Analysis Of Airflow Research Articles

Postoperative functional evaluation of obstructive sleep apnea syndrome by computational fluid dynamics.

The aim of this study is to evaluate the efficacy of uvulopalatopharyngoplasty and the corresponding postoperative airflow. Eleven patients diagnosed with obstructive sleep apnea syndrome who complained of snoring and apnea were enrolled in this study. Computational fluid dynamics (CFD) was implemented. CFD could be accomplished in nine cases. Airflow analysis was not possible in cases with a high respiratory event index (REI) score. Before surgery, stenosis was identified in the oropharynx and epiglottic area. And the airflow velocity and pressure were found to have significantly decreased in the oropharynx postoperatively, while in the epiglottic area, those data had increased postoperatively in some cases. The velocity and pressure of the oropharynx are related to REI score. From the CFD analysis, airflow analysis is important for evaluating the apnea state. It is suggested that the postoperative function can now be predicted preoperatively.

CFD Investigation of Vehicle’s Ventilation Systems and Analysis of ACH in Typical Airplanes, Cars, and Buses

The simulation of the ventilation and the heating, ventilation, and air conditioning (HVAC) systems of vehicles could be used in the energy demand management of vehicles besides improving the air quality inside their cabins. Moreover, traveling by public transport during a pandemic is a concerning factor, and analysis of the vehicle’s cabin environments could demonstrate how to decrease the risk and create a safer journey for passengers. Therefore, this article presents airflow analysis, air changes per hour (ACH), and respiration aerosols’ trajectory inside three vehicles, including a typical car, bus, and airplane. In this regard, three vehicles’ cabin environment boundary conditions and the HVAC systems of the selected vehicles were determined, and three-dimensional numerical simulations were performed using computational fluid dynamic (CFD) modeling. The analysis of the airflow patterns and aerosol trajectories in the selected vehicles demonstrate the critical impact of inflow, outflow, and passenger’s locations in the cabins. The CFD model results exhibited that the lowest risk could be in the airplane and the highest in the bus because of the location of airflows and outflows. The discrete CFD model analysis determined the ACH for a typical car of about 4.3, a typical bus of about 7.5, and in a typical airplane of about 8.5, which were all less than the standard protocol of infection prevention, 12 ACH. According to the results, opening windows in the cars could decrease the aerosol loads and improve the low ACH by the HVAC systems. However, for the buses, a new design for the outflow location or an increase in the number of outflows appeared necessary. In the case of airplanes, the airflow paths were suitable, and by increasing the airflow speed, the required ACH might be achieved. Finally, in the closed (recirculating) systems, the role of filters in decreasing the risk appeared critical.

CFD Study of Airflow and Microclimate Patterns Inside a Multispan Greenhouse

Understanding and improving greenhouses requires the analysis and modelling of energy and mass exchange phenomena. The mastery of all these physical mechanisms can make it possible to propose technological solutions to control the greenhouse climate. This study presents an analysis and simulation of air flow, temperature and humidity patterns ,in ½-ha multi-span greenhouse with oblique side walls,covered by insect proof nets.The site is located in the coastal area of southern Morocco. The fundamental calculation of climatic conditions is based on CFD, wich uses the mass, momentum and energy conservation equations. The dynamic influence of the insect screens and tomato crop on airflow movement, was described ,using the concept of the porous medium approach proposed by Darcy and Forchheimer.The coupling of convective and radiative exchanges at the plastic roof cover is considered. A good agreement was observed between the measured and simulated values for inside air temperatures and relative humidity. Insect screens significantly reduced airflow and increased thermal gradients inside the greenhouse. The results clearly showed the heterogeneity of the greenhouse’s internal climate, which infects agricultural production in quantity and quality

Experimental study on the influence of model variations on the airway occlusion of an obstructive sleep apnea patient

This study deals with the analysis of model parameters to mimic the airway collapse of an obstructive sleep apnea patient during nasal breathing. Different material properties and geometry variations of a patient-specific airway model are analyzed in detail. The patient-specific airway geometry is obtained from MRI data. A completely rigid model is compared to two partly elastic variations with different elasticities. Furthermore, the influence of the nasal cavities and the treatment effect of a mandibular protrusion are studied. Rigid model parts are 3D-printed and elastic parts cast from silicone. The models are analyzed under the impact of a transient airflow which is realized through a computer controlled piston pump. The results suggest, that, for moderate deformations, the elasticity of the soft tissue replicate influences rather the level of the pressure drop inside the airway than the shape of the pressure curve. The same suggestion can be made for the influence of the nasal cavities. Often, the spatial location of the minimum pressure is taken as the collapse site of the airway geometry. This study demonstrates, that the spatial locations of the minimum pressure and the maximum deformation do not match. This reveals the importance of a coupled approach of soft tissue and airflow analysis in the search of the collapse site and therefore the best treatment option. A treatment effect of the mandibular protrusion can be anticipated with an accurate patient-specific airway model.

