Fluid Flow Structure in Arterial Bypass Anastomosis

2005 ◽  
Vol 127 (4) ◽  
pp. 611-618 ◽  
Author(s):  
C. M. Su ◽  
D. Lee ◽  
R. Tran-Son-Tay ◽  
W. Shyy
Keyword(s):  
Fluid Flow ◽  
Flow Structure ◽  
Bypass Graft ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Arterial Bypass ◽  
Flow Recirculation ◽  
Area Reduction ◽  
Complex Flow Structure

The fluid flow through a stenosed artery and its bypass graft in an anastomosis can substantially influence the outcome of bypass surgery. To help improve our understanding of this and related issues, the steady Navier-Stokes flows are computed in an idealized arterial bypass system with partially occluded host artery. Both the residual flow issued from the stenosis—which is potentially important at an earlier stage after grafting—and the complex flow structure induced by the bypass graft are investigated. Seven geometric models, including symmetric and asymmetric stenoses in the host artery, and two major aspects of the bypass system, namely, the effects of area reduction and stenosis asymmetry, are considered. By analyzing the flow characteristics in these configurations, it is found that (1) substantial area reduction leads to flow recirculation in both upstream and downstream of the stenosis and in the host artery near the toe, while diminishes the recirculation zone in the bypass graft near the bifurcation junction, (2) the asymmetry and position of the stenosis can affect the location and size of these recirculation zones, and (3) the curvature of the bypass graft can modify the fluid flow structure in the entire bypass system.

Computational Analysis of Fluid Flow in Pebble Bed Modular Reactor Using Different Turbulence Models

2010 ◽  
Author(s):  
Akshay Gandhir ◽  
Yassin Hassan
Keyword(s):  
Fluid Flow ◽  
Pressure Drop ◽  
Flow Structure ◽  
Computational Study ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Packed Bed ◽  
Complex Flow ◽  
Fluid Flow Characteristics

A steady state computational study was done to obtain the pressure drop estimation in different packed bed geometries, and describe the fluid flow characteristics for such complex structures. Two out of the three Bravais lattices were analyzed, namely, simple cubic (symmetric) and body centered cubic (staggered). STARCCM+ commercial CFD software from CD-ADAPCO was used to simulate the flow. To account for turbulence effects standard k-epsilon and realizable k-epsilon models were used. Various cases were analyzed with Modified Reynolds number ranging from 10,000 to 50,000. Each model showed different results as far as the velocity and flow structure is concerned. However, for each case the flow structure showed similar features such as vortex formation downstream and between pebbles due to complex flow separation [1]. The pressure drop obtained from each model was found to be in reasonable agreement with the existing data.

Natural Convection in a Horizontal Cavity Partially Occupied by a Porous Media Saturated by a Coolant Liquid

2006 ◽  
Author(s):  
Fakhreddine S. Oueslati ◽  
Rachid Bennacer ◽  
Habib Sammouda ◽  
Ali Belghith
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Natural Convection ◽  
Flow Structure ◽  
Boussinesq Approximation ◽  
Density Variation ◽  
Heat Fluxes ◽  
Complex Flow ◽  
Coupled Equations ◽  
Complex Flow Structure

The natural convection is studied in a cavity witch the lower half is filled with a porous media that is saturated with a first fluid (liquid), and the upper is filled with a second fluid (gas). The horizontal borders are heated and cooled by uniform heat fluxes and vertical ones are adiabatic. The formulation of the problem is based on the Darcy-Brinkman model. The density variation is taken into account by the Boussinesq approximation. The system of the coupled equations is resolved by the classic finite volume method. The numerical results show that the variation of the conductivity of the porous media influences strongly the flow structure and the heat transfer as well as in upper that in the lower zones. The effect of conductivity is conditioned by the porosity which plays a very significant roll on the heat transfer. The structures of this flow show that this kind of problem with specific boundary conditions generates a complex flow structure of several contra-rotating two to two cells, in the upper half of the cavity.

Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Energy Equations

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

Flow Field Analysis of Under-Expanded Supersonic Jets Impinging on an Inclined Flat Plate: Analysis With PSP/Schlieren Images and CFD Simulations

2005 ◽  
Author(s):  
Kozo Fujii ◽  
Akira Oyama ◽  
Nobuyuki Tsuboi ◽  
Moto Tsukada ◽  
Hirofumi Ouchi ◽  
...  
Keyword(s):  
Flat Plate ◽  
Flow Structure ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Flow Fields ◽  
Field Analysis ◽  
Geometrical Parameters ◽  
Complex Flow ◽  
Plate Analysis ◽  
Complex Flow Structure

Flow fields of Mach number 2.2 jet impinging on an inclined flat plate are experimentally investigated using the Pressure Sensitive Paints (PSP) and Schlieren flow visualization. The flow filed structure is mainly determined by two geometrical parameters (nozzle-plate distance and plate angle against the jet) and one flow parameter (pressure ratio). The results suggest that all the observed flow fields can actually be classified into three types of flow structure based on the three parameters above. As an extension of the authors’ earlier work, experiments are carried out for higher plate angles. The new results show the effectiveness and limitation of the classification that we proposed. To find out the flow structure, some of the flow fields are computationally simulated. Good agreement of the pressure distributions with the experiment validates the simulation. Although analysis so far is limited, the result reveals three dimensional complex flow structure that created pressure peaks over the plate surface.

