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Journal articles on the topic 'Turbulent flow'
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Anand, Abhirath, Christian Poelma, and Angeliki Laskari. "LED-based PIV Of A Particle-Laden Turbulent Free-Surface." Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (July 8, 2024): 1–14. http://dx.doi.org/10.55037/lxlaser.21st.50.
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An experimental method is proposed to study dispersed two-phase flows at an airwater interface, a family of flows of practical significance in environmental and industrial settings. The applicability of this technique is demonstrated through the study of a lightly-deformed turbulent free-surface laden with floating particles (`floaters'). A low-mean turbulent flow is generated in a turbulence box actuated by a 10×10 synthetic jet array. Using LEDs and a single camera, free-surface flow measurements are carried out by Particle Image Velocimetry (PIV) simultaneously with Lagrangian tracking of the floaters, allowing the potential to characterise the coupling between the floater dynamics and the (sub)surface flow. Discrimination of the dispersed and continuous phases is carried out based on size. Individual floaters and clusters of floaters are successfully tracked throughout the field of view while they navigate through elongated and circular regions of high and low vorticity, characteristic features typically observed when a subsurface turbulent flow interacts with a free surface. Preliminary results of the floater-fluid interactions are presented to highlight the potential of this technique to better our understanding of floaterladen turbulent free surfaces.
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Kellnerova, Radka, Libor Kukacka, Vaclav Uruba, Klara Jurcakova, and Zbynek Janour. "Detailed analysis of POD method applied on turbulent flow." EPJ Web of Conferences 25 (2012): 01038. http://dx.doi.org/10.1051/epjconf/20122501038.
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Semwogerere, Twaibu, R. Awichi, J. D. Lwanyaga, Esemu Joseph Noah, Verdiana G. Masanja, and H. Nampala. "An Application of Computational Fluid Dynamics to Optimize Municipal Sewage Networks; A Case of Tororo Municipality, Eastern Uganda." JOURNAL OF ADVANCES IN MATHEMATICS 18 (January 10, 2020): 18–27. http://dx.doi.org/10.24297/jam.v18i.8345.
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Two-phase pipe flow is a common occurrence in many industrial applications such as sewage, water, oil, and gas transportation. Accurate prediction of liquid velocity, holdup and pressure drop is of vast importance to ensure effective design and operation of fluid transport systems. This paper aimed at the simulation of a two-phase flow of air and sewage (water) using an open source software OpenFOAM. Numerical Simulations have been performed using varying dimensions of pipes as well as their inclinations. Specifically, a Standard k- turbulence model and the Volume of Fluid (VOF) free water surface model is used to solve the turbulent mixture flow of air and sewage (water). A two dimensional, 0.5m diameter pipe of 20m length is used for the CFD approach based on the Navier-Stokes equations. Results showed that the flow pattern behaviour is influenced by the pipe diameters as well as their inclination. It is concluded that the most effective way to optimize a sewer network system for Tororo Municipality conditions and other similar situations, is by adjusting sewer diameters and slope gradients and expanding the number of sewer network connections of household and industries from 535 (i.e., 31.2% of total) to at least 1,200 (70% of total).
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Luo, Kun, San Xia Zhang, Zhi Ying Gao, Jian Wen Wang, Sheng Hua Zhu, Li Ru Zhang, and Jian Ren Fan. "Large-Eddy Simulation of Flow around a Horizontal-Axis Wind Turbine." Applied Mechanics and Materials 291-294 (February 2013): 450–55. http://dx.doi.org/10.4028/www.scientific.net/amm.291-294.450.
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Three-dimensional flow around a horizontal-axis wind turbine has been investigated with LES method coupled with sliding mesh and experimental measurement. The boundary conditions are set as the same as those of the experiment. The images of the pressure distribution, flow rate distribution, turbulent intensity, velocity vector and vortices of the wind turbine are presented to show the three-dimensional flow characteristics around the wind turbine. The relationship between flow and sound is further studied by analyzing the flow parameters pulsation spectrum to get the sound pressure level. LES results are compared with the wind-tunnel measurements collected with PIV, and good agreement is observed. The results serve as a reference for optimum design of the wind turbine with high functional performance and low level noise generation.
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Fan, Aiwu, Junjie Deng, Jian Guo, and Wei Liu. "A numerical study on thermo-hydraulic characteristics of turbulent flow in a circular tube fitted with conical strip inserts." Applied Thermal Engineering 31, no. 14-15 (October 2011): 2819–28. http://dx.doi.org/10.1016/j.applthermaleng.2011.05.007.
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Protsenko, E. A., and S. V. Protsenko. "Stationary and Non-Stationary Periodic Flows Mathematical Modelling using Various Vortex Viscosity Models." Computational Mathematics and Information Technologies 7, no. 4 (January 3, 2024): 30–38. http://dx.doi.org/10.23947/2587-8999-2023-7-4-30-38.
