# Publications 32

Here we present a list of publications that were a result of projects funded by EuHIT or were published by members of EuHIT consortium.

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• Article
Drahotský, Jakub; Hanzelka, Pavel; Musilová, Věra; Macek, Michal; du Puits, Ronald; Urban, Pavel
EPJ Web of Conferences. 2018, Vol. 180. DOI: 10.1051/epjconf/201818002020
• Publication URL https://www.epj-conferences.org/articles/epjconf/abs/2018/15/epjconf_efm2018_02020/epjconf_efm2018_02020.html
• Abstract Modelling of large-scale natural (thermally-generated) turbulent flows (such as the turbulent convection in Earth’s atmosphere, oceans, or Sun) is approached in laboratory experiments in the simplified model system called the Rayleigh-Bénard convection (RBC). We present preliminary measurements of vertical temperature profiles in the cell with the height of 4.7 m, 7.15m in diameter, obtained at the Barrel of Ilmenau (BOI), the worldwide largest experimental setup to study highly turbulent RBC, newly equipped with the Luna ODiSI-B optical fibre system. In our configuration, the system permits to measure the temperature with a high spatial resolution of 5 mm along a very thin glass optical fibre with the length of 5 m and seems to be perfectly suited for measurement of time series of instantaneous vertical temperature profiles. The system was supplemented with the two Pt100 vertically movable probes specially designed by us for reference temperature profiles measurements.
• Article
König, Franziska; Zanoun, El-Sayed; Öngüner, Emir; Egbers, Christoph
Review of Scientific Instruments. 2014, Vol. 85, Issue 7. DOI: 10.1063/1.4884717
• Publication URL http://scitation.aip.org/content/aip/journal/rsi/85/7/10.1063/1.4884717
• Abstract The CoLaPipe is a novel test facility at the Department of Aerodynamics and Fluid Mechanics, Brandenburg University of Technology Cottbus-Senftenberg (BTU Cottbus-Senftenberg), set up to investigate fully developed pipe flow at high Reynolds numbers ($$Re_{m} \leq 1.5 \times 10^{6}$$). The design of the CoLaPipe is closed-return with two available test sections providing a length-to-diameter ratio of $$L/D = 148$$ and $$L/D = 79$$. Within this work, we introduce the CoLaPipe and describe the various components in detail, i.e., the settling chamber, the inlet contraction, the blower, bends, and diffusers as well as the cooling system. A special feature is the numerically optimized contraction design. The applications of different measuring techniques such as hot-wire anemometry and static pressure measurements to quantitatively evaluate the mean flow characteristics and turbulence statistics are discussed as well. In addition, capabilities and limitations of available and new pipe flow facilities are presented and reconsidered based on their length-to-diameter ratio, the achieved Reynolds numbers, and the resulting spatial resolution. Here, the focus is on the facility design, the presentation of some basic characteristics, and its contribution to a reviewed list of specific questions still arising, e.g., scaling and structural behavior of turbulent pipe flow as well as the influence of the development length on turbulence investigations.
• Article
du Puits, Ronald; Willert, Chris
Physics of Fluid. 2016, Vol. 28, p. 044108. DOI: 10.1063/1.4947261
• Abstract We report measurements of the near-wall flow field in turbulent Rayleigh-Bénard convection in air (Pr = 0.7) using particle image velocimetry. The measurements were performed in a thin, rectangular sample at fixed Rayleigh number Ra = 1.45 × 1010. In particular, we focus on the evolution of the boundary layer that a single convection roll generates along its path at the lower horizontal plate. We identify three specific flow regions along this path: (i) a region of wall-normal impingement of the down flow close to one corner of the sample, (ii) a region where a shear layer with almost constant thickness evolves, and (iii) a region in which this boundary layer grows and eventually detaches from the plate surface at the opposite corner of the sample. Our measurements with a spatial resolution better than 1/500 of the total thickness of the boundary layer show that the typical velocity field as well as its statistics qualitatively varies between the three flow regions. In particular, it could be verified that the shear layer region covering about 75 of the total area of the plate is in transition to turbulence at the Rayleigh number as low as investigated in the present work.
