Cavitating flow over a circular cylinder is investigated over a range of cavitation numbers (σ = 5 to 0.5) for both laminar (at Re = 200) and turbulent (at Re = 3900) regimes. We observe non-cavitating, cyclic and transitional cavitation regimes with reduction in freestream σ. The cavitation inside the Kármán vortices in the cyclic regime, is significantly altered by the onset of "condensation front" propagation in the transitional regime. At the transition, an order of magnitude jump in shedding Strouhal number is observed as the dominant frequency shifts from periodic vortex shedding in the cyclic regime, to irregular-regular vortex shedding in the transitional regime. In addition, a peak in pressure fluctuations, and a maximum in St versus σ based on cavity length are observed at the transition. Shedding characteristics in each regime are discussed using dynamic mode decomposition (DMD). A numerical method based on the homogeneous mixture model, fully compressible formulation and finite rate mass transfer developed by Gnanaskadan & Mahesh (Intl. J. Multiphase Flows, vol. 70, 2015, pp. 22-34) is extended to include the effects of non-condensable gas (NCG). It is demonstrated that the condensation fronts observed in the transitional regime are supersonic (referred as "condensation shocks"). In the presence of NCG, multiple condensation shocks in a given cycle are required for complete cavity condensation and detachment, as compared to a single condensation shock when only vapor is present. This is explained by the reduction in pressure ratio across the shock in the presence of NCG effectively reducing its strength. In addition, at σ = 0.85 (near transition from the cyclic to the transitional regime), presence of NCG suppresses the low frequency irregular-regular vortex shedding. Vorticity transport at Re = 3900, in the transitional regime, indicates that the region of attached cavity is nearly two-dimensional with very low vorticity, affecting Kármán shedding in the near wake. Majority of vortex stretching/tilting and vorticity production is observed following the cavity trailing edge. In addition, the boundary-layer separation point is found to be strongly dependent on the amounts of vapor and gas in the freestream for both laminar and turbulent regimes. 1 2 ρ∞U 2 ∞ , where p ∞ , ρ ∞ and U ∞ are pressure, density and velocity in the freestream respectively) in the freestream is sufficiently dropped, cavities develop †

This work investigates computationally the modeling of sugarcane bagasse pyrolysis in a bubbling fluidized bed reactor. An Euler−Euler multiphase approach, as invoked by the open code MFIX (Multiphase Flow with Interphase eXchanges), is adopted, and the simulations are carried out in a two-dimensional Cartesian domain. While several pyrolysis kinetic models have been developed for wood, coal, and generic biomass, generally using thermogravimetric analysis, no such model has been specifically tested or adapted to simulate sugarcane bagasse pyrolysis in fluidized bed reactors through computational fluid dynamics. In the present study, seven pyrolysis kinetic models available in the literature are implemented as MFIX user-supplied routines and evaluated within given operational temperature ranges. Initially, well-established wood pyrolysis results are used to validate the implementations. Following validation, six kinetic schemes are employed to simulate sugarcane bagasse pyrolysis. Results for the products distribution, formation reaction rate profiles, and tar composition at different operating temperatures of the fluidized bed reactor are obtained for all models and compared to published experimental results. Based on the assessed predictive performances of the models, indications are drawn for the most appropriate models to simulate the reactor under different operating conditions.

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The effect of non-condensable gas in cavitating flow over a circular cylinder is investigated using a homogeneous mixture model. The numerical method to simulate turbulent cavitating flows developed by Gnanaskandan and Mahesh [1] for the mixture of water and vapor is extended to include the effect of non-condensable gas. The damping effects due to the presence of gas in the mixture are discussed. Finally, distribution of gas and vapor in the near wake of cylinder is investigated.

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