This paper gives an overview about prediction capabilities and the development of noise reduction technologies appropriate to reduce high lift noise and propeller noise radiation for future low noise transport aircraft with short takeoff and landing capabilities. The work is embedded in the collaborative research centre SFB 880 in Braunschweig, Germany. Results are presented from all the acoustics related projects of SFB 880 which cover the aeroacoustic simulation of the effect of flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new propeller arrangements for minimum exterior noise due to acoustic shielding as well as the prediction of vibration excitation of aircraft structures, reduced by porous materials.

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The expected computational power that will become available in the next years and decades will allow the introduction of more accurate simulations at earlier aircraft design stages. It is thus mandatory to identify and consequently develop multi-disciplinary optimization capabilities based on high-fidelity methods enabling the design of the future aircraft. The paper will give an overview of the latest development conducted at DLR in this field. Three representative applications will demonstrate benefits and limitations of the capabilities developed. Nomenclature FFD= Free-Form Deformation CD = Drag Coefficient CFD = Computational Fluid dynamics CL = Lift coefficient C SFC = Thrust Specific Fuel Consumption DC = Drag Counts (1DC=0.0001) HTP = Horizontal Tail Plane M  = Cruise Mach Number MTOW = Maximum Take-Off Weight RANS = Reynolds Averaged Navier-Stokes Equations Re = Reynolds Number VTP = Vertical Tail Plane W = Weight

For application in BEM/FMM shielding calculations a simple analytical model for the loading noise of contra rotating open rotors (CRORs) with different rotational speeds is derived. Following previous work of S.L.A. Glegg, the model is formulated in frequency domain and the pressure is approximated by a set of dipoles on circles on the propeller disk. The dipole strength depends on the blade loading function and can be obtained, e.g., by CFD calculations. For arbitrary rotational speeds, the blade loading function is not a perodic function on the propeller disk anymore and must be approximated, e.g., by a least-squares Fourier approximation. The CROR model is checked against a time domain solution using rotating dipoles and validated with data from a test of Rolls-Royce's open rotor model rig 145 in DNW. The lowest three and most dominant peaks in the spectrum of the uninstalled rotor are well predicted by the method with errors less than 3dB with a correct directivity. For higher frequencies larger errors are observed. The CROR model has been developed for shielding calculations with the DLR BEM/FMM code. Some information about the code is given and the applicability of the model is demonstrated for a CROR installed at a modified DLR F6 aircraft geometry.

System noise has been integrated as an additional design objective within conceptual aircraft design. The DLR system noise prediction tool PANAM accounts for individual noise sources depending on their geometry and operating conditions. PANAM is integrated into the existing aircraft design framework PrADO from the Technical University of Braunschweig in order to realize a design-to-noise simulation process. In addition, a ray-tracing tool from DLR, SHADOW, is incorporated into the simulation framework in order to account for structural engine noise shielding. The overall simulation process is then applied to identify promising low-noise aircraft concepts. The presented application aims at fan noise reduction through shielding. For the selected reference aircraft, the fan is a major noise source during both landing and takeoff. It is demonstrated, that the aircraft designers influence on the environmental vehicle characteristics is significant at the conceptual design phase. Usually, a trade-off between extensive engine noise shielding and economical flight performance is inevitable. The new design-to-noise process is well suitable to assess all four measures of ICAOs balanced approach.