 Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 124 journals)
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- Onset of Penetrative Convection in a Multilayered Heat-generating Porous
System with Thin Air Interlayers-
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Abstract: Abstract The study is devoted to a new problem concerning the onset of penetrative convection via internal heating in a multilayered air-porous system under the gravitational field. The system consists of porous sublayers separated by thin air interlayers. The governing equations are supplemented by the effective boundary conditions which contain the interlayer parameter and parameter of thermal conductivity jump. The parameters are combinations of the relative air interlayer depth, Darcy number and thermal conductivity ratio. The numerical results show that the large-scale convection covering the entire unstably stratified upper region initiates in a multilayered system with porous sublayers of equal depth and permeability. The addition of air interlayers speeds up the convection onset and increases the wavelength of convective patterns. The effect becomes stronger as the number of porous sublayers increases because the number of air interlayers also increases. Local convection can be obtained when the permeability of any one porous sublayer exceeds that of the other porous sublayers by an order of magnitude or more. The local flow originates in the highly permeable porous sublayer that belongs to the upper half of the system. Convection becomes of a large scale at any other position of this sublayer. It is found that the permeability ratio can be both destabilizing and stabilizing. It is explained by a transition from the large-scale to local convective regimes. The destabilizing effect of air interlayers is observed for both local and large-scale regimes in the multilayered system with a highly permeable porous sublayer.
PubDate: 2023-03-18
- Effects of Thermocapillary and Natural Convection During the Melting of
PCMs with a Liquid Bridge Geometry-
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Abstract: Abstract The results of a numerical investigation of the melting of a PCM occupying an axisymmetric volume in the presence of gravity are presented. The PCM is held between two circular supports maintained at different temperatures. The melting process, which is analyzed for n-octadecane, is affected by a combination of thermocapillary and natural convection. If the PCM is heated from above, the convective motion driven by the thermocapillary force is opposed by the buoyant force, which reduces the heat transfer rate. If the PCM is heated from below, natural convection acts in the same sense as thermocapillary convection and the heat transfer rate is increased. The volume \(\mathcal {V}\) of the PCM relative to an ideal cylinder, which selects the shape of the PCM/air interface, is found to play an important role. The overall effect of natural convection on heat transfer is characterized by the ratio of the melting time in microgravity to that of the same system with gravity. This gain factor is greater (less) than unity when heating from below (above) and depends strongly on \(\mathcal {V}\) , particularly for smaller PCM volumes.
PubDate: 2023-03-13
- Volume of Fluid Simulations of Heat Transfer in Liquid-Liquid Segmented
Flows in Microfluidic channel-
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Abstract: Abstract This study presents the investigations on the effect of heat transfer on droplet formation in T-type microfluidic channel. Mineral oil acts as a continuous phase, and water acts as a dispersed phase. The Volume of Fluid model is used to investigate the formation of droplets of water in oil in the microchannel. The physical properties of both fluids change with an increase in temperature of dispersed phase, of which the dominant properties are viscosities of fluids and interfacial tension. The parameters such as droplet diameter, distance between two consecutive droplets and detachment time were studied with respect to temperature in the range of 300 K to 325 K. These properties are also studied at different flow rate ratios 0.125, 0.25, and 0.5. The distance between two consecutive droplets was found to decrease with the increase in temperature due to the rapid motion of droplets in the temperature zone. The droplet detachment time also decreases, due to the decrease in interfacial forces which hold the droplets in the dispersed phase. The droplet diameter decreases initially with the increase in temperature, but it was observed that after 320 K the diameter of the droplet increases due to the coalescence of two consecutive droplets downstream in the microchannel. This temperature is reported as a limiting condition for thermally controlled water-in-oil microemulsions.
