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To study the characteristics of nasal airflow in the presence of nasal cycle by computational fluid dynamics. CT scan data of a healthy Chinese individual was used to construct a three-dimensional model of the nasal cavity to be used as simulation domain. A sinusoidal airflow velocity is set at the nasal cavity entrance to reproduce the breathing pattern of a healthy human. There was a significant difference in the cross-sectional area between the two sides of the nasal cavity. Particularly, the decongested side is characterized by a larger cross-section area, and consequently, by a larger volume with respect to the congested side. The airflow velocity, pressure, and nasal resistance were higher on the congested narrow side. The temperature regulation ability on the congested narrow side was stronger than that on the decongested wider side. During the nasal cycle, there are differences in the nasal cavity function between the congested and decongested sides. Therefore, when evaluating the impact of various factors on nasal cavity function, the nasal cycle should be considered. [ABSTRACT FROM AUTHOR]

In order to study the problems of unreasonable airflow distribution and serious dust pollution in a heading surface, an experimental platform for forced ventilation and dust removal was built based on the similar principles. Through the similar experiment and numerical simulation, the distribution of airflow field in the roadway and the spatial and temporal evolution of dust pollution under the conditions of forced ventilation were determined. The airflow field in the roadway can be divided into three zones: jet zone, vortex zone and reflux zone. The dust concentration gradually decreases from the head to the rear of the roadway. Under the forced ventilation conditions, there is a unilateral accumulation of dust, with higher dust concentrations away from the ducts. The position of the equipment has an interception effect on the dust. The maximum error between the test value and the simulation result is 12.9%, which verifies the accuracy of the experimental results. The research results can provide theoretical guidance for the application of dust removal technology in coal mine. [ABSTRACT FROM AUTHOR]

Lagrangian stochastic models (LSM) are widely used to model the dispersion of sea spray droplets injected from the water surface into the marine atmospheric boundary layer (MABL) and for evaluation of the spray impact on the exchange fluxes between the atmosphere and the ocean. While moving through the MABL the droplets pass through the region of high gradients of air velocity, temperature and humidity occurring in the vicinity of the air–water interface. In this case, the applicability of LSMs constructed under the assumption of weakly inhomogeneous flows is questionable. In this work, we develop a Lagrangian stochastic model taking into account the strongly inhomogeneous structure of the airflow in MABL and, in particular, the anisotropy of turbulence dissipation rate. The model constants and the diffusion matrix coefficients are calibrated by comparison of the LSM prediction for the profiles of droplet concentration and the exchange fluxes of sensible and latent heat against the results of direct numerical simulation of turbulent, droplet-laden airflow over a waved water surface. [ABSTRACT FROM AUTHOR]

Multi-parameter study on the subsonic equilibrium air plasma flows in the cylindrical discharge channel of an induction RF-plasmatron IPG-3 with the maximum operating power of 1 MW is presented. Simulations are carried out by numerical solution of full Navier–Stokes equations coupled with a two-dimensional equation for high-frequency electric field; the discretization of the equations is performed on a staggered Cartesian mesh. An effective method for calculation of the transport coefficients for ionized multi-component air (including the plasma conductivity) in the temperature range 300–15000 K is applied, with the higher-order approximations by the Sonine polynomial in the Chapman–Enskog method. Simulation results are presented, including the flow fields, electric field, and thermodynamic parameters of the air plasma in the discharge channel of a high-power induction plasmatron. The results obtained reveal for the first time the structure and parameters of a plasma torch in a large-diameter (200 mm) discharge channel at powers up to 300 kW, providing the axial specific enthalpies at the channel outlet as high as 68 MJ/kg. [ABSTRACT FROM AUTHOR]

The smelting reduction of vanadium–titanium magnetite (VTM) with oxygen-rich side-blown bath smelting furnace (OSBF) is a promising process. However, the study on the behavior of gas–liquid multiphase flow in the OSBF in ironmaking process is deficient. In present work, a 3D simulation model of the OSBF is established to investigate the multiphase flow of gas–slag–metal in the furnace during the VTM smelting process. The bubbles motion, slag phase distribution, flow field distribution, and the flow status in the bath during the smelting process are obtained by combining the Coupled Level Set Volume of Fluid (CLSVOF) method and the Realizable k-ε model. The analysis of the characteristics of gas–slag–metal multiphase flow in the horizontal and vertical directions in the bath indicates that the gas and slag in the bath are evenly mixed, the fluctuation of the slag iron interface is subtle, and the turbulence of the molten iron layer is weak, which is conductive to the smelting process. In addition, the effects of primary air flow, slag layer thickness, and slag viscosity on the smelting process are also studied, and the appropriate operation conditions were recommended. This provides a theoretical basis for the operation and optimization design of the OSBF. [ABSTRACT FROM AUTHOR]

