@inproceedings{KleinGhasemiSeeligetal., author = {Klein, Marten and Ghasemi, Abouzar and Seelig, Torsten and Borcia, Ion-Dan and Harlander, Uwe and Will, Andreas}, title = {DNS of inertial wave attractors in a librating annulus with height-dependent gap width}, series = {15th European turbulence conference (ETC), Delft, The Netherlands (2015)}, booktitle = {15th European turbulence conference (ETC), Delft, The Netherlands (2015)}, abstract = {Direct numerical simulations (DNS) of inertial wave attractors have been carried out in a librating Taylor-Couette system with broken mirror symmetry in the radial-axial cross-section. The inertial wave excitation mechanism and its localisation at the edges was clarified by applying boundary layer theory. Additional resonance peaks in the simulated response spectra were found to agree with low-order wave attractors obtained by geometric ray tracing. Numerics and theory are in qualitative agreement with recent lab experiments.}, language = {en} } @inproceedings{BorciaHarlander, author = {Borcia, Ion-Dan and Harlander, Uwe}, title = {Inertial waves inside a liquid confined between two rotating coaxial cylinders: the case of small Ekman number}, language = {en} } @misc{HarlanderSukhanovskiiAbideetal., author = {Harlander, Uwe and Sukhanovskii, Andrei and Abide, St{\´e}phane and Borcia, Ion-Dan and Popova, Elene and Rodda, Costanza and Vasiliev, Andrei and Vincze, Miklos}, title = {New Laboratory Experiments to Study the Large-Scale Circulation and Climate Dynamics}, series = {Atmosphere}, volume = {14}, journal = {Atmosphere}, number = {5}, doi = {10.3390/atmos14050836}, pages = {19}, abstract = {The large-scale flows of the oceans and the atmosphere are driven by a non-uniform surface heating over latitude, and rotation. For many years scientists try to understand these flows by doing laboratory experiments. In the present paper we discuss two rather new laboratory experiments designed to study certain aspects of the atmospheric circulation. One of the experiments, the differentially heated rotating annulus at the Brandenburg University of Technology (BTU) Cottbus, has a cooled inner cylinder and a heated outer wall. However, the structure of the atmospheric meridional circulation motivates a variation of this "classical" design. In the second experiment described, operational at the Institute of Continuous Media Mechanics (ICMM) in Perm, heating and cooling is performed at different vertical levels that resembles more the atmospheric situation. Recent results of both experiments are presented and discussed. Differences and consistencies are highlighted. Though many issues are still open we conclude that both setups have their merits. The variation with heating and cooling at different levels might be more suited to study processes in the transition zone between pure rotating convection and the zone of westerly winds. On the other hand, the simpler boundary conditions of the BTU experiment make this experiment easier to control.}, language = {en} } @inproceedings{SeeligBorciaKleinetal., author = {Seelig, Torsten and Borcia, Ion-Dan and Klein, Marten and Ghasemi, Abouzar and Will, Andreas and Egbers, Christoph and Schaller, Eberhard and Harlander, Uwe}, title = {Inertial waves and wave attractors in a rotating annulus with inner or outer cylinder libration}, series = {European Geosciences Union (EGU), 10th General Assembly, Vienna, Austria, 07 - 12 April 2013}, booktitle = {European Geosciences Union (EGU), 10th General Assembly, Vienna, Austria, 07 - 12 April 2013}, language = {en} } @misc{HarlanderBorciaVinczeetal., author = {Harlander, Uwe and Borcia, Ion-Dan and Vincze, Miklos and Rodda, Costanza}, title = {Probability Distribution of Extreme Events in a Baroclinic Wave Laboratory Experiment}, series = {Fluids}, volume = {7}, journal = {Fluids}, number = {8}, issn = {2311-5521}, doi = {10.3390/fluids7080274}, abstract = {Atmospheric westerly jet streams are driven by temperature differences between low and high latitudes and the rotation of the Earth. Meandering jet streams and propagating Rossby waves are responsible for the variable weather in the mid-latitudes. Moreover, extreme weather events such as heat waves and cold spells are part of the jet stream dynamics. For many years, a simple analog in the form of a simplified laboratory experiment, the differentially heated rotating annulus, has provided insight into the dynamics