PubDate: 2023-03-10
- Development and Validation of a Novel Head-down Tilt Microgravity
Simulation Device for Canines-
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Abstract: Abstract The simulation of a microgravity environment on earth is an effective strategy to perform studies on the physiological effects of microgravity. Studying the microgravity-related physiological changes in canines is more effective rather than studying those in smaller animals such as rats. However, presently, no microgravity simulation models have been established with respect to canines. A novel canine head-down tilt microgravity (CHDTM) simulation device was developed based on the characteristic physiological structure and habits of canines. Beagles were subjected to head-down tilt (HDT) rest at tilt angles of −6° and −12°, respectively, for 21 d, or subjected to HDT bed rest (−12°) for 7, 14, and 21 d, respectively. The changes in the bone and muscle metabolisms of beagles subjected to this HDT model was investigated, including the hind limb muscle content, the expression of myosin, troponin, MuRF-1, and atrogin-1 in their soleus muscles, and the serum concentrations of alkaline phosphatase (ALP), osteocalcin, and calcium. The CT imaging of femurs was performed to estimate the cortical thickness (Ct.Th), bone area (BArea), bone volume/tissue volume (BV/TV), and trabecular number (Tb.N). The simulated state of weightlessness of the beagles in the −12° groups for 21 d significantly affected the bone (serum ALP, osteocalcin and calcium content, bone density) and muscle metabolism (hind limb circumference, the expression of myosin, troponin, MuRF-1, and atrogin-1 in soleus muscles) of the canines, which is consistent with the results of previous studies associated with the physiological effects of microgravity. The parameters in the beagles in the −12° HDT groups for 7 and 14 d were not significantly different from Control group. The weightlessness simulation was successful when beagles were subjected to −12° HDT for 21 d. The novel CHDTM simulation device developed in the study could be used in the weightlessness simulation experiment and pharmaceutical development of large animals.
PubDate: 2023-03-01
- Direct Simulation on the Dynamics of Liquid Films Flowing Down a Fiber
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Abstract: Abstract Direct simulations on the dynamics of a liquid film coating on the outer surface of a vertical fiber are performed in the present paper. A domain mapping technique has been used on solving the Navier-Stokes problem in stream function form and predicts the dynamics of the various flow regimes with remarkable accuracy. We investigated the morphologies that develop in the coating flow down fiber and analyze the effects of Bond number and fiber diameter on the maximum liquid film height and drop speed. The results showed that the Bond number and fiber diameter have a significant effect on the instability. The transition between the Plateau-Rayleigh and convective regimes occurs at the conditions when the flow transitions from absolutely to convectively unstable.
PubDate: 2023-03-01
- Dust Cloud Convections in Inhomogeneously Heated Plasmas in Microgravity
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Abstract: Abstract Convection is a phenomenon that often occurs in the presence of temperature gradients. In microgravity, free convection can not occur due to the lack of buoyancy. However, during parabolic flights we observed convections of microparticles in a gas discharge within the cylindrical plasma chamber of the setup PK-4. The microparticles and the plasma were exposed to a thermal gradient. There, the cloud convections and dust waves were observed. Analysis by tracking the microparticles’ trajectories showed that the vortices were induced by thermal creep, a gas flow that commonly occurs in gases with low pressures at inhomogeneously heated solid interfaces. This effect has driven a gas convection which in turn caused the convection of the microparticle cloud.
PubDate: 2023-02-27
- Human Bone Loss Assessed by High-Resolution Peripheral Quantitative
Computed Tomography and Ultrasonic Transmission Techniques-
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Abstract: Abstract This study aims to investigate bone loss and recovery during simulated microgravity by high-resolution peripheral quantitative computed tomography (HR-pQCT) and ultrasonic transmission techniques, and to compare the efficacy of state-of-the-art ultrasonic transmission and backscatter techniques in assessing bone loss. Thirty-six male volunteers went through 90-day 6-degree head-down tilt bed rest and 180-day recovery. HR-pQCT was adopted to evaluate bone mineral density (BMD) and microstructure properties. Ultrasonic transmission measurements of calcaneal properties were performed, and were compared to previously reported backscatter measurements. The deterioration of the human skeleton was verified through significant bone loss (Total volumetric BMD (Tt.vBMD) reduced up to 2.16% until 30-day post-recovery) and microstructure deterioration (Cortical thickness reduced up to 6.88% after 90-day bed rest). Ultrasonic transmission measurements possessed comparable standardized long-term precision errors with HR-pQCT measurements. The ultrasonic transmission parameters exhibited significant correlations with bone densities (R up to 0.61, p < 0.001) and microstructure properties (R up to 0.60, p < 0.001) throughout bed rest and recovery periods. Multiple regression indicated that Tt.vBMD contributed significantly and independently in determining transmission parameters. The observed cortical thinning and changes in compartmental bone densities and areas provided evidence for the mechanism of endocortical bone transforming into the trabecular bone in response to bed rest. The results suggested the effectiveness of the transmission technique in monitoring immobilization-induced bone loss. The comparison between ultrasonic transmission, backscatter and HR-pQCT measurements promoted the application of the ultrasonic technique in assessing disuse-induced bone deterioration in long-term bed rest or spaceflights missions.