Volumetric Three-Componential Velocity Measurements (V3V) of Flow Structure Behind Mangrove-Root Type Models

2020 ◽  
Author(s):  
Amirkhosro Kazemi ◽  
Eduardo E. Castillo ◽  
Oscar Curet ◽  
Ruben Hortensius ◽  
Pothos Stamatios
Keyword(s):  
Flow Structure ◽  
Vortex Structure ◽  
Streamwise Velocity ◽  
Circular Cylinders ◽  
Complex Flow ◽  
Time Resolved ◽  
Mangrove Root ◽  
Mangrove Roots ◽  
A Chain ◽  
Complex Flow Structure

Abstract Mangrove roots produce complex flow structure interactions with their environment, which affect the nutrient, habitat and aquatic animals. Analysis of the flow structure behind the roots extends to a broad range of mangrove-inspired applications that provides understanding into complex flows encountered in unidirectional riverine flows. In this work, we modeled the mangrove roots with a cluster of rigid circular cylinders to investigate the vortex structure downstream of the models. The vortex organization of the patch of cylinder wakes was studied experimentally by time-resolved volumetric three-componential volumetric velocimetry (V3V) at Reynolds numbers 1014 and 3549. The results show that the vortex structure in the 3-D flow field reveals a regular shedding at Re = 1014, forming von Kármán vortices dominating the 3D motion. The flow structure behind rigid patches is coherent and the streamwise velocity remains unchanged. The regime for a flexible patch at Re = 3549 produces an intricate pattern where the multiple counter-rotating vortexes distorted substantially and forming a chain of rhombus-like vortex cells in the near wake. The information for the 3D flow feature provides useful information to a robust structure for Seawall erosion.

Pressure Fluctuations Around Steam Control Valve: Steam Experiments and CFD Calculations

2007 ◽  
Author(s):  
Ryo Morita ◽  
Fumio Inada
Keyword(s):  
Power Plant ◽  
Pressure Fluctuations ◽  
3D Structure ◽  
Flow Characteristics ◽  
Control Valve ◽  
Working Fluid ◽  
Complex Flow ◽  
Piping Systems ◽  
The Difference ◽  
Complex Flow Structure

In some cases, a steam control valve (figure 1) in a power plant causes large vibrations in piping systems that can be attributed to pressure fluctuations generated in the valve under the partial-valve-opening (middle-opening) condition. For the maintenance and the management of the plant, the valve system needs to be improved to prevent the onset of hydrodynamic instabilities. However, in the case of the steam control valve, it is difficult to understand the flow characteristics in detail experimentally because the flow around the valve has a complex 3D structure and becomes supersonic (M>1). For these reasons, the details of the flow around the valve are not fully understood before, and CFD simulations are required to understand the underlying complex flow structure associated with the valve. In our previous researches, a mechanism of the pressure fluctuations in the middle opening condition, named “rotating pressure fluctuations”, were clarified and a suppression shape were developed by experiments and CFD calculations. However, as we used air as a working fluid in our previous researches instead of steam that is used in the power plant, we couldn’t consider effects of condensation and difference of change of the state quantities between air and steam. In this report, we have conducted steam experiments and CFD calculations by original code to clarify the effects of the difference of the fluids. As a result, in the middle opening condition, we have observed spike-type pressure fluctuations and their rotation in the experiment, and valve-attached flow and local high-pressure region in the CFD result. These results indicate the pressure fluctuations observed in steam experiments and CFDs are the same as rotating pressure fluctuations observced in air researches.

Numerical study of transonic cavity flows using large-eddy and detached-eddy simulation

2007 ◽  
Vol 111 (1117) ◽  
pp. 153-164 ◽  
Author(s):  
P. Nayyar ◽  
G. N. Barakos ◽  
K. J. Badcock
Keyword(s):  
Energy Content ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
Promising Alternative ◽  
Eddy Simulation ◽  
Massively Separated Flows ◽  
Large Eddy

Numerical analysis of the flow in weapon bays modelled as open rectangular cavities of length-to-depth (L/D) ratio of 5 and width-to-depth (W/D) ratio of 1 with doors-on and doors-off is presented. Flow conditions correspond to Mach and Reynolds numbers (based on cavity length) of 0·85 and 6·783m respectively. Results from unsteady Reynolds-averaged Navier-Stokes (URANS), large-eddy simulation (LES) and detached-eddy simulation (DES) are compared with the simulation methods demonstrating the best prediction of this complex flow. It was found that URANS was not able to predict the change of flow characteristics between the doors-on and doors-off configurations. In addition, the energy content of the cavity flow modes was much better resolved with DES and LES. Further, the DES was found to be quite capable for this problem giving accurate results (within 3dB of) experiments and appears to be a promising alternative to LES for modelling massively separated flows.

Measurements of Flow Modification by Particle Deposition Inside a Packed Bed Using Time-Resolved PIV

2008 ◽  
Author(s):  
Elvis E. Dominguez-Ontiveros ◽  
Carlos Estrada-Perez ◽  
Yassin A. Hassan
Keyword(s):  
Heat Transfer ◽  
Velocity Field ◽  
Flow Structure ◽  
Particle Deposition ◽  
Packed Bed ◽  
Packed Bed Reactor ◽  
Temperature Fields ◽  
Complex Flow ◽  
Flow Modification ◽  
Complex Flow Structure

In the Advanced Gas Cooled Pebble Bed Reactors for nuclear power generation, the fuel is spherical coated particles. The energy transfer phenomenon requires detailed understanding of the flow and temperature fields around the spherical fuel pebbles. Detailed information of the complex flow structure within the bed is needed. Generally, for computing the flow through a packed bed reactor or column, the porous media approach is usually used with lumped parameters for hydrodynamic calculations and heat transfer. While this approach can be reasonable for calculating integral flow quantities, it may not provide all the detailed information of the heat transfer and complex flow structure within the bed. The present experimental study presents the full velocity field using particle image velocity technique (PTV) in a conjunction with matched refractive index fluid with the pebbles to achieve optical access. Velocity field measurements are presented delineating the complex flow structure.

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