Clocking in Low-Pressure Turbines

The effect of stator clocking has been experimentally and computationally investigated using a low-speed, two-stage, low-pressure turbine (LPT) which was specifically designed to maximize the clocking potential by aligning the stator 1 wake segments with the stator 2 leading edge along the span. It was verified that the wake segments are aligned to within 10% of stator pitch across the span. The measured clocking effect on the work extraction is 0.12% and on efficiency is 0.08%. Although the effect of clocking is small, it is repeatable, periodic across four stator pitches and consistent between independent measurements. Furthermore, factors to consider for a reliable clocking investigation are discussed. The measurements revealed that the majority of the clocking effect on the work extraction occurs in stage 2 and it originates at stator 2 exit. This indicates that the flow is being processed differently within stator 2. There is also an effect on the stage 1 work. In each blade row, the measured clocking effect on the lost work is similar across the span. The computations with meshed cavities do not capture any clocking effects in stage 1. This indicates that an unsteady viscid phenomenon within rotor 1 is not captured by the fully turbulent calculation, e.g., unsteady transition. However, the computations do capture the measured clocking effect on the stage 2 work extraction. It is hypothesized that the clocking effect on stator 2 flow turning is dominated by a steady, inviscid process.