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This study presents a numerical analysis of turbulent air flow through a rectangular duct fitted with two perforated vertical baffle plates, focusing on flow characteristics and pressure distribution. The analysis employs two-dimensional differential equations, solved using the finite volume method. The k-e turbulence model, implemented in Fluent software, elucidates the turbulence dynamics. Boundary conditions, including the entrance velocity field and exit atmospheric pressure, were varied to comprehensively evaluate the system. The model's validity was established against experimental data at a Reynolds (Re) number of 87300, demonstrating excellent comparability at a distance of 0.525 m from the duct entrance. The research aims to investigate the effects of different Re numbers (10,000, 20,000, and 30,000) on various parameters in a duct equipped with two perforated, nozzleshaped vertical baffles, each comprising eight trapezoidal sections forming seven nozzles. Parameters analyzed include the velocity profile, pressure drop, turbulent kinetic energy, dynamic pressure coefficient, and skin friction coefficient. The study finds that the insertion of perforated vertical baffles enhances mixing, particularly at higher Re numbers. Axial velocities attain maximum values above the bottom baffle and below the top baffle, with multiple re-circulation zones observed at strategic locations including above, below, and behind the baffles. Significant findings include the occurrence of maximum vertical velocity values at Re=30000 upstream of the bottom baffle, and a substantial re-circulation zone immediately upstream of the upper baffle. The channel's thermal enhancement factor is noted to improve with decreasing levels of skin friction as the Re number increases. Pressure values rise at the junctions where the duct's inner walls meet the upper surfaces of the baffles. Turbulent kinetic energy across the duct is categorized into three distinct zones based on the Re number: Zone 1, between the entry and the first baffle, exhibits minimal turbulence influence; Zone 2, located between the baffles, shows a peak turbulent kinetic energy of about 3 m²/s² near the nozzle exits and the bottom of the top baffle; Zone 3, extending from the second baffle to the outlet, records the highest turbulent kinetic energy rate at a Re number of 30,000. [ABSTRACT FROM AUTHOR]

Spraying liquid jets in the transverse airflow is suitable for creating tiny droplets in the combustion chamber. This paper numerically investigated the effect of airflow turbulence intensity on liquid jet penetration and breakup. The large-eddy simulation method is used for numerical solutions. The level set model and volume of fluid (VOF) model are combined for two-phase crossflow modeling. Elliptical and circular nozzles with different aspect ratios and diameters were used to obtain liquid jet trajectories. Other trajectory equations due to different nozzle shapes were obtained for laminar flow. It is shown that the liquid jet trajectory depends on momentum ratio and dimensionless length. For turbulence flow, as results show, when the turbulence intensity of the transverse airflow increases, the energy in the flow vortexes also increases, so the breakup point approaches the liquid jet location. Also, as the turbulence intensity of the transverse airflow increases, the liquid jet trajectory and its penetration depth are not affected significantly because the dynamic energy of turbulence fluctuations is negligible compared to the air main flow. i.e., at 10 %, turbulence intensity equals 1 percent of the primary energy dynamics of the main flow. [ABSTRACT FROM AUTHOR]

COVID-19 virus, which is a member of the coronavirus family, is a virulent virus that is transmitted by physical contact or air and results in death in infected people. People infected by the COVID-19 virus must be kept in quarantine in a closed area. Therefore, it is very important for the health of the individuals (patient, doctor, nurse, etc.) in the isolation room that, where the area kept closed is completely free of virus. This study was conducted to examine the flow dynamics of the air in the isolation chamber. With the simultaneous operation of the sanitized air machine and the ventilation in the room, it is aimed to investigate the virus killing effect of the air mixed with each other. The flow dynamics, velocity, temperature and turbulence kinetic energy of the air in the isolation chamber were examined. Investigations were carried out to ensure that the mixture of the two air in the room was better and distributed throughout the room. [ABSTRACT FROM AUTHOR]

