Investigations of a boxed rotor: The STAR II rotor in DLR's test hall

Abstract

The second Smart Twisting Active Rotor (STAR II) project aims at investigating active twist on a conventional blade design in the DNW-LLF wind tunnel. Prior to the wind tunnel test, the rotor is first tested for correct operation in the rotor test hall at the German Aerospace Center (DLR) in Braunschweig. This test shall ensure that all the instrumentation, but also the active twist, works correctly along with setting up the tracking of the blades before shipping the whole test setup to the DNW-LLF wind tunnel. From previous rotor tests in this hall, it was observed that vibration levels increased drastically above certain thrusts. Since there were no PIV tests carried out within this test chamber, it was decided to carry out CFD simulations to obtain visualizations of the flow and to find the origins of these vibrations. The rotor test hall was approximated by a simple box. With the help of CFD simulations carried out by DLR and JAXA, the initial guess of potential recirculation could be confirmed. The recirculation effect and vibrations become stronger with increasing thrust and therefore limits the maximum thrust in the test hall. This paper details the results of the CFD simulation and presents them along with initial experimental data from the rotor test hall.