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Dr Sotos Generalis

Turbulence, chaos or order? - Their source and role in dynamics
British Science Festival event: Find out about the complicated world of turbulent flow. See how we try to unravel its secrets and what we can learn about its structure from simulations.

Phone number
0121 204 3639  

Email
S.C.Generalis@aston.ac.uk 

Key publication

Hairpin vortex solution in planar Couette flow: A tapestry of knotted voices, made the front page of the Physical Review Letters, which is the publication of choice to announce the most important findings in high-energy physics from the whole world.
View the press release

Research

Dr Sotos Generalis's research concentrates on the numerical solution of the strongly non-linear Navier-Stokes equations as applied to the stability problems concerning incompressible plane-parallel shear flows.

The non-linear Navier-Stokes equations are solved with the aid of a Galerkin-type technique in order to identify the hierarchical transition to turbulence. The (generalized) case of transition of fluid flow patterns from the laminar stage to the early stages of the turbulent regime in plane parallel shear flows is a major subject in the fluid dynamics research because of its considerable importance to applications in engineering and geophysics.

Theoretical investigations aided by the advance of powerful hardware coupled by parallel experimental studies of plane parallel shear flows have provided significant insights in identifying the transition mechanisms from laminar to turbulent flow. Recent work on the strongly non-linear studies of Couette flow have appeared on the cover issue of the Physical Review Letters.

Dr Generalis has also worked in the application of computational fluid dynamical techniques to a variety of problems in polymer processing, complex reaction mechanisms and reactor design.

Recent awards

Transition to Turbulence in Ventilated Double Glazing

Project Acronym: T2T-VDG 
Project status: Indicative start date December 2012
Programme type: Seventh Framework Programme 
Subprogramme Area:Marie-Curie Action: "International Incoming Fellowship" 
Contract type:International Incoming Fellowships (IIF) 
Marie-Curie Intra-European Fellow: Dr Takeshi Akinaga.

Objective: Pioneering numerical techniques, that have not been employed before concurrently, are proposed in this project. They can capture the transition to turbulence of shear flow and in the process offer the capability of proposing methods for the state of the art control of such transitions. The proposed methods can enhance the calculation of fluid flow by identifying the hierarchical bifurcation of the evolving states and can be captured in an engineering orientated software (computational) tool that will aid the real life implementation of these, otherwise, generalised but tried mathematical techniques. In this sense the predictive power of the underlying mathematical modelling techniques, upon which the engineering tool will be crucially dependent, will display their true potential. The novel methods can be used to pinpoint the transition of the flow from its laminar (basic) state to its fully developed (turbulent) state with pinpoint accuracy and for arbitrary geometrical configurations. The ensuing stability analysis will be a unique attribute of this mathematically engineered software.

Our software, in brief, that unifies the above mentioned techniques, will be able to oversee the development of the fluid flow throughout its evolution, from birth to turbulent arrival. It is the ultimate aim of this set of programmes to apply the resulting software to complex configurations applicable to a variety of every day engineering configurations. Simple geometries will be considered at first to act as benchmarks and common ground for the two different state of the art software avenues at our disposal: the proprietary code developed at Aston University and a commercially available CFD code. We intend to use the results of our studies for the design and industrial implementation of a new concept that is at the heart of European energy, environment and socioeconomic focus: ventilated double glazing.

Transition to Turbulence of Volumetrically Heated Flows

Project Acronym: T2T-VHF
Project status: Commencing January 2012
Programme type: Seventh Framework Programme
Subprogramme Area:Marie-Curie Action: "Intra-European fellowships for career development"
Contract type:Intra-European Fellowships (IEF)
Marie-Curie Intra-European Fellow: Dr Gregory Cartland Glover.

Objective: Numerical techniques are proposed that can capture the transition to turbulence of shear flow and in the process they offer the capability of state of the art control of such transitions. The methods can enhance the calculation of fluid flow by identifying the hierarchical bifurcation of the evolving states. Thus, the predictive power of the underlying mathematical models is strengthened. Concurrently they offer the unique possibility of unifying the results with those obtained by techniques that are developed with the sole aim of capturing the fully developed turbulent state.

We intend to use the results of our studies to be applicable to the Nuclear Industry to model regime transition in complex systems where molten metal, molten salt and water are used as the coolant. Operating regimes of interest include the thermo-hydraulic behaviour of the coolant in reactors undergoing passive decay heat removal. Meteorological and geological applications will also be considered as a by-product of our studies.

Leverhulme Trust Research Grant

The intermediate particle flow: multiscale experiments and modelling

with Dr Yassir Makkawi (PI) and Professor Rafaela Ocone (CI)

Aims and Objectives of the Award:
The aim of this proposal is twofold; firstly, we intend to carry out experiments to obtain three-dimensional detailed information on the particle dynamics in wet and dry flow conditions, with particular focus on the intermediate and dense flow regimes. Secondly, by reassessing the existing theories on particles frictional and collisional interactions and by interpreting the experimental data taken, we plan to deduce a constitutive equation for the solid stresses at the intermediate flow regime in dry and slightly wet conditions, allowing for smooth merge of rapid-intermediate-dense flow regimes.
 
