Flow of cooling air in an electric generator model - An experimental and numerical study

Artikel i vetenskaplig tidskrift, 2014

The need for electric power is continuously increasing. The power output of existing electric generators is forced to its limit, and the new intermittent electric energy sources increase the variations of the operating conditions of the electric generators in the power system. This requires better cooling of the heat that is generated by the electric losses in generators. New experimental and numerical techniques need to be developed and validated, to increase the knowledge of the cooling processes and to improve the accuracy of the design tools. The present work focuses on the flow of air through electric generators, as a necessary and important first step towards future accurate and detailed convective heat transfer analysis.A half-scale model of an electric generator is designed and manufactured specifically for detailed experimental and numerical studies of the flow of cooling air through the machine. The model is slightly simplified compared to the original geometry, to benefit from the use of geometry parameterization, and with numerical mesh quality in mind already at the design of the experimental set-up. Special care is taken to provide optical access for accurate and detailed Particle Image Velocimetry (PIV) measurements inside the machine.The experimental measurements include PIV measurements at the inlet and inside the machine, and total pressure measurements at the outlet of the stator channels.Computational Fluid Dynamics (CFD) simulations are performed using two approaches. In one approach the inlet flow rate is specified from the experimental data, as is commonly done in the literature. In the other approach the flow rate is determined from the numerical simulation, independently of the experimental results, yielding predictions differing by 2-7% compared to the experimentally estimated values. The results of both approaches capture the experimental flow details to a high level of accuracy. Mesh sensitivity studies highlight the need of a specific resolution of the baffle edges.