NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Structure of rough-wall turbulent boundary layersRecent experiments have shown that, in rough-wall turbulent boundary layers, drag varies systematically with the spanwise aspect ratio lambda(z) (span/height) of roughness elements. In this paper, the effect of lambda(z) on turbulence structure has been examined. Based on lambda(z), the roughness in a transversely grooved surface with lambda(z) much greater than 1 is the opposite extreme of model plant canopies with lambda(z) much less than 1, studied in wind tunnels, whereas sandgrain is an intermediate type. Second-, third-, and fourth-order turbulence moments have been measured in turbulent boundary layers over transversely grooved and smooth surfaces and compared with available turbulence structure measurements over other types of surfaces. The near-wall turbulence structure is found to vary with lambda(z). The instantaneous motions involved in the flux of shear stress near the wall in smooth and transversely grooved surfaces are opposite in sign to those in three-dimensional roughness. The former is explained in terms of hairpin vortices alone, while the latter group is modeled to have an additional vortex (the so-called necklace vortex which straddles a three-dimensional roughness element near its base).
Document ID
19880059091
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Bandyopadhyay, Promode R.
(NASA Langley Research Center Hampton, VA, United States)
Watson, Ralph D.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 13, 2013
Publication Date
July 1, 1988
Publication Information
Publication: Physics of Fluids
Volume: 31
ISSN: 0031-9171
Subject Category
Fluid Mechanics And Heat Transfer
Accession Number
88A46318
Distribution Limits
Public
Copyright
Other

Available Downloads

There are no available downloads for this record.
No Preview Available