Simultaneous PIV and thermography measurements of partially blocked flow in a differentially heated rotating annulus

Abstract

A radial barrier has been mounted in a differentially heated rotating annulus that partially blocks the azimuthal flow component. The experiment can be seen as an analog to geophysical flows with constrictions, e.g., the Antarctic Circumpolar Current. However, the experiment has been carried out without a particular natural flow in mind. The main interest was to observe a baroclinic annulus flow that does not become saturated. Hence, in contrast to the annulus flow without a barrier, the partially blocked flow remains transient and surface heat fluxes associated with baroclinic life cycles can be studied. The annulus can be subdivided into the upstream half of the barrier, where waves amplify, and the downstream half of the barrier, where waves decay. In the upstream half, the azimuthal mean flow is moderate but with a significant positive eddy radial heat flux. In the downstream half, we find a strong jet in the mean azimuthal flow and furthermore an increased radial mean temperature gradient. The latter points to a weakened or even reversed radial eddy heat flux in the lee side of the barrier. Temperature anomalies appear as large bulges in the outer part of the annulus. Moreover, an outward shift of vortex centers can be observed with respect to centers of temperature anomalies. This phase shift between pressure and temperature anomalies differs from that of classical Eady modes of baroclinic instability.

Benchmarking in a rotating annulus: a comparative experimental and numerical study of baroclinic wave dynamics

“…The extra potential energy stored in this unstable configuration is then converted into kinetic energy, exciting drifting wave patterns of temperature and momentum anomalies. The basic underlying physics of such baroclinic waves has been subject of extensive theoretical (EADY, 1949;MASON, 1975;LORENZ, 1963), numerical (WILLIAMS, 1971;MILLER and BUTLER, 1991;VON LARCHER et al, 2013) and experimental (FRÜH and READ, 1997;SITTE and EG-BERS, 2000;VON LARCHER et al, 2005;HARLANDER et al, 2012) research throughout the past decades. Furthermore, some studies focused on the quantitative comparison of temperature statistics (GYÜRE et al, 2007) and propagation dynamics of passive tracers (JÁNOSI et al, 2010) obtained from annulus experiments and from actual atmospheric data.…”

An experimental study of regime transitions in a differentially heated baroclinic annulus with flat and sloping bottom topographies

“…Seelig et al, 2012;Read, 1992) and experimental (e.g. Früh and Read, 1997;von Larcher and Egbers, 2005;Harlander et al, 2012) research throughout the past decades. Furthermore, some studies focused on the quantitative comparison of temperature statistics (Gyüre et al, 2007) and propagation dynamics of passive tracers (Jánosi et al, 2010) obtained from annulus experiments and from actual atmospheric data.…”

Orthogonal Decomposition Methods to Analyze PIV, LDV, and Thermography Data of Thermally Driven Rotating Annulus Laboratory Experiments

“…In Section 17.3.2 we discussed simultaneous surface temperature and PIV measurements. From these data the surface eddy heat flux can be derived [Harlander et al, 2012a]. A future systematic study of the surface eddy heat flux for different flow regimes and annulus geometries would help to understand better the transient eddies and their feedback on the mean flow [Wilson and Williams, 2006].…”

“…At the barrier, the gap width is reduced from 75 to 43 mm and the fluid depth is reduced from 135 to 95 mm. More details can be found in the work of Harlander et al [2012a]. Figure 17.7 shows a sequence of surface temperature images taken from an experiment in standard geometry with = 4.6 rpm and T = 2.8 K. We see the baroclinic wave after 69, 73, and 77 revolutions.…”

“…Therefore, amplitude and phase information is contained in a single CEOF. More specifically, we will apply a combined CEOF Analysis to find connected propagating anomalies of surface temperature and velocity [Harlander et al, 2012a]. Frequently, the dominant components of a high-dimensional process are captured with often surprisingly few "modes" and thus the CEOF analysis is an efficient technique for dimension reduction.…”