Effects of Large Tip Clearance and Turbulence Intensity on Aerodynamic Performance in a Turbine Cascade

Abstract

Turbomachines have been widely used from power generation to aero-naval propulsion. Therefore, numerous studies have been devoted to improve their performance by reducing losses. Especially for aerodynamic performance, numerous efforts have been made to understand aerodynamic loss generation mechanisms in various types of such turbomachines. Geometric and flow parameters are known to affect the aerodynamic losses. The geometric parameters such as blade configurations include tip clearance (TC), aspect ratio, and roughness. The flow parameters such as inlet flow conditions include turbulence intensity (Tu), incidence angle, Reynolds number, and Mach number. Tip clearance (TC) is an evitable gap between rotating (rotors) and stationary (casing) components. The typical tip clearance of a turbine in aero engines is roughly 1% of its blade chord length. However, in smaller turbines e.g., turbopumps, the tip clearance becomes larger than 10% of the blade chord length. In a gas turbine, an incoming flow from a combustor is highly turbulent. Effects of the turbulence of the incoming flow past a turbine blade row having large (realistic) tip clearance on aerodynamic performance e.g., loss generation and deviation have not been reported hitherto. This study, therefore, aims to identify experimentally how the turbulent intensity of the incoming flow influences loss and deviation at a turbine rotor row (in a linear cascade) with a large tip clearance. To this end, three selected turbulence intensity values, 0.6%, 3.3% and 5.3% for four selected tip clearances, 1%, 3%, 10% and 15% of the blade chord were considered at a fixed Reynolds number of 200,000.