The flow over a short intake is characterised by a strong interaction with the fan, that can only be captured when the rotor blades are modelled in the numerical simulations. In this paper, we use a coupled methodolog...The flow over a short intake is characterised by a strong interaction with the fan, that can only be captured when the rotor blades are modelled in the numerical simulations. In this paper, we use a coupled methodology to derive indications about relevant geometric variables affecting the high-incidence operation of an ultra-high bypass ratio turbofan intake with a length-to-diameter ratio of 0.35. By reproducing the effect of the fan through a body force model, we carry out a parametric study of the influence of the contraction ratio and the scarf angle at take-off conditions for a grid of 28 different three-dimensional shapes. The analysis of the selected performance metrics distributions at three angles of attack of 16., 24., and 28. reveals that a contraction ratio higher than 1.20 is needed to avoid separation at high incidence. While for an attached inlet the best performance is found with a moderate scarf angle, in presence of a developed separation the distortion level reduces as the scarf decreases up to negative values. We discuss the correspondence between the distortion indexes and the flow field, highlighting the origin of the detachment for the different geometries, according to the operating condition, and analysing the fan operation in the most distorted case. Finally, we assess the influence of modelling the rotor in the simulations, showing that its suppression effect on the separation at a given incidence depends on the intake geometric features.展开更多
Low pressure ratio fans of modern civil turbofans suffer from reduced stall margin in the take-off operating line and at part-speed,requiring variable geometry devices.Variable area nozzles(VAN)are one of the investig...Low pressure ratio fans of modern civil turbofans suffer from reduced stall margin in the take-off operating line and at part-speed,requiring variable geometry devices.Variable area nozzles(VAN)are one of the investigated solutions to control engine operating conditions throughout the mission.In this paper,we present a multi-fidelity modelling approach for an ultra-high bypass ratio turbofan engine with a VAN,combining a zero-dimensional thermody-namic cycle simulator using a realistic fan map with two-and three-dimensional detailed computational fluid dynamics(CFD)simulations for internal/external flow coupling.By adopting a novel algorithm to match the cycle conditions to the CFD solutions,the propulsive performance of the turbofan is analysed in a reference aircraft mission.The numerical method captures the effect on thrust generation and nacelle drag,providing a more reliable estimation of the impact of VAN on engine operation and efficiency.Low-speed mission points are confirmed to be those that benefit the most from an enlarged fan nozzle area,with a possible improvement of 3%in terms of thrust and specific fuel consumption at take-off and approach using a 10%larger area,similarly predicted by both 2D and 3D models.A preliminary acous-tic evaluation based on semi-empirical noise models indicates a modest effect on noise emis-sions,with up to 1 dB reduction in microphone signature at the sideline for a nozzle area increased by 10%.展开更多
文摘The flow over a short intake is characterised by a strong interaction with the fan, that can only be captured when the rotor blades are modelled in the numerical simulations. In this paper, we use a coupled methodology to derive indications about relevant geometric variables affecting the high-incidence operation of an ultra-high bypass ratio turbofan intake with a length-to-diameter ratio of 0.35. By reproducing the effect of the fan through a body force model, we carry out a parametric study of the influence of the contraction ratio and the scarf angle at take-off conditions for a grid of 28 different three-dimensional shapes. The analysis of the selected performance metrics distributions at three angles of attack of 16., 24., and 28. reveals that a contraction ratio higher than 1.20 is needed to avoid separation at high incidence. While for an attached inlet the best performance is found with a moderate scarf angle, in presence of a developed separation the distortion level reduces as the scarf decreases up to negative values. We discuss the correspondence between the distortion indexes and the flow field, highlighting the origin of the detachment for the different geometries, according to the operating condition, and analysing the fan operation in the most distorted case. Finally, we assess the influence of modelling the rotor in the simulations, showing that its suppression effect on the separation at a given incidence depends on the intake geometric features.
文摘Low pressure ratio fans of modern civil turbofans suffer from reduced stall margin in the take-off operating line and at part-speed,requiring variable geometry devices.Variable area nozzles(VAN)are one of the investigated solutions to control engine operating conditions throughout the mission.In this paper,we present a multi-fidelity modelling approach for an ultra-high bypass ratio turbofan engine with a VAN,combining a zero-dimensional thermody-namic cycle simulator using a realistic fan map with two-and three-dimensional detailed computational fluid dynamics(CFD)simulations for internal/external flow coupling.By adopting a novel algorithm to match the cycle conditions to the CFD solutions,the propulsive performance of the turbofan is analysed in a reference aircraft mission.The numerical method captures the effect on thrust generation and nacelle drag,providing a more reliable estimation of the impact of VAN on engine operation and efficiency.Low-speed mission points are confirmed to be those that benefit the most from an enlarged fan nozzle area,with a possible improvement of 3%in terms of thrust and specific fuel consumption at take-off and approach using a 10%larger area,similarly predicted by both 2D and 3D models.A preliminary acous-tic evaluation based on semi-empirical noise models indicates a modest effect on noise emis-sions,with up to 1 dB reduction in microphone signature at the sideline for a nozzle area increased by 10%.
