Imperial College London

ProfessorJohn ChristosVassilicos

Faculty of EngineeringDepartment of Aeronautics

Professor of Fluid Mechanics
 
 
 
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Contact

 

+44 (0)20 7594 5137j.c.vassilicos

 
 
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Assistant

 

Miss Jackie O'Neill +44 (0)20 7594 5079

 
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Location

 

CAGB 314City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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167 results found

Lamballais E, Dairay T, Laizet S, Vassilicos JCet al., 2019, Implicit/explicit spectral viscosity and large-scale SGS effects, ERCOFTAC Series, Pages: 107-113

© Springer Nature Switzerland AG 2019. In order to investigate the scale-selective influence of SGS on the large scale dynamics, DNS and LES are performed for the Taylor-Green vortex problem. An a priori analysis confirms the interest of the hyperviscous feature at small scale as used in implicit LES, SVV and VMS. However, the assumption of zero SGS dissipation at very large scales is found unrealistic for the high Reynolds number and coarse LES mesh considered. A posteriori analysis shows that SGS modelling based on the assumption of an inviscid cascade leads to a bottleneck effect on the kinetic energy spectrum with a significant underprediction of the total SGS dissipation. The simple addition of a constant eddy viscosity, even targeted to be optimal in terms of SGS dissipation, is unable to give realistic results. To allow accurate predictions by LES, a specific closure that incorporates both the hyperviscous feature (i.e. regularisation) and the expected SGS dissipation at large scales has to be developed.

BOOK CHAPTER

Portela FA, Papadakis G, Vassilicos JC, 2018, Turbulence dissipation and the role of coherent structures in the near wake of a square prism, PHYSICAL REVIEW FLUIDS, Vol: 3, ISSN: 2469-990X

JOURNAL ARTICLE

Yasuda T, Vassilicos JC, 2018, Spatio-temporal intermittency of the turbulen energy cascade, JOURNAL OF FLUID MECHANICS, Vol: 853, Pages: 235-252, ISSN: 0022-1120

JOURNAL ARTICLE

Basbug S, Papadakis G, Vassilicos JC, 2018, Reduced mixing time in stirred vessels by means of irregular impellers, PHYSICAL REVIEW FLUIDS, Vol: 3, ISSN: 2469-990X

JOURNAL ARTICLE

Melina G, Bruce PJK, Nedic J, Tavoularis S, Vassilicos JCet al., 2018, Heat transfer from a flat plate in inhomogeneous regions of grid-generated turbulence, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, Vol: 123, Pages: 1068-1086, ISSN: 0017-9310

JOURNAL ARTICLE

Paul I, Papadakis G, Vassilicos JC, 2018, Direct numerical simulation of heat transfer from a cylinder immersed in the production and decay regions of grid-element turbulence, JOURNAL OF FLUID MECHANICS, Vol: 847, Pages: 452-488, ISSN: 0022-1120

JOURNAL ARTICLE

Zheng S, Bruce PJK, Graham JMR, Vassilicos JCet al., 2018, Weakly sheared turbulent flows generated by multiscale inhomogeneous grids, JOURNAL OF FLUID MECHANICS, Vol: 848, Pages: 788-820, ISSN: 0022-1120

JOURNAL ARTICLE

Srinath S, Vassilicos JC, Cuvier C, Laval J-P, Stanislas M, Foucaut J-Met al., 2018, Attached flow structure and streamwise energy spectra in a turbulent boundary layer, PHYSICAL REVIEW E, Vol: 97, ISSN: 2470-0045

JOURNAL ARTICLE

Paul I, Papadakis G, Vassilicos C, DNS of heat transfer from a cylinder immersed in the production and decayregions of grid-element turbulence, Journal of Fluid Mechanics, ISSN: 0022-1120

The present DNS study, the first of its kind, explores the effect that the location of a cylinder, immersed in the turbulent wake of a grid-element, has on heat transfer. An insulated single square grid-element is used to generate the turbulent wake upstream of the heated circular cylinder. Due to fine-scale resolution requirements, the simulations are carried out for a low Reynolds number. Three locations downstream of the gridelement, inside the production, peak and decay regions, respectively are considered. The turbulent flow in the production and peak regions is highly intermittent, non-Gaussian and inhomogeneous, while it is Gaussian, homogeneous, and fully-turbulent in the decay region. The turbulence intensities at the location of the cylinder in the production and decay regions are almost equal at 11%, while the peak location has the highest turbulent intensity of 15%. A baseline simulation of heat transfer from the cylinder without oncoming turbulence was also performed. Although the oncoming turbulent intensities are similar, the production region increases the stagnation point heat transfer by 63%, while in the decay region it is enhanced by only 28%. This difference cannot be explained only by the increased approaching velocity in the production region. The existing correlations for the stagnation point heat transfer coefficient are found invalid for the production and peak locations, while they are satisfied in the decay region. It is established that the flow in the production and peak regions is dominated by shedding events, in which the predominant vorticity component is in the azimuthal direction. This leads to increased heat transfer from the cylinder, even before vorticity is stretched by the accelerating boundary layer. The frequency of oncoming turbulence in production and peak cases also lies close to the range of frequencies that can penetrate the boundary layer developing on the cylinder, and therefore the latter is very responsive to the impinging d

JOURNAL ARTICLE

Basbug S, Papadakis G, Vassilicos JC, 2018, Reduced power consumption in stirred vessels by means of fractal impellers, AICHE JOURNAL, Vol: 64, Pages: 1485-1499, ISSN: 0001-1541

JOURNAL ARTICLE

Paul I, Papadakis G, Vassilicos JC, 2018, Evolution of passive scalar statistics in a spatially developing turbulence, PHYSICAL REVIEW FLUIDS, Vol: 3, ISSN: 2469-990X

