Department of Applied Maths and Theoretical Physics
The definition of a wave is a means of transferring energy from one place to another without bulk motion. Waves appear all over physics, whether light waves, sound waves, elastic waves or other less obvious varieties. Wave motion is ubiquitous, and an understanding of wave motion is of fundamental importance.
The Waves Group studies problems of wave motion, normally, but not exclusively, drawn from fluid dynamics. These include problems as diverse as turbomachinery noise, theoretical hydrodynamic stability, fluid-structure interactions and development of computational methods. This work has a great variety of applications and much of our research is funded by industry.
Below is a broad brush description of some of the current themes of our work. We are interested in other problems as well, the most prominent research area omitted below is random scattering (contact Mark Spivack for more details).
(Nigel Peake, Benoît Pier)
Research has been conducted on a wide of problems arising in the generation and propagation of sound. Most interest has focused on turbomachinery noise, and much of the work has been sponsored by Rolls Royce and Hitachi. High levels of acoustic radiation are produced when turbulence is ingested into a fan and by the hydrodynamic interaction between the various blade rows, and we have studied a range of problems concerned with the sound produced when unsteady vortical flow interacts with a solid object such as a fan blade. Other work has been concerned with predicting the effects of aeroengine intake scarfing, whereby the the shape of the engine intake is changed so as to produde some improvement in the noise exposure on the ground.
We are also interested in a range of issues associated with the acoustics of swirling flow. The behaviour of small-amplitude wave motions in irrotational steady flow is well-understood, but interesting effects arise in the presence of mean vorticity. Duct acoustics in strong swirl has been studied, with relevance to the flow behind a rotating fan, and the effects of swirl on the stability and acoustics of diverging jets are also under investigation.
(Sevag Arzoumanian, Robert Hunt, Paul Metcalfe, Nigel Peake, Benoît Pier, Mark Spivack)
Although, for certain problems, it is relatively simple to write down solutions of the governing equations of fluid dynamics, is it is less simple to show that these solutions can observed in the real world. To do this, one has to show that the solution is stable, and the stability of flows is an old problem of hydrodynamics.
The extension of fluid stability theory to handle interactions between the fluid and any elastic structures present is a rather active research topic at the moment. A variety of counterintuitive and complicated behaviours can occur, which we are currently investigating. The picture below shows the response of a finite baffle in mean flow to (single period) forcing. Note that although the forcing is periodic, frequencies generated in the startup persist and change the nature of the solution at large times.
Another related area of research is that of flow over a ribbed membrane. This is a model of a ship's hull, and it is of interest to examine its energy transmission properties. Recent work has allowed us to study this problem in more realistic situations, and some very interesting behaviour has been found. This problem is strongly related to some problems in solid-state physics and Hamiltonian stability theory, and conceals a large amount of interesting physics and mathematics. Some recent work by group members connects this behaviour to the theory of quantum chaos.
(David Hunt, Caroline Lowe, Nikos Nikiforakis, Graeme Thorn, Blandine Walker)
Information about this aspect of our work is available from the Laboratory of Computational Dynamics.
Complaints, comments and suggestions to Adrian Lloyd.