Microgravity Science and Technology最新文献

In the present study, opposed flow flame spread over several fuel configurations of thin cellulosic fuels are investigated experimentally in normal gravity and microgravity environments. The fuel is configured in different shapes, namely, planar, hollow cylindrical (circular duct), C channel, and L channel, with the help of specifically designed fuel sample holders. The flame spread phenomena are examined for each configuration in both normal gravity and microgravity environments under ambient conditions of 21% oxygen and 1 atm. pressure. The microgravity experiments are conducted using a 2.5 s drop tower facility. The flame spread rates are measured at various opposed flow speeds. The effective flow speed accounts for the induced reference buoyant flow speed and externally imposed flow. The flame spread rates for each configuration are plotted against the effective flow speed ranging from 10 cm/s to 40 cm/s. While there is a nonmonotonic increasing-decreasing flame spread rate trend with respect to the effective opposed flow speed for all configurations, the flame spread rate can vary significantly with changes in the configuration. The C-channel configuration shows the highest flame spread rate compared with the other configurations of the same scale and identical experimental conditions. The effect of fuel size on the flame spread rate is also investigated for the duct configuration. The flame spread rate is noted to increase with the increase in fuel diameter.

This work summarizes the first results from a cloud seeding in microgravity experiment built by the Saudi Space Agency (SSA) and conducted on the International Space Station (ISS). The microgravity conditions provided in the ISS enable examining the interaction between the seeding agent, silver iodide, and the water droplets. Silver iodide particles dynamics of radius of 0.6, 0.3, 0.2, and 0.1 μm are examined in the ground and at the ISS at room temperature and atmospheric pressure in four 5cm³ chambers. Meanwhile, computer simulations are employed to examine the dynamics of seeding agent falling under the effect of gravity. It is found that microgravity conditions along with reducing seeding particles’ size enhance the interaction between seeding particles and the water droplets by increasing the period at which particles staying in the air before dropping down to the floor of the experiment. Humidity level in the experiment is observed to decrease onboard of the ISS because of the interaction between seeding agent and the water droplets.

The research on granular column collapse under various gravity levels is of great significance for the study of granular rheology and its applications in reduced-gravity space engineering. We firstly reviewed a rare experimental investigation that observed a gravity-related run-out distance of the granular column collapse in this paper. To identify the origin of the gravity-related run-out distance, a unified constitutive model was used to simulate the behavior of granular materials in these experiments based on a large deformation numerical method, the smoothed particle hydrodynamics (SPH). The parameters of this constitutive model were also discussed. Numerical simulations can reproduce the run-out distances that positively correlate with the gravity level, above 0.03 g in particular. Based on the numerical and constitutive analysis, this gravity-related runout distance is attributed to the combined influence of gravity-induced pressure and shear strain rate levels on granular flow.

This work investigates the capillary rise dynamics of highly wetting liquids in a divergent U-tube in the microgravity conditions provided by 78th European Space Agency (ESA) parabolic flight. This configuration produces a capillary-driven channel flow. We use image recording in backlight illumination to characterize the interface dynamics and dynamic contact angle of HFE7200 and Di-Propylene Glycol (DPG). For the case of HF7200, we complement the interface measurements with Particle Tracking Velocimetry (PTV) to characterize the velocity fields underneath the moving meniscus. In the DPG experiments, varying liquid column heights are observed, with a notable decrease in meniscus curvature when the contact line transitions from a pre-wetted to a dry substrate. In contrast, for HFE7200, the interface consistently advances over a pre-wetted surface. Despite this, a reduction in meniscus curvature is detected, attributed to inertial effects within the underlying accelerating flow. PTV measurements reveal that the region where the velocity profile adapts to the meniscus velocity decreases as interface acceleration increases, suggesting a direct relationship between acceleration and the velocity adaptation length scale.

According to the existing scenarios of interplanetary missions, the Moon is considered as an intermediate base on the way to deep space. In order to prepare for landing and work on the Moon, it is important to study the applicability of countermeasures in such missions. The paper presents the results of a pilot study performed during a short-term spaceflight (12 days). A new experience of using countermeasure impacts of lower body negative pressure (LBNP) at the early stages of adaptation to microgravity conditions has been gained. To assess the effectiveness of LBNP and changes in human physical performance after the spaceflight, we conducted tests on a treadmill, a bicycle ergometer, and testing with model tasks of on-planetary activity "express test". Regulatory mechanisms of the cardiovascular system proved to be quite effective when creating decompression up to -20 mm Hg, which is less than in preparation for returning to Earth. In the treadmill test, a lower speed was achieved after the spaceflight than before (13 km/h and 15 km/h, respectively) and cardiovascular system response to the change in load was slower. At the same time changes in such physiological parameters as oxygen consumption, respiratory rate and pulmonary ventilation were minimal. In the bicycle ergometer test, peak heart rate values were higher after the spaceflight than before, the physiological value of the standard exercise increased. «Express test» showed the positive dynamics from the first day to the third after returning to Earth: the performance of a dual task, the task of controlling the movement of the non-leading hand, and getting up from the supine position improved. Thus, assessment of the state of gravity-dependent physiological systems after short-term flight indicates the decrease of functional reserves of the organism and the necessity to develop appropriate countermeasures. The study was one of the first steps in the development of new medical control operations at the stage of paradigm shift from orbital flights to deep space exploration.

