Flow Modelling Over Twin-Nozzle Afterbodies Using Phoenics

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Flow Modelling Over Twin-Nozzle Afterbodies Using Phoenics

WHEN a high-speed jet aircraft is flying at transonic speeds — near or just above the speed of sound — a large proportion of the total drag of the aircraft will come from the afterbody of the fuselage. This may be as much as 30–40%, which is a very significant amount to the aircraft designer. The flow over the afterbody is also important because it affects the behaviour of the fin, and because if the flow is oscillatory, this can have adverse consequences on the airccraft. The necessity of maximising knowledge of the after-body flow while minimising the cost of wind-tunnel and in-flight testing is bringing computational fluid dynamics (CFD) into prominence. British Aerospace has recently commissioned a study by CHAM (Concentration Heat and Momentum Ltd) in the application of the extremely sophisticated CFD code PHOENICS to the problem. The study has concentrated upon predicting the effect of jet entrainment on the surface pressure distribution around the afterbody, an area which has previously been difficult to model computationally. A large amount of experimental work has already been carried out using wind-tunnel measurements, and the study sought first to validate the program by reference to experimental data.