CFD Analysis of Hot Gas Ingestion Mechanisms for the Vertical Descent Phase of a Harrier Aircraft

Abstract

Hot Gas Ingestion (HGI) can be a problematic feature of STOVL aircraft during the descent phase of landing, or while on the ground. The hot exhaust gases from the downwards pointing nozzles can be re-ingested into the engine intakes, causing power degradation or reduced engine surge margin. The flow-fields that characterise this phenomenon are complex, with supersonic impinging jets and cross-flows creating large ground vortices and fountain up-wash flows. As a partner in the PUMA DARP (Unsteady Methods Focus Group), the Cambridge University Engineering department CFD Lab are trying to model this flow-field in order to validate the Rolls-Royce HYDRA CFD code against experimental data obtained from detailed Rolls-Royce HGI tests. The HYDRA code has been developed to include a suitable mesh deformation technique for the descending aircraft configuration. The code is applied to predict the occurrence of HGI, by simulating experimental results from a 1/15th scale model of a descending Harrier. Based on these computational results, this paper studies the aerodynamic mechanisms that govern HGI, in terms of the near-field and far-field effects and their impact on the magnitude of temperatures at the engine intake. The trends in experimental engine intake temperature profiles are explained by analysis of these mechanisms. Following a more thorough validation of these results, the HYDRA code will provide a valuable tool for predicting the occurrence of HGI. The CFD method can then be used for the analysis of other STOVL aircraft as well as configuration changes aimed at preventing HGI.