The recirculation flow after different cross-section shaped high-rise buildings with applications to ventilation assessment and drag parameterization

The building cross-section shape significantly affects the flow characteristics around buildings,especially the recirculation region behind the high-rise building.Eight generic building shapes including square,triangle,octagon,T-shaped,cross-shaped,#-shaped,H-shaped and L-shaped are examined to elucidate their effects on the flow patterns,recirculation length L and areas A using computational fluid dynamics(CFD)simulations with Reynolds-averaged Navier-Stokes(RANS)approach.The sizes and positions of the vortexes behind the buildings are found to be substantially affected by the building shapes and subsequently changing the recirculation flows.The recirculation length L is in the range of 1.6b-2.6b with an average of 2b.The maximum L is found for L-shaped building(2.6b)while the shortest behind octagon building(1.6b).The vertical recirculation area Av is in the range of 1.5b^(2)-3.2b^(2)and horizontal area Ah in 0.9b^(2)-2.2b^(2).The L,Av and Ah generally increase with increasing approaching frontal area when the wind direction changes but subject to the dent structures of the#-shaped and cross-shaped buildings.The area-averaged wind velocity ratio(AVR),which is proposed to assess the ventilation performance,is in the range of 0.05 and 0.14,which is around a three-fold difference among the different building shapes.The drag coefficient parameterized by Ah varies significantly,suggesting that previous models without accounting for building shape effect could result in large uncertainty in the drag predictions.These findings provide important reference for improving pedestrian wind environment and shed some light on refining the urban canopy parameterization by considering the building shape effect.

Analysis on Lean Blowout of Swirl Cup Combustor at Atmospheric Pressure Condition

The experimental data of lean blowout fuel/air ratio of a rectangular swirl cup combustor with different inlet temperatures was obtained at atmospheric pressure condition.Numerical simulations both burning and non-burning were performed corresponding to the experimental data at lean blowout.Results indicated that the size of the recirculation region in the primary zone was obviously smaller when burning than non-burning,but the locations of the cores of their recirculation regions were almost the same.The increase of inlet air temperature didn't mean the rise of the temperature of recirculation region core.The location of the maximum temperature in the primary zone was not the same as that one of the core temperature of the recirculation region.Further more,the reasons were analyzed how the lean blowout fuel/air ratio changed with the inlet temperature increasing under the actions of factors both positive and negative to combustion,and this would be helpful to deepen the understanding of the lean blowout process of swirl cup combustor.