Numerical Simulation and Analysis of Airflow in the Condensing Zone of Compact Spinning with Lattice Apron

Abstract The airflow field pattern in the condensing zone plays a vital role in the pneumatic compact spinning, which significantly affects the yarn's qualities. This study aimed to analyze the effects of the different negative air pressures on fiber condensing in compact spinning with lattice apron using ANSYS. The results of airflow simulations reveal that by increasing the negative pressure, the flow velocity increases, leading to a more tremendous increase in the transverse condensing effects. Additionally, a better convergence led to reduced fiber width and eliminated the spinning triangle. Experimental results showed that the three yarns spun with the highest negative pressure had better strength, hairiness, and evenness than those spun with lower negative pressure.

Experimental investigation of internal air flow during slow piston compression into isothermal compressed air energy storage

Compressed air could be a solution for the future mass storage of renewable energies. The isothermal compression and expansion of air by liquid piston is a solution that offers good performance and significant power. Lengthening the compression chamber and slowing down piston displacement may be advantageous for quasi-isothermal development. Presented here is an analysis of the internal air flow during slow piston compression inside a compression chamber with a very low stroke-to-bore ratio. The existence of two consecutive flow regimes is produced repeatably by 2D PIV (particle image velocimetry) measurement. First, a highly-structured regime develops with air speeds significantly higher than the piston advance speed, and a general recirculation of the air. The symmetry of this structure is confirmed with a simple flow distribution model. A second, more disorderly, flow regime then takes over for the remainder of the compression. The transition between the two regimes observed is also described, highlighting instabilities in the high shear zones in the transition from the first regime to the second.

Fluid flow simulation of industrial fixed bed mixed-flow grain dryer using k-ω SST turbulence model

The fluid dynamics analysis on industrial, mixed-flow grain dryers with fixed bed using computational techniques is necessary to assist the design of such equipment contributing to cost reduction in the dryer projects and agricultural drying operations that involve the production of grains in the world. This study presents a Computational Fluid Dynamic (CFD) solution for air flow analysis in an industrial dryer. The air flow at the inlet and outlet of the dryer was investigated using the k-ω SST turbulence model. The dryer region with soybean was considered as a laminar porous medium flow in the permanent and isothermal regime, having for the model a simplified geometry with the tower considered as a porous medium and the air inlet and outlet as a turbulent fluid domain. The flow was treated with a permanent and isothermal regime. Dryer flow and pressures were used according to design parameters. To validate the k-ω SST turbulence model, the velocity profile at the dryer inlet was obtained experimentally, which presented results with good agreement between the numerical and the experimental model. The model obtained satisfactory results of the computational validation of the air flow in the dryer with good convergence requiring a minimum of computational effort, being suitable for the simulation of industrial-scale dryers, as to its air flow through a tower, operating with fixed bed soybean in the steady and isothermal regime. Keywords: computational methods, fixed bed, porous medium, soybean dryer, turbulent flow DOI: 10.25165/j.ijabe.20211402.5321 Citation: Visconcini A R, Andrade C M G, Costa A M S. Fluid flow simulation of industrial fixed bed mixed-flow grain dryer using k-ω SST turbulence model. Int J Agric & Biol Eng, 2021; 14(2): 226–230.

