Computation of the Unsteady Fan-system Coupling using Actuator Surface Approach

B2 - Theoretical & Numerical Methods for Axial Fans

Fan performances are assessed in airway configurations according to the ISO-5801 standard. On the other hand, the design process of industrial fans usually relies on CFD that assumes the same standard configurations or at most minor variations such as, for example, the inclusion of inflow distortions. Mostly these variations are introduced only in special cases and only if these are located near the fan itself. However, in the recent years, due to the tough industry market and the request to reduce system size while increasing ventilation efficiency, the needs to simulate complex ventilation systems by means of CFD based methodologies drastically increased. In such situations, including real fan geometry inside the computational domain would be extremely expensive from a computational point of view and too slow for industrial purposes. When the element to be studied is not just the fan but the whole ventilation system, single components must be described by means of synthetized methodologies. In particular, fans can be represented by simple pressure rise or actuator disks which introduce them in the duct systems by means of body forces inside the momentum equation.
Different methodologies were proposed in open literature (van der Spuy et al., 2009), here we focus on a new actuator disk and line methodology to simulate the presence of an axial fan, and a pressure discontinuity to account for the presence of a gravity damper. These methodologies are able to account for radial flows in the actuator disk and, if run in unsteady mode, to include the effect of rotation of the fan, as well as the real number of blades, with a modification similar to the one assessed in Sorensen and Shen (2002) for wind turbines actuator disks.
In the final paper the methodology will be validated with a parametric study that account for a fan and a gravity damper placed downstream. The capability of the model will be assessed against different mesh densities and will account for different relative positions between the fan and the gravity damper.

[1] van der Spuy, Sybrand J., von Backström, T. W., Kröger, D. G., 2009, Performance of low noise fans in power plant air cooled steam condensers, Noise Control Engineering Journal, Volume 57, Number 4, 1 July 2009, pp. 341-347(7)
[2] Sorensen, J. N. and Shen, W. Z., 2002, Numerical Modeling of Wind Turbine Wakes, J. Fluids Eng. 124(2), 393-399 (May 28, 2002)