Microchannel Emulsification: From Computational Fluid Dynamics to Predictive Analytical Model

Langmuir ◽  
2008 ◽  
Vol 24 (18) ◽  
pp. 10107-10115 ◽  
Author(s):  
Koen C. van Dijke ◽  
Karin C. P. G. H. Schroën ◽  
Remko M. Boom
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Analytical Model ◽  
Microchannel Emulsification

scholarly journals Rapid pivot feeding in pipefish: flow effects on prey and evaluation of simple dynamic modelling via computational fluid dynamics

2008 ◽  
Vol 5 (28) ◽  
pp. 1291-1301 ◽  
Author(s):  
Sam Van Wassenbergh ◽  
Peter Aerts
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Analytical Model ◽  
Dynamic Modelling ◽  
Head Rotation ◽  
Theoretical Models ◽  
Cfd Simulations ◽  
Deceleration Phase ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Effects

Most theoretical models of unsteady aquatic movement in organisms assume that including steady-state drag force and added mass approximates the hydrodynamic force exerted on an organism's body. However, animals often perform explosively quick movements where high accelerations are realized in a few milliseconds and are followed closely by rapid decelerations. For such highly unsteady movements, the accuracy of this modelling approach may be limited. This type of movement can be found during pivot feeding in pipefish that abruptly rotate their head and snout towards prey. We used computational fluid dynamics (CFD) to validate a simple analytical model of cranial rotation in pipefish. CFD simulations also allowed us to assess prey displacement by head rotation. CFD showed that the analytical model accurately calculates the forces exerted on the pipefish. Although the initial phase of acceleration changes the flow patterns during the subsequent deceleration phase, the accuracy of the analytical model was not reduced during this deceleration phase. Our analysis also showed that prey are left approximately stationary despite the quickly approaching pipefish snout. This suggests that pivot-feeding fish need little or no suction to compensate for the effects of the flow induced by cranial rotation.

Hydrodynamics of Jets From Guillotine Steam Generator Tube Rupture: Modeling, Analytical Results, Computational Fluid Dynamics Calculation, and Comparison With Experimental Data

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
J. L. Muñoz-Cobo ◽  
L. E. Herranz ◽  
A. Escrivá
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Analytical Model ◽  
Steam Generator ◽  
Initial Step ◽  
Reynolds Stresses ◽  
Experimental Conditions ◽  
Steam Generator Tube ◽  
Gas Jets

In this work we study the hydrodynamics of characteristic gas jets resulting from guillotine breaks of steam generator tube rupture sequences (SGTR) in pressurized nuclear power reactors. As an initial step towards describing an “in-bundle” gas jet, a hydrodynamic model of free gas jets emerging from a guillotine break under prototypical SGTR conditions has been developed. First we have studied the jet characteristic for an isolated tube; the analytical model estimates variables such as trajectories, centerline velocities, velocity distribution, and Reynolds stresses. We have performed model comparisons with experimental data for different experimental conditions with different mass flow rates, and we have found good agreement of the model with the experimental results. Additionally, an “ad hoc” expression has been derived for the centerline jet velocity, which has been experimentally confirmed. Consistently with the experimental data and the computational fluid dynamics (CFD) calculations the analytical model predicts no outflow near the jet center. As a complementary issue, we have performed CFD calculations for a guillotine tube rupture when the tube is surrounded by several rows of neighboring tubes, in this case the jet trajectories are affected by the Coanda effect near the tubes.

Analytical and Computational Fluid Dynamics Models of Wells Turbines for Oscillating Water Column Systems

2021 ◽  
Vol 144 (5) ◽  
Author(s):  
L. Ciappi ◽  
M. Stebel ◽  
J. Smolka ◽  
L. Cappietti ◽  
G. Manfrida
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Water Column ◽  
Analytical Model ◽  
Energy Resource ◽  
Computational Domain ◽  
Oscillating Water Column ◽  
Sea Waves ◽  
Hexahedral Elements ◽  
Dynamics Models

Abstract The sea is an important renewable energy resource for its extension and the power conveyed by waves, currents, tides, and thermal gradients. Amongst these physical phenomena, sea waves are the source with the highest energy density and may contribute to fulfilling the global increase of power demand. Despite the potential of sea waves, their harnessing is still a technological challenge. Oscillating water column systems operating with Wells turbines represent one of the most straightforward and reliable solutions for the optimal exploitation of this resource. An analytical model and computational fluid dynamics models were developed to evaluate the functioning of monoplane isolated Wells turbines. For the former modeling typology, a blade element momentum code relying on the actuator disk theory was applied, considering the rotor as a set of airfoils. For the latter modeling typology, a three-dimensional multi-block technique was implemented to create the computational domain with a fully mapped mesh composed of hexahedral elements. The employment of circumferential periodic boundary conditions allowed for the reduction of computational power and time. The models use Reynolds-averaged Navier-Stokes (RANS) or u-RANS schemes with a multiple reference frame approach or the u-RANS formulation with a sliding mesh approach. The achieved results were compared with analytical and experimental literature data for validation. All the developed models showed good agreement. The analytical model is suitable for a fast prediction of the turbine operation on a wide set of configurations during the first design stages, while the computational fluid dynamics (CFD) models are indicated for the further investigation of the selected configurations.

