arXiv subjects

Brendan B. Plapp

Publications and source records attributed to Brendan B. Plapp.

4 recordsLinked to original sources

arXiv2001

Anomalous self-similarity in two-dimensional turbulence

Our velocity measurements on a quasi-two-dimensional turbulent flow in a rapidly rotating annulus yield an inverse cascade with E(k)~k^{-2} rather than the expected E(k)~k^{-5/3}. The probability distribution functions for longitudinal velocity differences, δ_v(r)=v(x+r)-v(x), are self-similar (scale independent) but strongly non-Gaussian, which suggests that the coherent vortices play a significant role. The structure functions, <[δ_v(r)]^p>~r^{ζ_p}, exhibit anomalous scaling: ζ_p=p/2 rather than ζ_p=p/3 as in the 1941 Kolmogorov theory.

physics.flu-dyn↗

arXiv1998

Dynamics and Selection of Giant Spirals in Rayleigh-Benard Convection

For Rayleigh-Benard convection of a fluid with Prandtl number σ\approx 1, we report experimental and theoretical results on a pattern selection mechanism for cell-filling, giant, rotating spirals. We show that the pattern selection in a certain limit can be explained quantitatively by a phase-diffusion mechanism. This mechanism for pattern selection is very different from that for spirals in excitable media.

patt-sol↗

arXiv1997

Transition from Spatiotemporal Chaos to Ideal Straight Rolls in Rayleigh-Benard Convection

For Rayleigh-Benard convection in a square cell with a fluid of Prandtl number one, we report experimental results on the transition between a stationary pattern of ideal straight rolls (ISR) and the spatiotemporal chaotic state of spiral defect chaos (SDC). In contrast to experiments in circular geometries, we found ISR states below a particular value of the control parameter and SDC states above this value. By characterizing the pattern with a global measure, the pattern entropy, we found that the transition from SDC to ISR showed similarities to phase transitions in equilibrium finite-size systems.

patt-sol↗

arXiv1996

Core Dynamics of Multi-Armed Spirals in Rayleigh-Benard Convection

We report experimental observations of the core dynamics of multi-armed, rotating spirals in Rayleigh-Benard convection for a fluid with Prandtl number near one. In addition to the large-scale rotation of the spirals, we found a cyclic core motion within a central area of radius r = appr. (n lambda/2), where n is the number of spiral arms ending in the core and lambda is the wavelength of the pattern. The dynamics of the core was much faster than the large-scale spiral rotation. We observed multi-armed spirals for which the two periods were commensurate and others for which they were incommensurate.

patt-sol↗