Measurements of Cooling Effectiveness Along the Tip of a Turbine Blade

In a gas turbine engine, turbine blades are exposed to temperatures above their melting point. Film-cooling and internal cooling techniques can prolong blade life and allow for higher engine temperatures. This study examines a novel cooling technique called a microcircuit, which combines internal convection and pressure side injection on a turbine blade tip. Holes on the tip called dirt purge holes expel dirt from the blade, so other holes are not clogged. Wind tunnel tests are used to observe how effectively dirt purge and microcircuit designs cool the tip. Tip gap size and blowing ratio are varied for different tip cooling configurations.

Results show that the dirt purge holes provide significant film cooling on the leading edge with a small tip gap. Coolant injected from these holes impacts the shroud and floods the tip gap reducing tip leakage flow.

With the addition of a microcircuit, coolant is delivered to a larger area of the tip. In all cases, cooling levels are higher for a small tip gap than a large tip gap. Increased blowing ratio does not have a dramatic effect on microcircuit film-cooling at the midchord but does improve internal cooling from the microcircuit. While the combined dirt purge holes and microcircuit cool the leading edge and midchord areas, there remains a small portion of the trailing edge that is not cooled. Also, results suggest that blowing from the microcircuit diminishes the tip leakage vortex. Overall, the microcircuit appears to be a feasible method for prolonging blade life.