Influence Of Gravity Research Articles

Novel flat plate pulsating heat pipe with ultra sharp grooves

• Diffusion bonding was applied for the fabrication of flat plate PHPs. • Ultra-sharp grooves in the evaporator improved the heat transfer capacity of a PHP. • The proposed PHPs perform effectively for heat fluxes up to 1200 W (20.9 W/cm 2 ). • The gravity influence becomes negligible for powers beyond 600 W (10.4 W/ cm 2 ). • The PHPs appear to be a good alternative for temperature control of electronics. Pulsating heat pipe (PHP) is a very efficient solution for electronics cooling. Several strategies can be applied to improve the thermal performance of PHPs. In this context, the heat transfer enhancement of a flat plate pulsating heat pipe with a channel modification in the evaporator region, resulting in ultra sharp lateral grooves, was investigated experimentally. Chamfers were machined in the lateral walls of thirteen semi-circular cross section U-turn channels, drilled in flat copper plates. To form the sharp-grooved circular channels, two plates were faced against each other and diffusion bonded, resulting in a monolithic piece with high quality channels. The ultra sharp grooves had an angle of 29.1 ± 2.9°. The lateral grooves work as artificial nucleation sites, helping in the bubble formation, and act as a capillary medium, spreading the liquid over the evaporator region, delaying the dry-out. Therefore, the device could be less dependent on gravity, enabling it to be considered for applications in microgravity environments. To ascertain the efficiency of the proposed device, its performance was compared with another similar PHP with the same external geometry and with round ordinary cross-section channels of the same 2.5 mm channel diameter. Distilled water was selected as the working fluid, which, as predicted by literature models, worked at confinement conditions. As usual, the thermal behaviors of PHPs were characterized by their temperatures and pressures, depending on the operation conditions. The best filling ratio for each PHP was experimentally determined, considering heat loads from 20 up to 350 W (from 0.35 up to 6.1 W/cm 2 ). The influence of the ultra sharp grooves on the thermal performance of the PHP was investigated for a large range of power inputs, reaching up to 1200 W (20.9 W/cm 2 ), for the best filling ratio. The gravity influence in the PHP operation was evaluated by tests in three orientations: gravity-assisted, horizontal and against-gravity. Both cross-section profile PHPs performed effectively well for heat fluxes up to 20.9 W/ cm 2 , even in the against-gravity position, showing that the devices are suitable for temperature control of electronics, including those with high heat fluxes. Besides, the gravity effect could be neglected for heat powers beyond 600 W (10.4 W/ cm 2 ), which make them adequate for microgravity applications. The presence of ultra sharp grooves in the evaporator section of the PHP reduced by 2.1 °C the average evaporator temperature, decreased the temperature variations among sections and improved the thermal performance by 12% in the horizontal and gravity-assisted orientation.

Mason–Weaver theory: Revised and extended for a semi-infinite domain

Mason and Weaver developed equations to describe small particles settling under the influence of gravity and Brownian motion, including the limiting case for an infinitely deep suspension. We encountered this common convection–diffusion equation and no-flux boundary conditions in a model for dynamics of adsorbed polymers in dead end pores of a depolymerization catalyst. Close examination reveals that the Mason–Weaver solution is not correct for the infinite domain with a non-uniform initial condition. In this paper, we obtain the time dependent Green’s function for the no flux boundary condition and also for a more general reactive boundary condition. We demonstrate how the results provide solutions, via superposition, which provide solutions for several boundary conditions and all initial conditions.

Experimental study on the effect of surface temperature on the frost characteristics of an inverted cold plate under natural convection

• Frosting experiments on inverted cold plate at micro scale are carried out • Four frosting stages are illustrated with three key dividing moments defined • Uneven frost layer could be quantitatively reflected by its surface roughness • Big converged droplets and falling of branches influence the frosting process • Reverse melting phenomenon and its dynamic variation law are analyzed Frosting is frequently seen in nature and engineering fields. To avoid the drawbacks and take advantage of frost, analyzing the frost characteristics is meaningful. Frosting experiments on an inverted cold plate at surface temperatures of −30 ∼ -10 °C under natural convection are carried out. Frost characteristics, including frosting stages, frost layer thickness and surface roughness, dynamic frosting rate and reverse melting, are analyzed and discussed. Results show that stages of droplet condensation and coalescence, solidified liquid tip-growth and frost layer growth are within 220 s with their frost thickness less than 450 × 10 -6 m. Formation of large condensate droplets under influence of gravity causes a longer solidification time to 160.2 s and decreases the surface roughness. As surface temperature decreases, frost thickness increases and surface roughness fluctuates more intensely, with its amplitude maximum at 102.29 × 10 -6 m. Dynamic frosting rates at different surface temperatures increase linearly and then declines in a curve, and their trend varies when first reverse melting occurs. At the surface temperature of −25 °C, amount and time of reverse melting are 9.42 × 10 -8 m 2 and 1.25 s, respectively, leading to the largest downward of dynamic frosting rate. Contributions of this study are expected to provide a more in-depth understanding of frosting and thus provide a reference for optimal defrosting control in engineering applications.

