Dr Zahir Hussain and Prof Stephen Garrett
In today’s connected world, once the current COVID-19 situation passes, the demand for air travel is expected to rebound sharply and remain high in the long-term. This is seen by plans for the proposed expansion of airports and, in the current situation, the acceleration of freight delivery via air, which will lead to aircraft noise becoming a serious and growing problem. More importantly, the world’s global oil supply is decreasing rapidly, which will cause its price to escalate in the long-term future. Meanwhile, the aviation industry remains a huge consumer of oil, contributing heavily to global warming with 2% of global emissions of carbon dioxide and nitrogen oxide. Consequently, sustainability and environmental impact are top-level requirements in the EU’s Beyond Vision 2020 guidelines for the design of future aircraft up to 2050.
One strategy is to enhance aircraft efficiency and engine design, through improved aerodynamics and eradicating turbulent airflow. Indeed the reduction of aerodynamic drag by as much as 10-15% has been shown to yield significant savings in fuel, reduced emissions and noise. Specifically, current wing and aero-engines are inefficient and encounter high-drag issues, lending significant potential for designing the next generation of fuel-efficient and environmentally sustainable aircraft wings and engines. The aeronautical industry has been conservative in implementing these targets, with existing wind tunnel research proving incredibly expensive. Conversely, Computational Fluid Dynamics (CFD) is now widely acknowledged as a more economical alternative.
The project’s aim is to use an existing code developed as part of the Hussain’s EPSRC New Investigator (NI) grant (EP/R028699/1) in order to model swirling flow in a lined annular duct, which has applications in the dynamics of the turbine stage of an aeroengine.
For swirling duct flow, the PhD student will use an object-oriented code developed by Hussain for rotating cone boundary-layer flow  to conduct a full 3D numerical stability analysis to reveal the optimum engineering parameter values for stable swirling flow in a duct, which delay turbulence. Analytical studies of the problem will also be investigated, including an energy analysis, asymptotic WKB theory and the effects of nonlinearity, via existing collaboration with Dr Sharon Stephen (Sydney, Australia). The governing parameters of axial flow and swirl are known to interact in a complex and competing nature for a rotating cone , and so shedding further light on their effect on the underlying stability in this extended shear flow will reveal pathways to delay turbulent-transition
Furthermore, distinct numerical and theoretical flow models will be directly comparable with each other, as well as the existing findings for swirling duct flow by .
 Hussain, Z., Garrett, S.J., Stephen, S.O. & Griffiths, P.T. 2016 The centrifugal instability of the boundary layer on a rotating cone in an enforced axial flow, J. Fluid Mech., 788, 70–94.
 Fildes, M., Hussain, Z., Unadkat, J. & Garrett, S. J. 2020 Analysis of boundary layer flow over a broad rotating cone in still fluid with non-stationary modes. Physics of Fluids. 32(12), 124118.
 Mathews, J.R. & Peake, N. 2018 The acoustic Green's function for swirling flow with variable entropy in a lined duct, J. Sound & Vibration, 419, 630–653.