Estimates on diagnostic methods for investigations of thermal convection between spherical shells in space

Abstract

Thermal convection in a spherical shell represents an important model in fluid dynamics and geophysics. Investigations on thermal convective instabilities occurring in the spherical gap flow under terrestrial conditions are of basic importance, especially for the understanding of symmetry-breaking bifurcations during the transition to chaos. Microgravity experiments on thermal convection with a simulated central force field are important for the understanding of large-scale geophysical motions such as the convective transport phenomena in the Earth's liquid outer core. More than one diagnostic tool is needed to examine and characterize the different flow types. Flow visualization, Wollaston shearing interferometry and laser Doppler velocimetry should be available for space experiments. This report summarizes concurrent theoretical, numerical and experimental studies for the preparation of a Get Away Special (Shuttle) experiment as well as a Space Station experiment inside the Fluid Science Laboratory. The special experimental device for investigations of supercritical and turbulent thermal convection in spherical shells under a central force field with respect to geophysical simulations is called an electrohydrodynamic container. A central symmetric force field similar to the gravity field acting on planets can be produced using the effect of the dielectrophoretic force field by applying a high-voltage potential difference to the inner and outer sphere.

Thermal convection in rotating spherical shells: An experimental and numerical approach within GeoFlow

“…Fig. 6 gives the principle of set-up Wollaston shearing interferometry as used measurement method [13]. It shows a modular Wollaston shearing interferometer which also works as Schlieren and shadowgraphy by changing only the optical component in focal point of lense L 2 , which is Wollaston prism, cutting edge or just nothing, respectively.…”

Experiments on Core Dynamics

“…Apart from space experiments made in the microgravity environment of Earth's orbit (Hart et al, 1986;Egbers et al, 1999), all laboratory investigations of rotating spherical convection in planetary cores rely on the centrifugal force as a substitute for the radial gravity force. It is not difficult for centrifugal acceleration to dominate over laboratory gravity in a rotating apparatus.…”

Laser Doppler velocimetry using powerful solid-state light sources

“…It has probably turned out to be the most important optical instrument for the investigations of turbulent flows due to its precise velocity measurement with high temporal and spatial resolution. The requirements to verify the results from direct numerical simulation (DNS) and applications planned in sophisticated experiments, for instance microgravity measurements aboard the International Space Station (ISS) [22], have initiated straight-ahead improvements of LDV. Recently, successful attempts on micron resolution velocimetry techniques were reported [23,24].…”