Investigation on Weld Characteristic, Welding Position, Microstructure, and Mechanical Properties in Orbital Pulse Current Gas Tungsten Arc Welding of AISI 304L Stainless Steel Pipe

Orbital pipe welding is carried out in this study by Pulse Current Gas Tungsten Arc Welding (PC-GTAW) without metal filler (autogenous) of AISI 304L stainless steel pipe. The dimensions of the specimen are 114 mm outside diameter and the thickness of 3 mm. This study investigates the effect of pulse current parameters, weld position, and pulse width on the characteristics of weld geometry, mechanical properties, and microstructure. The welding method used in this study is the continuous current and pulse current. The mean current of each parameter is the same at 100 ± 0.5 Amperes, but in the pulse current, there are variations in peak current, base current, peak current time, and the base current time. The welding speed used is constant at 1.4 mm/s. The result of weld geometry on the outside of pipe has shown that the flat (0°) position is concave and the overhead (180°) position is convex due to the influence of gravity. The microstructure indicates that the fine cellular dendritic structures appear at PC-GTAW. The PC-GTAW can produce good mechanical properties such as the tensile strength and the micro-hardness. The tensile strength of the specimen is reduced 14.23 % from the base metal at parameter 65-B and the flat position.

Is the equivalence principle useful for understanding general relativity?

The equivalence principle (EP) is at the heart of general relativity (GR), tested in many aspects. In discussion, it is often referred to explaining qualitatively the influence of gravity on physical phenomena, but is this qualitative approach supported by the theory? We compare clock rates, frequency shifts, light deflection, and time delay in simple static spacetimes to the analogous phenomena seen by accelerated observers in Minkowski space. In contrast to previous studies, we do not assume that the gravitational field is weak and see, as we proceed, how the field is constrained by the EP. Special care is taken that results are only observer-, but not coordinate-dependent. By this, we clarify some of the issues raised in the literature and show which gravitational effects can and which cannot be simulated by acceleration. The paper may also serve as a starting point for discussions on the implications of the EP.

Methylcellulose-Chitosan Smart Gels for Hairstyling

Methylcellulose and chitosan served as promising ingredients for a thermoresponsive hair styling gel after successful application in the medical industry. Both ingredients uphold the clean beauty standard without infringing on performance. By combining these two ingredients, a hair gel can be created that promises an extended hold of style once a heated external stimulus, such as a curling wand, is applied to the hair. Chitosan serves as the cationic biopolymer to adhere the gel to the hair, whereas the methylcellulose acts as the smart biopolymer to lock the desired hairstyle in place. Various ranges of chitosan and methylcellulose concentrations were explored for formulation optimization with rheology and curl drop testing. The rheology testing included a flow sweep test to understand the shear-thinning behavior of the sample as well as the effect of concentration on viscosity. Another rheology test completed was a temperature ramp test from room temperature (25 °C) to 60 °C to study the effect of heat on the various concentrations within the samples. A curl drop test was performed as well, over a 48-h period in which the different samples were applied to wet hair tresses, dried, curled, and hung vertically to see how the style held up over a long period of time with the influence of gravity.

Urban modelling and forecasting of landuse using SLEUTH model.

The present study performs landcover modelling using the SLEUTH model. The urban land use changing factors are calibrated to predict the Land Use Land Cover (LULC) for a densely populated and developing smart city, Prayagraj, India. This research aims to use the SLEUTH model for simulating the future urban growth with the help of historical LULC (1990–2020), road network and elevation data. The influence of road gravity and slope resistant coefficients is very significant in this study's outcome. The built-up area of the region increased from 40.22 km2 (5.10% of total area) in 1990 to 85.89 km2 (10.89%) in 2020. According to prediction results, in the next 20 years, the built-up growth rate would be 1.9% and approximated built-up area would be 118.66 km2 (14.98%) in the year 2040. The quality of the result has been quantified in terms of best fit value of Optimal SLEUTH Metric (OSM) and validated against the existing LULC. The study utilises a spatially explicit urban growth model with 30 m resolution remote sensing data and provides future landuse of Prayagraj city.

