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Contactless Inductive Flow Tomography (CIFT) is a flow measurement technique allowing for visualizing the global flow in electrically conducting fluids. The method is based on the precise measurement of very weak induced magnetic fields arising from the fluid motion under the influence of one or several primary excitation magnetic field(s). The simultaneous use of more than one excitation magnetic field is necessary to fully reconstruct three-dimensional liquid metal flows, yet is not trivial as the scalar values of induced magnetic field at the sensors need to be disentangled for each contribution of the excitation fields. Another approach is to multiplex the excitation fields. Here the temporal resolution of the measurement needs to be kept as high as possible. We apply two trapezoidal-shaped excitation magnetic fields with perpendicular direction to each other to a mechanically driven liquid metal flow. The consecutive application by multiplexing enables to determine the flow structure in the liquid with a temporal resolution down to 3 s with the existing equipment.

Recent decades have seen enormous progress in the experimental investigation of fundamental processes that are relevant to geophysical and astrophysical fluid dynamics. Liquid metals have proven particularly suited for such studies, partly owing to their small Prandtl numbers that are comparable to those in planetary cores and stellar convection zones, partly owing to their high electrical conductivity that allows the study of various magnetohydrodynamic phenomena. After introducing the theoretical basics and the key dimensionless parameters, we discuss some of the most important liquid-metal experiments on Rayleigh–Bénard convection, Alfvén waves, magnetically triggered flow instabilities such as the magnetorotational and Tayler instability, and the dynamo effect. Finally, we summarize what has been learned so far from those recent experiments and what could be expected from future ones.

The effects of thermal convection on turbulence in accretion discs, and particularly its interplay with the magnetorotational instability (MRI), are of significant astrophysical interest. Despite extensive theoretical and numerical studies, such an interplay has not been explored experimentally. We conduct linear analysis of the azimuthal version of MRI (AMRI) in the presence of thermal convection and compare the results with our experimental data published before. We show that the critical Hartmann number (Ha) for the onset of AMRI is reduced by convection. Importantly, convection breaks symmetry between m=±1 instability modes (m is the azimuthal wavenumber). This preference for one mode over the other makes the AMRI-wave appear as a ``one-winged butterfly''.

In this paper, we present numerical and experimental results on helicity oscillations in a liquid-metal Rayleigh–Bénard convection cell with an aspect ratio of 0.5. While the numerical simulations use the finite volume library OpenFOAM, the experimental results are obtained by means of contactless inductive flow tomography. We find that helicity oscillations occur during transitions of flow states with different roll numbers that are characterized by significant changes in the Reynolds number. However, helicity oscillations are also observed when the number of rolls is constant and the Reynolds number is changing only very slowly. Notably, the helicity oscillations observed during the transient double-roll state exhibit characteristics remarkably similar to those associated with the Tayler instability, which points to a rather generic and universal character of this phenomenon. Helicity oscillations are also discussed as a possible mechanism for synchronizing the solar dynamo by tidal forces of the orbiting planets.

The Eddy Current Flow Meter is an inductive velocity sensor which can be used in liquid metal applications, such as liquid metal cooled fast reactors. There it can be used as part of the safety instrumentation in order to monitor the coolant flow through subassemblies under normal operating conditions or to detect and locate blockages in case of a local freezing of the coolant. Typically the Eddy Current Flow Meter is used in pipe flows where the flow is mostly parallel to the sensor axis, whereas the flow angle may change significantly above subassemblies in a liquid metal cooled reactor. In the first part, the paper therefore deals with investigating the influence of varying flow angles on the performance of the Eddy Current Flow Meter. By performing measurements in a model experiment, the effect of different flow angles on the measured velocities will be demonstrated. In the second part of the paper, multiple Eddy Current Flow Meters in an array are used to detect and locate blockages in an array of seven subassemblies in the same model experiment. All experiments are carried out at room temperature with a liquid alloy of gallium, indium and tin.

