Archivio della ricerca di Triestehttps://arts.units.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Thu, 04 Mar 2021 07:04:32 GMT2021-03-04T07:04:32Z1041Influence of container shape on scaling of turbulent fluctuations in convectionhttp://hdl.handle.net/11368/2832655Titolo: Influence of container shape on scaling of turbulent fluctuations in convection
Abstract: We perform large-eddy simulations of turbulent convection in a cubic cell for Rayleigh numbers, Ra, between 10^6 and 10^10 and the molecular Prandtl number, Pr = 0.7. The simulations were carried out using a second-order accurate finite-difference method in which subgrid-scale fluxes of momentum and heat were both parametrized using a Lagrangian and dynamic Smagorinsky model. The scaling of the root-mean-square fluctuations of density
(temperature) and velocity measured in the cell center are in excellent agreement with the scaling measured in the laboratory experiments of Daya and Ecke [Phys. Rev. Lett. 87, 184501 (2001)] and differ substantially from that observed in cylindrical cells. We also observe the time-averaged spatial distributions of the local heat flux and density fluctuations, and find that they are strongly inhomogeneous in the horizontal midplane, with the largest
density gradients occurring at the corners at the midheight, where hot and cold plumes mix in the form of strong counter-rotating eddies.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11368/28326552014-01-01T00:00:00ZLarge Eddy Simulation of Turbulent Rayleigh-Benard Convection in a Cubic Cellhttp://hdl.handle.net/11368/2917787Titolo: Large Eddy Simulation of Turbulent Rayleigh-Benard Convection in a Cubic Cell
Abstract: No abstract
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/11368/29177872018-01-01T00:00:00ZReorientations of the large-scale flow in turbulent convection in a cubehttp://hdl.handle.net/11368/2917570Titolo: Reorientations of the large-scale flow in turbulent convection in a cube
Abstract: Large-eddy simulations of turbulent Rayleigh-Benard convection were conducted for a fluid of Prandtl number ยด
Pr = 0.7 confined in a cube, for Rayleigh numbers of 106 and 108. The model solves the unsteady Navier-Stokes
equations under the Boussinesq approximation, using a dynamic Smagorinsky model with a Lagrangian averaging
technique for the subgrid terms. Under fully developed conditions the flow topology is characterized by a
large-scale circulation (LSC) developing in a plane containing one of the diagonals of the cell, while two
counter-rotating vortices consequently develop in the other diagonal plane, resulting in a strong inflow at the
horizontal midplane. This flow structure is not static, with the LSC undergoing nonperiodic reorientations, or
switching, between the two diagonal planes; hence, we supplement the observations of the three-dimensional
time-averaged flow structures with single point measurements (time series) to shed light on the dynamics of
the reorientations. For all observations, this switching results from a lateral rotation of the LSC in which
some finite time spent in a transient state where the large-scale circulation is parallel to one set of side walls;
there are, importantly, no observations consistent with so-called cessations of the LSC, in which it decays
and then reforms in another plane without such a rotation. The average switching rate for the LSC is in
excellent agreement with the results of Bai et al. [K. Bai, D. Ji, and E. Brown, Phys. Rev. E 93, 023117
(2016)]
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/11368/29175702017-01-01T00:00:00ZTurbulent convection and large scale circulation in a cube with rough horizontal surfaceshttp://hdl.handle.net/11368/2978893Titolo: Turbulent convection and large scale circulation in a cube with rough horizontal surfaces
Abstract: Large-eddy simulations of thermal convection are presented and discussed for a cube with rough horizontal surfaces. Two types of roughness are considered: uniformly placed pyramids, and grooves aligned parallel to one set of sidewalls. The Rayleigh number is 108, the Prandtl number 0.7, and the aspect ratio 1, as in a previous study [N. Foroozani, J. J. Niemela, V. Armenio, and K. R. Sreenivasan, Phys. Rev. E 95, 033107 (2017)10.1103/PhysRevE.95.033107], except that the meshes here are finer. When the thermal boundary layers are sufficiently large relative to the characteristic roughness height, i.e., for hydrodynamically smooth conditions, the mean properties of the large scale circulation (LSC) are qualitatively similar to the case of smooth surfaces. In particular, the LSC is always aligned along one of the diagonals of the cube. When the boundaries are hydrodynamically rough, the same result holds true only for the case of pyramidal structures; for grooved surfaces, the LSC is forced to be parallel to the sidewalls on average, alternating rapidly between the two diagonals of the cube with a mean period of the order 10 turnover times. Our analysis suggests that the difference from the pyramidal case is due to the breaking of the horizontal x-z symmetry under conditions of hydrodynamical roughness, and the corresponding directional concentration of plume emission along the grooves, from which the LSC is generated, providing a strong restoring force. Furthermore, in this study we observed a small reduction in heat transport for both roughness configurations which is in good agreement with past studies.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/11368/29788932019-01-01T00:00:00Z