Dynamics In Microgravity Research Articles

Bloodstain pattern dynamics in microgravity: Observations of a pilot study in the next frontier of forensic science

As humanity advances into a space-faring species, the risk of injury by multiple means and intentions will follow. Expanding understanding of how forensic science adapts to extraterrestrial environments is a novel and inevitable expansion into the next forensic frontier. This study considers the unique challenges of bloodstain pattern analysis in microgravity environments. Specifically, observation in novel experimentation aboard a parabolic flight research airplane which yielded fluid dynamic behaviors in a microgravity environment that provides practical understanding of Earth-based and off-world bloodstain applications.

Bubble nucleation and growth on microstructured surfaces under microgravity

Understanding the dynamics of surface bubble formation and growth on heated surfaces holds significant implications for diverse modern technologies. While such investigations are traditionally confined to terrestrial conditions, the expansion of space exploration and economy necessitates insights into thermal bubble phenomena in microgravity. In this work, we conduct experiments in the International Space Station to study surface bubble nucleation and growth in a microgravity environment and compare the results to those on Earth. Our findings reveal significantly accelerated bubble nucleation and growth rates, outpacing the terrestrial rates by up to ~30 times. Our thermofluidic simulations confirm the role of gravity-induced thermal convective flow, which dissipates heat from the substrate surface and thus influences bubble nucleation. In microgravity, the influence of thermal convective flow diminishes, resulting in localized heat at the substrate surface, which leads to faster temperature rise. This unique condition enables quicker bubble nucleation and growth. Moreover, we highlight the influence of surface microstructure geometries on bubble nucleation. Acting as heat-transfer fins, the geometries of the microstructures influence heat transfer from the substrate to the water. Finer microstructures, which have larger specific surface areas, enhance surface-to-liquid heat transfer and thus reduce the rate of surface temperature rise, leading to slower bubble nucleation. Our experimental and simulation results provide insights into thermal bubble dynamics in microgravity, which may help design thermal management solutions and develop bubble-based sensing technologies.

Three-Dimensional Numerical Simulation of Bubble Dynamics in Microgravity under the Influence of Nonuniform Electric Fields

A three-dimensional VOSET method is used along with the adaptive mesh refinement (AMR) method to simulate the behaviors of a bubble departing from the outside wall of a horizontal square-cross-section tube in microgravity under the influence of nonuniform electric fields. The effects of gravity, electric field intensity, fluid permittivity, and bubble initial position on the bubble detachment and rising are investigated and analyzed. Computational results show that the gravity and electric fields have significant influences on the bubble detachment and rising velocity and rising trajectory. Decrease in gravity results in the decrease in the buoyancy exerted on the bubble, considerably mitigating the rising capability of the bubble and delaying the bubble detachment. Imposing a nonuniform electric field, which exhibits physically the strongest intensity in regions near the tube wall, can supply an additional driving force as a replacement of the buoyancy to accelerate the bubble detachment and rising. It is also shown that a larger electric field intensity or larger ratio of liquid permittivity to gas permittivity leads to a larger deformation, easier detachment, and larger rising velocity, of the bubble. The nonuniformity of the electric fields can also affect the bubble motion trajectory and result in the asymmetric deformation of the bubble.

In situ and real time characterization of interface microstructure in 3D alloy solidification: benchmark microgravity experiments in the DECLIC-Directional Solidification Insert on ISS

Dynamical microstructure formation and selection during solidification processing, which has a major influence on the properties in the use of elaborated materials, occur during the growth process. In situ observation of the solid-liquid interface morphology evolution is thus necessary. On earth, convection effects dominate in bulk samples and may strongly interact with microstructure dynamics and alter pattern characterization. Series of solidification experiments with 3D cylindrical sample geometry were conducted in succinonitrile (SCN) –0.24 wt%camphor (model transparent system), in microgravity environment in the Directional Solidification Insert of the DECLIC facility of CNES (French space agency) on the International Space Station (ISS). Microgravity enabled homogeneous values of control parameters over the whole interface allowing the obtaining of homogeneous patterns suitable to get quantitative benchmark data. First analyses of the characteristics of the pattern (spacing, order, etc.) and of its dynamics in microgravity will be presented.

Observations on braided thin wire nucleate boiling in microgravity

A microgravity experiment was conducted on the Space Shuttle Endeavor (STS-108) to observe sustained nucleate boiling of water. Subcooled water was boiled with a single strand and a braid of three 0.16 mm diameter and 80 mm long Nichrome resistive wires. A CCD video camera recorded the experiment while six thermistors recorded the temperature of the fluid at various distances from the heating element. This paper reports experimental results in observations, measurements, and data analysis. Bubble explosions were found to take place shortly after the onset of boiling for both the single and braid of wires. The explosion may produce a high heat transfer rate, as it generates a cloud of microbubbles. The number, size, and departure rate of the bubbles from the heater wire were measured and compared with theoretical models as a function of time. The temperature measurements revealed a complex temperature distribution in the fluid chamber due to bubbles ejected from the wire that carried thermal energy close to the temperature sensors. Drag forces on departing bubbles were calculated based on bubble movement and used to predict bubble propagation. Results from this experiment provided further understanding of nucleate boiling dynamics in microgravity for the eventual design and implementation of two-phase heat transfer systems in space applications.

