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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]

Contemporary high pressure ratio centrifugal compressors have a narrow stable operating. In order to achieve a wider stable operating region, some anti-surge measures can be used, such as an internal recirculation channel (IRC). This article presents a study of the airflow in IRC of a centrifugal compressor. A model of such channel was designed and manufactured in order to investigate the influence of various IRC inlet slot geometry on air flow parameters. Numerical simulation of the airflow for selected variants was also performed. Results of the simulation together with results of the experiment enable us to analyse the airflow in the area of the inlet slot and to find out its most suitable geometry. [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]

Abstract: Punched longitudinal vortex generators (LVGs) were employed to enhance air-side heat transfer on the wavy fin surface of flat tube used in direct air-cooled condenser. The heat transfer enhancement of four types of the longitudinal vortex generators with different attack angles were compared by numerical simulations. It was found that the delta winglet pair with attack angle 25° could reach the greatest performance evaluation criteria (PEC) under the conditions of the inlet air flow velocity varied from 1m/s to 5m/s. The influences of locations on the wavy fin surface and the row number of the longitudinal vortex generators were also discussed. One delta winglet pairs at the middle of the wavy fin surface and the minimum row number, n =1, with the average PEC is 1.23, has the best heat transfer performance of all conditions, which can be recommended for practical applications. Experimental study in wind tunnel with flow field visualization by Particle Image Velocimetry (PIV), as well as the numerical simulations verified that the delta winglet pairs can generate obvious longitudinal vortex pairs at the down-sweep zone, which can enhance the heat transfer between the cooling air flow and heated wall surface with acceptable pressure loss. [Copyright &y& Elsevier]

• Direct numerical simulation of droplet evaporation without any empirical parameter. • Identification of a sharp layer of interface cells for occurrence of phase change. • Algebraic compressive differencing scheme to maintain high resolution of interface. • Satisfactory prediction of droplet evaporation for a wide range of cases. • Sessile droplets gain averagely 29 percent of heat for evaporation from ambient gas. This study presents a sharp-interface algebraic volume-of-fluid (SA-VOF) approach towards direct numerical simulation of evaporating droplets in a finite-volume framework. An interface identification scheme is introduced to determine a sharp layer of interface cells where liquid-vapor phase change occurs. The rate of vaporization is directly computed from the local gradient of the vapor mass fraction at the interface without any tuning parameter in the evaporation model. In addition, a modified compressive differencing scheme is employed to maintain high resolution of the interface. A solver based on the SA-VOF approach is developed and validated by several case studies including the Stefan problem for evaporation in one dimension, evaporation of sessile droplets in the constant contact angle mode, and evaporation of droplets suspended in a flowing air stream. Comparisons between numerical predictions and either analytical solutions or experimental data show that the SA-VOF approach not only computes the evaporation rate with high accuracy but also ensures highly resolved liquid-vapor interface. The solver demonstrates the capability in revealing minute details of the complex characteristics associated with droplet evaporation. [ABSTRACT FROM AUTHOR]

With increasing urbanization, urban air pollutants are becoming more and more relevant to human health. Here, combined with meteorological observation data, a numerical simulation of typical urban blocks in Shanghai was carried out to understand the spread of air pollutants caused by road traffic sources (ground–level and viaduct–level). Firstly, we analyzed the wind environment characteristics. Then, we quantitatively analyzed the pollutant distribution profiles and the contributions of two pollutant sources (PSV). Finally, we analyzed seven urban morphological parameters based on ventilation efficiency indices. Results revealed the following. (1) Ventilation patterns within the architectural complex are determined by local geometry; (2) Pollutants released at ground level were dominant when the Z–plane < 8 m high, and pollutants released from the viaduct source were 0.8–6.1% higher when the Z–plane ≥ 8 m high; (3) From ground level to a height of 60 m, the spatially–averaged normalized concentration (C*) tended to decrease gradually with distance from the source. C* increased irregularly with an increase in distance between 60 m and 86 m. Above 86 m, C* tended to increase linearly; (4) Vertical profiles of C* around buildings were building–specific, and their rate of change was inconsistent with height increases. In general, the correlations between C* and VRw, and between C* and KEturb were larger on the windward side of PSV upstream buildings than on the leeward side. Buildings downstream of the PSV showed the opposite situation; (5) At pedestrian level, the seven urban morphological parameters had no significant correlation with VRw, Cir*, and Czs*. [ABSTRACT FROM AUTHOR]

