Effect of coolant pulsation on film cooling performance on flat plate

Combined with infrared thermography tests, large eddy simulation was used to study the square-wave pulsating film cooling on flat plate at the time-averaged blowing ratios of 0.5 and 1.5. The effects of two pulsating pa-rameters including frequency and amplitude were discussed in detail. At low blowing ratio, the introduction of coolant pulsation leads to the decrease of cooling effectiveness, and the effect of pulsating amplitude is much more pronounced than frequency. At high blowing ratio, cooling effectiveness can be enhanced by coolant pulsation at low amplitude, but reduced at high amplitude. As the typical vortex structure in pulsating film cooling, the starting vortex is formed as the jet is turned on. The interaction between hairpin vortex and starting vortex shows that, at high pulsating amplitude, the starting vortex can help coolant detach from the wall, and has an adverse influence on cooling performance. The statistical characteristics and power spectrum density of instantaneous velocity were investigated. It was found that the introduction of coolant pulsation can result in the increases of eddy energy and turbulent kinetic energy in the near filed region, but this effect becomes weaker and weaker as the streamwise distance increases.