Functional diversity has proven to be more responsive than traditional taxonomic diversity to alterations for a wide set of communities, especially in aquatic ecosystems. Habitat alterations are among the most relevant causes of biodiversity loss in freshwater ecosystems, nevertheless their effect on functional diversity has been scarcely investigated so far. In this study, functional diversity of fish communities in the River Po basin, north Italy, were related to habitat quality at different spatial scales. Land use and riparian vegetation were identified as the most influent factors on freshwater fish functional diversity. On the other hand, habitat descriptors at smaller scale did not influence functional diversity of fish. The evidenced responses were driven by the contribution of exotic species, which maximized ecological niche occupancy, either by exploiting increased habitat heterogeneity or by interaction with native species. Moreover, traits filtering, disadvantaging large predators such as salmonids, was also observed in the studied communities, but likely this effect was related to other factors than habitat alterations. Overall, this study confirms that land use changes can be considered as valid proxies for anthropogenic alterations. Moreover, possible effects at ecosystem level, also related to the spread of exotic species, could be hypothesized, giving that traits mostly influencing the observed patterns of diversity in communities were related to trophic niche, a factor that has been associated with crucial processes like nutrient cycling or energy transfer.

The quest for an unambiguous detection of magnetorotational instability (MRI) in experiments is still ongoing despite recent promising results. To conclusively identify MRI in the laboratory, a large cylindrical Taylor-Couette experiment with liquid sodium is under construction within the DRESDYN project. Recently, we have analyzed the nonlinear dynamics and scaling properties of axisymmetric standard MRI with an axial background magnetic field in the context of the DRESDYN-MRI experiment. In this sequel paper, we investigate the linear and nonlinear dynamics of nonaxisymmetric MRI in the same magnetized Taylor-Couette flow of liquid sodium. We show that the achievable highest Lundquist Lu=10 and magnetic Reynolds Rm=40 numbers in this experiment are large enough for the linear instability of nonaxisymmetric modes with azimuthal wave number |m|=1, although the corresponding critical values of these numbers are usually higher than those for the axisymmetric mode. The structure of the ensuing nonlinear saturated state and its scaling properties with respect to Reynolds number Re are analyzed, which are important for the DRESDYN-MRI experiment having very high Re≳106. It is shown that for Re≲4×104, the nonaxisymmetric MRI modes eventually decay, since the modified shear profile of the mean azimuthal velocity due to the nonlinear axisymmetric MRI appears to be stable against nonaxisymmetric instabilities. By contrast, for larger Re≳4×104, a rapid growth and saturation of the nonaxisymmetric modes of nonmagnetic origin occurs, which are radially localized near the inner cylinder wall, forming a turbulent boundary layer. However, for all the parameters considered, the saturation amplitude of these nonaxisymmetric modes is always a few orders smaller than that of the axisymmetric MRI mode. Therefore, the results of our previous axisymmetric study on the scaling properties of nonlinear MRI states also hold when nonaxisymmetric modes are included.

Measuring the flow velocity of liquid metals is a challenging task due to their high temperatures, their opacity and in many cases their chemical reactivity. There are several inductive methods to measure the flow velocity of liquid metals such as contactless inductive flow tomography (CIFT) [1], the magnetic distortion probe [2], Lorentz force velocimetry [3], the phase shift sensor [4] and eddy current flow meters (ECFM)[5]. ECFMs are often used in liquid metal fast breeder reactors due to their reliability and simple design. A disadvantage of the ECFM is that its output signal is influenced not only by changes in the flow velocity, but also by the electrical conductivity of the liquid metal, which depends on its temperature. Therefore, the ECFM must be calibrated according to the expected range of flow velocities and temperatures of a particular application, while simultaneously determining the temperature to distinguish between velocity and temperature changes. To solve this problem, we propose a new measurement method [6] that allows the simultaneous measurement of flow velocity and electrical conductivity by creating a so-called look-up table (LuT).

We propose a self-consistent explanation of Rieger-type periodicities, the Schwabe cycle, and the Suess-de Vries cycle of the solar dynamo in terms of resonances of various wave phenomena with gravitational forces exerted by the orbiting planets. Starting on the high-frequency side, we show that the two-planet spring tides of Venus, Earth, and Jupiter are able to excite magneto-Rossby waves, which can be linked with typical Rieger-type periods. We argue then that the 11.07-year beat period of those magneto-Rossby waves synchronizes an underlying conventional alpha-Omega dynamo by periodically changing either the field storage capacity in the tachocline or some portion of the alpha-effect therein. We also strengthen the argument that the Suess-de Vries cycle appears as an 193-year beat period between the 22.14-year Hale cycle and a spin-orbit coupling effect related with the 19.86-year rosette-like motion of the Sun around the barycenter.