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Introduction. Mathematical modelling of currents is an urgent research topic in the field of hydrodynamics and oceanography. Despite ongoing research in the field of developing accurate and efficient numerical methods for solving Navier-Stokes equations that take into account vortex viscosity, the problems of accurate prediction and control of turbulence remain unresolved. The influence of nonlinear effects in vortex viscosity models on the accuracy of forecasts and their applicability to various flow conditions also remains relevant. The aim of the study is to study the influence of linearized and quadratic bottom friction and two turbulence models on the numerical solution of stationary and non-stationary periodic flows. Special emphasis is placed on comparing numerical results with analytical solutions within the framework of using various models of bottom friction.Materials and Methods. The computational models used in this study are based on a simplified two-dimensional wave model and full three-dimensional Navier-Stokes equations. The classical model of shallow water motion and the 2D model without taking into account dynamic changes in the geometry of the reservoir surface are derived from a system of equations for a spatially inhomogeneous three-dimensional mathematical model of wave hydrodynamics of a shallow reservoir. Analytical solutions were found by linearization of the equations, which obviously has its limitations. A distinction is made between two types of nonlinear effects – nonlinearities caused by higher-order terms in the equations of motion, i. e. terms of advective acceleration and friction, and nonlinear effects caused by geometric nonlinearities, this is due, for example, to different water depths and reservoir widths, which will be important when modelling a real sea.Results. The results of modeling stationary and non-stationary periodic flows in a schematized rectangular basin using linearized bottom friction are presented. The influence of linearization on the numerical solution is investigated in comparison with analytical profiles using models calculating bottom friction in a quadratic formulation. In combination with quadratic bottom friction, two turbulence models are studied: the constant vortex viscosity and the Prandtl mixing length model. The results obtained as a result of three-dimensional modelling are compared with the results of two-dimensional modeling and analytical solutions averaged in depth.Discussion and Conclusion. New approaches to modelling and studying flows with variable vortex viscosity are proposed, including analysis of the influence of linearization and the use of various turbulence models. For the linearized and quadratic formulations of bottom friction, it is proved that the numerical results for the case of stationary flow show great similarity with analytical solutions, since the surface height is much less than the water depth and advection can be neglected. The numerical results for the unsteady flow also show a good agreement with the theory. Unlike analytical solutions, numerical modelling has minor deviations in the long run. The study of flows, within the framework of using various turbulence models, will make it possible to take into account the influence of nonlinear effects in vortex viscosity models on the accuracy of forecasts and their applicability to various flow conditions. The results obtained make it possible to better understand and describe the physical processes occurring in shallow waters. This opens up new possibilities for applying mathematical modelling to predict and analyze the impact of human activities on the marine environment and to solve other problems in the field of oceanology and geophysics.
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RAFIEE, Seyed Ehsan, and Mohammad Bagher Mohammad SADEGHIAZAD. "THREE-DIMENSIONAL COMPUTATIONAL PREDICTION OF VORTEX SEPARATION PHENOMENON INSIDE THE RANQUE-HILSCH VORTEX TUBE." Aviation 20, no. 1 (April 11, 2016): 21–31. http://dx.doi.org/10.3846/16487788.2016.1139814.
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The air separators are used to provide safe, clean and appropriate air to the helicopter’s engine. In this operational study, the separation process inside a Ranque-Hilsch air separator cleaning system has been investigated to analyze the impact of choosing the appropriate turbulence model for predicting the separation process inside the air separator. This research is directed towards presenting a computational fluid dynamic explanation performed on a counter-flow air separator using air at different magnitudes of air flow fraction and applying different turbulence models. In a numerical investigation of counter-flow air separator, air has been chosen and its vortex separation phe- nomenon has been analyzed as a function of flow fraction. Furthermore, a numerical analysis to compare the outputs of a seven equation RSM turbulence model applied for the study of vortex separation of a counter-flow air separator with some two-equation turbulence methods, namely, k-ε and k-ω model as well as LES has been presented. All of the turbulence numerical methods are seen to present and predict the same flow pattern inside an air separator, but, with various details. The results show that among the tested methods the RSM creates the most accurate separation pattern. The numerical results are validated by some available experimental data with good agreement.
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Castelain, Thomas, Igor Kurek, Pierre Lecomte, and Christophe Bailly. "Turbulence Analysis From Long-Exposure-Time Acquisitions With Interferometric Rayleigh Scattering." Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (July 8, 2024): 1–13. http://dx.doi.org/10.55037/lxlaser.21st.89.
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This study focuses on the analysis of long-exposure-time interferograms obtained with an Interferometric Rayleigh Scattering (IRS) set-up pointing at a high subsonic isothermal jet flow. The objectives are twofold: retrieve from seeding-free optical measurements the mean characteristics of this flow - in particular the mean velocity profile in the jet shear-layer - and determine higher order statistics for the flow velocity in the shear layer. The results are compared to those obtained on the same test bench by use of hot wire anemometry, and conclusions about the relevancy of the approach together with potential improvements are deduced therefrom.
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Sidoryakina, V. V. "Mathematical Model of Spreading Oil Pollution in Coastal Marine Systems." Computational Mathematics and Information Technologies 7, no. 4 (January 3, 2024): 39–46. http://dx.doi.org/10.23947/2587-8999-2023-7-4-39-46.