Analysis of the Leakage Behavior of Francis Turbines and Its Impact on the Hydraulic Efficiency—A Validation of an Analytical Model Based on Computational Fluid Dynamics Results

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Jürgen Schiffer ◽  
Helmut Benigni ◽  
Helmut Jaberg
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Distribution ◽  
Analytical Model ◽  
Analytical Approach ◽  
Analytical Calculation ◽  
Francis Turbine ◽  
Centrifugal Pumps ◽  
Present Contribution ◽  
Disk Friction

The present contribution addresses the analysis of the leakage behavior of a small hydro Francis turbine using an analytical approach, which was validated based on the results of computational fluid dynamics (CFD). For a custom-designed Francis turbine with a specific speed of nq = 41.9 rpm, the flow chambers resulting from the labyrinth geometry were added to a traditional full CFD model of the turbine and numerical simulations were performed for several operation points ranging from part load (Qmin = 0.5 × Qopt) to over load (Qmax = 1.3 × Qopt). Consequently, the single losses occurring in the runner seals on crown and band side as well as the pressure distribution within the runner side spaces could be evaluated and compared to the results gained with an analytical approach, which was originally developed to calculate the leakage flow of centrifugal pumps. The comparison of the pressure distribution achieved with the numerical simulation and the analytical calculation shows that both approaches match well if the angular velocity of the fluid ωFluid trapped in the runner side spaces is calculated in an appropriate way. Furthermore, the achieved results demonstrate that the use of the analytical model enables the calculation of the disk friction and leakage losses with sufficient accuracy. This paper contributes to the improvement of the performance prediction of Francis turbines based on combined numerical and analytical calculations.

Computational Analysis of Undulatory Batoid Motion for Underwater Robotic Propulsion

2014 ◽  
Author(s):  
Nicholas Sharp ◽  
Virginia Hagen-Gates ◽  
Evan Hemingway ◽  
Molly Syme ◽  
Juelyan Via ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Analytical Model ◽  
Computational Analysis ◽  
Underwater Robotics ◽  
Collision Dynamics ◽  
Multiparticle Collision Dynamics ◽  
Propulsion Mechanism ◽  
Bioinspired Robotics ◽  
Biological Literature

Underwater fish of the class Batoidea, commonly known as rays and skates, use large cartilaginous wings to propel themselves through the water. This motion is of great interest in bioinspired robotics as an alternative propulsion mechanism. Prior research has focused primarily on the oscillating kinematics used by some species which resembles flapping; this study investigates undulatory motion induced by propagating sinusoidal waves along the fin. An analytical model of undulatory kinematics is presented and correlated with biological literature, and the model is then simulated via unsteady computational fluid dynamics and multiparticle collision dynamics. A bioinspired robot, Batoid Underwater Robotics Testbed (BURT), was developed to test the kinematics of the undulating propulsion system proposed. Finally, BURT was utilized as a platform to investigate engineering challenges in undulating Batoid robotics.

Evaluation of Paddle Wheels in Generating Hydroelectric Power

2012 ◽  
Author(s):  
Yucheng Liu ◽  
Yoosef Peymani
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Modeling And Simulation ◽  
Analytical Model ◽  
Relative Velocity ◽  
Hydroelectric Power ◽  
Dynamics Modeling ◽  
Efficiency Curve ◽  
Computational Fluid Dynamics Modeling ◽  
Analytical Algorithm

This paper presents an innovative analytical model to correctly evaluate the performance of a paddle wheel in generating hydroelectric power. The deficiencies of current analytical model in evaluating such performance are pointed out and overcome by the developed analytical algorithm. Important factors that affect the paddle wheel’s performance, such as the drag force, relative velocity, efficiency curve of generator, are considered in the developed method. The presented method and analytical results are validated through CFD (Computational Fluid Dynamics) modeling and simulation.

Optimization and Uncertainty Analysis of a Diesel Engine Operating Point Using Computational Fluid Dynamics

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Daniel M. Probst ◽  
Peter K. Senecal ◽  
Peter Z. Chien ◽  
Max X. Xu ◽  
Brian P. Leyde
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Diesel Engine ◽  
Optimal Design ◽  
Fuel Consumption ◽  
Analytical Model ◽  
Design Space ◽  
Uncertainty Propagation ◽  
Injection Duration ◽  
Engine Operating Point

