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Pneumatic yarn splicing is a complex process that involves the simultaneous movement of two strands of counter-rotating yarn. Depending on the process and structural parameters of the mingling chamber, the airflow field is more dominant in influencing the wrapped effectiveness of untwisted filaments and consequently the splice strength. This study establishes a computational domain of a mingling chamber comprising an inlet channel, accelerating channel, rotating channel, and groove channel. The renormalization-group k–ε turbulence model is adopted to simulate the vortex patterns in the rotating channel under different inlet pressure. Furthermore, a transient mass flow test bench based on the isothermal principle is used to verify the numerical simulation results by comparing the mass flow of a pneumatic splicer. A wrapped model of spliced yarn is presented to describe the effects of wrapped force determined by the characteristic of vortex patterns on the strength of spliced yarn. A strength tester is also used to acquire the strength of spliced yarn produced under different inlet pressures and interpret the reliability of theoretical analysis. Comparisons between numerical results and experimental data show that the inlet pressure of the mingling chamber clearly affects the vorticity of the vortex and the strength of spliced yarn. The vorticity of the vortex will be enhanced with increasing inlet pressure and improve splice strength to avoid insufficient twisting of the yarn end. However, excessive twisting of the yarn end, as reflected by splice strength, would occur if the inlet pressure strengthens continually. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulations are conducted to investigate the impact of the blockage of vehicles in tunnel on the performance of semi-transverse smoke control system. Two well-known CFD tools, i.e., FDS 6.0.1 and ANSYS FLUENT 14, are used for mutual verification. The smoke pattern in tunnel without blockage is studied as a benchmark and the proposed semi-transverse smoke control system can maintain tenable conditions for safe egress. The scenarios with blockages of 2m and 4m high are studied respectively. The simulation results demonstrate the presence of blockage significantly changes the flow pattern in tunnel. The bulk mass flow rates are reduced from the blocked side while increased from the unblocked side. The unbalanced airflow drives more smoke to the blocked side and makes this side impassable for evacuation within a few minutes. The scenarios with symmetric blockages of the same heights are further studied for comparison and smoke is well confined within the defined smoke zone. Tentative simulations are conducted to improve the environment in tunnel by increasing the smoke extraction rate. For a blockage ratio of 26.6%, even a 50% increase in the smoke extraction rate can hardly maintain tenable condition throughout the tunnel. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the transient 3D numerical simulations of natural convection of air around a circular finned tube (24.9 mm OD ) kept in a small chimney. The annular plain fins are considered in this study. The effects of fin spacing to fin diameter ratio (0.057 mm ⩽ S / D f ⩽ 0.24 mm), chimney height (400–1000 mm) and ambient to surface temperature difference (10 K ⩽ T s ⩽ 65 K) on the heat transfer and the driving force have been investigated. The results are presented in terms of the temperature contours, velocity vectors, heat transfer and the driving force. It has been found that the heat transfer coefficient increases with an increase in the fin spacing upto an optimum value ( S = 8 mm) for all the fin geometries, and beyond S = 8 mm, the heat transfer coefficient decreases. The separation of the thermal boundary layer with a variation in the fin spacing and its effects on the heat transfer and driving force has been shown. For a fixed fin spacing, the heat transfer rate, heat transfer coefficient and the driving force increases with an increase in the fin diameter, however, for D f > 41 mm, the rate of increase in the heat transfer coefficient reduces. The heat transfer coefficient increases with an increase in the chimney height and it has been found that the effect of chimney height on the heat transfer coefficient is a resultant effect of the air outlet temperature and the driving force generated by the chimney. The base to ambient temperature difference has been varied to observe the temperature sensitivity on the heat transfer coefficient and flow patterns. In the last section, various circular and elliptical tube designs have been investigated, and it is found that, the elliptical tube with minimum ellipticity ( b / a = 0.33) and circular tube with smallest diameter (7 mm) provides better heat transfer coefficient than the other circular and elliptical designs. [ABSTRACT FROM AUTHOR]

