Study of the effect of external periodic flow perturbations on heat transfer intensity in the impact jet

Abstract

The aim of this work is to experimentally study unsteady heat transfer in an impact jet flowing onto a heated surface with the presence of large-scale structures and separated flows, as well as to search for possible mechanisms for controlling heat transfer by introducing external disturbances into the flow. In the work, a series of experiments was carried out to study an axisymmetric jet flowing normally onto a heated surface. The jet was both under natural conditions with different flow regimes and under external excitation at various frequencies and amplitudes. The instantaneous and average velocity and temperature fields in the near-wall part of the jet are measured using the PIV and PLIF methods. The correlations of velocity fluctuations and temperature fluctuations, which characterize the intensity of turbulent heat transfer, are calculated. It is shown that at different frequencies of external excitation of the jet, the intensity of turbulent transfer in the region of jet impingement on the wall changes. In the region of jet impingement on the wall, flow separation was recorded. It is shown that the interaction of the coherent structure with the wall leads to a local increase in the outflow of heat from the heated surface. The distributions of the heat transfer coefficient along the heated surface were also measured using a thermal imaging camera for various flow regimes, distances from the nozzle exit to the barrier, frequencies and amplitudes of the external flow disturbance. It is shown that when the jet is excited at different frequencies of the jet excitation, the heat transfer increases or decreases.