Near-field investigation of chevron nozzle mechanisms

A detailed investigation into the effect of chevron nozzles on the near-field acoustics of a separate flow exhaust system was conducted at the University of Cincinnati Anechoic Test Facility. Chevrons with varying numbers of lobes and levels of penetration were selected to provide insight into the effects of these geometric parameters on the acoustic near field. Tests were conducted at two different nozzle operating conditions and the chevrons were shown to produce substantial modifications to the near field over a wide range of frequencies. The chevrons were most effective at lower frequencies where the peak noise region was reduced by 5-7 dB and dramatically reduced in size. At higher frequencies, the chevrons provided strong noise suppression downstream of approximately seven equivalent nozzle diameters with increases closer to the nozzle lip. The nozzle penetration was shown to have the most significant impact on the acoustic near field with more subtle differences being seen with respect to the number of chevron lobes.