Draining a viscous liquid from a partially filled, finite-size cylindrical tank through a tube imbedded in the liquid is viewed as selective withdrawal from the lower layer of viscous liquid in an identical tank, with the fluid of the upper layer being air or low-viscosity gas. Contrary to previous approaches that simplify the problem by considering a tank of infinite extent in the horizontal direction and approximating the withdrawal tube as a point mass sink, the model presented here employs a detailed flow geometry of a finite-size tank with a withdrawal tube of comparable radius. An Arbitrary Lagrangian–Eulerian (ALE) method is utilized in the numerical model to track the motion and deformation of the free surface. The results of simulations made with the present model show that the mean curvature at the tip of the free surface depends on the flow rate of drainage and the distance of the unperturbed free surface from the tube inlet; the mean curvature at the free surface tip is not influenced by the size of the tank when the tank-to-tube radius ratio exceeds a value of 30, in agreement with experimental results. The simulations reveal that a critical parameter for the system under investigation is the ratio of tube wall or tube support thickness or the horizontal distance of liquid from the tube inlet, at the level of the inlet, to the tube radius. When this parameter is correctly identified, results of simulations collapse on experimental results regarding the mean curvature of free surface at the tip. [ABSTRACT FROM AUTHOR]

Numerical simulations are conducted to model the transient development of the buoyancy-driven natural ventilation. The simulations are compared with experimental data and theoretical predictions in the literature to validate the numerical model. The airflow behavior of three cases, i.e., the initial indoor temperature is equal to, higher and lower than the outdoor temperature, were analyzed by the numerical results, respectively. The results show that transient flow development of the last case is relatively complex in naturally ventilated rooms with inner heat sources due to the transformation from downward ventilation to upward ventilation. Vent area, heat source power and vertical position of the source are the main factors affecting the airflow rate, vertical temperature difference in the occupied zone and indoor thermal comfort, while the vent shape and the horizontal position of heat source on the floor seem to have marginal influence on the transient natural ventilation. In addition, initial indoor temperature is also a crucial factor influencing the establishment of steady state of the transient ventilation besides the vent and heat source characteristics. [ABSTRACT FROM AUTHOR]

Numerical simulations of the gas-seeding strategies required for planar laser-induced fluorescence in a Mach 10 (approximately Mach 8.2 postshock) airflow were performed. The work was performed to understand and quantify the adverse effects associated with gas seeding and to assess various types of seed gas that could potentially be used in future experiments. In prior experiments, NO and NO2 were injected through a slot near the leading edge of a flat-plate wedge model used in NASA Langley Research Center's 31 in. Mach 10 air tunnel facility. In this paper, nitric oxide, krypton, and iodine gases were simulated at various injection rates. Simulations showing the deflection of the velocity boundary layer for each of the cases are presented. Streamwise distributions of velocity and concentration boundary-layer thicknesses, as well as vertical distributions of velocity, temperature, and mass distributions, are presented for each of the cases. A comparison between simulated streamwise velocity profiles and experimentally obtained molecular tagging velocimetry profiles using a nitric oxide seeding strategy is performed to verify the influence of such a strategy on the boundary layer. The relative merits of the different seeding strategies are discussed. The results from a custom solver based on OpenFOAM version 2.2.1 are compared against results obtained from ANSYS® Fluent version 6.3. [ABSTRACT FROM AUTHOR]