This study investigates the mixing processes of liquid jets in supersonic crossflows at a Mach number of 2.1 by using numerical simulations that employ the Coupled Level-Set/Volume-of-Fluid (CLSVOF) method, which is based on the Delayed Detached Eddy Simulation (DDES). The instantaneous spray morphology from the simulations agreed well with the experimental data. The spray presents the 'Ω' shape when viewed from the front, and the maximum error in the penetration depth was 15% from a side perspective. The direction of the air movement determined the shape of the liquid column shearing and breaking. In turn, the breaking process of the liquid jet significantly affects the structure of the air flow. Three-dimensional flow around the liquid column occurred when the supersonic incoming flow impinged on the liquid column, ultimately forming counter-rotating vortex pairs (CVP) in the inner region of the spray. Evolution of the reverse vortex pair accelerated the mixing process of the spray. Single liquid jet was used as a basis to further study double jets in Mach 2.1 airflow. The results show that the breaking length and penetration depth of the downstream jet are significantly improved. [ABSTRACT FROM AUTHOR]

The current study highlights the superiority of nozzles with forwarding airflow to produce the commingled yarns for thermoplastic composite applications. A new cost-effective nozzle that can produce good quality commingled yarns at low air pressure is introduced. 3D CFD simulation and experimental studies are conducted to investigate the effect of aerodynamics of three different cylindrical nozzle configurations (CONF) on the commingling process efficiency. Nozzle CONF I and II work on backwards airflow principles among these configures, while CONF III functions with forwarding airflow. Commingling process efficiency of nozzle designs is analysed in terms of vorticity magnitude, turbulence kinetic energy, turbulence intensity and radial velocity values obtained from the simulation study. Additionally, the structure of hybrid yarns is qualitatively analysed to support the simulation study. The study concludes that nozzle CONF I and III holds the excellent potential of mixing both reinforcement and matrix filaments across the yarn structure. In addition, these nozzles can form stable nips in the yarn structure and make the textile preforming effortless. Nozzle CONF III offers better yarn quality parameters over other nozzles at low processing pressure. [ABSTRACT FROM AUTHOR]

The flow of products through the aft-end of a detonation combustor is intrinsically unsteady, ultimately resulting in periodic and nonuniform flow parameters at the exit plane of a rotating detonation combustor. Therefore, the integrated design of the nozzle and combustion chamber is an important challenge in rotating detonation engines (RDEs). This paper describes a thorough three-dimensional numerical simulation of a hydrogen–air rotating detonation combustor with/without an aerospike nozzle and investigates the nozzle flow without a combustor. The simulation results allow us to analyze the coupling characteristics of the rotating detonation combustor and the aerospike nozzle. The new features of the shock wave dynamics and expansion characteristics in the nozzle with/without an integrated RDE combustor are compared. For the same rotating detonation combustor exit, the propagation mode of the detonation wave and backpressure in the RDE combustor exit are affected by the aerospike nozzle. The intensity of the shock wave and the angle with respect to the direction of the air flow are lower with the aerospike nozzle than in the nozzleless model, which is consistent with the effect of backpressure increase on the shock dynamics. Regardless of whether the nozzle is connected to the combustor, the nozzle affects the dynamic alternation of the design point state to over-expansion and under-expansion along the circumferential direction. The shock wave intensity and total pressure recovery inside the nozzle with the combustor are slightly stronger than those in the nozzle without the combustor. Consequently, the thrust and total pressure recovery of the nozzle integrated with the RDE combustor are enhanced by 7% and 5.6%, respectively. Thus, decoupling the nozzle from the rotating detonation combustor is feasible for testing the design performance of the unsteady nozzle. [ABSTRACT FROM AUTHOR]

