Numerical Simulation Of Airflow Research Articles

Numerical Simulation of Air Flow in Model Room

AbstractEfficient, and appropriate indoor air environment is important issue in building design. Air flow patterns which are formed in the room are mainly depended on its geometrical parameters. Investigation of flow patterns are performed on a relatively simple geometry of model room, with a small obstacle (partition) in it. There are several interesting flow phenomena which are present in the model room: flow through sudden geometry expansion, stagnation flow with lateral boundaries, flow over the obstacle, etc. Since the air velocities are low, it is assumed that flow is incompressible. Numerical calculations of these patterns have been done using RANS modeling approach. For all calculations an extended version of open‐source CFD software OpenFOAM was used. Several turbulence models have been used for RANS approach, with special attention on their performance in capturing unsteady flow phenomena. Comparison of obtained numerical results and available experimental results for mean velocities shown good agreement. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental and numerical analysis of air flow in a dead-end channel

This study summarises the results of experimental testing and numerical simulations of airflow in a laboratory model of a blind channel aired by a forced ventilation system. The aim of the investigation is qualitative and quantitative verification of computer modelling data. The components of the velocity vector are measured using Particle Image Velocimetry. Two turbulence models, the standard k-ε model and the Reynolds Stress Model, were used in a numerical calculation. A comparison of the magnitude of the velocity vector and the kinetic energy of turbulence obtained by the experimental methods and numerical calculations shows that in qualitative terms, the predicted velocity field correlates well with the measurement data. The mean relative error between the results of the calculations and measurements for the magnitude of the velocity vector and the kinetic energy of turbulence is about 29% for the Reynolds Stress Model and 33% for the standard k-ε model.

Experimental and Numerical Analysis of Air Flow, Heat Transfer and Thermal Comfort in Buildings with Different Heating Systems

Abstract Monitoring of temperature, humidity and air flow velocity is performed in 5 experimental buildings with the inner size of 3×3×3 m3 located in Riga, Latvia. The buildings are equipped with different heating systems, such as an air-air heat pump, air-water heat pump, capillary heating mat on the ceiling and electric heater. Numerical simulation of air flow and heat transfer by convection, conduction and radiation is carried out using OpenFOAM software and compared with experimental data. Results are analysed regarding the temperature and air flow distribution as well as thermal comfort.

Верификация задачи численного моделирования течения воздуха в осевой компрессорной ступени

Верификация задачи численного моделирования течения воздуха в осевой компрессорной ступени

Numerical simulation of heat and hydraulic characteristics of heat exchange surfaces of plate-finned heat exchangers

The article presents the results of numerical simulation of airflow in the channel of heat exchange surface. Based on these results, the surface characteristics have been constructed. Evaluation of simulation results in comparison with experimental data is given.

Auto Radiators – Study Regarding Air Flow along the Channels

In this paper will be presented the results of the measurements and experimental data processing performed on aluminium auto radiators manufactured in Romania. Also, will be exposed numerical simulations of air flow through an auto radiator, from the models studied. It will be study the convective heat exchange efficiency through Nusselt number and intensity of heat transfer by forced convection of air through the fins with sinusoidal profile using Colburn criterion. Further, the numerical simulation of air flow through a mini channel created by a fin with sinusoidal profile, considered on the width of the device, highlights the heat diffusivity through Prandtl number, along this channel, depending on the particularities of its geometric shape.

1E24 実形状肺細葉モデル内の気流シミュレーション

To reveal mechanism of airflow in alveolus, numerical simulation of airflow considering the expansion and contraction of acinar model was conducted using a realistic pulmonary acinus model. Pulmonary acinar model based on synchrotron micro-CT of mice. Model scale was 893 × 727 × 930 μm^3. The expansion and contraction deforming was changed sinusoidally with time as the moving boundary condition. To evaluate fluid mixing mechanism, streamline was drawn. Consequently, generation and disappearance of the vortex was observed periodically near wall surface of pulmonary acinar model.