In this study, it is aimed to investigate the effects of central ventilation system hood design on capture performance. Commercial computational fluid dynamic (CFD) software was used to optimize the hood design and predict capture performance. Thanks to the CFD software, the hood with real dimensions was modeled and numerical analyzes were carried out. In numerical analysis, the turbulent flow in the hood was prevented by the air guide attached to the hood. In this way, an increase was achieved in the hood capture velocity and airflow rate. With the information obtained as a result of CFD analysis, hood prototypes were created and real environment experiments were carried out. Numerical analysis performed at different flow rates were confirmed by experimental analyzes. As a result, CFD analysis showed that the air guide added to the hood prevents turbulence in the air flow and increases the hood performance. [ABSTRACT FROM AUTHOR]

Recent research has shown that particles in the air and harmful gases in the environment increase the risk of various respiratory diseases and mortality rates. For effective ventilation, particles and harmful gases in the environment must be captured before they are released into the environment. Air flow control valves (AFCVs) play an active role in the capture of particles and harmful gases in the environment with central ventilation system. In the study, an innovative AFCV, which is the most critical part of central ventilation systems, has been developed. Performance criteria in the innovative AFCV design have been the capture rate, the flow rate and turbulence intensity. In this study, six valves are designed as an alternative to the current valve. The designed valves were mounted on the central ventilation system hood and numerical analysis was performed. ANSYS Fluent software was used for the analysis. The best and worst valves were determined as a result of numerical analysis. Prototypes of the determined valves were created and experimental verification tests were carried out. Again, numerical analyses simulating the experimental tests were performed with these two valves. The experimental test results and numerical analysis results were compared. As a result, due to the innovative AFCV design, the air flow and the capture speed have been increased and the turbulence intensity has been reduced. [ABSTRACT FROM AUTHOR]

Heat rejection from electronic components by heat sink is still a viable cooling solution. The optimal heat sink design enables higher heat transfer performance. The purpose of the present study is to predict the effectiveness of heat sink elliptical closely spaced fins subjected to impinging air cooling. The air fan is the main source of impinging air, then its position and direction with the heat sink take the main role in present work. Two positions of fan location are studied. The first position where the fan is outside the heat sink and the second case where the fan is existed in a cut out template. So there are one impinging air inlet with four transverse outlets and one axial exit opposite to the air flow inlet. Reynolds number were taken at a range 3400-16000, the flow was turbulent so k-ε model turbulence model was used as our choice to simulate mean flow characteristics for turbulent flow conditions. The heat sink base was subjected to constant heat flux condition and proposed with range between 10000-40000 kW/m² to keep the base temperature at a temperature around 100 °C. The Results of temperature contour lines depicted a variation from the base to the extended surfaces tips. The comparison between the two cases results showed high temperature difference in the case with the cut out template. Nusselts numbers indicated that the second case performed better in heat transfer than the first case. The experimental and numerical results showed a good agreement with a difference not exceeding 2%. [ABSTRACT FROM AUTHOR]

The near-ground turbulent flow of nature air should have an important influence on the wind-sand flow, because of the vegetation and/or micro-topography. However, due to the complexity of turbulent flows, the effects of such turbulences and dust particles are still unknown. In this paper, the large eddy simulation–discrete element method was used to simulate the wind-sand flow. The results show that the response time of the wind-sand flow to turbulence is approximately 1.6 s. In addition, the response time increases rapidly as the particle size increases. The turbulence impact on the sand transport rate first increases and then decreases as the wind velocity fluctuation intensity increases. The sand transport rate is enhanced when the turbulence intensity is less than 0.25, whereas it is weakened when the turbulence intensity exceeds 0.25. Furthermore, the smaller the particle size, the more significant the effect. The effect of turbulence is mainly concentrated at 0.1–0.2 m from the ground and the turbulence increases the height of the wind-sand flow. [ABSTRACT FROM AUTHOR]

