Time-dependent Airflow Research Articles

Inverse modeling of indoor instantaneous airborne contaminant source location with adjoint probability-based method under dynamic airflow field

Accurate and prompt identification of airborne contaminant source location in indoor environment is of vital importance for building operation safety. Successful inverse tracking algorithm to identify airborne contaminant location usually requires limited sensor readings and indoor airflow information as input. Such mathematical algorithm under steady-state indoor airflow scenario has been intensively investigated. However, in many built environment scenarios, air velocity direction and magnitude keeps changing with time, making the transportation process of airborne contaminant significantly different from it under steady-state airflow. This paper mainly focuses on the airborne contaminant source location identification under dynamic airflow, by employing an adjoint probability-based inverse tracking method. The mathematical model and process of indoor instantaneous contaminants source location identification under dynamic air flow field is investigated and presented. Case studies using Computational Fluid Dynamics (CFD) tool by unsteady RANS simulation are conducted on a subway station model as well as an aircraft cabin, in which case experimental validation is also conducted. The capability of the new method is verified for air contaminant source location identification under dynamic indoor airflow.Practical implications: Successful identification of airborne contaminant source location under dynamic airflow field implies the capability of the method to locate an airborne contaminant source by limited sensor information and time-dependent airflow field in real-time. Practically the time-dependent airflow field data can be obtained through CFD simulation with unsteady RANS model with monitored time-dependent boundary condition.

Numerical investigation of flow-induced deformation along the human respiratory upper airway

Fluid–structure interaction (FSI) was considered to predict the compliant wall deformation in human respiratory upper airway. Timedependent airflow was analyzed by the large eddy simulation technique. The surface deformation along the respiratory airway was evaluated by linear structural analysis via a unidirectional FSI approach without considering the tissues, muscles, and bones surrounding the airway. Human subcutaneous tissue and corresponding animal data were used to establish the mechanical properties of the inner tissues throughout the respiratory airway. Although the lowest local pressure was found near the junction between the larynx and trachea, a relatively large deformation was observed in the distributed area between the nasal cavity and trachea. Furthermore, the mean velocity at the location of maximum deformation is negatively correlated with the pressure but is positively correlated with the deformation amount over time.

FE Modeling of Human Vocal Tract Acoustics.<BR> Part II: Influence of Velopharyngeal Insufficiency on Phonation of Vowels

Developed FE models of acoustic spaces of nasal and vocal tract for vowels /u:/, /a:/ and /i:/ are used to study the influence of velofaryngeal insufficiency on phonation of these vowels. Acoustics frequency-modal characteristics are studied by modal analysis and numerical simulation of acoustic signals in time domain is performed by transient analysis of the FE models. The vocal tract is excited by time dependent airflow at the position of vocal folds, and the time and frequency responses are calculated near the lips and nose. The theoretical results are partly compared with acoustic measurements on physical models designed by the rapid prototyping technique from the FE models, and by clinical investigation.

Simulation of the ice accretion process on a transmission line cable with differential twisting

Cable rotation caused by ice accretion was specifically modelled and simulated for this paper. Both ice loads and wind-on-ice loads were taken into account during the modelling, and the quantity for the wind-on-ice loads was obtained by integrating air pressure and air shear along the airflow boundary. Air pressure and air shear were both evaluated through time-dependent airflow computations. Two types of overhead transmission line cables, namely, the Bersimis cable and an overhead ground wire, were examined using the new model, and a number of conclusions were drawn. The validity and reliability of the modelling methods were confirmed by comparing the simulation results with those obtained from experimental measurements.Key words: airflow computation, cable rotation, ice accretion, computer modelling, simulation.

Two-dimensional modelling of the ice accretion process on transmission line wires and conductors

The main objective of this paper is to introduce a new 2-D icing model, of which the primary purpose is the simulation of the ice accretion process on overhead power line cables. The parameters of the model, such as the Local Collision Efficiency (LCE) and the local Heat Transfer Coefficient (HTC), were evaluated on the basis of time-dependent airflow computations and water droplet trajectory calculations. For wet accumulations, the movement of a surface water film was monitored at each time step so as to obtain the film's thickness and direction. In order to validate the present model, a number of experimental tests were carried out at the CIGELE Atmospheric Icing Research Wind Tunnel (CAIRWT). The results show that, on the whole, the proposed ice model performed well in simulating and predicting ice-grown shapes under dry and wet icing conditions.

1118 人体近傍環境の数値シミュレーション

Particulate matters less than 2.5μm (PM_<2.5>) are lately focused attention for human health. Numerical simulations were carried out to investigate the two-dimensional, time-dependent air flow and the motion of particulate matters including human breath. As a result, the time-dependent particle concentration and the number of particles in the vicinity of human face were obtained A detailed discussion will be presented in the paper.

Soil Clean Up byin-situAeration. XV. Effects of Variable Air Flow Rates in Diffusion-Limited Operation

Abstract A model for soil vapor extraction (SVE) is developed which includes the effects of mass transport kinetics of VOC between nonaqueous phase liquid (NAPL) droplets and the aqueous phase, and between the aqueous and vapor phases. The model permits time-dependent gas flow rates in the vapor extraction well. The model is employed to demonstrate the effectiveness of certain types of pilot-scale SVE experiments in determining the rate of mass transport processes. It is also used to explore several time-dependent air flow schedules for SVE well operation. The results indicate that the use of suitably selected air flow schedules in SVE can result in greatly reduced volumes of air to be treated for VOC removal with relatively little increase in the time required to meet remediation standards.

Thermal modeling of integrated roof air heater for passive solar space heating of a non-air-conditioned building

This communication presents the periodic heat transfer analysis for solar space heating of an unconditioned building with an integrated roof air heater. The system consists of an air duct within the roof such that the air is continuously or intermittently forced to circulate the cooler room air through the inlet of the air duct. Time dependence of the air flow is represented by a step function of time for daily operation and, hence, has been expressed as a Fourier series in time. The analysis takes into account air ventilation, ground heat conduction and furnishings. The effects of depth of the air duct from the outer surface of the roof and the magnitude and duration of air flow rate on indoor air temperature have been studied for a typical cold winter day in Delhi. It is seen that a time dependent air flow through the duct is desirable from the point of view of increasing the indoor air temperature in the case of a bare roof. However, in the case of a blackened and glazed roof, continuous air flow is needed for increasing the room air temperature. The results are desirable from the point of view of efficient space heating of solar passive buildings.