Photo of Professor Vassilios Theofilis

Professor Vassilios Theofilis

Chair in Aerospace Engineering Mechanical, Materials & Aerospace Eng

Research

Flow Physics and Control of 3-D Separation on 3-D Swept Wings

A closely coupled theoretical/numerical/experimental fundamental research is underway, aiming at understanding and characterizing the physical mechanisms that lead to the formation of large-scale 3-D separation structures on finite span swept back wings, as well as the dynamical evolution of these structures as a function of the following geometrical and flow parameters. Work at the University of Liverpool deals with theoretical aspects of this collaborative effort, undertaken together with two US institutions, Rensselaer Polytechnic Institute (RPI, Troy, NY), whose Principal Investigator is Prof. M. Amitay, in charge of the experimental aspects at low- and high-Re, as well as experimental flow control, and Florida State University (FSU, Tallahassee, FL), with Principal Investigator Prof. Kunihiko Taira, in charge of high-fidelity large-scale computations. The findings from this study are anticipated to provide guidance on improving aerodynamic performance of future-generation air vehicles at high-angles of attack.

Instability Analysis of Laminar Separation Bubbles in Supersonic Flow

A combined global modal and non-modal analysis of linear instability mechanisms arising in the separation zone formed by the interaction of a shock system with a nominally spanwise homogeneous laminar boundary layer and a finite-angle wedge in supersonic flow is underway at the University of Liverpool, in parallel with detailed high-fidelity large-eddy simulations of the same configuration, which take place at the University of Maryland, USA, under the direction of Prof. Pino Martin. The objective of the proposed effort is to discover unifying characteristics in the different classes of instabilities present in these flows, and reach closure in the long-standing debate regarding the origin of low-frequency oscillations appearing and limiting performance in systems in supersonic and hypersonic motion.

DSMC simulations and stability analyses of shock-dominated separated hypersonic flows

Shock-dominated hypersonic laminar flows over a double cone are investigated in a collaborative effort with Prof. Deborah Levin of the University of Illinois Urbana Champaign, USA, using a combination of time accurate Direct Simulation Monte Carlo (DSMC) methods with the residuals algorithm of global linear theory, at unit Reynolds numbers in the range of 1e5 [1/m] at Mach 16. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region, exhibit unsteadiness which has been analyzed by global linear theory. It is found that the laminar separation zone localised at the cone junction and the entire shock system are synchronised in their motion, which can be described as a temporally decaying global mode. As the Reynolds number increases, a Kelvin-Helmholtz instability arising at the shear layer in the post-shock region undergoes linear amplification. Results obtained provide guidance regarding the necessary time that needs to elapse during experimentation at these conditions, for reliable determination of surface properties such as heat transfer through the wall.

Research Collaborations

Miki Amitay

Project: Flow Physics and Control of 3-D Separation on 3-D Swept Wings (2017-2020), Flow Physics of Stall-and Separation Cells and Their Control (2013-2017)
External: Rennselaer Polytechnic Institute, Troy, NY, USA (https://faculty.rpi.edu/node/35848)

US Air Force Office of Scientific Research, FA9550-17-1-0222
US Air Force Office of Scientific Research, FA9550-13-1-0059

Hugh Blackburn

Project: Instability and Control of Massively Separated Flows (2010-2012)
External: Monash University, Melbourne, Australia (https://research.monash.edu/en/persons/hugh-blackburn)

EU-FP7-PEOPLE-IRSES-ICOMASEF-GA-247651

Tim Colonius

Project: A Unified View of Global Instability of Compressible Flow over Open Cavities (2003-2006)
External: California Institute of Technology, USA (http://colonius.caltech.edu)

European Office of Aerospace Research and Development, FA8655-03-1-3059

Rama Govindarajan

Project: Instability and Control of Massively Separated Flows (2010-2012)
External: International Centre for Theoretical Sciences Bangalore, India (https://en.wikipedia.org/wiki/Rama_Govindarajan)

EU-FP7-PEOPLE-IRSES-ICOMASEF-GA-247651

Deborah Levin

Project: Prediction and analysis of hypersonic flow instabilities
External: University of Illinois at Urbana Champaign, IL, USA (https://aerospace.illinois.edu/directory/profile/deblevin)

Direct Simulation Monte Carlo (DSMC) and global instability analyses of unsteady, laminar shock-dominated separated flows at hypersonic speeds

Marcello F. A. de Medeiros

Project: CNPq Ciência Sem Fronteiras (2012-2015)
External: Universidade São Paulo, Brasil (http://www5.eesc.usp.br/saa/index.php?option=com_comprofiler&task=userprofile&user=89&Itemid=176)

Brasil, CNPq Grant 401605/2012-4

Julio R Meneghini

Project: Instability and Control of Massively Separated Flows (2010-2012)
External: Universidade São Paulo, Brasil (http://www.rcgi.poli.usp.br/professor-julio-meneghini/)

EU-FP7-PEOPLE-IRSES-ICOMASEF-GA-247651

Spencer Sherwin

Project: Global instability of Low Pressure Turbine Flows (2003-2006)
External: Imperial College London, UK (https://www.imperial.ac.uk/people/s.sherwin)

US Air Force Office of Scientific Research

Julio Soria

Project: Impinging supersonic jets: instabilities and control I (2012-2015) & II (2016-2018)
External: Monash University, Melbourne, Australia (https://www.monash.edu/engineering/juliosoria)

Australian Research Council, DP130104003
also: EU-FP7-PEOPLE-IRSES-ICOMASEF-GA-247651

Bruno Wiesler

Project: Fly High (2012-2013)
External: Fachhochschule Joanneum

EU Lifelong Learning Program 518156-LLP-1-2011-1-AT-COMENIUS-CMP

Sam Taira

Project: Flow Physics and Control of 3-D Separation on 3-D Swept Wings (2017-2020)
External: Florida State University, Tallahassee, FL, USA (http://www.eng.fsu.edu/~ktaira/group.html)

US Air Force Office of Scientific Research, FA9550-17-1-0222

Pino Martin

Project: Global Modal and Non-Modal Instability Analyses of Shock-Induced Separation Bubbles (2016-2019)
External: University of Maryland, USA (https://aero.umd.edu/faculty/martin)

US Air Force Office of Scientific Research