Conference Agenda

Computational fluid dynamics (CFD) has the prediction capability to influence decisions early in the design process. In order to assess the state-of-the-art of CFD and its prediction capability in the medical devices industry, the U.S. Food and Drug Administration (FDA) proposed two benchmark models for validation. CFD submissions from 23 participants were also made available [1]. The focus of this work is to explore hybrid and multi-block structured meshing strategies and their impact on solution accuracy for one of the benchmark cases, a centrifugal blood pump. Designed to operate across a large range of flow conditions, the blood pump is geometrically simple, consisting of four blades attached to a rotor base and shaft.

The meshing strategies considered include hybrid viscous unstructured and multi-block structured meshes. Highlighting meshing best practices, an emphasis is placed on mesh quality characteristics such as included angles, skewness, and orthogonality.

For the hybrid viscous unstructured mesh, an advancing normal technique starting from a quad-dominant surface mesh generates the required near-wall resolution. During the viscous extrusion process, elements are subject to quality checks allowing the front to stop locally if necessary to improve overall cell quality. The final front of the viscous extrusion transitions to an isotropic tetrahedral off-body mesh, completing the computational domain surrounding the rotor. Using a structured O-H topology at the interface between the rotor housing and pipes, path-based algebraic extrusions create the volume mesh within the inlet and outlet pipes.

To create the multi-block structured mesh, spatial dimensioning criteria used in the unstructured process served as guidelines for the surface and volumetric blocking topology development. Each block of the point-matched structured grid used transfinite interpolation for initialization and elliptic smoothing where required.

Caelus v8.04 [2], a derivative of OpenFOAM, was used to perform the simulations. In order to compare results with Malinauskas [1], a steady-state moving reference frame (MRF) simulation was run using the realizable κ-ε turbulence model. Shown below is the two-dimensional profile of the velocity magnitude |U_xy| at a pump condition of 6 L/min and 3500rpm.

Modelling of filter applications is characterized by the coverage of a wide range of length scales, from single fibres and single particles up to complete filter houses in plant engineering.

For the simulation of filtration applications on a macroscopic scale, the OpenFOAM toolbox already provides a set of useful numerical models, for instance porous zones or porous baffles to realize the flow resistance of filter media.

We developed a number of suitable OpenFOAM solvers and appropriate numerical models to meet the requirements of an extended application range.

The numerical solvers and models we implemented so far cover pure depth filtration, cake filtration of the combination of both. For the depth filtration fixed 3D cell zones can be used, with models for deposition probability and penetration depth. The cake filtration is based on dynamically growing 3D cell zones. Continuing towards the macroscopic scales the filter media are modelled based on thin-shell cyclic patches, which have much lower requirements on the geometrical resolution of the filter elements, and which store additional parameters like filter media thickness or deposited mass on a cell face level.

As laws of resistance the Darcy- and Forchheimer models are implemented, for the mesoscale application the Ergun equation and its variants.

The focus on the Lagrangian particle tracking as the key element of the dynamic filtration modelling requires an improved parallel processing of the steady state particle tracking algorithm. Additional stall detection methods for the particle movement prevent deadlocks. Local adaptive time stepping methods improve the accuracy of the particle trajectories.

The numerous numerical models, solvers and utilities shall be combined into a comprehensive framework for the modelling of filtration applications.

The benefit for the user is in particular the combinability of the different models for his specific application. With a unified case structure and solver control the error rate can be reduced, as well as the training time, while the scope of applications is extended.

For our developers the software maintenance and the support will be simplified. For the extension of existing models and the addition of new models the framework will provide suitable templates.

In this study we investigate shock wave-boundary layer interactions of high enthalpy Mach 7 reacting flow on a double wedge model with fixed fore- and varied aft-angles. Both 2-D and 3-D results were conducted for thermally equilibrium conditions. Viscosity of each specie is calculated by the formulation offered by Blottner and the mixture viscosity is found out by Wilke’s formula. Thermophysical properties of each specie were determined by JANAF thermodynamic package. Backward and forward reaction rates are calculated from Arrhenius Law. For high enthalpies, we modeled air with 5 species including 19 chain reactions. Numerical computations in this study were performed by a newly coded open-source Navier-Stokes solver, which was developed within the framework of OpenFOAM. Validation processes of newly- developed code for reacting and non-reacting two dimensional cases were completed. We compared our results with numerical and experimental results available in the literature. The solver is tested for thermally non-equilibrium cases. Numerical Schlieren images of our 2-D and 3-D results were compared. Surface heat flux distributions that are available in the literature were used to validate our solver.

The main process in wastewater treatment usually consists in a biological treatment for organic matter removal, but, if additionally, nutrient removal is required, a more advanced treatment process is needed. However, conventional configurations for Biological Nutrient Removal (BNR) entail complex treatment systems, which imply a significant increase in the volume needed and energy consumption compared to only organic matter removal processes.

In that context, the Group of Environmental Engineering of the University of Cantabria (Spain) has patented several biological reactors with the aim of fulfilling the mentioned challenges. Concretely, AnoxAn (Tejero et al. 2010) unifies the anaerobic and anoxic zones of the conventional BNR configurations in a single reactor. However, the multi-environmental behaviour (hydraulic separation must be maintained between anaerobic and anoxic zones) and singular elements configuration (mixing devices and baffles) in AnoxAn entail a complex hydrodynamic operation that must be deeply studied.

At this aim, a 3D Computational Fluid Dynamics (CFD) based model is built in OpenFOAM® (v1812) and successfully validated using three different Residential Time Distribution (RTD) experimental tests (pulse and step tracer tests). Turbulent flow is simulated with the standard k-ε model and tracer transport is reproduced by means of a passive scalar transport equation.

Besides, specific modelling approaches for singular elements are validated, achieving significant computational cost savings. Concretely, the baffle between anoxic and clarification zone is modelled as a one phase porous media and the impeller with a plane disk approach that reproduces the three main velocities in rotational motion (axial, radial and tangential).

A two-stage numerical resolution is implemented: (i) First, hydrodynamic steady state solution is reached using SIMPLE algorithm and, then (ii) transient resolution for tracer transport is performed using PIMPLE algorithm. The transient solution is essential for having high spatial flow and tracer concentration resolution at every time of each RTD experiment simulated.

With the results obtained with the transient simulations, an exhaustive hydrodynamic analysis is performed. As a result, dead volumes and short circuiting zones are tracked, quantified and studied. Finally, singular elements influence in the hydraulic performance of AnoxAn is also analyzed.