61 Turbine research facility modifications performed for the specific research program

The Pennsylvania State University currently operates a highly loaded axial flow turbine stage for aerodynamic and heat transfer research. The fully operational facility is of large-scale low-speed nature with modern turbine design attributes. The Axial Flow Turbine Research Facility (AFTRF) is an open circuit facility 91.4 cm in diameter and a hub to tip radius of 0.73, with advanced axial turbine blading configurations as designed by GE (Evendale). The facility consists of a large bellmouth inlet, a turbulence generating grid followed by a test section with a nozzle vane row and a rotor. There are 23 nozzle guide vanes and 29 rotor blades followed by outlet guide vanes. A variable through-flow is provided by two auxiliary, adjustable pitch axial flow fans and an aerodynamically designed exhaust throttle. This system allows accurate control of the mass flow through the turbine stage up to a maximum of 22,000 cfm. The two fans connected in series produce a pressure rise of 74.7 mm Hg (40 inches of water height) with a mass flow rate of 10.4 cubic meter per second under nominal operating conditions. The power generated is absorbed by an eddy current brake. The rotor and nozzle vane passages are instrumented with high frequency instrumentation to measure steady and unsteady pressures and shear stresses. A three component LDV system is currently operational in the facility. The facility is instrumented with two modern probe traversing systems in the rotating frame. Measurements in the rotor passages and downstream of the rotor can be taken in the radial direction and in the circumferential direction using a stepping motor controlled custom designed traverser. The facility also includes a 150 channel coin and brush type slip ring device to transfer data from the rotating frame of reference to the stationary frame for further processing. The current research program required extensive modification to turbine blades. Design manufacturing and assembly of a new cooling air transfer system from the stationary frame to rotating frame was necessary. An air-transfer device including two custom manufactured seals working against plasma coated rotating surfaces were contracted out to a specialist manufacturing facility. A special calibrated orifice and robust pressure vtransducerss were installed in the rotor frame of reference for accurate coolant mass flow rate measurements of the coolant air injected from the tip trench. Cooling plenum chambers, radial cooling holes, tip trenches and discrete cooling holes were precision machined in computer controlled five-axis machine tools. The tip trench and cooling system sizing was completed under the supervision of engineering staff at Solar Turbines Inc. Since extensive rotor modifications were completed, a dynamic balancing of the turbine rotor was also performed after the re-assembly process. An instrumented disk cavity flow simulator allowing the researcher to create realistic cavity flow scenarios was used. Different cavity flow patterns were generated by a root cooling, disk impingement and radial injection system. The disk cavity flow system were integrated in the tight axial space between the rotor disk and the nozzle guide vane assembly. The coolant/leakage flows originating from the disk cavity space were monitored by a set of total pressure and temperature sensors located at the inlet and exit of the turbine stage. The change in the total to total efficiency of the turbine stage due to endwall coolant/leakage was properly documented. The research program also included the measurement of the three dimensional aerodynamic field in the rotating frame by using sub-miniature five hole probes. This action required operating a computer controlled radial-circumferential probe traverser that can move with respect to the turbine rotor. The facility was also modified for the proposed convective heat transfer coefficient measurements using liquid crystal thermography. This effort required obtaining color liquid crystal images of the rotor tip that is in rotational motion at 1330 RPM. A high resolution digital camera and a stroboscope system resulted in the acquisition of the color images that are currently under investigation. The previous P S U studies dealing with the acquisition of liquid crystal images in rotational environment and the use of Inconel surface heater foils were extremely supportive of the current study.

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