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

Abstract

In this paper, a multi-row effusion cooling configuration with scaled gas turbine combustor conditions is studied numerically. 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 field. 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 8000Hz, 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.

Impact of inflow turbulence on large‐eddy simulation of film cooling flows

“…Anisotropy and Bogard [4] conducted studies at a FST intensity of 20% , where the large scale turbulent structures from the mainstream flow su-perseded the turbulent structures generated by the shear layer of the coolant jet, elevating the mixing and reducing the cooling effectiveness. A hybrid LES-RANS approach is used by Chen and Xia [5] to study an effusion cooling array with FST generated with a synthetic coherent eddy method at a FST intensity of 5% . Kelvin-Helmholtz structures are observed in the shear layer of the first hole before breaking down into smaller, three-dimensional structures.…”

“…The interaction between the mainstream and the coolant flow provides coherent, two-dimensional structures that form in the shear layer before breaking down at x = 3 D , shown in Fig.9a and b. These shear layer instabilities are also present in the effusion case of Chen and Xia[5] , while Bogey et al[21] discusses these linear instabilities forming in laminar jet flow.Unlike NoTurb , the fluctuations of 01NWL1 ( Fig.9 c) provide the near-wall three-dimensional hairpin-like structures that are present in turbulent boundary layer flow. These structures can qualitatively be seen to interact with the shear layer ( Fig.9 d), destabilising the flow's ability to form coherent structures as shown in NoTurb .…”