New single vortex generation method for flame/vortex interaction using flow behind a rotating cylinder

This paper investigates a new experimental method to generate a single two-dimensional translated vortex for flame/vortex interaction studies. A rotating cylinder is immersed in a uniform flow and, its rotating speed is impulsively reduced. This sudden action triggers the generation of a single vortex when both the initial and the final rotation speeds are in the range of a steady-state regime. Flow visualization allows confirming the applicability of this method, while a complementary two-dimensional numerical simulation is conducted to understand the vortex formation process. A vorticity layer is detached from the cylinder, initiating a feeding process and gradual growth of a single leading vortex. The feeding process is saturated at a specific distance from the cylinder and, vortex separation from the vorticity layer is observed. At the final stage of the formation process, the generated vortex is advected away and, a steady-state regime is again established behind the cylinder. The vortex characteristics appear to be related to the normalized reduction in the rotation rate ∆α, defined as the initial and final rotation rates difference normalized by the initial rotation rate. Several combinations of initial and final rotation rates corresponding to different normalized reductions are investigated experimentally and numerically. The results allow understanding the effect of this parameter; a higher normalized reduction generates a stronger, more rapidly growing vortex. However, its trajectory is related to the wake deviation corresponding to the final rotation rate.

Medical students’ experience and perceptions of their final rotation in psychiatry

<p><strong>Background.</strong> Evaluation of specific courses, rotations or attachments in medical education is common practice.<strong> </strong></p><p><strong>Objective.</strong> To evaluate medical students’ perceptions of their final psychiatry rotation of 7 weeks. </p><p><strong>Methods.</strong> A questionnaire was developed for medical students to give feedback on their psychiatry rotation at Weskoppies Hospital in Tshwane, South Africa. Four scores were developed: (<em>i</em>) a clinical exposure score for psychiatric conditions encountered during the rotation; (<em>ii</em>) an ethics exposure score comprising confidentiality and informed consent; (<em>iii</em>) an admissions exposure score for different admission options; and (<em>iv</em>) a perception score related to students’ experience of the rotation. The evaluation took place over a period of 4 years, between 2006 and 2009.</p><p><strong>Results.</strong> Over the study period, 87% of 708 students completed the questionnaire. The higher number of female respondents (63%) was in accordance with the general student profile. The four resulting scores were: clinical exposure 67%; ethics exposure 78%; admissions exposure 86%; and perceptions 75%. The main strengths of the rotation were identified as the positive learning environment, exposure to patients, discussions and ward conferences, and approaches followed.</p><p><strong>Conclusions. </strong>The conceptualisation of the tool to elicit specific scores was useful for presenting the findings. The student feedback provided valuable information for the psychiatry curriculum planners and teachers, and led to further adaptations to the structure of the rotations and the learning opportunities provided.</p>

Disorientation Relations during the Early Stages of Recrystallization in Medium and Low SFE fcc Metals

The objective of this paper is to identify the predominant crystallographic relations between deformed state and recrystallized grains during the early stages of recrystallization of fcc metals with medium and low stacking fault energy. The experimental investigations, based on SEM/EBSD measurements, have focused on the transformations which occur in plane strain compressed single crystals with stable orientations. After annealing the disorientation across the recrystallization front 'defines' the final rotation by angles in the ranges of 25-35oand 45-55oaround axes mostly grouped near the <122>, <012>, <112> and <111> directions located around the normals of all four {111} slip planes.

Unsteady flow in a rotating torus after a sudden change in rotation rate

We consider the temporal evolution of a viscous incompressible fluid in a torus of finite curvature; a problem first investigated by Madden & Mullin (J. Fluid Mech., vol. 265, 1994, pp. 265–217). The system is initially in a state of rigid-body rotation (about the axis of rotational symmetry) and the container’s rotation rate is then changed impulsively. We describe the transient flow that is induced at small values of the Ekman number, over a time scale that is comparable to one complete rotation of the container. We show that (rotationally symmetric) eruptive singularities (of the boundary layer) occur at the inner or outer bend of the pipe for a decrease or an increase in rotation rate respectively. Moreover, on allowing for a change in direction of rotation, there is a (negative) ratio of initial-to-final rotation frequencies for which eruptive singularities can occur at both the inner and outer bend simultaneously. We also demonstrate that the flow is susceptible to a combination of axisymmetric centrifugal and non-axisymmetric inflectional instabilities. The inflectional instability arises as a consequence of the developing eruption and is shown to be in qualitative agreement with the experimental observations of Madden & Mullin (1994). Throughout our work, detailed quantitative comparisons are made between asymptotic predictions and finite- (but small-) Ekman-number Navier–Stokes computations using a finite-element method. We find that the boundary-layer results correctly capture the (finite-Ekman-number) rotationally symmetric flow and its global stability to linearised perturbations.

Nonlinear Spin-Up of a Rotating Stratified Fluid: Experimental Method and Preliminary Results

We consider the nonlinear spin-up of a rotating stratified fluid in a conical container. An analysis of similarity-type solutions to the relevant boundary-layer problem (Duck et al, 1997) has revealed three types of behavior for this geometry. In general, the boundary-layer evolves to either a steady state, a growing boundary-layer, or a finite-time singularity depending on the initial to final rotation rate ratio, and a “modified Burger number.” We emphasize the experimental aspects of our continuing spin-up investigations and make some preliminary comparisons with the boundary-layer theory, showing good agreement. The experimental data presented is obtained through particle tracking velocimetry. We briefly discuss the qualitative features of the spin-down experiments which, in general, are dominated by nonaxisymmetric effects. The experiments are performed using a conical container filled with a linearly stratified fluid, the generation of which is nontrivial. We present a general method for creating a linear density profile in containers with sloping boundaries.