Tip-Shaping for HP Turbine Blade Aerothermal Performance Management

Abstract

A large portion of the over-tip leakage flow is often transonic for a typical high pressure (HP) turbine blade. It has been observed that the tip heat transfer is noticeably lower in a high speed flow tip region than in a low speed region. The present study therefore investigates the feasibility of controlling blade heat transfer by tip shaping to locally accelerate the flow to a transonic regime. The results show that a significant heat load reduction can be achieved by the local flow acceleration. Such over-tip-shaping provides a great potential as an effective means to control heat load distribution (and hence thermal stress) over the blade tip surface. The feasibility of the concept and flow physics have been demonstrated in detail by CFD analyses, with and without the effect of moving casing. The experimental results obtained from a high speed linear cascade facility have also been presented. The novel tip-shaping concept proposed in this paper could provide a potential for promoting choking inside the tip gap as a new way to control the over-tip leakage mass flow.

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

“…It should be noted that the turbine blade should be rotating in operation, but the present simulations assume the blade to be stationary. Since the work of Zhou [20] indicated that a tangential viscous fore is imposed by endwall motion, and a scrapping 22 vortex is formed in the main flow passage, it can be concluded that the leakage vortex shape may be altered due to the interaction between leakage vortex and scraping vortex, and then it affects the leakage loss characteristics.…”

“…Shyam and Ameri [21] suggested a diverging pathway for the tip leakage flow that may reduce the shock wave strength and consequently lessen the heat transfer fluctuations. Then, Zhang et al [22] proposed to locally accelerate the flow in the front part of the blade tip through a convergent-divergent nozzle to significantly reduce the overall heat transfer. More recently, Maesschalck et al [23] developed an optimization strategy to produce a set of blade tip profiles with enhanced aerothermal performances for a number of tip gap flow conditions.…”

Characterization of the Unsteady Aerodynamics of Optimized Turbine Blade Tips through Modal Decomposition Analysis

“…Carved tip designs, on the other hand, employ a contoured surface to control the acceleration of the leakage stream in the gap and force it to choking conditions [8]. This allows effectively decoupling the blade tip load from the spillage mass flow, breaking the mutual dependency between the work extraction process and the blade aerodynamic performance [9].…”

Experimental and Numerical Investigation of Optimized Blade Tip Shapes: Part I — Turbine Rainbow Rotor Testing and CFD Methods

“…As an alternative to squealer tips, a decoupling of tip aerodynamic performance and work extraction could be achieved by employing carved profiles [13]. Contoured geometries are specifically designed to choke the tip gap flow (mass flow limiter) for increasing blade tip loads [14], and to reduce the tip heat transfer.…”