Study of airflow regime upon optic inside frequency multiplying device and achievement of cleaning technique

Based on demands of avoiding adsorption of particulate contaminants on optic and pledging an ultra-high cleanliness inside frequency multiplying device (FMD), cleaning technique combining air knives is subtly selected to form an antifouling barrier to protect surface of optic. Airflow analysis is one of prerequisites and necessities to comprehend mechanism of cleaning realization either at atmospheric pressure where the whole device operates during laser target shooting or under vacuum which is an approach to restrain ultraviolet damage on optic. Firstly, it is determined through theoretical calculations that airflow regime under low pressure vacuum is a kind of compressible continuous flow. Subsequently, by means of simulation investigation and experimental research methods on variation regularity of air curtain barrier formed by air knife, it is exhibited that the attenuation rates of air speed are rather drastic at the beginning and the airflow purged out by air blade will eventually gather under both pressure states. However, air curtains formed vary in morphology representing fascinating results that air curtain evolves into "camel peak shape" under atmospheric pressure and "half-moon pattern" under low vacuum. Finally, design sizes of air diversion ducts on metal frame are reasonably optimized to reach suitable diversion ratios of airflow. And the optimum design that the widths of the ducts under vacuum are about twice as long as ones at atmospheric pressure demonstrates that there truly are intense demands on research of unknown and severity under conditions of vacuum.

Coupled Computation Fluid Dynamics Models for Air Flow and Thermal Analysis of Marine Engine Room

Abstract Thermal management of machinery spaces of marine vessels using a heating ventilation and air conditioning (HVAC) system is needed to maintain the temperature within the tolerable limit for efficient combustion in internal combustion engines and proper functioning of on-board electronic devices by removing high heat generations from in-house auxiliary systems. This study presents a numerical methodology using coupled simple and detailed computational fluid dynamics (CFD) models of air passages and engine components. The developed method is found to have a good agreement with the experimental results. Further, different layouts of vents and heat-generating components in the engine room are analyzed to obtain air flow and temperature distributions. It is found that the locations of vents and heat generating components have a significant effect on the maximum temperature distribution in the engine room.

Computational analysis of gas permeability of slip flow through microannulus replete by based‐circular Sierpinski porous medium

AbstractThere are wide applications for flow in a microporous medium. In this study, a computational analysis of airflow through a porous microannulus constructed by circular‐based Sierpinski has been performed in a slip flow regime, where several parameters played an important role in the flow characteristics. These parameters are the Knudsen number, the average friction factor, radius ratio, and porosity. The impacts of these parameters on permeability and the gas flow characteristics are examined and analyzed thoroughly. The ranges of the investigated parameters are as follows (0.001 ≤ Kn ≤ 0.1 and the porosity range is 0.75 ≤ ε ≤ 0.95). The results showed that porosity has a significant impact on the velocity distribution and Darcy number. The Knudsen number has also a direct effect on the velocity distribution, while it has a positive logarithmic proportionality with a dimensionless permeability but the radius ratio does have a neglected effect on the Darcy number. Moreover, the effect of the average friction factor has an inverse proportional relationship to the Darcy number.

Deviation Analysis of Pitot Static Probe Airflow Receiving for Civil Aircraft

The pitot static probe provides the atmospheric pitot pressure and static pressure information for the Air Data system for calculating flight parameters for flight. The installation angle of the f pitot static probe directly affects the accuracy of its airflow receiving, and directly affects the judgment of the aircraft and the crew. In this paper, we have conducted an in-depth analysis of the airflow receiving deviation of the pitot static probe, and simulated the large changes in flight parameters of a certain type of aircraft under different installation deviation angles. Finally, commonly used deviation treatment suggestions are given for the installation deviation of the full static pressure probe of a certain type of aircraft.

Effects of Modulus of Elasticity on airflow in Human Respiratory airway

In this work, Computational analysis of air flow in human respiratory tract model is done by the use of CFD technique. Fluid Structure Interaction (FSI) method is used on the third-to-sixth generation simplified respiratory tract model for computational study. The modulus of Elasticity is varied in a range of 1 to 5 MPa and its effect on flow-physics is captured inside human airway model. The variation of velocity and its effect on deformation has been captured for both rigid and flexible model and its analysis is carried out. The result from simulation shows that as the Modulus of elasticity increases, wall deformation decreases.

