Structural Modeling and Validation of an Active Twist Model Rotor Blade

Abstract

DLR has been researching on active twist rotor blade control intensively for at least 15 years now. This research work included the design and manufacturing of model rotor blades with in the blade skin integrated actuators. As a main subject, numerical benefit studies with respect to rotor noise, vibration, and performance were carried out with DLR's rotor simulation code S4. Since this simulation code is based on a modal synthesis, it uses the natural blade frequencies and mode shapes to model the blade dynamics. Both, natural blade frequencies as well as mode shapes, are computed in advance employing a finite element beam model of the blade. Each beam element possesses certain structural properties that are derived from an ANSYS model for certain cross sections of the blade. Since model rotor blades are built for wind tunnel testing, they are highly instrumented with sensors and therefore vary in their structural properties along span. Modifications in the structural properties due to the instrumentation are not included in the ANSYS model. However, to account for these variations, two different experimental methods have been developed. This way, the most important structural properties can be determined for the real blade and the structural blade model can be improved. The paper describes the development of an advanced structural blade model for rotor simulation purposes and shows a validation of the structural blade model based on the measured non-rotating and rotating frequencies.