Abstract
High pitch-chord ratio turbine stages are a novel class of high enthalpy drop impulse turbines. Significant limitation of traditional design approach for such turbines is a low partial admission rate due to low volumetric flow rates. The main idea of high pitch-chord ratio design is in increase of the stage load coefficient with decrease of the flow angles. The latter allows to provide higher partial admission rate and, hence, higher stage efficiency compared with the traditional design approach. As a consequence, efficiency of the high pitch-chord ratio stages varies between 65% and 75%, whereas partially admitted stages efficiency tend not to exceed 60%. High pitch-chord ratio nozzles have a rectangular cross section. This feature leads to a vortex pair occurrence in a nozzle flow path. An interaction of these vortices for transand supersonic stages leads to additional losses and comparably low nozzle efficiency. The present paper aimed at first, establishing the design criteria which are essential for the nozzle efficiency, and, second, finding the optimal ratios of the proposed criteria. CFD simulation approach is used for the study. The gained deliverables are helpful for increasing of the nozzle velocity ratio.
Highlights
Development of modern propulsion systems for transport, marine and space applications leads to new requirements for weight-size parameters and cost effectiveness for such installations
The last obstacle inevitably tends to a growth of a pressure ratio per stage, transonic / supersonic flow regime occurrence and, dramatic decreasing of a stage efficiency
Investigations of supersonic axial impulse turbines with axisymmetric nozzles and partial admission provided by Natalevich (1979) [3], Dorney et al (1999) [4], Tog and Tousi
Summary
Development of modern propulsion systems for transport, marine and space applications leads to new requirements for weight-size parameters and cost effectiveness for such installations. Decreasing of turbine weight-size parameters is related with decreasing of its stages number and consequent increase of a load per stage. The special design of the nozzle vanes and rotor blades is required to fulfill the new spatial and cost effectiveness limitations. Loaded turbines may have both impulse and reaction design and often have partial admission as in the works of Kurzrock (1989) [1], Kunte and Seume (2013) [2].
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