PubDate: 2023-02-21
- Modeling and Analysis of Cyclone Separation Efficiency Based on Spacecraft
Heat Pump System-
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Abstract: Abstract The heat pump can effectively achieve high power and extremely high-temperature heat dissipation of manned spacecraft. The cyclone oil–gas separator is the core component of the heat pump system to separate lubricating oil and prevent it from entering the heat exchanger. In this paper, a one-dimensional separation efficiency calculation model is built based on the geometry of the cyclone oil–gas separator, which can implement the fast calculation of the separation efficiency. At the same time, the structural parameters of the separator, the operating parameters, and the physical properties of the oil–gas mixture entering into the separator have been analyzed to obtain the influence rules on the separation efficiency, which can guide the design of the separator and the system operating conditions of the compressor.
PubDate: 2023-02-13
- The Temperature-Controlled Biological Samples Exposure Payload(TC-BIOSEP)
for Balloon-Based Astrobiology Research-
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Abstract: Abstract The Earth’s near space refers to the sea level of 20-100 km, the stratosphere in the Earth’s near space has complicated environmental conditions. The environmental conditions of Earth’s near-space in the stratosphere are so complicated that are hard to simulate in the laboratory. The primary goal of the flight mission in this work is to make the light-energy-utilizing biology samples exposed to harsh environmental conditions, find highly adaptable light-energy-utilizing biological strains and study their survival and long-term adaptation mechanisms, screen adaptable biological strains, and provide a scientific basis for biological exploration in near space. Which will further lay the foundation for the construction of the crust micro-ecosystem and promote research on the colonization technology of the Mars-like surface environment. In order to achieve these scientific objectives, a Temperature-Controlled Biological Samples Exposure Payload(TC-BIOSEP) with the function of active temperature control is designed to carry out biological exposure scientific experiments in the Earth’s near space. The TC-BIOSEP participated in a flight mission on September 17, 2021. The total exposure time of flat flight exceeded 2 h, and the altitude reached 35 km above sea level. In this flight mission, the TC-BIOSEP had loaded dozens of organisms such as microorganisms, algae, and nematodes to the stratosphere. The TC-BIOSEP has obtained significant experiment data and has shown high reliability without any malfunction in the whole flight process. The flight experiment has manifested that TC-BIOSEP can be used as a comprehensive experimental platform for Earth’s near-space astrobiology research.
PubDate: 2023-02-08
- Dynamic Modeling and Control for a Double-State Microgravity Vibration
Isolation System-
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Abstract: Abstract The microgravity vibration isolation systems (MVIS) are characterized by system coupling, uncertainties, nonlinearity, variable mass and momentum of inertia. These characteristics lead to a challenging control system design problem. In this paper, a double-stage microgravity vibration isolation system is introduced. The relative motion dynamics and absolute motion dynamics of the system are established via Newton's law, thereafter the linearized and decoupled model is derived for control design. A robust backstepping controller is proposed to suppress the accelerations transmitted to the payload, as well as to address the challenges of system uncertainties and nonlinearity. The validity of the relative motion dynamics of the system is demonstrated by comparing the experimental data with the simulation results. The Lyapunov theory is used for proving the stability of the proposed controller. Simulations show that the robust backstepping controller is capable of suppressing microgravity acceleration disturbances from 1 to 100 Hz at around 19 dB and tracking the displacement to zero position fast, which performs well in the time domain and frequency domain.
