INTERFERENCE EFFECTS ON GLOBAL WIND LOADS AND WIND INDUCED RESPONSES FOR GROUP HYPERBOLOIDAL COOLING TOWERS

Different interference effects on global wind loads and wind induced responses for group hyperboloidal cooling towers (HCTs) were studied based on wind tunnel tests on rigid models and dynamic calculations of wind induced structural responses. The basis of the study was the different influences of latitude wind pressure distribution on the drag coefficient C_D and meridian axial force F_T. In group-tower conditions, interference effects on the wind pressure distribution of the target tower can be classified into three types: shielding effect from the upwind tower in tandem and staggered arrangement which decreases the windward pressure (Ⅰ); drawing effect from the downwind tower in side-by-side and staggered arrangement which increases the leeward suction (Ⅱ); wake vortex induced effect from the upwind tower in tandem and staggered arrangement which increases the fluctuating pressure in windward and sideward areas (Ⅲ). These three effects exert different influences on C_D and F_T. C_D is mainly determined by the windward and leeward pressure, hence effect Ⅰ and Ⅱ result in drop and rise of the mean C_D respectively. Stronger fluctuating latitude pressure induced by effect Ⅲ leads to greater Root Mean Square (RMS) of C_D. However, F_T is mainly determined by the windward and sideward pressure, therefore effect Ⅰ and Ⅲ result in drop and a rise of F_T respectively and effect Ⅱ hardly alters F_T. Compared with the single tower condition, the aggravation of F_T in group towers mainly stems from the increase of the fluctuating pressure. For group towers with a commonly-used tower distance, the sensitivity of interference effects to wind direction is much greater than that to the distance amongst towers. For group-tower layouts, the range of adverse wind directions for the double-row layout is wider than that of a single-row layout. According to the present study, the tower layout and wind direction indeed amplified the F_T of the collapsed towers located in the back row when the Ferrybridge accident happened.