The heat sink is used to enhance heat rejection from heated surface to air. The seize and the geometry of the heat sink with the shape of the extended surfaces have a great influence on the heat transfer coefficient. The first step to get the optimal design is to predict the heat transfer by conduction in solid walls of heat sink and then by convection between the solid and air flow. The purpose of the present study is to predict the effectiveness of closely spaced parallel rectangular fin array arrangement. The electronic processor was represented by the copper heat sink base with thermal conductivity of 401 W/m.K. The 72 fins with the geometry above mentioned were exposed to heat transfer with conduction and convection along all the boundaries except the bottom from which heat flow toward air flow domain. Mesh generation at a specific cells, number of element and number of nodes were taken under temperature difference validation. The experiments were done under impinging air flow rate with Reynolds number ranged between 4000-16000. The flow was turbulent so the k-Δ turbulence model needed to simulate mean flow characteristics. Constant heat fluxes boundary conditions were proposed with range between 10000-70000 kW/m2. The Results of temperature contour lines depicted a heat trend from the hot base through the extended surfaces to the fin tips. The fins were aligned in the core of heat sink showed higher temperature gradient compared with the fins existed in lines surrounded the core. The thermal resistance decreased as the Reynolds number increased and the Nusselt number increased as the Reynolds number increased and also when the heat flux increased. The Reynolds number depicted increasing as the Nusselt number increased and so the heat rejected from the heat sink base increased. There is a good agreement between the experimental and simulating results at error percentage not exceed 2%. [ABSTRACT FROM AUTHOR]

Summary: This study investigated the influence of the longitudinal airflow on the smoke propagation in a tunnel by large‐eddy simulation, which is now widely applied to study the turbulent flow. The smoke movement characteristics were studied in detail, with varying the longitudinal airflow in the tunnel. Six fire scenarios have been simulated with Fire Dynamics Simulator (FDS) and the results of the longitudinal distribution of CO concentration, temperature distribution, interface height, stratification, and the efficiency of smoke extraction in the tunnel have been analyzed to evaluate the different fire cases. FDS predicted a CO concentration distribution compared to calculated values using the Hu model. Furthermore, the predicted maximum smoke temperatures are compared to those given by the Kurioka model. A reasonably good agreement has been obtained for both models. The obtained results showed that the increase of the forced airflow velocity has for results a loss of stratification and significant decrease in the efficiency of extraction. [ABSTRACT FROM AUTHOR]

An analysis of the airflow around an AeroDesign aircraft did perform to verify the turbulence generated by the propeller's high rotation and its possible propagation to the aircraft surfaces, which may impair its stability and control. The airflow behavior through the propeller and around the aircraft was verified using a computational tool to run the simulations. For this, it was considered two computational domains of unstructured tetrahedral mesh: a cylindrical for the propeller and a rectangular for the aircraft as a whole. The governing equations were solved using the standard k-epsilon and standard k-omega turbulence models. Later the results' convergence, it was observed that the streamlines around the aircraft were well behaved, despite the turbulence produced by the propeller's high rotation. The results did not affect the aircraft's overall moments according to its gravity center, consequently being able to validate the stability qualities of the analyzed aircraft. [ABSTRACT FROM AUTHOR]

Centrifugal fan in series is the core facility for pneumatic transportation. Its operation is required to be adjusted real time as the flow rate of transported materials changes. For optimisation performance, internal flow of a type 700 three-stage fan at rated rotation speed is analysed with FLUENT6.3 for various total pressure. Multiple reference frame (MRF) model is used for the impellers rotation in simulation, and Re-Normalisation group (RNG) κ-ɛ turbulence model and Roe-FDS flux type with first-order upwind difference scheme are used for calculation of compressible flow under various total pressure. Flow characteristics are obtained and differences of total pressure and velocity distribution in every impeller are analysed in different conditions, and velocity distribution on meridian plane as well as section of wind guide plates and volute are compared. Results show that there are many vortexes and backflows in fan with higher total pressure, and the lower pressure, the more smoothly flows, besides flow at inlet and outlet of impellers and in guide plates is seriously influenced by total pressure. Curves of P-Q and P-η at 4600 r/min are predicted based on simulation, which is helpful reducing the impact caused by off-design operation and improving efficiency.

