15th European Turbulence Conference 2015
August 25-28th, 2015, Delft, The Netherlands

Invited speakers:

Prof. Marc Brachet. Ecole Normale Superieure, Paris, France

Prof. Peter G. Frick, Institute of Continuous Media Mechanics, Perm, Russia

Prof. Bettina Frohnapfel,  Karlsruher Institut fur Technology, Germany

Prof. Andrea Mazzino, Dipartimento di Fisica, University of Genova, Italy

Prof. Bernhard Mehlig. Department of Physics, University of Gothenburg, Sweden

Prof. Lex Smits, Mechanical and Aerospace Engineering, Princeton University, USA

Prof. Chao Sun Physics of Fluids, University of Twente, The Netherlands

Prof. Steve Tobias, Applied Mathematics, University of Leeds, United Kingdom

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15:00   Jets and Wakes 2
Chair: bendiks boersma
15 mins
Giorgia Sinibaldi, Francesco Battista, Paolo Gualtieri, Luca Marino, Giovanni Paolo Romano, Carlo Massimo Casciola
Abstract: Experimental and Direct Numerical Simulation data of a turbulent round jet fed by a turbulent pipe are compared in the near field. The Reynolds number achieved in both the experiment and the simulation, Re = 16000, allows a direct comparison of both the average and the fluctuating velocity statistics. In the experiments the jet is fed with olive oil droplets with a Stokes number St ' 1 whose dynamics is compared against the corresponding DNS simulation to asses the ability of particles to reproduce high order turbulence statistics and to asses the accumulation properties of inertial particles in the near field.
15 mins
Low Reynolds Number Effects on Jets from Round, Square and Elliptical Orifices
Seyed Sobhan Aleyasin, Mark Tachie, Mike Koupriyanov, Tom Epp
Abstract: An experimental study was undertaken to investigate low Reynolds number effects on mixing characteristics and turbulent transport phenomena in the near and intermediate regions of free orifice jets. The cross-sections examined were round, square and ellipse of aspect ratio 3. For each orifice cross-section, detailed velocity measurements were obtained at the following 4 Reynolds number based on the equivalent diameter and maximum velocity: 2500, 4300, 8500 and 17000. A high resolution particle image velocimetry was used to conduct measurements in the symmetry planes that extend from the exit to 15 equivalent diameters. Preliminary results show that an axis-switching happens at 2.7 equivalent diameters in the case of ellipse nozzle which leads to a higher spread rate compared to square and round ones. Also increase in Reynolds number decreases the jet widths.
15 mins
Direct numerical simulation of the flow around a wing section at moderate Reynolds numbers
Seyed Mohammad Hosseini, Ricardo Vinuesa, Philipp Schlatter, Ardeshir Hanifi, Dan Henningson
Abstract: A three dimensional direct numerical simulation has been performed to study the flow around the asymmetric NACA-4412 wing at a moderate chord Reynolds number (Rec = 400, 000) with an angle of attack of 5◦ . The flow case under investigation poses numerous challenges for a numerical method due to the wide range of scales and complicated flow physics induced by the geometry. The mesh is optimized and well resolved to account for such varying scales in the flow. An unsteady volume force is used to trip the flow to turbulence on both sides of the wing at 10% chord. Full turbulent statistics are computed on the fly to further investigate the complicated flow features around the wing. The present simulation shows the potential of high-order methods in simulating complex external flows at moderately high Reynolds numbers.
15 mins
Reynolds number effect on 3D turbulent offset jet reattaching to a free surface
Mohammad Shajid Rahman, Mark Tachie, Baafour Nyantekyi-Kwakye
Abstract: Experimental study was carried out to investigate the effect of Reynolds number on 3D offset jet reattaching to above free surface. Sharp edged square nozzle was used to produce the jets, and the measurements were performed at the following six different Reynolds numbers: 2300, 3700, 5100, 7900, 10300 and 11900. Detailed velocity measurements were made in the symmetry plane. From the PIV data, the mean velocity and turbulence statistics were obtained to study the effects of Reynolds number on the salient features of the jet flow. Preliminary results on streamwise mean velocity decay along the nozzle centerline, contours of streamwise mean velocity and Reynolds shear stress are presented herein.
15 mins
2d-LCA - an alternative to x-wires
Jaroslaw Puczylowski, Joachim Peinke, Michael Hölling
Abstract: The 2d-Laser Cantilever Anemometer (2d-LCA) is an novel anemometer for two-dimensional velocity measurements in fluids. It uses a mico-structured cantilever with a specifically designed tip as a sensing element and is capable of performing measure- ments with extremely high temporal (≈ 100kHz) and spatial (≈ 140μm) resolutions. Another big feature is a large angular range of 180◦ in total. The performance of the 2d-LCA has been verified by means of comparative measurements with commercial x-wires in laboratory-generated turbulent flow. We are able to show that both measurement techniques provide comparable statistics.
15 mins
Turbulent entrainment in jets and plumes
Maarten van Reeuwijk, John Craske
Abstract: We perform direct simulation of a statistically steady jets and plume and present the value of the entrainment coefficient decomposed into 1) turbulence production; 2) buoyancy effects; and 3) deviations from self-similarity. We explain theoretically how the two cases are linked and present a generalisation valid for forced and lazy plumes.
15 mins
Dispersion in unsteady jets and plumes
John Craske, Maarten van Reeuwijk
Abstract: We investigate the transport of both passive and active scalars in fully developed turbulent axisymmetric jets and plumes using data from direct numerical simulation. In both cases we simulate the response of the flow to an instantaneous increase in the scalar flux at the source and our focus is on the determination of the rate at which the resulting disturbance propagates and spreads in the longitudinal direction. We apply Taylor's theory of shear-flow dispersion to free-shear flows and therefore model the way in which departures from self-similarity result in the longitudinal mixing of integral quantities. The resulting integral models exhibit a good agreement with the simulation data and, in the case of passive scalar transport, admit an analytical similarity solution. For the case of active scalar transport we examine the buoyancy flux in an unsteady plume and show that the momentum-energy framework, rather than the classical volume-momentum framework, provides the natural setting from which to view the effects of dispersion. Consequently, we demonstrate the effect that dispersion has on turbulent entrainment and the way in which a plume responds to source perturbations in its buoyancy flux.
15 mins
Hybrid simulation of wake vortices of landing aircraft in a turbulent environment
Anton Stephan, Frank Holzäpfel, Takashi Misaka
Abstract: Wake-vortex evolution during landing of a long range aircraft is investigated in a turbulent environment. The simulations cover final approach, touchdown on the tarmac, and the evolution of the wake after touchdown. An ambient turbulent crosswind and headwind field is generated in a pre-simulation. The wake is initialized using a RANS-LES coupling approach. The further development of the vortical wake is investigated by large-eddy simulation until final decay. Strong three-dimensional deformations appearing after touchdown and linkings with the ground are studied. The downwind vortex is strongly advected with crosswind and decays quickly. The interaction of plate line disturbances and end effects in a turbulent environment leads to irregular decay pattern.