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1
Wang, S. K., S. J. Lee, O. C. Jones, and R. T. Lahey. "Statistical Analysis of Turbulent Two-Phase Pipe Flow." Journal of Fluids Engineering 112, no. 1 (1990): 89–95. http://dx.doi.org/10.1115/1.2909374.
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The statistical characteristics of turbulent two-phase pipe flow have been evaluated. In particular, the autocorrelation functions and the power spectral density functions of the axial turbulence fluctuations in the liquid phase were determined. The high frequency content of the power spectrum in bubbly two-phase pipe flow was found to be significantly larger than in single-phase pipe flow and, in agreement with previous studies of homogeneous two-phase flows (Lance et al., 1983), diminished asymptotically with a characteristic −8/3 slope at high frequency. The power spectrum and the autocorrelation functions in two-phase pipe flow, although distinctively different from those in single-phase pipe flow, were insensitive to the local void fraction and the mean liquid velocity when plotted against wave number and spatial separation, respectively. Finally, the dissipation scale, determined from the shape of the autocorrelation function, indicated that the turbulent dissipation rate in two-phase pipe flow was significantly greater than that in single-phase pipe flow.
2
Pakhomov M. A. and Terekhov V. I. "Effect of sudden constriction of a flat duct on forced convection in a turbulent droplet-laden mist flow." Technical Physics Letters 49, no. 4 (2023): 14. http://dx.doi.org/10.21883/tpl.2023.04.55868.19453.
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Numerical modeling of the flow structure and heat transfer in a gas-droplet turbulent flow in a duct with forward-facing step is carried out. The two-dimensional RANS equations are used in the numerical solution. The Eulerian two-fluid approach is used for describing the flow dynamics and heat transfer in the gaseous and dispersed phases. The turbulence of the carrier phase is described using an elliptical Reynolds stress model with taking the presence of dispersed phase. It is shown that finely-dispersed droplets are involved in the separation recirculation motion of the gas phase. The addition of evaporating droplets to a single-phase turbulent flow in the forward-facing step leads to a significant intensification of heat transfer (more than 2 times) compared to a single-phase air flow, all other parameters being equal. This effect is enhanced with an increase in the initial mass fraction of the water droplets. Keywords: Numerical simulation, Reynolds stress transport model, forward-facing step, droplet evaporation, turbulence, heat transfer enhancement.
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Roy, R. P., V. Velidandla, and S. P. Kalra. "Velocity Field in Turbulent Subcooled Boiling Flow." Journal of Heat Transfer 119, no. 4 (1997): 754–66. http://dx.doi.org/10.1115/1.2824180.
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The velocity field was measured in turbulent subcooled boiling flow of Refrigerant-113 through a vertical annular channel whose inner wall was heated. A two-component laser Doppler velocimeter was used. Measurements are reported in the boiling layer adjacent to the inner wall as well as in the outer all-liquid layer for two fluid mass velocities and four wall heat fluxes. The turbulence was found to be inhomogeneous and anisotropic and the turbulent kinetic energy significantly higher than in single-phase liquid flow at the same mass velocity. A marked shift toward the inner wall was observed of the zero location of the axial Reynolds shear stress in the liquid phase, and the magnitude of the shear stress increased sharply close to the inner wall. The near-wall liquid velocity field was quite different from that in single-phase liquid flow at a similar Reynolds number. Comparison of the measurements with the predictions of a three-dimensional two-fluid model of turbulent subcooled boiling flow show reasonably good agreement for some quantities and a need for further development of certain aspects of the model.
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Lemenand, Thierry, Pascal Dupont, Dominique Della Valle, and Hassan Peerhossaini. "Turbulent Mixing of Two Immiscible Fluids." Journal of Fluids Engineering 127, no. 6 (2005): 1132–39. http://dx.doi.org/10.1115/1.2073247.
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The emulsification process in a static mixer HEV (high-efficiency vortex) in turbulent flow is investigated. This new type of mixer generates coherent large-scale structures, enhancing momentum transfer in the bulk flow and hence providing favorable conditions for phase dispersion. We present a study of the single-phase flow that details the flow structure, based on LDV measurements, giving access on the scales of turbulence. In addition, we discuss the liquid-liquid dispersion of oil in water obtained at the exit of the mixer/emulsifier. The generation of the dispersion is characterized by the Sauter diameter and described via a size-distribution function. We are interested in a local turbulence analysis, particularly the spatial structure of the turbulence and the turbulence spectra, which give information about the turbulent dissipation rate. Finally, we discuss the emulsifier efficiency and compare the HEV performance with existing devices.
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Пахомов, М. А., та В. И. Терехов. "Влияние внезапного сужения плоского канала на вынужденную конвекцию в турбулентном газокапельном течении". Письма в журнал технической физики 49, № 7 (2023): 16. http://dx.doi.org/10.21883/pjtf.2023.07.54915.19453.
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Numerical modeling of the flow structure and heat transfer in a gas-droplet turbulent flow in a duct with forward-facing step is carried out. The two-dimensional RANS equations are used in the numerical solution. The Eulerian two-fluid approach is used for describing the flow dynamics and heat transfer in the gaseous and dispersed phases. The turbulence of the carrier phase is described using an elliptical Reynolds stress model with taking the presence of dispersed phase. It is shown that finely-dispersed droplets are involved in the separation recirculation motion of the gas phase. The addition of evaporating droplets to a single-phase turbulent flow in the forward-facing step leads to a significant intensification of heat transfer (more than 2 times) compared to a single-phase air flow, all other things being equal. This effect is enhanced with an increase in the initial mass fraction of the water droplets.
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Rosti, Marco E., Zhouyang Ge, Suhas S. Jain, Michael S. Dodd, and Luca Brandt. "Droplets in homogeneous shear turbulence." Journal of Fluid Mechanics 876 (August 9, 2019): 962–84. http://dx.doi.org/10.1017/jfm.2019.581.
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We simulate the flow of two immiscible and incompressible fluids separated by an interface in a homogeneous turbulent shear flow at a shear Reynolds number equal to 15 200. The viscosity and density of the two fluids are equal, and various surface tensions and initial droplet diameters are considered in the present study. We show that the two-phase flow reaches a statistically stationary turbulent state sustained by a non-zero mean turbulent production rate due to the presence of the mean shear. Compared to single-phase flow, we find that the resulting steady-state conditions exhibit reduced Taylor-microscale Reynolds numbers owing to the presence of the dispersed phase, which acts as a sink of turbulent kinetic energy for the carrier fluid. At steady state, the mean power of surface tension is zero and the turbulent production rate is in balance with the turbulent dissipation rate, with their values being larger than in the reference single-phase case. The interface modifies the energy spectrum by introducing energy at small scales, with the difference from the single-phase case reducing as the Weber number increases. This is caused by both the number of droplets in the domain and the total surface area increasing monotonically with the Weber number. This reflects also in the droplet size distribution, which changes with the Weber number, with the peak of the distribution moving to smaller sizes as the Weber number increases. We show that the Hinze estimate for the maximum droplet size, obtained considering break-up in homogeneous isotropic turbulence, provides an excellent estimate notwithstanding the action of significant coalescence and the presence of a mean shear.
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Akeel, M. Ali Morad, M. Qasim Rafi, and Ahmed Ali Amjed. "STUDY OF THE BEHAVIOURS OF SINGLE-PHASE TURBULENT FLOW AT LOW TO MODERATE REYNOLDS NUMBERS THROUGH A VERTICAL PIPE. PART I: 2D COUNTERS ANALYSIS." EUREKA: Physics and Engineering, no. 6 (November 30, 2020): 108–22. https://doi.org/10.21303/2461-4262.2020.001538.
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This study presents a model to investigate the behavior of the single-phase turbulent flow at low to moderate Reynolds number of water through the vertical pipe through (2D) contour analysis. The model constructed based on governing equations of an incompressible Reynolds Average Navier-Stokes (RANS) model with (k-ε) method to observe the parametric determinations such as velocity profile, static pressure profile, turbulent kinetic energy consumption, and turbulence shear wall flows. The water is used with three velocities values obtained of (0.087, 0.105, and 0.123 m/s) to represent turbulent flow under low to moderate Reynolds number of the pipe geometry of (1 m) length with a (50.8 mm) inner diameter. The water motion behavior inside the pipe shows by using [COMSOL Multiphysics 5.4 and FLUENT 16.1] Software. It is concluded that the single-phase laminar flow of a low velocity, but obtained a higher shearing force; while the turbulent flow of higher fluid velocity but obtained the rate of dissipation of shearing force is lower than that for laminar flow. The entrance mixing length is affected directly with pattern of fluid flow. At any increasing in fluid velocity, the entrance mixing length is increase too, due to of fluid kinetic viscosity changes. The results presented the trends of parametric determinations variation through the (2D) counters analysis of the numerical model. When fluid velocity increased, the shearing force affected directly on the layer near-wall pipe. This leads to static pressure decreases with an increase in fluid velocities. While the momentum changed could be played interaction rules between the fluid layers near the wall pipe with inner pipe wall. Finally, the agreement between present results with the previous study of [1] is satisfied with the trend
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du Cluzeau, A., G. Bois, and A. Toutant. "Analysis and modelling of Reynolds stresses in turbulent bubbly up-flows from direct numerical simulations." Journal of Fluid Mechanics 866 (March 5, 2019): 132–68. http://dx.doi.org/10.1017/jfm.2019.100.