PubDate: 2023-02-08
- Numerical Investigation of Flow Patterns and Plug Hydrodynamics in a 3D
T-junction Microchannel-
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Abstract: Abstract A three-dimensional (3D) numerical simulation of a two-phase flow liquid/liquid is performed in a rectangular microchannel with a T-junction. The volume of fluid (VOF) method was used under ANSYS Fluent to capture the interface between the two phases. The dynamic mesh adaptation technique together with the assumption of symmetry plane helps us to reduce the computational cost. The study focuses on the flow patterns and hydrodynamics of plugs. So, the influence of the flow rate ratio \(q\) , the capillary number \(Ca\) , and the viscosity ratio on the liquid film, the plug/droplet shape, and velocity are examined here. Particularly, the plug/droplet lengths predicted by the simulation show good agreement with the experimental and correlation available in the literature. The results revealed six distinct flow patterns by dispersing water in a continuous phase of silicone oil. By decreasing the flow rate ratio as well as the viscosity ratio, the liquid film thickness increases in the corners and side planes. In turn, this greatly impacts the liquid film velocity and the plug velocity. Furthermore, capillary number (based on two-phase flow velocity) is also shown to have a greater impact than viscosity ratio and flow rate ratio on plug shape, with the curvature radii of the tail always larger than the front one.
PubDate: 2023-02-06
- Optimization for Thermal Control System of Centrifuge and Operating Status
Prediction Experiment in Orbit-
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Abstract: Abstract According to the characteristics of science payload, an adaptive design is made for the centrifuge thermal control system of standard experiment rack and the thermal control system is optimized due to the constraints of platform resources. Referring to the operating conditions of in-orbit environment, it compares the advantages and disadvantages of vapor compression refrigeration, the Stirling cycle and thermoelectric cooler. Finally, the two-stage thermal control scheme combined air–liquid heat exchanger with thermoelectric cooler is chose. In consideration of the actual condition in orbit, a ground mirror-image experiment platform is built to carry out the thermal performance experiments of thermal control system under variable working conditions, such as different science payload heat load, different temperature of liquid supply on platform, and voltage change of thermoelectric cooling component. By means of experimental research, it verifies the rationality of the thermal control system and obtains the thermal control parameters status under the in-orbit condition, which improves the safety and reliability of the system. Once the experiment rack is launched with Space Station in the future, the space-ground comparison between the in-orbit equipment and the ground mirror-image experimental platform will provide more data reference for the study of the influence of microgravity.
PubDate: 2023-02-04
- Zero-Offset Analysis on Differential Wavefront Sensing Technique in
Gravitational Wave Detection Missions-
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Abstract: Abstract Benefiting from ultra-high angular resolution, differential wavefront sensing (DWS) technique is widely used in gravitational wave detection missions for suppressing the laser pointing jitter as well as sensing jitter of the test mass. However, the zero-offset property of the DWS which leads to absolute angular measurement error is rarely mentioned in previous researches. In this paper, we describe the mechanisms causing the DWS zero-offset with an analytical model as well as numerical method. With the analytical results, we analyze the static pointing error of the gravitational wave detection satellite induced by the DWS. As the error is far larger than the requirement of 10 nrad magnitude, a zero-offset reduction scheme is proposed. We also construct an experiment system for verifying the theoretical results. The experimental results show that the DWS zero-offset can be effectively suppressed with the proposed scheme.