Investigation of the flow-field in the upper respiratory system when wearing N95 filtering facepiece respirator

ABSTRACTThis article presents a reverse modeling of the headform when wearing a filtering facepiece respirator (FFR) and a computational fluid dynamics (CFD) simulation based on the modeling. The whole model containing the upper respiratory airway, headform, and FFR was directly recorded by computed tomography (CT) scanning, and a medical contrast medium was used to make the FFR “visible.” The FFR was normally worn by the subject during CT scanning so that the actual deformation of both the FFR and the face muscles during contact can be objectively conserved. The reverse modeling approach was introduced to rebuild the geometric model and convert it into a CFD solvable model. In this model, we conducted a transient numerical simulation of air flow containing carbon dioxide, thermal dynamics, and pressure and wall shear stress distribution in the respiratory system taking into consideration an individual wearing a FFR. The breathing cycle was described as a time-dependent profile of the air velocity through the respiratory airway. The result shows that wearing the N95 FFR results in CO2 accumulation, an increase in temperature and pressure elevation inside the FFR cavity. The volume fraction of CO2 reaches 1.2% after 7 breathing cycles and then is maintained at 3.04% on average. The wearers re-inhale excessive CO2 in every breathing cycle from the FFR cavity. The air temperature in the FFR cavity increases rapidly at first and then stays close to the exhaled temperature. Compared to not wearing an FFR, wearers have to increase approximately 90 Pa more pressure to keep the same breathing flow rate of 30.54 L/min after wearing an FFR. The nasal vestibule bears more wall shear stress than any other area in the airway.

Numerical simulations of airflow in the human pharynx of OSAHS patients

Abstract Abstract: Computational Fluid Dynamic simulations are performed in real patient individual pharynx geometries of an Obstructive Sleep Apnea patient. The Navier-Stokes equations as well as the Reynolds Averaged Navier-Stokes equations and k − ∊ and k −ω turbulence models are used. The velocity profile and pressure distribution of the patient without any treatment and the patient wearing a mandibular advancement appliance are compared to each other. The simulation results for the different model conditions all lead to similar results showing the robustness of the numerical solutions. The pressure loss along the pharynx is lower in the presence of a mandibular appliance, which can indicate the reduction of OSAHS severity.

Numerical simulation of airflow and temperature fields around an occupant in indoor environment

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.

Computational fluid dynamics simulation of the upper airway of obstructive sleep apnea syndrome by Muller maneuver.

This study aimed to use computer simulation to describe the fluid dynamic characteristics in patients with obstructive sleep apnea syndrome (OSAS) and to evaluate the difference between during quiet respiration and the Muller maneuver (MM). Seven patients with OSAS were involved to perform computed tomographic (CT) scanning during quiet respiration and the MM. CT data in DICOM format were transformed into an anatomically three-dimensional computational fluid dynamics (CFD) model of the upper airway. The velocity magnitude, relative pressure, and flow distribution were obtained. Numerical simulation of airflow was performed to discuss how the MM affected airflow in the upper airway. To measure the discrepancy, the SPSS19.0 software package was utilized for statistic analysis. The results showed that the shape of the upper airway became narrower, and the pressure decreased during the MM. The minimal cross-sectional area (MCSA) of velopharynx was significantly decreased (P<0.05) and the airflow velocity in MCSAs of velopharynx and glossopharynx significantly accelerated (P<0.05) during the MM. This study demonstrated the possibility of CFD model combined with the MM for understanding pharyngeal aerodynamics in the pathophysiology of OSAS.

Numerical simulation of airflow and micro-particle deposition in human nasal airway pre- and post-virtual sphenoidotomy surgery.

In the present study, the effects of endoscopic sphenoidotomy surgery on the flow patterns and deposition of micro-particles in the human nasal airway and sphenoid sinus were investigated. A realistic model of a human nasal passage including nasal cavity and paranasal sinuses was constructed using a series of CT scan images of a healthy subject. Then, a virtual sphenoidotomy by endoscopic sinus surgery was performed in the left nasal passage and sphenoid sinus. Transient airflow patterns pre- and post-surgery during a full breathing cycle (inhalation and exhalation) were simulated numerically under cyclic flow condition. The Lagrangian approach was used for evaluating the transport and deposition of inhaled micro-particles. An unsteady particle tracking was performed for the inhalation phase of the breathing cycle for the case that particles were continuously entering into the nasal airway. The total deposition pattern and sphenoid deposition fraction of micro-particles were evaluated and compared for pre- and post-surgery cases. The presented results show that sphenoidotomy increased the airflow into the sphenoid sinus, which led to increased deposition of micro-particles in this region. Particles up to 25 μm were able to penetrate into the sphenoid in the post-operation case, and the highest deposition in the sphenoid for the resting breathing rate occurred for 10 μm particles at about 1.5%.

