Twisted-wind effect on the flow field of tall building

Tall buildings in hilly terrain are very likely being attacked by topography-induced twisted wind. In this study, the effects of three wind profiles on second-generation benchmark building, i.e. conventional wind profile (CWP), two twisted wind profiles (TWP15 and TWP30) with maximum twisted angle (MTA) of 15°and 30°, are investigated by large eddy simulation. Wind tunnel tests under the same wind profiles are replicated to verify reliability of numerical results. Wind loads, flow motion, spatial correlation and mode patterns are comprehensively analyzed to elucidate underlying mechanism of TWP. The results show that with MTA increasing from 0° to 30°, mean lateral and torsional wind loads are significantly magnified while along-wind force is reduced, this variation is attributed to TWP-induced modification in flow field. Under TWP, fluctuating base moment are all weakened due to suppressed vortex shedding, moreover, fluctuating energy of DMD modes tend to accumulate toward low-frequency region, which could amplify background component of buffeting response. Notably, “twisted extensibility” is discovered in TWP, which magnifies vertical correlation and momentum exchange, thus generating larger torsional responses. These findings provide references for designing and constructing tall buildings in mountainous areas where twisted flows occur frequently.