Accession Number:

AD0730427

Title:

Roughness Criteria and the Relationships between Surface Roughness and Flow Noise

Descriptive Note:

Corporate Author:

DAVID W TAYLOR NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER BETHESDA MD

Personal Author(s):

Report Date:

1971-01-01

Pagination or Media Count:

8.0

Abstract:

Roughness criteria are usually given for the surfaces of structures to prevent premature structural failure, added drag, and added flow noise. Structural roughness criteria usually deal only with long wavelength roughness, or waviness, which is specified in terms of clearance under a batten of a particular length. Drag roughness criteria usually deal only with the short wavelength roughness as measured by a profile meter. Flow noise roughness criteria, however, must include both the long and short wavelength components of the roughness and, in the case of water, separate criteria are needed for boundary layer turbulence and cavitation induced noise. A more unified description of roughness and roughness criteria is given in terms of its wavenumber spectrum. Hydraulically smooth surfaces are believed to have no roughness related component of drag or turbulence induced flow noise. In water, for instance, the surface is considered to be hydraulically smooth if the roughness height in inches is less than about 0.01 divided by the free stream velocity in knots. The expected increase in turbulence induced flow noise in water and in air as a function of roughness and flow speed is then determined from available data on local skin friction. Author turbulence induced flow noise. In water, for instance, the surface is considered to be hydraulically smooth if the roughness height in inches is less than about 0.01 divided by the free stream velocity in knots. The expected increase in turbulence induced flow noise in water and in air as a function of roughness and flow speed is then determined from available data on local skin friction.

Subject Categories:

  • Marine Engineering
  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE