(101d) Recognition and Primary Test on Secondary Flow in T-Type Outlet

Authors: 
Jia, M., China University of Petroleum
Song, J., China University of Petroleum
Wei, Y., China University of Petroleum
Zhang, H., China University of Petroleum
Zhou, F., China University of Petroleum
This work presents a recognition and primary test on alternative secondary flow in T-type outlet. The phenomenon belongs to a kind of dean vortex. Dean vortexes always are found in 90 bend pipe, and a pair of vortexes presents an alternating cyclical vibration in some condition. In recent experiments, a phenomenon of unstable back-flow occurs in T-type outlet, and the phenomenon in experiment is shown in pictures. The numerical study is performed by Fluent CFD, in which a pure gas flow and gas-particle flow are simulated in a riser with a T-type outlet. Euler-Euler two-fluid model and RNG k-ε model was adopted. The momentary result of flow filed in T-type outlet is achieved either in pure gas condition and gas-solid condition. In same gas and particle velocity, 3 volume friction was chosen, such as 0.01(Gs=138 kg/m2·s), 0.03(Gs=414 kg/m2·s), 0.08(Gs=1104 kg/m2·s). In the results of pure gas, the basic flow field in T-type outlet possessed a pair of Dean Vortexes. In a certain condition, there existed a pair of switching vortexes, which alternatively occupied the main space of T-type outlet. The changing process of the switching vortex along with time was discussed. When gas velocity was 10 m/s, gas flow state cycle time was 0.16 s. In the results of gas-solid condition, flow states cycle time is 0.6, 0.9 and 1.1 when the particle volume friction was 0.01, 0.03 and 0.08. It mean that, a higher particle volume friction lead to a long flow state cycle time. Ignoring the calculation error, the flow states cycle time of gas-solid flow is much higher than the one of pure gas. This indicated that, affected by the delay effect from particle, gas-solid flow showed a lower frequency in switching than pure gas flow. And the flow states cycle time increased with the particle volume friction grow.
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