A Numerical Investigation For Flow Field Indoor Near The Exhaust Inlet

In the indoor space, the air near the indoor exhaust inlet remained stationary stateno more for the suction effect caused by the exhaust inlet, and the air flow toward theexhaust inlet, speed from scratch at the boundary of the region influenced by suction.Suction was used to exhaust the indoor contaminant, and the information of requiredvelocity to exhaust the contaminant needs to be know. In this paper, the flow field nearthe exhaust inlet and the region influenced by suction were explored numerically, andthe research situation was: the diameter of exhaust inlet was0.173m, the suction volumewas0.14m3/s and the ratio of the diameter of exhaust inlet to the distance betweeninstallation height to roof was0.17.Studies have shown that in the case of the ratio of the diameter of exhaust inlet tothe distance between installation height to roof less than0.35, the physical model couldbe simplified to the case that suction with single wall in large space. No-slip conditionand the wall fuction method was adopted to deal with the wall installed exhaust inlet,and the pressure inlet boundary conditions were used in all the boundary surfaces of thecomputational domain except for the wall. It was verified that RNGk turbulencemodel, standard wall function method and the standard pressure difference format canobtain better numerical simulation results for the flow field near the exhaust inlet withsingle wall in large space.Under the suction effect, the region where the velocity reached a certain value(called the working speed) was regard as the effective impact range, according todifferent needs to exhaust pollutants.For circular flanged exhaust, the sphere of influence varied with different workingspeed. At high speeds, the sphere of influence could be described as semi ellipsoid withthe long axis in the radial direction, when speed decreases, the major axis of the semiellipsoid becomes shorter in radial direction, and the minor axis of the semi ellipsoidbecomes longer in axial direction. In the case that the average velocity of the exhaustsection was5.96m/s, when the working speed was2m/s, the major axis of the semiellipsoid was0.7times the diameter, while the minor axis was0.45times the diameter,when the working speed was0.3m/s, the major axis of the semi ellipsoid was1.6timesthe diameter, and the minor axis was1.55times the diameter;For circular unflanged exhaust, considering the influence area in front of the suction inlet plane, the sphere of influence also varied with different working speed,similar to circular flanged exhaust. When the working speed was2m/s, the major axis ofthe semi ellipsoid was0.62times the diameter, while the minor axis was0.44times thediameter, when the working speed was0.3m/s, the major axis of the semi ellipsoid was1.28times the diameter, and the minor axis was1.23times the diameter;For rectangular flanged exhaust with the ratio of length to width was6:1, when theworking speed was0.3m/s, the farthest effect of distance along axis direction was1.54times the equivalent diameter of exhaust, the farthest effect of distance along thedirection parallel to the short side of rectangular exhaust was1.75times the equivalentdiameter, and the farthest effect of distance along the direction parallel to the long sideof rectangular exhaust was about2.13times the equivalent diameter.For rectangular unflanged exhaust with the ratio of length to width was6:1,considering the influence area in front of the suction inlet plane, when the workingspeed was0.3m/s, the farthest effect of distance along axis direction was1.21times theequivalent diameter of exhaust, the farthest effect of distance along the direction parallelto the short side of rectangular exhaust was1.21times the equivalent diameter, and thefarthest effect of distance along the direction parallel to the long side of rectangularexhaust was about1.78times the equivalent diameter.