Numerical Investigation into the Noise Emission of Integrated Contra-Rotating Open Rotors

• Applicant: Professor Dr.-Ing. Ewald Krämer
• Subject Area: Fluid Mechanics
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 247282928

The aim of the project is the expansion of the aerodynamic and aero-acoustic numerical process chain, consisting of a CFD solver and acoustic post-processing for the investigation into the noise shielding and reflection of an integrated contra-rotating open rotor (CROR) and its detailed validation with experimental data of a CROR model test bench installed at the Institute of Aerodynamics and Gas Dynamics. Despite its high efficiency, the CROR has not become accepted in civil aviation so far. The main reason for this is the high noise emission, which is the topic of many recent research projects. In addition to the avoidance of noise development, the integration of a CROR at the empennage of the aircraft shows great potential for noise reduction. In order to reliably predict the noise reducing impact of such integration effects qualitatively and quantitatively, an accurate comprehension of the aerodynamic and aero-acoustic phenomena is necessary. The noise generating flow mechanisms of an isolated CROR are indeed rudimentary understood, however, an in-depth knowledge of the expansion of sound of an integrated CROR does not exist. Experimental data of integrated CRORs are not freely accessible for research. Hence, there are numerical investigations but no validated simulation tools. Thus, currently a CROR test bench generating experimental data of aerodynamics and acoustics of a CROR integrated into an empennage with a pylon is built up. Thereby together with the numerical process chain, experimental and numerical data for an integrated CROR can be compared for the first time. Within this project, the numerical process chain will be expanded to calculating integrated CRORs and validated by the measured data. For this purpose, the current version of the CFD-solver will be used as well as a modified one with a higher order scheme, both together with the existing Ffowcs Williams-Hawkings solver. In addition, acoustic post-processing will be expanded with a combination of boundary-element method (BEM) and ray-tracing method (RTM). BEM will be executed for the calculation of the tonal part of the shielded and reflected sound, whereas RTM will be used for the simulation of higher frequencies. Both methods complement one another by covering different frequency domains, which is the advantage of the combination of these different methods. The expansion of low frequencies can be calculated with BEM because for this method a minimal discretization of the wavelength is necessary. In contrast to this, wavelengths have to be small against geometry for RTM, therefore the high frequency domain is covered with this method. The newly developed modules will be validated with measured data and subsequently used for the simulation of a full-scale integrated CROR.

• DFG Programme: Research Grants