The effects of temperature and composition stratifications on the ignition of a lean n -heptane/air mixture at three initial mean temperatures under elevated pressure are investigated using direct numerical simulations (DNSs) with a 58-species reduced mechanism. Two-dimensional DNSs are performed by varying several key parameters: initial mean temperature, T 0 , and the variance of temperature and equivalence ratio ( T ′ and ϕ ′) with different T − ϕ correlations. It is found that for cases with ϕ ′ only, the overall combustion occurs more quickly and the mean heat release rate (HRR) increases more slowly with increasing ϕ ′ regardless of T 0 . For cases with T ′ only, however, the overall combustion is retarded/advanced in time with increasing T ′ for low/high T 0 relative to the negative-temperature coefficient (NTC) regime resulting from a longer/shorter overall ignition delay of the mixture. For cases with uncorrelated T − ϕ fields, the mean HRR is more distributed over time compared to the corresponding cases with T ′ or ϕ ′ only. For negatively-correlated cases, however, the temporal evolution of the overall combustion exhibits quite non-monotonic behavior with increasing T ′ and ϕ ′ depending on T 0 . All of these characteristics are found to be primarily related to the 0-D ignition delays of initial mixtures, the relative timescales between 0-D ignition delay and turbulence, and the dominance of the deflagration mode during the ignition. These results suggest that an appropriate combination of T ′ and ϕ ′ together with a well-prepared T − ϕ distribution can alleviate an excessive pressure-rise rate (PRR) and control ignition-timing in homogeneous charge compression-ignition (HCCI) combustion. In addition, critical species and reactions for the ignition of n -heptane/air mixture through the whole ignition process are estimated by comparing the temporal evolution of the mean mass fractions of important species with the overall reaction pathways of n -heptane oxidation mechanism. The chemical explosive mode analysis (CEMA) verifies the important species and reactions for the ignition at different locations and times by evaluating the explosive index (EI) of species and the participation index (PI) of reactions. [ABSTRACT FROM AUTHOR]

In the mechanical ventilation room, human body will block the air flows and change the original airflow organization. In the crowd places, the influence of the crowd may greatly change the indoor air movement and even worsen the environment. So the effect can not be ignored. The paper studied the influence of the human body to the indoor air movement by using the method of Particle Image Velocimetry (PIV) and numerical simulation (CFD). The PIV experiment and numerical simulation contain two conditions. One condition is an empty room and another contains models of human body in the room. The paper compared the result of experiment and numerical simulation. Numerical simulations are demonstrated to be accurate in the two conditions, and the Standard k-ɛ model most accurately predicts the flow in a room contains crowd model. In this study, the numerical simulation and measurements show that the crowds will greatly change the air distribution and the residence time of the flows in the building. Therefore, it is important that crowds be considered in ventilation design. [ABSTRACT FROM AUTHOR]

Numbers of high-rise buildings form the street canyon, in which the exhaust of vehicles accumulate and do harm to the urban residents. So the study on the pollutant dispersion characteristics and influence factors of vehicles emission in city streets is of great significance. This paper analyses the influence factors of the vehicles emissions, gets the numerical simulation of the building's roof shape on both sides of the street and the influences of the relative height of buildings on both sides of the street canyon on the air flow field and pollutant diffusion concentration field. The results show that with the increase of height, the diffusion of vehicle emissions is in a downward trend in the street leeward and windward surface, the pollutants at the top of the street is obviously less than the vehicle emissions of pollutants in the street and the pollutants is obviously less affected by traffic flow at the top of the street. The results of this article can provide scientific basis about the control, monitoring and estimate of pollutant emission from the urban vehicle, and the rational layout and planning of the city's streets. [ABSTRACT FROM AUTHOR]

Different simplified simulation models of a Passive Downdraught Evaporative Cooling tower (PDEC) were compared by using experimental data. Among these, a series of tests on a Passive Downdraught Evaporative Cooling tower (PDEC) were carried out at the SyTIn (Systems for Technology Innovation) Laboratory of the Department of Architecture and Design, Politecnico di Torino. In addition, other monitored databases were taken from literature and used as input data for the simplified models. The collected inlet airflow data were used for calculating predicted outlet airflow values by using four equations and a software from literature. The comparison of those outlet airflow data allowed for assessing the effectiveness and the accuracy of the analysed simplified methods, which are also used for simulating the PDEC tower in several dynamic simulation software such as DesignBuilder coupled with EnergyPlus . The presented results could help designers in choosing amid different calculation models. [ABSTRACT FROM AUTHOR]

