Experimental investigation of a turbine sealing cavity exposed to free stream pressure fluctuation
The current investigation examines the impact of a new pulsed unsteady combustion to the turbine sealing cavity, which prevents hot gas ingestion into the inner machine. Sealing flow is ensured by relatively cold secondary air blowing radially through the rotor-stator-wheel space. The interaction between the sealing flow and the main gas flow however causes aerodynamic losses. These losses as well as the secondary compressor air should be kept at a minimum in order to increase the efficiency of the whole machine. The Hot-Acoustic-Testrig (HAT) allows an investigation of the subject under realistic flow conditions. Therefore a specific measurement section has been designed, which features a plenum to provide secondary air to the main flow. To simulate an pressure increasing combustion, a setup with 6 fast shifting valves was realized. The unsteady flow was measured by pressure tabs with a high time resolution. In the next step a characteristic linear cascade was designed to replace the turbine stator and generate a typical stator wake. Measurements of the total pressure loss over the cascade vanes have been conducted by means of a five-hole probe and by Particle Image Velocimetry. A considerable pressure loss inside the vane wake was observed at a Mach number Ma = 0.35. The nvestigation is a subproject of the Collaborative Research Center 1029 Substantial efficiency increase in gas turbines through direct use of coupled unsteady combustion and flow dynamics and gives an outlook to further steps.
Published in: Active Flow and Combustion Control 2014, September 10-12 2014, Berlin, Germany,