Richard McRoberts

Tanker Mission Implication on a Civil Aerial Refuelling Transport System’s Benefit Evaluation

As the emphasis on initiatives that can improve environmental efficiency while simultaneously maintaining economic viability has escalated in recent years, attention has turned to more radical concepts of operation. In particular, the cruiser–feeder concept has shown potential for a new generation, environmentally friendly, air-transport system to alleviate the growing pressure on the passenger air-transportation network. However, a full evaluation of realizable benefits is needed to determine how the design and operation of potential feeder-aircraft configurations impact on the feasibility of the overall concept. This paper presents an analysis of a cruiser–feeder concept, in which fuel is transferred between the feeder and the cruiser in an aerial-refueling configuration to extend range while reducing cruiser weight, compared against the effects of escalating existing technology levels while retaining the existing passenger levels. Up to 14% fuel-burn and 12% operating-cost savings can be achieved when ...

Metamodel Assisted Multi-Objective Global Optimisation of Natural Laminar Flow Aerofoils

A methodology for the multi-objective optimisation of natural laminar flow (NLF) aerofoils using a Kriging assisted multi-objective genetic algorithm is proposed. Kriging surrogates are built to model the variation of drag coefficient at two different flight conditions and are dynamically refined in promising regions of the design space as the optimisation progresses using an adaptive sampling technique. The optimisation is subject to constraints on moment coefficient and maximum lift coefficient; the latter of which is also estimated using a surrogate model. The maximum lift coefficient metamodel is dynamically refined when the error bounds on the Kriging prediction cross the constraint threshold. True objective function values are calculated at sample points by an interactive boundary layer solver in which prediction of transition onset location is achieved via the full linear stability theory and e N method. An adaption of the class-shape transformation technique is utilised to parameterise the aerofoil geometry and define the design space. The design methodology was found to be capable of identifying a set of Pareto optimal wing sections that exhibit low drag and extended regions of laminar flow at both flight conditions.

Improving Feasibility of Point to Point Operations Through Civil Aerial Refuelling

Re-imagining of the aerial transportation system has become increasingly important as the need for significant environmental and economic efficiency gains has become ever more prevalent. A number of studies have highlighted the benefits of the adoption of air to air refuelling within civil aviation. However, it also opens up the potential for increased flexibility in operations through smaller aircraft, shifting emphasis away from the traditional hub and spoke method of operation towards the more flexible Point to Point operations. It is proposed here that one technology can act as an enabler for the other, realising benefits that neither can realise as a standalone. The impact of an air-to-air refuelling enabled point to point system is discussed, and the affect on economic and environmental cost metrics relative to traditional operations evaluated. An idealised airport configuration study shows the difference in fuel burn for point to point networks to vary from -23% to 28% from that of Hub and Spoke depending on the configuration. The sensitive natures of the concepts are further explored in a second study based on real airport configurations. The complex effect of the choice of a Point to Point or Hub and Spoke system on fuel burn, operating cost and revenue potential is highlighted. Fuel burn savings of 15% can be experienced with AAR over traditional refuelling operations, with point to point networks increasing the available seat miles (by approximately 20%) without a proportional increase in operating cost or fuel.

Implication of Tanker Mission Concept on the Benefits Evaluation of a Civil Air-to-Air Refuelling Transport System

As the emphasis on initiatives which can improve environmental efficiency while maintaining economic viability has escalated in recent years, attention has turned to more radical concepts of operation. In particular, the cruiser-feeder concept has shown potential for a new generation of environmentally friendly air transport system. However, full evaluation of realisable benefits needs to carefully consider the provision of a feeder service, and how the feeder design and operation impacts on the performance of the cruiser aircraft network. The paper presents an analysis of the cruiser-feeder concept in which fuel is transferred between the feeder and cruiser in an aerial refuelling configuration to extend range while reducing cruiser weight. Evaluation indicates that savings in the range of up to 9% fuel savings and 14% in total operating cost can be achieved over the existing operational model by adopting this mode of operation, compared to today’s standard fleet technology and performance. Moreover, these savings are not uniformly distributed across the network and that the system is highly sensitive to the routes which are serviced. The work undertaken in this project has been funded through the European Union Seventh Framework Programme under grant agreement 284741.

