scholarly journals The application of computational fluid dynamics to natural river channels: Eddy resolving versus mean flow approaches

Geomorphology ◽  
2012 ◽  
Vol 179 ◽  
pp. 1-20 ◽  
Author(s):  
C.J. Keylock ◽  
G. Constantinescu ◽  
R.J. Hardy
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
River Channels ◽  
Mean Flow

Improving Computational Fluid Dynamics Simulations for the Spallation Neutron Source Jet-Flow Target

2016 ◽  
Author(s):  
C. Barbier ◽  
E. Dominguez-Ontiveros
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Neutron Source ◽  
Jet Flow ◽  
Computational Time ◽  
Spallation Neutron Source ◽  
Mean Flow ◽  
Cfd Simulations ◽  
Flow Measurements ◽  
Piv Measurements

A liquid mercury target is used at Oak Ridge National Laboratory’s (ORNL [1]) Spallation Neutron Source (SNS [2]) to generate neutrons. The mercury is flowing in a stainless steel containment vessel for neutron spallation, but also to cool the vessel itself. Computational Fluid Dynamics (CFD) simulations have been used to estimate the temperature and pressure fields needed for the thermal stress analysis. Because of the geometry complexity, the high turbulence number, and the computational time requirements, generating a quality mesh that can accurately capture the flow and heat transfer has always been a challenge. However, with today’s High Performance Computing (HPC) advances, larger and larger meshes can now be used and better accuracy can be achieved. In this study, two meshing methods were used for the SNS jet-flow target: automatic tetrahedral method (ANSYS meshing) and manual hexahedral meshing (ICEM-CFD). Both methods are compared in terms of quality, size, ease of generation, convergence, and user-friendliness. Both meshes were used with ANSYS-CFX to simulate the steady, Newtonian, single phase, isothermal, incompressible and turbulent flow in the target. The Shear Stress Transport (SST) k-ω model developed by Menter [3] was used for turbulence modeling. The accuracy of the CFD simulations are tested against experimental data presented in the current paper. An in-depth series of Particle Image Velocimetry (PIV) measurements performed on a “visual jet-flow target”, an acrylic replica target running with water, are presented in the paper. Since flow measurements in mercury are difficult, a water loop was built to investigate the flow in the target and a potential gas injection in the flow to mitigate the pressure wave [4]. A PIV system on a precise translation stage was setup on the water loop to perform detailed and accurate PIV measurements. Mean flow velocity fields were used to validate the CFD simulations. The paper concludes on the choice for mesh generation for future target analysis, and the path forward for CFD simulations for the future SNS targets.

Computational Fluid Dynamics Study of Separated Flow Over a Three-Dimensional Axisymmetric Hill

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Varun Chitta ◽  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Separated Flow ◽  
Turbulent Shear ◽  
Turbulent Regime ◽  
Flow Transition ◽  
Mean Flow ◽  
Streamline Curvature

This paper investigates the ability of computational fluid dynamics (CFD) simulations to accurately predict the turbulent flow separating from a three-dimensional (3D) axisymmetric hill using a recently developed four-equation eddy-viscosity model (EVM). The four-equation model, denoted as k–kL–ω–v2, was developed to demonstrate physically accurate responses to flow transition, streamline curvature, and system rotation effects. The model was previously tested on several two-dimensional cases with results showing improvement in predictions when compared to other popularly available EVMs. In this paper, we present a more complex 3D application of the model. The test case is turbulent boundary layer flow with thickness δ over a hill of height 2δ mounted in an enclosed channel. The flow Reynolds number based on the hill height (ReH) is 1.3 × 105. For validation purposes, CFD simulation results obtained using the k–kL–ω–v2 model are compared with two other Reynolds-averaged Navier–Stokes (RANS) models (fully turbulent shear stress transport k–ω and transition-sensitive k–kL–ω) and with experimental data. Results obtained from the simulations in terms of mean flow statistics, pressure distribution, and turbulence characteristics are presented and discussed in detail. The results indicate that both the complex physics of flow transition and streamline curvature should be taken into account to significantly improve RANS-based CFD predictions for applications involving blunt or curved bodies in a low Re turbulent regime.

