A new approach to g-level tolerability for fluid and material science experiments

Abstract

The g-level tolerability of Fluid and Material Science experiments is analyzed in the general case of quasi steady residual g-levels superimposed to high frequency g-jitters. The results of the non-dimensional Order of Magnitude Analysis (Napolitano's method) are extended to the non-linear problem accounting for non-zero average steady flow induced by high frequency oscillations, leading to a new criterion for assessing the maximum g-level in terms of the maximum allowable value of the vibrational Rayleigh number. The numerical analysis of the Thermo-Fluid-Dynamic (TFD) distortions, as function of the classical Rayleigh number (Ra g), for steady g, and of the vibrational Rayleigh number (Ra v), for high frequency g-jitters, is carried out by means of a time-averaged formulation obtained under the assumption of high frequencies and small amplitudes of the g-disturbances. On the basis of these results, the g-tolerability domain, in the plane (g/g0, Ω), is drawn for a study case on thermal diffusion in a fluid cell. Numerical solutions of the full time-dependent Navier-Stokes equations are carried out to evaluate the range of applicability of the time-averaged formulation. Finally, combined steady and average vibrational convection, corresponding to the realistic situation of steady residual g-levels superimposed to high frequency periodic g-jitters is considered, and particular attention is focused on the evolution, as function of the time, of the TFD distortions in the transient energy diffusion phase.