MULTI-POINT DESIGN OPTIMIZATION OF A HIGH BYPASS RATIO FAN BLADE

摘要

The overall aerodynamic performance of thefan blade of a high bypass ratio aero engine isnot only determined by its conventionalaerodynamic parameters, such as pressure ratioand efficiency, but also the mass flow ratio ofingested water in the bypass duct during rainingestion airworthiness test. To ensure the enginereliablibity, the larger percentage of ingestedwater passing through the bypass duct is alwaysdesirable. In conventional fan blade airfoil designpractice, the pressure ratio and efficiency arefirst preliminarily determined for the designpoint, usually the cruise condition, and the massflow ratio of ingested water in bypass duct is thencalulated for the approach condition for theaccessment of its rain ingestion performance.With this approach, many iterations are usuallyneeded before the ideal design results can beobtained, and such interations can be aconsiderable part of the design cost. Toaccelerate the design procedure, a multi-pointoptimization method is proposed in this paper toconsider the multipal factors, i.e. the pressureratio, efficiency and the mass flow ratio ofingested water, all together. In this method, theBezier curve is used to parameterize the fanblade. The geometrical parameters are used asvariables while the pressure ratio, efficiency, andthe mass flow ratio of ingested water in bypassduct of the fan blade are used as the objectivefunctions. The flow-field of fan rotor under wateringestion conditions is evaluated by ANSYS CFX.An Eulerian-Lagrangian approach is used informulating the flow and droplet governingequations in the rotating reference frame. Inorder to resolve the difficulty of this highdimensionalmulti-objective optimizationproblem, the NSGA-II algorithm is used to obtaina more complete picture regarding the trade-offamong pressure ratio, efficiency and water massratio in bypass duct under three typicalconditions. A multi-point design optimization of atypical high bypass ratio fan blade is performedin this paper. The mass flow ratio of ingestedwater in bypass duct of the optimized fan blade ismuch larger than that of the baseline, while thepressure ratio and efficiency of the blade remainunchanged. The feasibility and efficiency of thisoptimization method are shown by this work.