Showing papers on "Tip clearance published in 1968"

Axial Turbine Performance Evaluation. Part A—Loss-Geometry Relationships

Abstract: Generalized loss correlations for full and partial admission turbines have been derived and critically compared with recently published data. Effects included are Reynolds number, blade angles, blade height, blade number, blade trailing edge thickness, tip clearance, and reaction. These generalized loss relationships are for use in optimization of turbines over a wide range of possible operating conditions.

Performance evaluation of a two stage axial-flow turbine for two values of tip clearance

Abstract: SUMMARY OF RESULTS The performance of a two-stage turbine was investigated at two values of tip clear- ance. Performance characteristics were first described for the turbine operating with the rotor tip clearance of 0. 031 inch (0. 079 cm) which was recommended for preliminary hot operation. These results were then compared with those obtained in a reference in- vestigation in which the design tip clearance of 0. 013 inch (0.033 cm) was used. results of this investigation are summarized as follows: 1. Static and total efficiencies (based on turbine-inlet and collector -exit conditions) were 0.785 and 0.792, respectively, for operation at design equivalent speed and pres- sure ratio with a tip clearance of 0.033 inch (0.079 cm). These values represent a 4- percentage-point decrease in efficiency when compared with the results obtained when the turbine was investigated at the design tip clearance of 0. 013 inch (0. 033 cm). loading, increased throughflow over the blade tips in the clearance space, and the re- duction of working blade

Experimental investigation of low aspect ratio and tip clearance on turbine performance and aerodynamic design

Abstract: : The aerodynamics of any cooled turbine are compromised by mechanical design, fabrication techniques, heat transfer, and cooling restrictions. Additional requirements of high outputs out of small turbomachinery packages result in limitations on the turbine that are unique to low-airflow, high- pressure-ratio, small-category machines. These practical considerations limit the tip clearance, axial chord lengths, tolerances, and geometry. The resultant blading is usually of low-aspect-ratio type, and characteristically high secondary losses predominate. The report presents the aerothermodynamic design considerations of three turbine flowpaths, which were cold-flow tested to evaluate the performance effects of span aspect ratio and tip clearance on turbine efficiency. Complete maps were generated for the three configurations, and tip clearance effects were evaluated at design speed over a range of pressure ratios. Rotor blade aspect ratios were tested from 0.41 to 1.26, and blade heights varied from 0.36 inch to 1.09 inches. Rotor tip clearance was varied from 1.5 to 5.0 percent of the blade span. Results of the investigation suggest that predominance of high secondary losses should allow a design with high-aspect-ratio blading and low wheel speeds to produce the same performance as low-aspect-ratio blading with high rim speeds.