Numerical Simulation Of Airflow Research Articles

Characteristics of inertial deposition in a double bifurcation

A direct numerical simulation of air flow and particle motion is conducted for doubly bifurcated models in order to see the effect of the velocity profile distorted by the previous bifurcation on particle deposition, because particle deposition in a bifurcated airway is very sensitive to the velocity profile at the inlet, not the magnitude. Flow fields are solved using the FIDAP, an FEM code, and particle trajectories are obtained by a Lagrangean integration. Characteristics of air flow and particle motion in double bifurcations are quite different from what can be imagined based on results for single bifurcation models. The distorted velocity profile can reduce deposition efficiency in the second generation by about 50% when compared with the single bifurcation for the same Stokes number. The bifurcation geometry is also important for particle deposition, and the out-of-plane rotated geometry gives about 40% higher deposition than the in-plane bifurcations.

Numerical Simulation of Airflow Over Potential Telescope Sites

view Abstract Citations (4) References (3) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Numerical Simulation of Airflow Over Potential Telescope Sites De Young, David S. ; Charles, Richard D. Abstract Numerical simulation can provide a valuable tool in evaluating the characteristics of possible sites for new telescopes. This technique can provide accurate information about topographically induced atmospheric disturbances and turbulent boundary layers occurring in the high Reynolds number airflows over such sites. Results are given here for simulations of airflow at the two Gemini 8 m telescope sites on Mauna Kea and Cerro Pachon. These calculations permitted an informed choice to be made between two sites on Cerro Pachon; determined that upwind topographic features did not have a significant influence at the Mauna Kea site; and confirmed that the proposed height of the telescope pier would place the primary mirror above the turbulent boundary layer under the majority of wind directions and speeds. Publication: The Astronomical Journal Pub Date: December 1995 DOI: 10.1086/117751 Bibcode: 1995AJ....110.3107D Keywords: SITE TESTING full text sources ADS |

Numerical simulation of airflow in the human nasal cavity.

An anatomically correct finite element mesh of the right human nasal cavity was constructed from CAT scans of a healthy adult nose. The steady-state Navier-Stokes and continuity equations were solved numerically to determine the laminar airflow patterns in the nasal cavity at quiet breathing flow rates. In the main nasal passages, the highest inspiratory air speed occurred along the nasal floor (below the inferior turbinate), and a second lower peak occurred in the middle of the airway (between the inferior and middle turbinates and the septum). Nearly 30 percent of the inspired volumetric flow passed below the inferior turbinate and about 10 percent passed through the olfactory airway. Secondary flows were induced by curvature and rapid changes in cross-sectional area of the airways, but the secondary velocities were small in comparison with the axial velocity through most of the main nasal passages. The flow patterns changed very little as total half-nasal flow rate varied between resting breathing rates of 125 m/s and 200 ml/s. During expiration, the peaks in velocity were smaller than inspiration, and the flow was more uniform in the turbinate region. Inspiratory streamline patterns in the model were determined by introducing neutrally buoyant point particles at various locations on the external naris plane, and tracking their path based on the computed flow field. Only the stream from the ventral tip of the naris reached the olfactory airway. The numerically computed velocity field was compared with the experimentally measured velocity field in a large scale (20x) physical model, which was built by scaling up from the same CAT scans. The numerical results showed good agreement with the experimental measurements at different locations in the airways, and confirmed that at resting breathing flow rates, airflow through the nasal cavity is laminar.

Prediction method of passenger's thermal sensation by numerical simulation of air flow in an automobile passenger compartment

Prediction method of passenger's thermal sensation by numerical simulation of air flow in an automobile passenger compartment

Numerical simulation of air flow around multiple objects using the discrete vortex method

Abstract The discrete vortex method, a Lagrangian grid-free numerical technique, is employed to solve the two-dimensional Navier-Stokes equations for flow around multiple objects. The method, unlike the Eulerian approaches of finite differences and finite elements, avoids the introduction of numerical viscosity at high Reynolds numbers. A boundary integral equation method for the potential flow component is included here to make vortex simulations in and around complex geometries more feasible. A fast adaptive multipole expansion algorithm is incorporated into the code to reduce the time needed to calculate the vortex interactions. Test problems examined include flow around one circular cylinder, and two cylinders in tandem at various gaps. Numerical results are in excellent agreement with published experimental results and other computational studies. Applicability of the method to indoor and outdoor air pollution problems is discussed, specifically with regard to contaminant transport in recirculating regions.

