Petr A. Nikrityuk

Spin-up of a liquid metal flow driven by a rotating magnetic field in a finite cylinder: A numerical and an analytical study

This paper presents a combined numerical and analytical study of the impulsive axisymmetric spin-up from rest of an isothermal liquid metal in a closed cylinder. The motion of the liquid is caused by the action of a low-frequency, low-induction rotating magnetic field, whose magnetic Taylor number is in the range (0.01–0.9) Tacr3D with Tacr3D given by Grants and Gerbeth [“Linear three-dimensional instability of a magnetically driven rotating flow,” J. Fluid Mech. 463, 229 (2002)]. The computations were performed for cylindrical containers of aspect ratios (diameter/height) R equal to 0.5, 1, and 2. The numerical simulations are compared with the predictions of an analytical model, valid for small Ekman numbers E extending a former work by Ungarish [“The spin-up of liquid metal driven by a rotating magnetic field,” J. Fluid Mech. 347, 105 (1997)]. The first phase of the motion from rest is an initial adjustment: the inviscid fluid begins to rotate due to the externally forced azimuthal acceleration, and co...

Use of time-modulated AC magnetic fields for melt flow control during unidirectional solidification

Abstract A new electromagnetic stirring approach using a combination of rotating (RMF) and travelling magnetic fields (TMF) is proposed, where both fields are applied subsequently in form of rectangular pulses. The strategy to utilise time-modulated RMF and TMF is aimed at overcoming the known deficiencies of conventional stirring, in particular flow-induced macrosegregation. This paper considers the directional solidification of Al–Si alloys from a water cooled copper chill. The results demonstrate that melt agitation using modulated magnetic field offers a considerable potential for a well aimed modification of casting properties by an effective control of the flow field, but, this goal requires a well considered optimisation of the magnetic field parameters.

The impact of turbulent flow on the solidification of metal alloys driven by a rotating magnetic field

Abstract The formation of Taylor-Görtler vortices inside a melt, driven by a rotating magnetic field, is an intrinsic phenomenon occurring at supercritical Taylor numbers. In this work we numerically study their impact on the macrosegregation and the shape of the mushy zone during unidirectional solidification of Al–7wt-%Si alloy. The weakly turbulent flow was modelled by means of direct numerical simulations in an axisymmetric approach, where the transient heat and mass transfer were simulated by means of a standard mixture model. Both types of solidification, columnar and equiaxed, were considered by the application of both a permeability and a hybrid model to treat the fluid flow in the mushy zone. Our results demonstrate that in the case of columnar solidification the Taylor-Görtler vortices cause both a wavy shape of the mushy zone and segregations in the form of a fir tree with a distinct accumulation of silicon along the axis of the cylinder.

Electromagnetically Forced Convection during Solidification of a Binary Metal Alloy

The main aim of this work is to study numerically the influence of an external rotating magnetic field on the convection process within liquid binary metal alloy undergoing solidification. Based on the continuum model of two-phase flow the transient transport of momentum, energy and species in presence of a Lorentz force during solidification of Pb25wt%Sn alloy is modeled. The geometry under study is a cylindrical mold with adiabatic walls and cooled bottom. The calculations showed that a swirling flow of the liquid phase (generated by a rotating magnetic field of 1 mT) develops a mushy zone front with convex shape where the maximum is located on the axis of rotation.