Abstract
This paper studies the computational modelling of the flow separation over the engine nacelle lips under the off-design condition of significant crosswind. A numerical framework is set up to reproduce the general flow characteristics under crosswinds with increasing engine mass flow rate, which include: low-speed separation, attached flow and high speed shock-induced separation. A quasi-3D (Q3D) duct extraction method from the full 3D (F3D) simulations has been developed. Results obtained from the Q3D simulations are shown to largely reproduce the trends observed (isentropic Mach number variations and high-speed separation behaviour) in the 3D intake, substantially reducing the simulation time by a factor of 50. The agreement between the F3D and Q3D simulations is encouraging when the flow either fully attached or with modest levels of separation but degrades when the flow fully detaches. Results are shown to deviate beyond this limit since the captured streamtube shape (and hence the corresponding Q3D duct shape) changes with the mass flow rate. Interestingly, the drooped intake investigated in the current study is prone to earlier separation under crosswinds when compared to an axisymmetric intake. Implications of these results on the industrial nacelle lip design are also discussed.
Highlights
Gas–turbine engines are generally housed in nacelles
The drooped intake investigated in the current study is prone to earlier separation under crosswinds when compared to an axisymmetric intake
The framework is demonstrated to be capable of capturing low speed separation, ė Interestingly, the drooped attached flow and high speed shock-induced separation with increasing m
Summary
Gas–turbine engines are generally housed in nacelles. An optimal intake design is the one which provides a uniform distribution of the air flow to the downstream components with minimum total pressure loss over a wide range of operating conditions. To circumvent the consequent increase in the weight and drag, engine manufacturers are exploring the possibility of employing shorter intakes and slimmer nacelle lips [1,2]. Such designs are much more susceptible to flow separation due to the reduced diffusion capability of the intake, under the off-design conditions of high crosswinds and high-incidence. The nacelle lip skin would be designed to maximise cruise performance, since cruise is generally the longest flight phase [3]. To cater for the off-design conditions of high-incidence and crosswind, the actual lip shapes used in commercial aircraft intakes are a compromise.
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