Surface tension of liquid Fe, Nb and 304L SS and effect of drop mass in aerodynamic levitation

The oscillating drop method has been widely used for surface tension measurements of liquids at high temperatures such as molten metals. An experimental device that permits such measurements has been developed at IRDL. This device relies on aerodynamic levitation for the sample to be contactless and on acoustic excitation to make it oscillate at its resonance frequency, which is related to the surface tension with Rayleigh’s equation. Beforehand, experimentally, a lateral gas jet blows and controls the rotation of the drop due to its unpredictable behavior. Moreover, the effect of drop mass, usually studied for electromagnetic levitation, remains unknown for aerodynamic levitation. To fill this knowledge gap, levitated drops of different masses were numerically modeled to observe the influence of gravity or additional oscillation modes. It resulted that for light mass drops, such as those used for our surface tension measurement, it is not significant. Finally, our results on iron, niobium, and 304L stainless steel have been compared with the literature. For pure metals, we observed a similar decreasing behavior versus temperature. For steel, results highlighted the impact of experimental parameters on the surface tension (length of experiments and composition of the atmosphere). These measurements thus provide original results that will be useful for the numerical modeling of innovative industrial processes such as additive manufacturing or welding.

Adaptive perceptual responses to asymmetric rotation for testing otolithic function

This study aimed to test the role of the otolithic system in self-motion perception by examining adaptive responses to asymmetric off-axis vertical rotation. Self-movement perception was examined after a conditioning procedure consisting of prolonged asymmetric sinusoidal yaw rotation of the head on a stationary body with hemicycle faster than the other hemicycle. This asymmetric velocity rotation results in a cumulative error in spatial self-motion perception in the upright position that persists over time. Head yaw rotation conditioning was performed in different head positions: in the upright position to activate semicircular canals and in the supine and prone positions to activate both semicircular canals and otoliths with the phase of otolithic stimulation reversed with respect to activation of the semicircular canals. The asymmetric conditioning influenced the cumulative error induced by four asymmetric cycles of whole-body vertical axis yaw rotation. The magnitude of this error depended on the orientation of the head during the conditioning. The error increased by 50% after upright position conditioning, by 100% in the supine position, and decreased by 30% in the prone position. The enhancement and reduction of the perceptual error are attributed to otolithic modulation because of gravity influence of the otoliths during the conditioning procedure in supine and prone positions. These findings indicate that asymmetric velocity otolithic activation induces adaptive perceptual errors such as those induced by semicircular canals alone, and this adaptation may be useful in testing dynamic otolithic perceptual responses under different conditions of vestibular dysfunction.

Tunneling analysis of Kerr–Newman black hole-like solution in Rastall theory

Hamilton–Jacobi ansatz is used to analyze boson charged particles tunneling in Rastall gravity Kerr–Newman black hole (BH) surrounded by perfect fluid matter through the horizon. The geometrical BH parameters are observed, how these are affecting the radiation utilizing the Lagrangian gravity equation. In this paper, the corrected Hawking temperature is computed by considering the effects of quantum gravity. In our analysis, the Rastall gravity BH solution surrounded by perfect fluid matter effects on Hawking radiation is analyzed graphically. Moreover, the stability and instability of Rastall gravity BH are investigated. The influence of quantum gravity and rotation parameters on BH radiation are also observed by graphical representation.

Local well-posedness for the motion of a compressible gravity water wave with vorticity

In this paper we prove the local well-posedness (LWP) for the 3D compressible Euler equations describing the motion of a liquid in an unbounded initial domain with moving boundary. The liquid is under the influence of gravity but without surface tension, and it is not assumed to be irrotational. We apply the tangential smoothing method introduced in Coutand-Shkoller [10,11] to construct the approximation system with energy estimates uniform in the smooth parameter. It should be emphasized that, when doing the nonlinear a priori estimates, we need neither the higher order wave equation of the pressure and delicate elliptic estimates, nor the higher regularity on the flow-map or initial vorticity. Instead, we adapt the Alinhac's good unknowns to the estimates of full spatial derivatives.

