Nicoleta Scurtu

Pulsating and traveling wave modes of natural convection in spherical shells

A numerical study is made of the natural convective fluid motion in the spherical shell geometry, i.e., the gap between two concentric spheres. The case of homogeneously heated inner sphere and cooled outer sphere is considered for the radius ratio η=0.714 and Prandtl number Pr=0.7. Patterns of fluid flow are established by the variation of the Rayleigh number Ra and its heat transfer is characterized by the Nusselt number Nu. For small values of the Rayleigh number, a crescent shaped axisymmetric vortex is formed and is regarded as the basic flow. By increasing the Rayleigh number, two transitions occur to a fully developed three-dimensional irregular flow. On the first bifurcation branch, a pulsating wave flow was found with petal-like formations pulsating in meridional direction. On the second branch, a traveling wave flow exists with an azimuthal rotation of the spirally distributed petal patterns. Various characteristics of the flow patterns are investigated as well as their transition to chaos. Both...

Experimental investigation of the eccentric Couette Flow with superimposed cross flow

The technical or industrial aspect of the Couette Flow has been the subject of various papers and the effect of eccentricity resulting in a variable height of the gap between outer and inner cylinder has been investigated. Without doubt eccentricity is one dominant parameter characterizing the flow. However, technical applications such as journal bearings have another particular feature, which has an impact on the basic Couette flow. A permanent supply of fluid is introduced through feed holes, which merges with the rotating flow to compensate the losses at the ends or sides of the bearing. Hence, three dimensional flow structures exist in the vicinity of the feed holes. The presented paper gives experimental of a Couette flow with a gap width of less than 10% relative to the inner diameter and rotating inner cylinder. An eccentricity of 50% in relation to the mean gap is considered. The results are shown in form of velocity profiles, which are obtained experimentally and are compared with analytical data and computed data. Moreover, a refined experimental set-up is presented, which allows velocity measurements with greater precision together with a wider range of adjustment possibilities for eccentricity and feed hole location.