Dr. Rob Miller undertook his undergraduate, PhD and a research fellowship at Oxford University. For the last eight years he has been a Lecturer in Turbomachinery at the Whittle Laboratory in Cambridge University. He has just been made Reader in Energy Technology at Cambridge University. He won Turbomachinery Committee Best Paper Awards at IGTI in 2007 and 2008, a Heat Transfer Committee Best Paper Award in 2005 and an AIAA Air Breathing Propulsion Best Paper Award, 2007-8 across all conferences. His research interests include all areas of turbomachinery, unsteady flows and pressure gain combustion for gas turbines.

Abstract: The small size of the leading edges of a compressor blade, typically 0.5mm in thickness, leads to a number of practical design problems. Firstly, during the design process, structural requirements often force the designer into making the leading edge thicker than they would ideally like. Secondly, during manufacture process, small inaccuracies can lead to significant variations in the geometry of the leading edge. Finally, during service, erosion can alter the leading edge geometry. In practice a combination of these effects often leads to gas turbines operating at ~1.2% below their optimal efficiency. The aim of this talk is to show how industry can change design, manufacture and operating practice to ensure that optimal efficiency is always achieved.
The reason for the performance reduction is that very small changes in the leading edge geometry can cause a small leading edge separation bubble. Because of their small size, typically less than 1mm, these separation bubbles commonly go unnoticed, however, their presence causes early boundary layer transition and thus raises profile loss by approximately 30%. This is equivalent to a 1.2% drop in stage efficiency.
What industry requires is a performance criterion which can be used to accept or reject blades, either in the design process, on the production line or in service. In this talk such a criterion will be developed based on the height of the leading edge over-speed, ‘spike’. The criterion is investigated both experimentally and computational. The experiments are undertaken in a large scale compressor stage. The criterion is then validated on a wide range of leading edge geometries.
With the rising importance of climate change it is imperative that we put in place procedures which ensure that gas turbines operate at their peak performance throughout life. To achieve this automated leading edge inspection equipment should be installed on productions line and in service shops and the criterion outlined in this talk be used to accept or reject blades.

More information: Prof. Pavel Šafařík