A comparison of simulated and experimental IR measurements at low to moderate wind speeds

The surface temperature field due to free-convection and/or forced turbulence at low to moderate wind speeds is examined experimentally and numerically. The objective of the research is to examine the scaling of the thermal boundary layer as the flow evolves from a free-convection regime to a shear-driven regime. The information will be used to assess models of the thermal boundary layer as the turbulence transitions from free-convection to sheared turbulence at low wind speeds. The experiments were performed at the University of Delaware´s Air-Sea Interaction Laboratory Wind-Wave-Current facility using an Amber Model 4256 IR Camera sensitive to image the air-water interface. The numerical simulations were performed using a spectral algorithm. A constant heat flux boundary condition is used in conjunction with a rigid lid approximation to model the free-surface. All fluid properties are held constant. A Boussinesq approximation is used to represent the temperature effects on buoyancy. The effect of the wind is modeled as a steady shear stress acting on the free-surface. For the low wind speeds, the dominant physical process is the ascension of a warm plume into the wind-sheared near-surface region. The surface temperature exhibits a characteristic fish-scale pattern. As the flow transitions from free-convection to forced turbulence, a similar, but more complicated thermal pattern evolves. Some of the thermal structure in the laboratory experiments is similar to that observed in simulations of forced turbulence near a free-surface