Acoustic  emission  (noise)  from  wind  turbines  is  curtailing  the  growth  of  wind  energy,  which  is  currently  the  primary  renewable  energy  source  in  the  US  and  in  the  world.  A majority of the noise radiated from wind turbines is generated aerodynamically – due to interaction of wind with blade surfaces. Aerodynamic sound (aeroacoustics) is an issue not just  for  wind  turbines  but  also  for  aircraft,  jet  engines,  combustion  turbines  used  for  electricity generation, cooling fans, and ventilation systems.

A solution to the problem of aerodynamic noise generation is available in nature but has not yet been leveraged to develop silent machines. The nocturnal owl is known to have a silent  flight  both  when  gliding  and  flapping.  This  has  been  known  for  decades,  but  the  physical  mechanisms  enabling  its  silent  flight  are  not  well  understood.  Previous investigations  have  identified  three  feather  features  that  are  unique  to  the  owl.  Experimental  investigations  have  demonstrated  that  these  unique  feather  features  are responsible for the owl’s acoustic stealth.  However, these experiments alone are unable to identify  the  reasons/mechanisms  behind  noise  reduction.  This  is  because  it  is  nearly  impossible  to  measure  the  flow  with  the  spatial  and  temporal  accuracy  required  to  fully understand these mechanisms.   

This project supports very high resolution simulations to bridge the scientific gap between experimental results and theoretical understanding. A systematic numerical investigation of  the  unique  owl  feather  features  is  proposed  to  answer  key  questions  that  will  help  unravel  the  mystery  behind  owl’s  silent  flight.  The  extremely  high  spatial  and  temporal resolution offered by high-­fidelity numerical simulations will enable source diagnostics to identify  how  the  unique  feather  features  curb  noise  generation.  The  knowledge  and  understanding  gained  from  these  simulations  can  empower  us  to  design  nearly  silent energy conversion-­‐ and various other engineering machines.

The simulations will use a well-­established high-­order accurate flow solver, FDL3DI, and an in-­house  acoustics  solver.   This  computational  framework  has  been  verified  against  experimental  data  for  a  model  aeroacoustics  problem.  The  simulations  results  will  be combined  with  ongoing  experimental  measurements  at  Virginia  Tech  to  allow  a  comprehensive  understanding  of  silent  owl  flight  and  provide  a  transformative  jump towards developing nearly silent energy conversion machines.