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Introduction. The negative consequences that may arise due to an accidental oil spill are difficult to account for, since they disrupt many natural processes and relationships within the ecosystem of the reservoir. After an oil spill, a dense layer of oil film forms on the water surface quite quickly, preventing access to air and light (after a spill of one ton of oil, an oil slick about 10 mm thick forms on the surface of the reservoir after 10 minutes). As a result, the fauna and flora of the reservoir suffer. If the accident occurred in the coastal zone near a populated area, then the toxic effect is enhanced, because petroleum products in combination with various pollutants of human origin can form dangerous compounds. For high-risk areas (the main routes of transportation of petroleum products, places of their bunkering and unloading, etc.), it is necessary to predict various scenarios for the spread and transformation of oil pollution, taking into account their multifractional composition, turbulent diffusion and advective transport, destruction under the influence of natural factors. The aim of the work is to build a linearized non-stationary spatially heterogeneous mathematical model of transport and transformation of oil pollution, taking into account the above factors.Materials and Methods. The oil that has entered the aquatic environment is represented as a surface and suspended substance in the water column. Oil is subject to a variety of transformation processes: advection, gravitational spreading, emulsification, dispersion, dissolution, biodegradation, etc. The study of these processes and their forecasting, as a rule, requires the development of mathematical and software. In mathematical and numerical modeling, one should start from the system of Navier-Stokes equations and continuity equations, as well as introduce additional physical tolerances of the flow geometry, acceptable and justified in each case, as shown by world experience and objective analysis of the physical picture of processes. Mathematical modeling of the oil distribution process in coastal marine systems has been performed.Results. Mathematical oil distribution model has been created, taking into account its multifractional composition. It is assumed that oil fractions can be in water in dissolved or undissolved states. The modeling takes into account such physical characteristics of particles as density, acceleration of gravity, molar mass, etc. After the linearization of the problem under consideration, difference schemes using extended uniform grids were constructed.Discussion and Conclusion. Pollution caused by an oil spill in the aquatic environment occurs very quickly and is often very destructive. An important factor will be prompt response, which plays a crucial role in minimizing its negative consequences. Modeling of the oil spill process can be useful for determining the location and condition of oil at sea, conducting a risk analysis of the spread of the substance and developing measures to localize and eliminate pollution.
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Pribytkov, I. A., and S. I. Kondrashenko. "AERODYNAMICS OF JETS INTERACTING WITH A FLAT SURFACE." Izvestiya. Ferrous Metallurgy 62, no. 4 (June 20, 2019): 263–69. http://dx.doi.org/10.17073/0368-0797-2019-4-263-269.
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In this paper, the development features of a single free jet of hightemperature nitrogen interacting with a flat surface were studied. Calculation of the heat exchange process during heating by the attacking jets is very difficult to implement analytically due to complexity of the gas-dynamic processes occurring both in a single jet and in a system of jets interacting with the metal. The computational difficulties are aggravated by the fact that when interacting with the surface the jet as such disappears. The flat (fan) flow interacts with the surface: form, aerodynamic properties and thermal state of the flow strongly differ from those of the original jet. The studies were conducted on the basis of numerical simulation in the FloEFD software and computing complex for multiphysical simulation based on solution of the equations of gas dynamics and heat transfer. The solved system of equations consisted of Navier-Stokes equations, equations of energy and continuity and was supplemented by k – ε turbulence model. A three-dimensional model was developed for simulation, the necessary properties, initial and boundary conditions were specified. In the study of aerodynamics of a single high-temperature jet interacting with the surface, the main defining values were: nitrogen flow rate from the nozzle U0 , nitrogen temperature T, internal diameter of the nozzle d0 , distance from the nozzle section to the surface h, distance from the critical point (point of intersection of the jet axis with the surface) along the flow radius r. Data on the gas velocity decrease as the jet develops due to the loss of initial energy to engage the motionless surrounding gas in motion, is presented. The studies have shown that increase in the initial velocity of gas outflow brings the area of higher velocities closer to the surface both in the jet itself and in the fan jet. This factor contributes to heat transfer intensification. In addition, high speeds increase the total thickness of the fan flow and reduce the thickness of hydrodynamic boundary layer, which increases with distance from the critical point.
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Laba, Paulo Henrique, Nelson Luís da Costa Dias, and Cleo Quaresma Dias Júnior. "A TKE analysis for the roughness sublayer of an Amazon forest under unstable atmospheric conditions." Ciência e Natura 46, esp. 2 (December 16, 2024): e87711. https://doi.org/10.5902/2179460x87711.
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The equation of turbulence kinetic energy (TKE) quantifies the intensity of turbulence, the mechanisms generating it, transporting it, and dissipating it. Given the well-known difficulty in applying Monin-Obukhov Similarity Theory in the roughness sublayer, the development of new approaches to understand the flow in this region of the atmosphere is necessary. By calculating the terms of TKE and their balance using a reduced TKE diagram, we sought to investigate the characteristics of turbulence over an Amazon forest located at the ATTO Project experimental site. To do so, using data from three sonic anemometers at heights of 35m, 50m and 81m installed on one of the experiment towers and collected between August and October 2021 for the daytime period, we computed the terms of mechanical production P , thermal production B, storage S, vertical turbulence transport Tv, and dissipation εe of TKE. At the chosen analysis height (66m - average between the two upper sonic anemometers) and after quality control, we obtained 42 one-hour blocks. It was observed that in over 90% of the cases, εe was the largest term. The second-largest term was B (≈ 57%) and the third was P (≈ 40%), showing a certain balance regarding production mechanisms. However, upon balancing them, the existence of a residual term, not explained by Tv, was found. This residual was predominantly negative, which may indicate the effect of vegetation and topography on the flow. It was also noted that in 70% of the blocks, the transport of TKE was upwards. S, on the other hand, is at least 2 orders of magnitude smaller than P , being negligible. Additionally, we calculated the dimensionless standard deviation for vertical wind speed, which showed good agreement with what is expected in the inertial sublayer (ISL).