JOURNAL ARTICLE

Dairay T, Lamballais E, Laizet S, Vassilicos JCet al., 2018, Physical Scaling of Numerical Dissipation for LES, DIRECT AND LARGE-EDDY SIMULATION X, Vol: 24, Pages: 149-155, ISSN: 1382-4309

JOURNAL ARTICLE

Diaz-Daniel C, Laizet S, Vassilicos JC, 2017, Direct numerical simulations of a wall-attached cube immersed in laminar and turbulent boundary layers, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW, Vol: 68, Pages: 269-280, ISSN: 0142-727X

JOURNAL ARTICLE

de la Cruz JMG, Vassilicos JC, Rossi L, 2017, Statistical independence of the initial conditions in chaotic mixing, PHYSICAL REVIEW E, Vol: 96, ISSN: 2470-0045

JOURNAL ARTICLE

Steiros K, Bruce PJK, Buxton ORH, Vassilicos JCet al., 2017, Effect of blade modifications on the torque and flow field of radial impellers in stirred tanks, PHYSICAL REVIEW FLUIDS, Vol: 2, ISSN: 2469-990X

JOURNAL ARTICLE

Portela FA, Papadakis G, Vassilicos JC, 2017, The turbulence cascade in the near wake of a square prism, JOURNAL OF FLUID MECHANICS, Vol: 825, Pages: 315-352, ISSN: 0022-1120

JOURNAL ARTICLE

Zhou Y, Vassilicos JC, 2017, Related self-similar statistics of the turbulent/non-turbulent interface and the turbulence dissipation, JOURNAL OF FLUID MECHANICS, Vol: 821, Pages: 440-457, ISSN: 0022-1120

JOURNAL ARTICLE

Melina G, Bruce PJK, Hewitt GF, Vassilicos JCet al., 2017, Heat transfer in production and decay regions of grid-generated turbulence, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, Vol: 109, Pages: 537-554, ISSN: 0017-9310

JOURNAL ARTICLE

Basbug S, Papadakis G, Vassilicos JC, 2017, DNS investigation of the dynamical behaviour of trailing vortices in unbaffled stirred vessels at transitional Reynolds numbers, PHYSICS OF FLUIDS, Vol: 29, ISSN: 1070-6631

JOURNAL ARTICLE

Dairay T, Lamballais E, Laizet S, Vassilicos JCet al., 2017, Numerical dissipation vs. subgrid-scale modelling for large eddy simulation, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 337, Pages: 252-274, ISSN: 0021-9991

JOURNAL ARTICLE

Diaz-Daniel C, Laizet S, Vassilicos JC, 2017, Wall shear stress fluctuations: Mixed scaling and their effects on velocity fluctuations in a turbulent boundary layer, PHYSICS OF FLUIDS, Vol: 29, ISSN: 1070-6631

JOURNAL ARTICLE

Paul I, Papadakis G, Vassilicos JC, 2017, Genesis and evolution of velocity gradients in near-field spatially developing turbulence, JOURNAL OF FLUID MECHANICS, Vol: 815, Pages: 295-332, ISSN: 0022-1120

JOURNAL ARTICLE

Laval J-P, Vassilicos JC, Foucaut J-M, Stanislas Met al., 2017, Comparison of turbulence profiles in high-Reynolds-number turbulent boundary layers and validation of a predictive model, JOURNAL OF FLUID MECHANICS, Vol: 814, ISSN: 0022-1120

JOURNAL ARTICLE

Steiros K, Bruce PJK, Buxton ORH, Vassilicos JCet al., 2017, Power consumption and form drag of regular and fractal-shaped turbines in a stirred tank, AICHE JOURNAL, Vol: 63, Pages: 843-854, ISSN: 0001-1541

JOURNAL ARTICLE

Dairay T, Vassilicos JC, 2016, Direct numerical simulation of a turbulent wake: The non-equilibrium dissipation law, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW, Vol: 62, Pages: 68-74, ISSN: 0142-727X

JOURNAL ARTICLE

Goto S, Vassilicos JC, 2016, Unsteady turbulence cascades, PHYSICAL REVIEW E, Vol: 94, ISSN: 2470-0045

JOURNAL ARTICLE

Obligado M, Dairay T, Vassilicos JC, 2016, Nonequilibrium scalings of turbulent wakes, PHYSICAL REVIEW FLUIDS, Vol: 1, ISSN: 2469-990X

JOURNAL ARTICLE

Melina G, Bruce PJK, Vassilicos JC, 2016, Vortex shedding effects in grid-generated turbulence, PHYSICAL REVIEW FLUIDS, Vol: 1, ISSN: 2469-990X

JOURNAL ARTICLE

Alves Portela F, Papadakis, Vassilicos, Scale by scale energy budget in the near wake of a square cylinder, XXIV ICTAM

We study the energy cascade downstream of, but close to, a square cylinder Re = 3900 using two-point statistics, by means of DNS. Shortly after the mean recirculation region the turbulent energy spectrum exhibits a near −5/3 slope in the frequency domain. Our DNS analysis of the general Kármán-Howarth-Monin equation show that the production, transport, advection and fluctuating pressure terms cannot be neglected as they are in the Richardson-Kolmogorov equilibrium theory. Even so, the term which is interpreted as an interscale energy flux divergence in the case of homogeneous turbulence is close to −ε over a significant range of small scales, where ε is the turbulence dissipation rate.

CONFERENCE PAPER

Boschung J, Peters N, Laizet S, Vassilicos JCet al., 2016, Streamlines in stationary homogeneous isotropic turbulence and fractal-generated turbulence, FLUID DYNAMICS RESEARCH, Vol: 48, ISSN: 0169-5983

JOURNAL ARTICLE

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