Flow Instability in Low-Pressure Turbine Blade Passages

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Abstract
The unsteady interaction among shocks, spontaneous condensation and boundary layers were measured in a cascade of tip section turbine blades with steam conditions similar to those that would be experienced by the blade under actual field conditions. Test conditions covered the Mach number range of 1.0 to 1.4, based upon isentropic exit conditions. Inlet temperature conditions were such as to provide fully dry runs, runs with shock and condensation being approximately coincident, and runs with the condensation occurring upstream of the shock. Unsteady pressure data were provided by six miniature pressure transducers embedded in the suction surface of one of the blades in the region of the impingement of the trailing edge shock from the adjacent blade. Spatial integration of the individual transducer signals provided fluctuating forces over the region measured. Unsteady forces were generally low but the nature and level of the fluctuating forces were different near a Mach number of 1.0, where several distinct spikes were present, and responses for some frequencies reached nearly one percent of the steady forces.

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