Precessing sphere Shear-driven parametric instability in a precessing sphere
نویسندگان
چکیده
The present numerical study aims at shedding light on the mechanism underlying the precessional instability in a sphere. Precessional instabilities in the form of parametric resonance due to topographic coupling have been reported in a spheroidal geometry both analytically and numerically. We show that such parametric resonances can also develop in spherical geometry due to the conical shear layers driven by the Ekman pumping singularities at the critical latitudes. Scaling considerations lead to a stability criterion of the form, |Po| > O(E), where Po represents the Poincaré number and E the Ekman number. The predicted threshold is consistent with our numerical simulations as well as previous experimental results. When the precessional forcing is supercriticial, our simulations show evidence of an inverse cascade, i.e. small scale flows merging into large scale cyclones with a retrograde drift. Finally, it is shown that this instability mechanism may be relevant to precessing celestial bodies such as the Earth and Earth’s moon.
منابع مشابه
The Instability of Precessing Flow
This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution , reselling , loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to dat...
متن کاملStagnation Knots in Precessing Jets
The problem of the formation of a stagnation knot in the head of a precessing stellar jet is investigated from both an analytical and numerical point of view. This dense structure is formed via a similar method to that proposed by Steffen (these proceedings) for the formation of FLIERS in planetary nebulae. Initial results suggest that the formation of a stagnation knot is possibly an intrinsic...
متن کاملPrecessing Jets and Molecular Outflows: A 3-D Numerical Study
– 2 – We present 3-D numerical hydrodynamical simulations of precessing supersonic heavy jets to explore their evolution, how they differ from straight jets and how well they serve as a model for generating molecular outflows from Young Stellar Objects. The dynamics are studied with a number of high resolution simulations on a Cartesian grid (128x128x128 zones) using a high order finite differe...
متن کاملPrecessing warped accretion discs in X-ray binaries
We study the radiation-driven warping of accretion discs in the context of X-ray binaries. The latest evolutionary equations are adopted, which extend the classical alpha theory to time-dependent thin discs with non-linear warps. We also develop accurate, analytical expressions for the tidal torque and the radiation torque, including self-shadowing. We investigate the possible non-linear dynami...
متن کاملDynamics of a fluid inside a precessing cylinder
The instability of a fluid inside a precessing cylinder is studied theoretically and experimentally. This study is motivated by aeronautics and geophysics applications. Precessional motion forces hydrodynamics waves called Kelvin modes whose structure and amplitude are predicted by a linear inviscid theory. When a forced Kelvin mode is resonant, a viscous and weakly nonlinear theory has been de...
متن کامل