We reveal and analyze an efficient magnetic dynamo action due to precession-driven hydrodynamic turbulence in the local model of a precessional flow, focusing on the kinematic stage of this dynamo. The growth rate of the magnetic field monotonically increases with the Poincaré number Po, characterizing precession strength, and the magnetic Prandtl number Pm, equal to the ratio of viscosity to resistivity, for the considered ranges of these parameters. The critical Po for the dynamo onset decreases with increasing Pm. To understand the scale-by-scale evolution (growth) of the precession dynamo and its driving processes, we perform spectral analysis by calculating the spectra of magnetic energy and of different terms in the induction equation in Fourier space. To this end, we decompose the velocity field of precession-driven turbulence into two-dimensional (2D) vortical and three-dimensional (3D) inertial wave modes. It is shown that the dynamo operates across a broad range of scales and exhibits a remarkable transition from a primarily vortex-driven regime at lower Po to a more complex regime at higher Po where it is driven jointly by vortices, inertial waves, and the shear of the background precessional flow. Vortices and shear drive the dynamo mostly at large scales comparable to the flow system size, and at intermediate scales, while at smaller scales it is mainly driven by inertial waves. This study can be important not only for understanding the magnetic dynamo action in precession-driven flows, but also in a general context of flows where vortices emerge and govern the flow dynamics and evolution.

(1) Background: The surveillance of SARS‐CoV‐2 RNA in urban wastewaters allows one to monitor the presence of the virus in a population, including asymptomatic and symptomatic individuals, capturing the real circulation of this pathogen. The aim of this study was to evaluate the performance of different pre‐analytical and analytical methods for identifying the presence of SARS‐CoV‐2 in untreated municipal wastewaters samples by conducting an inter‐laboratory proficiency test. (2) Methods: three methods of concentration, namely, (A) Dextran and PEG‐6000 two‐phase separation, (B) PEG‐8000 precipitation without a chloroform purification step and (C) PEG‐8000 precipitation with a chloroform purification step were combined with three different protocols of RNA extraction by using commercial kits and were tested by using two primers/probe sets in three different master mixes. (3) Results: PEG‐8000 precipitation without chloroform treatment showed the best performance in the SARS‐CoV‐2 recovery; no major differences were observed among the protocol of RNA extraction and the one‐step real‐time RT‐PCR master mix kits. The highest analytic sensitivity was observed by using primers/probe sets targeting the N1/N3 fragments of SARS‐CoV‐2. (4) Conclusions: PEG‐8000 precipitation in combination with real‐time RT‐PCR targeting the N gene (two fragments) was the best performing workflow for the detection of SARS‐CoV‐2 RNA in municipal wastewaters.

Magnetorotational instability (MRI) is the most likely mechanism for efficient transport of angular momentum in accretion disks. However, despite numerous efforts, the quest for an unambiguous realization of MRI in experiments is still ongoing. To conclusively identify MRI in the laboratory, a large Taylor-Couette experiment with liquid sodium is under construction at the Helmholtz-Zentrum Dresden-Rossendorf within the DRESDYN project. Recently, we have determined the optimal range of parameters for the onset of an axisymmetric mode of the standard MRI (SMRI) with a purely axial background magnetic field and analyzed its nonlinear evolution, saturation and scaling properties in the context of the DRESDYN-MRI experiment. In this sequel paper, we continue SMRI studies and investigate the linear and nonlinear dynamics of non-axisymmetric modes of the instability in a similar magnetized Taylor-Couette setup. For the linear stability analysis, we use $Pm=\nu/\eta \sim 10^{-5}$ typical of liquid sodium used in the experiment. We show that the achievable magnetic Reynolds $Rm\sim 40$ and Lundquist $Lu\sim10$ numbers in this experiment are large enough for the growth of non-axisymmetric $|m|=1$ SMRI modes. For fixed $\mu$, the critical $Rm_c$ for the onset of non-axisymmetric SMRI is about 2-3 time higher than that of axisymmetric SMRI. We follow the evolution of these modes from their exponential growth in the linear regime all over to nonlinear saturation. The structure of the saturated state and its scaling properties with respect to Reynolds number $Re$ are analyzed, which is relevant and important for the DRESDYN-MRI experiment having very high Reynolds numbers ($\sim 10^6$). We show that for $Re \lesssim 10^4$, the magnetic energy of non-axisymmetric SMRI modes does not saturate and eventually decays due to the modification of the radial shear profile of the mean azimuthal velocity by the nonlinear axisymmetric SMRI, that is, the modified shear profile appears to be s

n this paper, we present an experimental investigation that centers on exploring the fluid dynamics within a precessing cylinder. Our research is part of the DRESDYN project at Helmholtz-Zentrum Dresden-Rossendorf, specifically focusing on the precession dynamo experiment. The primary objective of our study is to examine how different rotation configurations influence the dominant flow modes inside the precessing cylinder, specifically considering the prograde and retrograde rotations. Our main focus lies on two significant flow modes: the directly forced mode (m1, k1) and the non-geostrophic axisymmetric mode (m0, k2). These modes hold substantial potential for precession-driven dynamo action. By analyzing the outcomes between the prograde and retrograde configurations, we gain valuable insights into the prevailing flow patterns within the precessing cylinder.

