The accuracy with which experimental investigations of turbine performance need to be undertaken require either a semi- or fully-automated control of the operating point as any variation can compromise the reliability of the measurements. Fundamentally, both the mass flow rate through the turbine and the applied brake torque need to be adjusted in real-time so that the required operating point is maintained.
This paper describes the development of a time accurate computational simulation of the unsteady dynamics of a largescale, low-speed turbine facility when its operating point is determined by a full-authority control system. The motivation for the development of the computational simulation was to be able to safely undertake parametric studies to refine the control system and to investigate the cause of monotonic excursions of the operating point which were observed after a major rebuild.
The monotonic excursions of the turbine operating point could only be reproduced by the computational simulation after an unsteady aerodynamic coupling between the turbine exit flow and the downstream centrifugal fan had been incorporated. Based on this observation a honeycomb was installed upstream of the fan in the turbine facility. This eliminated the monotonic excursions and the fractional noise of the operating point was reduced by 37%. When combined with an earlier refinement of the control system the factional noise was reduced by a factor of three. This enables the number of repeated measurements to be reduced by nine and still obtain the same quality of data.