On the method of determining instantaneous wall shear stress from near-wall velocity measurements in wall turbulence

2021 ◽  
Vol 33 (12) ◽  
pp. 125105
Author(s):  
Qigang Chen ◽  
Yanchong Duan ◽  
Qiang Zhong ◽  
Zhongxiang Wang ◽  
Lei Huang
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Wall Turbulence ◽  
Velocity Measurements ◽  
Wall Velocity ◽  
Wall Shear ◽  
Near Wall

scholarly journals Spectral Characteristics of the Near-Wall Turbulence in an Unsteady Channel Flow

2005 ◽  
Vol 74 (1) ◽  
pp. 172-175 ◽  
Author(s):  
Sedat F. Tardu
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Channel Flow ◽  
Spectral Characteristics ◽  
Time Lag ◽  
Wall Turbulence ◽  
Centerline Velocity ◽  
Wall Shear ◽  
Unsteady Channel Flow ◽  
Near Wall

The modulation characteristics of the turbulent wall shear stress and longitudinal intensities in the inner layer are experimentally investigated in an unsteady channel flow wherein the centerline velocity varies in time in a sinusoidal manner. The fluctuating wall shear stress and velocity signals are temporally filtered and subsequently phase averaged. It is shown that the outer structures corresponding to the low spectrum range have a constant time lag with respect to the centerline velocity modulation. The inner active structures, in particular those with a frequency band containing the mean ejection frequency of the corresponding steady flow dominate the dynamics of the near-wall unsteady turbulence. The structures respond to the imposed shear oscillations in a complex way, depending both on their characteristic scales and the thickness of the oscillating shear zone in which they are embedded.

A Dynamic Procedure for Wall-Modeled Large-Eddy Simulation of High Reynolds Number Flows

2011 ◽  
Author(s):  
Soshi Kawai
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Eddy Simulation ◽  
High Reynolds Number ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Shear ◽  
High Reynolds ◽  
Near Wall

This paper addresses the error in large-eddy simulation with wall-modeling (i.e., when the wall shear stress is modeled and the viscous near-wall layer is not resolved): the error in estimating the wall shear stress from a given outer-layer velocity field using auxiliary near-wall RANS equations where convection is not neglected. By considering the behavior of turbulence length scales near a wall, the cause of the errors is diagnosed and solutions that remove the errors are proposed based solidly on physical reasoning. The resulting method is shown to accurately predict equilibrium boundary layers at very high Reynolds number, with both realistic instantaneous fields (without overly elongated unphysical near-wall structures) and accurate statistics (both skin friction and turbulence quantities).

Numerical Simulation of Wall Shear Stress Conditions and Platelet Localization in Realistic End-to-Side Arterial Anastomoses

2003 ◽  
Vol 125 (5) ◽  
pp. 671-681 ◽  
Author(s):  
P. Worth Longest ◽  
Clement Kleinstreuer
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Bypass Graft ◽  
Self Regulation ◽  
Suture Line ◽  
Cellular Level ◽  
Vascular Surface ◽  
Wall Shear ◽  
Wall Interactions ◽  
Near Wall

Research studies over the last three decades have established that hemodynamic interactions with the vascular surface as well as surgical injury are inciting mechanisms capable of eliciting distal anastomotic intimal hyperplasia (IH) and ultimate bypass graft failure. While abnormal wall shear stress (WSS) conditions have been widely shown to affect vascular biology and arterial wall self-regulation, the near-wall localization of critical blood particles by convection and diffusion may also play a significant role in IH development. It is hypothesized that locations of elevated platelet interactions with reactive or activated vascular surfaces, due to injury or endothelial dysfunction, are highly susceptible to IH initialization and progression. In an effort to assess the potential role of platelet-wall interactions, experimentally validated particle-hemodynamic simulations have been conducted for two commonly implemented end-to-side anastomotic configurations, with and without proximal outflow. Specifically, sites of significant particle interactions with the vascular surface have been identified by a novel near-wall residence time (NWRT) model for platelets, which includes shear stress-based factors for platelet activation as well as endothelial cell expression of thrombogenic and anti-thrombogenic compounds. Results indicate that the composite NWRT model for platelet-wall interactions effectively captures a reported shift in significant IH formation from the arterial floor of a relatively high-angle (30 deg) graft with no proximal outflow to the graft hood of a low-angle graft (10 deg) with 20% proximal outflow. In contrast, other WSS-based hemodynamic parameters did not identify the observed system-dependent shift in IH formation. However, large variations in WSS-vector magnitude and direction, as encapsulated by the WSS-gradient and WSS-angle-gradient parameters, were consistently observed along the IH-prone suture-line region. Of the multiple hemodynamic factors capable of eliciting a hyperplastic response at the cellular level, results of this study indicate the potential significance of platelet-wall interactions coinciding with regions of low WSS in the development of IH.

The Law of the Wall for Swirling Flow in Annular Ducts

1989 ◽  
Vol 111 (2) ◽  
pp. 160-164 ◽  
Author(s):  
R. J. Kind ◽  
F. M. Yowakim ◽  
S. A. Sjolander
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Swirling Flow ◽  
Tangential Velocity ◽  
Wall Region ◽  
Law Of The Wall ◽  
Resultant Velocity ◽  
The Law ◽  
Wall Shear ◽  
Near Wall

Expressions for the logarithmic portion of the law of the wall are derived for the axial and tangential velocity components of swirling flow in annular ducts. These expressions involve new shear-velocity scales and curvature terms. They are shown to agree well with experiment over a substantial portion of the flow near both walls of an annulus. The resultant velocity data also agree with the law of the wall. The success of the proposed logarithmic expressions implies that the mixing-length model used in deriving them correctly describes flow-velocity behavior. This model indicates that the velocity gradient at any height y in the near-wall region is determined by the wall shear stress, not by the local shear stress. This suggests that the influence of wall shear stress is dominant and that it determines the near-wall wall flow even in flows with curvature and pressure gradient. A physical explanation is suggested for this.

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