Deep mining results in an increasingly serious hazard. Based on the principle of heat transfer and radiant cooling, a three-dimensional heat transfer model of the working face was established. The influence of the inlet airflow parameter, the surrounding wall temperature and other parameters on the temperature distribution of airflow along the working face were analyzed under the radiation cooling mode. The results show that the increment of airflow temperature in several sections along the working face decreases by 0.67 °C, 0.48 °C, 0.40 °C, 0.36 °C, 0.33 °C, 0.29 °C respectively. The farther away from the airflow inlet, the more obvious the cooling effect was. The airflow temperature of the working face is positively correlated with the airflow inlet temperature and the surrounding wall temperature, and is negatively correlated with the airflow velocity. The research provides a good solution for the working face cooling of deep mines, and also provides a theoretical reference for the research on the radiation cooling technology of the working face. [ABSTRACT FROM AUTHOR]

The ventilation system plays a crucial role in every building. Proper design and optimization of its operation increase the comfort of users due to efficient air exchange and at the same time control its velocity in the rooms. The aim of this paper is the analysis of the effect of plenum box entry on the velocity profile concerning the diffuser face panel. This issue may sometimes be ignored at the design stage but can significantly affect the airflow from the diffuser and consequently increase the risk of draft. The results of the PIV experimental measurements and numerical simulations concerning various entries of the plenum box (top and side) were investigated in this study. The measurements were used to develop the mathematical and numerical models, which were then used to assess the effect of localization of the spigot of the plenum box on its operation. The numerical analysis was carried out on plenum boxes with the air diffuser with a face panel composed of square grid perforations. Analyses show that the entries significantly affect both the way of air distribution inside the plenum box and the profile of the airflow and its velocity under the simulated air diffuser. [ABSTRACT FROM AUTHOR]

The space scientific payload rack is a multifunctional experimental platform, and the requirements of the environmental temperature index are different for diversified experimental modules inside. The air cooling system is an important part of the rack thermal control system. A new type of air cooling system with small size and flexible arrangement is proposed in this paper, that is, micro air ducts with pinhole-sized air vents. The rack physical models of new and traditional air cooling modes are established, respectively. The numerical simulation of the inner air flow is carried out by Ansys Fluent CFD software (Ansys Inc., Canonsburg, PA, USA), which verifies that compared with the traditional method, the temperature field and flow field of the new air cooling method are more uniform, and the heat sources located at the edge of the rack can also be cooled better. [ABSTRACT FROM AUTHOR]

The space scientific payload rack is a multifunctional experimental platform, and the requirements of the environmental temperature index are different for diversified experimental modules inside. The air cooling system is an important part of the rack thermal control system. A new type of air cooling system with small size and flexible arrangement is proposed in this paper, that is, micro air ducts with pinhole-sized air vents. The rack physical models of new and traditional air cooling modes are established, respectively. The numerical simulation of the inner air flow is carried out by Ansys Fluent CFD software (Ansys Inc., Canonsburg, PA, USA), which verifies that compared with the traditional method, the temperature field and flow field of the new air cooling method are more uniform, and the heat sources located at the edge of the rack can also be cooled better. [ABSTRACT FROM AUTHOR]

The dispersion of particulate matter emitted by road transport to the vicinity of roads is predominantly influenced by the character of the air velocity field. The air flow depends on factors such as the speed and direction of the blowing wind, the movement of cars, and the geometries of the buildings around a road. Numerical modeling based on the control volume method was used in this study to describe the relevant processes closely. Detailed air velocity fields were identified in the vicinity of a straight road surrounded by various patterns of built-up urban land. The evaluation of the results was generalized to exponential expressions, affecting the decrease of the mass concentration of fine particles with the increasing distance from the road. The obtained characteristics of the mass concentration fields express the impact of the building geometries and configurations on the dispersion of particulate matter into the environment. These characteristics are presented for two wind speeds, namely, 2 m·s−1 and 4 m·s−1. Furthermore, the characteristics are introduced in relation to three wind directions: perpendicularly, obliquely, and in parallel to the road. The results of the numerical simulations are compared with those obtained via the in-situ measurements, for verification of the validity of the linear emission source calculation. [ABSTRACT FROM AUTHOR]

