Fluid dynamics during Random Positioning Machine micro-gravity experiments

Carole A.D. Leguy, René Delfos, Mathieu J.B.M. Pourquie, Christian Poelma, Jerry Westerweel, Jack J.W.A. van Loon*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


A Random Positioning Machine (RPM) is a device used to study the role of gravity on biological systems. This is accomplished through continuous reorientation of the sample such that the net influence of gravity is randomized over time. The aim of this study is to predict fluid flow behavior during such RPM simulated microgravity studies, which may explain differences found between RPM and space flight experiments. An analytical solution is given for a cylinder as a model for an experimental container. Then, a dual-axis rotating frame is used to mimic the motion characteristics of an RPM with sinusoidal rotation frequencies of 0.2 Hz and 0.1 Hz while Particle Image Velocimetry is used to measure the velocity field inside a flask. To reproduce the same experiment numerically, a Direct Numerical Simulation model is used. The analytical model predicts that an increase in the Womersley number leads to higher shear stresses at the cylinder wall and decrease in fluid angular velocity inside the cylinder. The experimental results show that periodic single-axis rotation induces a fluid motion parallel to the wall and that a complex flow is observed for two-axis rotation with a maximum wall shear stress of 8.0 mPa (80 mdyne/cm2). The experimental and numerical results show that oscillatory motion inside an RPM induces flow motion that can, depending on the experimental samples, reduce the quality of the simulated microgravity. Thus, it is crucial to determine the appropriate oscillatory frequency of the axes to design biological experiments.

Original languageEnglish
Pages (from-to)3045-3057
Number of pages13
JournalAdvances in Space Research
Issue number12
Publication statusPublished - 15 Jun 2017

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