Heat transfer coefficient distribution on the pole face of a hydrogenerator scale model F. Torriano a, * , N. Lancial b, c, d , M. Lévesque a , G. Rolland d , C. Hudon a , F. Beaubert b, c , J.-F. Morissette a , S. Harmand b, c a Institut de recherche d’Hydro-Québec, Varennes, Canada b Université Lille Nord-de-France, Lille, France c UVHC TEMPO/DF2T, Valenciennes, France d Électricité de France R&D, Clamart, France highlights  Temperature measurements and 3D simulations of the pole of a hydrogenerator scale model were done.  Lower heat transfer coefficient values are found closer to the trailing edge of the pole.  The highest heat transfer coefficient values are found in an intermediate region of the pole.  Heat transfer coefficients along the pole face at 300 rpm average about four times those at 50 rpm. article info Article history: Received 31 December 2013 Accepted 19 April 2014 Available online 10 May 2014 Keywords: Hydrogenerator Heat transfer coefficient Salient pole machine FEM CFD abstract This paper focuses on the effect of rotation on heat transfer mechanisms in rotating machines with the purpose to improve the understanding of thermal phenomena and cooling of hydrogenerators. Using a simplified scale model equipped with a heated pole, it was possible to measure the temperature dis- tribution on the pole surface and to deduce, through numerical simulations, the heat transfer co- efficients. The results show an asymmetric profile in the tangential direction since lower h values are found closer to the trailing edge due to the presence of a flow recirculation zone. Furthermore, the heat transfer profiles indicate that, although fans improve cooling at the top and bottom ends of the pole, the highest h values are found in an intermediate region. This is due to the flow from the fans that enters the interpole space and only after penetrating a certain distance in the axial direction it exits through the air gap and goes around the pole face. The study also shows that the heat transfer coefficients along the pole face at 300 rpm average about four times those at 50 rpm. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Salient pole synchronous machines are essential to convert the mechanical energy of water turbines into electrical energy. One of the most common causes of reduced hydrogenerators service life is deterioration of insulation material due to overheating. It is thus critical to monitor temperatures during operation to ensure that the hot-spot value does not exceed the critical limit. Moreover, since overheating is often caused by poor circulation of the cooling fluid, it is necessary to understand the flow dynamics and heat transfer mechanisms in the various generator components (i.e., end-winding, pole face, etc.). A hybrid approach, based on experi- mental measurements and numerical simulations, is needed to improve the understanding of thermofluid phenomena as the nu- merical methods have not yet achieved sufficient maturity to be used alone. In fact, the mesh size required to discretize the computational domain may reach 100 million elements and modeling phenomena such as turbulence remains quite complex. On the other hand, experimental measurements require a consid- erable instrumentation effort and access to prototypes is often limited. A laboratory scale model thus appears to be the best so- lution to acquire data in order to validate numerical models. This approach was chosen by IREQ (Institut de recherche d’Hydro- Québec), EDF (Électricité de France) and TEMPO/DF2T (Université Lille Nord-de-France) which developed a common strategy to share knowledge in the field of hydrogenerators thermofluid analysis. * Corresponding author. E-mail address: torriano.federico@ireq.ca (F. Torriano). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng http://dx.doi.org/10.1016/j.applthermaleng.2014.04.048 1359-4311/Ó 2014 Elsevier Ltd. All rights reserved. Applied Thermal Engineering 70 (2014) 153e162