An efficient winglet coverage for aeroengine turbine blade flat tip and its loss map

Abstract

The stage efficiency of an axial-flow turbine is influenced considerably by the leakage loss over its blade tip. The objective of this experimental study is (i) to find the best winglet coverage for the blade flat tip in an aeroengine turbine cascade of strong reaction and (ii) to know its full aerodynamic performance. In order to do this, aerodynamic losses for seven different winglets of new streamlined design are measured and then the loss map for the best winglet is completed with the variations of h/s (tip gap-to-span ratio) and w/p (winglet width-to-pitch ratio) for the first time, by employing five-hole probe measurement system. The result shows that double-sided winglets lead to lower loss than single-sided ones and the double-sided winglet covering pressure-side and upstream suction-side is found to be the best one. The loss map for the best winglet reveals that higher h/s leads to higher loss for any w/p, and higher w/p results in lower loss for any h/s. With increasing h/s, the loss reduction by the best winglet of w/p = 5.0% becomes more considerable and is closer to that by the one of w/p = 10.0%. Regardless of h/s, the present best winglet tip has lower loss than the full squealer tip that is widely employed in modern gas turbines.