CFD analysis of ventilation systems for gas turbine enclosures

The fans performance are assessed in configurations according, traditionally, to international standards such as ISO-5801. Similar reference to the so-called standardised airways is used in the design process of industrial fans which provide the ISO test-bench. In recent years, the objective of fan optimization has, in most cases, been re-focused on the optimization of the fan-system coupling in a view to solve for the dynamics of such coupling (either mechanically or aerodynamically). This has been true when ventilating systems are equipped with components such as bended inlets, spinner cones, gravity dampers, that could be responsible for influencing the fan aerodynamic response. In all these cases, when using CFD, accounting for a real fan geometry inside the domain would be extremely expensive from a computational point of view and too slow for industrial purposes. When the objective under investigation is the whole ventilation system, it is necessary to account for the single components by means of synthetized methodologies. In particular, fans can be accounted for by simple pressure rise or actuator disks that synthetize their aerodynamic response in the systems of ducting by means of body forces inside the momentum equation. In the paper the methodology is briefly presented and applied to resolve the fluid-dynamics behaviour of two gas turbine ventilation systems.