CFD Analysis of the Transient Turbulent Flow in Sliding Gate Valves

This work presents an analysis of the transient turbulent flow within flue-gas valves. These sliding-gatetype valves are used for pressure control of an FCC (Fluidized Catalytic Cracking) unit regenerator. Downstream these valves, refractory layer damage has been taking place during unit operations and it is supposed to be caused by fatigue due to pressure oscillations along the walls. The purpose of the CFD model is to calculate the oscillating mechanical forces due to fluctuating pressure field and use them as input for structural dynamic analysis using ANSYS. Two turbulence modeling approaches are used to study the pressure fluctuations in these valves: the RANS (Reynolds Averaged Navier-Stokes Equations) and the LES (Large Eddy Simulation) approaches. The latter is supposed to be capable of capturing higher frequencies. This is a required feature of the model, as some experimental measurements using accelerometers located externally to the wall, have shown accelerating frequencies as high as 250 Hz. Thus, the model used has to be capable to predict these frequencies. Nevertheless, the RANS k-ε approach is also used in order to evaluate differences between the turbulence approaches and to compare the capabilities of each one in the context of this research, since the k-ε approach demands less computational efforts. The simulations are carried out using CFX 5.6 solver. Some preliminary models for the structural analysis are also presented.

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