Experimental investigation of stratorotational instability using a thermally stratified system: instability, waves and associated momentum flux

Stratorotational instability (SRI) has been proposed as a mechanism for outward angular momentum transport in Keplerian accretion disks [1]. A particular designed Taylor-Couette laboratory experiment with axial stratification is suitable for studying the instability. Bottom endplate is cooled and top endplate is heated to achieve axial stratification. Due to constructive constraints, endplates are visually unamenable and quantitative measurement techniques in the co-rotating frame can only be done by looking through the outer cylinder. For this purpose, we built a co-rotating mini-PIV (Particle Image Velocimetry) system with a camera having a tilted viewing angle regarding the horizontal laser sheet. We perform measurements of the azimuthal and radial component of the velocity in axial stably stratified Taylor-Couette flow. The absolute error of the mini-PIV system is 2% and we realised that stratified Taylor-Couette flows have smaller Ekman end-wall effects than homogeneous ones. In the presentation [2] we focus on the flow structure, the drift rate of SRI modes and the radial momentum flux as a function of the Reynolds number along the Keplerian line (Ω ∝ r^-3/2). The structure in form of trapped boundary Kelvin modes and the drift rate corresponds well with earlier predictions. We also demonstrate that in the Rayleigh stable flow regime the SRI can provide a significant amount of outward momentum flux which makes this instability interesting in the context of accretion disks and also of atmospheric vortices where rotation and stratification also play a significant role.

References [1] Gellert, M., Rüdiger, G.: Stratorotational instability in Taylor-Couette flow heated from above. J. Fluid Mech. 623, 375-385 (2009) [2] Seelig, T., Harlander, U., Gellert, M.: Experimental investigation of stratorotational instability using a thermally stratified system: instability, waves and associated momentum flux. Geophysical & Astrophysical Fluid Dynamics 112(4), 239-264 (2018)