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SUMMARYThe volume of uid (VOF) method is used to perform two-phase simulations (gas-liquid). The governing Navier-Stokes conservation equations of the ow ÿeld are numerically solved on two-dimensional axisymmetric or three-dimensional unstructured grids, using Cartesian velocity components, following the ÿnite volume approximation and a pressure correction method. A new method of adaptive grid local reÿnement is developed in order to enhance the accuracy of the predictions, to capture the sharp gasliquid interface and to speed up the calculations. Results are compared with experimental measurements in order to assess the e ciency of the method.

This is the published version of the paper.This version of the publication may differ from the final published version. The cavitation structures formed inside enlarged transparent replicas of tapered Diesel valve covered orifice nozzles have been characterized using high speed imaging visualization. Cavitation images obtained at fixed needle lift and flow rate conditions have revealed that although the conical shape of the converging tapered holes suppresses the formation of geometric cavitation, forming at the entry to the cylindrical injection hole, string cavitation has been found to prevail, particularly at low needle lifts. Computational fluid dynamics simulations have shown that cavitation strings appear in areas where large-scale vortices develop. The vortical structures are mainly formed upstream of the injection holes due to the nonuniform flow distribution and persist also inside them. Cavitation strings have been frequently observed to link adjacent holes while inspection of identical real-size injectors has revealed cavitation erosion sites in the area of string cavitation development. Image postprocessing has allowed estimation of their frequency of appearance, lifetime, and size along the injection hole length, as function of cavitation and Reynolds numbers and needle lift. Permanent repository link

Background— The ideal bifurcation stenting technique is not established, and data on the hemodynamic characteristics at stented bifurcations are limited. Methods and Results— We used computational fluid dynamics analysis to assess hemodynamic parameters known affect the risk of restenosis and thrombosis at coronary bifurcations after the use of various single- and double-stenting techniques. We assessed the distributions and surface integrals of the time averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (t r ). Single main branch stenting without side branch balloon angioplasty or stenting provided the most favorable hemodynamic results (integrated values of TAWSS=4.13·10 −4 N, OSI=7.52·10 −6 m 2 , t r =5.57·10 −4 m 2 /Pa) with bifurcational area subjected to OSI values >0.25, >0.35, and >0.45 calculated as 0.36 mm 2 , 0.04 mm 2 , and 0 mm 2 , respectively. Extended bifurcation areas subjected to these OSI values were seen after T-stenting: 0.61 mm 2 , 0.18 mm 2 , and 0.02 mm 2 , respectively. Among the considered double-stenting techniques, crush stenting (integrated values of TAWSS=1.18·10 −4 N, OSI=7.75·10 −6 m 2 , t r =6.16·10 −4 m 2 /Pa) gave the most favorable results compared with T-stenting (TAWSS=0.78·10 −4 N, OSI=10.40·10 −6 m 2 , t r =6.87·10 −4 m 2 /Pa) or the culotte technique (TAWSS=1.30· 10 −4 N, OSI=9.87·10 −6 m 2 , t r =8.78·10 −4 m 2 /Pa). Conclusions— In the studied models of computer simulations, stenting of the main branch with our without balloon angioplasty of the side branch offers hemodynamic advantages over double stenting. When double stenting is considered, the crush technique with the use of a thin-strut stent may result in improved immediate hemodynamics compared with culotte or T-stenting.

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