Streamwise pseudo-vortical structures and associated vorticity in the near-wall region of a wall-bounded turbulent shear flow |
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Authors: | N Kasagi M Hirata K Nishino |
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Institution: | (1) Department of Mechanical Engineering, University of Tokyo, 113 Bunkyo-ku, Tokyo, Japan |
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Abstract: | Streamwise pseudo-vortical motions near the wall in a fully-developed two-dimensional turbulent channel flow are clearly visualized in the plane perpendicular to the flow direction by a sophisticated hydrogen-bubble technique. This technique utilizes partially insulated fine wires, which generate hydrogen-bubble clusters at several distances from the wall. These flow visualizations also supply quantitative data on two instantaneous velocity components, and w, as well as the streamwise vorticity,
x
. The vorticity field thus obtained shows quasi-periodicity in the spanwise direction and also a double-layer structure near the wall, both of which are qualitatively in good agreement with a pseudo-vortical motion model of the viscous wall-region.List of symbols
C
i
,c
i
,d
i
constants in Eqs. (2), (3) and (4)
-
H
channel width (m)
-
Re
H
Reynolds number (= U
c
H/)
-
Re
Reynolds number (= U
c
/)
-
T
period (s)
-
t
time (s)
-
U
mean streamwise velocity (m/s)
-
U
c
center-line velocity (m/s)
-
u
friction velocity (m/s)
-
u, , w
velocity fluctuations (m/s)
-
x, y, z
coordinates (m)
- *
displacement thickness (m)
-
momentum thickness (m)
-
mean low-speed streak spacing (m)
-
kinematic viscosity (m2/s)
-
phase difference
-
x
streamwise vorticity fluctuation (1/s)
- ( )+
normalized by u
and
- (–)
root mean square value
- (–)
statistical average
This paper was presented at the Ninth Symposium on Turbulence, University of Missouri-Rolla, October 1–3, 1984 |
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Keywords: | |
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