Heat Transfer in a Turbine Cavity: An Investigation into Correlation-Based Heat Transfer Compared to Computational Fluid Dynamics

Abstract

The Secondary Air System (SAS) is a vital component of modern gas turbine engines. As combustor outlet temperatures continue to increase, the cooling air supplied by the SAS is essential for maintaining component functionality throughout the flight envelope. Due to the critical role of cooling air, accurate thermal analysis of SAS components is required to assess component longevity. Although a validated Computational Fluid Dynamics (CFD) with conjugate heat transfer can model this problem with high accuracy, the computational cost makes such simulations impractical for full flight-cycle analyses. As an alternative, a thermal-only Finite Element Analysis (FEA) approach can be employed using estimated fluid flow behaviour. In this approach, convective heat transfer coefficients at fluid–solid interfaces are obtained using Nusselt number correlations. This work investigates the performance of different heat transfer correlations and evaluates their accuracy for an arbitrary turbine cavity. Overall, the correlations provided adequate temperature predictions for solid SAS components for a steady-state analysis. More specific correlations accounting for rotational effects yielded improved accuracy, in some cases predicting temperatures within a few degrees of those obtained from conjugate CFD simulations. To further improve accuracy, particularly within the fluid domain, the influence of the viscous sub-layer friction should be considered in the thermal model. In conclusion, this study demonstrates that, with careful selection of heat transfer correlations, good estimates of the SAS temperatures can be achieved using a thermal-only FEA approach. However, the accuracy of the method strongly depends on the quality of the underlying fluid flow estimations.