The Results of Calculations of the Axial Turbine Stage with Different Meridional Outlines of Its Adjustable Nozzle Vane

Abstract

Turbomachines with adjustable (rotary) nozzle vanes (ANV) find increasingly broader use in various technical fields owing to their featuring lower loss of efficiency in comparison with other flow rate changing methods. Improvement of their efficiency is becoming more important while fulfilling the manufacturability and reliability requirements. Three options for shaping the meridional outlines of the adjustable nozzle vane (ANV) and the blades themselves, which are rather complex items for manufacture, are studied by calculation: option 1 – with conventional cylindrical meridional surfaces and blades cut at the ends with spherical surfaces, which ensure an acceptable (around 0.3 mm) minimum tip clearance above the leading and trailing edges only at the smallest of the possible blade angles, and in the root section – only at the maximum blade angle (of the required range); option 2 – with spherical outlines and blades cut along a sphere equidistant to the outline spheres (with a clearance of around 0.3 mm); option 3 – with flat meridional outlines in the form of a polyhedral prism and blades with flat ends equidistant to the prism faces (with a clearance of around 0.3 mm); The results of calculations carried out in the ANSYS CFX software package are described and analyzed, which have shown a slight advantage in efficiency ηri (by around 2%) for options 2 and 3. For these options, the decrease in efficiency with an increase in the flowrate above its design value is less noticeable than for option 1, and with flowrates lower than the design one, the values of efficiency ηri are the same for all options.