horizontal down-facing disk. Temperature and related refractive index fields have been calculated using a mathematical model based on the coupled flow and heat transfer equations. To avoid the complex and time-consuming computation of ray trajectory using the differential ray equation, we developed a simple method based on the application of the standard Snell law at each surface isotherm in the medium. Using this technique, we plotted the trajectory of rays bundle traveling in the medium and calculated the deflection angle. Comparison with shadowgraph images showed a good agreement with the simulation and explained the existence of a caustic induced by the thermal boundary layer acting as a schlieren lens.