Entry Velocity Research Articles

Developing Turbulent Flow in Pipes and Analysis of Entrance Region

Turbulent flows have complex structures due to its nature and its’ analyses are hard either by numerical or experimental means. Hydrodynamic development of turbulent flow is also complex. In this study, velocity distribution in hydrodynamic entrance length of pipes is investigated depending on axial and radial locations. Literature was surveyed for a single empirical expression that provides velocity profile directly according to Reynolds number, radial and axial locations. Requisite for computational fluid dynamics in hydrodynamic entry length of pipes is stressed by assessing turbulence magnitudes in radial and axial directions. Evaluation of the region and its properties are conducted from heat transfer perspective. An axisymmetric pipe entrance region was analyzed by means of a commercial CFD code with nondimensional parameters. Four different Reynolds numbers that are 5x103, 1x104, 5x104, 1x105 were used in calculations. k-ϵ turbulence model and standard wall functions were used for turbulence modeling. Hydrodynamic entry length, velocity profiles and turbulence indicator parameters results are presented by means of axial and radial profiles. According to the obtained results, radial velocity component values exist that would lead to radial thermal convection in hydrodynamic entrance length. It is found that simultaneous development of velocity profiles and turbulence quantities leads to characteristic velocity profiles. Also, it is seen that a good resolution in hydrodynamic entrance length can be easily achieved by computational fluid dynamics.

Characteristics of Slamming Pressure and Force for Trimaran Hull

In this paper, the characteristics of the impact pressure and force of a trimaran section was studied by Computational Fluid Dynamics (CFD). The time domain features of the slamming pressure or force showed a strong correlation with the penetration depth regardless of the specific ways of water entry. The effects of velocity and acceleration on the impact pressure and force were analyzed. It was found that the initial impact of the main hull and the wet-deck slamming were predominantly affected by the entry velocities, whilst the acceleration had almost no effect for initial impact. The impact velocity presented a quadratic relation with slamming pressure/forces, and the relation between acceleration and wet-deck slamming pressure/force was linear. These were consistent with the patterns implied by analytical models such as the Wagner or MLM (Modified Logvinovich model) theories.

Enhancement of the Photovoltaic Potential in Mimosa pudica-Based Dye for Sensitization of the Working Electrode in the Construction of Solar Cell

Abstract The potential enhancement of extract from Mimosa pudica (M. pudica) leaf for sensitizing TiO2 layer toward the production of the organic solar cell is investigated. A unique diffusion model that incorporates the concentration of the extract in the TiO2 layer is adopted. The diffusion characterization of the extract into the TiO2 provides a proper understanding of the dynamics of the extract within the layer. This research applies the combination of experimental and numerical techniques toward the investigation of the diffusion characteristics in M. pudica extract. Experimental chromatograph of the extract is conducted in order to reveal the properties and concentration of the extract. Three different thicknesses of TiO2 deposit are sensitized at different hours in order to monitor the absorbance. Using the finite volume method (FVM), the adsorption and diffusion characteristics of the extract into the layer of TiO2 are modeled. The current–voltage characteristics of the cell are combined in series as a standard module and applied to an audited office space. The cell area characterized is 0.3848 cm2, and the conversion efficiency of 1.35% is obtained. The concentration model of the extract in TiO2 and the entrance velocity is presented. The experimental and numerical results compared favorably. However, it is anticipated that additional taxonomical characterization of M. pudica and advanced investigation into organic matrix composite will provide a useful guide for the synthesis of the natural dye and enhance the conversion efficiency of the solar module for renewable power generation.

