PIV Measurement of Air Flow in a Hydro Power Generator Model

Other conference contribution, 2012

Cooling of electrical generators is of high importance since an uncontrolled temperature rise can lead to formation of hot spots which can cause material failure. The efficiency of the machines in converting the mechanical energy to electricity is also affected by temperature, as the electric resistances of the cables and windings are temperature dependent. In order to tackle the problem, air is used as a cooling fluid, which circulates through the stator and rotor in the generator. Despite the fact that electrical generators have been used for many years, the knowledge about the cooling air flow inside them is still limited. Understanding the air flow inside the generators leads us into better predictions of heat transfer. The knowledge is also important when modifying the stator and rotor shapes, or when innovating new air cooling systems. In this work, a generator model has been specially designed to perform fluid flow measurement. Rapid Prototyping was used to build the model due to its capability to create complex geometries in good accuracy in a short time. Planar two-component Particle Image Velocimetry (2D-2C) was used to measure the fluid velocity inside the stator channels. A section of the stator was built in fully transparent material, to give optimal optical access. The flow path inside the channels was small and thus the optical view was prone to light scattering and reflection from the walls. A marker paint was used to paint the channel walls black, leaving just one transparent wall. A special dummy channel without coils and baffles was manufactured, for use when measuring in the middle channel rows. Stereo PIV (2D-3C) was used to measure the fluid velocity outside the stator body. In total 15 measurement planes were created to capture the overall picture of the flow. This data was then interpolated to get an overview of the flow field around the stator body. The results show that the tangential velocity component dominates the flow outside the stator. The flow outside is highly swirling and three-dimensional. Inside the stator channels the fluid moves radially with large recirculation region (almost half of the stator channel width) behind the coil. Phase-averaged measurements show that the flow structures inside the channels are independent of the rotor pole position.