Unsteady heat flux in a cylinder stagnation region with high freestream turbulence

A new technique for obtaining unsteady heat transfer measurements in a steady-flow facility has been used to determine the magnitude of surface heat flux fluctuations in the stagnation region of a circular cylinder subjected to a turbulent freestream. A commercially available glue-on thin film gauge was adhesively bonded to a heated cylinder and placed behind a coarse turbulence-generating grid in a steady-flow wind tunnel. In conjunction with a temperature bridge, the gauge was operated in the constant-current mode. Unsteady surface temperature fluctuations in the stagnation region of the cylinder were digitally recorded over a range of Reynolds numbers. A numerical finite difference scheme was used to calculate the corresponding unsteady heat flux assuming a one-dimensional heat conduction model. Time-averaged local heat transfer coefficients around the circumference of the cylinder were measured using electrically heated copper strips embedded in the surface of the cylinder at 10° intervals. Results indicate that the heat transfer unsteadiness, defined as the ratio of the rms to mean, is a maximum at the stagnation point. Simultaneous velocity and temperature measurements made at the stagnation point revealed a clear cross correlation between the two signals. The thin-film gauge was also operated with analog circuitry designed to perform the temperature/heat flux transformation directly. Excellent agreement in the rms of the heat flux signals from the two methods was obtained.