of the meandering jet stream. In the present study, probability density distributions of extreme events from a long-term laboratory experiment are studied and compared to the atmospheric probability density distributions. Empirical distributions of extreme value monthly block data are derived for the experimental and atmospheric cases. Generalized extreme value distributions are adjusted to the empirical distributions, and the distribution parameters are compared. Good agreement was found, but the distributions of the experimental data showed a shift toward larger extreme values, and some explanations for this shift are suggested. The results indicate that the laboratory model might be a useful tool for investigating changes in extreme event distributions due to climate change. In the laboratory context, the change can be modeled by an increase in total temperature accompanied by a reduction in the radial heat contrast.}, language = {en} } @inproceedings{Borcia, author = {Borcia, Ion-Dan}, title = {Attractors, eigenvalues and mean flow interactions in a fluid confined between two co-rotating cylinders}, language = {en} } @misc{KleinSeeligKurganskyetal., author = {Klein, Marten and Seelig, Torsten and Kurgansky, Michael V. and Ghasemi, Abouzar and Borcia, Ion-Dan and Will, Andreas and Schaller, Eberhard and Egbers, Christoph and Harlander, Uwe}, title = {Inertial wave excitation and focusing in a liquid bounded by a frustum and a cylinder}, series = {Journal of Fluid Mechanics}, journal = {Journal of Fluid Mechanics}, number = {vol. 751}, issn = {1750-6859}, doi = {10.1017/jfm.2014.304}, pages = {255 -- 297}, abstract = {The mechanism of localized inertial wave excitation and its efficiency is investigated for an annular cavity rotating with Ω0 . Meridional symmetry is broken by replacing the inner cylinder with a truncated cone (frustum). Waves are excited by individual longitudinal libration of the walls. The geometry is non-separable and exhibits wave focusing and wave attractors. We investigated laboratory and numerical results for the Ekman number E ≈ 10-6. inclination α = 5.71◦ and libration amplitudes ε 0.2 within the inertial wave band 0 < ω < 2Ω0 . Under the assumption that the inertial waves do not essentially affect the boundary-layer structure, we use classical boundary-layer analysis to study oscillating Ekman layers over a librating wall that is at an angle α = 0 to the axis of rotation. The Ekman layer erupts at frequency ω = f∗, where f∗ ≡ 2Ω0 sin α is the effective Coriolis parameter in a plane tangential to the wall. For the selected inclination this eruption occurs for the forcing frequency ω/Ω0 = 0.2. For the librating lids eruption occurs at ω/Ω0 = 2. The study reveals that the frequency dependence of the total kinetic energy Kω of the excited wave field is strongly connected to the square of the Ekman pumping velocity wE (ω) that, in the linear limit, becomes singular when the boundary layer erupts. This explains the frequency dependence of non-resonantly excited waves. By the localization of the forcing, the two configurations investigated, (i) frustum libration and (ii) lids together with outer cylinder in libration, can be clearly distinguished by their response spectra. Good agreement was found for the spatial structure of low-order wave attractors and periodic orbits (both characterized by a small number of reflections) in the frequency windows predicted by geometric ray tracing. For 'resonant' frequencies a significantly increased total bulk energy was found, while the energy in the boundary layer remained nearly constant. Inertial wave energy enters the bulk flow via corner beams, which are parallel to the characteristics of the underlying Poincar{\´e} problem. Numerical simulations revealed a mismatch between the wall-parallel mass fluxes near the corners. This leads to boundary-layer eruption and the generation of inertial waves in the corners.}, language = {en} } @misc{HarlanderLeGalBorciaetal., author = {Harlander, Uwe and Le Gal, Patrice and Borcia, Ion-Dan and Le Diz{\`e}s, St{\´e}phane and Chen, Jun and Favier, Benjamin}, title = {The linear instability of the stratified plane Poiseuille flow}, series = {17th European Turbulence Conference, ETC 2019, September 3 - 6, 2019, Torino, Italy}, journal = {17th European Turbulence Conference, ETC 2019, September 3 - 6, 2019, Torino, Italy}, address = {Turin}, pages = {1}, language = {en} }