Numerical simulation of water entry of a symmetric/asymmetric wedge into waves using OpenFOAM

This paper presents a dynamic overset mesh based two-dimensional Numerical Wave Tank (NWT) model to study the water entry of a wedge into water waves in the process of offshore lowering. The NWT model is developed by integrating an incompressible multiphase flow solver on the dynamic overset mesh and a wave generation library in OpenFOAM. Numerical results of water entry of a symmetric/asymmetric wedge into the still water are presented to validate the NWT model by comparing with the published data. A series of numerical simulations of water entry of a symmetrical/asymmetrical wedge into regular waves are carried out, and the pressure coefficients, total force and free surface profiles are presented. Based on the parametric study on the water entry of a wedge into waves, the influence of wave amplitude, water entry velocity, and water entry location (wave peak, wave trough, cross point with the still water level) is analyzed. The numerical solutions provide the fundamentals for the further research on the safe control of water entry of payloads during the offshore installation.

ОЦЕНКА ЧУВСТВИТЕЛЬНОСТИ ГАЗЛИФТНОГО ЗОНДА В СИСТЕМЕ КОНТРОЛЯ ГЕРМЕТИЧНОСТИ ОБОЛОЧЕК ТВЭЛОВ ПО МОДЕЛИ РАСТВОРЕНИЯ/ДЕГАЗАЦИИ ГАЗООБРАЗНЫХ ПРОДУКТОВ ДЕЛЕНИЯ В СВИНЦОВОМ ТЕПЛОНОСИТЕЛЕ

Gas-lift probe is an element of cladding failure detection system of perspective lead cooled reactor. Its function is local measurement of gaseous fission product activity in the coolant and the most defected fuel assembly localization. In the coolant leaving the defected fuel assembly the specific activity of gaseous fission products is higher than the average one in the primary circuit. In the barbotage channel of gas-lift probe gaseous fission products diffuse through the bubble interface surface into the volume of the bubbles. The bubbles deliver gaseous fission product to interface surface in the separation volume. The gas enriched with radioactive gaseous fission product goes to measurement volume of the probe. The more significant the damage and the closer the defective fuel assembly is located to the probe input, the more gaseous fission product activity will be registered. The paper presents a model of gaseous activity transfer from cladding defect to probe measuring volume. The gaseous activity transfer is described on the basis of the inert gases dissolution/degassing processes in lead. The gas-lift probe sensitivity was estimated as the ratio of the entry velocity of gaseous activity into the measurement volume to the exit one into the coolant through fuel assemblies cladding defects. A gas-lift probe sensitivity for exposed fuel surface calculated as an example. Gaseous fission products with significant gamma radiation are considered. The calculation results are presented in the article.

Comparative morphology and morphometry of the micropyle of two Korean rice-fishes, Oryzias latipes and Oryzias sinensis (Pisces, Adrianichthyidae)

The morphology and morphometry of the micropyle of two Korean rice fishes, Oryzias latipes and O. sinensis, were investigated by light microscopy and scanning electron microscopy. Obtained from adult gravid females during the spawning season, the full-grown eggs of each species have a single micropyle at the animal pole. For the two species, the micropyles are similar in appearance, but there exist some differences in detail. The egg is larger in O. latipes than in O. sinensis (1,123.3-1,465.5 µm vs. 823.1-1,152.1 µm in diameter), and the outer diameter of a single micropyle for O. latipes is nearly two times larger than that of O. sinensis (18.5-22.4 µm vs. 10.0-12.5 µm). The micropylar diameter to egg diameter ratio (1.6 ± 0.1% vs. 1.0 ± 0.1%) is also larger in O. latipes than O. sinensis. In regard to micropyle structure, the two showed distinguishing characteristics: O. latipes has a funnel-shaped micropyle consisting of two regions, an outer gradual pit and an inner narrow canal, while O. sinensis has a conical-shaped micropyle having only a deep narrow canal. Consequently, these differences in micropylar structure between the two Korean rice-fishes may be considered as a useful taxonomic characteristic in closely related taxa and seem to be structural adaptations to shape and control entry velocity of spermatozoa into the micropyle.