Proposal for a STEAM education program for creativity exploring the roofline of a hanok using GeoGebra and 4Dframe

This research was conducted to confirm the feasibility of a STEAM education program in which the mathematics, physics, and Korean traditional arts underlying the hanok roofline are investigated using educational tools of GeoGebra and 4Dframe. This paper contends that this program has the potential to engage students in knowledge restructuring regarding the perception of the hanok’s architectural beauty, Newton's concept of gravity, and mathematical functions. The Octagonal Pavilion in Tapgol Park in Seoul, South Korea, a representative hanok, was used as an educational resource. GeoGebra is used to determine that the roofline of the Octagonal Pavilion generally follows the formula of the catenary curve and then the roofline is modelled using 4Dframe. The catenary form of the roofline of the hanok is linked to the Korean sense of beauty in the pursuit of naturalness under the influence of gravity and organically harmonizes with the environment. The class described in this study, in which the curve of the roofline of the Octagonal Pavilion is explored using GeoGebra and 4Dframe, can help develop creative and critical thinking in students in the context of STEAM education. The findings of this study have the potential to expand the scope of STEAM education to include content for creative education.

Determining Alloy Nucleation Core Origin and Grain Refinement Strategy Based on the Dependence Degree of Content Difference

What is nucleation core origin during alloy solidification, especially for equiaxed grains? Different dependence degrees of the magnitude or occurrence of element content variation could shed light on this long-standing issue in actual large ingots. Here, based on etched surface height and grayscale, element content distributions within the solid fraction in continuous casting billets and additive manufacturing samples are first obtained by only a two-dimensional surface. Then, combined with the phylogenetic trees, the rank correlation is applied to measure the dependence of content differences during initial solidification. Assessments of external dependence degrees are helpful to determine nucleation core origin and low internal dependence degree facilitates grain refinement. Moreover, in continuous casting, some nucleation cores in the central equiaxed grain zone are confirmed to originate from the edge-chilled zone and high equiaxed grain area ratio under a low superheat, which is attributed to the low ratio of temperature gradient to growth rate rather than remelting fewer cores originating from the chilled zone. In addition, the floating behavior of separated grains originating from the chilled zone can be affected by gravity force, but these grains should be more active when increasing the casting superheat that may weaken the influence of gravity to a certain extent.

Lump interaction phenomena to the nonlinear ill-posed Boussinesq dynamical wave equation

In this manuscript, we discuss the dynamical behavior of ill-posed Boussinesq (IPB) dynamical wave equation. This equation depicts how long wave made in shallow water propagates due to the influence of gravity. The different wave structures are extracted by the utilization of Hirota's bilinear method (HBM) and different test function approaches. The wave structures in the forms of novel breather waves, lump solutions, two-wave solutions, and rogue wave solutions are obtained. Furthermore, with assistance of appropriate parameters, the acquired solutions' physical behavior is drawn out in 3 dimensional, and contour profiles. As a consequence of the obtained results, we can claim that the used methodology is simple, dynamic, extremely effective, and will serve as a useful tool for solving more severely nonlinear problems in a variety of domains, most notably ocean and coastal engineering. Additionally, our findings provide an important first step in comprehending the structure and physical behavior of complex structures. We hope that our findings will contribute significantly to our understanding of ocean waves. This work, we believe, is timely and will be of interest to a broad range of professionals involved in ocean engineering models. The obtained results are useful in grasping the fundamental scenarios of nonlinear sciences. With the help of Mathematica, the obtained results are verified by inserting them into the governing equation.

Using the method of mathematical planning of the experiment in the development of a quality control method of aerva lanata l. herb