Simulation of air flow over a heated flat plate using anisotropic k- ε model

Numerical simulation of air flow over a heated flat plate was performed using the anisotropic k- ε model. The wall functions for velocity and temperature were modified using universal functions, and the bouyant term in the dissipation equation was eliminated. The calculated results were compared with those from wind tunnel experiments. The calculated mean velocity, turbulent intensity and mean temperature showed good agreement with profiles measured in the wind tunnel.

Simulation of air flow over a heated flat plate using anisotropic k-ɛ model

Numerical simulation of air flow over a heated flat plate was performed using the anisotropic k-ε model. The wall functions for velocity and temperature were modified using universal functions, and the bouyant term in the dissipation equation was eliminated. The calculated results were compared with those from wind tunnel experiments. The calculated mean velocity, turbulent intensity and mean temperature showed good agreement with profiles measured in the wind tunnel.

Modeling Particle Transport in Slot-inlet Ventilated Airspaces

Numerical simulation of airflow and transport of neutrally buoyant bubbles in a slot-ventilated airspace was conducted. Airflow was simulated using the k-e turbulence model. Transport of neutrally buoyant bubbles was calculated using the equation of motion of a particle. Scale model experiments were also performed. Air velocities were measured using a three-dimensional hot-film anemometer. Neutrally buoyant bubbles were introduced at selected locations and tracked. Comparison between numerical simulation and experimental results showed good correspondence in velocity fields and in bubble trajectories, fates, and residence times. Thus, this work demonstrated the suitability of using the solution procedure to model bubble transport in slot-inlet ventilated airspaces. Numerical simulation was then used to predict the transport of 5-mm particles. Results did not show any significant difference between 3-mm bubbles and 5-mm particles (rp = 1500 kg/m3) on predicted fates and residence times indicating that 3-mm neutrally buoyant bubbles can be used to model 5-mm particles.

Numerical simulation of air flow over breaking waves

The air flow above breaking monochromatic Stokes waves is studied using a numerical nonlinear model of the turbulent air flow above waves of finite amplitude. The breaking event (spilling breaker) is parameterized by increasing the local roughness at the downwind slope of the wave, just beyond the crest. Both moderate slope waves and steep waves are considered. Above steep breaking waves, a large increase (typically 100%) in the total wind stress — averaged over the wave profile — is found compared to nonbreaking moderate slope waves. This is due to the drastic increase of the form drag, which arises from the asymmetrical surface pressure pattern above breaking waves. Both increase of wave slope (sharpening of the crest) and increase of local roughness in the spilling breaker area cause this asymmetrical surface pressure pattern. A comparison of the numerical results with the recent experimental measurements of Banner (1990) is carried out and a good agreement is found for the structure of the pressure pattern above breaking waves and for the magnitude of enhanced momentum transfer.

Numerical Simulation of Air Flows in Gymnasia

The designers of ventilation systems need to predict the air flow patterns in order to optimize design and to ensure a healthy interior. Numerical simula tion is a powerful tool to obtain the air flow patterns. In the present study, a computer program which solves the three-dimensional conservation equa tions of mass, momentum, energy, and contaminant concentration is used. The program is based on the κ-e turbulence model with wall function expres sions for solid boundaries. Flow fields are computed for two gymnasia, of 24 × 12× 9 m3 and 44 × 23 × 10 m3, with variations in the ventilation rate, the arrangement of inlet and outlet, heating system, and the number of occupants. The simulation gives the field results for air velocity, temperature, contami nant concentration, percentage of dissatisfied people due to draught, and pre dicted percentage of dissatisfied due to thermal comfort.