Results of numerical simulations of turbulent reacting flows in a channel with sudden expansion with due allowance for injection of hydrogen jets into a supersonic (M = 4) air flow are reported. The simulations are performed in a three-dimensional unsteady formulation with the use of the ANSYS Fluent software under the conditions of experiments performed in the IT-302M high-enthalpy wind tunnel. The computations predict a self-oscillatory regime with intense oscillations of pressure and integral heat release. The period-averaged pressure distribution is in reasonable agreement with the experimental measurements, and the frequency of pressure oscillations is within the range obtained in the experiments. Based on a detailed analysis of the flow characteristics within the full cycle of oscillations, the feedback mechanism responsible for the emergence of self-supported oscillations is refined. [ABSTRACT FROM AUTHOR]

Construction ventilation runs through the entire construction process of large underground caverns and is the key to ensuring construction progress and project safety. For the specific underground cavern group of pumped-storage power plants, a three-dimensional model is constructed, and the CFD method based on fluid mechanics theory is used to simulate the ventilation flow field of the underground cavern group. Through the comparison of the airflow in the main caverns and the air velocity distribution law, Quantitative analysis of the influence of the diameter of the ventilation shaft and the inclination of the shaft on the ventilation flow field shows that when the diameter of the ventilation shaft is 8 m and the inclination of the shaft is 80°, the ventilation effect in the underground cavern group is the best. Applying this scheme to engineering practice and conducting on-site tests, the average relative error of the measuring points is 11.32% by comparing the measured data and the simulation results, which verifies the correctness of the CFD method used. It provides reference value for studying the construction ventilation of underground caverns. [ABSTRACT FROM AUTHOR]

A mathematical model of the process of unsteady conjugate heat transfer of a thermionic thermal protection system during supersonic air flow around a spherically-blunted cone is investigated. Estimates of the effect of evaporation (emission) of electrons from the emitter surface on lowering the temperature of the composite shell of the thermoelectronic thermal protection are made. The influence of different angles of attack on heat transfer modes in the system of multielement thermionic thermal protection has been studied. Qualitative agreement of calculated results with the known data has been found. [ABSTRACT FROM AUTHOR]

A rotary dust collector that operates on the principle of a centrifugal separator has been developed. A feature of its design is the presence of a bypass recirculation channel of purified air with a flow regulator, two outlet pipes with flow unswirlers in the form of spiral channels. The calculation of the motion of dust particles with a density of 3000 kg/m3 and a diameter from 1 to 100 μm has been performed. Research has been carried out to improve the efficiency of the apparatus using a central compositional plan and to establish rational design and operation parameters of the mixer of recirculation air and air being purified. [ABSTRACT FROM AUTHOR]

Rainfall infiltration on a soil slope is usually an unsaturated seepage process that can be described by a water-air two-phase flow model. The effect of pore air pressure on rainfall infiltration has been widely recognized and validated by means of numerical simulations and laboratory experiments. However, whether a slope can actually seal pore air continues to be debated by researchers. In this study, a water-air two-phase flow model is used to simulate the rainfall infiltration process on a soil slope, and a field experiment is conducted to realistically test the sealing conditions of a slope. According to the numerical simulation, the areas of water and air flow in and out on the slope surface are relatively stable and can be classified as the "inhalation zone" and "overflow zone", respectively. Intermittent rainfall on the soil slope has an amplifying effect on pore air pressure because rainfall intensity is usually at the millimeter level, and it causes pore air pressure to reach the cm level. A field experiment was performed to determine whether a slope can realistically seal pore air and subsequently verify the regularity of rainfall infiltration. Air pressure sensors were buried in the slope to monitor the pore air pressures during the rainfall process. The monitoring results show that the pore air pressure in the slope changed, which indicates that the slope can seal air. Moreover, the amplification effects of intermittent rainfall on pore air pressure were observed for natural rainfall, which agrees well with the numerical simulation results. [ABSTRACT FROM AUTHOR]

Wall-mounted swirling ventilation is a new type of system in mechanized excavation faces with a dust suppression performance that is closely related to the blowing-to-suction flow ratio. Physical and simulation models were developed according to the No. C103 mechanized excavation face in the Nahe Coal Mine of the Baise Mining Bureau, Guangxi Province to optimize the blowing-to-suction flow ratio for wall-mounted swirling ventilation. Both the k-ε turbulence model and the discrete phase model were utilized to simulate airflow field structures and dust concentration distribution patterns at various blowing-to-suction flow ratios. The results suggest that higher blowing-to-suction flow ratios increase the airflow field disturbance around the working face and weaken the intensity of the axial air curtain. On the other hand, both the intensity of the radial air curtain and the dust suppression effect are enhanced. At a blowing-to-suction flow ratio of 0.8, the wall-mounted swirling ventilation system achieved the most favorable dust suppression performance. Both the total dust and respirable dust had their lowest concentrations with maximum efficiencies of reducing both types at 90.33% and 87.16%, respectively. [ABSTRACT FROM AUTHOR]

