Experimental and Numerical Study of Swirling ... - Solid Mechanics

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V θ / V b
V θ / V b
V θ / V b
1.5
5.0
1.0
measurement 1
5.0
measurement 1
0.0
0.5
4.0
−5.0
0.0
3.0
−10.0
−0.5
2.0
−15.0
−1.0
1.0
−20.0
measurement 1
−1.5
−1.0 −0.5 0.0 0.5 1.0
0.0
−1.0 −0.5 0.0 0.5 1.0
−25.0
−1.0 −0.5 0.0 0.5 1.0
X / R
v (a)
X / R
v (b)
X / R
v (c)
1.5
5.0
1.0
0.5
measurement 1
measurement 2
5.0
4.0
measurement 1
measurement 2
0.0
−5.0
0.0
3.0
−10.0
−0.5
2.0
−15.0
−1.0
1.0
−20.0
measurement 1
measurement 2
−1.5
−1.0 −0.5 0.0 0.5 1.0
0.0
−1.0 −0.5 0.0 0.5 1.0
−25.0
−1.0 −0.5 0.0 0.5 1.0
X / R
v (d)
X / R
v
(e)
X / R
v
(f)
1.5
5.0
1.0
0.5
measurement 1
measurement 2
5.0
4.0
measurement 1
measurement 2
0.0
−5.0
0.0
3.0
−10.0
−0.5
2.0
−15.0
−1.0
1.0
−20.0
measurement 1
measurement 2
−1.5
−1.0 −0.5 0.0 0.5 1.0
0.0
−1.0 −0.5 0.0 0.5 1.0
−25.0
−1.0 −0.5 0.0 0.5 1.0
X / R
v (g) X / R
v (h)
X / R
v (i)
V z / V b
V z / V b
V z / V b
Fig. 7 Normalized time averaged profiles with 50 % closed ports: (a) tangential velocity profile at z/D = 0.963; (b) axial velocity profile at
z/D = 0.963; (c) axial vorticity Profile at z/D = 0.963; (d) tangential velocity profile at z/D = 2.016; (e) axial velocity profile at z/D = 2.016; (f)
axial vorticity Profile at z/D = 2.016; (g) tangential velocity profile at z/D = 3.068; (h) axial velocity profile at z/D = 3.068; (i) axial vorticity
Profile at z/D = 3.068.
1976). Due to a velocity discontinuity, a shear layer develops
on the fluid side and on the wall side a boundary layer is
developed (Rajaratnam, 1976). For confined swirling flows
with a tangential wall-jet like profile, analogous to plane
wall jets, a tangential velocity jet is issued to the cylinder
walls. The maximum tangential velocity is observed at a
radial distance from the curved wall where the shear layer
meets the wall boundary layer and minimum tangential velocity
is observed in the vortex center. A similar vθ profile is
observed for z/D = 3.068 but with a smaller magnitude thus
indicating decay in the swirl (Fig. 7g).
A significant change in the axial velocity profile is observed
at the positions close to the cylinder inlet where, compared
to fully open and 25 % port closure, it has changed to
jet-like profile i.e. the peak velocity magnitude is at the center
of the cylinder and decreases radially towards the wall
(Fig. 7b). However, there is a rapid decay in the velocity
peaks from position z/D = 0.963 to z/D = 2.016 and again
at z/D = 3.068 where a uniform distribution of vz is observed
cf. Fig. 7e,h.
For 50 % intake port closure, the mean axial vorticity at
z/D = 0.963 is shown in Fig. 7c. The ripples in the axial vorticity
profile is due to the measurement noise. The vorticity
of the vortex core region is still stronger than other radial
positions at that cross-sectional plane but less pronounced
compared to the vorticity at z/D = 0.963 and with 25 % port
closure. The maximum value of the axial vorticity has re-
ω z
ω z
ω z
duced to nearly half of the maximum value at z/D = 0.963
for 25 % intake port closure.
The mean axial vorticity distribution at z/D = 2.016 and
z/D = 3.068 (Fig. 7f,i) respectively, the vorticity is more
uniformly distributed. This indicates that the initial strength
of the vortex core decreases along the flow downstream by
transferring vorticity to other weak vortical regions.
The turbulent kinetic energy increases further with the
increase in the partial closure of the intake port from 25%
to 50% cf. Fig. 9b. The vortex core region now has a very
low TKE value. The maximum value of TKE is observed in
the region X/R = 0.4 to0.6. This indicates that the overall
velocity variance in the center of the jet-like axial velocity is
very low. The asymmetric distribution of TKE in the vortex
core region can be understood from an asymmetric jet-like
profile of mean axial velocity component.
5.4 Ports Closed by 75 %
The tangential velocity exhibits a solid body rotation throughout
the cylinder i.e. peak vθ in the entire cylinder is shifted
to the near wall positions cf. Fig. 8a,d,g.The overall tangent
velocity magnitude decays downstream the flow.
At z/D = 0.963 the axial velocity component vz still has
a jet-like profile (Fig. 8b). However, the profile has a sharp
peak compared to the 50 % intake port closure (Fig. 7b).