Hybrid LES-RANS study of an effusion cooling array with circular holes.

• An unstructured hybrid LES-RANS approach has been applied to predict the adiabatic cooling effectiveness of a multi-row effusion array with circular holes. • Detailed time-averaged velocity and temperature profiles are presented showing far richer contents of the resolved Reynolds stresses over the modelled counter-parts from RANS. • The coverage and formation of the coolant film are studied by examining various flow and thermal properties, which con firm the plate surface is better protected towards the downstream rows. • The analysis of turbulent flowstructures and multi-jets interaction is performed using energy spectra and spectral coherence, which reveals the importance of resolving the off-wall flow mixing in order to predict the cooling effectiveness. A multi-row effusion cooling configuration with scaled gas turbine combustor conditions is studied numerically, using a novel wall-proximity-based hybrid LES-RANS approach. The distribution of the coolant film is examined by surface adiabatic cooling effectiveness (ACE). Simulation results have shown that the accuracy of cooling effectiveness prediction is closely related to the resolution of turbulent flow structures involved in hot-cold flow mixing, especially those close to the plate surface. The formation of the coolant film in the streamwise direction is investigated. It is shown that the plate surface directly downstream the coolant holes are covered well by the coolant jets, while surface regions in between the two columns of the coolant holes could not be protected until the coolant film is developed sufficiently in the spanwise direction in the downstream region. More detailed study has also been carried out to study the time-averaged and time-dependent flow fields. The relation between the turbulent flow structures and coolant film distribution are also examined. The Kelvin–Helmholtz instability in the upper and lower coolant jet shear layer, is found to have the same frequency of around 8000 Hz , and is independent of the coolant hole position. Additionally, it is suggested by the spectral coherence analysis that those unsteady flow structures from the lower shear layer are closely related to the near wall flow temperature, and such effect is also independent of the coolant hole position. [ABSTRACT FROM AUTHOR]