This paper describes a numerical simulation of vibrations of an elastic rod whose height is significantly greater than its transverse dimension and which is placed perpendicularly to the external flow and rigidly mounted on a substrate. Simulation is carried out in the ANSYS software package using bidirectional coupling technology. The natural frequencies and vibration modes of the rod are calculated. The airflow structure is analyzed and its features in the vicinity of the model are described. The process of exciting the vibrations of an elastic rod under the action of an external flow is investigated and its stress-strain state is determined. Vibration modes in the direction of an incident flow and in the transverse direction are determined. It is shown that, if the first natural frequency and the vortex shedding frequency reach close values, the amplitude of the rod vibrations in the transverse direction sharply increases to a value approximately equal to 0.06 of the rod height, which is followed by natural vibrations with a constant amplitude in the transverse direction and variable amplitude in the direction of the incident flow. [ABSTRACT FROM AUTHOR]

We consider the process of multistage technological recirculation of aspiration air into transfer chutes, i.e., the return of aspirated air from the shelters of the technological equipment back to the technological process with an aim to reduce energy losses by creating aerodynamic drag in the path of motion of ejection air and maintaining the required values of thermal parameters in the equipment. It is recommended to equip the chutes with single-stage recirculation seals with minimum possible angles of air feed against the flow ejected by the reloaded bulk material, which would increase the energy efficiency of ventilation systems and decrease the amount of harmful substances ejected into the atmosphere. [ABSTRACT FROM AUTHOR]

Numerical simulations were conducted to study the effects of the pulverized-coal bias distribution in the primary air on the coal combustion and NOx generation characteristics of a 600-MW down-fired boiler with multiple-injection and multiple-staging combustion technology. The total pulverized-coal in the primary air was kept constant, and the ratio of the pulverized-coal mass flux in the fuel-rich coal/air flow to the total pulverized-coal mass flux (RPR) was set as 60%, 70%, 80%, and 90%. By changing the RPR, the excess air coefficient of the fuel-rich flow was adjusted from 0.700 to 0.467. It was found that numerical simulation results were almost in agreement with cold modeling and in situ experimental results respectively, including the flow fields in the lower furnace at the RPR of 80% and the heating processes for the fuel-rich coal/air flow at the RPR of 90%, which verified the rationality of the numerical model and the grid. The simulation results indicated that the change of RPR has little effect on the symmetry of the flow field in the furnace. With the increase of the RPR from 60 to 90%: (1) the maximum airflow declination angle near the tertiary air slot decreased from 71 to 66°, which indicates that the downward airflow penetration depth gradually decreased; (2) the ignition distance of the fuel-rich coal/air flow decreased from 1.2 to 0.9 m, and the high-temperature area in the furnace hopper decreased and the position gradually moved away from the hopper water walls; (3) the oxygen consumption rate at the initial combustion stage constantly accelerated, and the fuel NOx generation rate under the fuel-rich flow nozzle increased first and then decreased; (4) the NOx emissions at the furnace exit dropped from 778 to 662 mg/m3 at 6% O2, and the carbon in the fly ash decreased from 5.87 to 5.52%. Increasing the RPR reasonably controlled the excess air coefficient of the fuel-rich flow, and realized the high-efficiency combustion in the furnace and the reduction of NOx emissions simultaneously. [ABSTRACT FROM AUTHOR]

In this study, an intensive simulation platform is developed and implemented to simulate the three stages in the operational cycle of the liquid-fueled pulse detonation engine. The three stages encompass the liquid fuel injection and evaporation process, deflagration-to-detonation transition process, and detonation propagation process. The Lagrangian–Eulerian approaches are employed to model the discrete liquid fuel droplets and the continuous vapor phase, respectively. The breakup and evaporation of liquid droplets are modeled using sub-models, while the interactions between the liquid droplets and the vapor phase are expressed through the two-way interaction models. The Jet-A liquid fuel is injected into the detonation chamber as the fuel for the engine, while the air flow is used as the oxidizer. A reduced chemical kinetic model of fuel/air is used to model the combustion process. The simulation platform is systematically validated against the experimental data for every stage of the operating cycle. To study the influence of the inlet and operating conditions, the numerical simulations are performed for three different operating conditions, which are the change in inlet air temperature, the change in inlet air flow velocity, and the change in liquid fuel mass flow rate. The obtained results indicate that the mass fraction of pre-vaporization of fuel plays an important role in the successful DDT process and/or detonation onset. The deflagration can successfully transit to detonation for both the cases of complete and incomplete vaporization of the liquid droplets inside the detonation chamber. The deflagration cannot successfully transit to detonation for the case of too lean or too rich fuel vapor in the mixture. The calculated burning temperature and Chapman–Jouguet (C–J) detonation velocity are slightly lower in the cases of the incomplete vaporization when compared to the complete vaporization cases. In addition, our numerical results show that the burning process occurs in two stages in the incomplete vaporization case: The first burning stage plays a main role in the successful DDT process, while the second burning stage only plays the role of augmentation. [ABSTRACT FROM AUTHOR]

