Noise modelling and analysis of aircraft engines with contra-rotating open rotor fans

The growing demand for jet engines offering reduced emissions and fuel consumption, has encouraged research on Contra Rotating Open Rotors, which seem to fulfill these requirements. Besides the aforementioned qualities of CRORs, a clear disadvantage is the greater than usual noise generation, due to the location of the fan rotor outside the nacelle. Thus, recent work has concentrated on optimizing noise emissions, in order to overcome the drawbacks of the open rotor. The outcome of these investigations was the basis for developing audio files which simulate the noise generated by CRORs.  In order to achieve this goal, data files containing the calculated sound emissions of an open rotor aircraft engine, were derived from earlier research work. These data files comprise of sound pressure level versus frequency results, for 41 measurements made during each stage of flight (approach, sideline and takeoff).  The main course required the creation of sinusoidal tones of equal amplitude and duration, throughout the frequency domain, using Mathworks Matlab. After processing and sorting the input data, the tones were imported into a Digital Audio Workstation software (Ableton Live). Each audio file was severed into 41 clips and its sound pressure level was altered every 0.5 seconds, according to the original data files. Consequently a 20.5 second long audio file was created. Finally, the Virtual Studio Technology plug-in Blue Cat FreqAnalyst was utilized in order to obtain a spectrum analysis of the audio signal, throughout the time domain.  The above process was applied once for every single stage of flight and thus, three digital audio files were created, which are now available for research procedures regarding aircraft noise.  The availability of these audio files is of significant importance, as they originate from research on aircraft engines of innovative design, which are still under development. Therefore, the final simulated sounds enhance the capability of perceiving the sound of future engines, not only optically, through the use of graphs and calculations, but acoustically as well. In addition, they can provide comparison between the calculative data and the actual effect of aircraft noise on human hearing.