Numerical Simulation of Bubble Dynamics in Microgravity

A numerical method for the simulation of two-phase flows under microgravity conditions is presented in this paper. The level set method is combined with the moving mesh method in a collocated grid to capture the moving interfaces of the two-phase flow, and a SIMPLER-based method is employed to numerically solve the complete incompressible Navier-Stokes equations, and the surface tension force is modeled by a continuum surface force approximation. Based on the numerical results, the coalescence process of two bubbles under microgravity conditions (10 − 2×g) is compared to that under normal gravity, and the effect of gravities on the bubbles coalescence dynamics is analyzed. It is showed that the velocity fields inside and around the bubbles under different gravity conditions are quite similar, but the strength of vortices behind the bubbles in the normal gravity is much stronger than that under microgravity conditions. It is also found that under microgravity conditions, the time for two bubbles coalescence is much longer, and the deformation of bubbles is much less, than that under the normal gravity.

Actin dynamics in mouse fibroblasts in microgravity

After stimulating with the growth factor PDGF, cells exhibit abundant membrane ruffling and other morphological changes under normal gravity conditions. These morphological changes are largely determined by the actin microfilament system. Now these actin dynamics were studied under microgravity conditions in mouse fibroblasts during the DELTA mission. The aim of the present study was to describe the actin morphology in detail, to establish the effect of PDGF on actin morphology and to study the role of several actin-interacting proteins involved in introduced actin dynamics in microgravity. Identical experiments were conducted at 1G on earth as a reference. No results in microgravity were obtained due to a combination of malfunctioning hardware and unfulfilled temperature requirements.

Simulation of capillary flow with a dynamic contact angle

A number of theoretical and empirical dynamic contact angle (DCA) models have been tested in a numerical simulation of liquid reorientation in microgravity for which experimental validation data are available. It is observed that the DCA can have a large influence on liquid dynamics in microgravity. Correct modelling of the DCA is found to be essential for realistic numerical simulation, and hysteresis effects cannot be ignored.

Surfactant-bearing drop dynamics in microgravity

Experiments of large amplitude nonlinear oscillations of axially symmetric surfactant-bearing (triton or bovine serum albumin) water drops with different initial aspect ratios and drop volumes were performed during the second United States Microgravity Laboratory, USML-2 in November 1995. Through the numerical simulation of the oscillations of these surfactant-bearing water drops using the boundary integral method, the surface dilatational viscosity and the surface shear viscosity are found to play a major role in these oscillations. How they influence the damping coefficient and the drop oscillation frequency will be presented. The numerical and analytical results and a physical picture of the relation between the surface viscosities and the damping coefficient will be described. In addition, the relation between the initial drop aspect ratio, the surface viscosities, and the surface rotational velocity will also be presented. [Work supported by NASA through JPL, Contract No. 958722.]

Drop dynamics in microgravity

The dynamics of liquid drops in microgravity were observed in the Drop Physics Module flown aboard the second United States Microgravity Laboratory (USML-2) in 1995. Water drops with varying concentrations of the surfactants Triton-X 100 and Bovine Serum Albumin were suspended in air and deformed by an acoustic standing wave. When the deforming force was removed, the drops oscillated freely about a spherical equilibrium shape, as opposed to the oblate equilibrium shape of a drop levitated in 1-g. Drop diameters between 1 and 3 cm were observed. Frequencies and decays for the dynamics have been extracted from the data. Results are compared to theoretical models and experiments in 1-g. Results for frequency shifts due to large amplitude oscillations are also presented. [Work supported by NASA through JPL, contract 958722.]

Force-State Characterization of Struts Using Pinned Joints

As part of a research effort to study the microgravity dynamics of a truss with pinned joints, a single strut with a single clevis-tang pinned joint was characterized. Experimental data was collected using a force-state mapping technique. The strut was subjected to axial dynamic loads and the response of the strut was measured. The force-state map aids visualization of the strut dynamics. Finite element modeling of the response was explored. An example is presented that uses a method of manual determination of the finite element model parameters. The finite element model results correspond well with the measured strut response.

Cryogenic design of the liquid helium experiment Critical Dynamics in Microgravity

Although many well-controlled experiments have been conducted to measure the static properties of systems near criticality, few experiments have explored the transport properties in systems driven far away from equilibrium as a phase transition occurs. The cryogenic design of an experiment to study the dynamic aspect of critical phenomena is reported here. Measurements of the thermal gradient across the superfluid (He II)-normal fluid (He I) interface in helium under microgravity conditions will be performed as a heat flux holds the system away from equilibrium. New technologies are under development for this experiment, which is in the definition phase for a space shuttle flight.

Effect of gravity on the thermal conductivity measurement of4He nearT λ

Precision measurements near the superfluid (λ) transition of4He is limited by a gravity induced inhomogeneity inT λ. Critical Dynamics in Microgravity (DYNAMX, a NASA preproject) will study the thermal conductivity in the nonlinear region in Microgravity. Unlike the study of static properties, the thermal conductivity can be derived from the measurement of the spatial temperature profile which is essentially alocal measurement of the temperature gradient. We present a method which, in principle, fully removes the apparent impact of gravity from the measurement. The inevitably finite spatial resolution of the probe and temperature resolution of the thermometer, however, make microgravity essential to study the region of interest.

Fluid statics and dynamics in microgravity

Research into fluid physics under reduced gravity conditions has been stimulated by basic research and numerous applications. For example, research includes the shape and stability of liquid surfaces; the bifurcation of convective flows; the stability of Marangoni flows; and with respect to applications, surface tension tanks; spacecraft dynamics; crystal growth; the production of composite materials and the extremely large field of life sciences. The stability criteria of liquid bridges between coaxial circular discs are discussed. The stability of liquid volumes at edges is considered. Respective experiments performed in parabolic flights of a KC-135 aircraft, in sounding rockets and in the Spacelab are reported. Special attention is paid to the various effects of Marangoni convection on crystal growth and on the separation of binary liquid mixtures exhibiting a miscibility gap.