The compressible gas flows of interest to aerospace applications often involve situations where shock and expansion waves are present. Decreasing the characteristic dimension of the computational cells in the vicinity of shock waves improves the quality of the computed flows. This reduction in size may be accomplished by the use of mesh adaption procedures. In this paper an analysis is presented of an adaptive mesh scheme developed for an unstructured mesh finite volume upwind computer code. This scheme is taylored to refine or coarsen the computational mesh where gradients of the flow properties are respectively high or low. The refinement and coarsening procedures are applied to the classical gas dynamic problems of the stabilization of shock waves by solid bodies. In particular, situations where oblique shock waves interact with an expansion fan and where bow

The process of oil well plugging is largely used in oil industry. In this process, a cement plug (higher density fluid) is placed over the drilling fluid (lower density) to seal and abandon the well. The success of the operation depends on several aspects, such as the density ratio and the rheology of the fluids. A numerical analysis of the transient flow just after the cement placement in vertical wells is performed, using Fluent software (Ansys Inc.). The conservation equations of mass and momentum are solved using the finite volume technique. The volume of fluid method is used to deal with the multiphase flow - cement / drilling fluid. Both the drilling fluid and the cement paste are viscoplastic liquids, modeled by the Herschel-Bulkley equation. The analysis of flow displacement and interface configuration between these fluids is an important tool for the process optimization. The effects of the density ratio and yield stress on the flow pattern are investigated. It is shown that the flow is highly unstable and that the above mentioned parameters strongly affect the process.

The motion of air bubbles in a yield stress fluid is analyzed numerically using a 2D approach and the finite volume technique. The multiphase flow is simulated using the volume of fluid method (VoF), which solves the conservation equations of mass and momentum coupled to a transport equation for the volume fraction of the fluids. The effects of yield stress, bubble size, number and position of bubbles rising in a viscoplastic fluid confined between vertical parallel plates are analyzed and discussed. The results indicate that the yield stress has great impact on the rising velocity. In the case of multiple bubbles flowing vertically, it is observed that the displacement of one bubble influences the rising velocity of the others, causing them to approach each other. As the distance between the bubbles increases the interference is reduced and the bubbles begin to flow as single ones. When two bubbles are horizontally positioned, they can approach or move away from each other, depending on the initial distance between them. Furthermore, the bubbles shape is analyzed as a function of the governing parameters. It is observed that for lower Reynolds number the bubbles present a circular shape, but as inertia increases the bubble becomes ellipsoidal.

The use of reinforced polymer composites has continued to show substantial growth due to desirable cost and performance characteristics, especially related to mechanical properties. Wollastonite and glass fibers are materials that can be used to improve polymer performance. Its vast array of applications suggests potential usage in various fields of work (e.g., plastics, friction materials paintings, coating, and construction products), but there is not much data available in the literature related to rheological properties of fiber reinforced polymers. In this work, a study of shear and extensional properties of composite materials containing wollastonite and glass fibers is performed using rotational and extensional rheometry. Suspensions containing different concentrations of wollastonite and glass fibers, in Newtonian and viscoelastic matrices are investigated. Results are obtained for different concentrations and temperatures. It is observed that even the addition of low fiber concentration can affect both shear and elongational properties, leading to different final products characteristics. POLYM. COMPOS. 34:1269–1278, 2013. © 2013 Society of Plastics Engineers

SUMMARYThe compressible gas ows of interest to aerospace applications often involve situations where shock and expansion waves are present. Decreasing the characteristic dimension of the computational cells in the vicinity of shock waves improves the quality of the computed ows. This reduction in size may be accomplished by the use of mesh adaption procedures. In this paper an analysis is presented of an adaptive mesh scheme developed for an unstructured mesh ÿnite volume upwind computer code. This scheme is tailored to reÿne or coarsen the computational mesh where gradients of the ow properties are respectively high or low. The reÿnement and coarsening procedures are applied to the classical gas dynamic problems of the stabilization of shock waves by solid bodies. In particular, situations where oblique shock waves interact with an expansion fan and where bow shocks arise around solid bodies are considered. The e ectiveness of the scheme in reducing the computational time, while increasing the solution accuracy, is assessed. It is shown that the reÿnement procedure alone leads to a number of computational cells which is 20% larger than when alternate passes of reÿnement and coarsening are used. Accordingly, a reduction of computational time of the same order of magnitude is obtained.