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Bezzerrouk, Mohamed Amine, Rabie Naceur, Mohamed Bousmaha, Ahmed Akriche, Ismail Hattabi, and Djamel Sahel. "Experimental and CFD analysis of performance of solar chimney power plant prototype." Journal of Applied Energies 2, no. 1 (July 8, 2023): 11–26. https://doi.org/10.57137/jae.v2i1.14.
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The solar chimney is a low-temperature power station generating electricity. The most important parameterizes the value of the air velocity along the chimney. A 3D numerical model is developed to estimate and analyze various parameters of the solar chimney power plant prototype set up in Ibn Khaldoun University, Tiaret. Computational simulations have been conducted using the commercial computational fluid dynamics (CFD) code COMSOL 5.2. The turbulence model k-ε was tested to present the distribution of the air flow characteristics such as the velocity, the temperature, the pressure, and the turbulence characteristics. The results were validated by comparing them with the experimental data of the prototype. The results revealed the same value of the velocity in the experimental prototype and numerical model equal 2.5 m/s, the temperature recorded (72-76) °C in the prototype and 72°C in a numerical model. The comparison between the numerical and the experimental results showed a good agreement.
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Volavy, Jaroslav, Matej Forman, and Miroslav Jicha. "Influence of the turbulence representation at the inlet on the downstream flow pattern in LES of backward-facing step." EPJ Web of Conferences 25 (2012): 01099. http://dx.doi.org/10.1051/epjconf/20122501099.
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Shabani, Saman, Amir Abass Abedini, and Ali Mohammadtabar. "The Effect of the Pipe Bending Angle on the Pressure Losses Vane Elbow Pipes." Asian Review of Civil Engineering 8, no. 1 (May 5, 2019): 1–8. http://dx.doi.org/10.51983/tarce-2019.8.1.2287.
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Pressure loss is one of the significant parameters in designing pipe bends. In this paper, the pressure distribution and pressure losses induced by turbulent flows in a circular cross-sectioned piping elbow with or without guide vane were simulated. The flow distribution in the piping elbow was simulated by the k- model using control volume method. The main objective of this study is to characterize the effect of changing the angle of pipe bend and Reynolds number on the flow separation of single-phase turbulent flow through numerical simulation. Results were validated by other experimental results and then loss coefficient was calculated in different angles from 45 to 135-degree pipe bend in various radius ratios with or without guide vane. Despite the fact that increasing pipe angle increased the pipe bend loss coefficient, using guide vane in the pipe elbow decreased this coefficient. In the radius ratio 1.5 with one guide vane, the loss coefficient of the pipe bends decreased by 50 percent in all degrees. Results revealed that the use of two vanes in pipe bend is more effective on the reduction of elbow pressure losses. Moreover, two guide vanes can decrease loss coefficient more than 50 percent. Also, the results indicated that loss coefficient decreased by increasing Reynolds number.
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Vorobyov, A. A., A. S. Vataev, J. S. Vatulin, V. S. Mayorov, and A. N. Tsybulsky. "Evaluation of the dynamics of high-speed rolling stock." Transport Technician: Education and Practice 5, no. 4 (December 5, 2024): 437–44. https://doi.org/10.46684/2687-1033.2024.4.437-444.
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When moving on an overpass, a rolling stock is exposed to a complex combination of air flows formed as a result of displacement and inertial entrainment of air masses by the moving body, as well as lateral air mass flows from the open space. The aerodynamic loading formed in this way differs from the variant of train movement on a high embankment.A numerical simulation of the aerodynamic load on a high-speed train when it moves on overpasses located in areas of intense wind exposure was performed. An assessment of the stability of the rolling stock under the effect of the “drift” phenomenon was carried out: the simultaneous action of a crosswind and inertial pressurization of air masses. Combinations of aerodynamic impact components were determined, under which conditions for an unacceptable decrease in the level of weight load on the running wheels of the bogies are formed. Limit values of the speed mode of train movement were established depending on the aerodynamic load formed under storm conditions.The results of the studies showed the presence of a certain correlation between the level of turbulence of the disturbed air environment in the corridor of movement of a railway vehicle and reactions in the contact groups “running wheels – rail head” of the front and rear bogies.
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Zharikov, М. V. "The Implementation Model of a Consensual Refnancing Rate for the BRICS Countries." Finance: Theory and Practice 23, no. 1 (February 27, 2019): 66–78. http://dx.doi.org/10.26794/2587-5671-2019-23-1-66-78.
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The relevance of the research subject is due to the fact that countries look for adaptive approaches to the turbulence of the international monetary system (IMS). The approaches of the BRICS countries to the IMS transformation have been fully studied in the economic literature. However, there are no researches on foundation of an advanced central bank as an alternative supranational monetary institution in the new international fnancial architecture. The article objective is to develop a mechanism for setting up the refnancing rate for the BRICS countries in case of the integration hypothesis the currency union, and the lender of last resort and the general unit of accounts. A liberal pricing method has been used to create the model. There is a hypothesis that the refnancing rate should be set at a higher level than that of the People’s Bank of China’s and lower than that of Brazil, Russia, India and South Africa’s, since it has comparative advantages in crediting. The mechanism of the consensual rate of the BRICS countries is based on the assumption that the amount of money in circulation may vary by an amount that does not cause negative consequences for national economies. The fundamental difference between the results of this study is in optimization of the credit resources flow, which implies their distribution within certain limits and in several stages. The main provisions indicate that the optimal rate may provide a background for the coordination of monetary policies in the BRICS countries within the Central bank. The practical relevance of the model is that it can be used to establish the refnancing rate in the BRICS countries. The model suggests that the optimal crediting value in the BRICS countries should ft the GDP growth limits. To conclude, the optimal refnancing rate is a key issue in forming a monetary union and a common currency in the BRICS countries.
