Evaluation of the Principle of Aerodynamic Superposition in Forced Response Calculations

The validity of the principle of superposition for forced response analysis is evaluated by its application to a research propfan stage. The counter-rotating propfan features transonic flow conditions and aerodynamic interaction between the blade rows. The computed unsteady aerodynamics are verified by compar- ison with rig measurements. A forced response analysis based on the principle of superposition is conducted, similar to the current practice in turbomachinery design. For reference, a fully coupled simulation of the propfan forced response is undertaken. This simulation does not rely on the principle of superposition, and the model can also resolve non-linear interaction effects beyond the valid- ity of the linear superposition principle. The comparison shows a full validity of the superposition principle for the present case: Computed blade vibration amplitudes, as well as the unsteady aerodynamics inside the blade passages, are correct, even in quantitative terms. This supports the application of the superpo- sition principle for forced response analysis within the industrial design process.