Cavity Formation during Asymmetric Water Entry of Rigid Bodies

This work numerically evaluates the role of advancing velocity on the water entry of rigid wedges, highlighting its influence on the development of underpressure at the fluid–structure interface, which can eventually lead to fluid detachment or cavity formation, depending on the geometry. A coupled FEM–SPH numerical model is implemented within LS-DYNA, and three types of asymmetric impacts are treated: (I) symmetric wedges with horizontal velocity component, (II) asymmetric wedges with a pure vertical velocity component, and (III) asymmetric wedges with a horizontal velocity component. Particular attention is given to the evolution of the pressure at the fluid–structure interface and the onset of fluid detachment at the wedge tip and their effect on the rigid body dynamics. Results concerning the tilting moment generated during the water entry are presented, varying entry depth, asymmetry, and entry velocity. The presented results are important for the evaluation of the stability of the body during asymmetric slamming events.

Investigation of Fluid-Induced Vibration and Heat Transfer of Helical Elastic Coiled Tube

The study of fluid-induced vibration of helical elastic coiled tubes to enhance heat transfer is very important for engineering practice and energy saving. Fluid-induced vibration and enhanced heat transfer of a helical elastic coiled tube heat exchanger were analyzed based on its finite element model, by using a two-way fluid–solid coupling method. Vibration response of the helical elastic coiled tubes, heat transfer coefficient per unit volume, and Nusselt number in vibration and nonvibration were studied at different entrance velocities and winding numbers. The results illustrate that there are a lot of vortexes in the heat exchanger and around the helical elastic coiled tubes. In the range of the entrance velocity , the vibration frequency is constant, whereas the vibration amplitude increases, and the tube vibration enhances the heat transfer of the helical elastic coiled tubes by 0.38%, 0.89%, 1.93%, and 13.65%, respectively. As the winding number increases from 5 to 9, it has a greater effect on the vibration amplitude, and the tube vibration enhances the heat transfer of the helical elastic coiled tubes by 1.93%, 3.39%, and 3.59%, respectively.

SENSITIVITY RESEARCH ON MODELS OF EARTH ENTRY AND IMPACT EFFECTS BY ASTEROIDS

Asteroid impact on Earth is one of the potential threats to human beings. Engineering models of Earth entry and impact effects by asteroids have been developed in order to estimate ground hazard by planetary defense communities nowadays. However, there are large uncertainties in input parameters of these models, which not only brings trouble to use of the model, but also greatly affects results of hazard estimate. Ranges of input parameters are analyzed, of Which baseline values are taken as maximum probability values or recommended values in literatures. Furthermore, by changing one or more input parameters based on ranges and baseline values, AICA (Asteroid Impact Consequence Analysis) code developed by authors of this paper, are used to study sensitivity of output parameters, such as energy deposition, airburst altitude, radius of 4psi overpressure and 3rd degree burn, to input parameters. The results are given for stony asteroids with diameter of 60~300~m and entry velocity of 12~40~km/s. It is indicated by results that airburst altitude of asteroid trends to decrease, with increase of size, strength at 1st breakup and mass fraction of debris cloud, and with decrease of entry velocity and ablation coefficient. Drag coefficient of asteroid and fragment, as well as strength scaling exponent, has little effect on airburst altitude and ground damage range. Radius of overpressure and thermal radiation damage generally increases with increase of size and entry velocity. If mass fraction of debris cloud is less than 50%, airburst altitude and ground damage range will fluctuate. But a large value for mass fraction of debris cloud, such as 80%, is reasonable according to analysis of many meteor events at present. Luminous efficiency only affects damage range of thermal radiation. Under the computational condition in this paper, radius of 3rd degree burn is less than that of 4-psi overpressure, indicating that the main type of ground hazard is overpressure caused by airburst.

