Aeromechanical Design and Test of a Modern Highly Loaded Fan

Abstract

The paper describes the aeromechanic design of a modern highly loaded fan blisk. The state of the art fan has been designed in a wholistic approach involving input from the disciplines of aerodynamics, structural dynamics, impact, design/make and aeroelasticity. This holistic approach puts large demands for the predictive capability of the involved disciplines. However it will be shown that the final design matches the predictions very well with even exceeding some of the targeted key parameters. The fan was designed aerodynamically to exhibit very high loading and yet was also required to have improved performance and stability characteristics relative to the current state-of-practice in fan design. Integrity requirements necessitated that the previously-stated aerodynamic design goals be achieved with increased blade thicknesses relative to state-of-practice designs. Despite the high loading at the aerodynamic design point the fan was also designed for a maximum operating range at part speed conditions. At these conditions flutter limits the operating range and needs to be avoided at any possible operating condition within the flight envelope. During design phase the part speed flutter phenomenon has been addressed by a combination of using simple aeromechanical design criteria in the early stages aided by CFD analysis in the later stages to verify the flutter behaviour of intermediate designs. The combination of low fidelity criteria and advanced CFD analysis lead to a fast convergence into a final design which met all requirements. The final design has been extensively tested in order to capture aerodynamic parameters and establish the boundaries of the safe operating range. The test results show that the fan met the key performance parameters and even exceeds some of the requirements. In terms of flutter margin the predicted values could largely be confirmed.