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We aimed to provide realistic three-dimensional (3D) models to be used in numerical simulations of peristaltic flow in patients exhibiting difficulty in swallowing, also known as dysphagia. To this end, a 3D model of the upper gastrointestinal tract was built from the color cryosection images of the Visible Human Project dataset. Regional color heterogeneities were corrected by centering local histograms of the image difference between slices. A voxel-based model was generated by stacking contours from the color images. A triangle mesh was built, smoothed and simplified. Visualization tools were developed for browsing the model at different stages and for virtual endoscopy navigation. As result, a computer model of the esophagus and the stomach was obtained, mainly for modeling swallowing disorders. A central-axis curve was also obtained for virtual navigation and to replicate conditions relevant to swallowing disorders modeling. We show renderings of the model and discuss its use for simulating swallowing as a function of bolus rheological properties. The information obtained from simulation studies with our model could be useful for physicians in selecting the correct nutritional emulsions for patients with dysphagia.

A numerical simulation on a six-row helicalsegmented finned tube in a staggered layout is performed with the Reynolds Averaged Navier-Stokes (RANS) approach. The turbulence effect is represented with the k-e RNG model, and a fixed temperature in each tube row considers the inside fluid temperature. The tube bank is represented by a small finned tube bank and a single interacted module. The small finned tube bank considers symmetry conditions on the sides of the computational domain. The single interacted module considers periodic boundary conditions for velocity, pressure, and temperature. Both simulations are compared to develop the basis of complex simulations such as repetitive finned tube modules. Average values on parallel planes to the streamwise direction for velocities, pressures, and temperatures are compared in both simulations. The comparative analyses show deviations lower than 11% for the velocity field, 12% for the pressure field, and 10% single for the temperature field. Therefore, results show an appropriate flow representation with periodic boundary conditions. [ABSTRACT FROM AUTHOR]

A numerical simulation is conducted to study the effect of a turbulent airflow on heat transfer on cuboid food. The simulation is carried out with the Large Eddy Simulation approach. Periodic boundary conditions are implemented to represent a drying chamber as a single isolated zone where the phenomenon is conserved. Conjugate modelling is performed by coupling air-food phases by boundary conditions of continuity at the food interface. Numerical code is validated with empirical correlations of Nusselt number. Results show that low stream wise separations (0.25) present the best and worst heat transfer. Therefore, the best heat transfer on the cuboid food is found at span wise distances higher than 0.5and stream wise separations higher than 0.25. These separations are recommended to have a reasonable food drying control. [ABSTRACT FROM AUTHOR]

A helically segmented finned tube bank is simulated as a single isolated finned tube module in order to reduce computational domain in 99%. The numerical simulation is conducted with the Reynolds Averaged Navier–Stokes Equations (RANS) approach and the turbulence effect is modeled with the k – ɛ RNG model. The finned tube geometry is represented by means of cut-cell method, whereas the inside fluid temperature is considered by means of an average temperature. Periodic boundary conditions are implemented and, as a consequence, new terms in momentum and energy equations should be included to represent pressure drop and cooling air flow. Results show the effect of implementing periodic boundary conditions on turbulent kinetic energy, and its dissipation rate only is reflected on local properties in the zones of high flow interaction. Predictions are validated with experimental data and the best correlations available in the open literature. Results show good precision and the same tendency in the velocity field. The numerical-mean friction factor and Nusselt number present deviations of 0.67% and 2.98%, respectively. Therefore, an appropriate representation of turbulent flows is obtained and the numerical model can be applied to studies on heat exchangers at industrial scale. [ABSTRACT FROM AUTHOR]

Abstract: A new numerical procedure which considers a modification to the artificial acoustic stiffness correction method (AASCM) is here presented, to perform simulations of low Mach number flows with the compressible Navier–Stokes equations. An extra term is added to the energy fluxes instead of using an energy source correction term as in the original model. This new scheme re-scales the speed of sound to values similar to the flow velocity, enabling the use of larger time steps and leading to a more stable numerical method. The new method is validated performing Large Eddy Simulations on test problems. The effect of a crucial numerical parameter alpha is evaluated as well as the robustness of the method to variations of the Mach number. Numerical results are compared to the existing experimental data showing that the new method achieves good agreement increasing the time-step, and therefore accelerating the computation for low-Mach convective flows. [Copyright &y& Elsevier]

Abstract: A computational fluid dynamic model is used to analyze the transport processes of a passive scalar generated in the mixing of two fluids or flows in a pipeline x-junction. Turbulent flow field is computed for the merging of streams using two and three-dimensional simulations, which are achieved employing Cartesian coordinates, BFC and a cut cell method. These different numerical solving methods are compared. The numerical model is validated through an experimental set-up. Different parameters are measured for various operating conditions. The influence of the angle between pipe inlets is studied to establish the optimal condition in which the passive scalar concentration in both outlets is similar. [Copyright &y& Elsevier]

We present the numerical simulations of the flow in a simple mechanical device inspired by the snapping-claw mechanism of alpheidae shrimps. The simulations were based on the entropically damped artificial compressibility (EDAC) method. The governing equations of fluid dynamics were discretized using high-order spatial and temporal schemes. The solid bodies were modeled on the computational domain by using the immersed boundaries method. High-speed video and Particle Image Velocimetry (PIV) measurements of the flow generated in a physical model were used to validate the numerical results. Based on these, we were able to explain the behavior of the flow during the entire length of the closing of the device's claw and moments after. A simple model was also implemented to predict the steam dynamics. The experimental results confirmed the numerical results. The cavitation process in the mechanical device was correctly modeled and understood. [ABSTRACT FROM AUTHOR]

Abstract: The Large Eddy Simulation approach is used to perform a numerical simulation of a flow around a circular tube bundle. The model uses the immersed boundaries technique to represent tube geometry in the Cartesian grid. Simulation is conducted in an area away from the boundaries, where the flow is considered homogenous and, thus, the three Cartesian directions are considered periodic. The results are compared with experimental data in terms of mean velocity and turbulence quantities, showing good agreement in general. [Copyright &y& Elsevier]