Study of an effusion-cooled plate with high level of upstream fluctuation

The flow field and surface adiabatic coolant-film effectiveness (ACE) distribution of a combustor representative effusion cooling array with cylindrical cooling holes has been studied both experimentally and numerically. Both studies focus on the influence of inflow turbulence, especially the high inflow turbulence which is always present in the combustor environment but rarely studied in the literature. A fluctuating inflow at roughly 20% intensity level is generated in the wind tunnel, and distributions of ACE measured for blowing ratios (BR) between 1.8 and 4.1. For comparison, ACE distributions are also measured at a low inflow turbulence intensity of 5%. For further investigation on the mechanism of inflow turbulence effects, hybrid large eddy simulations (LES) are carried out at a BR of around 1.8 under both low and high inflow turbulence intensities. The fluctuating inflow is generated using the Synthetic Eddy Method (SEM) with similar turbulence intensity. The predicted surface ACE distributions of the 2 cases are compared with the measurements. More detailed studies of the flow field are carried out based on the numerical results. The effects of inflow fluctuation levels are studied by comparing various flow statistics between the low and high fluctuation cases. The formation of the coolant film is also studied based on the development of the coolant film thickness. The interaction between the upstream and downstream coolant jets is investigated by visualising the coolant jet centre trajectory, as well as analyzing the turbulence structures, spectra and coherence at selected positions. These analysis clearly show that the highly fluctuating inflow results in an enhanced mixing of the coolant and mainstream. In the high turbulence intensity case, this leads to wider span-wise and shorter stream-wise film coverage over the first few rows of the array. These effects diminish as soon as a thick coolant film is formed in the downstream, especially at high BR conditions.