Relation between Vortex Sound Generation and Wind Resistance

1951 ◽  
Vol 23 (5) ◽  
pp. 634-634
Author(s):  
Wolf W. von Wittern
Keyword(s):  
Sound Generation ◽  
Wind Resistance ◽  
Vortex Sound

scholarly journals SIMULATION OF VORTEX SOUND USING THE VISCOUS/ACOUSTIC SPLITTING APPROACH

2011 ◽  
Vol 35 (1) ◽  
pp. 39-56
Author(s):  
Ting H. Zheng ◽  
Shiu K. Tang ◽  
Wen Z. Shen
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Incompressible Flow ◽  
Analytical Solutions ◽  
Numerical Approach ◽  
Sound Generation ◽  
Vortex Sound ◽  
Acoustic Interaction ◽  
Unsteady Interaction ◽  
Good Agreement

A numerical viscous/acoustic splitting approach for the calculation of an acoustic field is applied to study the sound generation by a pair of spinning vortices and by the unsteady interaction between an inviscid vortex and a finite length flexible boundary. Based on the unsteady hydrodynamic information from the known incompressible flow field, the perturbed compressible acoustic terms are calculated and compared with analytical solutions. Results suggest that the present numerical approach produces results which are in good agreement with the analytical solutions. The present investigation verifies the applicability of the viscous/acoustic approach to flow structure-acoustic interaction.

Why Do Vortices Generate Sound?

1995 ◽  
Vol 117 (B) ◽  
pp. 252-260 ◽  
Author(s):  
Alan Powell
Keyword(s):  
Mach Number ◽  
Incompressible Flow ◽  
Vortex Rings ◽  
Inviscid Fluid ◽  
Fluid Density ◽  
Sound Generation ◽  
Simple Argument ◽  
Low Mach Number ◽  
Vortex Sound ◽  
Moving Vortex

Emphasizing physical pictures with a minimum of analysis, an introductory account is presented as to how vortices generate sound. Based on the observation that a vortex ring induces the same hydrodynamic (incompressible) flow as does a dipole sheet of the same shape, simple physical arguments for sound generation by vorticity are presented, first in terms of moving vortex rings of fixed strength and then of fixed rings of variable strength. These lead to the formal results of the theory of vortex sound, with the source expressed in terms of the vortex force ρ(u∧ ζ) and of the form introduced by Mo¨hring in terms of the vortex moment (y∧ ζ′), (ρ is the constant fluid density, u the flow velocity, ζ = ∇ ∧u the vorticity and y is the flow coordinate). The simple “Contiguous Method” of finding the contiguous acoustic field surrounding an acoustically compact hydrodynamic (incompressible) field is also discussed. Some very simple vortex flows illustrate the various ideas. These are all for acoustically compact, low Mach number flows of an inviscid fluid, except that a simple argument for the effect of viscous dissipation is given and its relevance to the “dilatation” of a vortex is mentioned.

Why Do Vortices Generate Sound?

1995 ◽  
Vol 117 (B) ◽  
pp. 252-260 ◽  
Author(s):  
Alan Powell
Keyword(s):  
Mach Number ◽  
Incompressible Flow ◽  
Vortex Rings ◽  
Inviscid Fluid ◽  
Fluid Density ◽  
Sound Generation ◽  
Simple Argument ◽  
Low Mach Number ◽  
Vortex Sound ◽  
Moving Vortex

Emphasizing physical pictures with a minimum of analysis, an introductory account is presented as to how vortices generate sound. Based on the observation that a vortex ring induces the same hydrodynamic (incompressible) flow as does a dipole sheet of the same shape, simple physical arguments for sound generation by vorticity are presented, first in terms of moving vortex rings of fixed strength and then of fixed rings of variable strength. These lead to the formal results of the theory of vortex sound, with the source expressed in terms of the vortex force ρ(u∧ ζ) and of the form introduced by Mo¨hring in terms of the vortex moment (y∧ ζ′), (ρ is the constant fluid density, u the flow velocity, ζ = ∇ ∧u the vorticity and y is the flow coordinate). The simple “Contiguous Method” of finding the contiguous acoustic field surrounding an acoustically compact hydrodynamic (incompressible) field is also discussed. Some very simple vortex flows illustrate the various ideas. These are all for acoustically compact, low Mach number flows of an inviscid fluid, except that a simple argument for the effect of viscous dissipation is given and its relevance to the “dilatation” of a vortex is mentioned.

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