This study presented an iterative approach to simplify computer simulated persons (CSPs) based on the mesh decimating algorithm [1]. The approach could largely simplify 3D-scanned manikins while maintaining their key geometrical features. The level of simplification could be quantified through controlling the iteration number of simplification. CFD computations of human thermal plume in a quiescent room were performed using CSPs with different levels of simplification. The numerical results were compared against the experimental data available in the literature. The results demonstrated that within the scope of this study, the CSP simplification only affected the predicted airflow field in the thermally-affected regions where the normalized air velocity was larger than 0.5. The predictive error increased with the dimensionless simplification index ( SI ). When SI was less than 3.5 × 10 −4 , the error induced by CSP simplification could be safely ignored. Contaminant transport in a densely occupied airliner cabin section was also simulated using the simplified CSPs. The results revealed that although the CSP simplification only affected airflow field prediction of the thermal plume regions, it could enlarge the predictive error of contaminant transport in the whole computational domain. In addition, this study found that the CSPs yielded from the algorithm were more numerically stable in terms of CFD computations. [ABSTRACT FROM AUTHOR]

This paper deals with studying of the aerodynamics characteristics in a residential building with a patio system connecting the inside with the outside. The numerical simulation is based on the resolution of the Navier–Stokes equations in conjunction with the standard k-ε turbulence model. These equations are solved by a finite-volume discretization method. The comparison between our numerical and experimental results developed using a wind tunnel shows a good agreement and confirms the validity of the numerical method. This proposed design presents an outlining environment suitable building in Tunisia. [ABSTRACT FROM AUTHOR]

An accurate prediction of flow and thermal fields around an human body provides valuable information in designing an efficient ventilation system. This study tries to address this issue by investigating the flow structure around an human body subjected to a displacement ventilation system through the computational fluid dynamics (CFD). For this purpose, both the large eddy simulation (LES) and hybrid LES–RANS methods are employed. The RAST one-equation model (OEM) and the dynamic Smagorinsky model (DSM) are utilized as a sub-grid scale (SGS) modeling for the LES while for the hybrid LES–RANS method, the SST–SAS version is applied. Predicted results are compared with available experimental measurements in the literature. Comparisons show that the OEM has a better performance in reproducing the correct level of velocity and temperature fields around the body as well as in other locations of the room while the SST–SAS model fails to predict these quantities accurately, especially around the occupant's body. Above all, the OEM provides a good compromise between accuracy and robustness in predicting the airflow and temperature fields in an indoor environment. [ABSTRACT FROM AUTHOR]

• The guide vane is added to the air inlet chamber of the intercooler. • An end-to-end model of the intercooler guide vane based on PSO-SVR algorithm. • Structure parameters of guide vane are optimized using genetic algorithm. In order to fundamentally solve the problem of poor air flow uniformity in the cooling pipe of the heavy-duty vehicle intercooler, which leads to poor heat exchange effect, this paper innovatively proposes to add a guide vane in the air chamber of the intercooler. The air flow uniformity in the cooling pipe of the heavy-duty vehicle intercooler is investigated under different structural parameters of guide vane based on the established end-to-end model. In fact, the end-to-end prediction model is innovatively proposed to characterize the relationship between the structural parameters of guide vane and performance parameters without conducting the high-cost and long-term experiments or numerical simulation. Besides, structure parameters of guide vane with the optimal airflow uniformity coefficient are obtained using genetic algorithm (GA), that is, the diversion angle (α) is 18°, the width of rectangular holes in the guide vane (L) is 6 mm and the number of rectangular holes in the guide vane (N) is 3. To demonstrate the effectiveness of the proposed method, the optimized intercooler is validated and it is found that the airflow uniformity coefficient of the optimized intercooler is 0.983, which is 5.25% higher than the original structure, the outlet temperature is reduced by 8.2 °C. [ABSTRACT FROM AUTHOR]