We present a new shallow-water formulation of forced magnetohydrodynamic Ross- by waves originating in the tachocline of solar-like stars. As a novelty to former descriptions, we add an external tidal potential to the equations and further include a linear damping law, allowing us to study wave motions driven by arbitrary tidal forces. The model is applied to the specific case of our sun, where we consider the action of the tidally dominant planet Jupiter. We present an explicit analytic solution to this problem, which we finally use to estimate char- acteristic responding wave amplitudes.

A magnetohydrodynamic dynamo process is supposed to take place in the interior of the Sun or stars as well as in planets and smaller celestial bodies like the ancient moon or the asteroid Vesta. The ubiquity and diversity of astrophysical dynamo action, and the importance of the magnetic fields for formation and evolution of the objects generating them, has motivated related studies in the laboratory. A new dynamo experiment is currently under construction at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), in which a fluid flow of liquid sodium will be forced by a precessing cylindrical container. In the 1970s, a similar but much smaller experiment was conducted by R. Gans, who found a threefold amplification of an external magnetic field, indicating that dynamo action can be expected in the vicinity of the transition from a laminar flow state to vigorous turbulence if the system is sufficiently large. In the new dynamo precession experiment the knowledge of the velocity field is necessary in order to achieve the optimal structure of the flow and to understand the interaction of fluid flow and magnetic field and the associated transfer of kinetic energy into magnetic energy. Our present study focuses on the experimental and numerical estimation of the structure of a precession driven flow field, its scaling with rotation and precession, and its dynamical evolution. We determine the amplitude of characteristic flow contributions in terms of inertial modes, which allows a robust and accurate detection of the transition between laminar and turbulent state. It further turns out that most of the kinetic energy can be related to very few large scale inertial modes. Finally, the determination of the orientation of the rotation axis of the fluid motion shows that the qualitative behavior of the precession driven flow in a cylinder is roughly similar to the predictions given by Busse's theory for a planetary-like setup in a spheroid.

Der Vortrag beschäftigt sich mit Theorien und Experimenten zur Entstehung und Wirkung kosmischer Magnetfelder. Ein besonderer Schwerpunkt liegt auf der Vorstellung des DRESDYN-Experiments am HZDR.

The upcoming DRESDYN (DREsden Sodium facility for DYNnamo and thermohydraulic studies) precession experiment will test the possibility to achieve magnetohydrodynamic dynamo action solely driven by precession. Here, after the description of the experi- mental facility, we present the results from direct numerical simulations with the aim to understand the flow behavior and its dynamo capability. The main conclusion is that in the nonlinear regime the nutation angle is an essential governing parameter which determines the flow structures and the possibility of dynamo action. We obtain clear indications about the optimum configuration for the future experimental runs.

Mit der kontaktlosen induktiven Strömungstomografie (CIFT) lassen sich Geschwindigkeitsfelder in elektrisch leitfähigen Flüssigkeiten global bestimmen. Kenntnisse über den Strömungszustand in Metallschmelzen sind für industrielle Prozesse, wie das Stranggießen von Stahl, von immenser Bedeutung und können auch in der Grundlagenforschung nutzbringend angewendet werden, z.B. zur Analyse von konvektiven Flüssigmetallströmungen als Modellsysteme des Wärmetransportes. Das Verfahren beruht auf der präzisen Messung kleinster Magnetfeldänderungen durch geeignete Sonden und der nachfolgenden Rekonstruktion der Strömungsstruktur durch die Lösung eines linearen inversen Problems. In dieser Veröffentlichung geben wir einen Überblick über die Entwicklungen der letzten Dekade und diskutierten je einen Anwendungsfall für CIFT aus der grundlegenden und der angewandten Fluiddynamik. >>Contactless Inductive Flow Tomography (CIFT) is a flow measurement technique that can reconstruct the global 3D flow in electrically conducting fluids. Knowledge of the flow conditions in liquid metals is of outmost importance for industrial processes as continuous casting of steel. CIFT can also be applied to fundamental research, e.g. to measure convective liquid metal flows. The technique is based on the precise measurement of very small magnetic field changes and the subsequent reconstruction of the flow field by solving the linear inverse problem. This publication illustrates one use-case from fundamental and applied fluid mechanics each.