The paper presents studies on the correctness of the application of the simplified Boer formula for estimating the components of the angular velocity vector of the spacecraft using the example of the small ISOI spacecraft (SXC3-219). The simplification consists in neglecting the total derivative of the induction vector of the Earth's magnetic field in time compared to the local derivative. This is due to the fact that measurements are carried out quite often. Therefore, the magnetic induction vector in two adjacent dimensions can be considered unchanged. The aim of the work is to estimate the error in determining the angular velocity due to this simplification. The presented results show the admissibility of neglecting the full derivative, provided that the measurement frequency is sufficient. Reference metrological tests were carried out, in which a gyroscopic angular velocity vector meter was selected as the reference measuring instrument. The errors in the estimates of micro-accelerations and the control moment, which are a consequence of the error in determining the angular velocity, are calculated.

The behavior of a liquid drop placed on an oscillating solid substrate is studied. The vibrations are normal to the plane of the substrate. The amplitude of the vibrations is assumed to be small compared to the radius of the drop, and the vibration frequency is suppose to be much larger than the frequencies of the natural oscillations of the drop shape. The effect of vibrations on the drop shape is studied for a small values of the vibration parameter equal to the ratio of the vibration pressure to the capillary pressure. It is assumed that the drop surface in the absence of vibrations is hemispherical. Under the influence of vibrations, the drop height decreases and the base area increases. In this case, the surface deformation changes proportionally to the vibration parameter. At finite values of the vibration parameter, the quasi-equilibrium shape can differ significantly from spherical. In this case, the problem for pulsations is solved numerically using the boundary element method. To determine the average shape of a drop at finite values of the vibration parameter, the variational principle is used. The obtained results are in good agreement with the solution in the limit of small values of the vibration parameter. With an increase in the vibration parameter, the average contact angle decreases, the area of the base area increases, and the height decreases.

The present article investigates the stability of the mixed convective flow of nanofluids through a horizontal porous channel under the influence of a constant pressure gradient, utilizing the local thermal nonequilibrium (LTNE) model. The governing equations are derived by integrating the Oberbeck-Boussinesq theory with the Darcy model for low-permeability porous media. Using linear stability theory, we formulate a generalized eigenvalue problem (GEP) in terms of non-dimensional parameters. The weighted residual Galerkin method (WRGM) is then employed to solve the GEP, and the results are compared analytically. The findings of this study reveal that a horizontal pressure gradient initiates convection in an oscillatory mode rather than a stationary one. We identify that the interphase scaled heat transfer coefficient, thermal diffusivity ratio, nanoparticle volume fraction, and horizontal pressure gradient collectively influence the onset of oscillatory convection. Notably, our investigation into Titanium Oxide (TiO₂), Copper Oxide (CuO), and Aluminum Oxide (Al₂O₃) nanoparticles reveals that TiO₂ particles enhance the onset of convection compared to Al₂O₃ and CuO, while CuO nanoparticles exhibit greater thermal stability. Further, the nonlinear stability analysis is performed using the method of lines in conjunction with regularization and finite difference schemes for spatial derivatives. The time evolution of all field variables is simulated through the visualization of streamlines and isotherms, providing a detailed representation of the system's dynamics. Additionally, the critical values of the Darcy-Rayleigh number are computed and compared for both linear and nonlinear stability analyses. The results demonstrate the equivalence of linear instability and nonlinear stability boundaries in the absence of a constant pressure gradient, whereas subcritical instability becomes apparent in its presence. These insights advance our understanding of mixed convective flows in porous media, with potential implications for various engineering and environmental applications.

In this work, we propose a ternary phase-field model for separation of water from a water/oil mixed drop using Lamb waves. In this model, we describe a Cahn–Hilliard/Navier–Stokes model for the simulation of incompressible flows composed of three immiscible components, where surface tension, gravity, and the acoustic streaming force of Lamb waves act on a water/oil mixed drop are taken into account through volumic forces. To test the present model, we further conduct separation experiments of oil–water mixtures driven by surface acoustic waves on a non-piezoelectric substrate. The numerical results are in good agreement with the experimental solutions illustrate that present model has the good capability in the study of the separation of water from a water/oil mixed drop using Lamb waves.

This work is a theoretical investigation into the effect of finite droplet inertia on combined gravitational and thermocapillary interactions of spherical drops covered with an incompressible surfactant film. The significance of droplet inertia is indicated by the magnitude of the Stokes number St. Initial calculations are a continuation of previous results from St = 0 to finite Stokes numbers at (varvec{O(1)}) drop-to-medium viscosity and thermal conductivity ratios. Interesting outcomes, such as stable tandem motion and complex relative trajectories, are observed. At more realistic (varvec{O(10)}) ratios, the results tend to be dampened from those at lower values, although unusual behavior still occurs. Finally, interactions are determined for two physical systems, water drops in air and mercury drops in n-pentane. At normal gravity, two limits are usually possible. In order for the thermocapillary and gravitational contributions to be equal, the drops and their corresponding Stokes numbers must be small, while for larger drops at higher St, gravity is the dominant driving force. For water droplets in air with radii less than 10 (varvec{mu })m, van der Waals forces control the interactions. However, drop inertia is the most important factor for droplets with radii greater than 25 (varvec{mu })m. Even a small thermocapillary effect can have noticeable consequences on the relative trajectories for intermediate-sized drops. Some comments are made on the difficulty in experimentally reproducing the theoretical results, with a recommendation of centi- or milligravity conditions.