Ingo Borchers

Generic wind tunnel study on side edge noise

The aeroacoustic phenomena of flap side edge noise and the associated noise source mechanisms are discussed. Further, a systematic and parametric wind tunnel study is presented which considers generic side edge models instead of specific flap side edge configurations. A particular test set-up allowed isolating the side edge noise from all other aerodynamic noise sources. The tests provided information on side edge far field noise of reference flat angular edges of different thicknesses, selected rounded and sharp side edge geometries as well as selected low noise side edge designs. On basis of these results several concepts to control the dominant noise source mechanisms and future steps towards a design optimization are addressed.

Analytical Modelling of Special Acoustic Absorbers

Main objective of the present work is the development of a three-dimensional model of Special Acoustic Absorbers (SAAs) and its application to SAA acoustic performance prediction. These absorbers consist of a circular volume with an inserted horn of conical or hyperbolic geometry. The model is based on a decomposition of the absorber volume into separate domains in which the equations of motion are solved separately. The overall behaviour is obtained by coupling the separate solutions via boundary conditions. Various horn geometries are accounted for through an approximation of the horn and annular domains by series of cylinders resp. annular cylinders. Viscous losses are included through application of a variational method. Predicted impedance and absorption spectra are compared with experimental results and good agreement is observed.

Active noise and vibration control for turboprop aircraft

Interior noise in modern turboprop aircraft is a serious problem as it is directly related to passenger comfort, crew performance, and aircraft weight. For turboprop aircraft the most important noise sources are the propellers generating intense low‐frequency noise which is, in general, difficult to reduce by passive measures. Therefore, extensive work has been conducted on active noise control using loudspeakers as secondary sources and microphones as error sensors. In addition, new control techniques have been investigated applying structural actuators for controlling the structural fuselage modes coupling to the critical acoustical modes. The present paper demonstrates the feasibility of using the new structural actuator technique in turboprop aircraft. Multiple piezoceramics have been attached to the structure of the Acoustic Test Cell (ATC) based on the Dornier 328 turboprop aircraft. The ceramics are driven according to a theoretical optimization process based on measured transfer functions. Noise r...