Development of a Couette–Taylor flow device with active minimization of secondary circulation

Abstract

A novel Taylor-Couette experiment has been developed to produce rotating shear flows for the study of hydrodynamic and magnetohydrodynamic instabilities which are believed to drive angular momentum transport in astrophysical accretion disks. High speed, concentric, corotating cylinders generate the flow where the height of the cylinders is twice the radial gap width. Ekman pumping is controlled and minimized by splitting the vertical boundaries into pairs of nested, differentially rotating rings. The end rings and cylinders comprise four independently driven rotating components which provide flexibility in developing flow profiles. The working fluids of the experiment are water, a water-glycerol mix, or a liquid gallium alloy.The mechanical complexity of the apparatus and large dynamic pressures generated by high speed operation with the gallium alloy presented unique challenges. The mechanical implementation of the experiment and some representative results obtained with Laser Doppler Velocimetry in water are discussed.

Angular momentum transport and turbulence in laboratory models of Keplerian flows

“…Schartman et al (2012) state that these incompatible results are caused by differing interpretations of finite-size effects, namely Ekman circulation produced by the axial boundaries. In the Princeton experiments (Ji et al 2006;Schartman et al 2009;Burin et al 2010;Schartman et al 2012) the aspect ratio is small (Γ ≈ 2) and therefore finite-size effects would likely dominate. To minimize Ekman circulation, their axial boundaries are split into pairs of rings that can independently rotate with respect to the cylinders.…”

“…To further address this issue from a numerical standpoint, Avila (2012) performed direct numerical simulations of our experimental geometry as well as the Princeton apparatus (Ji et al 2006;Schartman et al 2009;Burin et al 2010;Schartman et al 2012). Avila found that the axial boundaries drive secondary flows that enhance the global angular momentum transport.…”

“…To minimize Ekman circulation, their axial boundaries are split into pairs of rings that can independently rotate with respect to the cylinders. This method has been shown to reduce the effects of Ekman circulation in the bulk of the fluid (Schartman et al 2009). Furthermore, when Ekman circulation is not minimized their measured values of β for quasi-Keplerian flows are approximately half of the typical values presented here.…”

“…This split-ring approach has been further developed to allow for pairs of rings that can independently rotate with respect to the cylinders. Allowing the axial boundaries to independently rotate aids in the suppression of finite-size effects (Ji et al 2006;Schartman et al 2009;Burin et al 2010).…”

“…The torque is measured over the middle part of the inner cylinder of height L mid = 53.6 cm to minimize the influence of the endplates (similar to Lathrop et al 1992b,a). The torque is measured by a load cell imbedded inside the middle section of the inner cylinder in both the Twente and Maryland experiments, in contrast to measuring the torque on the drive shaft that would be affected by mechanical seals in the end plates or by velocimetry measurements, as in the Princeton experiments (Ji et al 2006;Schartman et al 2009;Burin et al 2010;Schartman et al 2012). …”