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Energy released in explosion of aluminum dust at a given concentration in air depends on pre-ignition turbulence. The combined effects of turbulence and concentration on aluminum dust/air explosion in a 20 L spherical vessel were examined by numerical calculation in this study. It is found that role of pre-ignition turbulence in the aluminum dust/air explosion is related to the nominal concentrations. At lower nominal concentrations, the turbulence is a dominant factor affecting an aluminum dust/air explosion over uniformity of aluminum dust suspended in air. However, at higher nominal concentrations, the uniformity of aluminum dust suspended in air is a dominant factor affecting an aluminum dust/air explosion over turbulence. [ABSTRACT FROM AUTHOR]

Different variants of ventilation of the cab of a truck were investigated by numerical simulation methods. An unsteady viscous gas flow was numerically simulated using the VP2/3 package. In the process of numerical simulation of this flow, the Reynolds equations closed with the use of the differential k- ω model of turbulence in the SST modification of Menter were solved numerically. On the basis of analysis of the fields of the velocity, pressure, and turbulence characteristics of the air flows in the truck cab, obtained as a result of their numerical simulation, the efficiency of ventilation of this cab was estimated. [ABSTRACT FROM AUTHOR]

The objective of this study is to experimentally and numerically investigate the aerodynamic behaviour and the effectiveness of an air curtain confining cavity and subjected to external lateral flow. Experiments were carried out on a scale down model (1:5) under isothermal conditions representing a generic configuration of a display case, using LDV and PIV techniques to investigate the air flow characteristics. A numerical approach based on computational fluid dynamics (CFD) Fluent code was used with two turbulence models: the standard k–ε model and the RSM. Comparisons of experimental and numerical data obtained with and without external perturbation make it possible to quantify the effect of the perturbation on the air curtain characteristics such as airflow patterns, velocity profiles, jet decay, and its stability as well as the ambient thermal entrainment. These comparisons also allow a critical evaluation of the performance of the two turbulence models for free and perturbed jets. [ABSTRACT FROM AUTHOR]

The departing information were rather scarce in terms of real processes taking place in the compression stage, but at the end we managed to have a full picture of the main parameters evolution during the compression inside this existing marine engine. The target of this paper was to show how, by using the reverse engineering techniques, one may replicate and simulate the functioning conditions and parameters of an existing marine engine. The air flow jet that enters the cylinder swirling via the intake valves has changing characteristics, same can be said about the exhaust jet through the exhaust valves as they open and close, and they can be ascertained, along with the turbulence creation from swirl and tumble due to compression and squish. The mail goal of an engine's design is to maximize the efficiency factors, to develop the most power from the least amount of fuel. Regarding fluid dynamics, the combustion and volumetric efficiency depend on the fluid dynamics in the engine manifolds and cylinders. Analysis in cold flow involves modeling the airflow in the transient engine cycle without reactions. The endgame is to catch the process of mixture formation by accurately accounting for the interaction of moving geometry with the fluid dynamics of the induction process. [ABSTRACT FROM AUTHOR]

The objective of this study is to experimentally and numerically investigate the aerodynamic behavior and the effectiveness of an air curtain confining cavity and subjected to external lateral stream. Experiments were carried out on a scale down model (1:5) representing a generic configuration of a display case, using LDV and PIV techniques to investigate the air flow characteristics. Two complementary modelling approaches were performed. The first is based on computational fluid dynamics (CFD) which enables to better understand the local air flow characteristics, while the second deals on the global fluxes exchanged between the air curtain, the ambient and the cavity. The good agreement obtained between CFD and experimental results allows to validate the numerical model and also to build the global model. Comparisons of experimental and numerical data obtained with and without external perturbation make it possible to quantify the effect of the perturbation on the air curtain characteristics such as airflow patterns, velocity profiles, maximum velocity decay, half-width jet growth and its stability as well as those related to the global fluxes exchanged between the air curtain and its surroundings. To evaluate the sealing performance of the air curtain with and without external perturbation, dimensionless parameters related to air tightness, thermal entrainment and thermal confinement efficiency were identified and analyzed. It was showed that for higher values of external lateral velocity, the performance of the air curtain was reduced consequently. [ABSTRACT FROM AUTHOR]