Magnetorotational instability (MRI) is considered as the most likely mechanism driving angular momentum transport in astrophysical disks. However, despite many efforts, a direct and conclusive experimental evidence of MRI in laboratory is still missing. Recently, performing 1D linear analysis of the standard version of MRI (SMRI) between two rotating coaxial cylinders with an imposed axial magnetic field, we showed that SMRI can be detected in the upcoming DRESDYN-MRI experiment based on cylindrical magnetized Taylor-Couette (TC) flow with liquid sodium. In this follow-up study, being also related to the DRESDYN-MRI experiments, we focus on the nonlinear evolution and saturation properties of SMRI and analyze its scaling behavior with respect to various param- eters of the basic TC flow using a pseudo-spectral code. We conduct a detailed analysis over the extensive ranges of magnetic Reynolds number Rm ∈ [8.5, 37.1], Lundquist number Lu ∈ [1.5, 15.5] and Reynolds number, Re ∈ [103, 105]. For fixed Rm, we investigate the nonlinear dynamics of SMRI for small magnetic Prandtl numbers down to P m ∼ O(10−4), aiming ultimately for those values typical of liquid sodium used in the experiments. In the saturated state, the magnetic en- ergy of SMRI and associated torque exerted on the cylinders, characterising angular momentum transport, both increase with Rm for fixed (Lu, Re), while for fixed (Lu, Rm), the magnetic energy decreases and torque increases with increasing Re. We also study the scaling of the magnetic en- ergy and torque in the saturated state as a function of Re and find a power law dependence of the form Re−0.6...−0.5 for the magnetic energy and Re0.4...0.5 for the torque at all sets of (Lu, Rm) and sufficiently high Re ≥ 4000. We also explore the dependence on Lundquist number and angular velocity. The scaling laws derived here will be instrumental in the subsequent analysis and com- parison of numerical results with those obtained from the DRESDYN-MRI exper

The old question of whether the solar dynamo is synchronized by the tidal forces of the orbiting planets has recently received renewed interest, both from the viewpoint of historical data analysis and in terms of theoretical and numerical modeling. We aim to contribute to the solution of this longstanding puzzle by analyzing cosmogenic radionuclide data from the last millennium. We reconsider a recent time-series of ¹⁴C-inferred sunspot data and compare the resulting cycle minima and maxima with the corresponding conventional series down to 1610 A.D., enhanced by Schove's data before that time. We fnd that, despite recent claims to the contrary, the ¹⁴C-inferred sunspot data are well compatible with a synchronized solar dynamo, exhibiting a relatively phase stable period of 11.07 years, which points to a synchronizing role of the spring tides of the Venus-Earth-Jupiter system.

The effect of the nutation angle on the flow inside a precessing cylinder is experimentally explored and compared with numerical simulations. The focus is laid on the typical breakdown of the directly forced m = 1 Kelvin mode for increasing precession ratio (Poincaré number), and the accompanying transition between a laminar and turbulent flow. Compared to the reference case with a 90° nutation angle, prograde rotation leads to an earlier breakdown, while in the retrograde case the forced mode continues to exist also for higher Poincaré numbers. Depending largely on the occurrence and intensity of an axisymmetric double-roll mode, a kinematic dynamo study reveals a sensitive dependence of the self-excitation condition on the nutation angle and the Poincaré number. Optimal dynamo conditions are found for 90° angle which, however, might shift to slightly retrograde precession for higher Reynolds numbers.

Magnetic fields are key ingredients for heating the solar corona to temperatures of several million Kelvin. A particularly important region with respect to this is the so-called magnetic canopy below the corona, where sound and Alfvén waves have roughly the same speed and can, therefore, easily transform into each other. We present the results of an Alfvén-wave experiment with liquid rubidium carried out in a pulsed field of up to 63 T. At the critical point of 54 T, where the speeds of Alfvén waves and sound coincide, a new 4 kHz signal appears in addition to the externally excited 8 kHz torsional wave. This emergence of an Alfvén wave with a doubled period is in agreement with the theoretical predictions of a parametric resonance between the two wave types. We also present preliminary results from numerical simulations of Alfvén and magneto-sonic waves using a compressible MHD code.