Simulation and experimental investigation of a ballistic compression soft recovery system

A soft recovery system is used to arrest a supersonic object over a limited distance in a controlled manner. This may be achieved through ballistic compression of gas. This work explains the motion of a supersonic object passing through a ballistic compression decelerator i.e., pressurized gas column initially sandwiched between two diaphragms. The accompanying mechanics is complex and includes diverse effects such as separation of shock from the supersonic object, travelling shocks, shock reflections, creation of a new shock, emergence and dissolution of contact discontinuities and expansion waves, and shock-shock interactions. In this work, these phenomena have been numerically and experimentally studied. While the method of characteristics was used to solve Euler’s equations in continuous regions, jump conditions derived from control volume considerations were used to obtain solutions across discontinuities. In this way, a duly validated finite difference method computer program was developed to analyze the problem. Finally, simulation predictions were validated by conducting experiments on a 7.62 mm soft recovery system tube. Our results showed that, an object having an entry velocity of 880 m/s, left the SRS with a velocity that was lower by 47% from simulation predictions. Further analysis showed that friction between the object and tube was a major contributor to this gap. Post accounting for friction, the difference between numerical analysis and experimental data got reduced to about 5% at most locations, and to 17% at the end of the SRS. We attribute this residual difference between observations and simulations to build up of pressure at a location post passage of shock by it. Our 2-D finite volume study results, which are consistent with earlier research, as well as with our experimental data, show that such a phenomenon is prominent particularly in narrow tubes due to development of significantly thick turbulent boundary layers.

Numerical and experimental study of cone-headed projectile entering water vertically based on MMALE method

The water entry behaviors of projectiles with different cone-headed angles were studied numerically, experimentally and theoretically, mainly focusing on the hydrodynamic impact in the initial stage. Based on MMALE algorithm, it was proposed a formula of impact deceleration, which relied on the initial entry velocity and cone-headed angle. Meanwhile, in order to verify the validity of the simulation model, experiments using accelerometer and high-speed camera were carried out, and their results were in a good agreement with simulation results. Also, theoretical calculation results of cavity diameter were compared with experiments and simulation results. It was observed that the simulation method had a good reliability, which would make forecast on impact deceleration in an engineering project.

Different closure patterns of the hollow cylinder cavities with various water-entry velocities

The vertical water-entry processes of a hollow cylinder with three different velocities are investigated both numerically and experimentally. Three different closure patterns and flow characteristics of the air-entraining cavities induced by water-entry processes are discovered and discussed. Our results show that three different closure patterns appear with the increase of entry velocity, the deep-closure, the surface closure on the through-hole jet and on the geometry wall. Three high-speed regions also appear during the water entry process and their characteristics are different with various closure patterns. Besides, with the increase of water entry velocity, the velocity variation will vary from increase to decrease, but their water depths all increase linearly due to the short time and small variations of velocities.

Swimming Behavior of Downstream Moving Fish at Innovative Curved-Bar Rack Bypass Systems for Fish Protection at Water Intakes

New types of fish guidance structures with vertical curved bars and a subsequent bypass system represent a promising technical solution for the protection and guidance of downstream moving fish at run-of-river hydropower plants and water intakes. These so-called “curved-bar rack bypass systems” (CBR-BSs) function as a mechanical behavioral barrier and are characterized by low hydraulic losses, a symmetrical downstream flow field and an overall high fish guidance efficiency in the laboratory for a wide array of European freshwater fish species. This paper presents the results of the hydraulic and live-fish laboratory tests of an optimized CBR-BS configuration with a bar spacing of 50 mm and 30° rack angle to the flow direction. The tests were conducted with six different fish species in an ethohydraulic laboratory flume at different approach flows (0.5 m/s, 0.7 m/s) and different bypass entrance velocities (0.6–1.0 m/s). A numerical model was used to simulate the flow fields in the CBR-BS in order to link the fish behavior to the hydrodynamic cues created by the CBR-BS. Lower approach flow velocities decreased the hydraulic cues of the CBR, which led to more rack passages. A 20% velocity increase towards the bypass entrance significantly increased the fish guidance efficiency compared to a 40% velocity increase. The tested CBR-BS resulted in overall higher interspecies fish protection and guidance efficiencies compared to the more commonly applied horizontal-bar rack with a narrow bar spacing of 20 mm. Recommendations for a sustainable and cost-effective application of CBR-BSs are given.

