Overseas travel to India and France

Lead Research Organisation: University of Cambridge
Department Name: Engineering


In many scientific and industrial situations, it is important to predict whether a small perturbation in a flow or system will grow (unstable) or decay (stable). The conventional technique is to decompose the perturbation into modes that are normal (i.e. orthogonal) in two spatial dimensions and to study the growth of each mode separately. This, however, often gives inaccurate results. As a simple example, this technique predicts that the flow in a pipe will be stable at all Reynolds (Re) numbers (i.e. at all velocities). In reality, however, the flow becomes turbulent at Re ~ 2000, depending on external noise and the pipe's roughness.This discrepancy arises because, in the third spatial dimension, the modes are non-normal (i.e. non-orthogonal). This means that they can feed energy into each other and should not be considered separately. This non-normal behaviour often causes strong transient growth at the intermediate times that are of most interest to scientists and engineers. For instance, in pipe flow, a non-normal analysis predicts that tiny perturbations will rapidly develop into stream-wise streaks at Re ~ 2000, agreeing with experimental evidence. In the last ten years there has been a surge of interest in non-normal stability analyses applied to fundamental fluid mechanics. One of the partners in this proposal, P. J. Schmid, has been instrumental in investigating and publicising the effect of non-normality on fluid mechanical instabilities and has written a very influential book on the subject. Another of the partners, R. I. Sujith, has pioneered some highly original work on non-normality in thermo-acoustic instabilities. He has shown that thermo-acoustic systems can be extremely non-normal and that their behaviour will not always be predicted well by a conventional stability analysis. The PI of this proposal, M. P. Juniper, has a background in both of these areas (combustion and fundamental flow instability). He has recently extended the work of RIS to include some of the techniques used by PJS on fluid mechanical instabilities.The three partners of this proposal met in France in June 2008 and drafted plans for further research collaboration. The purpose of the visits proposed here is to start work on the first of these projects, to map out future research directions and to outline a number of potential PhD projects.
Description This was a small grant for the PI (Matthew Juniper) to collaborate with Peter Schmid at Ecole Polytechnique France and R. I. Sujith at IIT Madras India.

Key findings were

- that we had much common ground, although we approached problems in different ways;

- that the PI could collaborate with R. I. Sujith on Thermoacoustics

- that the PI could collaborate with P. J. Schmid on the hydrodynamics of flames.

- Having sketched out the proposed joint work, the investigators wrote a proposal that was subsequently funded by EPSRC (AIM for Industry)
Exploitation Route The research in thermoacoustics and hydrodynamics is fundamental to the understanding of gas turbine engines. The ideas arising from this project are currently being investigated as part of the AIM for Industry proposal.
Description This was a small project in order to test feasibility of the AIM network (EP/G033803/1) and to start research projects between Cambridge and IIT Madras. It led to the AIM Network and the subsequent AIM Industry proposal (EP/H050310/1)
First Year Of Impact 2009
Sector Aerospace, Defence and Marine,Energy