Mode Of Azimuthal Wavenumber Research Articles

Effect of interfacial heat exchange on thermocapillary flow in a cylindrical liquid bridge in microgravity

The effect of interfacial heat exchange on thermocapillary flow in a cylindrical liquid bridge of 1 cst silicone oil (with Prandtl number 16.0) with aspect ratio 1.8 in microgravity, was investigated in an extended range of Biot number. With both constant and linearly distributed ambient temperature, the computed results predict that the marginal stability curve for the thermocapillary flow exhibits a roughly convex trend. In the range of small Biot number, however, a sharp local maximum exists with a special oscillation mode of azimuthal wave number m = 0, in contrast to the other cases with m = 1. In addition, the normalized “thermal” energy balance between the basic state and the critical perturbation of the thermocapillary flow was investigated. Finally, the effect of the interfacial heat exchange on the thermocapillary flow in a liquid bridge of low Prandtl number fluid in microgravity was investigated as a comparison.

Inviscid instability of the Batchelor vortex: Absolute-convective transition and spatial branches

The main objective of the study is to examine the spatio-temporal instability properties of the Batchelor q-vortex, as a function of swirl ratio q and external axial flow parameter a. The inviscid dispersion relation between complex axial wave number and frequency is determined by numerical integration of the Howard–Gupta ordinary differential equation. The absolute-convective nature of the instability is then ascertained by application of the Briggs–Bers zero-group-velocity criterion. A moderate amount of swirl is found to promote the onset of absolute instability. In the case of wakes, transition from convective to absolute instability always takes place via the helical mode of azimuthal wave number m=−1. For sufficiently large swirl, co-flowing wakes become absolutely unstable. In the case of jets, transition from absolute to convective instability occurs through various helical modes, the transitional azimuthal wave number m being negative but sensitive to increasing swirl. For sufficiently large swirl, weakly co-flowing jets become absolutely unstable. These results are in good qualitative and quantitative agreement with those obtained by Delbende et al. through a direct numerical simulation of the linear response. Finally, the spatial (complex axial wave number, real frequency) instability characteristics are illustrated for the case of zero-external flow swirling jets.

Satellite and hydrographic observations of low‐frequency wave motions associated with a cold core Gulf Stream ring

Thermal infrared data from the NOAA polar orbiting satellite and hydrographic observations from surface ships are used to estimate the eccentricity and the rotation rate of wavelike perturbations around the circumference of a Gulf Stream cyclonic eddy in April 1977. From the satellite data, the rotation rate is estimated at ω = (4.4 ± 0.1) × 10−6 s−1 for the period April 8–16. Estimates of ω are obtained from the trajectory of satellite‐tracked drifters and from changes in the sea surface temperature fields determined from expendable bathythermograph trace (XBT) surveys. A simple Eady model suggests the perturbations are stable modes of azimuthal wave number 2.