Taehyeung Kim

Airflow pattern around a worker in a uniform freestream

The effect of boundary layer separation on worker exposure is an important factor in the design of local exhaust ventilation. Three-dimensional airflow around a mannequin is examined by using flow visualization techniques and hot-film anemometry. Above the chest, a downwash effect is noted; from the chest to the elbows, a combination of downwash and vortex shedding is observed; and from the waist to the hip, vortex shedding appears to be dominant. A coherent vertical flow structure is observed close to the body. Vortex shedding frequency is determined by using hot-film anemometry. The dimensions of the reverse flow region and the area of the vortices are estimated from flow visualization videos.

Modeling a worker's exposure from a hand-held source in a uniform freestream

The phenomenon of boundary layer separation can be an important factor in determining a workers exposure to toxic airborne pollutants. A conceptual model was developed to understand this phenomenon and to predict the average concentration in the reverse flow region downstream of a worker in a uniform freestream. Subsequently, the assumptions of this model were tested experimentally in wind tunnel studies. On the basis of these results, a revised model is presented and validated by using a tracer gas method. The revised model provides a reasonable estimate of the average concentration in the reverse flow region of the mannequin. Empirical models are presented that relate both the average concentration in the reverse flow region and the breathing zone concentration to the body dimensions and the freestream air velocity. Applications and limitations of the results are discussed.

THE EFFECT OF CONTAMINANT SOURCE MOMENTUM ON A WORKER'S BREATHING ZONE CONCENTRATION IN A UNIFORM FREESTREAM

Several factors affecting breathing zone concentration were examined in a paint spray booth by using a tracer gas method. The variables in the study include contaminant momentum, the presence of a flat plate downstream of the worker, the distance between the contaminant source and the body, and the workers motion. A dramatic reduction in breathing zone concentration was observed when the spray gun emitted contaminants with high momentum. Reductions of 30-50% were observed because of the other variables. The source momentum effect was studied, subsequently, in a wind tunnel by measuring the breathing zone concentration of a mannequin with various flows through jets of different diameter, at varying freestream velocities. A functional relationship was determined between nondimensional breathing zone concentration and contaminant source momentum. This relationship is supported by numerical simulations. The effect of contaminant momentum on the near-wake flow field is discussed in conjunction with results from the numerical simulations.

Applications of WRF/CALPUFF modeling system and multi-monitoring methods to investigate the effect of seasonal variations on odor dispersion: a case study of Changwon City, South Korea

Changwon is an industrial city located in the southeastern region of South Korea. Surrounded by coastal and mountainous areas with contiguous industrial and residential areas, the city of Changwon has experienced a high number of malodor complaints in recent years. This study was carried out to investigate the effect of seasonal variations on odor dispersion from industrial to community areas, which were considerably higher from the late spring through fall according to complaint statistics. Investigation methods comprise the applications of electronic odor detector, questionnaire, olfactory system, weather observation data, and weather research and forecasting/CALPUFF modeling system. Results from all methods were consistent in showing that the change of seasons affected the direction of odor diffusion. From summer to early fall, the pollutions emitted from the industrial zone had the highest impact on the residential zone, covering the three most common areas of complaints for unpleasant odors. The reasons are that during the summer period, the reduction of a planetary boundary layer and the prevalence of a consistent sea breeze resulted in the presence of south–southwesterly ocean winds which swept through the factories to a residential area. In contrast, synoptic winds which prevailed during other seasons restrained sea breeze circulation, leading to diverse wind directions. During the fall season, the higher number of complaints could be attributed to a lower wind speed, which caused the poor spread of pollutants from the area with the topography of the basin.

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.

Evaluation of Green House Gases by Transportation Using Traffic Census Results from Changwon City

【In this study, which aims to estimate the volume of greenhouse gas emitted by road transportation vehicles in Changwon City, the emission rate was calculated on the basis of the actual traffic volume measured at major crossroads and compared with the results obtained from the methodology used to estimate the greenhouse gas emissions of road transportation provided in the IPCC 2006 GL guidelines (Tier 1, Tier 3). Analysis of the results of the comparison showed that the Tier 1 methodology, which was applied in the estimation of the rate of greenhouse gas emissions, carries a high probability of underestimation, while the Tier 3 methodology carries a relatively high probability of overestimation. Therefore, when considering the assignment of permissible rates of emission to local governments, the application of the methodology, i.e. whether one uses Tier 1 or Tier 3, may result in a large difference in the rate of allowable emissions. It is suggested that a method based on the actual volume of traffic would be the most reasonable one with regard to the development of a realistic plan.】

Numerical Calculation of Inertial Aspiration Efficiency of Aerosols into Thin-Walled Sampling Inlets

Unbiased sampling of airborne particulate from a flowing stream requires that the size distribution and concentration of aerosol collected be identical to that of the aerosol in the free stream. Sampling errors occur during aspiration of the aerosol from the free stream to the face of the inlet and during transmission of the aerosol along the sampling tube. Additional losses or gains may occur due to particle bounce from the front edge of the sampler. In this article, a numerical model for determining the aspiration component of overall sampling efficiency for an arbitrarily shaped thin-walled inlet is presented. The numerical simulations presented here are limited to examining the effect of pitch angle and velocity ratio on the aspiration efficiency. Both two- and three-dimensional numerical predictions of aspiration efficiency are compared with empirically based predictions from the unified model of Hangal and Willeke (1990). In general, the more realistic three-dimensional simulations were in better ag...