Application of FMI in Metal Casting Press-Forming Process

Accurate simulation of metal casting press-forming process needs to consider mutual coupling effects in a number of different fields of physics subsystem. Hydraulic systems, control systems and mechanical systems are the most important subsystems among them. It is difficult to create various subsystems in detail in a single modeling tools, so co-simulation technology is used to take advantage of different tools to achieve the entire physical process of system-level simulation. The paper researched the co-simulation in the Abaqus software and the Matlab software based on FMI standard, considered fully the coupling effect between different systems, and simulated the metal casting press-forming process. The simulation results showed that co-simulation based on FMI standard can be well suited for multi-disciplinary co-simulation in complex mechanical model, and played a well-guiding role in the engineering design. The co-simulation would take more computation time than traditional simulation, but it can be achieved to research the integrated features of system and to reduce greatly experiments costs and prototype trial risks by using this technology.

Feasibility Study for Flow-Induced Vibration in Stud Pipe Using Computational Fluid Dynamics

Piping systems in a nuclear plant can be damaged by high-cycle fatigue due to acoustic-induced vibration. Moreover, if the frequency of the vibration in the piping system is overlapped with a natural frequency of the piping, the magnitude of the amplitude will be increased resulting in many problems. For example, the damage is considered as flow-induced acoustic resonance at the branch pipes of the safety relief valve in the main steam lines. This study has investigated the Computational Fluid Dynamics (CFD) analysis methodology to predict and quantify the vortex shedding frequencies and the pressure pulsation magnitude in the dead-end piping system. In order to estimate the vortex shedding vibration, a high level turbulent model should be applied. Such a turbulent model, however, requires a substantial amount of computing time. Therefore, the purpose of the study is to investigate the effects of the main pipe length and the sublayer inflation rate on the vortex shedding frequency and pressure pulsation magnitude. The results for the effects will be able to reduce the size of the fluid domain so that the computing time can be significantly decreased in using the high resolution turbulent models.

Performance of Francis Turbine Operating at Excess Load Condition

Computational fluid dynamics simulations are conducted to characterize the spatial and temporal characteristics of the flow field inside a Francis turbine operating in the excess load regime. A high-fidelity Large Eddy Simulation (LES) turbulence model is applied to investigate the flow-induced pressure fluctuations in the draft tube of a Francis Turbine. Probes placed alongside the wall and in the center of the draft tube measure the pressure signal in the draft tube, the pressure over the turbine blades, and the power generated to compare against previous studies featuring design point and partial load operating conditions. The excess load is seen during Francis turbines in order to satisfy a spike in the electrical demand. By characterizing the flow field during these conditions, we can find potential problems with running the turbine at excess load and inspire future studies regarding mitigation methods. Our studies found a robust low-pressure region on the edges of turbine blades, which could cause cavitation in the runner region, which would extend through the draft tube, and high magnitude of pressure fluctuations were observed in the center of the draft tube.

Blood Flow Simulations of Particle Trapping in Models of Arterial Bifurcations

This paper describes the particle trapping mechanism in blood flow in different arterial bifurcation models. For validation of CFD calculations, a T-junction model and a Y-junction model are analyzed. In both the models, there is one inlet pipe with two outlet pipes creating a symmetric bifurcation at some angle from the centerline of the inlet pipe. Naiver-Stokes (RANS) equations are solved for single phase laminar flow using the commercial CFD software ANSYS Fluent. After validation, Eulerian simulations are performed by using the Discrete Phase Model (DPM) for two-phase flow with particles injected in different bifurcation models with bifurcation angle of an outlet pipe varying from 80° to 100° w.r.t the centerline of the inlet pipe (90° being the bifurcation angle of T-junction). By changing the average Reynolds number of the flow and the injected particle diameters, the mechanism of particle trapping is investigated in laminar flow. The contours of velocity magnitude, pressure and wall shear stress are also obtained and analyzed. It is found that the particle trapping increases as the bifurcation angle decreases from 90° and becomes negligible as the bifurcation angle increases from 90°. This is a very important result which has never been reported in the previous literature. In addition, turbulent flow computations for T-junction flow are performed using the SST k-ω and Wray-Agarwal turbulence models. Finally, the influence of stenosis in Y-junction is studied and analyzed. The results have implications in understanding the hemodynamic flows in arterial bifurcations without and with stenosis.

