Speaker: Professor Jonathan Morrison, Imperial College
Research Centre: Research Centre for Fluid Dynamics, Turbulance and Flow Control Group
Title: Bluff Body Wake Control
The low-dimensional dynamics of a turbulent axisymmetric wake are examined by using the base pressure. It is shown that the most energetic structures retain the symmetry-breaking properties of laminar instabilities and appear as unsteady vortex shedding. On a very long timescale, the wake also exhibits a wholesale random rotation, such that in a rotating frame of reference, the shedding preserves reflectional symmetry apparent in the laminar instabilities. The base pressure can be increased by as much as 33% by the use of a high-frequency periodic jet issuing immediately below the point of separation. This phenomenon is explained by reference to the Poisson equation for pressure fluctuations. The use of base pressure for feedback control on an Ahmed car body is briefly outlined. In particular, it is shown that, by the use of flaps, the instability of the rectilinear wake may be controlled and, using a Fokker-Planck model to describe the phenomenon of instability illustrated on the axisymmetric model.
Professor Jonathan Morrison holds the chair of Experimental Fluid Mechanics in the Department of Aeronautics at Imperial College. He received his PhD from the University of Durham and became a member of faculty at Imperial College in 1991. His recent work has focused on fundamentals of wall turbulence including coherent structures and their relation to changes in imposed length-scale, energy transfer and pressure fluctuations. Novel approaches to flow control involve Electro-Active Polymers (EAP) both as actuators and as surface-pressure sensors, including ink-jet printing techniques. Travelling surface waves for drag reduction are being developed with support from Airbus, and QinetiQ. Recent work involves fundamental studies of the effects of large roughness on turbulent channel flow and turbulent boundary layers and instabilities as part of the LFC-UK Programme Grant. He is also Co-investigator on an EPSRC Programme Grant (partly funded by Rolls Royce) investigating turbine blade film cooling with highly porous surfaces. Previously, he has been Visiting Fellow at MAE, Princeton University. He is currently a member of the Aerodynamics Specialist Advisory Group of the ATI and sits on the advisory board of the UK Turbulence Consortium. He chairs the Management Board of the National Wind Tunnel Facility, funded by EPSRC and the ATI.
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When and where
3.00pm - 4.00pmFriday 24th March 2017