FILM COOLING STUDIES ON COMBINED THREE-DIMENSIONAL SLOT AND EFFUSION JET CONFIGURATION OF AN ANNULAR COMBUSTOR LINER

Abstract

A detailed numerical investigation has been carried out to study the film cooling characteristics of a combined three dimensional slot and effusion jet configuration of a combustor liner. The effect of slot jet geometry, effusion jet pattern and coolant mass flow ratio on film cooling performance is identified. Mass flow ratio is the flow parameter that determines the flow transition between pure slot and effusion film. The three-dimensional slot coupled with the staggered effusion array is studied at a range of blowing ratios (BR), i.e., BR= 0.6-3. The enhancement in adiabatic effectiveness obtained with combined film cooling over pure three-dimensional slot cooling is reported in terms of laterally averaged and area averaged effectiveness on the film cooled surface. The most commonly studied two-dimensional planar slot is seen to have a cooling behavior different from the three-dimensional slots employed in an actual combustor, where the discrete nature of three-dimensional slot jets resulted in a lower film cooling effectiveness. Additionally, the adiabatic film cooling effectiveness has a non-linear variation with the coolant mass flow ratio (MFR) at low BRs (<2), and a monotonic decrease with MFR at high BRs (>2). Within the low blowing ratio range, the maximum improvement in the area average adiabatic effectiveness is 14% at BR=1.8, whereas it is 34% at high blowing ratio, BR=3. The standard deviation of effectiveness, a measure of uniformity in film cooling, is also lower with the combined film cooling configuration. A maximum reduction of 32% in standard deviation is noticed for BR=2.4 at MFR=1.