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Validation of Unsteady Methods Against Turbine Data
Published December 09, 1996 by Institution of Mechanical Engineers in United Kingdom
Event: Latest Advances in the Aerodynamics of Turbomachinery with Special Emphasis upon Unsteady Flows
Flow unsteadiness in a model turbine stage has been analyzed using both 3D inviscid and 3D viscous CFD codes run 2D. The viscous code has been modified so that it is applicable to an arbitrary stator/rotor blade pitch ratio, thus overcoming one of the major drawbacks of earlier codes.
A direct memory storage technique has been used with the result that only one pitch from each blade row is calculated. The 2D predicted unsteady axial and tangential forces on the rotor blade section are compared with in-house test data, obtained at design and off-design speeds, in a single-stage purpose-built model turbine.
In general, most of the comparisons made between the predicted and the test results are encouraging and show reasonable to good agreement with the fluctuating force amplitudes obtained from unsteady blade surface pressure distributions. The viscous predictions give better agreement with the test data than the inviscid predictions.
The first harmonic (RMS) of the fluctuating forces is compared with the test data for different axial gaps between the stator and rotor blade for the root and tip sections of a steam turbine rotor blade. The viscous method gives the best prediction of the variation of RMS amplitude with gap, the inviscid method predicting amplitudes with up to twice the test level.