By considering the parametric variation of an individual boron particle in a boron agglomerate, the heat transfer, and the mass transfer between the boron particle agglomerate and the surroundings, an ignition and combustion model of a boron agglomerate is proposed. An experiment of a ramjet combustor using a boron-based slurry fuel is designed and operated for the purpose of validating the ramjet configuration and verifying the combustion of boron particles. Then a mathematical model for simulating a multiphase reacting flow within the combustor of a boron-based slurry fuel ramjet is established. Kerosene droplets and boron particles are injected discretely to the burner flowfield, and their trajectories are traced using the discrete phase model. The influence of the agglomerate size, bypass air mass flow rate, initial boron particle diameter, and boron particle content on the combustion efficiency of the slurry fuels is analyzed in detail. The results show that the combustion efficiency decreases with an increase in the agglomerate radius, initial boron particle diameter, and boron particle content. The combustion efficiency increases with an increase in the mass flow rate of bypass air. If the agglomerate diameter is greater than 100 μm or the bypass air mass flow rate is smaller than 50 g/s, the boron particles cannot be fully burned. [ABSTRACT FROM AUTHOR]

The steady flow test rig is a device for studying the influence of the intake and exhaust ports of the cylinder head on the flow motion inside the cylinder in internal combustion engines. In this paper, the swirl flow as a critical mixing mechanism inside the cylinders of internal combustion engines has been investigated by the vane type swirl meter measurement system in the steady state flow test rig with experimental and numerical simulation methods. In numerical simulations, the in-cylinder flow in the presence of the swirl meter is modeled using the multiple reference frame (MRF) method. Three dimensional numerical simulations are applied by using the finite volume method. The simulation results show good agreement with experimental results and showed to be a good alternative to compensate the limitations of the operating conditions of the test rig. In this work, a linear correlation between the rotational speed of the swirl meter and the torque is found. The study also showed that by increasing the pressure difference between the inlet and outlet of the cylinder, the speed of the in-cylinder swirl flow increased where a correlation between swirl flow velocity and pressure difference is proposed using an exponential function. The in-cylinder swirl flow velocity was determined for different test pressure and for different distance the vane-type swirl meter from cylinder head and it was seen that it is maximum when the vane-type swirl meter is located at 1.3 D from cylinder head for different test pressure. [ABSTRACT FROM AUTHOR]

In order to ensure safe production and occupational health at a large-mining-height fully mechanized mining face in a coal mine, the present study firstly establishes an airflow-dust coupled model based on gas/solid two-phase flow equations and combines numerical simulation and field measurement for analyzing the dispersion pattern of dust particles with various sizes for different coal cutter locations. Results show that, due to the existence of drums, airflow deviates from the original direction and enters the footway. Driven by the airflow, dust particles enter the footway at different locations depending on coal cutter locations. The coal-cutting location (denoted as Prl) and the location where dust particles enter the footway (denoted as Pdt) are correlated as follows: Pdt(Prl) = − 0.0007Prl2 + 1.0343Prl − 3.3536. When Prl < 55 m, dust particles produced by the rear drum during coal cutting enter the footway earlier than those produced by the front drum, leading to the first and second dust concentration peaks in respiratory zones of footway. Dust suppression effects are assessed in these regions based on the first and second dust concentration peaks. Due to the superposition of the concentration fields associated with dust particles 2.5, 7, and 20 μm in diameter, dust concentration 25 m down the leeward side of the coal cutter can reach 1440 mg/m3. The concentration of dust particles with a diameter of 40 μm drops steadily and approaches 0 at the return corner. The dust particles 80 μm in diameter are fully settled within 22 m down the leeward side of the coal cutter. A comparison with the field measurement indicates that the present simulation results are highly accurate.Graphical abstract [ABSTRACT FROM AUTHOR]

Numerical simulation was carried out in three-dimensional and axisymmetric formulations for the hydrodynamics and mixing of bottom- and tangentially blown air with different temperatures in a cyclone chamber with local supply of tangentially blown air. To calculate vortex flows in the chamber, use was made of the most popular turbulence models k-ε, k-ω, and SA. It has been established that the best correspondence between the results of calculation and experimental data on hydrodynamic parameters (velocity and pressure) and air mixing under nonisothermal conditions is furnished by the k-ε and k-ω models of turbulence. Good agreement of the results of numerical simulation of vortex flows in the indicated chamber in three-dimensional and axisymmetric formulations has been obtained. [ABSTRACT FROM AUTHOR]