In-Cylinder Flow Computational Fluid Dynamics Analysis of a Four-Valve Spark Ignition Engine: Comparison Between Steady and Dynamic Tests

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Damian E. Ramajo ◽  
Norberto M. Nigro
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Field ◽  
Steady Flow ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Mean Flow ◽  
Dynamic Simulations ◽  
Computational Fluid Dynamics Analysis ◽  
Cylinder Flow

Numerical and experimental techniques were applied in order to study the in-cylinder flow field in a commercial four-valve per cylinder spark ignition engine. Investigation was aimed at analyzing the generation and evolution of tumble-vortex structures during the intake and compression strokes, and the capacity of this engine to promote turbulence enhancement during tumble degradation at the end of the compression stroke. For these purposes, three different approaches were analyzed. First, steady flow rig tests were experimentally carried out, and then reproduced by computational fluid dynamics (CFD). Once CFD was assessed, cold dynamic simulations of the full engine cycle were performed for several engine speeds (1500 rpm, 3000 rpm, and 4500 rpm). Steady and cold dynamic results were compared in order to assess the feasibility of the former to quantify the in-cylinder flow. After that, combustion was incorporated by means of a homogeneous heat source, and dynamic boundary conditions were introduced in order to approach real engine conditions. The combustion model estimates the burning rate as a function of some averaged in-cylinder flow variables (temperature, pressure, turbulent intensity, and piston position). Results were employed to characterize the in-cylinder flow field of the engine and to establish similarities and differences between the three performed tests that are currently used to estimate the engine mean flow characteristics (steady flow rig, and cold and real dynamic simulations).

scholarly journals Hydrodynamic Analysis of Different Finger Positions in Swimming: A Computational Fluid Dynamics Approach

2015 ◽  
Vol 31 (1) ◽  
pp. 48-55 ◽  
Author(s):  
J. Paulo Vilas-Boas ◽  
Rui J. Ramos ◽  
Ricardo J. Fernandes ◽  
António J. Silva ◽  
Abel I. Rouboa ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Drag Coefficient ◽  
Hydrodynamic Force ◽  
Lift Coefficient ◽  
Flow Speed ◽  
Cfd Analysis ◽  
Mean Flow ◽  
Hydrodynamic Analysis ◽  
Computational Fluid Dynamics Cfd

The aim of this research was to numerically clarify the effect of finger spreading and thumb abduction on the hydrodynamic force generated by the hand and forearm during swimming. A computational fluid dynamics (CFD) analysis of a realistic hand and forearm model obtained using a computer tomography scanner was conducted. A mean flow speed of 2 m·s−1was used to analyze the possible combinations of three finger positions (grouped, partially spread, totally spread), three thumb positions (adducted, partially abducted, totally abducted), three angles of attack (a = 0°, 45°, 90°), and four sweepback angles (y = 0°, 90°, 180°, 270°) to yield a total of 108 simulated situations. The values of the drag coefficient were observed to increase with the angle of attack for all sweepback angles and finger and thumb positions. For y = 0° and 180°, the model with the thumb adducted and with the little finger spread presented higher drag coefficient values for a = 45° and 90°. Lift coefficient values were observed to be very low at a = 0° and 90° for all of the sweepback angles and finger and thumb positions studied, although very similar values are obtained at a = 45°. For y = 0° and 180°, the effect of finger and thumb positions appears to be much most distinct, indicating that having the thumb slightly abducted and the fingers grouped is a preferable position at y = 180°, whereas at y = 0°, having the thumb adducted and fingers slightly spread yielded higher lift values. Results show that finger and thumb positioning in swimming is a determinant of the propulsive force produced during swimming; indeed, this force is dependent on the direction of the flow over the hand and forearm, which changes across the arm’s stroke.

Prediction of Fluid Inertance in Nonuniform Passageways

2006 ◽  
Vol 128 (2) ◽  
pp. 266-275 ◽  
Author(s):  
D. Nigel Johnston
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Finite Element ◽  
Numerical Calculation ◽  
Incompressible Flow ◽  
Complex Geometry ◽  
Mean Flow ◽  
Poppet Valve ◽  
Noise Characteristics ◽  
Spool Valve

The dynamic response, stability, and noise characteristics of fluid components and systems can be strongly influenced by the inertance of the fluid in passageways, which are often of complex geometry. The inertance is a parameter that has often proved to be very difficult to accurately quantify, either theoretically or experimentally. This paper presents a method of numerical calculation of the inertance in a passageway, assuming inviscid, incompressible flow and zero mean flow. The method is simple to apply and can be applied to geometries of arbitrary complexity. Two simple but unorthodox ways of calculating inertance using a computational fluid dynamics and a finite element solid-modeling package are also demonstrated. Results are presented for a simple cylindrical orifice, a simple spool valve, and a conical poppet valve. The effect of the inertance on the response of a poppet valve is demonstrated.

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