Today, among the urgent tasks facing the pharmaceutical science of the Republic of Uzbekistan is the study of introduced medicinal plants. Of the promising plants Erva woolly - Aerva lanata Juss of the amaranth family (Amaranthaceae) deserves special attention. A perennial or biennial herbaceous plant grows in many countries of Africa, Saudi Arabia, India, Indonesia, etc. For the first time, Aerva lanata Juss. was introduced on the territory of the former USSR by the Transcaucasian zonal experimental station VILR (Kobuletti) in the mid-70s, then in Ukraine, Uzbekistan and Kazakhstan. Aerva lanata is a dioecious plant. The flowers of A. lanata are nectariferous. Pollination of Erva woolly occurs under the influence of gravity inside the flower, wind, insects and rainwater. Erva woolly with more than one pollination and seed dispersal mode is able to invade a variety of habitats with different environmental conditions and grow as widespread weeds. Among other Aerva species, A. lanata cultivar has a wide range of pharmacological activities such as sedative, antiulcer, antiasthma, antidiarrheal, antioxidant, antihyperglycemic, antimalarial, hypolipidemic and other activities. It is used as a diuretic, for acute kidney damage, as well as for ulcerative wounds, rheumatism. Given the availability of the raw material base necessary to meet the possible growth in consumer demand and its widespread use in traditional and scientific medicine to create effective, low-toxic drugs intended for the prevention and treatment of diseases of the urinary system, Aerva lanata Juss L. was chosen as the object of research. An important stage in the standardization of the final product is the quality control of the technological process and the raw materials entering the production to obtain the finished product. Particular attention is paid to the method of quantitative determination of one of the active substances or groups of biologically active substances that affect the therapeutic effect of finished pharmaceutical products. It is known that the quantitative determination of the active substance is carried out by its extraction from plant materials. In this regard, the problem arises - finding the optimal conditions for the process of extracting the active substance. In view of this, it becomes necessary to conduct research to determine the optimal conditions for the extraction process. The objective of the research: the use of the mathematical planning method of the experiment for the complete extraction of flavonoids from the herb Aerva lanata. To achieve this objective, the following tasks were defined: – selection of the mathematical planning method of the experiment; – selection of method for quantitative determination of flavonoids amount; – statistical analysis of the obtained results. Optimization of the process of extracting the amount of flavonoids from the herb of Aerva lanata, which is predominant in its raw materials, was carried out using the method of mathematical planning of experiments by Box and Wilson. The optimization problem was reduced to determining the values of technological parameters that ensure the maximum yield of total flavonoids from the plant. As an optimization parameter, Y was taken - the content of the sum of flavonoids in the extract, in % of its content in the raw material. Conclusion. This article presents the results of modeling and optimization of the process of obtaining the sum of flavonoids from the herb Aerva lanata Juss. L. A comprehensive quantitative assessment of the influence of three experimental factors (alcohol concentration, hydromodulus and extraction time) on the yield of the total flavonoids was carried out using the method of mathematical planning of the Box-Wilson experiment. The objective was achieved by building a mathematical model based on the first order regression equation: Y=1.20+0.185X1+0.091X2+0.111X3 The adequacy of this process is shown, a mathematical model and parametric identification of this model are presented. As a result of the statistical analysis of the obtained data, the following optimal conditions for the process of extracting the amount of flavonoids from the herb of Aerva lanata were revealed in the quantitative analysis of raw materials: alcohol concentration - 50%; hydromodule - 1:60; extraction time - 30 min. The maximum yield of the sum of flavonoids was 1.52% by weight of dry raw materials. The resulting mathematical model of the extraction process will allow further optimization of the extraction of compounds of natural origin, taking into account the quantitative influence of each factor.

Linear Stability of Magneto Viscoelastic Walter’s B ′ Type with Heat and Mass Transfer

In this paper, the couple influence of axial magnetic field and the heat and mass transfer on two rotating cylinders of Walter’s B ′ viscoelastic fluids by using the potential flow theory of viscoelastic fluid has been investigated. The normal mode method is used to compute the growth rate of disturbance. The influence of gravity is ignored at the interface, while the effect of surface tension is present in the analysis. The effect of the parameters on the stability is studied. It is found that the rotation of the inner cylinder induces stability. Furthermore, the viscoelastic ratio of fluids has a stabilizing influence. The heat and mass transfer, magnetic permeability ratio, and Ohnesorge number have a stabilized influence, while viscosity ratio of fluids, density ratio of fluids, and axial magnetic field have destabilizing influence on the considered system.

Dynamics of weakly evaporating and non-evaporating drops falling in air

The dynamics of evaporating and non-evaporating drops falling in air under the influence of gravity is experimentally and theoretically studied in this work. Water and drops with diameters 2.0 and 2.7 mm and acetone drops 1.8 and 2.0 in diameter were tracked for approximately 2 m, corresponding to a flight-time of almost one second; at the end of the observation region, in most cases, the drops reached velocities ∼80% terminal velocity. Vertical positions of falling drops as a function of time and horizontal positions at different heights were recorded. Initially, the motion of non-evaporating water drops was rectilinear with a remarkable reproducibility in all experimental runs, showing narrow standard deviations in their horizontal position. When the increasing Reynolds numbers reached approximately 700, trajectories of individual drops diverged from each other. This effect may be attributed to the laminar-turbulent transition of the drops wake. It was also observed that the spatial dispersion, along horizontal cuts along their fall, evolved from a narrow to a wider monomodal distribution to bimodal one as the traveled distance increases. The acetone drops evaporated as they fall and although their velocity increased, the diameter reduction prevented the drops from reaching the critical transition Reynolds number, maintaining the dispersion in the horizontal positions relatively narrow. A maximum volume loss due to evaporation of 13% is recorded at the lower end of the observation region. Simplified theories based on the drag coefficients of fixed spheres closely predict the drops vertical positions as a function of time, for both evaporating and non-evaporating drops. Calculations based on heat and mass transfer correlations for fixed spheres show a satisfactory agreement when compared with the experimental observations of the radii of evaporating drops as a function of time.