PubDate: 2023-02-03
- Coupling Enhancement Effect of the Magnetic Field and Wall Superheat on
Boiling Heat Transfer Characteristics of Magnetic Nanofluid (MNF) under
Reduced Gravity-
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Abstract: Abstract How to reduce or even eliminate the influence of gravity on boiling heat transfer, how to restrain the emergence of abnormally large bubbles and how to prevent the large decrease of critical heat flux (CHF) are the key to enhancing boiling heat transfer under reduced gravity. Magnetic nanofluid (MNF) boiling is one of the effective methods to solve the above problem. Under reduced gravity, the wall superheat has a crucial influence on the dynamics of the bubbles and boiling heat transfer. However, it has been unsolved whether the application of an external magnetic field can enhance the influence of wall superheat on boiling thermal dynamics or not. Based on the author's previous research, the influence of wall superheat on the enhanced heat transfer of MNF boiling under reduced gravity is further studied by using the computational model of MNF boiling heat transfer under external magnetic field. In this paper, the phase interface dynamics evolution and heat transfer characteristics of MNF boiling under the dual influence of wall superheat and magnetic field are described for the first time. The results show that the application of the magnetic field retards the flow state development of MNF film boiling compared with the results without the magnetic field. As the wall superheat increases, whether magnetic field is applied or not, the heat flux enhancement ratio with respect to wall superheat of 2 K under the various gravity level is almost the same. The effect of the wall superheat on boiling heat transfer characteristics under reduced gravity is enhanced by the application of external magnetic field. When the magnetic field of H = 20 kA/m is applied and the wall superheat is 6 K, under the three gravity levels of g/ge = 1.0, g/ge = 0.44 and g/ge = 0.11, the heat flux with respect to wall superheat of 2 K can be enhanced up to 22.7%, 53.9% and 150.1%, furthermore, the heat flux enhancement rate can be enhanced up to 10%, 18.7% and 12.6%, respectively.
PubDate: 2023-01-21
- A Model-based Design of the Water Membrane Evaporator for the Advanced
Spacesuit-
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Abstract: Abstract A spacesuit water membrane evaporator (SWME) based on the hollow fiber membrane bundle is regarded as a promising technology for the advanced thermal management system of the next-generation spacesuit. This paper focuses on theoretical modelling and finite element analysis for the SWME and parametrical optimization. The heat transfer process of the elongated hollow fiber membranes is studied via segment modelling and energy balance method. A comprehensive Finite element analysis is conducted in different dimensions to analyze the influence of fiber tube arrangements and the size of the evaporation chamber. An SWME prototype is also developed. Heat rejection experiments are conducted to verify the theoretical analysis. The work of this paper helps to gain a deep understanding of the heat dissipation process of the hollow fiber membranes and could be referred to for further optimization of the SWME devices.
PubDate: 2023-01-21
- Impact of heat and mass transport on Rayleigh–Taylor instability of
Walter’s B viscoelastic fluid layer-
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Abstract: Abstract The behavior of viscous fluid-Walter’s B viscoelastic fluid interface in a planar configuration is investigated through an irrotational flow theory. The interface is transferring heat and mass from one fluid phase to the other. The viscoelastic fluid lies above the viscous fluid, and therefore, the interface is accepting the Rayleigh–Taylor instability. The linear stability theory is employed, and an explicit relationship between perturbation’s growth and wavenumber is established. The implicit stability criterion is achieved and analyzed numerically through the Newton–Raphson numerical scheme. The nature of the interface is examined for various non-dimensional parameters such as Atwood number, Weber number, Froude number, Reynolds number, etc. by means of stability plots. The results are discussed for the various values of gravitational acceleration through the variation of the Froude number. The instability is postponed if the interface experiences more heat transfer. Additionally, compared to the Walter's B fluid interface, the Newtonian fluid interface has proven to be more stable.
PubDate: 2023-01-19
- Effect of Vibration On Characteristics of Granular Inclined Chute Flow
Under Low-gravity-
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Abstract: Abstract Prediction of the flow properties of granular materials is a major challenge in geophysics and industry. It is particularly important for planetary exploration to understand the effect of vibration on the flow characteristics of granular materials under low-gravity environments while there is still a deficiency in the very subject. In this paper, we apply discrete element numerical simulation method to obtain the parameters of granular flow (e.g., velocity, stress and volume fraction), and studies the effect of vibration on particle flow characteristics under low-gravity condition. The results indicate that the low-frequency vibration enhances the flow characteristics of the particles. The vibration enhances the granular flow by reducing the stress and volume fraction, and it exerts a greater effect on granular flow under low-gravity conditions than that under conventional ones.
