An evaluation of simplified CFD models applied to perimeter fans in air-cooled steam condensers

Modelling air-cooled condensers (ACCs) incorporating hundreds of fans, necessitates the use of simplified fan models when performing a computational fluid dynamics (CFD) analysis of the condenser. The perimeter fans in these ACCs are subjected to distorted inlet flow conditions. This paper compares the accuracy of three different simplified fan models and proposes an improved model, based on numerical and experimental results from representative fan configurations. Three different fan configurations are tested as perimeter fans in a three-fan test facility, and their results compared to CFD results. The experimental evaluation by particle image velocimetry (PIV) reveals the shape of the velocity profiles immediately upstream of the perimeter fan. The accuracy of the CFD-predicted flow field directly upstream of the perimeter fan varies according to the model used to represent the fan as well as the configuration of the specific perimeter fan. The paper indicates a discrepancy of as much as 30% between experimental and simulated volumetric effectiveness values for a specific simulation model and fan configuration. The standard and extended actuator disc fan models perform better than the pressure jump model in predicting the volumetric effectiveness of the perimeter fans, and the extended actuator disc model performs best at predicting fan inlet velocity profiles.