Transonic Turbine Blade Tip Aerothermal Performance With Different Tip Gaps—Part I: Tip Heat Transfer

Abstract

A closely combined experimental and computational fluid dynamics (CFD) study on a transonic blade tip aerothermal performance at engine representative Mach and Reynolds numbers (Mexit=1,Reexit=1.27×106) is presented here and its companion paper (Part II). The present paper considers surface heat-transfer distributions on tip surfaces and on suction and pressure-side surfaces (near-tip region). Spatially resolved surface heat-transfer data are measured using infrared thermography and transient techniques within the Oxford University high speed linear cascade research facility. The Rolls-Royce PLC HYDRA suite is employed for numerical predictions for the same tip configuration and flow conditions. The CFD results are generally in good agreement with experimental data and show that the flow over a large portion of the blade tip is supersonic for all three tip gaps investigated. Mach numbers within the tip gap become lower as the tip gap decreases. For the flow regions near the leading edge of the tip gap, surface Nusselt numbers decrease as the tip gap decreases. Opposite trends are observed for the trailing edge region. Several “hot spot” features on blade tip surfaces are attributed to enhanced turbulence thermal diffusion in local regions. Other surface heat-transfer variations are attributed to flow variations induced by shock waves. Flow structure and surface heat-transfer variations are also investigated numerically when a moving casing is present. The inclusion of moving casing leads to notable changes to flow structural characteristics and associated surface heat-transfer variations. However, significant portions of the tip leakage flow remain transonic with clearly identifiable shock wave structures.

Effects of Inlet Turbulence and End-Wall Boundary Layer on Aerothermal Performance of a Transonic Turbine Blade Tip

“…Qualitative differences of loss mechanism and tip heat transfer between highspeed and low-speed conditions were recognized [18][19][20][21]. More specifically, for the transonic part of the over tip flow, turbulent diffusion is shown to have a distinctively different impact on tip heat transfer than for its subsonic counterpart [18,19,21,22].…”

Aerothermal characteristics of a transonic tip flow in a turbine cascade with tip clearance variations

“…Zhang et al [10] reported the detailed experimental evidences of the heat transfer stripe distributions caused by the shock wave structures over the blade tips. Most recently, the overtip choking and shock structures [11] as well as its effects on tip heat transfer [12] were reported by Zhang et al and for even a modern winglet-tip design by O'Dowd et al [13].…”

“…Using numerical methods, Zhang et al [11] and Zhou [20] indicated that a tangential viscous force is imposed by the endwall motion, and it changes the flow physics within the tip gap, thus altering the heat transfer distribution over a transonic flat tip.…”

Heat/mass transfer over the plane tip equipped with a full coverage winglet in a turbine cascade: Part 1 – Winglet bottom surface data

“…Lee et al [7] investigated tip gap height effects on the flow structure and heat/-mass transfer over the tip surface of a turbine blade for power generation. Zhang et al [8] investigated transonic turbine blade tip heat transfer with different tip gaps.…”