Investigation of trimaran slamming under different conditions

In this paper, the slamming pressure and load characteristics of a trimaran cross-section under various conditions were investigated by CFD (Computational Fluid Dynamics) simulations. The computation model was first validated against experimental results. After that, the simulation of different types of motion, i.e. free fall with different mass and entry velocity, entry with constant velocity and harmonic motion with different entry velocities were analysed. It was found that the characteristics of the dynamics during slamming strongly correlates to penetration depth, regardless of the types of entry. Distinguishing features during the wet-deck slam were observed for free fall motion under different conditions, including pressure drop under the main hull during wet-deck slam. The maximum acceleration would start to decrease after the mass has reached a certain value, and the second acceleration peak (corresponding to the wet-deck slam) would be smaller than the first one if the falling height is large enough.

Experimental study on the propagation characteristics of the slamming pressures

The ship slamming pressure may exhibit a propagating feature and would have a significant influence on the local response of ship structure. This paper presents an experimental investigation on the characteristics of the slamming pressure, such as the slamming pressure coefficient, time duration, spatial pressure distribution and propagation speed. A series of experiments on the water entry of rigid and elastic wedges have been carried out for deadrise angles ranging from 0° to 45° and for drop heights ranging from 0.1 m to 1.0 m. Wedge plates with varying thicknesses are tested in the experiments to study the effect of structural elasticity on the propagating feature of the slamming pressure. Based on the experimental results, the spatial variation of the slamming pressure is analyzed. Besides, the effects of the water entry velocity, deadrise angle and wedge plate's structural elasticity on the propagating feature of the slamming pressure is studied. For the flat bottom slamming with a deadrise angle of 0°, the slamming pressure instantaneously acts on the structure, which shows no propagating feature and is close to the uniformly distributed pulse load. The propagation of slamming pressure is found to occur when the deadrise angle exceeds 0.2°. When the deadrise angle is between 4° and 45°, the pressure pulse shape is nearly unchanged during the propagation of the slamming pressure, and the ratio between the experimental speed of propagation and Wagner's theoretical speed is about 0.8. The effect of wedge plate flexibility on the slamming pressure is mainly observed in the cases with small deadrise angles. The wedge plate flexibility causes the duration of the slamming pressure to increase and the pressure coefficient to increase or decrease depending on the ratio between pressure duration and the structure's natural period.

Numerical simulation of water entry of an inclined cylinder

Water entry of cylindrical structures is a complex multiphase flow problem involving a three-phase medium interaction that occurs instantaneously. It is a nonlinear and unsteady process, which the physical understanding of mechanism in the aspect of evolution of cavity dynamics and multiphase flow field is yet to be fully understood. In the present work, a three-dimensional numerical model of six degrees of freedom (DOF) based on the shear stress transport (SST) k−ω eddy viscosity model was established to capture the complicated characteristics of the vertical water entry of an inclined cylinder at various entry velocities. A volume of fluid method for tracking air-water interface and a combined dynamic fluid body interaction and overlapping grid technology were used to simulate the complex motion. The numerical model with laminar and turbulent model was verified against the published experimental data of cavity evolution and motion characteristics. A parametric study was conducted to study the translational and rotational characteristics of the structure due to the effect of water entry velocity. The investigation revealed the secondary closure phenomenon during the water entry. The asymmetrical multiphase flow field showed that its dynamic characteristics change with space and time under the effect of cavity evolution.

