Search results for "Fluid Dynamic"
showing 10 items of 1034 documents
Direct numerical simulation of MR suspension: The role of viscous and magnetic interactions between particles
2009
A numerical method is developed with aim to simulate the magnetorheological (MR) suspension taking into account realistic magnetic forces. The MR suspension is described by spherical particles with nonlinear magnetic properties suspended in a shear flow. Inertia effects, Brownian motion and buoyancy forces are neglected. The hydrodynamic interaction between close particles is taken into account approximately. Results of some test simulations are presented.
Statistical analysis of the influence of forces on particles in EM driven recirculated turbulent flows
2011
The present paper contains an analysis of the statistical distribution of forces affecting non-conducting particles dispersed in an EM induced recirculated flow in induction furnaces. The simulation is conducted adopting the LES-based Euler-Lagrange approach in the limit of dilute conditions (one-way coupling). It is done by means of a development of OpenFOAM software code. The used Lagrange equation for particle tracking includes drag, EM, buoyancy, lift, acceleration and added mass forces. The relevant approximations for the forces are chosen on the basis of the statistical analysis of the non-dimensional parameters (particle Reynolds number, shear stress and acceleration parameter). The …
Transition to turbulence in toroidal pipes
2011
AbstractIncompressible flow in toroidal pipes of circular cross-section was investigated by three-dimensional, time-dependent numerical simulations using a finite volume method. The computational domain included a whole torus and was discretized by up to ${\ensuremath{\sim} }11. 4\ensuremath{\times} 1{0}^{6} $ nodes. Two curvatures $\delta $ (radius of the cross-section/radius of the torus), namely 0.3 and 0.1, were examined; a streamwise forcing term was imposed, and its magnitude was made to vary so that the bulk Reynolds number ranged between ${\ensuremath{\sim} }3500$ and ${\ensuremath{\sim} }14\hspace{0.167em} 700$. The results were processed by different techniques in order to confirm…
Chiral excitations of magnetic droplet solitons driven by their own inertia
2019
The inertial effects of magnetic solitons play a crucial role in their dynamics and stability. Yet governing their inertial effects is a challenge for their use in real devices. Here, we show how to control the inertial effects of magnetic droplet solitons. Magnetic droplets are strongly nonlinear and localized autosolitons than can form in current-driven nanocontacts. Droplets can be considered as dynamical particles with an effective mass. We show that the dynamical droplet bears a second excitation under its own inertia. These excitations comprise a chiral profile, and appear when the droplet resists the force induced by the Oersted field of the current injected into the nanocontact. We …
Testing the stage-discharge relationship of a sharp crested sluice gate deduced by the momentum equation for a free-flow condition
2018
Abstract In this paper the stage-discharge relationship of a sharp crested sluice gate is deduced by applying the momentum equation for a free flow condition. The theoretically deduced stage-discharge formula was then calibrated using experimental flume data obtained in previous investigations carried out for a free-flow condition. The deduced stage–discharge relationship is characterized by a momentum coefficient which is empirically estimated by the ratio between the height of the orifice and the water depth in the section upstream the gate. The relative errors are always less than or equal to - 10% to +10% and 71.4% of the errors are less than or equal to ± 2%.
X-rays from protostellar jets: emission from continuous flows
2006
Recently X-ray emission from protostellar jets has been detected with both XMM-Newton and Chandra satellites, but the physical mechanism which can give rise to this emission is still unclear. We performed an extensive exploration of a wide space of the main parameters influencing the jet/ambient interaction. Aims include: 1) to constrain the jet/ambient interaction regimes leading to the X-ray emission observed in Herbig-Haro objects in terms of the emission by a shock forming at the interaction front between a continuous supersonic jet and the surrounding medium; 2) to derive detailed predictions to be compared with optical and X-ray observations of protostellar jets; 3) to get insight int…
The discovery of an expanding X-ray source in the HH 154 protostellar jet
2006
We have performed, in October 2005, a deep Chandra X-ray observation of HH 154. Comparison with the previous (2001) Chandra observation allows to detect proper motion down to the level predicted by models of X-ray emitting shocks in the jet. The 2005 Chandra observation of HH 154 shows unexpected morphological changes of the X-ray emission in comparison with the 2001 data. Two components are present: a stronger, point-like component with no detectable motion and a weaker component which has expanded in size by approximately 300 AU over the 4 years time base of the two observations. This expansion corresponds to approximately 500 km/s, very close to the velocity of the X-ray emitting shock i…
Angular Energy Distribution of Collapsar-Jets
2008
Collapsars are fast-spinning, massive stars, whose core collapse liberates an energy, that can be channeled in the form of ultrarelativistic jets. These jets transport the energy from the collapsed core to large distances, where it is dissipated in the form of long-duration gamma-ray bursts. In this paper we study the dynamics of ultrarelativistic jets produced in collapsars. Also we extrapolate our results to infer the angular energy distribution of the produced outflows in the afterglow phase. Our main focus is to look for global energetical properties which can be imprinted by the different structure of different progenitor stars. Thus, we employ a number of pre-supernova, stellar models…
Jet dynamics and stability
2013
The dynamics and stability of extragalactic jets may be strongly influenced by small (and probable) di_erences in pressure between the jet and the ambient and within the jet itself. The former give rise to expansion and recollimation of the jet. This occurs in the form of conical shocks, or Mach disks, if the pressure di_erence is large enough. Pressure asymmetries within the jet may trigger the development of helical patterns via coupling to kink current-driven instability, or to helical Kelvin-Helmholtz instability, depending on the physical conditions in the jet. I summarize here the evidence collected during the last years on the presence of recollimation shocks and waves in jets. In th…
On the Origin of the X-Ray Emission in Protostellar Jets Close to the Launching Site
2019
Observations of stellar jets show evidence of X-ray emitting shocks close to the launching site. In some cases, the shocked features appear to be stationary (e.g. HH 154 and DG Tau). We aim at investigating the origin of X-ray emission and the effect of perturbations in X-ray emitting stationary shocks in stellar jets. We performed a set of 2.5-dimensional MHD numerical simulations modelling supersonic pulsed jets ramming into a magnetized medium, exploring different parameters for the model. We consider two cases: a jet less dense than the ambient medium (HH 154), and a jet denser than the ambient (DG Tau). In both cases, we found that the jet is collimated by the magnetic field forming a …