PIV Measurement of Air Flow in a Hydro Power Generator Model
Konferensbidrag (offentliggjort, men ej förlagsutgivet), 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.