To protect laborers in a working environment containing toxicvapor, particles and contaminants, an efficient ventilation facilityis essential. A well-designed industrial ventilation facility shouldcapture most of the pollutants. An exterior hood is one of the basictools for local industrial ventilation. The aspiration of an exteriorhood is able to extract pollutants into a certain space. A bell-likevolume below an exterior hood is usually used to characterize itscapture zone. Pollutants within this bell-like zone can be collectedand released into the atmosphere. However, a cross draft mayexist in the working site where an exterior hood operates due to,for example, flow induced by an air conditioner. Even a very slowcross draft at several centimeters per second could have a negativeinfluence on the capture zone. As a result, a cross draft does notonly change the shape of the capture zone, but also its captureefficiency. The bell-like capture volume becomes a Rankine body-of-revolution and the volume is contracted because of a crossdraft. Avoidance of the detrimental influence of a cross draft onthe capture zone becomes an important topic for the design andoperation of an exterior hood. This study is to propose a passivecontrol method which uses a flange and a baffle plate to overcomethe negative effect and to enhance the capture efficiency. Numeri-cal results are shown to investigate the effect of the proposedapproaches and compared with available experimental data pro-vided by Huang et al. f1–3g. Acceptable agreements are foundbetween numerical and experimental results.Local industrial ventilation has been used for a long time. Thedesign principles for an exterior hood date back to Dalla Valle f4gand Silverman f5g. They provided the empirical formula to deter-mine the axial velocity of an exterior hood according to the areaof the hood opening and the suction speed. Subsequent research-ers developed and modified the axial velocity formula for exteriorhoods with various shapes se.g., Garrison f6gd. In 1990, the Envi-ronmental Protection Agency sEPAd of the USA provided the prin-ciple of the capture efficiency for the design of an exterior hood.In academic research, Vincent f7g described the aspiration of anaerosol sampler in an air stream. The flow pattern in the flow fieldwas very similar to the present study. The concepts of a stagnationpoint, a dividing streamline or streamsurface were provided. Ing-ham and Hildyard f8g utilized potential flow theory to study theflow pattern around an aerosol sampler in a free stream. Theyprovided the solution to determine the location of the stagnationpoint. Sreenath et al. f9g conducted experiments to study the as-piration of an aerosol sampler in a wind tunnel. The stagnationpoint was located by flow visualization using the smoke-wiremethod. Kulmala f10g adopted a numerical model to study thecapture efficiency of an exterior hood operating in a cross draft.He mentioned that the main factors in the efficiency of the capturezone were the size of the exterior hood, its geometry and suctionspeed. Conroy et al. f11g studied the influence of a cross draft onan exterior hood using an analytical approach, numerical simula-tions, and experimental methods. He mentioned the concept of adividing streamline which is highly relevant to the capture effi-ciency. Chen et al. f12g utilized the dividing streamline to definethe capture zone for an exterior hood in a cross draft. The capturezone can be used as the indicator of the capture capability of anexterior hood. In terms of Chen et al.’s results, the capture zonelooks like a Rankine body-of-revolution when the speed ratio ofthe suction to the cross draft is larger than 2. Huang et al. f1,2gstudied the capture zones of hoods with circular and rectangularcross sections in a cross draft. Their experiments were performedin a wind tunnel. Flow fields were visualized using smoke andmeasured using a laser Doppler velocimetry sLDVd. They foundthat the geometric shape of the capture zone was mainly affectedby the ratio of the suction speed to the cross draft velocity and theaspect ratio of the rectangular cross section. They used the givensemiempirical formula based on the potential flow theory and ex-perimental data to determine the dividing streamline. Further-more, they also found that a circular hood has the same capturezone and characteristic lengths as a rectangular hood when theyhave the same area. As a result, the formula for the rectangularhood can also be applied to a circular hood.We employed a flange and a baffle plate to reduce the negativeeffect and proposed a 3D numerical model. Variations in flowstructure obtained by the established numerical model are shownin detail and explained in this paper. The flow problems underconsideration are shown in Fig. 1. The height and the width D ofthe exterior hood under consideration were 5 cm and 10 cm, re-spectively. The width W