Development of the Fluid Insert Noise Reduction Method Investigating Azimuthal Asymmetry

Open Access
Morgan, Jessica
Graduate Program:
Aerospace Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
July 13, 2018
Committee Members:
  • Philip John Morris, Dissertation Advisor
  • Philip John Morris, Committee Chair
  • Jose Palacios, Committee Member
  • Jacqueline Antonia O'Connor, Committee Member
  • Victor Ward Sparrow, Outside Member
  • Aeroacoustics
  • Supersonic
  • Noise Reduction
  • Jet Noise
  • PIV
Supersonic tactical aircraft engines create a high amplitude noise environment that leads to hearing loss for military personnel working on aircraft carriers and noise complaints around military bases. Between hearing loss compensation and noise lawsuits, aircraft jet noise costs the US government a substantial amount of money every year. The US military is highly invested in developing jet noise reduction technology to mitigate these issues and their corresponding costs. Penn State has developed an on-demand noise reduction method that uses fluid inserts. These inserts inject steady secondary air into the diverging section of a converging diverging nozzle. The fluid inserts generate streamwise vortices that break up the large scale turbulent structures that are the primary source of noise. In addition, the air injected by the fluid inserts weakens the shock cell structure that exists for non-perfectly expanded jets causing a reduction in the broadband shock associated noise. The fluid insert noise reduction method has shown up to a 5 dB noise benefit in the peak noise direction in laboratory small-scale testing. The purpose of this dissertation is to further the development of the fluid insert noise reduction method in preparation for eventual full-scale implementation. Development of this method includes: exploring the design by increasing the number of fluid corrugations and investigating azimuthal asymmetry, taking Particle Image Velocimetry (PIV) flow measurements to better understand the injector and core interactions, conduct moderate 1/7 scale experiments (a 5 time scale increase) to study the method’s performance at larger scales, and determine the thrust performance loss of the aircraft due to the operation of the injectors. The experiments and calculations of this dissertation reveal some key aspects of the fluid insert noise reduction method. Azimuthal asymmetry has little effect on the peak noise reduction. A more important factor is the azimuthal angular separation between fluid corrugations. The fluid corrugations have to be sufficiently spaced to allow the shear layer to thicken and penetrate into the core flow causing a reduction in the peak noise from large scale turbulence structures. There is a 4 dB peak noise reduction when the fluid corrugations have a 120 degree angular separation which decreases down to only 1 dB noise reduction when the fluid corrugations are 30 degrees apart. There are differences in noise reduction benefit between the small and moderate scale testing. The small scale testing shows up to a 5.5 dB peak noise reduction while the moderate scale has a maximum of 4 dB peak noise reduction. The moderate scale results are very promising for full scale implementation. Lastly, it is concluded that the fluid inserts reduce the thrust by less than 2% when using 5% of the total flow with the potential for even better performance.