Session Z29: CFD: General II

Analysis and Parametric Investigation of Different Arrangements of V-Shape Ribs on the Performance of an Optically-Enhanced Parabolic Trough Solar Collector

In this paper, a V-shape ribbed tube is utilized to improve the thermal performance of a parabolic trough collector (PTC). Six different rib arrangements were employed, and a detailed analysis is presented. Furthermore, the effect of adopting a secondary reflector (SR) on the temperature distribution around both a smooth and a ribbed parabolic trough receiver (PTR) tube is conducted. A computational fluid dynamics model is employed to study the heat transfer and fluid flow characteristics inside the tube. Results show that V-shape ribs are an effective tool to stir up the flow and increase the velocity gradient of the fluid near the inner surface of the tube. Moreover, results from the study show that the secondary reflector contributes to a further decrease in the tube surface temperature and hence improves the overall thermal efficiency of the collector. A parametric study is also carried out to investigate the thermal enhancement of a double-reflector parabolic trough collector when using an in-line mixed V-shape (IMVS) ribbed absorber tube, which shows the best enhancement among the investigated arrangements. Three different heat transfer fluids (HTFs) are investigated, and a wide range of fluid inlet temperatures are studied. Also, various geometric parameters of the V-shape rib are analyzed to determine the optimum design of such a modification to the wall of the absorber tube. The optimized ribbed tube design showed a performance enhancement of about 64%.   

CFD modeling of steam thermodynamics, heat transfer and bacteria deactivation in an innovative superheated steam dishwasher using OpenFOAM

Superheated steam is used as a cleaning and sterilization agent in various sectors including hotels and the food industry. In this talk, we consider an idealized three-dimensional dishwasher using superheated steam at 180 °C and 10 bar pressure as a cleaning agent, and discuss the effects of heat transfer, fluid flow, and phase change in the cleaning process. Computational fluid dynamics simulations were performed using the interThermalPhaseChangeFoam solver, a volume-of-fluid solver based on OpenFOAM that accounts for condensation phenomena. First-order Arrhenius kinetics was used to describe the inactivation of the heat-resistant bacterium Geobacillus stearothermophilus. The high-velocity turbulent steam jet reaching the plate increases its surface temperature and thereby kills the bacteria in a short time. A parameter study was also conducted with multiple nozzles and plates to reduce potential areas of low heat transfer and thus low bacterial inactivation. This work provides the basis for further solver development considering the three components of air, steam and water separately, and dishwasher optimization.

L. Abu-Farah and N. Germann. Simulations of thermal phase changes and bacterial inactivation in a superheated steam dishwasher, Physics of Fluids, in press.

 

    

Establishing a Baseline CFD Model for Examining Benefits of High-Flow Nasal Cannula Oxygen Therapy

High-flow nasal cannula oxygen therapy is a type of respiratory therapy that supplies oxygen to the body at high flow rates using a specific nasal cannula. Quantitative data describing the benefit that this therapy provides is still lacking within literature. The aim of this study is to create a baseline model that can be used for computational fluid dynamic (CFD) analysis using different cannulas and flow settings. The geometry analyzed is a partial representation of the human respiratory system. The meshing methods and quality validation are outlined. The process of establishing proper boundary conditions and solver settings for the model are discussed. After the initial model was finalized, the type and location of data to be collected was decided. Some of the data collected includes mole fraction O₂, turbulent kinetic energy, and volume flow rate. Mesh and time step independence studies were conducted during the validation process. The final mole fraction O₂ of the CFD model is 0.4 percentage points different than the experimental value. Further research for this topic includes introducing CO₂ into the boundary conditions and evaluating flush using different cannula and flow settings.   

Single- and two-way coupled overset interpolations to model fluid-structure interactions of oscillating foils in OpenFOAM

Overset method is highly stable in modelling fluid-structure-interactions that involve large displacements of rigid or flexible oscillating bodies. However, the accuracy of these models can differ based on the coupling process of overset algorithms in the FSI numerical solvers. Here, we perform a comparative evaluation of a new in-house single-way coupling framework for the calculated velocity and pressure fields on overlapping grids, and an existing two-way coupled overset solver in OpenFOAM that is integrated with the fluid-solid interface modelling in solids4Foam. Preliminary benchmark results for the flow around Hron-Turek flexible beam suggests the presence of non-physical pressure oscillations by two-way coupling process. These, however, are not evident for our new single-way coupled framework. This hints at a better accuracy of our numerical technique in handling structural deformations, based on the imposed fluid forces. Currently, our efforts focus on assessing these techniques in analyzing the performance of rigid and flexible oscillating bluff bodies with prescribed motion, or free-swimming conditions, at moderate Reynolds numbers (1000≤Re≤4000). This will be expanded by wake dynamics assessment in order to fully validate the solver’s capabilities and accuracy.   

