Studying the Casing Design Influence on the Losses in Unshrouded Turbine Blades

• Published in: Thermal engineering Vol. 69; no. 8; pp. 569 - 577
• Main Authors: Afanas’ev, I. V., Granovskii, A. V., Manaev, I. A.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.08.2022; Springer Nature B.V
• Subjects: Aerodynamics; Combined-Cycle Power Plants and Their Auxiliary Equipment; Engineering; Engineering Thermodynamics; Gas turbines; Gas-Turbine; Heat and Mass Transfer; Inserts; Ledges; Rotor blades; Rotor blades (turbomachinery); Steam-Turbine; Streamlining; Stresses; Tip clearance; Turbine blades; Working fluids; tip clearance losses; gas turbine; rotor blades; temperature stresses; vortex structure; deformation; open tip clearance
• DOI: 10.1134/S0040601522070011
• ISSN: 0040-6015

— At present, the majority of power-generating gas turbines produced by the world’s leading companies have unshrouded rotor blades of all stages except the last one and a number of turbines also have the last-stage rotor blades unshrouded. This became possible owing to the advent of tip clearance monitoring and control systems, the use of which makes it possible, depending on the plant operation mode, to secure highly efficient and reliable gas turbine operation. Since almost all stages of modern gas turbines operate at high working fluid temperatures, it is necessary to take into account significant temperature stresses arising in the turbine casing components and rotor blades; these stresses give rise to deformations, which are difficult to predict in advance. In some cases, the mutual displacements of cooled nozzle vane platforms upstream and downstream of the rotor blade, and also of the casing treatment inserts give rise to ledges at the periphery of rotor blades with an open tip clearance, the streamlining of which entails the occurrence of vortex zones. These vortex zones generate additional losses at the rotor blade periphery and affect the pattern of working fluid leakage through the tip clearance. Based on the example cases modeling possible casing designs at the wheel space periphery near the rotor blades, the flow structure and the level of losses are numerically analyzed as functions of tip clearance.