The moisture safety designs of basements used for habitation have become a topic of concern. Basements are prone to high moisture strain and have a limited outward drying ability compared with above-grade structures. The risk of interior moisture-related damage can be reduced if the basement walls are allowed to dry outward below grade. The use of vapour-permeable thermal insulation and the effect of air gaps behind dimpled membranes on the outward drying of concrete basement walls were investigated in this study. One- and two-dimensional hygrothermal simulations were conducted using WUFI®Pro and COMSOL Multiphysics®. First, the outward drying of concrete wall segments, previously investigated in a laboratory experiment, was simulated. Two EPS types and two dimpled membrane positions were compared, with an emphasis on the airflow through the air gap behind the membrane. Second, the long-term moisture performance of concrete basement walls was simulated. It was observed that when the dimpled membrane was placed between the concrete and exterior EPS, the bottom of the concrete segments dried faster than the top. When the dimpled membrane was placed on the exterior side, the concrete dried more uniformly along the height. Thus, the results indicated that the latter ensured outward drying of the concrete basement walls. However, the overall effect on the interior RH depended on the characteristics of concrete and the amount of interior and exterior insulation. Optimum drying was achieved when the thickness of interior insulation was reduced. The variability of the concrete properties used in basement walls requires further investigation. • The outward drying of thermally insulated basement walls is studied. • Two positionings of the dimpled membrane are compared. • Convective moisture transfer through the membrane's air gap is studied. • The use of interior vapour barriers and three concrete types are investigated. • The type of concrete significantly impacted the effect of outward drying. [ABSTRACT FROM AUTHOR]

Drying is a process of removing water from products down to a specific moisture content. It is an energy-intensive process widely-used for grain and biomass processing. Because of the complicated thermodynamics and transport phenomena involved in drying, it is challenging to analyse and optimise drying operations. In this study, computer simulations using a transient model are performed to simulate the real-time paddy drying, and analyse the exergy components, exergy efficiency, exergy loss and destruction of industrial-scale drying process under changing drying air temperature (60–80 °C) and flow velocity (0.56–0.83 m/s) and initial moisture content (0.22–0.3 g water/g wet matter) on a circulation counter-flow paddy dryer. Results show our model can predict paddy moisture content and temperature with mean relative deviations of 5.5% and 1.42%, respectively. Exergy efficiency of drying process is specified to be in the range of 28.75–35.68%. Main factor affecting drying rate and energy consumption in high moisture content regions of drying process is drying air flow velocity while that in low moisture content regions is drying air temperature. We also propose control strategy based on two-stage variable ventilation parameters that achieves high exergy utilization level, high drying rate, and high product quality for grain drying. • Transient model simulation replaced field experiments in industrial-scale grain drying. • Simulated and analysed detailed exergetic components. • Exergy analyses have been reported changing various parameters. • Presented energy-saving strategy of hot air drying based on process control. [ABSTRACT FROM AUTHOR]

New studies show that the elastic properties of the vocal folds (VFs) vary locally. In particular strong gradients exist in the distribution of elastic modulus along the length of the VF ligament, which is an important load-bearing constituent of the VF tissue. There is further evidence that changes in VF health are associated with alterations in modulus gradients. The role of VF modulus gradation on VF vibration and phonation remains unexplored. In this study the magnitude of the gradient in VF elastic modulus is varied, and sophisticated computational simulations are performed of the self-oscillation of three-dimensional VFs with realistic modeling of airflow physical properties. Results highlight that phonation frequency, characteristic modes of deformation and phase differences, glottal airflow rate, spectral-width of vocal output, and glottal jet dynamics are dependent on the magnitude of VF elastic modulus gradation. The results advance the understanding of how VF functional gradation can lead to perceptible changes in speech quality. [ABSTRACT FROM AUTHOR]

Although trees are numerous in urban areas, their dynamic effects on the wind flow are usually approximated or neglected altogether in many wind engineering studies, especially those based on numerical modeling. This study investigates the effect of the inclusion of trees in numerical simulations of wind flow in urban area. Three approaches are used to include the dynamic effect of trees: the basic approach (tree effects are neglected), the implicit approach (tree effects are included in the surface parameterizations), and the explicit approach (trees are represented by porous media). Several test cases have been adopted in order to cover a wide range of urban complexities, wind directions, foliage densities, and tree planting configurations. The results show that there are significant effects of trees when the explicit approach is used compared to the basic and the implicit approaches. Thus tree effects need to be considered using an explicit approach to simulate wind flow in urban area. Also, many parameters such as wind direction, foliage density, and urban configuration are believed to influence the intensity of trees effects. This study emphasizes the importance to explicitly consider the effects of trees in numerical model investigations for the wind flow in urban areas. [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]

