Time-Linearized Forced Response Analysis Of A Counter Rotating Fan; Part I: Theoretical Concept Of A Fully Time-Linear Forced Response Analysis

From 2010 to 2013, several institutes of the German Aerospace Center investigated a counter rotating fan arrangement called CRISP2. While having efficiency advantages over rotor-stator arrangements, counter rotating fans might be subject to increased aerodynamic excitation as well. It is well known that rotor-stator interaction (in this case rotor-rotor-interaction) can result in aerodynamic excitation of blades leading to high cycle fatigue. Therefore, forced response calculations and an estimation of the static and dynamic loads during operation are essential prior to production and rig tests.At the Institute of Aeroelasticity, loosely coupled approaches for forced response calculations have been employed for a number of years (VASANTHAKUMAR [1]).Due to a limited time frame for the forced response simulation, it was decided to use this loosely coupled approach for the forced response simulations in CRISP2 as well and to reduce its time consumption even more by using a time-linear approach for the forcing calculations. The theoretical concepts and their implementation into a forced response simulation are highlighted. Special consideration is given to the linearized unsteady simulations with gust boundary conditions that have been implemented into the DLR in-house flow solver TRACE [2].The advantages and drawbacks of a fully time-linear loosely coupled method compared to more accurate and complicated approaches are discussed.