Ventilation and dust removal is the most basic means of dust prevention in mines. In the paper, a highly simulated physical model of the goaf and multiple dust sources were established in order to obtain the optimal dust-removal air flow rate in the roadway. In addition, by combining the numerical simulation method, the influence of the flow rate on dust diffusion rules of the dust sources was analyzed. The research results showed that the mass concentration of the dust in the fully-mechanized working face was gradually decreased with the increase of the air flow rate at a certain range of 700–1600 m3/min. However, high air flow rate can cause the re-entrainment of the dust, contaminating the working environment again. It was confirmed that the optimal dust-removal air flow rate of the inlet air was within a range of 1500–1600 m3/min, which generated the lowest average mass of the dust in the working area suitable for normal operations. This range of air flow rate might be used as a reference in the mine ventilation design in order to provide the coal mine workers with a clean and safe production environment. In addition, the research method and results are of great significance to the formulation and development of effective dust control and dust removal cleaner production technology, and can be used as a reference for the ventilation design in underground projects such as non-coal mines and tunnels. Image 1003 • The innovative highly simulated physical model was established. • The effectiveness of numerical simulation was verified by field measurements. • The dust diffusion law under different air flow rate conditions was analyzed. • The optimal dust-removal air flow rate is obtained. [ABSTRACT FROM AUTHOR]

The aspects of numerical simulation of open refrigerated display cabinets are described. The numerical model based on the Smagorinsky turbulence model was developed using OpenFOAM. Validation of the model provided. Description of the design solutions for the air curtain and the air flows distribution schemes are given. The feasibility study of considered design solutions provided along with a theoretical background, supporting the relevance of considered solutions in refrigeration technology. A comparative analysis of a single- and double-jet air curtains for open refrigerated display cabinets was carried out. A comparative analysis of uniform and nonuniform distribution of the cool air flows supplied through the perforated back panel of the refrigerated display was carried out. The analysis of simulation results showed an advantage of considered modifications over the basic solution; herewith, the scheme with a nonuniform distribution of the air flows appeared to be more effective than a double-jet air curtain by 18%. [ABSTRACT FROM AUTHOR]

• The experimental study and numerical simulation on the in-cylinder flow of small motorcycle engine was investigated. • The evolution of the in-cylinder flow small motorcycle engine was illustrated well in this study. • Some flow characteristics in-cylinder small motorcycle engine was analyzed well and detail in this study. This study aimed at experimental and numerically investigating in-cylinder flows of a small motorcycle engine under steady-state conditions. The experiment was conducted in the engine head for a variety of fixed valve lifts at two pressure drops (300 and 600 mmH 2 O). Besides, this study attempted to analyze the characteristics of in-cylinder flows in a small engine by applying CFD methods. Looking at the results, there was a good agreement between the results of experiment and simulation in terms of flow coefficient, air flow rate and discharge coefficient at two pressure drops. In both horizontal and vertical planes, both increased valve lift and pressure drop delivered increased velocity and vorticity magnitude. An increase in pressure drop at the beginning of valve lift opening appeared to have no effect on the swirl ratio until the valve lift reached 5 mm. However, the swirl ratio got a 25% reduction when the valve lift reached 6.25 mm. An increase in pressure drop at the intake stroke did not deliver a significant effect on the tumble ratio and accumulated air mass. However, the accumulated air mass increased 3.77% at compression stroke. An increase in pressure drop delivered a significant effect on turbulent kinetic energy (TKE), turbulent length scale and turbulent kinematic viscosity. TKE reached its peak (200%) at 470 °CA, while turbulent length scale and turbulent kinematic viscosity reached their peaks at 590 °CA where the intake valve was almost closed. The increase in turbulence in fact produced a more homogeneous in-cylinder air-fuel mixing. Besides, the increase in turbulence directly increased the rate of fire propagation. Further study would be expected to focus on modifying the design of intake port for improving the air flow characteristics of small engines. Then, this study was expected to reduce the number of experiments required for investigating optimized parameters in small engines. [ABSTRACT FROM AUTHOR]