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Two-phase bubbly flows are found in many industrial applications. These flows involve complex local phenomena that are still poorly understood. For instance, two-phase turbulence modelling is still commonly based on single-phase flow analyses. A direct numerical simulation (DNS) database is described here to improve the understanding of two-phase turbulent channel flow at a parietal Reynolds number of 127. Based on DNS results, a physical interpretation of the Reynolds stress and momentum budgets is proposed. First, surface tension is found to be the strongest force in the direction of migration so that budgets of the momentum equations suggest a significant impact of surface tension in the migration process, whereas most modelling used in industrial application does not include it. Besides, the suitability of the design of our cases to study the interaction between bubble-induced fluctuations (BIF) and single-phase turbulence (SPT) is shown. Budgets of the Reynolds stress transport equation computed from DNS reveal an interaction between SPT and BIF, revealing weaknesses in the classical way in which pseudoturbulence and perturbations to standard single-phase turbulence are modelled. An SPT reduction is shown due to changes in the diffusion because of the presence of bubbles. An increase of the redistribution leading to a more isotropic SPT has been observed as well. BIF is comprised of a turbulent (wake-induced turbulence, WIT) and a non-turbulent (wake-induced fluctuations, WIF) part which are statistically independent. WIF is related to averaged wake and potential flow, whereas WIT appears when wakes become unstable or interact with each other for high-velocity bubbles. In the present low gravity conditions, BIF is reduced to WIF only. A thorough analysis of the transport equations of the Reynolds stresses is performed in order to propose an algebraic closure for the WIF towards an innovative two-phase turbulence model.
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Pérez, Tzayam, and José L. Nava. "Simulations of a Single-Phase Flow in a Compound Parabolic Concentrator Reactor." International Journal of Photoenergy 2018 (August 19, 2018): 1–8. http://dx.doi.org/10.1155/2018/2569251.
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This paper deals with the analysis and interpretation of flow visualization and residence time distribution (RTD) in a compound parabolic concentrator (CPC) reactor using computational fluid dynamics (CFD). CFD was calculated under turbulent flow conditions solving the Reynolds averaged Navier–Stokes (RANS) equation expressed in terms of turbulent viscosity and the standard k−ε turbulent model in 3D. A 3D diffusion-convection model was implemented in the CPC reactor to determine the RTD. The fluid flow visualization and RTD were validated with experimental results. The CFD showed that the magnitude of the velocity field remains almost uniform in most of the bulk reactor, although near and inside the 90° connectors and the union segments, the velocity presented low- and high-speed zones. Comparisons of theoretical and experimental RTD curves showed that the k−ε model is appropriate to simulate the nonideal flow inside the CPC reactor under turbulent flow conditions.
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Salhi, A., C. Rey, and J. M. Rosant. "Pressure Drop in Single-Phase and Two-Phase Couette-Poiseuille Flow." Journal of Fluids Engineering 114, no. 1 (1992): 80–84. http://dx.doi.org/10.1115/1.2910004.
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This paper is concerned with axial pressure gradient in single-phase and two-phase flow at low void fraction in a narrow annular space between two concentric cylinders, the inner one rotating. From experimental results, the coupling function (inertial forces/centrifugal forces) is parameterized by Taylor or Rossby numbers for two values of the intercylindrical width (clearance). The results are discussed with regard to different flow regimes and it is shown in particular that transition from the turbulent vorticed regime to the turbulent regime occurs at Ro ≃ 1. The proposed correlation agrees in a satisfactory manner to all the regimes studied in our experiments and in those given in the bibliography. In addition, original tests with a two-phase liquid/gas flow at 5 percent G.O.R. (gas oil ratio), for a finely dispersed gas phase are also reported. These results indicate a similar behavior to single-phase flows, justifying the transposition of the same correlation in the framework of the homogeneous model.
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Colin, Catherine, Jean Fabre, and Arjan Kamp. "Turbulent bubbly flow in pipe under gravity and microgravity conditions." Journal of Fluid Mechanics 711 (September 27, 2012): 469–515. http://dx.doi.org/10.1017/jfm.2012.401.
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AbstractExperiments on vertical turbulent flow with millimetric bubbles, under three gravity conditions, upward, downward and microgravity flows ($1g$, $\ensuremath{-} 1g$ and $0g$), have been performed to understand the influence of gravity upon the flow structure and the phase distribution. The mean and fluctuating phase velocities, shear stress, turbulence production, gas fraction and bubble size have been measured or determined. The results for $0g$ flow obtained during parabolic flights are taken as reference for buoyant $1g$ and $\ensuremath{-} 1g$ flows. Three buoyancy numbers are introduced to understand and quantify the effects of gravity with respect to friction. We show that the kinematic structure of the liquid is similar to single-phase flow for $0g$ flow whereas it deviates in $1g$ and $\ensuremath{-} 1g$ buoyant flows. The present results confirm the existence of a two-layer structure for buoyant flows with a nearly homogeneous core and a wall layer similar to the single-phase inertial layer whose thickness seems to result from a friction–gravity balance. The distributions of phase velocity, shear stress and turbulence are discussed in the light of various existing physical models. This leads to a dimensionless correlation that quantifies the wall shear stress increase due to buoyancy. The turbulent dispersion, the lift and the nonlinear effects of added mass are taken into account in a simplified model for the phase distribution. Its analytical solution gives a qualitative description of the gas fraction distribution in the wall layer.
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Roumet, Elie, Raksmy Nop, Nicolas Dorville, and Marie-Christine Duluc. "LES investigations of turbulent heat transfer structures with exponential power escalation." Journal of Physics: Conference Series 2766, no. 1 (2024): 012012. http://dx.doi.org/10.1088/1742-6596/2766/1/012012.
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Abstract The BORAX-type accident is a key scenario in the safety design of pool-type experimental nuclear reactors. It considers a reactivity insertion large enough to initiate an exponential power escalation with a period as small as tens of milliseconds, necessitating effective heat removal by the coolant system. This study presents a computational analysis of single-phase transient heat transfer under thermal-hydraulic conditions relevant to such reactors, focusing on turbulent channel flow between planar fuel plates with highly subcooled water. Our investigation uses Large Eddy Simulation (LES) performed with TrioCFD, the open-source CFD code developed by the French Atomic Energy Commission (CEA). Several modeling options are tested: incompressible flow with temperature as a passive scalar, incompressible flow with varying viscosity, and quasicompressible flow with temperature-dependent viscosity and mass density. To evaluate the accuracy of our physical models, all simulations were performed under uniform conditions, using the same experimental parameters, mesh, and numerical strategies. The specific examined scenario involves a highly subcooled turbulent channel flow at moderate pressure, experiencing an exponential power increase. We ensure detailed turbulence resolution at the Batchelor scale in the wall normal direction close to the heating wall. This communication presents a comparative study of LES simulations of the single-phase flow under exponential power excursion at the wall. Subsequent analyses focused on the impact of different velocity-temperature couplings on the prediction of wall heat transfer, incorporating comparisons with experimental infrared thermometry measurements. Early in the transient phase, temperature peaks are confined within turbulent streaks, as reported in the existing literature. However, as the exponential power transient unfolds, the viscous layer and streak structures destabilize, leading to a more dispersed distribution of hot spots. Preliminary findings suggest a transition in heat transfer modes from turbulence-driven to conduction during the final stages of the single-phase transient.
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Boertz, Hendrik, Albert Baars, Janusz T. Cieśliński, and Sławomir Smoleń. "Turbulence Model Evaluation for Numerical Modelling of Turbulent Flow and Heat Transfer of Nanofluids." Applied Mechanics and Materials 831 (April 2016): 165–80. http://dx.doi.org/10.4028/www.scientific.net/amm.831.165.