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Priyadarshi, Anupam, and Ram Chandra. "Bigger perturbations enhance higher trophic levels biomass, increase transfer efficiency and may sustain for bigger plankton biodiversity." ITM Web of Conferences 34 (2020): 02009. http://dx.doi.org/10.1051/itmconf/20203402009.
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Highly intermittent phytoplankton is ubiquitously observed when measurements are performed at micro-scale (< 1mm). The conventional way of plankton modelling is based on the mean-field approach in which only the first central-moment approximations is retained and ignored higher central moments). The conventional modeling approach may be suitable for mesoor bigger scale (km) but it is inappropriate for micro-scale (< 1mm) where observed overlap in the intermittent spatial distributions of predators and prey become more important for determining the flow of nutrients and energy up the food chain. A new modelling approach called closure modelling is developed to account intermittent phytoplankton using Reynold’s decomposition from turbulence theory and retaining higher central moment approximations in Taylor series. In this study, we developed a NPZD compartmental model to describe the interactions of nutrient (N), phytoplankton (P), zooplankton (Z) and detritus (D) using closure modelling which accounts mean and fluctuating parts of these plankton variables. The results obtained in NPZD compartmental model confirm that perturbation / heterogeneity supports higher trophic levels involved in the model. This reassured the earlier results observed in case of NP and NPZ models in which perturbations enhances P-biomass and Z-biomass respectively. It is observed that perturbation / heterogeneity and a statistical quantity called coefficient of variations of phytoplankton (CVp) (ratio of standard deviation and mean) are positively associated in plankton ecosystems. The perturbations / heterogeneity leads to higher transfer efficiency (Z-biomass/P-biomass) in plankton ecosystems. These results are robust i.e. independent of parameters choices. Perturbation / heterogeneity effects on community structure, species richness and may quantify the energy transfer along trophic levels through biological process from primary production to higher trophic levels. Based on our study, we hypothesize that the locations with high (CVp) are highly heterogeneous and have high transfer efficiency, while low (CVp) locations are less heterogeneous around Tokyo Bay.
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Fan, Yaning, Cheng Wang, Linfeng Jiang, Chao Sun, and Enrico Calzavarini. "Accelerations of large inertial particles in turbulence." Europhysics Letters, February 26, 2024. http://dx.doi.org/10.1209/0295-5075/ad2d15.
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Abstract Understanding the dynamics of material objects advected by turbulent flows is a long standing question in fluid dynamics. In this perspective article we focus on the characterization of the statistical properties of non-interacting finite-sized massive spherical particles advected by a vigorous turbulent flow. We study the fluctuations and temporal correlations of particle accelerations and explore their behaviours with respect to both the particle size and the particle mass density by means of fully-resolved numerical simulations. We observe that the measured trends can not be interpreted as the simple multiplicative combination of the two dominant effects: the spatial filtering of fluid accelerations and the added-mass-adjusted fluid-to-particle density ratio. We argue that other hydrodynamical forces or effects (e.g. preferential flow sampling) have still a significant role even at the largest particle sizes, which are here of the order of the integral scale of turbulence.
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Yang, Bo, Bingchen Liang, Qin Zhang, Xun Meng, Kraposhin Matvey, and Andrey Epikhin. "Numerical investigation of flow around two cylinders in tandem near a scoured bed." Physics of Fluids, July 7, 2022. http://dx.doi.org/10.1063/5.0098470.
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Flow mechanisms around two cylinders in tandem near a scour bed have been investigated using the three-dimensional unsteady Navier-Stokes equations with the Spalart-Allmaras improved delayed detached-eddy simulation model (SA-IDDES). A turbulent inlet boundary layer generation method is adopted to obtain more realistic inlet boundary conditions. Firstly, flow over a single cylinder at Re = 3900 and single cylinder near a scoured bed at Re = 6000 were simulated to validate the numerical model, boundary layer generation method, and grid density effect. Secondly, two cylinders in tandem arrangement near the scoured bed with six pitch ratios L /D are investigated numerically in terms of the hydrodynamic force, time-averaged flow fields and the instantaneous vortex characteristics. When L /D {less than or equal to} 2 .0, the vortex shedding process in the two cylinders' wake is significantly suppressed. The wake vortex intensity is small, and no apparent interaction with the scoured bed. However, when L /D {greater than or equal to} 2 .0, the periodic vortex shedding process in the two cylinders wake is observed, and the shedding vortices interact strongly with the scoured bed. Compared to the flow past tandem cylinders under the near flat wall or wall-free conditions, the scoured bed and the turbulent boundary layer will cause a significant decrease in the extreme negative pressure coefficient on the cylindrical surface. Moreover, the critical spacing for drag inversion and the transition from reattachment regime to the co-shedding regime is also reduced.
