Particulate flows in curved pipes are commonplace in a variety of settings and involve aerosol deposition in airways as well as solids or droplets impacting pipe walls. The presence of bends in such flows is well-known to be associated with large pressure drops and phase separation due to the centrifugal force. The consideration of bends is thus important in designing multiphase flow equipment and pipes. For example, natural gas transported in pipes is often wet and water droplets, as they pass through the bend, may impact the bend wall where they form a film; this may well influence the performance of separation equipment located downstream. Phenomena associated with flows through curved pipes, such as the formation of secondary flow patterns, are thus studied in this work in order to evaluate their effects on the disperse phase. In addition, the accuracy of the numerical simulations for such flows is often in question when compared with experiments. This may be due to a number of factors which include the selection of an appropriate multiphase model and turbulence closure, or numerical aspects such as the quality of the treatment of the near wall behavior. In the first part of this work, dilute particle flows in curved pipes are modeled using one-way and two-way coupled models. In one-way coupling simulations, the influence of the particles on the carrier phase is ignored. The influence of turbulence closures on the flow and particle trajectories are investigated. The "standard" k-å model and the Reynolds Stress Model (RSM) based on the Reynolds-Averaged Navier-Stokes (RANS) equation are employed with different near-wall treatments. For two-way coupling simulations, the drift flux model based on the mixture theory is used to consider the interaction between the phases. A realizable k-å model is employed to close the RANS equation and the Enhance Wall Treatment (EWT) is applied for the flow in the near-wall region. Results show that the pressure drop of a single phase flow along the curved pipe is well predicted by the turbulent closures studied. For one-way coupled simulations, RSM with EWT is accurate in estimating grade efficiency curves. Compared to other possible combinations, using RSM with EWT can improve the accuracy by as much as 19% in a 90° bend and up to 30% in a 180° bend. The results of these simulations have allowed the development of an improved correlation for predicting grade efficiency curves. For two-way coupled simulations, results show that the pressure drop is significantly affected by the disperse phase. The computed pressure has a good agreement with the empirical correlation of Paliwado. Bend design using the mixture model shows that 90° and 180° bends with the curvature ratios equal to 5 and 7 respectively can be used to achieve a high deposition efficiency with a relatively low pressure drop. Following the above studies, a modification of the Immersed Boundary (IB) method, an approach for the simulation of particles moving in a fluid, is introduced to perform a preliminary validation of the closures used in multiphase flow modeling. An algorithm is implemented to combine the MacCormack scheme with the IB method. The technique is applied to particulate-laden flow simulations. This data is used to verify the performance of the mixture model on estimating particle behaviors in Couette flows and Poiseuille flows. Results show that IB method based on the MacCormack scheme is promising in dealing with fluid-structure interaction especially for particulate-laden flows. Comparison between the DNS data and the mixture model indicates that the mixture model is not able to capture particle migration. To improve the performance, the lift force needs to be considered in the model used to close the slip velocity.
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