Ph. D.

A thin-film gage was used to measure the fluctuating component of heat transfer from a cylinder placed in a steady crossflow at Reynolds numbers, based on cylinder diameter, of approximately 19,000 and 30,000. Further, a one-dimensional flow pulsation at 13 Hz was added to the mean flow at a Reynolds number of 19,000, and the case of natural shedding locked on to exactly one-half the driving frequency was studied. A Gardon gage was also used to measure the time-averaged heat transfer under the same conditions. Both gages were mounted flush with the cylinder surface. The thin-film gage was maintained at a constant temperature by a constant temperature anemometer unit. A temperature controller actively matched the surrounding cylinder surface to the gage temperature to maintain a constant temperature boundary condition. The frequency response of the thin-film gage system was approximately 60 Hz. Representative time records of the instantaneous heat flux and the local fluid velocity were obtained at different locations by rotating the cylinder through 180°. Correlations between these signals in the time and frequency domain were also measured. Phase relationships between the unsteady heat transfer fluctuations and the local velocity were then obtained over the entire cylinder. In the attached boundary layer region, the heat flux signal was sinusoidal at the shedding frequency for the steady cases and at the driving frequency for the pulsating case. In the wake, however, the fluctuations were less organized in all cases. Here the magnitude of the fluctuations were higher than in the boundary layer region with peak-to-peak fluctuating amplitudes greater than 50% of the mean heat flux levels (as measured by the thin-film gage) over most of the wake. The phase relationship of the signals was nearly constant in the boundary layer region but varied with angular position in the wake indicating the existence of different flow regions in the wake. The local time-averaged heat transfer results reflect a 24% increase in heat transfer in the wake due to pulsation. This is a result of higher fluid velocities in the outer flow at 0 = 90° and in the wake regions when pulsations were added to the flow. A simple analytical model, based on the concept of an impinging jet that was oscillated back-and-forth across the wake, was developed to predict the heat transfer fluctuations in the wake. A parametric study was performed to determine the effect of changing the jet parameters on the predicted heat transfer fluctuations. Time records of the heat transfer fluctuations were obtained around the cylinder based on this model. The fluctuating amplitudes and phases of heat transfer (relative to the velocity) predicted by the model agreed well with the experimental values for the steady flow case. The increase of the local time-averaged heat transfer in the wake region due to flow pulsation was also predicted. / Ph.D.