Air-cooled steam condensers are an important component in the power generation industry. Large scale axial flow fans are used in these condensers and are the subject of many studies. However, the hub is often an overlooked design aspect. A smooth, rounded hub is often used without further consideration, due to the superior performance of such a hub. At a small testing facility scale, this hub configuration is easy to implement. However, manufacturing and installation of a hub on a large scale, such as in air-cooled steam condensers, is difficult and may have a greater effect on capital costs than on performance. This is difficult to assess without proper understanding of the effect hub configuration has on the performance of an axial flow fan. As such, this work compares the effect on performance of hub configuration on an axial flow fan through use of numerical modelling.

 

Numerical modelling is done in OpenFOAM, an open-sourced computational fluid dynamics (CFD) solver. CFD simulations are performed for a range of flow rates extending from blade stall to above design point flow rate. Three different hub configurations are considered with the first being that of a smooth rounded hub, in order to form a datum to compare to. The second, a square hub, consists of a simple cylinder with sharp corners. Lastly, a disk hub is considered, which consists of a cylinder with infinitesimal thickness, forming a two-dimensional disk.

 

It is found that the square and round hub perform similarly at the design point, however the square hub attains marginally superior total-to-static pressure rise and efficiency at a flow rate above the design point and performs worse at low flow rates. The disk hub, in contrast, results in higher total-to-static pressure rise and efficiency at a low flow rate, however is inferior at the design point and higher flow rates. The superior performance of the square hub is due to the formation of a separation vortex on the leading edge surface of the hub. This vortex interacts with the blade suction side stagnation point and improves the distribution of blade loading along the chord. The disk hub improves low flow rate performance by the formation of a large vortex wake downstream of the fan. This constricts the axial flow of the fan by the hub region and accelerates the axial flow along the midspan and tip region. This causes a decrease in angle of attack over the blade, which increases the fan stall margin and thus improves low flow rate performance.


The Effect of Hub Configuration on the Performance of an Air-Cooled Steam Condenser Fan

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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