Investigation of Utilizing Single Surface Depressions in Optimization of NLF Aerofoil Design

An environment has been created for the optimisation of aerofoil profiles with inclusion of small surface features. For TS wave dominated flows, the paper examines the consequences of the addition of a depression on the aerodynamic optimisation of an NLF aerofoil, and describes the geometry definition fidelity and optimisation algorithm employed in the development process. The variables that define the depression for this optimisation investigation have been fixed, however a preliminary study is presented demonstrating the sensitivity of the flow to the depression characteristics. Solutions to the optimisation problem are then presented using both gradient-based and genetic algorithm techniques, and for accurate representation of the inclusion of small surface perturbations it is concluded that a global optimisation method is required for this type of aerofoil optimisation task due to the nature of the response surface generated. When dealing with surface features, changes in the transition onset are likely to be of a non-linear nature so it is highly critical to have an optimisation algorithm that is robust, suggesting that for this framework, gradient-based methods alone are not suited.

An Experimental Study Into the Turbulence Characteristics of Laminar, Transitional and Turbulent Impinging Jets

Particle Image Velocimetry (PIV) has been utilised to obtain instantaneous velocity fields for water jets impinging perpendicularly on a solid surface. Time-averaged turbulence statistics are presented for laminar, transitional and turbulent jets in the Reynolds number range 3000 - 10000. A vortex identification algorithm is also employed to calculate the probability of a vortex existing at each discrete grid point based on all of the instantaneous fields. Significant turbulent mixing is induced by increasing the Reynolds number from 3000 to 4000, indicating transition commences in this range. The transition onset is characterised by a sudden increase in mean turbulent kinetic and velocity fluctuations as well as the coalescence of small scale vortices into large scale coherent structures. Further increasing the Reynolds number results in a decrease in the levels of non-dimensional turbulent kinetic energy in the shear layer implying a lesser proportion of the initial energy possessed by the jet is lost through dissipation resulting in favourable heat transfer characteristics at the impingement surface. The transitional jet with Re = 4000 proves to be an interesting case producing a strong wall jet with intense turbulent fluctuations that may result in large heat transfer rates over a greater radial distance.

A Heuristic Approach to Dynamic Design Space Definition for NLF Aerofoil Optimisation

A hybrid genetic algorithm has been developed and is benchmarked against a gradientbased and standard genetic algorithm (GA) to test the ability of each to generate natural laminar flow (NLF) aerofoil profiles. The performance characteristics of the GA and hybrid GA are assessed on a number of analytical test functions to illustrate the efficiencies gained from including a local search technique. A “meme pool” constructed from a variety of local searches is important for the algorithm to be robust as different local searches have inherent biases; however a trade-off between efficiency and robustness is seen to arise. For the engineering design problem it is shown that the hybridised method offers improvements in the total runtime of the algorithm and also generates superior designs than compared with a traditional GA. The capability to include problem specific knowledge in a hybrid algorithm is demonstrated along with the enhanced efficiencies that can be achieved.

Effect of three-dimensional surface perturbations on boundary layer transitional characteristics

The influence of a three-dimensional surface perturbation on the transitional boundary layer has been investigated experimentally. The perturbation height and longitudinal location relative to the leading edge have been varied to represent the effects of moving the location of a rivetted joint on a typical aerodynamic surface. A single hot wire probe was used survey the flow at a freestream turbulence intensity of 0.08% (Re=1.4x10 6 ) to 0.12% (Re=1.7x10 6 ). The experimental results indicate that while, for most configurations tested, the presence of a surface perturbation reduces the transitional Reynolds number, there are potential benefits to be realised with careful positioning of the rivet joint, promoting an increase in the transition onset location of up to 5%. This has a series of implications with respect to manufacturing tolerance analysis, and the manner in which tolerances are assigned to joints.