Numerical analysis of secondary airflow in a rotating cavity of a gas‐turbine at high operating points with vortex reducer implementation

Temperature and pressure ratios in gas turbines have grown over time to increase the performance and efficiency of the engine. This, in turn, has required improvements to the effectiveness of the secondary air system to enhance the cooling performance of critical components. Analysis of pressure losses in the secondary systems of aero gas turbines has identified a significant contribution in the bled airflow path through the compressor cavity between rotating disks. In this configuration, radial inflow usually occurs within an Ekman layer along the walls, while a free vortex condition appears in the cavity, generating losses and limiting transfer to the proximity of the wall. Nozzles acting as vortex reducers have shown promising performance under aeronautic conditions, although the complexity of the system limits the testing of popular theoretical models to low mass flows, based on a free vortex for a radially inward flow in a rotating cavity. For industrial applications, it is important to verify the behavior of these models at high operating points. Given that improving the performance of secondary air systems has increased in importance over time, the present study compares the one-dimensional theoretical models of Shvets and Owen with a three-dimensional Computational Fluid Dynamics (CFD) analysis verified against previous experimental values from literature. This approach allows a focus on different and more complex vortex reducer geometries while proving the usefulness of analytical techniques at high operating loads, underlying their limitations and allowing improvements to be proposed.

Deposition characteristics of soot and tire-wear particles on urban tree leaves

This study aims to analyze the deposition characteristics of particles of major tree species in urban areas of Korea by conducting experiments. To simulate black carbon (BC) particles emitted by automobiles among particulate matter floating in the roadside air, soot particles are generated using a diffusion flame burner, whereas tire wear particles are generated by the mechanical friction between tires and asphalt specimen. The deposition characteristics of the particles of each tree species are compared using a deposition chamber, which was designed and manufactured for exposing the trees to the BC particles based on air flow analysis. The five types of tree species that were used for the experiments were Zelkova serrata, Metasequoia glyptostroboides, Pinus densiflora, Euonymus japonicus, and Spiraea prunifolia f. simpliciflora. The particle deposition velocity was used to determine and compare the particle deposition per unit area for the different species and was found to be highest in Spiraea prunifolia f. simpliciflora, followed by, in descending order, Zelkova serrata, Euonymus japonicus, Pinus densiflora, and Metasequoia glyptostroboides for both soot and tire wear particles. Furthermore, the particle deposition rate was used to determine and compare the degree of particle deposition in a space of equal volume, which was found to be highest in Pinus densiflora, followed by, in descending order, Metasequoia glyptostroboides, Zelkova serrata, Spiraea prunifolia f. simpliciflora, and Euonymus japonicus; the highest particle deposition rate of the tire wear particles was in Spiraea prunifolia f. simpliciflora, followed by, in descending order, Pinus densiflora, Euonymus japonicus, Zelkova serrata, and Metasequoia glyptostroboides. For broad-leaved trees, the degree of soot particle deposition on the front side differed from that on the back side. The particle deposition velocity and particle deposition rate varied according to the tree species due to surface roughness and geometrical features of the leaves and branches. The concentration of BC particles in the roadside air, which is produced by passing motor vehicles, can be reduced if the tree species that have high particle deposition rates are planted along the roadside.

Non-uniform Airflow Analysis of a Greenhouse Extractor Axial with Conical Diffusers using CFD Simulation

Interest in wind energy use has increased in recent years, specifically in the study field of protected agriculture. To harness residual wind energy produced in an air exhaust system, a wind energy recovery system could be installed using a horizontal axis wind turbine, designed according to airflow conditions at the system outlet. For this reason, airstream in a greenhouse exhaust system was analyzed, wherefore a set of extractors with different number and blades wide, air attack angle, angular velocity and geometry exhaust duct were designed. Subsequently, some simulations were performed by Computational Fluid Dynamics based on different boundary conditions and according two pipeline geometric configurations: with simple and double conical diffuser. 3D model resolution was based on numerically solving the Navier-Stokes equations by means of a finite volume discretization method. With this information 36 2D images of velocity contours and another 36 in 3D of the output airflow streamlines were obtained, also speed and power curves were constructed with respect to geometric model and exhaust system. Moreover, air flow, torque, and power of exhaust system were determined. Finally, opening and flow angle values inside and outside the exhaust system airstream were estimated. By implementing a waste wind energy recovery system at a greenhouse extraction system outlet, will be possible to improve the use of generated airstream, which in most cases is expelled to the outside.