The effects of surface rib shapes on particle deposition in turbulent duct air flows were numerically studied based on the Reynolds stresses model (RSM) with UDF code correction and the discrete particle model (DPM). The shapes of the rib cross sections were square, triangular and circular. The ratios of rib height to duct diameter e/D were 0.1. The present air velocity distributions for both smooth and ribbed ducts as well as particle deposition velocity in a smooth duct are all in good agreement with previous related study data. An efficiency ratio has been defined to evaluate the particle deposition enhancement ratio together with the increase of flow drag. It is found that the square ribs have the maximum enhancement efficiency on particle deposition, compared with the other rib shapes. The maximum efficiency ratio can reach about 400 for small particles ( τ p + < 1 ) but only about 2 for large particles ( τ p + > 1 ) when the rib shape is square. Moreover, the mechanisms of particle deposition enhancement for different rib shapes were investigated and analyzed. [ABSTRACT FROM AUTHOR]

A numerical investigation of the influence of the opening angle of a circular cavity in an U-shaped channel and the Reynolds number of a fluid fl ow in this channel on the local characteristics and turbulence of this fl ow has been performed based on the solution of the Reynolds equations, closed by the old and new Menter shear-stress transfer models and two variants of this model accounting for the curvature of streamlines, with the use of multiblock computational technologies realized in the VP2/3 package. The results of calculations were compared with each other and with experimental data of I. Castro and R. Savelsberg. This comparison has shown that the best agreement between the numerical predictions and experiments is obtained in the case where calculations are performed within the framework of the Leshtsiner-Rody-Isaev approach with correction for the eddy viscosity of the fluid fl ow. It was established that with increase in the Reynolds number and in the opening angle of the cavity the circulation flow in the near-wall layer of the vortex trapped in the cavity intensifies at a practically constant vorticity in the core of the vortex. [ABSTRACT FROM AUTHOR]

This paper reports a numerical investigation of the buoyancy induced turbulent air flow in an inclined passive wall solar chimney (IPWSC) attached to a room (ventilated space) for ventilation applications over a range of controlling parameters. The standard k − ɛ turbulence model has been employed to model air turbulence in the solar chimney system. With an isoflux heating condition specified on the absorber wall, the ventilation performance of the IPWSC design has been examined over the Rayleigh number range of 1.36 × 10 13 ≤ Ra ≤ 1.36 × 10 16 and inclination angles from 0̊ to 6̊. The present numerical result shows that the turbulent kinetic energy and turbulent intensity in the solar chimney decrease with the increase of the inclination of the passive wall. The effectiveness of the IPWSC design for enhancing the thermally driven ventilation has been confirmed. Additional simulations have been carried out with a standalone solar chimney model. The result shows that the standalone model over-predicts the mass flow rate compared to that predicted by the attached model. The average difference in the predicted mass flow rates between the standalone model and the attached model with inclination angles from 0̊ to 6̊ at a representative Rayleigh number of Ra = 1.36 × 10 14 is around 10%. [ABSTRACT FROM AUTHOR]

This paper studied the particle deposition in turbulent duct air flows with smooth and ribbed walls numerically. The RSM model with turbulent fluctuation correction and Lagrangian track method were adopted to investigate the particle deposition enhancement by ribbed surface. The air flow velocity profiles for both smooth and ribbed-ducts as well as particle deposition velocity on smooth wall obtained in the present simulation were validated by agreeing well with the previous related study data. Particle deposition is significantly enhanced by surface ribs, especially in turbulent diffusion and eddy diffusion-impaction regimes. It is found that the captures of turbulent eddies induced by ribs and entrainments of large turbulent kinetic energy (T.K.E.) to the wall are the main mechanism for deposition enhancement of small particles. Moreover, pressure drop-weighted efficiency ratio of particle deposition enhancement for ribbed surface is evaluated in this study. The efficiency ratio for ribbed surface can reach more than 100 for particle sizes 0.2–3 μm but only about 2–3 for particle sizes 20–50 μm. This study shows that the repeated ribs on the surface could be an effective and efficient choice for particle deposition enhancement, especially for micron-meter particles. [ABSTRACT FROM AUTHOR]

Comparative analysis of the results of solution of the steady-state Reynolds equations closed with the use of the shear-stress transfer model for the air fl ow in a divergent channel with suction of the air from the surface of the cylindrical central body positioned in the circular vortex cavity built in the lower wall of the channel with the corresponding experimental data has been performed. [ABSTRACT FROM AUTHOR]