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Liu, Kexin, Xunjian Che, Xianshi Fang, Qian Li, Chenchen Zhao, and Weihua Cai. "Numerical investigation of entropy generation of turbulent flow in twisted tri-lobed tubes." Case Studies in Thermal Engineering, September 2023, 103454. http://dx.doi.org/10.1016/j.csite.2023.103454.
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Yang, Zhongjie, Jin Feng, Jingyu Wan, Xiaobin Yu, Zhangjin He, and Wanfu Zhang. "Evaluation of the flow state and static performance of smooth annular liquid seals." Journal of Vibroengineering, August 3, 2023. http://dx.doi.org/10.21595/jve.2023.23283.
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The static fluid-induced force and stiffness coefficient of the smooth annular seal directly affect the rotor system stability. In this paper, a computational fluid dynamics method is applied to investigate the flow characteristics of a smooth annular seal for various eccentricities, discharge/supply pressures and rotational speeds under different flow conditions (laminar, transition, and turbulent flow). The influence factors and formation mechanism of the static instability in the smooth annular liquid seal are analyzed. Results show that laminar flow dominates the flow state at a rotational speed of ω= 2000 rpm. As the rotational speeds increase, the transition flow (2000-7000 rpm) gradually transits to the turbulent regime (ω> 7000 rpm). The direct static stiffness decreases first and then increases from laminar to transition flow state, and the viscosity effect is the dominant factor. For transition and turbulent flow with high eccentricities (ε= 80 %), the dominant viscous effect and inertial effect lead to the negative radial force and negative direct static stiffness coefficients. The smooth annular liquid seal shows best performance in the laminar flow and worst performance in the turbulent flow.
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Nonomura, Taku, Takuma Ibuki, Yuta Ozawa, Keisuke Asai, and Akira Oyama. "Generalized estimation methods of turbulent fluctuation of high-speed flow with single-pixel resolution particle image velocimetry." Measurement Science and Technology, September 17, 2021. http://dx.doi.org/10.1088/1361-6501/ac27e9.
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Davies, Robert, David Dickinson, and Howard R. Wilson. "Kinetic ballooning modes as a constraint on plasma triangularity in commercial spherical tokamaks." Plasma Physics and Controlled Fusion, August 2, 2022. http://dx.doi.org/10.1088/1361-6587/ac8615.
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Abstract To be economically competitive, spherical tokamak (ST) power plant designs require a high β (plasma pressure/magnetic pressure) and sufficiently low turbulent transport to enable steady-state operation. A novel approach to tokamak optimisation is for the plasma to have negative triangularity, with experimental results indicating this reduces transport. However, negative triangularity is known to close access to the “second stability” region for ballooning modes, and thus impose a hard β limit. Second stability access is particularly important in ST power plant design, and this raises the question as to whether negative triangularity is feasible. A linear gyrokinetic study of three hypothetical high β ST equilibria is performed, with similar size and fusion power in the range 500-800MW. By closing the second stability window, the negative triangularity case becomes strongly unstable to long-wavelength kinetic ballooning modes (KBMs) across the plasma, likely driving unacceptably high transport. By contrast, positive triangularity can completely avoid the ideal ballooning unstable region whilst having reactor-relevant β, provided the on-axis safety factor is sufficiently high. Nevertheless, the dominant instability at long wavelength still appears to be the KBM, though it could be stabilised by flow shear.
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Mercier, Bertrand, Lionel Thomas, Benoît Tremblais, and L. David. "A robust pairing method for two-pulse Particle Tracking Velocimetry based on Coherent Point Drift." Measurement Science and Technology, February 20, 2024. http://dx.doi.org/10.1088/1361-6501/ad2b42.
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Abstract Particle Tracking Velocity has reached a high level of maturity in time-resolved measurements since the introduction and development of the Shake-The-Box algorithm. The effectiveness of this approach lies, in part, in its ability to exploit the temporal coherence of particle trajectories to reject the ghost particles while increasing the density of true particles. However, certain situations may prevent time-resolved measurements. In those cases, a two-pulse configuration is often the only option. This raises a challenge with regard to the capacity in separating the ghost from the true particles due to the lack of long-term trajectories. This article proposes a new approach to solve this problem using the coherent point drift (CPD) method. This method identifies a spatially coherent deformation field that models the transformation between two correlated sets of points. In the context of particle tracking velocimetry, the imposed spatial coherence of this calculation is believed to act in the same way as the temporal coherence that made Shake-The-Box successful. The CPD is governed by three parameters whose optimal values have been evaluated in the present contribution. These values were found to be weakly sensitive to the characteristics of the flow under study, ensuring that this method is robust without further tuning of the parameters. The method is then compared with the two-pulse implementation of Shake-The-Box (2P-STB) available in Davis 10.2. For this purpose, sets of realistic images were generated at two successive times for different configurations based of synthetically generated turbulent flows. The Iterative-Particle-Reconstruction in Davis 10.2 was then used to extract the list of particles to be processed by CPD. The comparison shows a better recall with 2P-STB than CPD, especially for large time intervals between frames, but an overall better rejection of ghost particles by CPD than 2P-STB, which was the expected benefit of this method.
