Acoustic Attenuation by Vaporization of Liquid Droplets -- Application to Noise Reduction in Aircraft Powerplants.
Final rept. 1 Mar 71-30 Nov 74,
CALIFORNIA INST OF TECH PASADENA KARMAN LAB OF FLUID MECHANICS AND JET PROPULSION
Pagination or Media Count:
A cloud of small water droplets in saturated air attenuates acoustic disturbances by viscous drag, heat transfer, and vapor exchange with the ambient gas. The mechanisms of these processes are analyzed to show that the viscous and heat transfer phenomena attenuate at frequencies above the reciprocal of the Stokes relaxation time, a frequency of about 10,000 Hz for 1-micron droplets. The processes associated with phase exhange attenuate at much lower frequencies in fact, the characteristic frequency of this attenuation may be controlled by choice of the liquid mass fraction. The strength of the phase exchange attenuation is, however, proportional to the mass of water vapor in the air, a factor controlled by air temperature.
- Jet and Gas Turbine Engines