A numerical simulation of airflows and SO2 concentration distributions in an arid south-western Valley

Three-dimensional numerical models were used to simulate wind and turbulence distributions in the Mohave Valley and plume transport from the Mohave Power Project, located at approximately 120 km south-south-east of Las Vegas, NV. The Modeled meteorological variables were input to a three-dimensional random-puff diffusion model to simulate observed tetroon trajectories and ground-level concentrations of SO2 in the Valley. Numerical simulations indicated that hourly averaged surface concentrations could differ considerably, even when the mean and turbulence variables of the airflows were kept statistically identical. The concentration variations resulted from the differences in initial turbulence velocity and inhomogeneous distributions of airflows that each puff encountered during transport. Because the range of variations is, in general, unknown for both measurements and simulations, it is difficult to assess the representativeness of the observed and simulated values, and therefore to evaluate quantitatively the modeled concentrations against observations.

Numerical Simulation of Air Flow and Inertial Deposition of Particles in a Bifurcating Channel of Square Cross Section

ABSTRACT Air flow pattern and inertial deposition of particles in a bifurcating channel of square cross section have been studied numerically. The Navier-Stokes equation for the air flow are solved...

The Numerical Simulation of Airflow and Dispersion in Three-Dimensional Atmospheric Recirculation Zones

Abstract A three-dimensional, nonhydrostatic numerical code using the two-equation turbulence closure was developed to model the atmospheric transport and diffusion of pollutants over buildings and a three-dimensional hill. The standard engineering two-equation, first-order turbulence closure was modified to account for surface layer effects and the reduced production of dissipation in the region above the surface layer found in an atmospheric boundary layer. The computations for the dispersion of a building rooftop release showed good agreement with wind tunnel measurements, except when very close to the ground. The transport and dispersion of a plume over a 300-m conical hill, Steptoe Butte, was also simulated. The computations are compared with near ground-level field measurements.

Comments on 3-D numerical simulation of airflow around a cubic model by means of the [formula omitted] model by S. Murakami and A. Mochida

Comments on 3-D numerical simulation of airflow around a cubic model by means of the [formula omitted] model by S. Murakami and A. Mochida

Three-dimensional numerical simulation of air flow around a cubic model by means of large eddy simulation

The unsteady, turbulent flowfield around a cubic model has been simulated by means of large eddy simulation (LES). The resolvable-scale flowfield has been obtained directly by solving the filtered, three-dimensional, time-dependent Navier-Stokes equations. The subgrid-scale motions were simulated by an SGS eddy viscosity model. The computed mean velocity dstributions and various turbulence statistics (i.e. turbulence intensity, velocity spectrum, integral scale, etc.) were compared to those obtained from wind-tunnel experiments to examine the accuracy of LES from the viewpoint of engineering applications. The correspondence between numerical simulation and wind-tunnel experiments is found to be good.

Three-Dimensional Numerical Model Simulations of Airflow Over Mountainous Terrain: A Comparison with Observations

Abstract Numerical simulations of airflow over two different choices of mountainous terrain and the comparisons of results with aircraft observations are presented. Two wintertime casts for flow over Elk Mountain, Wyoming where surface heating is assumed to be zero and one case for airflow over Mt. Withington, New Mexico where surface heating is strong are considered. In the Elk Mountain simulations the flow becomes approximately steady state since the upstream conditions are assumed to be constant and the surface heating is assumed to be zero. The response is significantly different in the two cases. In one case (dynamic Elk) strong lee waves formed with a horizontal separation of ∼10 km whereas in the second case (microphysical Elk) mainly weak untrapped waves formed with a vertical wavelength of ∼2.5 km. Because of the presence of the lee waves in the first case it is shown that the ridges south of Elk Mountain affect the flow near Elk Mountain. In the second case where there were no strong lee waves, ...