Abstract: This work presents an experimental and numerical analysis of the flow distribution in the cooling duct of a commercial refrigerated display cabinet. The analysis is carried out on a channel mock-up, in which the air is forced through the evaporator by two fans. A steady-state isothermal numerical analysis of the flow distribution is performed with the commercial code ANSYS-CFX and the k-epsilon method is used to model the turbulence. The numerical results are compared with the 3D air velocity fields, taken on three planes placed at different heights inside the duct, by the stereoscopic Particle Image Velocimetry (PIV) technique. Once validated, the model allows a better comprehension of the flow mal-distribution source and its effect on the velocity field at evaporator exit. [Copyright &y& Elsevier]

Abstract: A numerical study of hydrogen turbulent diffusion flame structure is carried out in the pressure range of 1–10 atm with a special emphasis on mixing. The investigation is conducted under constant volumetric fuel and air flows. Mixing is characterized by mixture fraction, its variance and the scalar dissipation rate. The flow field and the chemistry are coupled by the flamelet assumption. Mixture fraction and its variance are transported by computational fluid dynamic (CFD). Computational predictions are analysed at two radial stations (the first one represent the near-field region and the second one the far-field region). The computational results indicate a deterioration of mixing with pressure rise. As a result, flame reaction zone becomes thicker. In addition, mixing and flame structure sensitivity to pressure are found to be high in the first location. Further analysis revealed that the gas becomes increasingly heavy with pressure rise, which hampered its ability to mix. [Copyright &y& Elsevier]

Abstract: The Jean-Marie Tjibaou Cultural Center, designed by Renzo Piano, a world renown Italian architect and a recipient of the Pritzker Architecture Prize, was described as a piece of “Ecological Architecture” in New Caledonia. This building is recognized by its sustainable ventilation design concept that implements the unique ten shell-like structures for aeration enhancement. This paper presents an approach using the computational fluid dynamics (CFD)-based simulations to compare the numerical predictions with the original architectural insight for a verification of the architect''s thinking in his realization of the design purpose. In the analysis, we consider the incompressible isothermal turbulent airflow to examine the interaction of the flow with the building for a better understanding of the wind-driven self-sustaining ventilation mechanism. We also propose a modified model via enlarging the aeration opening with the least blockages along the wind pathway. The simulated results indicate that the improved design substantially enhances the air-intake effectiveness and realizes a satisfactory pressure balance for the Tjibaou Cultural Center. [Copyright &y& Elsevier]

Parameters of the vortex air flow in an isothermal model of the cyclone chamber are studied. The effect of the air velocity in nozzles on the values and character of the distribution of pressure and tangential and longitudinal velocities of air in the chamber is determined. Numerical modeling of the flow is performed, and it is shown that numerical calculation by the k-w turbulence model is in agreement with experimental data. [ABSTRACT FROM AUTHOR]

Abstract: The paper addresses numerical simulation of turbulent two-phase flow in a long vertical tube and turbulent two-phase free jet formed at the tube outlet, analyzing agreement between the numerical results and the results of corresponding experimental investigation carried out earlier. In the numerical analyses conducted, gas phase was modeled as an air flow (having a mass flow-rate in the range of 1.25–4.00g/s), while the sand particles of two different sizes (0.25–0.30 and 0.8–1.0mm) represented a discrete phase (particle to gas mass flow ratio of 0.72–4.08) in the two-phase flow considered. Gas-particle interaction was analyzed based on the gas velocities in the particle-laden two-phase flow and the particle-free gas flow, calculated and measured at various locations along the longitudinal axis and radius of the jet. Mathematical model of continuous phase flow was developed based on the single phase flow models, with certain corrections introduced to account for the effects of particles in the flow. In the simulation model developed, the flow analyzed was modeled as a two-phase mixture, with Eulerian simulation used to account for the gas phase behavior and the Lagrangian simulation modeling the particle movement in the two-phase flow considered. In order to appropriately close the system of time-averaged equations, k–ε turbulent model, deemed the most reliable, was used. Phase coupling i.e. fluid-particle interaction was modeled using the PSI-CELL concept. The results obtained via numerical simulation have shown a good agreement with the experimental data acquired. [Copyright &y& Elsevier]