This study describes the use of an analytical model, constructed using sequential design of experiments (DOEs), to optimize and quantify the uncertainty of a diesel engine operating point. A genetic algorithm (GA) was also used to optimize the design. Three engine parameters were varied around a baseline design to minimize indicated specific fuel consumption without exceeding emissions (NOx and soot) or peak cylinder pressure (PCP) constraints. An objective merit function was constructed to quantify the strength of designs. The engine parameters were start of injection (SOI), injection duration, and injector included angle. The engine simulation was completed with a sector mesh in the commercial computational fluid dynamics (CFD) software CONVERGE, which predicted the combustion and emissions using a detailed chemistry solver with a reduced mechanism for n-heptane. The analytical model was constructed using the SmartUQ software using DOE responses to construct kernel emulators of the system. Each emulator was used to direct the placement of the next set of DOE points such that they improve the accuracy of the subsequently generated emulator. This refinement was either across the entire design space or a reduced design space that was likely to contain the optimal design point. After sufficient emulator accuracy was achieved, the optimal design point was predicted. A total of five sequential DOEs were completed, for a total of 232 simulations. A reduced design region was predicted after the second DOE that reduced the volume of the design space by 96.8%. The final predicted optimum was found to exist in this reduced design region. The sequential DOE optimization was compared to an optimization performed using a GA. The GA was completed using a population of nine and was run for 71 generations. This study highlighted the strengths of both methods for optimization. The GA (known to be an efficient and effective method) found a better optimum, while the DOE method found a good optimum with fewer total simulations. The DOE method also ran more simulations concurrently, which is an advantage when sufficient computing resources are available. In the second part of the study, the analytical model developed in the first part was used to assess the sensitivity and robustness of the design. A sensitivity analysis of the design space around the predicted optimum showed that injection duration had the strongest effect on predicted results, while the included angle had the weakest. The uncertainty propagation was studied over the reduced design region found with the sequential DoE in the first part. The uncertainty propagation results demonstrated that for the relatively large variations in the input parameters, the expected variation in the indicated specific fuel consumption and NOx results were significant. Finally, the predictions from the analytical model were validated against CFD results for sweeps of the input parameters. The predictions of the analytical model were found to agree well with the results from the CFD simulation.

Improved Computational Fluid Dynamics Framework for Reactor Core Baffle Swelling Assessment 

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Yuliia Filonova ◽  
Yaroslav Dubyk ◽  
Vladislav Filonov ◽  
Vadym Kondratjuk
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Temperature Distribution ◽  
Analytical Model ◽  
Reactor Core ◽  
Generation Model ◽  
Cfd Analysis ◽  
Term Operation ◽  
Reactor Internals

Abstract This paper presents an improved estimation of reactor core baffle temperature distribution, during operation, at the nominal power level to address swelling problems of the reactor internals. Swelling is the main limiting factor in the reactor core internals long term operation of VVER-1000 nuclear units. The material irradiation-induced swelling and creep models are very sensitive to temperature distribution in metal; thus, a more detailed analysis of the core baffle metal thermohydraulic cooling characteristics is required. A framework for the computational fluid dynamics (CFD) analysis of VVER-1000 reactor baffle cooling is presented. First, an analytical model was developed to obtain boundary conditions (BCs) and simplify CFD analysis. Second, the CFD analysis was performed using 60 deg symmetry, which included core, baffle, and core barrel, and it is limited by the height of the baffle. Core is simplified as an equivalent coolant domain with considering of spatial volumetric energy release. Core baffle is presented as monolithic body with considering of gamma-ray heat generation. Model includes cooling ribs and simplified geometry of connecting studs, with cooling flow of the coolant through the nuts grooves. Calculated convection coefficient and temperature are in good agreement with analytical model and give a more accurate result comparing to RELAP5/mod3.2. Obtained temperature field was used to estimate baffle swelling process and justify safe long term operation of the reactor internals.

Improvement of One-Dimensional Analytical Model of Rotating Long Orifice with Chamfered or Radiused Inlet

2013 ◽  
Vol 444-445 ◽  
pp. 320-331
Author(s):  
Hong Wu ◽  
Peng Li ◽  
Dong Dong Liu ◽  
Zhi Tao
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Reynolds Number ◽  
Analytical Model ◽  
Working Conditions ◽  
Low Reynolds Number ◽  
Pressure Ratio ◽  
Acceptable Error ◽  
One Dimensional ◽  
Low Reynolds

In this paper, computational fluid dynamics calculations were conducted under various kinds of complex working conditions for rotating long orifice. As one of the most important structures of throttling and pressure limiting, orifice plays a significant role in flow control of the whole system. The existing empirical correlation was improved by correction on characteristics of low Reynolds number and compressibility. Then, improved one-dimensional analytical model of rotating long orifice with chamfered or radiused inlet was developed by programming. The model was verified against the results of commercial computational fluid dynamics codes. It turns out that the model has high precision, excellent convergence, and can predict the flow parameters under working conditions of low Reynolds number, supersonic and high pressure ratio with an acceptable error. And only geometric features, rotational speed and boundary conditions are required for one-dimensional modeling. Thus, it can be applied in the one-dimensional calculation and design of secondary air system widely.

Sign in / Sign up

Export Citation Format

Share Document