An Investigation of the Physical Mechanism of Heat Transfer Augmentation in Boundary Layer Flows Subject to Freestream Turbulence

Water tunnel experiments have been performed to examine how large scale, high intensity freestream turbulence affects heat transfer through a laminar flat plate boundary layer. Time-Resolved Digital Particle Image Velocimetry (TRDPIV) was used to examine the flow field along with time-resolved heat transfer from the wall. The surface heat flux was measured with a newly developed thin-film sensor called the Heat Flux Array (HFA) capable of measuring heat flux at 10 locations at frequencies to 35 Hz. Freestream conditions were controlled using passive grids producing turbulence intensities of 5.5% with integral length scales of 2 and 3.5cm. This was shown to increase mean convective heat transfer coefficients by up to 15% with fluctuations to 40% above cases of very low freestream turbulence. It was also shown that fluctuations in heat flux convected at approximately half the freestream velocity.