Numerical Simulation of Air Flow inside Acoustic Cyclone Separator

This paper presents a novel concept of cyclone separator, where sound waves are used to agglomerate fine particles. Sound waves generated by Hartmann acoustic generator are introduced into the secondary (core) air flow of cyclone separator. Results of numerical simulation of air flows inside conventional and acoustic cyclone separators are presented. It is shown that intensive pressure pulsations occur in acoustic generator's reflector. These pulsations generate an acoustic field. It is experimentally established that the average separation efficiency of conventional cyclone separator reaches 87.2% only, while separation efficiency of acoustic cyclone separator is approximately 97.5%. Obtained results show that air flows inside cyclone separator can be investigated numerically.

Numerical Simulation of Wind Environment in a Hill and Buildings Configuration

Numerical simulation of air flow over urban areas is an effective way to analyze and predict the wind environment. This paper presents two dimensional computer model results concerning the effects of buildings and/or a hill on the wind flow. The RANS equations and RNG κ-ε turbulence model used in the simulation are discretized by the finite volume method. The computational solution is based on a pressure correction algorithm of the SIMPLE-type. The inflow boundary conditions are given by wind tunnel experiment. In the presence of only a street canyon formed by two buildings, the ambient wind is accelerated and slightly curved at the roof level. When there exist a hill and a street canyon, the velocity in the canyon is affected by the upwind hill. Another simulation model, which has a hill and two street canyons, is used for comparison. There is a little difference in velocity between a single street canyon and two canyons in the presence of an upwind hill.

An experimental validation of a turbulence model for air flow in a mining chamber

In copper mines, excavation chambers are ventilated by jet fans. A fan is installed at the inlet of the dead-end chamber, which is usually 20-30m long. The effectiveness of ventilation depends on the stream range generated by the fan. The velocity field generated by the supply air stream is fully three-dimensional and the flow is turbulent. Currently, the parameters of 3D air flows are determined using the CFD approach. This paper presents the results of experimental testing and numerical simulations of airflow in a laboratory model of a blind channel, aired by a forced ventilation system. The aim of the investigation is qualitative and quantitative verification of computer modelling data. The analysed layout is a geometrically re-scaled and simplified model of a real object. The geometrical scale of the physical model is 1:10. The model walls are smooth, the channel cross-section is rectangular. Measurements were performed for the average airflow velocity in the inlet duct equal 35.4m/s, which gives a Reynolds number of about 180 000. The components of the velocity vector were measured using the Particle Image Velocimetry approach. The numerical procedures presented in this paper use two turbulence models: the standard k-ε model and the Reynolds Stress model. The experimental results have been compared against the results of numerical simulations. In the investigated domain of flow – extending from the air inlet to the blind wall of the chamber – we can distinguish two zones with recirculating flows. The first, reaching a distance of about lm from the inlet is characterized by intense mixing of air. A second vortex is formed into a distance greater than lm from the inlet. Such an image of the velocity field results from both the measurements and calculations. Based on this study, we can conclude that the RSM model provides better predictions than the standard k-ε model. Good qualitative agreement is achieved between Reynolds Stress model predictions and measured components of the velocity.

Numerical simulation of airflow and microparticle deposition in a synchrotron micro-CT-based pulmonary acinus model

The acinus consists of complex, branched alveolar ducts and numerous surrounding alveoli, and so in this study, we hypothesized that the particle deposition can be much influenced by the complex acinar geometry, and simulated the airflow and particle deposition (density = 1.0 g/cm3, diameter = 1 and 3 μm) numerically in a pulmonary acinar model based on synchrotron micro-CT of the mammalian lung. We assumed that the fluid–structure interaction was neglected and that alveolar flow was induced by the expansion and contraction of the acinar model with the volume changing sinusoidally with time as the moving boundary conditions. The alveolar flow was dominated by radial flows, and a weak recirculating flow was observed at the proximal side of alveoli during the entire respiratory cycle, despite the maximum Reynolds number at the inlet being 0.029. Under zero gravity, the particle deposition rate after single breathing was less than 0.01, although the particles were transported deeply into the acinus after inspiration. Under a gravitational field, the deposition rate and map were influenced strongly by gravity orientation. In the case of a particle diameter of 1 μm, the rate increased dramatically and mostly non-deposited particles remained in the model, indicating that the rate would increase further after repeated breathing. At a particle diameter of 3 μm, the rate was 1.0 and all particles were deposited during single breathing. Our results show that the particle deposition rate in realistic pulmonary acinar model is higher than in an idealized model.

