Improving Intermediate Pressure Turbine Performance by Using a Non-Orthogonal Stator

Intermediate Pressure (IP) turbines in high bypass ratio civil aeroengines are characterized by a significant increase in radius and a low aspect ratio stator. Conventional aerodynamic designs for the IP turbine stator have had leading and trailing edges orthogonal to the hub and casing end walls. The IP turbine rotor, however, is stacked radially due to stress limits. These choices inevitably lead to a substantial gap between the IP stator and rotor at the outer diameter in a duct that is generally diffusing the flow due to the increasing radius. In this low Mach number study, the IP stator is redesigned, incorporating compound sweep, so that the leading and trailing edges are no longer orthogonal to the end walls. Computational investigations showed that the non-orthogonal stator reduces the flow diffusion between the stator and rotor which yields two benefits: the stator trailing edge velocity was reduced, as was the boundary layer growth on the casing endwall within the gap. Experimental measurements confirm that the turbine with the non-orthogonal stator has an increased efficiency (by 0.49%), whilst also increasing the work output (by 4.6%), at the design point.