This paper presents a comparative assessment of two urban morphologies representing the urban transformations that occurred between 1976 and 2013 in downtown Rio de Janeiro. The work documents the impact of the city morphology changes on the air flow pattern, which is known to change the energy needs at the scale of the city. Special attention is dedicated to the comfort at pedestrian level and the potential for natural ventilation in a building of reference. The study was performed by means of numerical simulations based on the RANS k-ϵ turbulence model. The results show an increment in wind velocity at pedestrian level and a pressure difference rise between the building facades. New high-rise buildings increase the stagnation area in the leeward region, the boundary layer height, and the turbulence level. [ABSTRACT FROM AUTHOR]

Two-phase flow is studied numerically one-dimensionally using a two-fluid equation system. A hyperbolic type of governing equation is applied in our simulation. The segregated solution method is promoted and adopted in this article. By establishing mass conservation-based pressure correction, the SIMPLE algorithm is extended to two-phase flow simulations. Numerical results for well-known two-fluid air/water flow benchmark problems are presented and discussed. [ABSTRACT FROM AUTHOR]

The paper proposes a new air-jet spinning method for the preparation of continuous twisted nanofiber yarns. The nozzle-twisting device is designed to create the 3-D rotating airflow to twist nanofiber bundles. The airflow characteristics inside the twisting chamber are studied numerically. The airflow field distribution and its effect on nanofiber yarn spinning at different pressures are also discussed. [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]

Two-dimensional direct numerical simulations were conducted for bluff-body stabilized flames of a lean hydrogen/air mixture at near-blowoff conditions in a meso-scale channel. Parametric simulations were conducted by incrementally varying the inflow velocity in the vicinity of the blowoff limit, and the corresponding flame response was monitored. The present study is a showcase of combustion DNS with embedded boundary representation, and full demonstration of the detailed visualization of the near-blowoff flame characteristics. As the inflow velocity approaches blowoff limit, the flame dynamics exhibit a complex sequence of events, such as periodic local extinction and recovery, and regrowth of the bulk flame by the flame segments attached behind the bluff-body. The total extinction is observed as the attached flames shrink down and are no longer able to regrow the bulk flames. Despite the disparity in the physical scale under study, the observed sequence of the extinction pathway shows a strong similarity with experimental observations at larger scale combustion systems. [ABSTRACT FROM AUTHOR]

A helically segmented finned tube bank is simulated as a single isolated finned tube module in order to reduce computational domain in 99%. The numerical simulation is conducted with the Reynolds Averaged Navier–Stokes Equations (RANS) approach and the turbulence effect is modeled with the k – ɛ RNG model. The finned tube geometry is represented by means of cut-cell method, whereas the inside fluid temperature is considered by means of an average temperature. Periodic boundary conditions are implemented and, as a consequence, new terms in momentum and energy equations should be included to represent pressure drop and cooling air flow. Results show the effect of implementing periodic boundary conditions on turbulent kinetic energy, and its dissipation rate only is reflected on local properties in the zones of high flow interaction. Predictions are validated with experimental data and the best correlations available in the open literature. Results show good precision and the same tendency in the velocity field. The numerical-mean friction factor and Nusselt number present deviations of 0.67% and 2.98%, respectively. Therefore, an appropriate representation of turbulent flows is obtained and the numerical model can be applied to studies on heat exchangers at industrial scale. [ABSTRACT FROM AUTHOR]

