Comparative analysis of flow and heat transfer in turbine blade tip clearances across actual and approximate cascade configurations

Simplified linear and annular cascades have frequently been used by researchers to conduct extensive experimental and numerical studies on flow and heat transfer in tip clearances of turbine rotor blades. However, these studies often ignore the differences in flow and heat transfer characteristics between actual cascade configurations (the fully representative annular cascades with rotating, three-dimensional twisted blades and realistic geometric scaling) and approximate cascade configurations (simplified models including both static blade and static shroud setups, as well as static blades with moving shroud simulating relative motion). This study employs three-dimensional steady Reynolds averaged Navier–Stokes simulations with the standard k–ω turbulence model to systematically analyze different relative motion mechanisms, including actual blade rotation (within the actual cascade), shroud rotation/translation (as part of approximate cascades), static conditions (also part of approximate cascades), and various operating conditions covering typical engineering values of tip clearance ranges (0.5%–8% span), based on a gas turbine rotor blade. Key flow phenomena identified include the presence of corner vortex structures dominating flat tip flows, while squealer tips exhibit complex vortex systems comprising pressure side cavity vortexes, suction side cavity vortexes, and scraping vortexes (SV) under relative motion conditions. Under static conditions, the SV is absent. The flat tip with shroud translation effectively simulates the impact of clearance variations under the actual blade rotation condition. This study provides a theoretical basis for selecting experimental cascade configurations and offers critical support and data references for evaluating gas turbine performance and optimizing blade designs.