Direct numerical simulations (DNS) are performed to investigate the effect of the interface position of water-air flow on turbulence statistics and flow structures in wall-bounded water-air turbulent flow through a straight channel. Water depths of 90 and 180 viscous wall units, referred to as shallow-water and deep-water cases, respectively, are examined. Water-to-air density and viscosity ratios of 831.7 and 55.56 are considered to model a realistic flow condition at temperature of 25 °C and pressure of 1 atm. The Reynolds number and Froude number are set to 180 and 1.22 x 10-4, respectively, for both shallow-water and deep-water case, based on the friction velocity at the bottom wall, the half depth of the channel, and water density and viscosity. The Navier-Stokes equations are solved using a time-splitting projection method on an octree grid structure, while the deformation of the interface between water and air is computed using a volume-of-fluid method. With the presence of the water-air interface, velocity profiles in deep-water and shallow-water cases are found to slightly deviate from the log-law profile for a single phase turbulent flow in a channel. The deviation is magnified when the interface is placed closer to the log-law region. Turbulent velocity fluctuations in the water stream are found to be associated with quasi-streamwise vortices and hairpin vortices. The quasi-streamwise vortices which are attached close to the wall are found in both deep-water and shallow- water cases. However, the hairpin vortices of which leading portions are lifted away from the wall are found to be diminished in the shallow-water case while they are clearly observed in the deep-water case. [ABSTRACT FROM AUTHOR]

The article focuses on the robustness of a CFD-based procedure for the quantitative evaluation of the nasal airflow. CFD ability to yield robust results with respect to the unavoidable procedural and modeling inaccuracies must be demonstrated to allow this tool to become part of the clinical practice in this field. The present article specifically addresses the sensitivity of the CFD procedure to the spatial resolution of the available CT scans, as well as to the choice of the segmentation level of the CT images. We found no critical problems concerning these issues; nevertheless, the choice of the segmentation level is potentially delicate if carried out by an untrained operator. [ABSTRACT FROM AUTHOR]

With the use of the domestic software suite of computational hydrodynamics Flow Vision based on application of the method of control volumes, numerical simulation of air composition and delivery by a centrifugal compressor employed for supercharging a piston engine has been carried out. The head-flow characteristics of the compressor, as well as the 3D fields of flow velocity and pressure distributions in the elements of the compressor flow passage, including the interblade channels of the impeller, have been obtained for various regimes. In the regimes of diminished air flow rate, surging phenomena are identified, characterized by a return flow. The application of the technique of numerical experiment will make it possible from here on to carry out design optimization of the compressor flow passage profile and thus to improve its basic characteristics - the degree of pressure increase, compressed air flow rate, and the efficiency - as well as to reduce the costs of the development and production of compressors. [ABSTRACT FROM AUTHOR]

An analysis of the convective heat exchange in the separation air and oil flows in banks of heated round tubes and their hydraulic losses at Reynolds numbers changing in a wide range from 100 to 400 for the laminar flow and from 10 to 8·10 for the turbulent fl ow has been performed. For solving the Navier-Stokes and energy equations, multiblock computational technologies realized in the VP2/3 package and original procedures for correction of the pressure gradient in a fl ow and its mean-mass temperature were used. The Reynolds-averaged Navier-Stokes equations were closed using the Menter shear-stress transfer model modified with account for the curvature of streamlines within the framework of the Leshtsiner-Rody approach with an Isaev-Kharchenko-Usachov constant equal to 0.2. The results of numerical simulation were compared with the corresponding experimental data of A. Zhukaukas. The dependence of the local and integral characteristics of a fl ow of a heat-transfer agent in a staggered bank of round tubes on the properties of this agent was determined. [ABSTRACT FROM AUTHOR]

We present detailed numerical results for two-dimensional viscous air-water flow of a non-linear progressive water wave when the speed of the opposing wind varies from zero to 1.5 times the wave phase speed. It is revealed that at any speed of the opposing wind there exist two rotating airflows, one anti-clockwise above the wave peak and one clockwise above the wave trough. These rotating airflows form a buffer layer between the main stream of the opposing wind and the wave surface. The thickness of the buffer layer decreases and the strength of rotation increases as the wind speed increases. The profile of the average $$x$$ -component of velocity reveals that the water wave behaves as a solid surface producing larger wind stress compared to the following-wind case. [ABSTRACT FROM AUTHOR]