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In this work, Nusselt number and friction factor are calculated numerically for turbulent pipe flow (Reynolds number between 6000 and 12000) with constant heat flux boundary condition using nanofluids. The nanofluid is modelled with the single-phase approach and the simulation results are compared with experimental data. Ethylene glycol and water, 60:40 EG/W mass ratio, as base fluid and SiO2 nanoparticles are used as nanofluid with particle volume concentrations ranging from 0% to 10%. A prior turbulence model evaluation of k-ε-, k-ω- and k-ω-SST-model revealed substantial deviations between the tested models and resulted in applying the k-ω-SST-model for the simulation. Nusselt number predictions for the nanofluid are in agreement with experimental results and a conventional single-phase correlation. The mean deviation is in the range of 5%. Friction factor values show a mean deviation of 1.5% to a conventional single-phase correlation, however, they differ considerably from the nanofluid experimental data.
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Motegi, Kosuke, Yasuteru Sibamoto, Takashi Hibiki, Naofumi Tsukamoto, and Junichi Kaneko. "Opposing Mixed Convection Heat Transfer for Turbulent Single-Phase Flows." International Journal of Energy Research 2024 (January 16, 2024): 1–22. http://dx.doi.org/10.1155/2024/6029412.
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Convection, wherein forced and natural convections are prominent, is known as mixed convection. Specifically, when a forced convection flow is downward, this flow is called opposing flow. The objectives of this study are to gain a comprehensive understanding of opposing flow mixed convection heat transfer and to establish the prediction methodology by evaluating existing correlations and models. Several heat transfer correlations have been reported related to single-phase opposing flow; however, these correlations are based on experiments conducted in various channel geometries, working fluids, and thermal flow parameter ranges. Because the definition of nondimensional parameters and their validated range confirmed by experiments differ for each correlation reported in previous studies, establishing a guideline for deciding which correlation should be selected based on its range of applicability and extrapolation performance is important. This study reviewed the existing heat transfer correlations for turbulent opposing flow mixed convection and the single-phase heat transfer correlations implemented in the thermal–hydraulic system codes. Furthermore, the authors evaluated the predictive performance of each correlation by comparing them with the experimental data obtained under various experimental conditions. The Jackson and Fewster, Churchill, and Swanson and Catton correlations can accurately predict all the experimental data. The effect of the difference in the thermal boundary conditions, i.e., uniform heat flux and uniform wall temperature, on the turbulent mixed convection heat transfer coefficient is not substantial. The authors confirmed that heat transfer correlations using the hydraulic-equivalent diameter as a characteristic length can be used for predictions regardless of channel-geometry differences. Furthermore, correlations described based on nondimensional dominant parameters can be used for predictions regardless of the differences in working fluids. The authors investigated the extrapolation performance of the mixed convection heat transfer correlations for a wide range of nondimensional parameters and observed that the Jackson and Fewster, Churchill, and Aicher and Martin correlations exhibit excellent extrapolation performance with respect to natural and forced convection flows, indicating that they can be applied beyond the parameter range validated experimentally.
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Milanovic, Sasa, Milos Jovanovic, Zivan Spasic, and Boban Nikolic. "Two-phase flow in channels with non-circular cross-section of pneumatic transport of powder material." Thermal Science 22, Suppl. 5 (2018): 1407–24. http://dx.doi.org/10.2298/tsci18s5407m.
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The paper presents a numerical simulation of two-phase turbulent flow in straight horizontal channels of pneumatic transport with non-circular cross-section. For the granular flow simulation, we have chosen the flow of solid particles of quartz, flour, and ash in the flow of air, which is transporting fluid. During the modeling of the flow, the transported solid particles are reduced to spherical shapes. A correction of the stress model of turbulence is performed by taking into account the influences of the induction of secondary flows of the second order in the gas phase. The full Reynolds stress model was used for modeling the turbulence, and the complete model is used for the turbulent stresses and turbulent temperature fluxes. All numerical experiments were conducted for the same initial flow conditions and a single uniform grid was adopted for all numerical experiments. The flow is observed in a straight channel of a square cross-section and dimensions of sides of 200 mm and the length of 80 Dh. During the simulation, the fineness of the numerical grid was also tested, and the paper shows results of the numerical grid of the highest resolution beyond which the fineness does not influence the obtained results. The paper offers graphics of velocities of the solid particles transported by the transporting fluid (air) along the channel.
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Mirabi, Mohammad Hossein, Ehsan Jabbari, Taher Rajaee, and Keivan Seiiedi Niaki. "Experimental investigation of turbulent flow in a rectangular bonneted slide gate and eliminating random fluctuating loads." Physics of Fluids 35, no. 1 (2023): 015155. http://dx.doi.org/10.1063/5.0134664.
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Bonneted slide gates are widely used in dam bottom outlets for flow regulation. High kinetic energy flow generates turbulence, which induces vibrations in bonneted slide gates under partially open conditions. Significant vibrations can indicate problems and cause damage or expedited deterioration of the gate if left unchecked. This experimental study focuses on two aspects: turbulent flow formation due to rectangular bonneted slide gates and elimination of random fluctuating loads on the gate using a turbulence inhibitor. Five reservoir heads were combined with nine gate openings (10%–90%) to produce 45 different discharges of 12–182 l/s. The different types of the gate flow create different turbulence and random loads based on the water–air mixture and the kinetic energy of the flow. Flow analysis indicates considerable random static pressure fluctuations under the slide gate. The results show the formation of swirling secondary flows in the gate's side guide slots, and their movement and collision with the gate are the leading cause of the turbulent multiphase flow and random fluctuations in static pressure. Also, the use of turbulence inhibitors on the gate can prevent the formation of secondary flows, which results in a 98.92% reduction in the amplitude of random static pressure fluctuations and the elimination of the random fluctuating loads on the slide gate. After removing the swirling secondary flows, a stable air boundary layer was formed under the gate. Finally, the gate flow changed from a turbulent two-phase flow to a steady single-phase jet of water.
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Alsulaiei, Zaher Mohammed Abed, Haider Jabaur Abid, R. Shakir, and Hawra Salah Hamid Ajimi. "Forecast Study on the Overall Coefficient for Passage of Single-Phase and Passage of Single-Phase in an Annular to Plain Tubes Heat Stream." IOP Conference Series: Earth and Environmental Science 1223, no. 1 (2023): 012028. http://dx.doi.org/10.1088/1755-1315/1223/1/012028.
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Abstract To prevent buoyancy effects from increasing the overall heat transfer coefficient due to low heat flux, smooth vertical circular tubes require forced convection conjectures. Previous research has focused on mixed convection in turbulent regions and has limited studies on forced convective heat transfer. This study aims to investigate the predictable overall coefficients of heat transfer performance under specific conditions of forced convection, considering both vertical up flow and down flow through the smooth circular test section. The recommended Reynolds numbers for water are (7201.6–14577.4) and (3186.7–6396.75) for single-phase and single-phase annular passages, respectively, with a heat application range of (50–500 W). The overall coefficient of heat transfer is (333.91 - 432.95 W/m2.K) and (169.76 - 251.20 W/m2.K) for single-phase and single-phase annular passages, respectively. The flow was turbulent for all heat fluxes.
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Thakre, S. S., and J. B. Joshi. "MOMENTUM, MASS AND HEAT TRANSFER IN SINGLE-PHASE TURBULENT FLOW." Reviews in Chemical Engineering 18, no. 2-3 (2002): 83–293. http://dx.doi.org/10.1515/revce.2002.18.2-3.83.
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DE ZHOU, MING, and I. WYGNANSKI. "The response of a mixing layer formed between parallel streams to a concomitant excitation at two frequencies." Journal of Fluid Mechanics 441 (August 15, 2001): 139–68. http://dx.doi.org/10.1017/s0022112001004827.
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Simultaneous excitation of a turbulent mixing layer by two frequencies, a fundamental and a subharmonic, was investigated experimentally. Plane perturbations were introduced to the flow at its origin by a small oscillating flap. The results describe two experiments that differ mainly in the amplitudes of the imposed perturbations and both are compared to the data acquired while the mixing layer was forced at a single frequency.Conventional statistical quantities such as: mean velocity profiles, widths of the flow, turbulent intensities, spectra, phase-locked velocity and vorticity fields, as well as streaklines were computed. The rate of spread of the flow under concomitant excitation at the two frequencies was much greater than under a single frequency, although it remained dominated by two-dimensional eddies. The Reynolds stresses and turbulence production are associated with the deformation and orientation of the large coherent vortices. When the major axis of the coherent vortices starts leaning forward on the high-speed side of the flow, the production of turbulent energy changes sign (i.e. becomes negative) and this results in the flow thinning in the direction of streaming. It also indicates that energy is extracted from the turbulence to the mean motion. Resonance phenomena play an important role in the evolution of the flow. A vorticity budget showed that the change in mean vorticity was mainly caused by the nonlinear interaction between coherent vorticities. Nevertheless, the locally dominant frequency scales the mean growth rate, the inclination and distortion of the mean velocity profiles as well as the phase-locked vorticity contours.
