scholarly journals Barriers to front propagation in laminar, three-dimensional fluid flows

2018 ◽  
Vol 97 (3) ◽  
Author(s):  
Minh Doan ◽  
J. J. Simons ◽  
Katherine Lilienthal ◽  
Tom Solomon ◽  
Kevin A. Mitchell
Keyword(s):  
Three Dimensional ◽  
Fluid Flows ◽  
Front Propagation

Visualizing Fluid Flows With X-Rays

2007 ◽  
Author(s):  
Theodore J. Heindel ◽  
Terrence C. Jensen ◽  
Joseph N. Gray
Keyword(s):  
Computed Tomography ◽  
Flow Visualization ◽  
Three Dimensional ◽  
Fluid Flows ◽  
X Rays ◽  
Radiographic Images ◽  
Optical Access ◽  
X Ray ◽  
X Ray Computed ◽  
Density Map

There are several methods available to visualize fluid flows when one has optical access. However, when optical access is limited to near the boundaries or not available at all, alternative visualization methods are required. This paper will describe flow visualization using an X-ray system that is capable of digital X-ray radiography, digital X-ray stereography, and digital X-ray computed tomography (CT). The unique X-ray flow visualization facility will be briefly described, and then flow visualization of various systems will be shown. Radiographs provide a two-dimensional density map of a three dimensional process or object. Radiographic images of various multiphase flows will be presented. When two X-ray sources and detectors simultaneously acquire images of the same process or object from different orientations, stereographic imaging can be completed; this type of imaging will be demonstrated by trickling water through packed columns and by absorbing water in a porous medium. Finally, local time-averaged phase distributions can be determined from X-ray computed tomography (CT) imaging, and this will be shown by comparing CT images from two different gas-liquid sparged columns.

Effects of Inclination Angle of Ribs on the Flow Behavior in Rectangular Ducts

2004 ◽  
Vol 126 (4) ◽  
pp. 692-699 ◽  
Author(s):  
Xiufang Gao ◽  
Bengt Sunde´n
Keyword(s):  
Velocity Component ◽  
Flow Direction ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Fluid Flows ◽  
Streamwise Velocity ◽  
Flow Structures ◽  
Local Flow ◽  
Flow Motion ◽  
Streamwise Velocity Component

The flow behavior in rib-roughened ducts is influenced by the inclination of ribs and the effect is investigated in the present study by Particle Image Velocimetry (PIV). The local flow structures between two adjacent ribs were measured. The Reynolds number was fixed at 5800. The flow field description was based on the PIV results in planes both parallel and perpendicular to the ribbed walls at various locations. The rib angle to the main flow direction was varied as 30 deg, 45 deg, 60 deg and 90 deg. The ribs induce three dimensional flow fields. The flow separation and reattachment between adjacent ribs are clearly observed. In addition, the inclined ribs are found to alter the spanwise distribution of the streamwise velocity component. The streamwise velocity component has its highest values at the upstream end of the ribs, and decreases continuously to its lowest values at the downstream end. Strong secondary flow motion occurs over the entire duct cross section for the inclined ribs. The flow structures between two consecutive ribs show that the fluid flows along the ribs from one end of the ribs to the other end, and then turns back at the transverse center. Downwash and upwash flows are observed at the upstream end and downstream end of the ribs, respectively.

Simulation of Evaporating Spray and Comparison With Droplet Temperature Measurement Obtained by Rainbow Refractometer

2000 ◽  
Author(s):  
Tevfik Gemci ◽  
James Hom ◽  
Norman Chigier
Keyword(s):  
Droplet Size ◽  
Three Dimensional ◽  
Fluid Flows ◽  
Computational Results ◽  
Droplet Temperature ◽  
Temperature Distributions ◽  
Phase Doppler Interferometry ◽  
Computational Work ◽  
Evaporating Spray ◽  
Rainbow Refractometry

Abstract Both experimental and computational work are important in the study of spray evaporation and combustion; therefore, it is essential that a link between the two areas be established. In this study, measurements of a full cone spray using phase-Doppler interferometry and Rainbow Refractometry are presented and compared with computational results. The computation results were acquired using a KIVA-3V code, which is specifically designed to analyze transient, two- and three-dimensional, chemically reactive fluid flows with sprays. Specifically, in this study, the droplet size, velocity and temperature distributions were measured at various locations within the full cone spray. Using the same initial and boundary conditions, computation results were obtained at corresponding locations and compared with the experimental results. The experimental and computational results agree very well and indicate similar droplet size, velocity and temperature distributions at the corresponding locations. Additionally, the cooling rates and movement of the droplets show the same trends.

Modeling and Simulations of Deteriorated Turbulent Heat Transfer in Wall-Heated Cylindrical Tube

2019 ◽  
Vol 4 (3) ◽  
Author(s):  
Prasad Vegendla ◽  
Rui Hu
Keyword(s):  
Heat Transfer ◽  
Nuclear Power ◽  
Three Dimensional ◽  
Cylindrical Tube ◽  
Fluid Flows ◽  
Turbulent Heat Transfer ◽  
Wall Region ◽  
Turbulent Heat ◽  
Modeling And Simulations ◽  
Computational Fluid Dynamics Cfd

Abstract This paper discusses the modeling and simulations of deteriorated turbulent heat transfer (DTHT) for a wall-heated fluid flows, which can be observed in gas-cooled nuclear power reactors during pressurized conduction cooldown (PCC) event due to loss of force circulation flow. The DTHT regime is defined as the deterioration of normal turbulent heat transport due to increase of acceleration and buoyancy forces. The computational fluid dynamics (CFD) tools such as Nek5000 and STAR-CCM+ can help to analyze the DTHT phenomena in reactors for efficient thermal-fluid designs. Three-dimensional (3D) CFD nonisothermal modeling and simulations were performed in a wall-heated circular tube. The simulation results were validated with two different CFD tools, Nek5000 and STAR-CCM+, and validated with an experimental data. The predicted bulk temperatures were identical in both CFD tools, as expected. Good agreement between simulated results and measured data were obtained for wall temperatures along the tube axis using Nek5000. In STAR-CCM+, the under-predicted wall temperatures were mainly due to higher turbulence in the wall region. In STAR-CCM+, the predicted DTHT was over 48% at outlet when compared to inlet heat transfer values.

scholarly journals David J. Benney: Nonlinear Wave and Instability Processes in Fluid Flows

2020 ◽  
Vol 52 (1) ◽  
pp. 21-36 ◽  
Author(s):  
T.R. Akylas
Keyword(s):  
Nonlinear Wave ◽  
Evolution Equations ◽  
Flow Instability ◽  
Three Dimensional ◽  
Fluid Flows ◽  
Nonlinear Evolution Equations ◽  
Nonlinear Phenomena ◽  
New Paradigm ◽  
Applied Mathematician ◽  
Modulated Wave Trains

David J. Benney (1930–2015) was an applied mathematician and fluid dynamicist whose highly original work has shaped our understanding of nonlinear wave and instability processes in fluid flows. This article discusses the new paradigm he pioneered in the study of nonlinear phenomena, which transcends fluid mechanics, and it highlights the common threads of his research contributions, namely, resonant nonlinear wave interactions; the derivation of nonlinear evolution equations, including the celebrated nonlinear Schrödinger equation for modulated wave trains; and the significance of three-dimensional disturbances in shear flow instability and transition.

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