scholarly journals Lagrangian wall shear stress structures and near-wall transport in high-Schmidt-number aneurysmal flows

2016 ◽  
Vol 790 ◽  
pp. 158-172 ◽  
Author(s):  
Amirhossein Arzani ◽  
Alberto M. Gambaruto ◽  
Guoning Chen ◽  
Shawn C. Shadden
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Shear Stress ◽  
Vector Field ◽  
Wall Shear Stress ◽  
Residence Time ◽  
Vessel Wall ◽  
Schmidt Number ◽  
High Schmidt Number ◽  
Near Wall

The wall shear stress (WSS) vector field provides a signature for near-wall convective transport, and can be scaled to obtain a first-order approximation of the near-wall fluid velocity. The near-wall flow field governs mass transfer problems in convection-dominated open flows with high Schmidt number, in which case a flux at the wall will lead to a thin concentration boundary layer. Such near-wall transport is of particular interest in cardiovascular flows whereby haemodynamics can initiate and progress biological events at the vessel wall. In this study we consider mass transfer processes in pulsatile blood flow of abdominal aortic aneurysms resulting from complex WSS patterns. Specifically, the Lagrangian surface transport of a species released at the vessel wall was advected in forward and backward time based on the near-wall velocity field. Exposure time and residence time measures were defined to quantify accumulation of trajectories, as well as the time required to escape the near-wall domain. The effect of diffusion and normal velocity was investigated. The trajectories induced by the WSS vector field were observed to form attracting and repelling coherent structures that delineated species distribution inside the boundary layer consistent with exposure and residence time measures. The results indicate that Lagrangian WSS structures can provide a template for near-wall transport.

Distribution of Mass Transfer Rate and Wall Shear Stress Behind Simple Rectangular Stenosis in Pulsating Flow

1989 ◽  
Vol 111 (1) ◽  
pp. 47-54 ◽  
Author(s):  
R. Yamaguchi
Keyword(s):  
Mass Transfer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Transfer Rate ◽  
Schmidt Number ◽  
Fluid Dynamic ◽  
Mass Transfer Rate ◽  
Pulsating Flow ◽  
Flow Through ◽  
Wall Shear

The distributions of mass transfer rate and wall shear stress in sinusoidal laminar pulsating flow through a two-dimensional asymmetric stenosed channel have been studied experimentally and numerically. The distributions are measured by the electrochemical method. The measurement is conducted at a Reynolds number of about 150, a Schmidt number of about 1000, a nondimensional pulsating frequency of 3.40, and a nondimensional flow amplitude of 0.3. It is suggested that the deterioration of an arterial wall distal to stenosis may be greatly enhanced by fluid dynamic effects.

Near-Wall Measurements in Turbulent Boundary Layers Using Laser Doppler Anemometry

2002 ◽  
Author(s):  
T. Gunnar Johansson ◽  
Luciano Castillo
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Pressure Gradient ◽  
Laser Doppler Anemometry ◽  
Reynolds Numbers ◽  
Mean Velocity ◽  
The Mean ◽  
Wall Shear ◽  
Near Wall

Near wall measurements have been performed in a zero pressure gradient turbulent boundary layer at low to moderate local Reynolds numbers using Laser-Doppler Anemometry in order to investigate how accurately the wall shear stress can be determined. Also, scaling problems are particularly difficult at low Reynolds numbers since they involve simultaneous influences of both inner and outer scales and this is most clearly observed in the near-wall region. In order to fully describe the zero pressure gradient turbulent boundary layer at low to moderate local Reynolds numbers it is necessary to accurately measure a number of quantities. These include the mean velocity and Reynolds stresses, and their spatial derivatives all the way down to the wall (y+∼1). Integral parameters that need to be measured are the wall shear stress and boundary layer thickness, particularly the momentum thickness. Problems with the measurement of field properties get worse close to a wall, and they get worse for increasing local Reynolds number. Three different approaches to measure the wall shear stress were examined. It was found that small measurement errors in the mean velocity close to the wall significantly reduced the accuracy in determining the wall shear stress by measuring the velocity gradient at the wall. The constant stress layer was found to be affected by the advection terms. However, it was found that taking the small pressure gradient into account and improving on the spatial resolution in the outer part of the boundary layer made the momentum integral method reliable.

Wall Shear Stress Inference From Two and Three-Dimensional Turbulent Boundary Layer Velocity Profiles

1973 ◽  
Vol 95 (1) ◽  
pp. 61-67 ◽  
Author(s):  
F. J. Pierce ◽  
B. B. Zimmerman
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Three Dimensional ◽  
Law Of The Wall ◽  
Layer Velocity ◽  
Wall Shear ◽  
Near Wall

A method is developed to infer a local wall shear stress from a two-dimensional turbulent boundary layer velocity profile using all near-wall data with the Spalding single formula law of the wall. The method is used to broaden the Clauser chart scheme by providing for the inclusion of data in the laminar sublayer and transition region, as well as the data in the fully turbulent near-wall flow region. For a skewed velocity profile typical of pressure driven three-dimensional turbulent boundary layer flows, the method is extended to infer a wall shear stress for a three-dimensional turbulent boundary layer. Either wall shear stress or shear velocity values are calculated for two different sets of three-dimensional experimental data, with good agreement found between calculated and experimental results.

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