Vortex zones in an exhaust hood in front of an impermeable plane

The paper presents the results of the study of the flow to the ventilation exhaust device in a form of a circular exhaust hood with a flange, located in front of an impermeable plane. Local exhaust devices are the most rational type of localization of harmful substances in industrial and civil buildings. However, they consume a large amount of energy, so the ways to increase their efficiency are relevant and are the subject of numerous studies around the world. One of the promising ways to reduce the aerodynamic drag of such devices is shaping their inlet sharp edges by the outlines of vortex zones. However, when the hood is located above an impermeable plane, the outlines are not known. This study is carried out numerically, so at the first stage the adequacy of the computation model is demonstrated by comparing it with the known data on the resistance of this kind of devices. Furthermore, the dependences for the local drag coefficient are constructed for the flange dimensions in the range d/R = 0.5; 1.5; 2.5; 5 and distances to the impermeable plane in the range s/R = 0.5; 1; 2; 5. The authors found the outlines of both the first vortex zone, formed at flow separating from the sharp edge of the flange, and the second vortex zone, formed at the point of the flange connection to the exhaust channel. The plotted curves showed that the zones sizes are significantly dependent on the distance s/R. The property of geometric similarity for the first vortex zone was found, which will make it possible to construct the first vortex zone using the dependence for the scale factor without numerical simulation. The constructed outlines of the vortex zones will be further used to develop shaped designs of ventilation exhaust hoods.