Numerical and experimental models have been developed to investigate the effect of implementing in-line and staggered arrangement of dimple on heat transfer augmentation and pressure drop of the air flow through a multilouvered fin bank. Three-dimensional simulations of single row of louvers have been conducted for the aforementioned geometry. Simulations are performed for different Reynolds number. The simulation revealed that heat transfer and temperature augmentations occur due to existence of a circulation region created by dimple. Additionally, continuous temperature gradients have been observed over the louver surface with the highest temperature at the base of the louver and the lowest temperature at the middle of the louver. Besides, the difference between these two points is more obvious in higher Reynolds numbers, especially in the first louvers. Fin efficiency and fin effectiveness have been calculated to assess the louver performance. The air-side performance of heat exchanger is evaluated by calculating Colburn j factor and Fanning friction f factor. Results show that implementing dimples on the louver surface increase j factor and f factor. The present results indicated the staggered arrangement, in comparison with in-line arrangement, could effectively enhance the heat transfer performance. The results show that both fin bank performance and louver effectiveness will be increased against an acceptable increase in pressure drop. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to highlight state-of-the-art digital human modeling applications in aviation and aerospace industry, generate research interest and promote application of digital human modeling technology among audience of diverse background including researchers, students, trainees, etc. in academia and industry; designers; engineers; and ergonomists associated with aviation and aerospace sectors. Design/methodology/approach - Comprehensive literature search was performed and, subsequently, all publications identified were studied thoroughly at least by abstracts. Available information has been segregated under different headings and depicted systematically for easy understanding by readers. Findings - Virtual human modeling technology has been used in assessing reach and accessibility in aircraft cockpits, creating accurate posture libraries, performing vision analysis for pilots, determining design modifications to accommodate female users, predicting probable pilot behavior in proposed cockpit design, simulating air flow and heat transfer in fighter plane's cockpit, assessing comfort of airplane passenger seats, maintenance studies, human spaceflight training, verifying component accessibility, investigating impact of space suit parts and harnesses, etc. Traditional approach for ergonomic investigations (involving costly physical mockups and trials with real humans) can be effectively replaced by evaluations facilitated by digital mockups and digital humans. Research limitations/implications - Being a review paper, the present manuscript is purely academic in nature. Originality/value - The present paper represents critical review (with up to date references), leading to a comprehensive knowledge body about application of digital human modeling in aviation and aerospace industry. Avenues still to be explored have been identified and future research directions have been given aiming at aviation and aerospace completely human centric. [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]

To explore the effect of traffic pollution on indoor air quality of naturally ventilated buildings in the vicinity of a street canyon, the wind flow and pollutant distributions in and around buildings with different window opening percentages (i.e. WOP, the percentage of the total window opening area to the total facade area) were investigated by three-dimensional numerical simulations. The numerical results show that the WOP changes the pressure distribution around the downstream building, which is due to the infiltration of air into the street canyon through the opening windows of both the upstream and downstream buildings. When the indoor air of the downstream building is supplied by the outdoor air from the street canyon, the ventilation flux will be increased with increasing WOP. If the indoor air is taken in from the leeward side of the downstream building, however, the trend of the ventilation flux is found reverse. The results also indicate that the effective source intensity, which is introduced to quantify the amount of traffic pollutant entering into buildings through unit ventilation area, decreases as the WOP increases. When the WOP reaches 10%, the averaged effective intensity is reduced by 30% compared to the reference case when all windows are closed. It means that if a naturally ventilated room in the downstream building has a fixed ventilated area over different seasons, the room will take in more pollutants from outdoors in winter than in other seasons. [ABSTRACT FROM AUTHOR]

In this study, airflow and temperature distributions in the well-known International Energy Agency (IEA) Annex 20 room are predicted numerically to investigate the effects of the inlet turbulence intensity and the length scale on the flow characteristics, while considering the possibility of solution multiplicity related to chaos theory. The flow is considered to be turbulent, steady, incompressible, and two-dimensional. Computations are performed using the standard k – ɛ , RNG k – ɛ , standard k – ω , and shear stress transport k – ω turbulence models with scalable and automatic wall functions, and the results are compared with numerical and experimental results from the literature. The validated turbulence model is then used to investigate the effects of the turbulence intensity and the length scale. At a low inlet turbulence intensity value (Tu = 0.01), the length scale variation has no influence on the flow pattern. However, the length scale affects the flow pattern at a high inlet turbulence intensity value (Tu = 0.4). At constant low and medium length scale values, an increase in the inlet turbulence intensity from 0.01 to 0.4 affects the flow pattern. However, an increase in the turbulence intensity has no influence on the flow pattern at a constant high length scale value. [ABSTRACT FROM AUTHOR]