In present research, two turbulent opposed impinging air jets issuing from triangular nozzles with fixed and variable exit velocity ratios and different nozzle-to-nozzle distances have been studied numerically and then compared with rectangular and circular nozzles. The finite volume method has been applied for solving mass and momentum equations. The turbulence model being used here is k-ε RNG. Distributions of pressure, turbulence, kinetic energy and its dissipation rate in various regions especially on the impingement regions have been obtained with high accuracy. Study of the nozzle geometries has shown the advantage of triangular nozzles over other geometries. First, the triangle's base in nozzle geometry has an important role in our study case which, mixing two flows and regions with high turbulence intensity, directly depends on it. Second, our results show that circular and rectangular nozzles have less efficiency than triangular nozzles in mixing applications. Third and last, it was found that the radial jet being created by opposed jets has some similarities to free jets. In this investigation, air in standard atmospheric pressure has been applied as working fluid. [ABSTRACT FROM AUTHOR]

This paper presents numerical results and experimental data of the airflow inside a low-speed wind tunnel made of wood, with a square test section with length of 0.79 m and side of 0.2 m. The experimental tests were performed in the exit region of the tunnel test section using a Pitot tube and a hot wire anemometer. The numerical predictions were obtained by solving the Reynolds-Averaged Navier-Stokes (RANS) equations using the Shear Stress Transport k-ω turbulence model with the ANSYS-CFX® code. A numerical solution of a fully developed turbulent channel flow is also presented for comparison purposes. The numerical values of axial velocity were compared with the measurements in the exit region of the tunnel. The turbulent kinetic energy was compared with experimental data in the central point of the exit cross-section of the tunnel. The results are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the airflow in a room that contains a heat source is simulated numerically. The flow is considered turbulent and buoyant. The results of the mathematical model are validated with available experimental data at specific locations in the domain. A simple geometry is adopted, consisting of a room with a door that plays the role of both inlet–outlet for the fluid (air). At the centre of the room a methane burner is placed to serve as a heat source. The problem is simulated using two turbulence models, the well-known standard k–ε model and the RNG k–ε model, both modified to account for buoyancy effects on turbulence. The burner is considered as a volumetric heat source. It is concluded that the fire plume development as well as the distributions of velocity and temperature are reasonably well predicted. Following this conclusion, both models are also applied to a different, more complex geometry that consisted of two rooms communicating via a door, while the heat source was placed in the first room. Unfortunately, there are no experimental data to compare with for this case, but the results appear plausible. Finally, important design factors, such as mass flow rates and neutral-plane heights, are calculated utilizing the CFD results, and are compared with those obtained by well-known empirical correlations. It is concluded that the bi-directional flow existing through the burning-room vent is similarly predicted by both turbulence models; the RNG k–ε model leading to higher, and more accurate predictions of temperature variations within the hot upper layer, at least for the single-room case. [Copyright &y& Elsevier]

Abstract: Ripples and transverse dunes in areas of abundant sand supply increase in height and spacing as a function of time, grain size, and excess shear velocity. How and why each of these factors influence ripple and transverse dune size, however, is not precisely known. In this paper, the controls on the height and spacing of ripples and transverse dunes in areas of abundant sand supply are investigated using a numerical model for the formation of eolian bedforms from an initially flat surface. This bedform evolution model combines the basic elements of Werner''s [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107–1110.] cellular automaton model of dune formation with a model for boundary layer flow over complex topography. Particular attention is paid to the relationship between bed shear stress and slope on the windward (stoss) side of evolving bedforms. Nonlinear boundary layer model results indicate that bed shear stresses on stoss slopes increase with increasing slope angle up to approximately 20°, then decrease with increasing slope angle as backpressure effects become limiting. In the bedform evolution model, the linear boundary layer flow model of Jackson and Hunt [Jackson, P.S., Hunt, J.C.R., 1975. Turbulent wind flow over a low hill. Quarterly Journal of the Royal Meteorological Society 101, 929–955.], generalized to 3D, is modified to include the nonlinear relationship between bed shear stress and slope. Bed shear stresses predicted by the modified Jackson and Hunt flow model are then used to predict rates of erosion and deposition iteratively through time within a mass-conservative framework similar to Werner [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107–1110.]. Beginning with a flat bed, the model forms ripples that grow in height and spacing until a dynamic steady-state condition is achieved in which bedforms migrate downwind without further growth. The steady-state ripple spacing predicted by this model is approximately 3000 times greater than the aerodynamic roughness length of the initially flat surface, which is a function of grain size and excess shear velocity. Once steady-state ripples form, they become the dominant roughness element of the surface. The increase in roughness associated with ripple formation triggers the same bedform instability that created ripples, causing dunes to form at a larger scale. In this way, the numerical model of this paper suggests that ripples and dunes are genetically linked. Transverse dunes in this model have a steady-state height and spacing that is controlled by the effective roughness length of the rippled surface, which is shown to be on the order of 500 times greater than the original roughness length, but varies significantly with the details of ripple morphology. The model predictions for ripple and dune spacing and their controlling variables are consistent with field measurements from the published literature. The model of this paper provides a preliminary process-based understanding of the granulometric control of ripples and dunes in areas of abundant sand supply and unidirectional prevailing winds, and it argues for a genetic linkage between ripples and dunes via a scaling relationship between eolian bedform size and the aerodynamic roughness length. [Copyright &y& Elsevier]

