Stefan Kröber

Simultaneous Multiplane PIV and Microphone Array Measurements on a Rod-Airfoil Configuration

The influence of the elastic rotor blade deformation and the aerodynamic interference from the fuselage on the rotor aerodynamics as well as rotor noise characteristics was studied. A BO105 Main Rotor /Tail Rotor/Fuselage (FUS) configuration is chosen for the numerical simulations. A coupling of unsteady free wake 3-D panel method (UPM) and Airbus Helicopters’ (formerly: Eurocopter) rotor code HOST was conducted to account for the effect of elastic blade deformation as well as compressibility correction. The effect of fuselage is simulated by using two fuselage models in UPM, (1) potential theory in form of a panelized fuselage and (2) an analytic fuselage influence formulation derived from isolated fuselage simulation based on (1).Measurement techniques based on microphone-arrays are well-known and common practice on scaled models in wind tunnels with closed test section. Usually, full-scale Reynolds numbers are not achieved. To increase the Reynolds number measurements are performed in cryogenic and/or pressurized wind tunnels. At the DLR Institute of Aerodynamics and Flow Technology the microphone array measurement technique was further developed to perform measurements in a cryogenic wind tunnel at temperatures down to 100 K. In order to use a microphone array in a cryogenic environment, coming to grips with cold hardiness and ensuring long term stability of the array fairing and the electronic devices, especially the microphones, are the primary challenge. In a first step measurements of the radiated noise from a single rod configuration have been conducted in the cryogenic wind tunnel DNW-KKK using a prototype microphone array designed for cryogenic environment. Measurements were carried out with a wide range of operational flow parameters. The measured sound radiation results showed a very good agreement with theory and a Reynolds number dependency of the measured and predicted sound power was shown.

Examination of the Influence of Flow Speed on the Coherence Lengths in Turbulent Boundary Layers at High Subsonic Mach Numbers

Wind tunnel measurements of wall pressure fluctuation were conducted at high subsonic Mach number. The data was analyzed in order to calculate the spatial decay of coherence of turbulent structures in the turbulent boundary layer as a function of the Strouhal number. The decay parameter determined from the measurements was compared with the predictions from the coherence length model of Efimtsov. The Mach number was varied in order to investigate the influence of a change in flow speed on the decay parameter for various Strouhal numbers.