3-D laser images of splash-form tektites and their use in aerodynamic numerical simulations of tektite formation

Ten splash-form tektites from the Australasian strewn field, with masses ranging from 21.20 to 175.00 g and exhibiting a variety of shapes (teardrop, ellipsoid, dumbbell, disk), have been imaged using a high-resolution laser digitizer. Despite challenges due to the samples’ rounded shapes and pitted surfaces, the images were combined to create 3-D tektite models, which captured surface features with a high fidelity (≈30 voxel mm−2) and from which volume could be measured noninvasively. The laser-derived density for the tektites averaged 2.41 ± 0.11 g cm−3. Corresponding densities obtained via the Archimedean bead method averaged 2.36 ± 0.05 g cm−3. In addition to their curational value, the 3-D models can be used to calculate the tektites’ moments of inertia and rotation periods while in flight, as a probe of their formation environment. Typical tektite rotation periods are estimated to be on the order of 1 s. Numerical simulations of air flow around the models at Reynolds numbers ranging from 1 to 106 suggest that the relative velocity of the tektites with respect to the air must have been <10 m s−1 during viscous deformation. This low relative velocity is consistent with tektite material being carried along by expanding gases in the early time following the impact.

Simulations of High Reynolds Number Air Flow Over the NACA-0012 Airfoil Using the Immersed Boundary Method

The immersed-boundary method is coupled to an incompressible-flow Reynolds-averaged Navier Stokes solver, based on a two-equation turbulence model, to perform unsteady numerical simulations of airflow past the NACA-0012 airfoil for several angles of attack and Reynolds numbers of 5.0×105 and 1.8×106. A preliminary study is performed to evaluate the sensitivity of the calculations to the computational mesh and to guide the creation of the computational cells for the unsteady calculations. Qualitative characterizations of the flow in the vicinity of the airfoil are obtained to assess the capability of locally refined grids to capture the thin boundary layers close to the airfoil leading edge as well as the wake flow emanating from the trailing edge. Quantitative analysis of aerodynamic force coefficients and wall pressure distributions are also reported and compared to experimental results and those from body-fitted grid simulations using the same solver to assess the accuracy and limitations of this approach. The immersed-boundary simulations compared well to the experimental and body-fitted results up to the occurrence of separation. After that point, neither computational approach provided satisfactory solutions.

Effect of Orifice Introduction on the Pneumatic Separation of Spherical Particles

In order to recycle important rare metals (such as tantalum) in the print circuit boards of waste electronic equipment, the devices must first be delaminated from the board. The devices are then separated into each device type such as capacitors, resistors, thermistors and so on. In this study, the effect of orifices on spherical particles was clarified through numerical simulations of airflow and air­solid multiphase flow in a vertical single-column pneumatic separator. Airflow velocity profiles and particle trajectories were investigated for different numbers of orifices using spherical particles of identical size and different densities. By introducing multiple orifices, the eccentricity of the velocity profile in the vertical direction could be corrected. This eccentricity is caused by the presence of a mesh, which recovers heavy particles after they pass through the second orifice. When the distance between orifices ranged from 400 to 625mm, it was expected that high-speed and high-efficiency separation between orifices would be possible. It implies that step-by-step separation could be conducted in a single separation column. However, under the calculation conditions of our study, the orifices did not affect the separation efficiency because this factor depends on the velocity profile around the feeding position. The separation rate was maximized when the orifices were separated by 625mm.

Two Dimension Numerical Simulation of Airflow over Complex Terrains at Low Altitude

In order to avoid the problems of existing methods, a numerical simulation method for two-dimensional airflow over complex terrains is developed in this paper for the engineering use of flight dynamics. Based on the potential flow theories, the effects of terrains on the wind field are considered by a serial of two-dimensional vortexes, whose strengths are solved by combining with the ground boundary conditions. Numerical examples are studied by the proposed method, and the method is also evaluated by comparing the results with ones from the existing method. The result shows that the two-dimensional profile of complex terrains could be described by a cubic spline curve precisely. The computation procedure proposed in this paper is very simple and efficient, and it could provide a result of wind field with considerable accuracy. Therefore, this method could be used for flight principle evaluation and flight simulators. Finally, through simulate flight path, discussing effect of terrains on track.