In this paper, a review is presented on the experimental investigations and the numerical simulations performed to analyze the thermal-hydraulic performance of the air-cooled heat exchangers. The air-cooled heat exchangers mostly consist of the finned-tube bundles. The primary role of the extended surfaces (fins) is to provide more heat transfer area to enhance the rate of heat transfer on the air side. The secondary role of the fins is to generate vortices, which help in enhancing the mixing and the heat transfer coefficient. In this study, the annular and plate fins are considered, the annular fins are further divided into four categories: (1) plane annular fins, (2) serrated fins, (3) crimped spiral fins, (4) perforated fins, and similarly for the plate fins, the fin types are: (1) plain plate fins, (2)wavy plate fins, (3) plate fins withDWP, and (4) slit and strip fins. In Section 4, the performance of the various types of fins is presented with respect to the parameters: (1) Reynolds number, (2) fin pitch, (3) fin height, (4) fin thickness, (5) tube diameter, (6) tube pitch, (7) tube type, (8) number of tube rows, and (9) effect of dehumidifying conditions. In Section 5, the conclusions and the recommendations for the future work have been given. [ABSTRACT FROM AUTHOR]

A numerical model has been used to characterize the development of a region of enhanced cooling in an alpine valley with a width of order $$10$$ km, under decoupled stable conditions. The region of enhanced cooling develops largely as a region of relatively dry air which partitions the valley atmosphere dynamics into two volumes, with airflow partially trapped within the valley by a developing elevated inversion. Complex interactions between the region of enhanced cooling and the downslope flows are quantified. The cooling within the region of enhanced cooling and the elevated inversion is almost equally partitioned between radiative and dynamic effects. By the end of the simulation, the different valley atmospheric regions approach a state of thermal equilibrium with one another, though this cannot be said of the valley atmosphere and its external environment. [ABSTRACT FROM AUTHOR]

Complex topography modifies local weather characteristics such as air temperature, rainfall and airflow within a larger regional extent. The Cape Peninsula around Cape Town, South Africa, is a complex topographical feature responsible for the modification of rainfall and wind fields largely downstream of the Peninsula. During the passage of a cold front on 2 October 2002, an extreme wind event associated with tornado-like damage occurred in the suburb of Manenberg, however synoptic conditions did not indicate convective activity typically associated with a tornado. A numerical regional climate model was operated at very high horizontal resolution (500 m) to investigate the dynamics of the event. The model simulated an interaction between the topography of the peninsula and an airflow direction change associated with the passage of the cold front. A small region of cyclonic circulation was simulated over Manenberg that was embedded in an area of negative vorticity and a leeward gravity wave. The feature lasted 14 min and moved in a north to south direction. Vertically, it was not evident above 220 m. The model assessment describes this event as a shallow but intense cyclonic vortex generated in the lee of the peninsula through an interaction between the peninsula and a change in wind direction as the cold front made landfall. The model did not simulate wind speeds associated with the observed damage suggesting that the horizontal grid resolution ought to be at the scale of the event to more completely understand such microscale airflow phenomena. [ABSTRACT FROM AUTHOR]

The paper presents numerical simulations of water infiltration in unsaturated porous media containing coarse-textured inclusions embedded in fine-textured background material. The calculations are performed using the two-phase model for water and air flow and a simplified model known as the Richards equation. It is shown that the Richards equation cannot correctly describe flow in the presence of heterogeneities. However, its performance can be improved by introducing appropriately defined effective capillary and permeability functions, representing largescale behaviour of the heterogeneous medium. [ABSTRACT FROM AUTHOR]

In this work a prediction was numerically modeled for a catalytically stabilized thermal combustion of a lean homogeneous mixture of air and hydrogen. The mixture flows in a narrow rectangular channel lined with a thin coating of platinum catalyst. The solution using an in-house code is based on the steady state partial differential continuity, momentum and energy conservation equations for the mixture and species involved in the reactions. A marching technique is used along the streamwise direction to solve the 2-D plane-symmetric laminar flow of the gas. Two chemical kinetic reaction mechanisms were included; one for the gas phase reactions consisting of 17 elementary reactions; of which 7 are forward-backward reactions while the other mechanism is for the surface reactions-which are the prime mover of the combustion under a lean mixture condition-consisting of 16 elementary reactions. The results were compared with a former congruent experimental work where temperature was measured using thermocouples, while using PLIF laser for measuring water and hydrogen mole fractions. The comparison showed good agreement. More results for the velocities, mole fractions of other species were carried out across the transverse and along the streamwise directions providing a complete picture of overall mechanism-gas and surface-and on the production, consumptions and travel of the different species. The variations of the average OH mole fraction with the streamwise direction showed a sudden increase in the region where the ignition occurred. Also the rate of reactions of the entire surface species were calculated along the streamwise direction and a surface water production flux equation was derived by calculating the law of mass action's constants from the concentrations of hydrogen, oxygen and the rate of formation of water near the surface. [ABSTRACT FROM AUTHOR]