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Bellani, Gabriele, Margaret L. Byron, Audric G. Collignon, Colin R. Meyer, and Evan A. Variano. "Shape effects on turbulent modulation by large nearly neutrally buoyant particles." Journal of Fluid Mechanics 712 (September 27, 2012): 41–60. http://dx.doi.org/10.1017/jfm.2012.393.
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AbstractWe investigate dilute suspensions of Taylor-microscale-sized particles in homogeneous isotropic turbulence. In particular, we focus on the effect of particle shape on particle–fluid interaction. We conduct laboratory experiments using a novel experimental technique to simultaneously measure the kinematics of fluid and particle phases. This uses transparent particles having the same refractive index as water, whose motion we track via embedded optical tracers. We compare the turbulent statistics of a single-phase flow to the turbulent statistics of the fluid phase in a particle–laden suspension. Two suspensions are compared, one in which the particles are spheres and the other in which they are prolate ellipsoids with aspect ratio 2. We find that spherical particles at volume fraction ${\phi }_{v} = 0. 14\hspace{0.167em} \% $ reduce the turbulent kinetic energy (TKE) by 15 % relative to the single-phase flow. At the same volume fraction (and slightly smaller total surface area), ellipsoidal particles have a much smaller effect: they reduce the TKE by 3 % relative to the single-phase flow. Spectral analysis shows the details of TKE reduction and redistribution across spatial scales: spherical particles remove energy from large scales and reinsert it at small scales, while ellipsoids remove relatively less TKE from large scales and reinsert relatively more at small scales. Shape effects are far less evident in the statistics of particle rotation, which are very similar for ellipsoids and spheres. Comparing these with fluid enstrophy statistics, we find that particle rotation is dominated by velocity gradients on scales much larger than the particle characteristic length scales.
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MCCRAY, Marshall C., and Paul G. A. CIZMAS. "Experimental investigation of the critical Reynolds number for bubbly two-phase flow." INCAS BULLETIN 15, no. 3 (2023): 47–55. http://dx.doi.org/10.13111/2066-8201.2023.15.3.4.
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The critical Reynolds number for dispersed bubbly two-phase flows, gas in liquid, was experimentally investigated. In this experiment, the gas was air and the liquid was water. Water flowed upward through a vertical, translucent pipe, and air was introduced into the water prior to the test section by means of a basswood microbubbler. Dye was injected into the water to indicate when the flow transitioned from laminar to turbulent. Mixtures with gas volume fractions up to 10% were tested, and the Reynolds numbers for which the flow transitioned from laminar to turbulent were recorded. The data showed that the critical Reynolds number fell to roughly one-half of its original single-phase liquid value once the gas volume fractions exceeded 0.1%. These results indicate that the presence of even small amounts of bubbles causes pre-mature transition to turbulence.
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Skouloudis, A. N., and J. Wu¨rtz. "Film-Thickness, Pressure-Gradient, and Turbulent Velocity Profiles in Annular Dispersed Flows." Journal of Fluids Engineering 115, no. 2 (1993): 264–69. http://dx.doi.org/10.1115/1.2910134.
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A regional model has been described for dispersed turbulent two-phase flow which accounts for the transverse variation of velocity. The two-phase turbulence parameters are introduced in direct analogy to well-known single-phase flow parameters which are then correlated to experimental data. The advantages of this approach are its simplicity and the absence of arbitrary parameters which need calibration at different experimental ranges. Its generality has been tested by comparisons at high and low operating pressures with air-water and steam-water mixtures. Comparisons between calculated and measured values have been carried out for the film thickness and the pressure gradient at different experimental setups.
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Bolotnov, Igor A., Richard T. Lahey, Donald A. Drew, and Kenneth E. Jansen. "Turbulent cascade modeling of single and bubbly two-phase turbulent flows." International Journal of Multiphase Flow 34, no. 12 (2008): 1142–51. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2008.06.006.
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Al-Dulaimi, M. J., F. A. Hamad, A. A. Abdul Rasool, and K. A. Ameen. "Effect of sand particles on flow structure of free jet from a nozzle." Journal of Mechanical Engineering and Sciences 13, no. 3 (2019): 5542–61. http://dx.doi.org/10.15282/jmes.13.3.2019.21.0447.
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The Characteristics of single and two- phase flow from a circular turbulent free jet from a nozzle of 10 mm diameter were investigated experimentally and numerically. The measurements were conducted for ReJ = 10007 - 31561. The velocity was measured at location from the nozzle y/D (0-8) in axial and radial directions. The two phase measurement were done by using natural construction sand as a solid phase of sizes (220,350,550) µm and loading ratios (mass flow ratio of sand to mass flow rate of air) in the range (0.18-1.38). Two phase air velocity of jet showed that the introducing of natural sand particles gives lower jet velocity attributed to momentum transfer to particles. The smaller particle size leads to lower values of velocity. The velocity found to be decreased with loading ratio increase. The numerical simulation was performed for single and two phase jet flow. RNG K-ε turbulence model was used to simulate the flow of fluid and the discrete phase model to simulate the particles flow. The results form numerical simulation showed a good agreement with experimental results.
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Pakhomov, Maksim A., and Viktor I. Terekhov. "RANS Modeling of Turbulent Flow and Heat Transfer in a Droplet-Laden Mist Flow through a Ribbed Duct." Water 14, no. 23 (2022): 3829. http://dx.doi.org/10.3390/w14233829.
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The local structure, turbulence, and heat transfer in a flat ribbed duct during the evaporation of water droplets in a gas flow were studied numerically using the Eulerian approach. The structure of a turbulent two-phase flow underwent significant changes in comparison with a two-phase flow in a flat duct without ribs. The maximum value of gas-phase turbulence was obtained in the region of the downstream rib, and it was almost twice as high as the value of the kinetic energy of the turbulence between the ribs. Finely dispersed droplets with small Stokes numbers penetrated well into the region of flow separation and were observed over the duct cross section; they could leave the region between the ribs due to their low inertia. Large inertial droplets with large Stokes numbers were present only in the mixing layer and the flow core, and they accumulated close to the duct ribbed wall in the flow towards the downstream rib. An addition of evaporating water droplets caused a significant enhancement in the heat transfer (up to 2.5 times) in comparison with a single-phase flow in a ribbed channel.
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Ardekani, M. N., M. E. Rosti, and L. Brandt. "Turbulent flow of finite-size spherical particles in channels with viscous hyper-elastic walls." Journal of Fluid Mechanics 873 (June 24, 2019): 410–40. http://dx.doi.org/10.1017/jfm.2019.413.
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We study single-phase and particle-laden turbulent channel flows bounded by two incompressible hyper-elastic walls with different deformability at bulk Reynolds number $5600$. The solid volume fraction of finite-size neutrally buoyant rigid spherical particles considered is $10\,\%$. The elastic walls are assumed to be of a neo-Hookean material. A fully Eulerian formulation is employed to model the elastic walls together with a direct-forcing immersed boundary method for the coupling between the fluid and the particles. The data show a significant drag increase and the enhancement of the turbulence activity with growing wall elasticity for both the single-phase and particle-laden flows when compared with the single-phase flow over rigid walls. Drag reduction and turbulence attenuation is obtained, on the other hand, with highly elastic walls when comparing the particle-laden flow with the single-phase flow for the same wall properties; the opposite effect, drag increase, is observed upon adding particles to the flow over less elastic walls. This is explained by investigating the near-wall turbulence, where the strong asymmetry in the magnitude of the wall-normal velocity fluctuations (favouring positive $v^{\prime }$), is found to push the particles towards the channel centre. The particle layer close to the wall contributes to turbulence production by increasing the wall-normal velocity fluctuations, so that in the absence of this layer, smaller wall deformations and in turn turbulence attenuation is observed. For a moderate wall elasticity, we increase the particle volume fraction up to $20\,\%$ and find that particle migration away from the wall is the cause of turbulence attenuation with respect to the flow over rigid walls. However, for this higher volume fractions, the particle induced stress compensates for the decreasing Reynolds shear stress, resulting in a higher overall drag for the case with elastic walls. The effect of the wall elasticity on the overall drag reduces significantly with increasing particle volume fraction.
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Platonov, Dmitriy, Andrey Sentyabov, Sergey Shtork, Sergey Skripkin, and Dmitriy Dekterev. "NUMERICAL SIMULATION OF THE FLOW WITH DISPERSE PHASE IN A TANGENTIAL VORTEX CHAMBER." Eurasian Journal of Mathematical and Computer Applications 13, no. 1 (2025): 100–107. https://doi.org/10.32523/2306-6172-2025-13-1-100-107.
