The Dyson Professor of Fluid Mechanics

Academic Division: Energy, Fluids and Turbomachinery

Research group: Fluids

Telephone: +44 1223 7 68449

Email: grh20@cam.ac.uk

Research interests

My research centres around the fluid dynamics laboratory where I use a combination of laboratory measurement and flow visualisation techniques, primarily within water-filled visualisation tanks, to tackle problems that have arisen either in response to the needs of industry or as a result of scientific curiosity. I couple this experimental approach with theoretical modelling in order to gain further insight into the physics of these flows and, where possible, to generalise the results of the experiments to enable wider application. I have experience of using computational fluid dynamics and am currently collaborating on a DNS study, although I have not chosen to use these tools extensively.

I have solved a range of problems in fluid dynamics, involving both steady and time-dependent flows, using this combined experimental and theoretical approach. These encompass flows of a fundamental nature, with broad applications across fluid mechanics (e.g. on dense vortex dynamics, turbulent entrainment across density interfaces, plume dynamics, stratification of rooms and tunnels, radial jets and their induced flows, fountain flows, and those of a very practical nature with immediate engineering application (e.g. jet-enhanced removal of airborne contaminants, the extraction of fumes from gas-metal arc welding, the fluid mechanics of revolving doors, modelling the ventilation of modern multi-storey atrium buildings, the night purging of heat from buildings.

The focus of my research has been on industrial and environmental fluid dynamics and has developed from questions concerning the movement and exchanges of air, heat and contaminants within rooms of buildings and the exterior environment. The development of buoyancy-driven flows, e.g. turbulent thermal plumes or fountains of cool air, within the confines of these stratified environments has formed an additional focus. My research thus concerns both steady- and time-dependent turbulent flows within complex (often interlinked) geometries which are driven by density contrasts and/or turbulent entrainment. What has always fascinated me with these problems is that even tiny density differences can result in bulk movements of air, and as a consequence, have a profound influence on heat and contaminant transport and ultimately, within the application of a room, on energy requirements for heating and cooling, as well as human comfort. The use of these flows to enhance understanding of the natural ventilation of buildings has been of major interest to me. Whilst I have worked on turbulent flows resulting from large density differences (e.g. non-Boussinesq plumes above fires within tunnels), I have primarily focused on flows established by small density differences as typical in rooms and numerous other environmental applications.

A goal central to my research has been to develop an understanding of how to ventilate buildings effectively and thereby achieve sustainable low-energy designs for the future. En-route to this goal it has become clear that a number of formidable challenges in fluid mechanics stand in the way, as the flows of interest are typically turbulent, involve interaction with density stratification and develop within complex geometries. My research towards the central goal has and continues to expose many previously untackled problems, often of a fundamental nature, and thus, with application and significance to far wider areas of engineering fluid mechanics.

My work has been motivated, in part, by the fact that of the energy buildings consume (notably this is almost half of the energy used by modern cities), about 40% is simply to heat and ventilate. Moreover, as we spend the vast majority of our time indoors, what particularly motivates me is that research breakthroughs provide a means of directly improving everyday lives as well as dramatically reducing energy expenditure through the development of effective low-energy design. My research has shown that many modern ‘low-energy’ designs are misguided and ineffective, e.g. glazed atria do not typically enhance airflow and cooling as designers intend and, rather soberingly, the current design guidance offered to practitioners is largely erroneous. As a consequence, there is much that can continue to be done to significantly reduce energy consumption. This requires an understanding of the underlying fluid mechanics and modelling these flows, in order to provide a validated predictive capability that can be used by architects and ventilation engineers, is and remains a significant challenge.

Teaching activity

• Environmental fluid mechanics
• Hydrodynamic stability