For suppressing the automotive troubles like an overheating of the drum/disc brake units or the in-wheel motor devices, authors propose the new automotive wheel with the blade shape spokes, which can work as the cooling fan, by use of the blade design procedure of the turbomachinery. In this paper, the prototype automotive wheels with the centrifugal or axial type blades were prepared to confirm the flow generation by proposed wheels experimentally and numerically, as the preliminary step. The proposed wheel brings the increase of the air flow through the wheel compared with the traditional wheel, which has the rectangle shape spokes. At a same time, the required power for the rotation wheel rotation with cooling fan also increase about 2-4% of the traditional one. Furthermore, the swirling inlet flow, which generates by the rotating cylindrical rim, may greatly influences the discharge performance of the wheel with the axial blades. [ABSTRACT FROM AUTHOR]

The potential of using the Euler equations to numerically simulate the evolution of localized energy deposition zones interacting with a normal shock in quiescent air and in a supersonic channel flow is demonstrated. Simulation results are compared with available experimental data for an optical discharge in quiescent air and with results calculated for a supersonic flow using the Navier-Stokes equations with allowance for real gas effects. The possibility of predicting gasdynamic effects using the T- and q-models of energy deposition for perfect gas is justified. The variation of the gasdynamic structure and flow parameters near an energy deposition zone developing in a quiescent medium and interacting with a normal shock is analyzed in detail for different energy deposition powers. [ABSTRACT FROM AUTHOR]

In this study, a novel cooling strategy through ventilating ambient air to the front surface of the hot chips of the high power light-emitting diodes (LEDs) was proposed to tackle the ever tough issues facing the conventional thermal management approaches. Preliminary thermal resistance analysis, numerical simulation and conceptual experiments were carried out to evaluate the cooling performance thus enabled. In the system analysis, a thermal network model was established to characterize the thermal resistance of an ordinary high power LED light and that of the newly proposed light module. Through ventilating the high speed ambient airflow directly onto the chip surface, the thermal resistance of the whole light could be evidently reduced and additional pathway was thus opened for releasing heat from the chips. Further, three-dimensional finite volume simulations were adopted to investigate the temperature distribution of the new light. It was found that even without heat sink or active cooling at the back part of the LED light, the new method via cooling the front part still works well. Lastly, a conceptual experiment was performed, which again demonstrated that cooling the LED at its front surface suggests an effective way to maintain the safe running of LED light within an allowable temperature scale just as cooling the light at the back part. The present method initiates a new way for future thermal management of high power LEDs. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation on the momentum and thermal characteristics of an intercooler connection hose that is in use in the 1.3 SDE 75 CV type FIAT engine. Computational analyses are carried out with ANSYS FLUENT v.12.0.1, where both stationary and vibrating scenarios are handled. The work is structured in accordance with the 'Subsystem Functional Description for Charge Air Hoses Fiat 225 Euro 5' FIAT standard, where the air mass flow rate, temperature, and gage pressure at the hose inlet are identified as $$ {\mathop m\limits^ \cdot }$$ = 0.085 kg/s, T = 90°C, and P = 130 kPa, respectively. In the stationary case, it is determined that the pressure loss value in the air domain of the hose is Δ P = 1.50 kPa; moreover, the corresponding data for the temperature drop is Δ T = 0.80°C. Vibration is characterized by employing simple harmonic motion at the engine side of the hose. The fluid-solid interaction methodology showed that pressure loss values grow due to vibration; moreover, the impact of vibration came out to generate diverse fluctuation schemes at different sections of the hose. [ABSTRACT FROM AUTHOR]

This study has been conducted to investigate numerically the characteristics of train-induced unsteady airflow in a subway tunnel. A three-dimensional numerical model using the dynamic layering method for the moving boundary of a train is applied. The validation of the present study has been carried out against the experimental data obtained by Kim and Kim [1] in a model tunnel. After this, for the geometries of the tunnel and subway train which are very similar to those of the Seoul subway, a three-dimensional unsteady tunnel flow is simulated. The predicted distributions of pressure and air velocity in the tunnel as well as the time series of mass flow rate at natural ventilation ducts reveal that the maximum exhaust mass flow rate of air through the duct occurs just before the frontal face of a train reaches the ventilation duct, while the suction mass flow rate through the duct reaches the maximum value just after the rear face of a train passes the ventilation duct. The results of this study can be utilized as basic data for optimizing the design of tunnel ventilation systems. [ABSTRACT FROM AUTHOR]

