"Das DLR Projekt STELAR”

Abstract

The DLR project STELAR (Stall and Transition on Elastic Rotor Blades) ran from 2012 to 2015 and during that time was one of the major projects within the rotorcraft research area of the DLR. It was the successor to the DLR Project SIMCOS (2008-2011), which primarily investigated 2D dynamic stall, and has been succeeded by the DLR Project FAST-Rescue (2016-2019) which investigates design, noise, performance and flight envelope limitations of helicopters. The project investigated dynamic stall in both 2D and 3D, Dynamic stall control, unsteady boundary layer transition, and fluid structure coupling. The primary targets of the project STELAR were: • Enable the DLR-TAU code to perform fully elastic computations of a rotor in forward flight with boundary layer transition. • Perform converged three dimension dynamic stall computations using the DLR-TAU code and provide 3D experiments for validation. • Control dynamic stall using actively and passively adaptive measures. • Investigate unsteady boundary layer transition both experimentally and numerically The project invested heavily in wind tunnel measurements, with four tests in the Transonic Wind tunnel Göttingen (TWG), three tests in the one-meter wind tunnel Göttingen(1MG) and two tests in the Sideflow Wind tunnel Göttingen (SWG). Three new wind tunnel models were built and a further wind tunnel model heavily modified. The development of two new environments for rotor simulations was finished, including a classical coupling with the comprehensive code HOST, and an innovative coupling with the multibody simulation code SIMPAK. The investigation of unsteady boundary layer transition on rotor blades was advanced experimentally by hot-film measurements which were evaluated for the first time by a fully automated algorithm. These measurements were compared to two new measurement techniques developed in STELAR for the measurement of unsteady boundary layer transition positions: Differential Infrared Thermography (DIT) and standard deviation of pressure (σCP). A full validation of the new methods was achieved and the transition could be shown to be a result of both the instantaneous pressure distribution and the history of the flow. An investigation of both eN and γ -Reθ transition methods for the pitching airfoil for very fine grids and timesteps was undertaken in parallel with the implementation of correlation-based transition models for coarse grids and full rotor configurations into the TAU code.