Aerothermal Investigations of Tip Leakage Flow in Axial Flow Turbines—Part I: Effect of Tip Geometry and Tip Clearance Gap

Abstract

A numerical study has been performed to investigate the effect of tip geometry on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. Base line flat tip geometry and squealer type geometries, namely, double squealer or cavity and suction-side squealer, were considered. The performances of the squealer geometries, in terms of the leakage mass flow and heat transfer to the tip, were compared with the flat tip at two different tip clearance gaps. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modeled using three different models, namely, standard k-ε, low Re k-ω, and shear stress transport (SST) k-ω, in order to assess the capability of the models in correctly predicting the blade heat transfer. The heat transfer and static pressure distributions obtained using the SST k-ω model were found to be in close agreement with the experimental data. It was observed that compared to the other two geometries considered, the cavity tip is advantageous both from the aerodynamic and from the heat transfer perspectives by providing a decrease in the amount of leakage, and hence losses, and average heat transfer to the tip. In general, for a given geometry, the leakage mass flow and the heat transfer to the tip increased with increase in tip clearance gap. Part II of this paper examines the effect of relative casing motion on the flow and heat transfer characteristics of tip leakage flow. In Part III of this paper the effect of coolant injection on the flow and heat transfer characteristics of tip leakage flow is presented.

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

“…The inclusion of a casing recess showed positive signs of reduced tip heat transfer, however, a small effect on the aerodynamic efficiency. Additional validated numerical studies by Krishnababu et al [12] and Yang et al [13,14] showed noticeable reductions of the tip leakage vortex and tip heat transfer with the squealer tip.…”

Performance of Partial and Cavity Type Squealer Tip of a HP Turbine Blade in a Linear Cascade

“…T i is calculated from mass-averaged total temperature at the inlet as suggested by Ameri and Bunker [25] and Krishnababu et al [10]. Average heat transfer coefficient, h, is defined as…”

“…Camci et al [9] experimentally studied the aerodynamic characteristics of partial squealer rims in the single-stage, low-speed, rotating Axial Flow Turbine Research Facility (AFTRF) of the Pennsylvania State University and found that the suction side squealer had a better aerodynamic performance with respect to cavity squealer. Krishnababu et al [10] performed a numerical investigation on the effects of blade tip geometry and found that cavity tip improved the aerodynamic performance and decreased the heat transfer rates to the blade tip. Kavurmacioglu et al [11] and Kavurmacioglu et al [12] carried out a numerical study in a rotational test rig (AFTRF) for aerodynamic performance of full-and partial-length squealer rims.…”

Tip Leakage Flow and Heat Transfer on Turbine Stage Tip and Casing: Effect of Unsteady Stator–rotor Interactions

“…The instantaneous heat flux in the rotor crown was twice the time-averaged values due to the strong shock interactions between blade rows. Krishnababu et al (2009aKrishnababu et al ( , 2009b investigated the effect of tip geometry in part 1 and effect of relative casing motion on the tip leakage flow and heat transfer characteristics in a single blade axial flow turbine. They performed numerical study using CFX 5.6 computational software.…”