The cost of LES (Large Eddy Simulation) modelling in various zones of gas turbine aeroengines is outlined. This high cost clearly demonstrates the need to perform hybrid LES-RANS (Reynolds Averaged Navier-Stokes) over the majority of engine zones-the Reynolds number being too high for pure LES. The RANS layer is used to cover over the fine streaks found in the inner part of the boundary layer. The hybrid strategy is applied to various engine zones. It is shown to typically give much greater predictive accuracy than pure RANS simulations. However, the cost estimates show that the RANS layer should be disposed with in the low-pressure turbine zone. Also, the nature of the flow physics in this zone makes LES most sensible. © 2012, Begell House Inc. All rights reserved.