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

Highlights: • A fluctuating inflow at roughly 5% and 20% intensity levels is generated in the wind tunnel, and distributions of ACE measured for blowing ratios (BR) between 1 and 4. • The ACE is found to increase with increasing BR at the 20% intensity level, but this effect is not evident at 5%. • Hybrid LES numerical simulations confirm these findings and reveal the driving factor being the enhanced mixing of mainstream and coolant due to the upstream velocity perturbations. • The analysis of flow structures and spectra reveals more detailed relation between the upstream fluctuation level and the formation/behaviour of the coolant film. 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 analysing the turbulence structures, spectra and coherence at selected positions. These analyses 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.