• Conference Paper
Tuliszka-Sznitko, Ewa; Kielczewski, Kamil
Journal of Physics C.S.. 2016.
• Publication URL http://iopscience.iop.org/article/10.1088/1742-6596/760/1/012035/pdf
• Keywords Taylor-Couette flow, Nusselt number distribution, torque
• Abstract he Taylor-Couette flow with radial temperature gradient is a canonical problem for the study of heat transfer in engineering issues. However, gaining insight into the transitional Taylor-Couette flow with temperature gradient still requires detailed experimental and numerical investigations. In the present paper we have performed computations for the cavity of aspect ratio Γ= 3.76 and radii ratios η= 0.82 and 0.375 with the heated rotating bottom disk and stationary outer cylinder. We analyse the influence of the end-wall boundary conditions and the thermal conditions on the flow structure, and on the distributions of the Nusselt number and torque along the inner and outer cylinders. The averaged values along the inner cylinder of the Nusselt number and torque obtained for different Re are analysed in the light of the results published in [2, 16, 17].
• Article
du Puits, Ronald; Resagk, Christian; Thess, André
New Journal of Physics. 2013, Vol. 15, Issue 1, p. 13040. DOI: 10.1088/1367-2630/15/1/013040
• Publication URL http://stacks.iop.org/1367-2630/15/i=1/a=013040
• Abstract We report highly resolved temperature measurements in turbulent Rayleigh–Bénard convection in air at a fixed Prandtl number $$Pr = 0.7$$. Extending our previous work (du Puits et al 2007 J. Fluid Mech. 572 231–54), we carried out measurements at various aspect ratios while keeping the Rayleigh number constant. We demonstrate that the temperature field inside the convective boundary layers of both horizontal plates is virtually independent on the global flow pattern accompanying the variation in the aspect ratio. Thanks to technical upgrades of the experimental facility as well as a significant improvement of the accuracy and reliability of our temperature measurement—and unlike in our previous work—we find that the measured profiles of the time-averaged temperature field neither follow a clear power-law trend nor fit a linear or a logarithmic scaling over a significant fraction of the boundary-layer thickness. Analyzing the temperature data simultaneously acquired at both horizontal plates, various transitions in the cross-correlation and the auto-correlation function of the temperature signals are observed while varying the aspect ratio $$\Gamma$$. These transitions might be associated with a change in the global flow pattern from a single-roll mode at $$\Gamma = 1$$ toward a double- or a multi-roll mode pattern at higher aspect ratios.
• Article
van Gils, Dennis P. M.; Bruggert, Gert-Wim; Lathrop, Daniel P.; Sun, Chao; Lohse, Detlef
Review of Scientific Instruments. 2011, Vol. 82, Issue 2. DOI: 10.1063/1.3548924
• Conference Paper
Usama, Syed; Kopec, Jacek M.; Tellez, Jackson; Kwiatokowski, Kamil; Redondo, Jose M.; Malik, Nadeem A.
The IV International AMMCS Interdisciplinary Conference. 4. 2017, Vol. 2017, Issue August 20-24, p. 2.
• Keywords Sparce grids, Fractal, Structure functions
• Abstract Flat 2D fractal grids alter turbulence characteristics downstream of the grid as compared to the regular grids with the same blockage ratio and mass inflow rates [1]. This has excited interest in the turbulence community for possible enhanced mixing and related applications. Recently, a new 3D multi-scale grid design has been proposed [2] such that each generation of length scale of grid elements is held in its own frame, in overall co-planar arrangement, Fig. 1. This produces a ‘sparse’ grid system whereby each generation of grid elements produces a turbulent wake pattern that interacts with the other wake patterns downstream. A critical motiva-tion here is that the effective blockage ratio in the 3D Sparse Grid Turbulence (3DSGT) design is significantly lower than in the flat 2D counterpart – typically the blockage ratio could be reduced from say 20 in 2D down to 4 in the 3DSGT. If this idea can be realized in practice, it could potentially greatly enhance the effi-ciency of turbulent mixing and transfer processes clearly having many possible applications. Work has begun on the 3DSGT experimentally using Surface Flow Image velocimetry (SFIV) [3] at the European facility in the Max Planck Institute for Dynamics and Self-Organization located in Gottingen, Germany and at the Tech-nical University of Catalonia (UPC) in Spain, and numerically using Direct Numerical Simulation (DNS) at King Fahd University of Petroleum & Minerals (KFUPM) in Saudi Arabia and in University of Warsaw in Poland. DNS is the most useful method to compare the experimental results with, and we are studying differ-ent types of codes such as Imcompact3d, and OpenFoam. Many variables will eventually be investigated for optimal mixing conditions. For example, the number of scale generations, the spacing between frames, the size ratio of grid elements, inflow conditions, etc. Fig 2. shows some early analysis of the data, the temporal struc-ture functions up to 5th order, Sn(t)=<|u(t)-u(0)|n>, n=2,3,4,5, from velocity time series in air at a point along the channel centreline.