Micro Flow Direction Analysis Using Gold Sputtered Planar V-Shaped Electrode Pattern

Sensing and detecting micro particles require a bulk fluid motion towards the sensing element in order to get a desirable response from the sensing element. Specially for low-concentrated fluid suspension response time is very long. So both for detection and sensing mechanism if the fluid flow is guided at a reasonable speed and at a low voltage and relatively low frequency which is suitable for bio-particles; the sensing mechanism can be enhanced largely. But sometimes it is required to re-accumulate or recombine the fluid. Previously parallel plate configuration was used to concentrate particle, but this is for the first time a V-shaped electrode pattern used to guide the bulk flow for concentration purpose. The V-shaped electrode set-up was made by following an unconventional way using sputtering machine which was cheaper than the conventional Photolithography method. AC-Electroosmosis from planar electrodes is a strong mechanism for creating micro-flows from several hundred microns away from the electrode surface. The mechanism for the AC Electroosmotic fluid flow is based on Capacitive charging which causes due to the generation of counter-ions at the electrode-electrolyte interface and Faradaic charging which is generated by the accumulation of co-ions. These two different methods are responsible for a converging and diverging surface flow of the fluid particles. At lower voltage capacitive charging method plays a significant role and most of the applied voltage drops occur at the electrical double layer but up to a certain voltage level Faradaic charging method takes over and starts dominating. The induced flow velocity by both methods has different relationship with the applied voltage. In this experiment Electrical Impedance Spectroscopy (EIS) was used to determine the suitable frequency range for the application & 2.12Vrms was used initially which is a very low voltage. An equivalent circuit for the setup was analyzed. Finally, an analysis was made on this setup using conductive fluid to observe the AC Electrothermal (ACET) effect. In our experiment the goal was to get an optimum velocity for concentration at low voltage and low frequency also to observe the guiding direction of the fluid flow in order to find a way to focus the fluid flow towards the desired direction.

Performance Evaluation of a Non-Linear Explicit Algebraic Reynolds Stress Model for Surface Mounted Obstacles

The presence of complex vortical structures, unsteady wakes, separated shear layers, and streamline curvature pose considerable challenges for traditional linear Eddy-Viscosity (LEV) models. Since Non-Linear Eddy Viscosity Models (NEV) models contain additional strain-rate and vorticity relationships, they can provide a better description for flows with Reynolds stress anisotropy and can be considered to be suitable alternatives to traditional EVMs in some cases. In this study, performance of a Non-Linear Explicit Algebraic Reynolds Stress Model (NEARSM) to accurately resolve flow over a surface mounted cube and a 3D axisymmetric hill is evaluated against existing experimental and numerical studies. Numerical simulations were performed using the SST k-ω RANS model, SST k-ω-NEARSM, SST-Multiscale LES model, and two variants of the Dynamic Hybrid RANS-LES (DHRL) model that include the SST k-ω and the SST k-ω-NEARSM as the RANS models. Results indicate that the SST k-ω RANS model fails to accurately predict the flowfield in the separated wake region and although the SST-NEARSM and SST-Multiscale LES models provide an improved description of the flow, they suffer from incorrect RANS-LES transition caused by Modeled Stress Depletion (MSD) and sensitivity to changes in grid resolution. The SST-DHRL and the SST-NEARSM-DHRL variants provide the best agreement to experimental and numerical data.