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The flow with a disperse phase in a tangential vortex chamber at high swirl numbers was studied using a numerical methods. The swirling flow is created using nozzles directed at an angle to the chamber axis. The numerical flow model was based on computational fluid dynamics methods and described the turbulent flow of water. Turbulence was simulated using the large eddy simulation method. Based on the results of single-phase flow simulation, particle motion was calculated using the Lagrange approach. The results of the single-phase flow simulation are consistent with the data from the corresponding experimental studies. The movement of particles depends significantly on their density. For massless particles, the average residence time of the particles is noticeably lower for a higher swirl number. The residence time of heavy particles is 1.5 - 2 times higher than the similar residence time of massless particles. At the same time, most of the heavy particles do not leave the tangential chamber and are deposited.
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Dodge, F. T., S. T. Green, and J. E. Johnson. "Characterization of Injection Nozzles for Gas-Solid Flow Applications." Journal of Fluids Engineering 113, no. 3 (1991): 469–74. http://dx.doi.org/10.1115/1.2909519.
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Laser phase-doppler velocimetry measurements have been used to characterize the particle-gas sprays produced by straight-tube nozzles that simulate idealized fuel injectors for solid fuel combustion systems. Tests were conducted on two nozzle sizes, for two particle sizes, two loading ratios, and two gas velocities. The Reynolds numbers was varied from 9500 to 19000, and the Stokes number from 1.9 to 61.4. It was found that the velocities of the particles in the spray decelerate more slowly, and the velocity profiles are generally more narrow, than for a single-phase free-jet. The turbulence level of the particles in the sprays was found to be less than half the turbulence level of a single-phase free-jet, and the turbulent velocity profiles were not yet fully developed at X = 40D. The hydrodynamic characteristics of the nozzles that are the most important for combustion systems were found to be: (a) the particle spray expands radially at a cone angle of 2° (measured at the radius corresponding to the peak of the particle mass flux distribution); and (b) the nozzle pressure drop and particle mass flow can be related by a correlation that depends on loading ratio, Reynolds number, Stokes number, and the pressure drop coefficient of the nozzle for a single phase flow.
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Chen, Xue, Xin Luan, Dalei Song, and Hua Yang. "Multiscale Analysis of Temporal Ocean Turbulence Intermittency." Marine Technology Society Journal 53, no. 3 (2019): 54–62. http://dx.doi.org/10.4031/mtsj.53.3.7.
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AbstractAn analysis of temporal intermittency in ocean turbulent energy transfer is given. Intermittency plays a major role in ocean turbulence, and the level of intermittency strongly depends on different scales of the flow. In this work, in order to understand the temporal aspects of intermittency, we extend our research to the ocean turbulent energy transfer process. Measurements of ocean turbulence are made from a moored turbulence measuring instrument (MTMI) deployed in the South China Sea. Signals related to ocean turbulence have been collected with two orthogonal shear probes at a single level for an extended period, which laid a valid foundation for the understanding of turbulent energy transfer characteristics. Our analysis of ocean turbulence data is based on the combined use of empirical mode decomposition (EMD) and of the wavelet transform method. First, a decomposition of ocean turbulent fields in a limited number of time scales is provided by the EMD method. Then, the wavelet transform method is performed to the decomposed signals to obtain the wavelet coefficients, which enables the detection of energy transfer in the flow. Finally, a novel intermittency measure based on Reynolds shear stress has been proposed to identify intermittent bursts of energy at different time scales. The new intermittency measure is estimated using the obtained wavelet coefficients and can be used as an indication of the turbulent kinetic energy transfer between two different time scales. In order to analyze the turbulent energy transfer process in detail, intermittency between the adjacent and nonadjacent time scales is presented. The results show that, in the locations where the ocean turbulent energy is being transferred between two time scales, the phase synchronization between the modes of field fluctuations occurs. This confirms that phase synchronization observed in ocean turbulence is due to the turbulent energy cascade, which helps improve our understanding of turbulent energy cascade and turbulent mixing processes in ocean dynamic systems.
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Capone, Alessandro, Fabio Di Felice, and Francisco Alves Pereira. "Particle Image Velocimetry measurements in a turbulent channel flow laden with elongated particles." Journal of Physics: Conference Series 2293, no. 1 (2022): 012005. http://dx.doi.org/10.1088/1742-6596/2293/1/012005.
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Abstract Particle Image Velocimetry is employed to investigate the turbulence modulation induced by dispersed elongated, rod-like particles in a turbulent channel flow. Particles with two different aspect ratios AR=40,80 are tested, at a volume fraction of 10-5. Carrier flow velocimetry data and distribution and orientation data of dispersed particles are obtained by an ad-hoc single-camera phase-discrimination technique. Carrier flow data shows that in the near-wall region turbulence modulation by particle occurrs as well as a decrease of average streamwise velocity. Analysis of conditional probability density function of particles location reveals that particles locations statistically match flow regions with instantaneous low vorticity and high streamwise velocity, in particular in the near-wall region.
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Pham, Thinh Quy Duc, Jichan Jeon, Daeseong Jo, and Sanghun Choi. "Two-Phase Flow Simulations Using 1D Centerline-Based C- and U-Shaped Pipe Meshes." Applied Sciences 11, no. 5 (2021): 2020. http://dx.doi.org/10.3390/app11052020.
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This study aims to investigate the pressure changes, bubble dynamics, and flow physics inside the U- and C-shaped pipes with four different gravitational directions. The simulation is performed using a 1D centerline-based mesh generation technique along with a two-fluid model in the open-source software, OpenFOAM v.6. The continuity and momentum equations of the two-fluid model are discretized using the pressure-implicit method for the pressure-linked equation algorithm. The static and hydrostatic pressures in the two-phase flow were consistent with those of single-phase flow. The dynamic pressure in the two-phase flow was strongly influenced by the effect of the buoyancy force. In particular, if the direction of buoyancy force is the same as the flow direction, the dynamic pressure of the air phase increases, and that of the water phase decreases to satisfy the law of conservation of mass. Dean flows are observed on the transverse plane of the curve regions in both C-shaped and U-shaped pipes. The turbulent kinetic energy is stronger in a two-phase flow than in a single-phase flow. Using the 1D centerline-based mesh generation technique, we demonstrate the changes in pressure and the turbulent kinetic energy of the single- and two-phase flows, which could be observed in curve pipes.
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Nakoryakov, V. E., O. N. Kashinsky, V. V. Randin, and L. S. Timkin. "Gas-Liquid Bubbly Flow in Vertical Pipes." Journal of Fluids Engineering 118, no. 2 (1996): 377–82. http://dx.doi.org/10.1115/1.2817389.
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Gas-liquid bubbly flow was investigated in vertical pipes for different flow conditions: fully developed turbulent downward flow in a 42.3 mm diameter pipe and upward flow in a 14.8 mm diameter pipe with liquid of elevated viscosity. Wall shear stress, local void fraction, and liquid velocity profiles, shear stress, and velocity fluctuations were measured using an electrodiffusional method. Results obtained demonstrate the existence of “universal” near-wall velocity distribution in a downward bubbly flow. The reduction of turbulent fluctuations is observed in downward flow as compared to a single-phase turbulent flow. The development of bubble-induced liquid velocity fluctuations in a “laminar” bubbly flow was studied.
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Fan, Wenyuan, and Henryk Anglart. "Progress in Phenomenological Modeling of Turbulence Damping around a Two-Phase Interface." Fluids 4, no. 3 (2019): 136. http://dx.doi.org/10.3390/fluids4030136.
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The presence of a moving interface in two-phase flows challenges the accurate computational fluid dynamics (CFD) modeling, especially when the flow is turbulent. For such flows, single-phase-based turbulence models are usually used for the turbulence modeling together with certain modifications including the turbulence damping around the interface. Due to the insufficient understanding of the damping mechanism, the phenomenological modeling approach is always used. Egorov’s model is the most widely-used turbulence damping model due to its simple formulation and implementation. However, the original Egorov model suffers from the mesh size dependency issue and uses a questionable symmetric treatment for both liquid and gas phases. By introducing more physics, this paper introduces a new length scale for Egorov’s model, making it independent of mesh sizes in the tangential direction of the interface. An asymmetric treatment is also developed, which leads to more physical predictions for both the turbulent kinetic energy and the velocity field.
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Morad, Akeel M. Ali, Rafi M. Qasim, and Amjed Ahmed Ali. "STUDY OF THE BEHAVIOURS OF SINGLE-PHASE TURBULENT FLOW AT LOW TO MODERATE REYNOLDS NUMBERS THROUGH A VERTICAL PIPE. PART I: 2D COUNTERS ANALYSIS." EUREKA: Physics and Engineering, no. 6 (November 30, 2020): 108–22. http://dx.doi.org/10.21303/2461-4262.2020.001538.