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Pettet, Donald, John Forrester, Mathew Nelson, and Tanya Bajaj. "Point-of-Care Ultrasound Findings in Occlusive Iliac Vein Thrombus During Pregnancy: A Case Report." Clinical Practice and Cases in Emergency Medicine, June 14, 2024. http://dx.doi.org/10.5811/cpcem.6658.
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Introduction: Diagnosing deep venous thromboses and venous thromboemboli (DVT/VTE) in pregnant patients presents a unique challenge for emergency physicians. The risk of DVT/VTE increases during pregnancy, and the potential consequences of misdiagnoses are severe. Point-of-care ultrasonography (POCUS) is frequently a first-line diagnostic imaging modality. However, recent studies have shown a high incidence of thromboses proximal to the common femoral vein during pregnancy, and these would not be visualized using compressive ultrasonography, which traditionally can only visualize thromboses distal to the femoral vein. Case Report: A 38-year-old female, 25-weeks primiparous, presented to the emergency department with a three-day history of left lower extremity swelling. Point-of-care three-point compression testing was used to evaluate for a DVT; however, no thrombus was visualized. Given high clinical suspicion, color and spectral Doppler testing were performed and demonstrated turbulent flow and reduced respiratory variation in the common femoral vein. This prompted further additional testing for a proximal DVT using magnetic resonance venography, which revealed an occlusive left external iliac thrombus. The patient was subsequently started on daily subcutaneous enoxaparin and discharged home with close follow-up. Conclusion: Emergency physicians play a critical role in evaluations for the presence of DVT/VTE, particularly in pregnant patients. We endorse the use of POCUS with three-point compression testing, as well as color and spectral Doppler imaging, to help identify proximal DVTs in this patient population. This case report can aid physicians in the diagnosis of this pathological condition that if left untreated can have severe consequences.
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Héas, Patrick, Olivier HAUTECOEUR, and Regis Borde. "3D WIND FIELD PROFILES FROM HYPERSPECTRAL SOUNDERS: REVISITING OPTIC-FLOW FROM A METEOROLOGICAL PERSPECTIVE." Physica Scripta, August 24, 2023. http://dx.doi.org/10.1088/1402-4896/acf3a8.
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Abstract In this work, we present an efficient optic flow algorithm for the extraction of vertically resolved 3D atmospheric motion vector (AMV) fields from incomplete hyperspectral image data measures by infrared sounders. The model at the heart of the energy to be minimized is consistent with atmospheric dynamics, incorporating ingredients of thermodynamics, hydrostatic equilibrium and statistical turbulence. Modern optimization techniques are deployed to design a low-complexity solver for the energy minimization problem, which is non-convex, non-differentiable, high-dimensional and subject to physical constraints. In particular, taking advantage of the alternate direction of multipliers methods (ADMM), we show how to split the original high-dimensional problem into a recursion involving a set of standard and tractable optic-flow sub-problems. By comparing with the ground truth provided by the operational numerical simulation of the European Centre for Medium-Range Weather Forecasts (ECMWF), we show that the performance of the proposed method is superior to state-of-the-art optical flow algorithms in the context of real infrared atmospheric sounding interferometer (IASI) observations.
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Carbone, Francesco, Daniele Telloni, Gary P. Zank, and Luca Sorriso-Valvo. "Chaotic advection and particle pairs diffusion in a low-dimensional truncation of two-dimensional magnetohydrodynamics." Europhysics Letters, May 23, 2022. http://dx.doi.org/10.1209/0295-5075/ac7250.
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Abstract The chaotic advection of fluid particle pairs is investigated though a low-order model of two-dmensional magnetohydrodynamic (MHD), where only five nonlinearly interacting modes are retained. The model is intrinsically inhomogeneous and anisotropic because of the influence of large-scale fluctuations. Therefore, even though dynamically chaotic, the fields are unable to form the typical scaling laws of fully developed turbulence. Results show that a super-ballistic dynamics, reminiscent of the Richardson’s law of particle-pairs diffusion in turbulent flows, is robustly obtained using the truncated model. Indeed, even in the strongly reduced truncation presented here, particle diffusion in MHD turbulence has the same laws as the separation of velocity of particle pairs. The inherent anisotropy only affects the scaling of diffusivity, by enhancing the diffusion properties along one direction for small time-scales. Finally, when further anisotropy is introduced in the system through Alfvén waves, fluid particles are trapped by these, and super-ballistic diffusion is replaced by Brownian-like diffusion. On the other hand, when the magnetic field is removed, the kinetic counterpart of the model does not show super-ballistic dynamics.
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Kim, K. K., A. Yu Panychev, and L. S. Blazhko. "Innovative energy sources for Hyperloop high-speed transport." BRIСS Transport 1, no. 1 (July 21, 2022). http://dx.doi.org/10.46684/2022.1.1.
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This article describes an innovative design of a solar-wind generator for a distributed energy Hyperloop high-speed system. The knowhow of this development is to mount flexible silicon solar panels (SP) on wind turbine blades, thus optimizing the thermal efficiency of solar panels. The basic dimensions of the wind turbine blades and the maximum internal flow velocities at the blade outlet (tips) are presented. At low wind velocities, it is rational to locate solar panels on the outer end (or the tip) of a blade, rather than along the blade length.The cooling effect can be increased by using materials with low thermal resistance for the SP and blades, or by reducing their thickness.To increase the heat transfer coefficient, it is recommended to use the airflow turbulence on the solar panel surface. In practice, this can be achieved both by changing the operating parameters and by introducing innovative design solutions.For better cooling of solar panels, it is recommended to use the technology of a wind flow sucked into the blade inner cavity. Changing the geometry of the outer end (tip) of the blades and the use of deflectors also give a better panel cooling parameters.