This paper presents numerical simulation results of an airflow inclinometer with sensitivity studies and thermal optimization of the printed circuit board (PCB) layout for an airflow inclinometer based on a genetic algorithm (GA). Due to the working principle of the gas sensor, the changes of the ambient temperature may cause dramatic voltage drifts of sensors. Therefore, eliminating the influence of the external environment for the airflow is essential for the performance and reliability of an airflow inclinometer. In this paper, the mechanism of an airflow inclinometer and the influence of different ambient temperatures on the sensitivity of the inclinometer will be examined by the ANSYS-FLOTRAN CFD program. The results show that with changes of the ambient temperature on the sensing element, the sensitivity of the airflow inclinometer is inversely proportional to the ambient temperature and decreases when the ambient temperature increases. GA is used to optimize the PCB thermal layout of the inclinometer. The finite-element simulation method (ANSYS) is introduced to simulate and verify the results of our optimal thermal layout, and the results indicate that the optimal PCB layout greatly improves (by more than 50%) the sensitivity of the inclinometer. The study may be useful in the design of PCB layouts that are related to sensitivity improvement of gas sensors. [ABSTRACT FROM AUTHOR]

A mathematical simulation of the carefully selected geometrical and operational aspects of the cross-flow Maisotsenko cycle heat and mass exchanger used for indirect evaporative air cooling is investigated. A two-dimensional heat and mass transfer model is developed to perform thermal calculations of the indirect evaporative cooling process. Presented numerical model was validated against experimental data. Simulations bring out unique features of the considered heat and mass exchanger and allow finding which of the selected geometrical and operational aspects (extending the dry working air part at fixed primary part size, increasing secondary air part at cost of a primary part, operating the HMX under uneven air flow distribution) have more significant impact on its performance. Simulation was performed for two operational conditions: variable inlet temperature and variable inlet air flow rate. [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]

A flight simulation model is established, which is composed of airflow over mountains model, pilot model and flight dynamics model. It is simulated that Boeing 747 aircraft in landing configuration gets through airflow over mountains induced by simple and complexterrain. The simulation results indicate that the main flight safety problems in airflow over mountains are angle of attack increasing and height losing or severe bumpiness. Pilot needs to pay attention to the change trend of the angle of attack and flight height. [ABSTRACT FROM AUTHOR]

Diffuser is one key component of the gas turbine combustor following the compressor. Its primary function is to slow down the air flow delivered by the compressor in order to promote efficient combustion and avoid large total pressure losses. The impacts of pre-diffuser wall angle and dump gap ratio on the performance of dump diffusers have been discussed in the previous work, but few work has been undertaken on designing diffusers with greater pre-diffuser wall angle. It was observed that apparent flow separation occurred on pre-diffuser wall when pre-diffuser wall angle amplified to certain degree. The pre-diffuser exit flow was distorted, indicating that the uniform exit conditions typically assumed in the diffuser design were violated. Skew distribution of the pre-diffuser outlet flow can result in strong transverse mixing for liquid, the total pressure loss of pre-diffuser increases significantly. In this paper, vortex generators were introduced to delay pre-diffuser separation. PIV system was used to obtain the velocity filed of dump diffuser in the non-reacting condition. Comparisons between experimental results and numerical simulations using different turbulence models show that Reynolds Stress Model (RSM) can better predict flow field of diffuser Calculations result indicated that vortex generators delayed pre-diffuser separation observably and the total pressure drop was reduced to five percent of previous value. [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]

We compare experiments and direct numerical simulations to evaluate the accuracy of the Stokes-drag model, which is used widely in studies of inertial particles in turbulence. We focus on statistics at the dissipation scale and on extreme values of relative particle velocities for moderately inertial particles (St < 1). The probability distributions of relative velocities in the simulations were qualitatively similar to those in the experiments. The agreement improved with increasing Stokes number and decreasing relative velocity. Simulations underestimated the probability of extreme events, which suggests that the Stokes drag model misses important dynamics. Nevertheless, the scaling behavior of the extreme events in both the experiments and the simulations can be captured by the same multi-fractal model. [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]