• Article
du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian
Phys. Rev. Lett.. 2014, Vol. 112, Issue 12, p. 124301. DOI: 10.1103/PhysRevLett.112.124301
• Publication URL http://link.aps.org/doi/10.1103/PhysRevLett.112.124301
• Abstract Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number $$\text{Ra} = 1.4 \times 10^{10}$$. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to $$I = 0.4$$ as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number $$\text{Re} \approx 200$$ is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.
• Article
Niemela, J. J.; Skrbek, L.; Sreenivasan, K. R.; Donnelly, R. J.
Nature. 2000, Vol. 404, Issue 6780, p. 837-840. DOI: 10.1038/35009036
• Abstract Turbulent convection occurs when the Rayleigh number (Ra)—which quantifies the relative magnitude of thermal driving to dissipative forces in the fluid motion—becomes sufficiently high. Although many theoretical and experimental studies of turbulent convection exist, the basic properties of heat transport remain unclear. One important question concerns the existence of an asymptotic regime that is supposed to occur at very high Ra. Theory predicts that in such a state the Nusselt number (Nu), representing the global heat transport, should scale as $$\text{Nu} \propto \text{Ra}^{\beta }$$ with $$\beta = 1/2$$. Here we investigate thermal transport over eleven orders of magnitude of the Rayleigh number ($$10^{6} \leq \text{Ra} \leq 10^{17}$$), using cryogenic helium gas as the working fluid. Our data, over the entire range of Ra, can be described to the lowest order by a single power-law with scaling exponent $$\beta$$ close to 0.31. In particular, we find no evidence for a transition to the $$\text{Ra}^{1/2}$$ regime. We also study the variation of internal temperature fluctuations with Ra, and probe velocity statistics indirectly.
• Article
Redondo, J.M.; Tellez, J.D.; Sanchez, J.M.
Trudy ISP RAN/Proc. ISP RAS. 2017, Vol. 29, Issue 2, p. 215-230. DOI: 10.15514/ISPRAS-2017-29(2)-8
• Keywords Convection; thermoelectricity; Peltier effect; experiments; numerical simulation; K-e Model; turbulence; digiFlow
• Abstract Local Diffusion and the topological structure of vorticity and velocity fields is measured in the transition from a homogeneous linearly stratified fluid to a cellular or layered structure by means of convective cooling and/or heating. Patterns arise by setting up a convective flow generated by an array of Thermoelectric devices (Peltier/Seebeck cells) these are controlled generating a buoyant heat flux. The experiments described here investigate high Prandtl number mixing using brine and fresh water in order to form density interfaces and low Prandtl number mixing with temperature gradients. The set of dimensionless parameters define conditions of numeric and small scale laboratory modeling of environmental flows. Fields of velocity, density and their gradients were computed and visualized using the open software tools of DigiFlow. When convective heating and cooling takes place in the side wall of a stratified enclosed cell, the combination of internal waves and buoyancy driven turbulence is much more complicated if the Rayleigh and Reynolds numbers are high. Higher order moments calculations and intermittency are important in order to study mixing in complex flows. Here some examples are shown using the Thermoelectric Convection Didactive Device (TCDD) built by BEROTZA, mainly in a symmetric two dimensional pattern, but many other combinations, using heating-cooling and angles with the vertical are possible in order to validate more complex numerical experiments.