The effect of working fluid and compressibility on the optimal solidity of axial turbine cascades

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Abstract

The blade solidity, namely the blade chordtopitch ratio, largely affects the fluiddynamic performance of turbomachinery. For turbomachines operating with air or steam, the optimal value of the solidity which maximizes the efficiency is estimated with empirical correlations such as the ones proposed by Zweifel (1945) and Traupel (1966). However, if the turbomachine operates with unconventional fluids, the accuracy of these correlations becomes questionable. Examples of such working fluids are the nonideal (dense) vapors of organic compounds (e.g., hydrocarbons, siloxanes) used to operate organic Rankine cycle (ORC) power systems. This study investigates the effect of both the working fluid and the flow compressibility on the optimum pitchtochord ratio of turbine stages. A first principle model for the profile losses is developed for this purpose. Charts providing the optimal pitchtochord ratio for unconventional turbine stages are then provided. Numerical simulations of the flow over a turbine stator cascade have been conducted to validate the model results and evaluate the influence of both working fluid, flow compressibility, and solidity value on the loss breakdown. The results show that the optimal solidity of turbine cascades value significantly increases with the flow compressibility. Therefore, models providing the optimal solidity based on the estimate of passage loss only are not suited for unconventional turbines.
Original languageEnglish
Title of host publicationProceedings of the 6th International Seminar on ORC Power Systems
Number of pages9
Publication statusPublished - 2024
Event6th International Seminar on ORC Power Systems - virtual event, Munich, Germany
Duration: 11 Oct 202113 Oct 2021
Conference number: 6

Publication series

NameInternational Seminar on ORC Power Systems
ISSN (Electronic)2709-7609

Conference

Conference6th International Seminar on ORC Power Systems
Abbreviated titleORC 2021
Country/TerritoryGermany
CityMunich
Period11/10/2113/10/21

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