Instabilities of the flow between a rotating and a stationary disk

Abstract

This experimental study is devoted to the description of the different patterns resulting from instabilities which appear in the flow between a rotating and a stationary disk enclosed by a stationary sidewall. With the help of visualizations we describe the different flow regimes as functions of two control parameters: the Reynolds number and the aspect ratio of the gap separating the disks, which are varied over large continuous ranges. Moreover, visualizations and ultrasonic anemometry lead to the description of the different instabilities and to the construction of a transition diagram that summarizes the domains of existence of the various patterns. Two different scenarios of transition are mainly followed by the flow. When the gap between the two disks is more than the thickness of the two disk boundary layers, circular and spiral waves destabilize the stationary disk boundary layer. Transition occurs in this case by the mixing of these waves. On the other hand, when the two boundary layers are merged, finite-size turbulent structures can appear. They consist of turbulent spots or turbulent spirals which invade the laminar domains as the Reynolds number of the flow is increased.

Large eddy simulation and measurements of turbulent enclosed rotor-stator flows

“…The transition to turbulence for separated boundary layer flows has been widely addressed experimentally [25,32] and numerically [35]. During the transition process in the laminar regime, the flow structures evolve from circular to spiral rolls.…”

A statistical study of spots in torsional Couette flow

“…A relaminarization of the flow was even observed at higher rotation speeds. The final transition process occurs by the nucleation of a growing number of tiny localized structures which were referred to "spots" by Schouveiler et al (13). Their appearance threshold is a function of the distance h between the discs and of the rotation rate Ω of the rotating disc.…”

“…As expected, dr affects the appearance of spots and figure 6-a) shows the influence of this gap width on the critical Reynolds number (2πΩRh/ν, where R is the radius of the rotating disc) where the spots appear. These measurements have been performed for each gap distance h. We performed four experiments (dr = 0.65, 1.25, 1.5 and 2 mm) and the results obtained by Schouveiler et al (13) for dr = 0.1 mm are also included in the figure. Figure 6 clearly shows that the gap size is a key parameter in the formation of spots and that the threshold is pushed to higher Reynolds numbers as the gap decreases as can be seen on figure 6-b).…”

Turbulence characteristics of the Bödewadt layer in a large enclosed rotor-stator system

“…Even though their geometry does not include any shaft, these values are close to the ones used in the present study, assuming that the effect of the shaft is less important for the occurrence of turbulence since the flow remains always laminar near the axis. Schouveiler et al [13] have identified two main routes for the transition to turbulence according to the aspect ratio. For G ≤ 14.01, the boundary layers are separated and the transition was found to occur through a sequence of supercritical bifurcations leading to wave turbulence, resulting from the interaction between circular and spiral rolls.…”