scholarly journals Mechanism of Momentum Exchange near a Roughness Element for Rough Wall Turbulent Boundary Layer

2007 ◽  
Vol 2 (1) ◽  
pp. 196-204
Author(s):  
Takatsugu KAMEDA ◽  
Kazuto KOREISHI ◽  
Shinsuke MOCHIZUKI ◽  
Hideo OSAKA
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Roughness Element ◽  
Rough Wall ◽  
Momentum Exchange

Near-Wall Turbulent Structure for the Boundary Layer Developing Over a K-Type Rough Wall in Low-Reynolds-Number

2003 ◽  
Author(s):  
Takatsugu Kameda ◽  
Hideo Osaka ◽  
Shinsuke Mochizuki
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Friction Coefficient ◽  
Roughness Element ◽  
Skin Friction Coefficient ◽  
Rough Wall ◽  
Momentum Exchange ◽  
Local Skin ◽  
Local Skin Friction ◽  
The Mean

Measurements of the mean and the turbulent velocities have performed in the vicinity of a roughness element for the turbulent boundary layer developed over a k-type rough wall, which consists of two-dimensional square ribs (10mm × 10mm × 400mm) arrayed with pitch ratio of 4. The Reynolds-number Rθ and k+ based on momentum thickness θ and roughness height k are about 500 and 50 respectively, and relative roughness height k / δ = 0.156. LDV (Laser Doppler Velocitimetry) that it is possible to measure reverse flow was applied to investigate the momentum-exchange process in the open-face (yT = 0(mm)) over cavities. The variation of the mean and turbulent quantities profiles at yT = 0(mm) depend on the evolution of a free-shear layer formed behind roughness elements and the behavior of eddies in the cavity. Pressure drag coefficient acting on the roughness element in the local skin friction coefficient is 88% in the present k-type rough wall. The momentum exchange for the mean flow and turbulence contribute 6% and 56% respectively to the local skin friction coefficient.

Small-scale characteristics of a turbulent boundary layer over a rough wall

1997 ◽  
Vol 342 ◽  
pp. 263-293 ◽  
Author(s):  
H. S. SHAFI ◽  
R. A. ANTONIA
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Outer Layer ◽  
Large Scale ◽  
Energy Dissipation Rate ◽  
Wall Layer ◽  
Rough Wall ◽  
Small Scale ◽  
Smooth Wall ◽  
Velocity Derivative

Measurements of the spanwise and wall-normal components of vorticity and their constituent velocity derivative fluctuations have been made in a turbulent boundary layer over a mesh-screen rough wall using a four-hot-wire vorticity probe. The measured spectra and variances of vorticity and velocity derivatives have been corrected for the effect of spatial resolution. The high-wavenumber behaviour of the spectra conforms closely with isotropy. Over most of the outer layer, the normalized magnitudes of the velocity derivative variances differ significantly from those over a smooth wall layer. The differences are such that the variances are much more nearly isotropic over the rough wall than on the smooth wall. This behaviour is consistent with earlier observations that the large-scale structure in this rough wall layer is more isotropic than that in a smooth wall layer. Isotropy-based approximations for the mean energy dissipation rate and mean enstrophy are consequently more reliable in this rough wall layer than in a smooth wall layer. In the outer layer, the vorticity variances are slightly larger than those over a smooth wall; reflecting structural differences between the two flows.

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