Personalized ventilation (PV) is aimed to improve the quality of inhaled air by delivering clean, humidified and temperature-controlled air directly to occupants' breathing zone. The purpose of this paper is to investigate the effect of PV devices on the concentrations of volatile organic compounds (VOCs) emitted from carpet and the temperature around an occupant in an office. Numerical simulations were conducted using the computational fluid dynamics (CFD) commercial software FLUENT 6.3 for solving the continuity, momentum, energy, turbulence and concentration equations, and the simulation results were validated against the existing experimental data [1]. Personal exposure effectiveness (PEE) and manikin-based equivalent temperature change (ΔT) were used as indices to evaluate the performance of the PV. The results showed that the existence of the PV device greatly influenced the temperature and VOCs distributions around the occupant, but had little effect on those in the other parts of the office. Two evaluation indices increased with an increase of air flow rate. However, PV's airflow rate had larger influence on Manikin-based equivalent temperature change than that on personalized exposure effectiveness. The ventilation strategies had a great influence on the two evaluation indices, and both of them decreased with an increase of ventilation rate. The findings of this research could contribute to the reduction of energy consumption and the improvement of utilization of PV devices. [ABSTRACT FROM AUTHOR]

The lower concentration limit of flammability of hydrocarbon-air mixtures has been studied experimentally and by numerical simulation. Simulation using a detailed mechanism of chemical reactions has shown that calculations results are in good agreement with experimental data on the effect of water vapor on the lean concentration limit of flammability of hydrocarbon mixtures with air. The presence of water vapor at low concentrations in the mixture does not affect the lower concentration limit of flammability, but, at the same time, significantly changes the flame propagation velocity. Key words: concentration limits of flammability, opposed-jet premixed flame, hydrocarbons. [ABSTRACT FROM AUTHOR]

An air flow past a single triangular sail-type blade of a wind turbine is analyzed by numerical simulation for low velocities of the incoming flow. The results of numerical simulation indicate a monotonic increase in the drag force and the lift force as functions of the incoming flow; empirical dependences of these quantities are obtained. [ABSTRACT FROM AUTHOR]

In this paper, several methods of incorporating anthropogenic heat release into the boundary layer are compared. The best scheme was one that included anthropogenic heat release in both the surface energy balance equation and the thermodynamic equations. In addition, it included diurnal variations and a distribution of heat based on building concentrations. We further investigated the influence of anthropogenic heat release on urban boundary layer structure and the urban heat island, and found that the contribution of anthropogenic heat release to the urban heat island is greatest in the evening and at night, and least at noon. The daily average contribution ratio of anthropogenic heat to urban heat island intensity in the winter is 54.5%, compared with just 43.6% in the summer. Anthropogenic heat strengthens the vertical movement of urban surface air flow, changing the urban heat island circulation. It also makes the urban boundary layer more turbulent and unstable, especially in the morning and evening. The degree of influence of anthropogenic heat release on local boundary layer structure depends on its importance to the surface energy budget. [ABSTRACT FROM AUTHOR]

Crisis phenomena arising in a subsonic air flow around a thick airfoil with vortex cells have been numerically simulated in the process of solving the nonstationary equations of mass and energy conservation and Reynolds equations closed by a model of shear-stress transfer with the use of the finite-volume factorization method. [ABSTRACT FROM AUTHOR]

Abstract.: A bridge built inside the reversed flow region of a sand dune will change the characteristics of wind-sand movement in this region. The Reynolds-averaged Navier-Stokes simulation and discrete particle tracing are used to simulate the wind-sand movement around a sand dune with a bridge built inside the reversed region. Three cases with different bridge positions are studied. The results show that 1) compared with the isolated dune case, a tall bridge built at the leeward toe leads to an increase in the deposition rate on the leeward slope and a longer reversed flow region downstream of the sand dune; meanwhile, the high speed of crosswind on the bridge indicates that some measures should be taken to protect trains from strong crosswind; 2) a low bridge at the leeward toe has little effect on the sand deposition and reversed flow region of the dune; however, low sand transport rate and crosswind speed on the bridge show that anti-crosswind/sand measures should be taken according to the actual situation and 3) a low bridge on the leeward slope has little effect on the length of reversed flow region, however, high crosswind speed and sand flux on the bridge reveal the need of anti-crosswind/sand measures on the bridge. Moreover, the bridges in the reversed flow region increase the sand flux near the leeward crest; as a result, the moving patterns of the sand dune are changed.Graphical abstract: [ABSTRACT FROM AUTHOR]

We investigate the average turbulent wind field over a barchan dune by means of Computational Fluid Dynamics. We find that the fractional speed-up ratio of the wind velocity over the three-dimensional barchan shape differs from the one obtained from two-dimensional calculations of the airflow over the longitudinal cut along the dune's symmetry axis - that is, over the equivalent transverse dune of same size. This finding suggests that the modeling of the airflow over the central slice of barchan dunes is insufficient for the purpose of the quantitative description of barchan dune dynamics as three-dimensional flow effects cannot be neglected. [ABSTRACT FROM AUTHOR]