Imperial College London

DrGeorgePapadakis

Faculty of EngineeringDepartment of Aeronautics

Reader in Aerodynamics
 
 
 
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Contact

 

+44 (0)20 7594 5080g.papadakis

 
 
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Location

 

331City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

68 results found

Xiao D, Papadakis G, 2018, Nonlinear optimal control of transition due to a pair of vortical perturbations using a receding horizon approach, JOURNAL OF FLUID MECHANICS, Vol: 861, Pages: 524-555, ISSN: 0022-1120

JOURNAL ARTICLE

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

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

Gallis MA, Torczynski JR, Bitter NP, Koehler TP, Plimpton SJ, Papadakis Get al., 2018, Gas-kinetic simulation of sustained turbulence in minimal Couette flow, PHYSICAL REVIEW FLUIDS, Vol: 3, ISSN: 2469-990X

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

© 2018 Cambridge University PressÂ. The present direct numerical simulation (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 grid-element, 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 11Â %, while the peak location has the highest turbulence intensity of 15Â %. 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 63Â %, while in the decay region it is enhanced by only 28Â %. 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

JOURNAL ARTICLE

Thomareis N, Papadakis G, 2018, Resolvent analysis of separated and attached flows around an airfoil at transitional Reynolds number, PHYSICAL REVIEW FLUIDS, Vol: 3, ISSN: 2469-990X

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

Jones G, Santer M, Debiasi M, Papadakis Get al., 2018, Control of flow separation around an airfoil at low Reynolds numbers using periodic surface morphing, JOURNAL OF FLUIDS AND STRUCTURES, Vol: 76, Pages: 536-557, ISSN: 0889-9746

JOURNAL ARTICLE

Jones G, Santer M, Papadakis G, 2018, Control of low Reynolds number flow around an airfoil using periodic surface morphing: A numerical study, JOURNAL OF FLUIDS AND STRUCTURES, Vol: 76, Pages: 95-115, ISSN: 0889-9746

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

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

Xiao D, Papadakis G, 2017, Nonlinear optimal control of bypass transition in a boundary layer flow, 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

Gallis MA, Bitter NP, Koehler TP, Torczynski JR, Plimpton SJ, Papadakis Get al., 2017, Molecular-Level Simulations of Turbulence and Its Decay, PHYSICAL REVIEW LETTERS, Vol: 118, ISSN: 0031-9007

JOURNAL ARTICLE

Thomareis N, Papadakis G, 2017, Effect of trailing edge shape on the separated flow characteristics around an airfoil at low Reynolds number: A numerical study, PHYSICS OF FLUIDS, Vol: 29, ISSN: 1070-6631

JOURNAL ARTICLE

Papadakis G, Lu L, Ricco P, 2016, Closed-loop control of boundary layer streaks induced by free-stream turbulence, PHYSICAL REVIEW FLUIDS, Vol: 1, ISSN: 2469-990X

JOURNAL ARTICLE

, 2016, Active flow control at low Reynolds numbers by periodic airfoil morphing

© 2016, (publisher Name). All rights reserved. This paper investigates the application of a periodically deforming airfoil surface for the purpose of flow control at low Reynolds numbers. A physical model has been fabricated by bonding Macro Fiber Composite (MFC) actuators to the underside of a NACA 4415 airfoil's suction surface. The results presented build on earlier work by Jones et al.1First, the behavior of the surface when actuated at a range frequencies is investigated through a combination of photogrammetric and laser sensor measurements. Second, the aerodynamic performance of this novel flow control technique is presented. It is shown that when the shear layer frequency ‘locks-in' to the surface motion significant improvements in performance are observed in a flight regime notorious for poor airfoil behavior.

CONFERENCE PAPER

, 2015, Open-loop flow control at low reynolds numbers using periodic airfoil morphing

© 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. This paper investigates the application of a periodically deforming airfoil surface for the purpose of flow control at low Reynolds numbers. A physical model has been fabricated by bonding Macro Fiber Composite actuators to the underside of an airfoil’s suction surface. This model is actuated using a high voltage amplifier and has been tested in a closed-loop wind tunnel at Rec = 5 × 104. It was found that at high enough actuation frequencies such a control technique reduces drag and simultaneously increases lift { thus achieving signif- icant improvements in performance in a flight regime notorious for poor airfoil behavior. Furthermore, by delaying the onset of stall, actuation was able to increase the maximum lift achievable by this airfoil section at Rec = 5 × 104which can be of benefit to small aircraft at take-off and landing where high lift coeffcients are required.

CONFERENCE PAPER

Lu L, Papadakis G, 2014, An iterative method for the computation of the response of linearised Navier-Stokes equations to harmonic forcing and application to forced cylinder wakes, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Vol: 74, Pages: 794-817, ISSN: 0271-2091

JOURNAL ARTICLE

Papadakis G, 2014, Wave Propagation in Tapered Vessels: New Analytic Solutions That Account for Vessel Distensibility and Fluid Compressibility, JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME, Vol: 136, ISSN: 0094-9930

JOURNAL ARTICLE

Whidborne JF, Lu L, Papadakis G, Ricco Pet al., 2014, Performance Limits for Control of Boundary Layer Streaks Induced by Free Stream Turbulence, 19th World Congress of the International-Federation-of-Automatic-Control (IFAC), Publisher: ELSEVIER SCIENCE BV, Pages: 7007-7012, ISSN: 2405-8963

CONFERENCE PAPER

Papadakis G, 2014, WAVE PROPAGATION IN TAPERED VESSELS: NEW ANALYTIC SOLUTIONS THAT ACCOUNT FOR VESSEL DISTENSIBILITY AND FLUID COMPRESSIBILITY, ASME Pressure Vessels and Piping Conference (PVP-2013), Publisher: AMER SOC MECHANICAL ENGINEERS

CONFERENCE PAPER

Pinto JMDR, Ricco P, Papadakis G, 2014, Wall-transpiration feedback control of laminar streaks using an adjoint approach, United-Kingdom-Automatic-Control-Council (UKACC) 10th International Conference on Control (CONTROL), Publisher: IEEE, Pages: 209-213

CONFERENCE PAPER

Lu L, Agostini L, Ricco P, Papadakis Get al., 2014, Optimal state feedback control of streaks and Gortler vortices induced by free-stream vortical disturbances, United-Kingdom-Automatic-Control-Council (UKACC) 10th International Conference on Control (CONTROL), Publisher: IEEE, Pages: 214-219

CONFERENCE PAPER

Papadakis G, 2011, New analytic solutions for wave propagation in flexible, tapered vessels with reference to mammalian arteries, JOURNAL OF FLUID MECHANICS, Vol: 689, Pages: 465-488, ISSN: 0022-1120

JOURNAL ARTICLE

Lu L, Papadakis G, 2011, Investigation of the effect of external periodic flow pulsation on a cylinder wake using linear stability analysis, PHYSICS OF FLUIDS, Vol: 23, ISSN: 1070-6631

JOURNAL ARTICLE

Zhang H, Papadakis G, 2010, Computational analysis of flow structure and particle deposition in a single asthmatic human airway bifurcation, JOURNAL OF BIOMECHANICS, Vol: 43, Pages: 2453-2459, ISSN: 0021-9290

JOURNAL ARTICLE

Papadakis G, 2010, Linear Stability Analysis and Buckling of Two-Layered Shells Under External Circumferential Loading: A Numerical Investigation, JOURNAL OF PRESSURE VESSEL TECHNOLOGY-TRANSACTIONS OF THE ASME, Vol: 132, ISSN: 0094-9930

JOURNAL ARTICLE

Papadakis G, 2010, BUCKLING SENSITIVITY ANALYSIS AND OPTIMAL DESIGN OF TWO-LAYERED SHELLS UNDER CIRCUMFERENTIAL STRAIN LOAD, ASME Pressure Vessels and Piping Division/K-PVP Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 763-770

CONFERENCE PAPER

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