Optimization of Tip Seal Grooves for Aerodynamic and Durability Improvements of Small-Core Turbines

Abstract

Abstract While the clearance gap between the turbine rotor tip and the outer case in a gas turbine engine is necessary for the operation of the machine, the gap is kept as small as possible due to the detrimental effect of the flow over the turbine tip. With the increased investments in ultra-high bypass ratio gas turbines, blade tip clearances are increasing in relative size to the turbine rotor, as engines move towards smaller core sizes. In this work, a constrained topology optimization of a rotor tip seal with discrete axisymmetric grooves was explored computationally using Reynolds-averaged Navier-Stokes simulations. The differential-evolution-based optimization was applied at two tip clearances representing a nominal and small-core-scaled geometry. Furthermore, optimizations were performed at each tip clearance for blade designs with flat and squealer tips. The multi-objective optimization was designed to simultaneously maximize rotor efficiency and minimize rotor tip heat load. Several tip seal designs were identified for each tip geometry and tip gap that both increased aerodynamic efficiency and reduced the total heat load into the rotor tip. However, some optimal tip seal designs were composed of grooves that were demonstrated to be detrimental in prior work. Furthermore, grooves were more effective at increasing aerodynamic efficiency when applied to flat tipped geometries — increasing the estimated rotor efficiency by up to 0.9 points over the ungrooved seal baseline with flat tipped blades, as opposed to 0.25 points of improvement over the ungrooved case with squealer tipped blades. Finally, for both tip configurations, optimal seal geometries that were obtained from the small-core scaled clearance gap optimizations generally maintained near optimal performance when evaluated at the design tip clearance, while those geometries developed at the design clearance experienced greater sensitivity to clearance gap changes.