A task-based parallel framework for ensemble simulations of rocket ignition: Verification and performance assessment

We have previously reported an integrated computational framework for exascale-oriented ensemble simulations of laser-induced ignition in a methane-oxygen rocket combustor (Maeda et al, arXiv. 2022). In this study, we perform continued performance verification and assessment of Hypersonic Task-based Research Solver (HTR) (Di Renzo et al., Comp. Phys. Comm. 2020), the reacting flow solver in the framework for high-fidelity simulations of turbulent combustion. HTR solves the compressible, multi-species Navier-Stokes equations with finite-rate chemistry on curvilinear grids, employing the task-based programming model built on the Legion runtime system for scalable and portable simulation on supercomputers with heterogeneous architectures. The accuracy and performance of the solver are analyzed using canonical reacting flow problems which  are relevant to laser-induced ignition and combustion. High-order shock capturing schemes and sub-grid scale models are tested on various curvilinear meshes. Various strategies of task-mapping on GPUs and CPUs are compared. Lastly, we discuss the influence of the choice of numerical schemes and models on the accuracy of the prediction of ignition success when applied to ensemble simulations of a three-dimensional model combustor.

    

Not Participating

The buoyancy-driven rise of gas bubbles and their passage through an interface between two stratified immiscible liquids is an interesting phenomenon that is relevant in numerous engineering applications such as carbon sequestration, microfluidics, and bubble column reactors. Depending on the physical properties of the liquids (density, viscosity, and surface tension), and size and velocity of the bubbles, various interfacial flow regimes are attained such as penetration, entrapment, rupture and entrainment. The evolution of non-axisymmetric and non-spherical bubbles also significantly alters the rising dynamics. Most previous studies have focused primarily on a single bubble, assuming a two-dimensional (2D) axisymmetric evolution in a straight line. In the present effort, we use numerical simulations to study a ternary system with three-dimensional (3D) bubbles penetrating an interface between two stratified fluids. These simulations utilize the latest multiphase flow capabilities of Ansys Fluent such as Polyhedral Unstructured Mesh Adaption (PUMA), physics-based adaptive time-stepping, and advanced stabilization numerics. This work highlights some of our recent validation efforts and provides insights on bubble shapes, trajectories, and wake characteristics.   

Numerical study of vortex-induced vibration of an array of elliptic cylinders

Harbor seals are able to track and hunt fish in low-visibility conditions by detecting fish swimming vortices through whiskers around their muzzle. To study such an operating principle of seal whiskers, we design an elliptic cylinder array in a circular arrangement to simulate this behavior. The cross-section of the whisker is equivalent to a two-dimensional ellipse with an aspect ratio of 2 and mass ratio of 2, and immersed in the laminar regime. Since the whisker will deflect under the influence of hydrodynamic force and affect the flow field accordingly, fluid-structure coupling calculation should be introduced to obtain the real vibration, that is, two-degree-of-freedom vortex-induced vibration (VIV) simulation of the entire array. The present work studies the remote coupling of flow around an elliptic cylinder array by analyzing the transverse and longitudinal response amplitudes, aerodynamic coefficients, Strouhal number, phase portrait, time response, orbital trajectory and wake mode pattern, and compares it with a single elliptic cylinder to reveal the characteristics of VIV of elliptic cylinder array, which lays a foundation for further study of flow characteristics of real whisker arrays.

    

A numerical study of forced convection from an oscillating isothermal circular cylinder

Forced convection from a heated circular cylinder in an incompressible two-dimensional shear flow is investigated. The 2-D equations in cylindrical polar coordinates of flow motion and energy equation are solved using a higher order compact (HOC) finite difference scheme on non-uniform grids. The effects of shear rate (K) on flow and heat transfer characteristics are investigated. The numerical simulations are performed for fixed frequency ration (f/f0) 1.0 by varying maximum angular velocity (αm) between 0.5 to 1.0 and shear rate (K) 0.0-0.1 at Reynolds number (Re) 150 and Prandtl number (Pr) 0.7. The instantaneous isotherm patterns are presented and discussed for different K values. Also, the variation of the Nusselt number is shown to elucidate the effect of Prandtl number.   

A remeshed vortex method for incompressible flows around 3D axisymmetric soft bodies

Soft elastic bodies and their interaction with fluid flows are routinely observed and studied in engineering and biological settings. From a computational standpoint, these are expensive problems to simulate, particularly in 3D scenarios. Nonetheless, often immersed bodies and surrounded flows are axisymmetric in nature, a feature that can be leveraged to significantly reduce computations demands. We outline here a remeshed vortex-based scheme to simulate flow-structure interaction around axisymmetric 3D bodies. The solid and liquid phases are modeled using a two-fluids approach, separated by a diffused interface on an Eulerian grid. Rigid and soft bodies are treated using the Brinkmann penalization and reference map technique, respectively. We validate our solver against various benchmarks and further illustrate its utility in a range of problems, from locomotion to particle manipulation.