Influence of Sliding Structure on Water Flowing Fracture Zone and Surface Subsidence in the Antidip of Overlying Strata Area

Sliding structure refers to the process and result of rock deformation caused by the continuous downward sliding and cutting of the upper stratum under the influence of gravity. In the process of tectonic formation, the strata go through two times of sliding to the south and then sliding to the north after the over thrusting and overstretching, so that the strata of the overthrusting and underthrusting strata are opposite to the inclination of the overthrusting and underthrusting strata, forming the anticlinal tectonic zone. Nowadays, under the conventional geological mining conditions, the underwater mining technology and surface subsidence laws are quite mature, but the fracture zone and surface movement characteristics of the sliding structure and the antioverturning mining are still rarely studied. This paper analyzes the dam damage in the mining process and discusses the three-dimensional reconstruction of laser scanning and the acquisition method of settlement information. The three-dimensional laser scanning technology is compared with the traditional monitoring technology. The deformation characteristics of surface structures above 25091 working face are revealed. The 3D laser point cloud shows that the uneven sinking of the dam is obvious and is associated with the uneven damage of the dam mass. The actual observation at the site shows that the uneven settlement of the dam on the surface was noticeable during the 25091 working face retraction. The damage on the east side of the dam was more serious and was accompanied by the generation of cracks running east-west. The DEM model of part of the surface and dam above the 25091 working face was obtained by 3D laser scanning technology. The model was analyzed to obtain information on surface subsidence. The study reveals that the uneven subsidence condition of the dam is apparent, with the overall characteristics of large subsidence on the east side of the dam and small subsidence on the west side of the dam. The displacement of the maximum surface subsidence point reflects the special phenomenon of overburden fracture and surface movement under the influence of overburden reverse inclination.

Stability study of centrifugal pendulum vibration absorbers in gravity field

In this study, Lyapunov stability theory was used to systematically investigate the stability of centrifugal pendulum vibration absorber (CPVA) in terms of the shape of the absorber path, mistuning levels, damping coefficient, number of absorbers, and force of gravity. Our approach improved upon previous studies by introducing a gravity term, optimising the calculation method, and using a function diagram to represent the asymptotically stable region to produce more accurate results. Our finding that the influence of gravity on the stability of the CPVA system is reflected in the change of the tuning order prompted us to define new terminology—’gravity mistuning factor ([Formula: see text])’ and ‘zone yielding to gravity ([Formula: see text])’—to intuitively reflect the influence of gravity. Comparison of the results obtained from numerical simulation based on a fully nonlinear equation of motion with analytical results revealed nonlinear dynamic characteristics such as bifurcation to asynchrony response, nonlinear jump, and beat phenomena. The approach and results of this study are more practical in settings in which gravity plays an important role, including vehicle engine idling, low-speed locomotive or marine engines, and drum washing machines.

Large-Eddy Simulation on the Aerodynamic and Thermal Characteristics in a Micropipe of the Hypersonic Engine Precooler.

The precooling air-breathing technique has become a study focus in the aerospace field. Research on the internal flow and heat-transfer mechanism of the precooler is important for design and optimization. A large-eddy simulation was used to study the aerodynamic and thermal characteristics in a micropipe of the hypersonic engine precooler with supercritical methane as coolant and fuel. Under the effect of buoyancy, the high-temperature and low-density fluid near the wall in the circumferential direction gradually accumulate to the top wall. The accumulation of low-density fluid enhances the thermal acceleration effect at the top wall, which intensifies the local turbulent relaminarization and forms an M-shaped velocity distribution, resulting in the weakening of the heat transfer. On the other hand, the high-density fluid gathers to the bottom wall under the influence of gravity, the local thermal acceleration effect is weakened, and the flow heat transfer is enhanced. The influence of the relationship between the turbulent burst and the turbulent heat transfer under the effect of buoyancy is analyzed. It is found that the low-speed ejection events and high-speed sweep events are strengthened at the bottom wall, especially the low-speed ejection. However, the occurrence of these events at the top wall is restrained to a certain extent.