Effect of Tip Gap and Squealer Geometry on Measured Heat Transfer Over a HPT Rotor Blade Tip

Abstract

The present study explores the effects of gap height and tip geometry on heat transfer distribution over the tip surface of a HPT first stage rotor blade. The pressure ratio (inlet total pressure to exit static pressure for the cascade) used was 1.2, and the experiments were run in a blow-down test rig with a four-blade linear cascade. A transient liquid crystal technique was used to obtain the tip heat transfer distributions. Pressure measurements were made on the blade surface and on the shroud for different tip geometries and tip gaps to characterize the leakage flow and understand the heat transfer distributions. Two different tip gap-to-blade span ratio of 1% and 2.6% are investigated for a plane tip and a deep squealer with depth-to-blade span ratio of 0.0416. For a shallow squealer with depth-to-blade span ratio of 0.0104, only 1% gap-to-span ratio is considered. The presence of the squealer alters the tip gap flow field significantly and produces lower overall heat transfer coefficients. The effects of different partial squealer arrangements are also investigated for the shallow squealer depth. These simulate partial burning off of the squealer in real turbine blades. Results show that in some cases, partial burning of squealers along the pressure surface may be beneficial in terms of overall reduction in heat transfer coefficients over the tip surface compared to the plain tip.

Aerothermal Performance of Shroudless Turbine Blade Tips with Relative Casing Movement Effects

“…A single, rather than a double squealer, was shown to have lower overall heat transfer. Additional work on squealer tips includes those by Kwak et al [7], Newton et al [8], and Nasir et al [9].…”

Effect of vane/blade relative position on heat transfer characteristics in a stationary turbine blade: Part 1. Tip and shroud

“…The suction side squealer tip provides the lowest heat transfer coefficient at the tip and near-tip region. Saxena et al [7,8] and Nasir [9] investigated the effects of tip geometry and unsteady wake on the tip flow and heat transfer for a blade using a steady state HSI-based liquid crystal technique. Yang et al [10,11], Acharya et al [12] and Saha et al [13] studied flow and heat transfer characteristics for blades with different leakage reduction strategies including squealer tip and winglet using a commercial program, FLUENT.…”