Abstract We show environmental effects from high-altitude overflights (above 24,500 feet, FL245). Three test cases are presented: Northern England (up to 7,000 flights/week), Ireland (6,000 flights/week) and Eastern Alps (up to 18,000 flights/week). The technical literature addresses the overflight legal rights, but the current environmental pressure has added another dimension neglected by existing agreements. The environmental characteristics addressed are engine exhaust emissions and high-altitude noise. The simulation methods rely on land-based and space-based ADS-B databases, a suite of aircraft performance simulation codes, including exhaust emissions. Missing information, such as the origin-destination pairing, has been included in the simulation methods where available. Aircraft performance is assessed in terms of duration (tropospheric or stratospheric), vertical distribution, flight directions and a variety of other metrics, including breakdown by aircraft type. When the origin/destination are available, it is possible to establish alternative weight profiles and a trend in the traffic patterns. The results show minimal differences for long-range aircraft with methods that lack origin-destination. This difference becomes larger as the weight profile decreases, or the requested range is shorter. The simulation method is valid anywhere in the world where there are ADS-B data.
Abstract This paper presents a novel test rig setup intended to investigate axial rubbing of adaptive face seals. This rig is designed to characterise the wear behaviour of the seal, especially during transient operation, perform thermal measurements, as well as provide the ability to analyse the aerodynamic stiffness of the bearing face flow prior to and after a rubbing event. The rig operating point can be controlled across a wide technically relevant operational range by adjusting the rotational speed, seal incursion depth and rate, as well as the air mass flow through the seal prior to the rub event. A broad variety of instrumentation allows for the build-up of an extensive database in order to better understand the transient behaviour of adaptive face seals during rubbing. The paper presents the overall concept of the rig, including its modular design to allow for extended experiments of axial rub without damage to the rotor and fast variation of bearing face design and material combinations. Moreover, a detailed error analysis of the measured and derived quantities, as well as an initial aerodynamic analysis and rub tests on a generic bearing face geometry, are discussed. In future work, the rig will be employed to investigate the rubbing process and quantify its effects on both the seal bearing face and the rotor disc. Subsequent tests will focus on a parameter study to systematically vary operating conditions and material combinations, therefore informing the design of new adaptive face seals which are robust to contact operation.
Abstract In this study, the aerodynamic effects of rotor blade twist geometry on the hover performance of the XV-15 tiltrotor were investigated. For this purpose, the twist distribution of the XV-15 tiltrotor was optimised under hover conditions using the artificial bee colony (ABC) algorithm coupled with a Blade Element Momentum Theory (BEMT)-based numerical model validated against the NASA Ames experimental data. The blade twist was parameterised using a fifth-order continuous polynomial, whose coefficients were optimised to minimise the power coefficient while maintaining a constant thrust. The developed model was subsequently employed to evaluate the aerodynamic performance of candidate twist distributions under the prescribed hover thrust condition. In addition to the single-objective optimisation, the trade-off between aerodynamic performance and total blade twist was evaluated within a Pareto-based multi-objective optimisation framework, with total blade twist treated as a geometric design metric associated with practical blade manufacturing considerations. The best-found solution reduced the power coefficient by approximately 8.63% and increased the figure of merit (FOM) by approximately 9.45% relative to the reference geometry within the present BEMT framework. This study presents a practical optimisation approach for the aerodynamic assessment of rotor blade twist distributions under hover conditions with relatively low computational cost.
Abstract A hybrid differential game approach is proposed to solve a target-attacker-defender (TAD) game, involving a target, an attacker and multiple defenders. For the attacker, successful evasion from the defenders is considered a prerequisite for intercepting the target. The qualitative differential game is employed in the evading phase to obtain the ranges within which the attacker’s guidance commands. The guidance laws of all agents are derived by solving a quantitative differential game, with the ranges obtained from the qualitative differential game treated as the feasible region for the attacker. All agents’ guidance laws form an equilibrium solution of the hybrid differential game. The designed guidance laws are applied to the terminal guidance scenario. Numerical simulations are conducted to verify the effectiveness of the design.
Abstract The approaching threshold in the design and optimisation of rotating components in gas-turbine engines has drawn attention to the inter-spool duct (ISD) due to its potential to enhance the aerodynamic efficiency of compression systems. The ISD is a crucial passage to deliver the required quantity and quality of the flow between low-pressure and high-pressure spools in a turbofan engine. In this study, an inter-spool duct is designed using a cubic Bezier curve matching the exit dimensions of a transonic compressor stage. In the first part of this study, the performance characteristics of the stand-alone compressor stage are validated at 80% and 90% of the design speed with experimental data. The second part analyses the integrated performance of the compressor stage and ISD at 100% of the speed using steady and unsteady numerical simulations. The performance characteristics of the integrated system show a reduction of 5.8% in the choke margin, but a 4.8% increase in the stall margin. The thick boundary layers on the duct walls have reduced the overall mass flow in the system by 1.6%. In addition, a component-wise loss decomposition through entropy generation is provided for the case with and without ISD. Signal processing of unsteady data is also performed, where the fast Fourier transformation (FFT) of the unsteady pressure signals acquired in the upper and lower walls of the duct inlet showed the frequency of the rotor stall ( 0.024 times upper B upper P upper F 0.024 × B P F $0.024\times BPF$ ) and the other two frequencies ( 0.4 times upper B upper P upper F 0.4 × B P F $0.4\times BPF$ and 0.61 times upper B upper P upper F 0.61 × B P F $0.61\times BPF$ ) related to stator instabilities.
