(c) The time averaged tangential velocity distributions
Fig. 7 The time averaged velocity profiles at five regions (local axial
coordinate z=0)
4 Results and
discussion
The turbulence characteristics of swirl flow was discussed in terms of
the turbulent kinetic energy (TKE) and Reynolds shear stresses. The
definition of TKE is given by
(1)
In which u, v, w indicate the radial, axial and tangential
velocity component, respectively. The TKE normalized with the square of
averaged axial velocity in the upstream of the separator inlet\({\overset{\overline{}}{V}}_{0}^{2}\) across the swirl chamber is
presented in Fig.8. As can be seen, the turbulent kinetic energy is more
concentrated in the core region, which is consistent with that in the
cyclones. Also can be seen is the decay of turbulent kinetic energy from
the swirl vane to the recovery vane. At P1 near the swirl vane, the peak
of the turbulent kinetic energy is more than one and is decreasing
gradually in the downstream to 0.3 at P5. An interesting point worthy to
be noticed is the redistribution of TKE, which presents as a single peak
between P1 and P2 and turns into a double peak style in the following.
All previous studies on swirl flows [4,11,18,19] indicates a single
peak of TKE. The formation of double peak stems from the difference of
separator configuration between cyclones and the separator herein. In
the design of cyclones, the light phase flows through the overflow port
and the heavy phase through the under flow phase, thus the axial
velocity in the core region is always opposite to that in the peripheral
region. However, the case concerned in this separator differs from the
fact that partial gas-liquid mixture is stripped out from the upstream
orifice and partial from the downstream orifice, resulting in the axial
velocity in recalling the averaged velocity distributions presented in
Ref. [5], the tangential and axial velocity component makes
significant difference from P2 to P3.
To clarify how each component weight in the overall turbulent kinetic
energy, the turbulent intensities in all three directions were plotted
in Fig.9. As can be seen, all the components present similar
distributing characteristics, among which the tangential turbulent
intensity play an absolutely major role, while the axial and radial
components play a minor effect. The weighting of each turbulent
intensity component is consistent with the measurement of Edral
[19,20].