WIND-INDUCED INTERFERENCE CRITERION FOR GROUPED COOLING TOWERS BASED ON THE INDEX OF REINFORCEMENT RATIO ENVELOPE

The wind-induced interference effect plays a controlling role in the design of cooling towers. Flow patterns around grouped cooling towers influence the 3-dimensional wind pressure distribution. To take into account the effects on structural internal force and reinforcement ratios due to aerodynamic amplification under grouped towers, it is a common practice in current loading codes to adopt single uniform interference factor (IF) to amplify simplified 2-dimensional wind pressure suitable for circular cylinders. For the purpose of assessing those equivalent wind loading parameters in terms of accuracy, rationality and economy, super large cooling tower groups with typical six-towers arrangements were selected to conduct case studies by wind tunnel tests and finite element method calculation. Mean wind pressure effects along the shells of the towers suffering from obvious interference were analyzed, and are compared with data of single tower. Reinforcement ratios along meridian and circumference directions inside and outside the tower shell were calculated under 16 flow directions and 20 loading combination cases. Envelope curves of maximal reinforcement ratio could be compared with those of isolated towers. Based on the notion of reinforcement ratio envelope, a new interference criterion was proposed with more accuracy and rationality. Its practical application was also validated based on a case study. Some principal conclusions can be summarized as follows. The reinforcement envelope curves along the shell height, considering 3-dimensional wind pressure distribution, various incoming flow angles and loading combination cases, can serve as a guiding criterion with satisfactory precision in practical design. Single interference factors suggested by the loading codes would be difficult to cover complex 3-dimensional wind pressure distribution caused by interference effects. Multiple interference factors changing with the shell height are recommended which can compromise convenience, economy and rationality in the design of cooling towers.