PubDate: 2023-01-07
DOI: 10.1007/s12217-022-10029-6
- Evaluation of Cardiac Autonomic Activity During + Gz Stress in
Military Pilots-
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Abstract: Abstract Acceleration forces are a substantial source of stress that is frequently experienced in high-performance military aircraft. There are a limited number of methods that can objectively evaluate the physiological effects of exposure to this stress. In our study, we aimed to evaluate the autonomic cardiac effects of + Gz stress exposure through QT interval parameters (QT, QTc, QTi), which are objective indicators, during centrifuge training of military pilots. Sixty-five healthy male pilots (with ages of 24.95 ± 5.95) were included in the study, and the Perceived Stress Scale-14 was used to determine their stress levels before training. During the centrifuge training, ECG data of the pilots were recorded under + 1.1 Gz and + 4.5 Gz acceleration exposures. From these data, heart rate, QT, QTc, and QTi levels were extracted with a computer program. The variations in these parameters with the increase in the exposure level of the acceleration force were examined. The QT interval shortened with the increased exposure to + Gz acceleration, whereas QTc prolonged, QTi increased and increased heart rate rose. While the shortening in the QT interval was not statistically significant, the increases in other parameters were found to be statistically significant. Autonomic imbalance due to + Gz stress is a high-risk condition that may lead to cardiovascular events in the future, and the diagnosis of this imbalance at an early stage is critical for the development of protective measures. The measurement of QTc and QTi parameters attracts attention as a useful method in determining the cardiac autonomic effects of + Gz stress during centrifuge training.
PubDate: 2023-01-03
DOI: 10.1007/s12217-022-10028-7
- Linear and Nonlinear Longwave Marangoni Stability of a Thin Liquid Film
Above or Below a Thick Wall with Slip in the Presence of Microgravity-
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Abstract: Abstract The linear and nonlinear thermocapillary instability of a liquid layer located above or below a thick horizontal wall with slip effect under gravity is investigated for the first time. A nonlinear evolution equation for the free surface deformation is obtained under the lubrication approximation. The curves of linear growth rate, maximum growth rate and critical Marangoni number are calculated under two physical conditions. First, gravity is directed from the liquid to the wall and has a stabilizing effect. Second, gravity is directed from the wall to the liquid (Rayleigh-Taylor instability). In the latter case, the liquid film is also subjected to stabilizing and destabilizing Marangoni numbers. The film is subjected to slip at the thick wall with finite thermal conductivity. A very important result is that slip is not always destabilizing. From the point of view of the growth rate, the slip parameter \(\beta\) changes its destabilizing role into a stabilizing one at a particular wavenumber, independent of \(\beta\) . Also, from the standpoint of the maximum growth rate, the slip parameter \(\beta\) is not always destabilizing. Magnitudes of the Marangoni number were found where \(\beta\) is stabilizing. Formulas to delimit where the role of \(\beta\) changes are derived analytically. The free surface profiles obtained from the nonlinear evolution equation show the stabilizing and destabilizing effects of the parameters. It is revealed that the Rayleigh-Taylor instability can be delayed, before the film free surface touches the wall.
PubDate: 2022-12-13
DOI: 10.1007/s12217-022-10022-z
- Profiles of Liquid on the Surface of Revolution with Varying Cross-section
under Microgravity-
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Abstract: Abstract Propellant tanks of satellites usually contain cylindrical structures. Under microgravity, liquid can spread on the revolution’s surface regardless of its size. This study focuses on liquid–gas interfaces on the surface of revolution under microgravity. Expressions of profiles of the liquid at equilibrium are proposed in this paper. The profiles have two cases according to the liquid contact angle and the geometry of the revolution. For given liquid contact angle and geometry of the revolution, the profile and volume of the liquid can be obtained by using the Shooting method with certain inputs. Numerical simulation is carried out with the Volume of Fluid method and the numerical results are in good agreement with theoretical predictions. Besides, dimensionless theoretical solutions of the profiles are proposed and the effects of the liquid contact angle and the geometry of the revolution on the profile of the liquid are analyzed in detail.
PubDate: 2022-12-12
DOI: 10.1007/s12217-022-10024-x
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