The magnetised spherical Couette (MSC) problem, a three dimensional magnetohydrodynamic paradigmatic model in geo- and astrophysics, is considered to investigate bifurcations to high-dimensional invariant tori and chaotic flows in large scale dissipative dynamical systems with symmetry. The main goal of the present study is to elucidate the origin of chaotic transients and intermittent behaviour from two different sequences of Hopf bifurcations involving invariant tori with four fundamental frequencies, which may be resonant. Numerical evidence of the existence of a crisis event destroying chaotic attractors and giving rise to the chaotic transients is provided. It is also shown that unstable invariant tori take part in the time evolution of these chaotic transients. For one sequence of bifurcations, the study demonstrates that chaotic transients display on-off intermittent behaviour. A possible explanatory mechanism is discussed.

Eddy Current Flow Meters (ECFM) are inductive sensors that are commonly used to measure the local flow rate or flow velocity of liquid metals in the vicinity of the sensor. One disadvantage of the ECFM is, that the measured voltage signals depend on the magnetic Reynolds number i.e. they are not only depending on the flow velocity but also on the electrical conductivity of the liquid metal. For applications where the temperature (and therefore also the electrical conductivity) is fluctuating significantly, the ECFM has to be calibrated in order to be able to distinguish between the influence of the flow velocity and the temperature on the measured signals. In this paper we present a method that allows the simultaneous measurement of electrical conductivity and flow velocity by using a so called Look-Up-Table method. When using this method, there is no need to calibrate the ECFM.

Nach einem ersten Überblick über die typischen Klimavariationen auf verschiedenen Zeitskalen beschäftigt sich der Vortrag hauptsächlich mit den physikalischen Mechanismen sowie der Abschätzung der Intensität solarer und anthropener Einflüsse auf das Klima. Zur Erklärung der Perioden der grundlegenden Zyklen des Sonnenmagnetfeldes wird ein modifiziertes Dynamomodell unter Einbeziehung der von den Planeten auf die Sonne ausgeübten Kräfte vorgestellt. Das präzessionsgetriebene Dynamoexperiment im Rahmen des DRESDYN-Projektes wird im allgemeinen Kontext mechanisch getriggerter bzw. beeinflusster Dynamos diskutiert.

A magnetohydrodynamic dynamo process is supposed to take place in the interior of the Sun or stars as well as in planets and smaller celestial bodies like the ancient moon or the asteroid Vesta. The ubiquity and diversity of astrophysical dynamo action, and the importance of the magnetic fields for formation and evolution of the objects generating them, has motivated related studies in the laboratory. A new dynamo experiment is currently under construction at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), in which a fluid flow of liquid sodium will be forced by a precessing cylindrical container. In the 1970s, a similar but much smaller experiment was conducted by R. Gans, who found a threefold amplification of an external magnetic field, indicating that dynamo action can be expected in the vicinity of the transition from a laminar flow state to vigorous turbulence if the system is sufficiently large. In the new dynamo precession experiment the knowledge of the velocity field is necessary in order to achieve the optimal structure of the flow and to understand the interaction of fluid flow and magnetic field and the associated transfer of kinetic energy into magnetic energy. Our present study focuses on the experimental and numerical estimation of the structure of a precession driven flow field, its scaling with rotation and precession, and its dynamical evolution. We determine the amplitude of characteristic flow contributions in terms of inertial modes, which allows a robust and accurate detection of the transition between laminar and turbulent state. It further turns out that most of the kinetic energy can be related to very few large scale inertial modes. Finally, the determination of the orientation of the rotation axis of the fluid motion shows that the qualitative behavior of the precession driven flow in a cylinder is roughly similar to the predictions given by Busse's theory for a planetary-like setup in a spheroid.

We demonstrate an efficient magnetic dynamo due to precession-driven hydrodynamic turbulence in the local model. Dynamo growth rate increases with Poincar\'{e} and magnetic Prandtl numbers. Spectral analysis shows that the dynamo acts over a broad range of scales: at large (system size) and intermediate scales it is driven by 2D vortices and shear of the background precessional flow, while at smaller scales it is mainly driven by 3D inertial waves. These results are important for understanding magnetic field generation and amplification in precessing planets and stars., Comment: 5 pages, 5 figures, submitted to Physical Review Letters