Energy and Buildings 43 (2011) 358–365 Contents lists available at ScienceDirect Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild Effect of inclined roof on the airflow associated with a wind driven turbine ventilator Shao Ting J. Lien ∗ , Noor A. Ahmed School of Mechanical and Manufacturing, University of New South Wales, Sydney NSW 2052, Australia article info Article history: Received 13 January 2010 Received in revised form 6 July 2010 Accepted 30 September 2010 Keywords: Inclined roof Ventilation Rotating turbine ventilator abstract Rotating wind driven turbine ventilator has been used as cost-effective environmental friendly natural ventilation device. Rotating wind driven turbine ventilator type of device is usually installed on the rooftop to extract air extract air flow from a building to improve air quality and comfort. Performance investigations carried thus far on turbine ventilator have ignored the effect of the inclination on rooftop. An experimental program was, therefore, formulated at the aerodynamic laboratory of the University of New South Wales to study such effect on a simulated rooftop. The results obtained from the measured forces and rotational speeds on different configurations indicate that the effect is minimal in extracting air from a building at low wind speed. The static pressure and skin friction distributions on the simulated roof further supports this finding. Two important conclusions can be drawn from the present investigation: firstly, the presence of the inclined roof may extend the safety margin in the operation of a turbine ventilator at high wind speed by reducing the magnitude of the total force that acts on the ventilator; secondly the dependency of the total fore on low Reynolds number suggests that the efficiency and reliability of operation of such ventilator should be boosted through the provision of other power source such as solar power at low wind speed. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction Although the design of turbine ventilator appears quite sim- ple, the associated flow field is deceptively complex and not fully understood. According to Lai [1], ‘a proper combination of tur- bine ventilator and natural ventilation will help tremendously the indoor air quality while it will also decrease the reliance on air con- ditioning and thus reduce the energy consummation. It is indeed a field of environmental design engineering that demands profound research’. Evaluation of the performance of turbine ventilators by Dale and Ackerman [2] and more recently a review on wind driven ventilation technique by Khan et al. [3] suggest that the device is quite effective in minimising excessive humidity, condensation, overheating and build-up of odour smokes and pollutant. Perfor- mance studies on rooftop ventilator conducted by Flynn and Ahmed [4], Rashid and Ahmed [5], Revel [6] and Khan et al. [7] point out that there are many factors that influence the performance of a turbine ventilator. They include, amongst others, the aerodynamic forces acting on the ventilator, the geometry, the weight or the rotational speed. These studies have been mainly carried out with the ven- ∗ Corresponding author. Tel.: +61 2 98583196/61 2 9385 4080, fax: +61 2 9663 1222. E-mail addresses: lien1122@hotmail.com (S.T.J. Lien), N.Ahmed@unsw.edu.au (N.A. Ahmed). tilator placed on a flat surface in a wind tunnel. But, in Australia and many countries around the world, the turbine ventilator oper- ates on buildings that have inclined rooftops. However, hardly any investigation into the effect of the inclination angle of the rooftop on the performance of a rotating turbine ventilator exists in the open literature that may facilitate further improvement of its per- formance. The studies on inclination angle of a roof alone have, for the most part, been associated with the overall wind induced lift loads [8–11]. Several experimental and numerical studies, Holmes [11], Stathopoulos and Zhou [12], for example, reinforce the fact that the wind flow over a roof is complex even for a rectangular building. The high turbulence level, severe pressure gradient, flow separa- tion and possible reattachment, all impose difficulties for accurate numerical modelling as well as experimental investigation. Other studies without a rooftop turbine ventilator indicate that the roof configurations as well as the inclination angle impact significantly on the natural ventilation rates inside a building [13] as well as the thermo performance of ventilated roof [14]. Broadly speaking, a wind driven turbine ventilator consists of a base and a top, which acts like a turbine. The motion of the top and the air surrounding it causes suction within the base. The mixed air exits the blade on one side [1,5] and constantly sheds unsteady wake which interacts with the boundary layer on the roofs. This type of interaction may be similar to those encountered in turbomachinary where the unsteady and highly three dimensional 0378-7788/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.09.027