Cavity flow induced by a fluctuating acceleration field

Abstract

Flow induced by a random acceleration field (g-jitter) is considered in two related situations that are of interest for microgravity fluid experiments: the random motion of an isolated buoyant particle and coarsening of a solid-liquid mixture. We start by analyzing in detail actual accelerometer data gathered during a recent microgravity mission, and obtain the values of the parameters defining a previously introduced stochastic model of this acceleration field.We then study the motion of a solid particle suspended in an incompressible fluid that is subjected to such random accelerations. The displacement of the particle is shown to have a diffusive component if the correlation time of the stochastic acceleration is finite or zero, and mean squared velocities and effective diffusion coefficients are obtained explicitly. Finally, the effect of g-jitter on coarsening of a solid-liquid mixture is considered. Corrections due to the induced fluid motion are calculated, and estimates are given for coarsening of Sn-rich particles in a Sn-Pb eutectic fluid, experiment to be 1 conducted in microgravity in the near future.

Impact of stochastic accelerations on dopant segregation in microgravity semiconductor crystal growth

“…The convective response of the velocity field in a cavity with a stochastic g-jitter transversal to a thermal gradient in a generic fluid configuration was studied in detail in [16]. Here we will extend that approach to include typical confined crystal growth configurations and the coupling of the dopant concentration field to the flow field.…”

“…[13], and stochastic modeling of g-jitters was applied to different physical processes relevant to both fundamental physics and space technology, such as in coarsening of colloidal suspensions [13], fluid-fluid interfaces [14,15] and in thermal natural convection [16]. In the present paper we pursue this approach in a realistic modelization of different prototypic setups of crystal growth in microgravity in the context of semiconductor materials.…”

“…Following Refs. [14][15][16], we will model a generic stochastic acceleration environment by means of the so-called narrow-band noise, a rather general Gaussian stochastic process that is characterized by three parameters: the noise intensity, a characteristic dominant frequency where it may be peaked, and a correlation time that controls band width of the frequency spectrum. This stochastic process interpolates between the two extreme cases of white noise and single-frequency noise.…”

Coarsening of solid-liquid mixtures in a random acceleration field

“…The analysis described in this section is based on actual g-jitter data collected during the SL-J mission ͑SAMS-258͒ that flew on September [13][14][15][16][17][18][19][20]1993. We have focused on the head A SAMS detector, and studied the series during the time window MET 0017 to MET 0023, roughly a period of six hours.…”

“…9 The approach presented in this paper, on the other hand, models g-jitter as a random process in time. 12,13 We assume that the process obeys Gaussian statistics, consistent with the assumption that many independent sources contribute to the acceleration field, thus requiring the knowledge of only the first two statistical moments of the effective acceleration field g ជ (t). We choose ͗g ជ ͘ϭ0, where ͗͘ denotes an ensemble average.…”