Evaluation of a Statistically Targeted Forcing Method for Synthetic Turbulence Generation in Large-Eddy Simulations and Hybrid RANS-LES Simulations

Computational fluid dynamics (CFD) results are presented for synthetic turbulence generation by a proposed statistically targeted forcing (STF) method. The new method seeks to introduce a fluctuating velocity field with a distribution of first and second moments that match a user-specified target mean velocity and Reynolds stress tensor, by incorporating deterministic time-dependent forcing terms into the momentum equation for the resolved flow. The STF method is formulated to extend the applicability of previously documented methods and provide flexibility in regions where synthetic turbulence needs to be generated or damped, for use in engineering level large-eddy and hybrid large-eddy/Reynolds-averaged Navier-Stokes CFD simulations. The objective of this study is to evaluate the performance of the proposed STF method in LES simulations of isotropic and anisotropic homogeneous turbulent flow test cases. Results are interrogated and compared to target statistical velocity and turbulent stress distributions and evaluated in terms of energy spectra. Analysis of the influence of STF model parameters, mesh resolution, and LES subgrid stress model on the results is investigated. Results show that the new method can successfully reproduce desired statistical distributions in a homogeneous turbulent flow.

A Computational Fluid Dynamic Study of a Momentum and Energy Method on Rough Surfaces

The Discrete Element Roughness Method (DERM) has been used to improve convective heat transfer predictions on surface roughness. This work aims to validate the core momentum-correlation of DERM through evaluating Computational fluid dynamics (CFD)-based solution of the flow around individual roughness elements with the goal of improving the correlations. More specifically, the matrix of scenarios evaluated using includes three different roughness elements at three different pressure drops (or flow rates). Results from these studies are to be used to validate and improve correlations used to approximate roughness in DERM. For further comparison, a fourth roughness element analyzed in previous work will also be compared. For each element, a steady and unsteady case are conducted and analyzed. The momentum loss results obtained from the CFD are then compared to the DERM-based predictions from the same roughness elements in search of any discrepancies. It is observed the momentum-correlation deviates from the CFD prediction with increasing element height.

Fluid-Structure Interaction Modeling and Validation of Idealized Left Ventricular Blood Flow

Fluid Structure Interaction (FSI) models are an essential tool in understanding the complex coupling of blood flow in the heart. The objective of this study is to establish a method of comparing data obtained from FSI models and benchtop measurements from phantoms to identify sources of flow changes for use in intraventricular flow analysis. Two geometries are considered: 1) a vascular model consisting of a straight channel with an ellipsoidal swell and 2) an idealized left ventricle (LV) model representative “acorn” shape. Two phantoms are created for each of the two geometries: 3D printed rigid phantoms from a resin and custom-made tissue-mimicking phantoms from a medical gel. Benchtop measurements are made using the phantoms within a custom flow loop setup with pulsatile flow. Computational Fluid Dynamics (CFD) simulations are conducted with a Smoothed Particle Hydrodynamics (SPH) model. The two flow channel geometries utilized in the experiments are replicated for the simulations. The cavity walls are defined by ghost particles that are rigidly fixed. Maximum pressure drops were 57 mmHg and 196 mmHg for the rigid swell and rigid LV, respectively, whereas maximum pressure drops were 155 mmHg for the gel swell and 140 mmHg for the gel LV. Calculations from the simulations resulted in a maximum pressure drop of 55 mmHg for the swell and 110 mmHg for the LV. This data serves as a first step in corroborating our methodology to utilize the information obtained from both methods to identify and better understand mutual sources of changes in flow patterns.

Using Computational Fluid Dynamics to Analyze Convection in Pin-to-Plane Plasma Discharge

Multiphysics simulations were conducted to model the role of naturally induced convection in heat and mass transport within a non-isothermal plasma discharge chamber. A pin-to-plane discharge into chamber containing carbon dioxide can be used to possibly decompose carbon dioxide. The present study characterizes the role that convection plays in the diffusion of various products such as ions and excited-state species throughout the test chamber. Multiphysics software including computational fluid dynamics was employed in a two-dimensional transient simulation of a closed reactor with a large pin serving as the cathode and a bottom plate serving as the anode. The mesh was adjusted to best capture important discharge phenomena, while the simulated time was varied to best characterize the chemical processes.. Mesh validation was undertaken using the relevant minimum sizes required by the plasma, fluid flow, and heat transfer solvers. The flow induced by natural convection from the discharge was then compared to the flow induced by natural convection around a resistance heater operating with the same power input as the plasma. The results of this simulation are used to inform improvements on a parallel experimental system used to study the discharge, such as placement of gas concentration sensors and to better understand the heat and mass transfer through the discharge.