Design Optimization of a Fan Blade under Boundary Layer Ingestion Flow

Abstract

Boundary layer ingestion (BLI) techniques have been shown to have the potential to greatly improve propulsive efficiency. The problem with BLI engines is that the distorted flow caused by the growth of the boundary layer can significantly reduce the performance of the engine. This study seeks to build on the results from previous studies by optimizing a baseline rotor design. The optimization process utilized a combination of the Tabu Search method with either the Conjugate Gradient Method (CGM) or the Nelder-Mead Simplex (NMS) algorithm. A custom tool called the Blade Altering Toolbox was developed to automate the design alteration process of the rotor geometry and was used in conjunction with the optimization schemes. Two objective functions were considered in the optimization study. The first objective function, Case T1, was an average of adiabatic efficiency and total pressure ratio while the second objective function, Case T2, was the product of the two. Both objective functions were ran using the Tabu Search algorithm. Case T1 yielded a 4.86% increase in the adiabatic efficiency with a 3.29% drop in the total pressure ratio over the baseline. Case T2 yielded a 4.75% increase in the adiabatic efficiency with only a 2.92% drop in the total pressure ratio. Case T2 was then extended using the CGM and the NMS algorithms. The results from both the Case T2 CGM and the NMS algorithms were virtually identical, yielding a 4.71% and a 4.75% increase in the adiabatic efficiency respectively, and a 2.92% and a 2.93% drop in the total pressure ratio respectively.