Tungsten and Molybdenum Surfaces Exposed to Warm Deuterium Ion Plasma with Q-Nonextensive Distribution of Electrons

This work is concerned with the effect of non-Maxwellian electrons and obliqueness of magnetic field on magnetized plasma sheath characteristics, in which plasma interacts with tungsten (W) and molybdenum (Mo) surfaces via non-neutral plasma sheath using two fluids model. It is assumed that the singly charged positive ions are treated as warm fluid whereas the electrons obey q-nonextensive distribution. It is found that the q-nonextensive distributed electrons and the temperature of ions affect the entrance velocity of positive ions, which is a key parameter in the plasma sheath formation. Also, the nonextensive parameter q affects the distribution of ions and electrons in the sheath region and their distributions explicitly related with the electrostatic potential variation. The parallel and perpendicular components of ions velocity are affected by the obliqueness of magnetic field. As the nonextensivity of electrons increases, the gradient in electric potential increases towards the wall and hence the impact energy also increases. The obliqueness of magnetic field and impact energy of ions is a key factor that determines the physical sputtering rate, particle reflection and absorption from the target surface. Furthermore, the probability of particle reflection coefficient from the W-surface is higher than that of Mo-surface.

Analysis on Fluid-Induced Vibration and Heat Transfer of Helical Elastic Tube Bundles

The study on fluid-induced vibration of helical elastic tube bundles (HETBs) to enhance heat transfer is of great significance in industrial production and energy utilization. The fluid-induced vibration response and the heat transfer property of a HETB heat exchanger were analyzed by using a two-way fluid–solid coupling method. The vibration frequency, displacement amplitude, and heat transfer coefficient were computed while considering varying entrance velocities and helix diameters. Numerical results demonstrate that the middle of the HETB vibrates the most violently, and the vibration is mainly in the vertical direction. There are a large number of vortices in the gaps between the tubes and the inner cavity of the heat exchanger. The vibration amplitude and heat transfer coefficient of the HETB increase significantly when the entrance velocity or helix diameter increases. The effect of vibration-enhanced heat transfer improves with the increase in entrance velocity. The mean value of the heat transfer coefficient at the upper side of the HETBs is 2.205 times that at the lower side.

Cavitation bubble dynamics and structural loads of high-speed water entry of a cylinder using fluid-structure interaction method

This paper describes an investigation of the motion, structural response, and cavitation bubble evolution of a cylinder in the high-speed water entry (HSWE) process using a fluid-structure interaction (FSI) method. The effectiveness and accuracy of the FSI method are verified by comparison with experimental results available in the literature. The results show that the cylinder structure is deformed when considering the coupling effect between the fluid and the structure, and the impact load during water entry presents obvious fluctuation characteristics. Meanwhile, the von Mises stress distribution on the two end faces of the cylinder is in a ring shape and propagates as the structure deforms. Moreover, the cavitation bubble dynamics, motion and structural loads of the cylinder under different water entry velocities are investigated. The load at the initial stage is greater with the increase of the water entry velocity, which in turn leads to more significant fluctuation characteristics, thereby increasing the deformation of the structure.

Investigation of the Ozerki meteoroid parameters

In the morning of June 21, 2018 (1:16 Universal Time (UTC)) the space body entered the Earth atmosphere in the Lipetsk region, Russia. This event was detected by a number of registration systems in cars, satellite observations of bolide light curve and subsequent dust trail. The videos, photos, satellite data allow us to calculate the trajectory and the orbit of the Ozerki bolide. The atmospheric entry velocity is 14. 9 ​± ​1 ​km/s. The height of the depression point is 32.8 ​± ​0.9 ​km and that of the maximum brightness is 27.2 ​± ​0.9 ​km. The pre-atmospheric orbit of the Ozerki meteoroid was also calculated: q ​= ​0.67 ​± ​0.04 AU, a ​= ​0.84 ​± ​0.02 AU, e ​= ​0.199 ​± ​0.030, i ​= ​18.44° ±3.05°, Ω ​= ​89.6561° and ω ​= ​335.29° ±5.15°. The geocentric radiant position is RA ​= ​307.51°±3° and DEC ​= ​43.11°±3.° The found material was called Ozerki meteorite and it is classified as an ordinary chondrite (L6). The estimated: mass of the meteoroid is 94 ​± ​20 tons, the energy is 2.5 ​± ​0.5 ​kt TNT, diameter is 3.7 ​± ​0.5 ​m.