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Shazad, Usman, and M. Iqbal. "Dynamical generation of macroscale magnetic fields and fast flows in a four-component astrophysical plasma." Physica Scripta, September 12, 2024. http://dx.doi.org/10.1088/1402-4896/ad7a32.
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Abstract We explore the possibility of the generation or amplification of macroscale magnetic fields and flows in a four-component astrophysical dusty plasma composed of mobile massless electrons and positrons, inertial positive ions and negatively charged static dust particles. The investigation demonstrates that when microscopic turbulent ambient plasma energy is predominantly kinetic, a straight dynamo (DY) mechanism is feasible. Conversely, a unified reverse-dynamo/dynamo (RDY/DY) mechanism is possible when the microscopic turbulent ambient plasma energy is primarily magnetic. Additionally, the evolution of Alfvén Mach numbers at the macro- and microscale are significantly affected by plasma species densities and invariant helicities. The potential implications of the present study for astrophysical settings are also highlighted.
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Alharbi, Rawan, Aisha Alshaery, H. O. Bakodah, Rahmatullah Ibrahim Nuruddeen, and J. F. Gómez-Aguilar. "Revisiting (2 + 1)-dimensional Burgers’ dynamical equations: analytical approach and Reynolds number examination." Physica Scripta, July 11, 2023. http://dx.doi.org/10.1088/1402-4896/ace666.
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Abstract Classical Burgers’ equation is an indispensable dynamical evolution equation that is autonomously devised by Burgers and Harry Bateman in 1915 and 1948, respectively. This important model is featured through a nonlinear partial differential equation (NPDE). Furthermore, the model plays a crucial role in many areas of mathematical physics, including, for instance, fluid dynamics, traffic flow, nonlinear acoustics, turbulence phenomena, and linking convection and diffusion processes to state a few. Thus, in the present study, an efficient analytical approach by the name “generalized Riccati equation approach” is adopted to securitize the class of (2 + 1)-dimensional Burgers’ equations by revealing yet another set of analytical structures to the governing single and vector-coupled Burgers’ equations. In fact, the besieged method of the solution has been proven to divulge various sets of hyperbolic, periodic, and other forms of exact solutions. Moreover, the method first begins by transforming the targeted NPDE to a nonlinear ordinary differential equation (NODE), and subsequently to a set of an algebraic system of equations; where the algebraic system is then solved simultaneously to obtain the solution possibilities. Lastly, certain graphical illustrations in 2- and 3-dimensional plots are set to be depicted - featuring the evolutional nature of the resulting structures, and thereafter, analyze the influence of the Reynolds number Ra on the respective wave profiles.
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Lanchava, Omar. "THE AERODYNANIIC CALCULATION OF RAILROAD TUNNELS LINE OF MARABDA-AKHALQALAQI." GEORGIAN SCIENTISTS, June 10, 2021. http://dx.doi.org/10.52340/gs.2021.309.
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The provided air expenses in tunnel are determined with the aerodynamic calculation of train motion pistol effect and after movement effect. It is ascertained, that for the tunnel conditions air expenses that are processed with pistol effect are approximately 2/3 removed towards train motion and 1/3 flows орposite to the free space between train and tunnel strengthening. The last one provokes air turbulence and represents common aerodynamic resistance stand face. Despite this, all galleries of Marabda-Akhalqalaqi train main lines can be aerated on expense of train pistol effect with aroused natural pressure. The use of his pressure could be more effective if every chamber and niche will be equipped with ventilation cavity on the both sides of tunnel. The every cavity section area should be 5.6 m2. The noted measures will shorten aerodynamic resistance a rouse by air flowing in distances and would be more outhunted by calculation of railroad tunnels line of Marabda—Akhalqalaqi.
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AL HASHMİ, Sulaiman, and Mingjie CHEN. "Thermal analysis of phase change materials storage in solar concenter." Journal of Energy Systems, July 18, 2023, 302–13. http://dx.doi.org/10.30521/jes.1082104.
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Thermal analysis of high-temperature phase change materials (PCM) is conducted with the consideration of a 20% void and buoyancy-driven convection in a stainless-steel capsule. The effects of the thermal expansion and the volume expansion due to phase change on the energy storage and retrieval process are explored. The used water to fill the void between two different wax paraffin and stearic acid spheres is considered as a potential PCM for concentrated solar power. The charging/discharging process into and from the capsule wall is simulated under different boundary conditions for laminar and turbulent flows. Computational models are conducted by applying an enthalpy-porosity method and volume of fluid method to calculate the transport phenomena within the PCM capsule, including an internal air void. A simplified two-dimensional model of the PCM contained within the spheres is constructed and thermal analyses are performed for the transition from solid to liquid states. Simulated charging process modes are compared with the theory. According to experiments, the temperature distributions from 40-60 mm without and with 60 mm with copper fin have different behavior. The paraffin takes less time than stearic acid for total transformation at a rate of 0.5. The size of the sphere increases over the amount of time and the phase of the sphere to complete changes as stearic acid expands more than paraffin during the transition. Inserting a rectangular fin, that is made from copper into the ball reduces the cycle time and increases output.