Abstract: Gas–solid two-phase flow in 180° curved duct is simulated using a two-way coupling Eulerian–Lagrangian approach. Reynolds averaged Navier–Stokes equations (RANS) and four turbulence models namely; standard k–ε model, RNG (Renormalization Group) based k–ε model, Low-Re k–ε model and an extended version of the standard k–ε model are adopted. The effects of particle rotation and lift forces are included in the particle tracking model. The present predictions are compared with published experimental data for single-phase and two-phase flows. The comparisons show that the RNG based k–ε model predicts the flow behaviour better than other models. Furthermore, the particles concentration and velocity are compared very well with published data. The effects of inlet gas velocity, bend geometry, loading ratio and particle size on the flow behaviour and bend pressure drop are also discussed. The results show that the flow behaviour is greatly affected by these parameters. [Copyright &y& Elsevier]

Three-dimensional turbulent flow and dispersion of gaseous pollutants carbon monoxide (CO) and nitrogen oxides (NOx) in a road tunnel was modeled using the standard k– ε turbulence model and solved numerically using the finite volume method. Vehicle emissions were estimated from the measured traffic flow rates and modeled as banded line sources along the tunnel floor. The effects of fan ventilation and piston effect of moving vehicles on the airflow and pollutant dilution were examined. The numerical results reveal that a peak velocity exists near the tunnel floor due to the piston effect of vehicles. The cross-sectional concentrations of air pollutants are non-uniformly distributed and concentrations rise with downstream distance. The piston effect of vehicles can alone provide 25%–34% dilution of air pollutants in the tunnel, compounded 43%–70% dilution effect according to the ventilation condition. [ABSTRACT FROM AUTHOR]

Theoretical and computational fluid dynamical techniques are employed to predict the two-dimensional turbulent air flows which are created by an Aaberg slot exhaust hood, which is reinforced by a two-dimensional wall jet flow. The aim of the two-dimensional model is to numerically reveal the characteristics of the air flow in the central plane of the Aaberg workbench. A further development of the potential model is through the inclusion of the finite slot. We have found that the numerical results for the streamlines and the lines of constant speed produced by the potential flow model are in good agreement with those obtained when using the full turbulent flow model and the air velocity distribution predicted by both the potential and turbulent models agree very well with all the available experimental data. The comparison between the potential and the turbulent models reveals that the potential model has the advantage over the turbulent model in that there is much less uncertainty in the results obtained due to the more accurate specification of the boundary conditions on the open boundaries at large distances from the hood. [ABSTRACT FROM PUBLISHER]

The article presents studies about sound. Findings in the study "Experimental Investigation of the Acoustic Field in a Bluff-Body Combustor," by R. Sivakumar and S. R. Chakravarthy, suggested that the natural acoustic modes shift to follow the vortex shedding trend with the Reynolds number of the air-flow. The study "Thermo-Acoustic Stability of a Helicopter Gas Turbine Combustor Using Large Eddy Simulation," by G. Boudier et al., involved the compressible Large Eddy Simulation (LES) of turbulent reacting flows.