Cooling air flow through the generator is used to minimize the deterioration of the generator due to high temperatures. The losses associated with the air cooling are however responsible for a substantial amount of the total generator losses. When the periphery speed is high the ventilation losses may amount to as much as half of the total loss. For a machine with lower peripheral speed the losses amount to approximately 5% of the total losses. Thus a more effective ventilation system would make the generator more efficient.

The main objective of the project is to, from a fluid mechanical point of view, create conditions to reduce machine damage and efficiency losses that can be related to poor/ineffective cooling.

PROJECT

The ultimate goal of the project is to numerically simulate the heat transfer inside a generator, with a high accuracy. This requires a good knowledge of the cooling air flow within the machine, which is rather complex and unsteady. Therefore, the main focus of the project, at first hand, is to resolve the air flow in a generator. Once the air flow is numerically determined down to details, the heat transfer simulations can be started. The simulations are performed using the open-source CFD software OpenFOAM.

Though the project focuses mainly on numerical simulations, experimental measurements are needed to validate the numerical results. A small generator at Uppsala University is chosen to base the numerical modelings and experimental measurements on.

RESEARCH CARRIED OUT UNTIL FALL 2010

• Different incompressible RAS turbulence models in OpenFOAM have been investigated and validated agains a backward-facing step test case to select the most appropriate one for the generator simulations.
• A detailed numerical study of the effect of different geometry changes to the rotor pole and the stator have been performed.
• Measurement facilities have been designed and made, and experimental measurements have been performed on the test rig.

Figure 1. The test rig at Uppsala University.

Figure 2. The rotor and the stator geometries in computations.

Figure 3. The velocity unit vectors in between the rotor poles in a computaional case.

Figure 4. The pressure measurement rake at the outlet of the channels.

FUTURE WORK
The numerical studies so far have been performed using a Multiple Reference of Frame method, where there is no actual movement of the mesh, but instead, source terms are added to the rotating region to simulate the movement of the rotor. A next step is to simulate the unsteady flow with help of a moving mesh. A test rig with optical access will be made at CHALMERS to perform experiments on and get a better understanding of the flow, though the generator at Uppsala University is suited for electromagnetic measurements and can not be reconstructed for optical measurements.

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