明星八卦

Flow control offers the potential to enhance aircraft aerodynamic performance and efficiency by reducing skin friction drag and pressure drag associated with boundary layer transition and separation. These efficiency gains are critical towards reducing the environmental impact of air transport to meet industry targets such as ACARE 2020 Vision and Flightpath 2050. Research activities include the fluid mechanics analysis of synthetic jet actuators; actuator modelling and optimisation and systems analysis to assess the implementation costs of flow control technologies (synthetic jets, pneumatic blowing, active dimples and plasma actuators) to existing and novel vehicle configurations.

Broadband self-noise and instability tonal self-noise can be produced by aerofoils with sharp trailing edges at flows with high Reynolds number and low Reynolds number respectively. These noise sources produce negative environmental impacts from operations of aerospace and wind turbine industries. For example, trailing edge self-noise radiated (such as that included in Figure below) is one of the main reasons for a high rate of refusal to grant planning permission for onshore wind farm across the country. The main research techniques undertaken are the application of boundary layer and aerofoil wake control techniques, such as trailing edge serration, spanwise flow oscillation and vertical blade devices. Most of these techniques are highly energy efficient and very attractive for industrial applications since they can be deployed on demand without introducing excessive profile drag.

The department also conducts research into the interaction aerodynamics of racing car wings and wheels in close proximity to one another. This research is aimed at investigating and understanding the fundamental and complex aerodynamic interactions that result from each of this elements acting in a combined manner. Figure below gives an example of a computational grid generated by staff to investigate these interactions under varied and diverse operating conditions.

Computational grid of a racing car wing and wheel operating in close proximity to each other

Another important aspect of aerodynamic and aeroacoustics research within the department involves the fundamental investigation, both within the experimental and computational domains, of aircraft landing gear. Aircraft landing gear is a significant contributor to aircraft noise in the approach phase of aircraft flight with significant disruption caused to the surrounding population. Research in this area is centred on the understanding of the unsteady aerodynamics over the landing gear and the subsequent generation of the acoustic disturbances which thereafter propagate throughout the surrounding far-field.

Research in this area has focussed on the effects of curvature on development of turbulent boundary layers and wakes. Both experimental and computational approaches have been adopted. The experimental studies have used wind tunnel testing and hot-wire anemometry in order to measure turbulence quantities, whereas computational studies have been based on RANS and LES methods.  Among the studies carried out is the study of the wake of a NACA0012 airfoil placed in a stream of air with a 90o curvature.

Contour plot of spanwise vorticity obtained using LES [Farsimadan, 2008]

Several staff within the department also undertake research into ‘morphing aircraft’ technologies; those being defined as systems, techniques and technologies which allow aircraft to change configuration in flight to achieve multiple and dissimilar flight performance characteristics and capabilities seamlessly. These changes provide aircraft multi-role capabilities from a single aerial platform allowing extended applicability with greater cost-effectiveness.

Example of a bi-stable morphing winglet concept for enhanced wing lift capability during take-off

Actual Flight testing in single-engined aircraft is also a focus of research within the department. This research aims to better understand the dynamics of light aircraft aviation, together with developing and enhancing technologies, systems, strategies, and the safety of light aircraft in the general aviation category.

This research focuses on the numerical study of flows in turbomachinery (as found in e.g. jet engines). This type of flow is highly unsteady and therefore difficult to understand. With the help of accurate numerical simulations the physics that play a role in these types of flows is explored. For example: the front part of a turbine blade experiences a high thermal loading because of the impinging hot exhaust gases from the combustor. It was found that the level of the free-stream turbulence in the exhaust gases significantly affects this thermal loading, which may potentially damage the turbine blades. Numerical simulations such as those shown in figure below are performed to identify and understand the physical mechanisms that are responsible for this increase in heat transfer. The newly achieved understanding can subsequently be used to improve existing models and to design new models to be employed in industrial codes that are routinely used to calculate flows in turbomachinery. With these new models, a more accurate prediction of the thermal loading on turbine blades can be obtained which helps, for example, in the development of more efficient blade-cooling strategies.

A hot cylinder is cooled by oncoming cold flow that contains free-stream fluctuations. The picture shows the boundary layer around the cylinder, coloured by the temperature

Staff within the department recently acquired a 1/5th scale helicopter rotor rig that is currently being used to investigate the structural and aerodynamic characteristics of rotary wing aircraft performance and dynamics. The rig is a test bed for the development of new and improved testing techniques, the development of new blade configurations and modifications, as well as the interrogation and investigation of fundamental flight characteristics and physics. The rig is fully instrumented with multiple sensors and instrumentation that allow real-time classification and acquisition of various critical parameters fundamental to the operation of rotary wing aircraft.

1/5th Scale model of a linx helicopter rotor