To achieve these aims, we propose to develop a state of the art apparatus to collect experimental data on particle dynamics; the experimental data, whilst contributing to an area where good data are scarce, will be used to model the solid stresses and validate the proposed model in a variety of flow conditions relevant to industrial applications.
 
The specific detailed objectives of the experimental part are:
  • To build a world class experimental facility for solid-gas flow that allows for the collection of precise data under different flow conditions, ranging from rapid transport to slow frictional flow in dry and slightly wet conditions;
  • To measure the particles’ concentration distribution, velocity and stresses for dry and slightly wet particle flow, with emphasis on the transition from the solid-like behaviour to the liquid-like behaviour;
  • To propose simple interpretations and mapping of the intermediate regime and identify its boundaries.
The specific detailed objectives of the theoretical part are:
  • To develop constitutive equations for the particle stress tensor that allows for smooth merge of different flow regimes.
  • To incorporate/validate the developed constitutive relations in a two-fluid computational model that is capable of predicting the complex hydrodynamics of dry and slightly wet particle flow in a number of relevant to industrial applications.

Royal Academy of Engineering Distinguished Fellowship Scheme

Professor Fujimura, (Tottori University, Japan)

Duration: One month (March 2012)
Prof Fujimura has developed techniques for establishing bifurcating secondary flow, responsible for the momentum and mass transfer in the channel of fluid flow, that are powerful devices applicable in the vicinity of the stability boundary of the laminar shear flow.
This technique will be combined with the fully non-linear programmes that exist at the involved.host Institution. This will create a new generation of programmes that will in turn incubate graduates to become engineers that have intimate knowledge of the mechanisms.


Selected publications


S.C. Generalis and T. Itano, 2010. Characterization of the hairpin vortex solution in plane Couette flow, Physical Review E, volume 82, 066308.

Symmetry of coherent Vortices in Plane Couette Flow, September 2009
By T. Itano, S. Generalis, S.Toh, J. Fletcher, European Turbulence Conference.

Range of validity of weakly nonlinear theory in the Rayleigh-Benard problem,

By Sotos Constantinou Generalis and Kaoru Fujimura, Journal of the Physical Society of Japan
Volume 78, no8, August 2009, 084401

Transition in Inclined Internally Heated Fluid Layers, 2008
By SC Generalis and FH Busse
Eurotherm 74, H.C.de Lange and A.A.Steenhoven, editors, FCV10

Pattern competition in homogeneously heated fluid layers,
By Gregory Cartland Glover and Sotos Constantinou Generalis, Engineering Applications of Computational Fluid Mechanics
Volume 3, No. 2, pp. 164–174, March 2009.

Generalis, S. & CartlandGlover, G. 2008, ”Homogeneously Heated Shear Flows”, Eurotherm 74, H.C.de Lange and A.A.Steenhoven, editors, FCV5.

Generalis, S. C., Cartland Glover, G. M. (2005). Modelling a biochemical reaction with computational fluid dynamics, International Journal of Chemical Reactor Engineering, Vol. 3: A50

Cartland Glover, G. M., Generalis, S. C., (2004). The modelling of buoyancy driven flow in bubble columns, Chemical Engineering and Processing 43(2), 101-115.

Cartland Glover, G. M., Generalis, S. C., (2004). Gas–liquid–solid flow modelling in a bubble column, Chemical Engineering and Processing 43(2), 117-126.

Blazej, M.(a), Cartland Glover, G.M.(b), Generalis, S.C.(b), & Markos, J.(a)*.  "Gas-Liquid Simulation of an Airlift Bubble Column Reactor". (a) Slovak Technical University, Slovak Republic. (b) Aston University, UK.  Chemical Engineering & Processing, 43, 2004, 137-144. {rated (number 20) in the list of Top 25 Papers published in this journal}

Nagata, M (a) & Generalis, S (b).  "Transition in Homogeneously Heated Inclined Plane Parallel Shear Flows". (a) Kyoto University, Japan. (b) Aston University, UK. Journal of Heat Transfer, 125, 795-803.

Nagata, M (a) & Generalis, S (b).  "Transition in Plane Parallel Shear Flows Heated Internally".  (a) Kyoto University, Japan. (b) Aston University, UK.  C. R. Mecanique, 332, 2004, 9-16.

Cartland Glover, G.M. & Generalis, S.*.  "Gas-Liquid-Solid Flow Modelling in a bubble Column".  Aston University, UK.  Chemical Engineering & Processing, 43, 2004, 117-126.

Cartland Glover, G. M., Blažej, M., Generalis, S. C., Markoš, J., (2003). Three-dimensional gas-liquid simulation of an airlift bubble column reactor, Chemical Papers, 57, 387-392.

Nagata, M (a) & Generalis, S (b).  "Transition in Convective Flows Heated Internally". (a) Kyoto University, Japan. (b) Aston University, UK.  Journal of Heat Transfer, 124, 2002, 635-642.

Cartland Glover, G. M., Generalis, S. C., Thomas, N. H., (2001). Three-phase flow in bubble columns, Chemical Engineering Technology 73, 753.

Cartland Glover, G. M., Generalis, S. C., Thomas, N. H., (2000). CFD and bubble column reactors: simulation and experiment, Chemical Papers 54, 361.