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This study presents a model to investigate the behavior of the single-phase turbulent flow at low to moderate Reynolds number of water through the vertical pipe through (2D) contour analysis. The model constructed based on governing equations of an incompressible Reynolds Average Navier-Stokes (RANS) model with (k-ε) method to observe the parametric determinations such as velocity profile, static pressure profile, turbulent kinetic energy consumption, and turbulence shear wall flows. The water is used with three velocities values obtained of (0.087, 0.105, and 0.123 m/s) to represent turbulent flow under low to moderate Reynolds number of the pipe geometry of (1 m) length with a (50.8 mm) inner diameter. The water motion behavior inside the pipe shows by using [COMSOL Multiphysics 5.4 and FLUENT 16.1] Software. It is concluded that the single-phase laminar flow of a low velocity, but obtained a higher shearing force; while the turbulent flow of higher fluid velocity but obtained the rate of dissipation of shearing force is lower than that for laminar flow. The entrance mixing length is affected directly with pattern of fluid flow. At any increasing in fluid velocity, the entrance mixing length is increase too, due to of fluid kinetic viscosity changes. The results presented the trends of parametric determinations variation through the (2D) counters analysis of the numerical model. When fluid velocity increased, the shearing force affected directly on the layer near-wall pipe. This leads to static pressure decreases with an increase in fluid velocities. While the momentum changed could be played interaction rules between the fluid layers near the wall pipe with inner pipe wall. Finally, the agreement between present results with the previous study of [1] is satisfied with the trend
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Ferran, Amélie, Sofía Angriman, Pablo D. Mininni, and Martín Obligado. "Characterising Single and Two-Phase Homogeneous Isotropic Turbulence with Stagnation Points." Dynamics 2, no. 2 (2022): 63–72. http://dx.doi.org/10.3390/dynamics2020004.
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It has been shown that, for dense, sub-Kolmogorov particles advected in a turbulent flow, carrier phase properties can be reconstructed from the particles’ velocity field. For that, the instantaneous particles’ velocity field can be used to detect the stagnation points of the carrier phase. The Rice theorem can therefore be used, implying that the Taylor length is proportional to the mean distance between such stagnation points. As this model has been only tested for one-dimensional time signals, this work discusses if it can be applied to two-phase, three-dimensional flows. We use direct numerical simulations with turbulent Reynolds numbers Reλ between 40 and 520 and study particle-laden flows with a Stokes number of St=0.5. We confirm that for the carrier phase, the Taylor length is proportional to the mean distance between stagnation points with a proportionality coefficient that depends weakly on Reλ. Then, we propose an interpolation scheme to reconstruct the stagnation points of the particles’ velocity field. The results indicate that the Rice theorem cannot be applied in practice to two-phase three-dimensional turbulent flows, as the clustering of stagnation points forms very dense structures that require a very large number of particles to accurately sample the flow stagnation points.
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Prakash, Vivek N., J. Martínez Mercado, Leen van Wijngaarden, et al. "Energy spectra in turbulent bubbly flows." Journal of Fluid Mechanics 791 (February 15, 2016): 174–90. http://dx.doi.org/10.1017/jfm.2016.49.
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We conduct experiments in a turbulent bubbly flow to study the nature of the transition between the classical $-5/3$ energy spectrum scaling for a single-phase turbulent flow and the $-3$ scaling for a swarm of bubbles rising in a quiescent liquid and of bubble-dominated turbulence. The bubblance parameter (Lance & Bataille J. Fluid Mech., vol. 222, 1991, pp. 95–118; Rensen et al., J. Fluid Mech., vol. 538, 2005, pp. 153–187), which measures the ratio of the bubble-induced kinetic energy to the kinetic energy induced by the turbulent liquid fluctuations before bubble injection, is often used to characterise bubbly flow. We vary the bubblance parameter from $b=\infty$ (pseudoturbulence) to $b=0$ (single-phase flow) over 2–3 orders of magnitude (0.01–5) to study its effect on the turbulent energy spectrum and fluctuations in liquid velocity. The probability density functions (PDFs) of the fluctuations in liquid velocity show deviations from the Gaussian profile for $b>0$, i.e. when bubbles are present in the system. The PDFs are asymmetric with higher probability in the positive tails. The energy spectra are found to follow the $-3$ scaling at length scales smaller than the size of the bubbles for bubbly flows. This $-3$ spectrum scaling holds not only in the well-established case of pseudoturbulence, but surprisingly in all cases where bubbles are present in the system ($b>0$). Therefore, it is a generic feature of turbulent bubbly flows, and the bubblance parameter is probably not a suitable parameter to characterise the energy spectrum in bubbly turbulent flows. The physical reason is that the energy input by the bubbles passes over only to higher wavenumbers, and the energy production due to the bubbles can be directly balanced by the viscous dissipation in the bubble wakes as suggested by Lance & Bataille (1991). In addition, we provide an alternative explanation by balancing the energy production of the bubbles with viscous dissipation in the Fourier space.
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Niazi Ardekani, M., P. Costa, W. P. Breugem, F. Picano, and L. Brandt. "Drag reduction in turbulent channel flow laden with finite-size oblate spheroids." Journal of Fluid Mechanics 816 (February 28, 2017): 43–70. http://dx.doi.org/10.1017/jfm.2017.68.
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We study suspensions of oblate rigid particles in a viscous fluid for different values of the particle volume fractions. Direct numerical simulations have been performed using a direct-forcing immersed boundary method to account for the dispersed phase, combined with a soft-sphere collision model and lubrication corrections for short-range particle–particle and particle–wall interactions. With respect to the single-phase flow, we show that in flows laden with oblate spheroids the drag is reduced and the turbulent fluctuations attenuated. In particular, the turbulence activity decreases to lower values than those obtained by accounting only for the effective suspension viscosity. To explain the observed drag reduction, we consider the particle dynamics and the interactions of the particles with the turbulent velocity field and show that the particle–wall layer, previously observed and found to be responsible for the increased dissipation in suspensions of spheres, disappears in the case of oblate particles. These rotate significantly slower than spheres near the wall and tend to stay with their major axes parallel to the wall, which leads to a decrease of the Reynolds stresses and turbulence production and so to the overall drag reduction.
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Peña-Monferrer, C., J. L. Muñoz-Cobo, and S. Chiva. "CFD Turbulence Study of PWR Spacer-Grids in a Rod Bundle." Science and Technology of Nuclear Installations 2014 (2014): 1–15. http://dx.doi.org/10.1155/2014/635651.
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Nuclear fuel bundles include spacers essentially for mechanical stability and to influence the flow dynamics and heat transfer phenomena along the fuel rods. This work presents the analysis of the turbulence effects of a split-type and swirl-type spacer-grid geometries on single phase in a PWR (pressurized water reactor) rod bundle. Various computational fluid dynamics (CFD) calculations have been performed and the results validated with the experiments of the OECD/NEA-KAERI rod bundle CFD blind benchmark exercise on turbulent mixing in a rod bundle with spacers at the MATiS-H facility. Simulation of turbulent phenomena downstream of the spacer-grid presents high complexity issues; a wide range of length scales are present in the domain increasing the difficulty of defining in detail the transient nature of turbulent flow with ordinary turbulence models. This paper contains a complete description of the procedure to obtain a validated CFD model for the simulation of the spacer-grids. Calculations were performed with the commercial code ANSYS CFX using large eddy simulation (LES) turbulence model and the CFD modeling procedure validated by comparison with measurements to determine their suitability in the prediction of the turbulence phenomena.
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INOUE, NORIHIRO, and JUNYA ICHINOSE. "SINGLE-PHASE HEAT TRANSFER AND PRESSURE DROP INSIDE INTERNALLY HELICAL-GROOVED HORIZONTAL SMALL-DIAMETER TUBES." International Journal of Air-Conditioning and Refrigeration 20, no. 04 (2012): 1250022. http://dx.doi.org/10.1142/s2010132512500228.
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An experimental study on pressure drop and heat transfer in single-phase was carried out using 10 types of internally helical-grooved and smooth small-diameter tubes with an outside diameter of 4 mm. The results are listed below: (1) In the turbulent flow region, fin height had the greatest effect, helix angle had only a minor effect, and the number of grooves had almost no effect upon the pressure drop versus the mass flow rate of the 4-mm grooved small-diameter tubes. In the laminar flow region, except for fin height, the shapes of the internal grooves had scarcely any effect upon pressure drop. (2) In the turbulent flow region, the heat transfer coefficients of the 4-mm grooved small-diameter tubes were greatly affected by fin height. The heat transfer coefficients became the maximum when a helix angle was near 15°, and there is a different tendency in the experiments of the pressure drop. On the other hand, there is almost no effect of the number of grooves. In the laminar flow region, there were no large differences in the heat transfer coefficients between the internally helical-grooved tubes and smooth small-diameter tube. (3) New empirical correlations for the friction factor and heat transfer coefficient in the laminar and turbulent flow regions were developed based on the experimental values. (4) The performance assessment in consideration of both heat transfer and pressure drop was indicated by using Colburn's analogy.
