Some Nonlinear Problems in Transonic Helicopter Acoustics.

Abstract

The nonlinear potential equation that determines the near aerodynamic and far acoustic fields of a hovering transonic helicopter blade is derived. Properties of this equation provide a qualitative description of characteristic surfaces associated with the nonlinear flow field. A simple linearized acoustic formula is developed; a nonlinearization scheme is then applied to this formula, and the linear and nonlinear acoustic pressure profiles, including propagating acoustic shock waves, are numerically determined and compared with experimental data. A tentative conclusion is that the radiated sound field should become measurably different when the blade tip first punctures the sonic surface associated with the rotor differential equation. This conjecture is suggested by the mathematical properties of the rotor equation and recent experimental work. (Author)

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Document Details

Document Type
Technical Report
Publication Date
May 01, 1979
Accession Number
ADA069564

Entities

People

  • Morris P. Isom

Tags

Communities of Interest

  • Air Platforms
  • Energy and Power Technologies
  • Space

DTIC Thesaurus Topics

  • Acoustic Waves
  • Acoustics
  • Aspect Ratio
  • Blade Tips
  • Computational Fluid Dynamics
  • Differential Equations
  • Equations
  • Experimental Data
  • Far Field
  • Flow Fields
  • Fluid Dynamics
  • Frequency
  • Mach Number
  • Near Field
  • Shock Waves
  • Sonic Boom
  • Waveforms

Fields of Study

  • Physics

Readers

  • Acoustical Oceanography.
  • Aerodynamics.
  • Finite Element Method (FEM) for solving Partial Differential Equations (PDEs)