Bubble dynamics inside a compliant blood vessel Strongly coupled FSI on a dynamic wedge mesh

Abstract In medical applications, ultrasound is no longer used exclusively for diagnostical purposes but also in a more intense and highly focused modification (HIFU) for interventional applications such as tumor treatment The goal of our present work is to develop a microscale model of the interaction between gas-filled microbubbles, blood and the respective blood vessel walls. A partitioned multi region black box interaction system that can accommodate the respective physical models for each region is envisaged (see The solver used for modeling the blood-wall interaction is based on icoFsiFoam (available in OF-1.5-dev) which provides interface coupling and dynamic mesh motion. Because the density ratio of blood and vessel wall is very close to unity, the components of the system show strong mutual influence and a strong coupling scheme has to be employed The bubble is represented in our model by the respective boundary of the fluid region (see Currently, we are running our calculations on a wedge mesh (see We kindly acknowledge the financial support of the Swiss National Science Foundation through NCCR Co-Me

Computational Fluid Dynamics of Dispersed Two-Phase Flows at High Phase Fractions

Abstract The two-phase flow in the finger pipe of a finger-type slug catcher is analysed using CFD techniques. The purpose of a finger-type slug catcher is to separate the liquid condensate from the natural gas. In order to design a high performance finger-type slug catcher, it is necessary that the fluid flow in the inlet header manifold is evenly distributed among the different fingers Here v t is the settling velocity of particles of a specified diameter. Different inlet header manifold configurations are defined and compared using the time-averaged mass flow at the finger inlets. A constant and increased pipe diameter was found to promote the mass flow balance. Additionally, by applying an extra split in the main header pipe, the equal flow distribution is significantly increased, see When the fluid flow in the inlet header manifold is evenly distributed among the different fingers, it is necessary to obtain stratified flow to promote liquid separation. The two-phase flow in the separation section is simulated to study the amount of liquid at the intersection with and through the gas riser, se

Mesh adaptation on the sphere using optimal transport and the numerical solution of a Monge-Ampère type equation

An equation of Monge-Ampère type has, for the first time, been solved numerically on the surface of the sphere in order to generate optimally transported (OT) meshes, equidistributed with respect to a monitor function. Optimal transport generates meshes that keep the same connectivity as the original mesh, making them suitable for r-adaptive simulations, in which the equations of motion can be solved in a moving frame of reference in order to avoid mapping the solution between old and new meshes and to avoid load balancing problems on parallel computers. The semi-implicit solution of the Monge-Ampère type equation involves a new linearisation of the Hessian term, and exponential maps are used to map from old to new meshes on the sphere. The determinant of the Hessian is evaluated as the change in volume between old and new mesh cells, rather than using numerical approximations to the gradients. OT meshes are generated to compare with centroidal Voronoi tesselations on the sphere and are found to have advantages and disadvantages; OT equidistribution is more accurate, the number of iterations to convergence is independent of the mesh size, face skewness is reduced and the connectivity does not change. However anisotropy is higher and the OT meshes are non-orthogonal. It is shown that optimal transport on the sphere leads to meshes that do not tangle. However, tangling can be introduced by numerical errors in calculating the gradient of the mesh potential. Methods for alleviating this problem are explored. Finally, OT meshes are generated using observed precipitation as a monitor function, in order to demonstrate the potential power of the technique

Numerical analysis of hydraulic jumps using OpenFOAM

[EN] The present paper deals with a hydraulic jump study, characterization and numerical modeling. Hydraulic jumps constitute a common phenomenon in the hydraulics of open channels that increases the shear stress on streambeds, so promoting their erosion. A three-dimensional computational fluid dynamics model is proposed to analyze hydraulic jumps in horizontal smooth rectangular prismatic open-air channels (i.e., the so-called classical hydraulic jump). Turbulence is modeled using three widely used Reynolds-averaged Navier Stokes (RANS) models, namely: Standard k ε, RNG k ε, and SST k ω. The coexistence of two fluids and the definition of an interface between them are treated using a volume method in Cartesian grids of several element sizes. An innovative way to deal with the outlet boundary condition that allows the size of the simulated domain to be reduced is presented. A case study is conducted for validation purposes (FR1 ∼ 6.10, Re1 ∼ 3.5·105): several variables of interest are computed (sequent depths, efficiency, roller length, free surface profile, etc.) and compared to previous studies, achieving accuracies above 98% in all cases. In the light of the results, the model can be applied to real-life cases of design of hydraulic structures.This research was conducted thanks to the funding provided by the VALi + D R&D Program of the Generalitat Valenciana (Spain). It would not have been possible without the contribution of Daniel Valero and Beatriz Nacher of the Hydraulics Laboratory of the School of Civil Engineering (Universitat Politecnica de Valencia).Bayón Barrachina, A.; López Jiménez, PA. (2015). Numerical analysis of hydraulic jumps using OpenFOAM. Journal of Hydroinformatics. 17(4):662-678. https://doi.org/10.2166/hydro.2015.041S66267817

Validation of a CFD-based numerical wave tank model for the power production assessment of the wavestar ocean wave energy converter

CFD-based numerical wave tank (CNWT) models, are a useful tool for the analysis of wave energy converters (WECs). During the development of a CNWT, model validation is vital, to prove the accuracy of the numerical solution. This paper presents an extensive validation study of a CNWT model for the 1:5 scale Wavestar point-absorber device. The previous studies reported by Ransley et al. [1] and Windt et al. [2] are extended in this paper, by including cases in which the power-take off (PTO) system is included in the model. In this study, the PTO is represented as a linear spring-damper system, providing a good approximation to the full PTO dynamics. The spring stiffness and damping coefficients in the numerical PTO model are determined through a linear least squares fit of the experimental PTO position, velocity and force data. The numerical results for free surface elevation, PTO data (position, velocity, force), generated power and pressure on the WEC hull are shown to compare well with the experimental measurement

Computational fluid dynamics‐based optimization of dimpled steam cracking reactors for reduced CO 2

Spherical dimples in cylindrical tubes enhance heat transfer and lead to a more uniform radial temperature profile. To combine these positive properties with a low pressure drop, a single dimple was optimized through a genetic algorithm. Multiple design parameters such as width, height, and curvature of the dimple were investigated. Heart-shaped dimples outperformed spherical dimples. Three-dimensional reactive simulations of a Millisecond propane steam cracking reactor showed that both the spherically dimpled and the heart-shaped dimpled coil positively affect the light olefin selectivity, mainly through an increase in propylene selectivity. The optimized dimples could reduce the high pressure drop penalty by 21%. Run length simulations proved that the optimized dimple shape results in an additional run length extension of 18%. Next to this, the fuel rate consumption can be decreased by 6% compared to a bare coil, which could theoretically result in 4% less CO2 emissions