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Abugnah, Elhadi Kh, Wan Saiful-Islam Wan Salim, Abdulhafid M. A. Elfaghi, Sami Al-Alimi, Yazid Saif, and Wenbin Zhou. "Numerical Study of Three-Dimensional Models of Single- and Two-Phase Nanofluid Flow through Corrugated Channels." Processes 12, no. 5 (2024): 870. http://dx.doi.org/10.3390/pr12050870.
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This study delves into computational fluid dynamics (CFDs) predictions for SiO2–water nanofluids, meticulously examining both single-phase and two-phase models. Employing the finite volume approach, we tackled the three-dimensional partial differential equations governing the turbulent mixed convection flow in a horizontally corrugated channel with uniform heat flux. The study encompasses two nanoparticle volume concentrations and five Reynolds numbers (10,000, 15,000, 20,000, 25,000, and 30,000) to unravel these intricate dynamics. Despite previous research on the mixed convection of nanofluids using both single-phase and two-phase models, our work stands out as the inaugural systematic comparison of their predictions for turbulent mixed convection flow through this corrugated channel, considering the influences of temperature-dependent properties and hydrodynamic characteristics. The results reveal distinct variations in thermal fields between the two-phase and single-phase models, with negligible differences in hydrodynamic fields. Notably, the forecasts generated by three two-phase models—Volume of Fluid (VOF), Eulerian Mixture Model (EMM), and Eulerian Eulerian Model (EEM)—demonstrate remarkable similarity in the average Nusselt number, which are 24% higher than the single-phase model (SPM). For low nanoparticle volume fractions, the average Nusselt number predicted by the two-phase models closely aligns with that of the single-phase model. However, as the volume fraction increases, differences emerge, especially at higher Reynolds numbers. In other words, as the volume fraction of the nanoparticles increases, the nanofluid flow becomes a multi-phase problem, as depicted by the findings of this study.
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Pakhomov, Maksim A., and Viktor I. Terekhov. "Eulerian-Eulerian Modeling of the Features of Mean and Fluctuational Flow Structure and Dispersed Phase Motion in Axisymmetric Round Two-Phase Jets." Mathematics 11, no. 11 (2023): 2533. http://dx.doi.org/10.3390/math11112533.
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The features of the local mean and fluctuational flow structure, carrier phase turbulence and the propagation of the dispersed phase in the bubbly and droplet-laden isothermal round polydispersed jets were numerically simulated. The dynamics of the polydispersed phase is predicted using the Eulerian–Eulerian two-fluid approach. Turbulence of the carrier phase is described using the second-moment closure while taking into account the presence of the dispersed phase. The numerical analysis was performed in a wide range of variation of dispersed phase diameter at the inlet and particle-to-fluid density ratio (from gas flow laden with water droplets to carrier fluid flow laden with gas bubbles). An increase in the concentration of air bubbles and their size leads to jet expansion (as compared to a single-phase jet up to 40%), which indicates an increase in the intensity of the process of turbulent mixing with the surrounding space. However, this makes the gas-droplet jet narrower (up to 15%) and with a longer range in comparison with a single-phase flow. The addition of finely dispersed liquid droplets to an air jet suppresses gas phase turbulence (up to 15%). In a bubbly jet, it is found that small bubbles (Stk < 0.1) accumulate near the jet axis in the initial cross-sections, while concentration of the large ones (Stk > 0.2) along the jet axis decreases rapidly. In the gas-droplet jet, the effect of dispersed phase accumulation is also observed in the initial cross-section, and then its concentration decreases gradually along the jet axis. For gas bubbles (Stk < 0.1), small turbulence attenuation (up to 6%) is shown.
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Elena Rita, Avram. "An experimental investigations of the single phase fluid flow through mini pipes with circular cross section." Scientific Bulletin of Naval Academy XXIII, no. 2 (2020): 25–31. http://dx.doi.org/10.21279/1454-864x-20-i2-003.
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The experimental investigation that has been conducted on the fluid flow in mini pipes with circular cross-sections are presented in this paper. The working fluid is water and its main physical-chemical analysis (pH, total hardness, electrical conductivity) were carried out. The liquid flow through mini pipes of 1, 2 and 3 mm diameter with simulated pressure drops from 1.01 to 61 bar is investigated and the experimental results are presented. The laminar and turbulent friction factor f at different pressure drop values, the transition from the laminar to turbulent flow, the effect of relative roughness, and the boundary-layer thickness, δ, are computed and studied. The experimental results are presented, discussed and analysed, according to the theoretical principles.
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Arosemena, A. A., H. Ali, and J. Solsvik. "Characterization of vortical structures in a stirred tank." Physics of Fluids 34, no. 2 (2022): 025127. http://dx.doi.org/10.1063/5.0083843.
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Data obtained from large eddy simulations of single-phase, turbulent flow of Newtonian and shear-thinning fluids in a baffled stirred tank reactor are considered to identify and characterize vortical structures. The identification proceeds through an objectivized Eulerian method, accounting for the inhomogeneities in the flow, which palliates some shortcomings of previous implementations. The characterization focuses on turbulent vortices larger than the dissipative scales and, to a lesser extent, on trailing and macro-instability vortices. The characterization performed through different statistical analyses includes aspects such as size, number density, shape, distribution and organization in space, and correlation with the kinetic energy due to turbulence and the periodic passage of the blades. To the authors' knowledge, some of these representative aspects have been rarely investigated or have not been addressed at all for the turbulent flow in a stirred vessel. The influence of changing the rotational speed of the tank and the rheology of the working fluid are explored as well. Finally, considering one-way coupling, some potential and practical implications for liquid–liquid and gas–liquid dispersed systems are briefly discussed.
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Jouybari, Ammar Kazemi, Saeed Dinarvand, Pedram Tehrani, Mohammad Eftekhari Yazdi, and Gholamreza Salehi. "Turbulent Flow and Heat Transfer of Al2O3–CuO Hybrid Nanofluids in Helically Micro-Finned Tubes Using Mass-Based and Discrete-Phase Models." Journal of Nanofluids 13, no. 5 (2024): 1134–44. https://doi.org/10.1166/jon.2024.2199.
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This numerical study investigates forced convective heat transfer and pressure drop in turbulent hybrid nanofluid flow through a helically finned tube with constant wall temperature. Both single-phase mass-based model (MBM) and discrete-phase method (DPM) approaches are employed to analyze and compare heat transfer characteristics in a three-dimensional helically micro-finned geometry. This study evaluated the effects of various volume flow rates between 0.4 to 1.2 m3/h (Reynolds numbers between 11510 to 34530) and nanoparticle concentrations ranging from 0.5% to 3% on water-base Al2O3–CuO hybrid nanofluids’ thermal and flow characteristics obtained from studied approaches. Results demonstrate that the utilized single-phase MBM predicts higher values for both average heat transfer coefficient and pressure drop compared to values obtained from the discrete phase method (DPM). For a 3.0% hybrid nanofluid, with volumetric flow rates ranging from 0.4 to 1.2 m3/h, the mean absolute percentage deviation (MAPD) in the average heat transfer coefficient between the multiphase DPM and single-phase MBM approaches, relative to pure water, is 1.5% to 7.5%. Also, by increasing the hybrid nanoparticle concentration from 0 to 3%, the deviation between single-phase and multi-phase approaches increases, reaching a maximum of 5.7% for the average heat transfer coefficient at a volume flow rate of 0.8 m3/h. However, at lower nanoparticle concentrations, both single-phase and multi-phase models produce similar results with minimal differences. The main novelty of the present work is that it compares the single-phase mass-based model with multi-phase DPM approaches. In addition, the combination of these modeling methods with the specific geometry of the present problem, turbulent regime, and the present hybrid nanofluid, for the first time in this study is considered. As a result, the single-phase approach offers a simpler and more cost-effective alternative to the more complex multi-phase methods for predicting nanofluid behavior in dilute solutions.
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Ali, Amjed Ahmed, Akeel M. Ali Morad, and Rafi M. Qasim. "A comparison study of the behaviors of single-phase turbulent flow at low to moderate Reynolds numbers through a vertical pipe: 3D counters analysis." EUREKA: Physics and Engineering, no. 3 (May 25, 2023): 15–28. http://dx.doi.org/10.21303/2461-4262.2023.002854.