Experimental and numerical analysis of temperature and air flow in the classroom using CFD

Day by day increase in temperature due to global warming. India is a sub-continent where temperature ranges about 35 °C–40 °C and some region where temperature reaches to 40 °C during summer. Hence students are not comfortable in the class room which results in poor concentration. To provide the comfort environment conventional devices like fans are more demandable during summer. Providing proper ventilation in the class room enhances the natural circulation of air which will reduce room temperature and also load on fans. CFD analysis was done with various parameters such as existing ventilation, without ventilation and with additional ventilation. The results are compared with experimental results. It is observed that after providing additional vent in the class room the temperature is in comfortable level.

DESIGN OF HVAC AIR DUCTS FOR ELECTRIC BUSES AND FLOW ANALYSIS WITH CFD METHOD

DESIGN OF HVAC AIR DUCTS FOR ELECTRIC BUSES AND FLOW ANALYSIS WITH CFD METHOD

The measuring system for air mass flow rate determination - difficult measuring conditions - case study

Accurate gas flow measurement is required in many industrial applications. In typical circumstances the most reliable option is the use of single-hole orifice flowmeters, which characterize with the simplicity of the construction, lack of moving parts and high accuracy. However, such devices require long straight duct sections in order to perform the proper measurement. Sometimes on existing installations, where the space is limited, there is no possibility to fulfill these requirements. Such problem appeared in power plant in Opole. Multi-hole orifice flowmeters can be a reasonable solution in this particular case. Due to their enhanced resistance to flow disturbance they require shorter duct sections and could provide a correct measurement. The paper presents the results of the numerical analysis of air flow in 6-hole orifice flowmeter. The calculations were performed for the existing duct geometry from power plant in Opole. The orifice pressure drop was estimated for a wide range of Reynolds number. The analysis of the numerical results showed that multi-hole orifice flowmeters can be used in investigated situation. The results of experimental measurements performed in Opole power plant are also included in the paper.

CFD analysis of air flow through the LNG ambient air vaporizer with longitudinal finned tubes

Ambient air vaporizers, depending on their efficiency, can be up to several meters high. Therefore, they can have a large outside surface area exposed to the wind. Forced air flow through the vaporizer structure have a beneficial effect on improving heat transfer from the environment. On the other hand, if the vaporizer is placed in the region of significant wind velocities, the wind forces acting on the structure can be considerable. This paper presents CFD analysis of air flow through the structure of the ambient air vaporizer with a 6 x 6 finned tube array. The effect of changing wind direction on the wind pressure and wind velocity distributions is investigated.

Computational Analysis of Airflow in Upper Airway under Light and Heavy Breathing Conditions for a Realistic Patient Having Obstructive Sleep Apnea

Background: Obstructive sleep apnea is a sleeping disorder that has troubled a sizeable population. There is an active area of research on obstructive sleep apnea that intends to better understand airflow behaviors and therefore treat patients more effectively. This paper aims to investigate the airflow characteristics of the upper airway in an obstructive sleep apnea (OSA) patient under light and heavy breathing conditions by using Turbulent Kinetic Energy (TKE), an accurate method in expressing the flow concentration mechanisms of sleeping disorders. It is important to visualize the concentration of flow in the upper airway in order to identify the severity level of the obstruction during sleep. Methods: Computational fluid dynamic (CFD) analysis was used as a solution tool to evaluate the airflow during light and heavy breathing conditions. A medical imaging technique was used to extract the 3D model from the CT scan images. Additionally, mesh generation and simulation were carried out via CFD software to evaluate the light and heavy breathing characteristics related to obstructive sleep apnea. Steady state Reynold’s averaged Navier-Stoke (RANS) with the k-ω shear stress transport (SST) turbulence model was utilized. The airflow characteristics were quantified using parameters such as pressure distribution, skin friction coefficient, velocity profile, Reynolds number, turbulent Reynolds number and turbulence kinetic energy. Results: Contour plots at different planes were used to visualize the airflow distribution as it passed through different cross-sectional areas of the airway. The results revealed that the presence of a smaller cross-sectional area of the airway caused an increase in airflow parameters, especially during heavy breathing. Furthermore, turbulent airflow conditions along the airway were noticed during heavy breathing. The severity of OSA could be measured by the turbulent kinetic energy which is able to show the behavior and concentration of mean flow. This study is expected to provide crucial and important results by visualizing the concentration of airflow mechanisms and characteristics of a patient’s airway during light and heavy breathing. These findings enable TKE to be used as a new tool for characterizing the severity of obstructive sleep apnea in the upper airways of patients.