Numerical investigations on the effect of swirling plume on natural draft dry cooling towers

Plume with swirling motions has been proven to be capable of enhancing the length of fire whirls. To investigate if the effect exists in natural draft dry cooling towers (NDDCTs), two methods to generate rotating motions inside cooling towers, including rotating the tower wall and adding tangential source term, have been simulated by FLUENT. The result shows that, in both cases, the air mass flow rate through the tower is enhanced as the swirl intensity increases at first and then decreases when the swirl number exceeds a critical value where vortex breakdown appears. It also illustrates that the swirl intensity generated by rotating the tower wall is relatively low due to the low viscosity of the air. On the other hand, adding source term shows to be able to generate swirl with higher intensity, and the results show that the tangential velocity profile utilized in the source term does not affect the performance significantly, but the tangential momentum is much more crucial instead. In addition, the vorticity-velocity interactions in swirling flows are utilized to explain the mechanism of the enhancement. Although swirl caused by artificial methods shows positive effects on the air mass flow rate enhancement, other verification schemes should also be investigated to confirm the effect in the later work.