In this paper, a general numerical methodology is developed and validated for the simulation of steady as well as transient thermal and electrical behaviors of thermoelectric generator (TEG)-based air flow self-cooling systems. The present model provides a comprehensive framework to advance the study of self-cooling applications by combining fluid flow, heat transfer and electric circuit simulations. The methodology is implemented by equation-based coupled modeling capabilities from multidisciplinary fields to capture the dynamic thermos-electric interaction in TEG elements, enabling the simulation of overall heating/cooling/power characteristics as well as spatially distributed thermal and flow fields in the entire device. Experiments have been conducted on two types of self-cooling arrangements to measure the device temperature, voltage and power produced by TEG modules. It was found that the computational model was able to predict the experimental results within 5% error. A parametric study was carried out using the validated model to study the effect of heat sink geometry and TEG arrangements on device temperature and power produced by the device. It was found that the power for self-cooling could be maximized by proper matching of the TEG modules to the fluid mover. Although an increase in fin density results in a rise in fan power consumption, a marked increase in net power and decreases in thermal resistance are observed. [ABSTRACT FROM AUTHOR]

In [1] the mechanisms of spray generation under hurricane winds were experimentallystudied and it was found that for friction velocity u* &#x003E; 1 m/s (for wind speeds at 10 m heightexceeding 20 m/s), bag-breakup determines the contribution to the formation of largedroplets. A typical event of this type begins with a small-scale increase in the water surface,which then turns into a "micro-sail", swells into a water film bounded by a thicker rim, andfinally explodes, producing hundreds of droplets. In the dynamics of engineering fluids [1],this phenomenon is known as the "bag-breakup" mode of liquid fragmentation in gasstreams. For the direct numerical simulation of the bag-breakup phenomenon, the Gerris FlowSolver was used. As an initial configuration for numerical simulation a drop of liquid wasplaced in the air flow. A drop of water with a diameter of 1 cm (the characteristic size of theperturbation from which the bag arises) placed in the air stream at a speed of 20 m/scorresponds best to the experimental situation, such a system is characterized by the Webernumber We = 54. Modeling the dynamics of two media with very different densities, such aswater and air, require a lot of computational time, so we used liquids that differ indensity by a factor of 10, but to keep the same Weber number, we changed theother parameters of the problem. The calculation was carried out with keeping thesame Reynolds number and also with the Reynolds number reduced and increasedby a factor of 10. In our simulation just as in an experiment under the action ofan air stream a drop is blown into a micro-sail that bursts to form a micro-spray.As the Reynolds number decreases (with increasing of viscosity of both media),the process of destruction of the drop after the formation of a micro-sail from itchanges. This work was partly supported by the RFBR grants (18-55-50005, 18-35-20068,19-05-00249). Carrying out experiments themselves was supported by Russian ScienceFoundation (18-77-00074). [1] Troitskaya Yu., et al., Sci. Rep. 7 1614 (2017). [ABSTRACT FROM AUTHOR]

The parameters of the dual slot die in an industrial melt blowing equipment are designed optimally using the orthogonal experimental design method. The air flow fields of different die parameters are simulated. Effects of the die parameters are analyzed using variance analysis. The results show that the inset distance and slot width have significant effects on the air flow field while effect of the slot angle is unremarkable. [ABSTRACT FROM AUTHOR]

The unsymmetrical air flow of the dual slot die in the melt blowing process is simulated. The diameter and transverse displacement of the threadline are obtained numerically. The result shows that the threadline diameter in the unsymmetrical air flow is larger than that in the symmetrical one. This paper helps to point out the research direction for producing finer melt blown fibers. [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]