(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].