PSP and LES Investigation on the Impact of Trench Depth on Flat Plate Film Cooling Through Shaped Holes

To increase film cooling effectiveness levels downstream of film cooling holes, trenches manufactured in the thermal barrier coating can be adopted. The performance of this solution depends on the trench geometrical characteristics, namely its depth and width. A LES based numerical study has been performed at Korea University to investigate the effects of trench configuration on the thermal protection, resulting in a 22% increase in cooling performance compared to the reference case without a trench. The present paper reports the results of an experimental investigation carried out at Bergamo University on a Plexiglass flat plate model with a set of three fan-shaped holes incorporated into an existing wind tunnel, replicating the numerical setup. PSP technique was used to measure the adiabatic film cooling effectiveness. Besides the standard shaped hole case, the best and worst trench configurations coming from a DoE approach have been examined at various coolant to mainstream blowing ratios M in the range between 0.5 and 3. Cases at M = 1.5 were used to cross check the prediction capability of the LES numerical simulation for the selected trenched cases. PSP and LES result to be in good agreement, also with literature data. The high depth/low width trench was shown to give improved performance for M larger than 1.