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The study presented three-dimensional (3D) analysis of water's upward flowing through the vertical pipe under turbulent characteristic considerations. Both numerical constructed and improved the model of 3D for cylindrical coordinates of governing equations for incompressible turbulent flow with the Reynolds Average Navier-Stokes (RANS) model using the improved constants of the (k–ε) type. The present model is then compared with a previous study to give the feasibility of the present single-phase turbulent flow parameters. The pipe length is tested to measure how much it affected the turbulent parameters though one of the expected factors is the turbulent time scale. On the other hand, the model is numerically examined to determine the velocity profile, shear rate, and surface deformation of the water domain. While the pressure distribution, turbulent kinetic energy, and turbulent dissipation rate, these parameters are classified as the mechanic's system factors. The simulation is done with wide software used to simulate industrial is COMSOL 5.4 Multiphysics software. The results obtained increased the velocity of three inlet water velocities used ranging from (0.087, 0.105, and 0.123 m/sec) of upward flow. High fluctuation in the water flow moves along the entire pipe length and it can notice the sensitivity to any change in water properties or mechanical properties. The liquid upward flow in turbulent conditions is suffered from many characteristics such them related to liquid properties and others related to the mechanics of the application through the systems. The interaction between the fluid film (fluid boarded the pipe inner diameter) has been observed by the shear rate and liquid surface deformation
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Rahmani, Ramin K., Theo G. Keith, and Anahita Ayasoufi. "Three-Dimensional Numerical Simulation and Performance Study of an Industrial Helical Static Mixer." Journal of Fluids Engineering 127, no. 3 (2005): 467–83. http://dx.doi.org/10.1115/1.1899166.
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In many branches of processing industries, viscous liquids need to be homogenized in continuous operations. Consequently, fluid mixing plays a critical role in the success or failure of these processes. Static mixers have been utilized over a wide range of applications such as continuous mixing, blending, heat and mass transfer processes, chemical reactions, etc. This paper describes how static mixing processes of single-phase viscous liquids can be simulated numerically, presents the flow pattern through a helical static mixer, and provides useful information that can be extracted from the simulation results. The three-dimensional finite volume computational fluid dynamics code used here solves the Navier-Stokes equations for both laminar and turbulent flow cases. The turbulent flow cases were solved using k-ω model and Reynolds stress model (RSM). The flow properties are calculated and the static mixer performance for different Reynolds numbers (from creeping flows to turbulent flows) is studied. A new parameter is introduced to measure the degree of mixing quantitatively. Furthermore, the results obtained by k-ω and RSM turbulence models and various numerical details of each model are compared. The calculated pressure drop is in good agreement with existing experimental data.
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Butcher, Daniel, Adrian Spencer, and Rui Chen. "Influence of asymmetric valve strategy on large-scale and turbulent in-cylinder flows." International Journal of Engine Research 19, no. 6 (2017): 631–42. http://dx.doi.org/10.1177/1468087417725232.
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Phase-locked particle imaging velocimetry measurements are carried out in a direct-injected spark-ignition single-cylinder optical research engine equipped with fully variable valve timing to assess the impact of asymmetric intake valve lift strategies on the in-cylinder flow. The engine was operated under a range of asymmetric strategies, with one valve following a full lift profile, while the second intake valve is scaled as a factor of the first, expressed as % maximum valve lift. Proper orthogonal decomposition combined with a proposed methodology allows instantaneous velocity fields to be decomposed into what are nominally demonstrated as coherent and turbulent constituent velocity fields. Analysis of the coherent fields reveals the behaviour of large-scale structures within the flow, subject to cyclic variation. In the case of 40% maximum valve lift, an increase in the flow cyclic variability is observed. This is found to be as a result of a switch between a flow dominated by a counter-rotating vortex pair and a single vortex. The impact of maximum valve lift on the bulk motion is further evident by an increase in the magnitude of swirl ratio from 0.5 to −6.0 (at 75°CA). Analysis of the turbulent constituent shows how the increased valve life asymmetry leads to increased turbulence during the intake stroke by over 250%. Finally, it is shown how the ensemble turbulence statistics may be misleading as stochastic fluctuations were found to be typically 66% of the total turbulent kinetic energy calculated from the ensemble statistic in the tested conditions.
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López, Juan A., Marco A. Ramírez-Argáez, Adrián M. Amaro-Villeda, and Carlos González. "Mathematical and Physical Modeling of Three-Phase Gas-Stirred Ladles." MRS Proceedings 1812 (2016): 29–34. http://dx.doi.org/10.1557/opl.2016.14.
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ABSTRACTA very realistic 1:17 scale physical model of a 140-ton gas-stirred industrial steel ladle was used to evaluate flow patterns measured by Particle Image Velocimetry (PIV), considering a three-phase system (air-water-oil) to simulate the argon-steel-slag system and to quantify the effect of the slag layer on the flow patterns. The flow patterns were evaluated for a single injector located at the center of the ladle bottom with a gas flow rate of 2.85 l/min, with the presence of a slag phase with a thickness of 0.0066 m. The experimental results obtained in this work are in excellent agreement with the trends reported in the literature for these gas-stirred ladles. Additionally, a mathematical model was developed in a 2D gas-stirred ladle considering the three-phase system built in the physical model. The model was based on the Eulerian approach in which the continuity and the Navier Stokes equations are solved for each phase. Therefore, there were three continuity and six Navier-Stokes equations in the system. Additionally, turbulence in the ladle was computed by using the standard k-epsilon turbulent model. The agreement between numerical simulations and experiments was excellent with respect to velocity fields and turbulent structure, which sets the basis for future works on process analysis with the developed mathematical model, since there are only a few three-phase models reported so far in the literature to predict fluid dynamics in gas-stirred steel ladles.
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Deniz Canal, Cansu, Erhan Böke, and Ali Cemal Benim. "Numerical analysis of pulverized biomass combustion." E3S Web of Conferences 321 (2021): 01001. http://dx.doi.org/10.1051/e3sconf/202132101001.
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Combustion of pulverized biomass in a laboratory swirl burner is computationally investigated. The two-phase flow is modelled by an Eulerian-Lagrangian approach. The particle size distribution and turbulent particle dispersion are considered. The radiative heat transfer is modelled by the P1 method. For modelling turbulence, different RANS modelling approaches are applied. The pyrolysis of the solid fuel is modelled by a single step mechanism. For the combustion of the volatiles a two-step reaction mechanism is applied. The gas-phase conversion rate is modelled by the Eddy Dissipation Model, combined with kinetics control. The results are compared with measurements.
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Nishad, Kaushal, Florian Ries, Yongxiang Li, and Amsini Sadiki. "Numerical Investigation of Flow through a Valve during Charge Intake in a DISI -Engine Using Large Eddy Simulation." Energies 12, no. 13 (2019): 2620. http://dx.doi.org/10.3390/en12132620.
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Apart from electric vehicles, most internal combustion (IC) engines are powered while burning petroleum-based fossil or alternative fuels after mixing with inducted air. Thereby the operations of mixing and combustion evolve in a turbulent flow environment created during the intake phase and then intensified by the piston motion and influenced by the shape of combustion chamber. In particular, the swirl and turbulence levels existing immediately before and during combustion affect the evolution of these processes and determine engine performance, noise and pollutant emissions. Both the turbulence characteristics and the bulk flow pattern in the cylinder are strongly affected by the inlet port and valve design. In the present paper, large eddy simulation (LES) is appraised and applied to studying the turbulent fluid flow around the intake valve of a single cylinder IC-engine as represented by the so called magnetic resonance velocimetry (MRV) flow bench configuration with a relatively large Reynolds number of 45,000. To avoid an intense mesh refinement near the wall, various subgrid scale models for LES; namely the Smagorinsky, wall adapting local eddy (WALE) model, SIGMA, and dynamic one equation models, are employed in combination with an appropriate wall function. For comparison purposes, the standard RANS (Reynolds-averaged Navier–Stokes) k- ε model is also used. In terms of a global mean error index for the velocity results obtained from all the models, at first it turns out that all the subgrid models show similar predictive capability except the Smagorinsky model, while the standard k- ε model experiences a higher normalized mean absolute error (nMAE) of velocity once compared with MRV data. Secondly, based on the cost-accuracy criteria, the WALE model is used with a fine mesh of ≈39 millions control volumes, the averaged velocity results showed excellent agreement between LES and MRV measurements, revealing the high prediction capability of the suggested LES tool for valve flows. Thirdly, the turbulent flow across the valve curtain clearly featured a back flow resulting in a high speed intake jet in the middle. Comprehensive LES data are generated to carry out statistical analysis in terms of (1) evolution of the turbulent morphology across the valve passage relying on the flow anisotropy map, (2) integral turbulent scales along the intake-charge stream, (3) turbulent flow properties such as turbulent kinetic energy, turbulent velocity and its intensity within the most critical zone in intake-port and along the port length, it further transpires that the most turbulence are generated across the valve passage and these are responsible for the in-cylinder turbulence.