L 005 Aorta Remodeling Responses to Distinct Atherogenic Stimuli: Hypertension, Hypercholesterolemia and Turbulent Flow/Low Wall shear Stress

2009 ◽  
Vol 10 (3) ◽  
pp. 32
Author(s):  
CM Prado ◽  
MA Rossi
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Wall Shear

Roughness Influence on Turbulent Flow Through Annular Seals

1994 ◽  
Vol 116 (2) ◽  
pp. 321-328 ◽  
Author(s):  
Victor Lucas ◽  
Sterian Danaila ◽  
Olivier Bonneau ◽  
Jean Freˆne
Keyword(s):  
Surface Roughness ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Dynamic Characteristics ◽  
Reynolds Equation ◽  
Mixing Length ◽  
Local Shear ◽  
Wall Shear ◽  
Local Shear Stress

This paper deals with an analysis of turbulent flow in annular seals with rough surfaces. In this approach, our objectives are to develop a model of turbulence including surface roughness and to quantify the influence of surface roughness on turbulent flow. In this paper, in order to simplify the analysis, the inertial effects are neglected. These effects will be taken into account in a subsequent work. Consequently, this study is based on the solution of Reynolds equation. Turbulent flow is solved using Prandtl’s turbulent model with Van Driest’s mixing length expression. In Van Driest’s model, the mixing length depends on wall shear stress. However there are many numerical problems in evaluating this wall shear stress. Therefore, the goal of this work has been to use the local shear stress in the Van Driest’s model. This derived from the work of Elrod and Ng concerning Reichardt’s mixing length. The mixing length expression is then modified to introduce roughness effects. Then, the momentum equations are solved to evaluate the circumferential and axial velocity distributions as well as the turbulent viscosity μ1 (Boussinesq’s hypothesis) within the film. The coefficients of turbulence kx and kz, occurring in the generalized Reynolds’ equation, are then calculated as functions of the flow parameters. Reynolds’ equation is solved by using a finite centered difference method. Dynamic characteristics are calculated by exciting the system numerically, with displacement and velocity perturbations. The model of Van Driest using local shear stress and function of roughness has been compared (for smooth seals) to the Elrod and Ng theory. Some numerical results of the static and dynamic characteristics of a rough seal (with the same roughness on the rotor as on the stator) are presented. These results show the influence of roughness on the dynamic behavior of the shaft.

MR-based wall shear stress measurements in fully developed turbulent flow using the Clauser plot method

2019 ◽  
Vol 305 ◽  
pp. 16-21
Author(s):  
Nina Shokina ◽  
Andreas Bauer ◽  
Gabriel Teschner ◽  
Waltraud B. Buchenberg ◽  
Cameron Tropea ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Stress Measurements ◽  
Fully Developed Turbulent Flow ◽  
Wall Shear

scholarly journals Modeling Blood Pulsatile Turbulent Flow in Stenotic Coronary Arteries

2020 ◽  
Vol 14 ◽  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Newtonian Fluid ◽  
Coronary Arteries ◽  
Pathological Condition ◽  
Flow Behavior ◽  
Wall Shear ◽  
Stenotic Arteries

Atherosclerosis is a potentially serious illness where arteries become clogged with fatty substances called plaques. Over the years, this pathological condition has been deeply studied and computational fluid dynamics has played an important role in investigating the blood flow behavior. Commonly, the blood flow is assumed to be laminar and a Newtonian fluid. However, under a stenotic condition, the blood behaves as a non-Newtonian fluid and the pulsatile blood flow through coronary arteries could result in a transition from laminar to turbulent flow condition. The present study aims to analyze and compare numerically the blood flow behavior, applying the k-ω SST model and a laminar assumption. The effects of Newtonian and non-Newtonian (Carreau) models were also studied. In addition, the effect of the stenosis degree on velocity fields and wall shear stress based descriptors were evaluated. According to the results, the turbulent model is shown to give a better overall representation of pulsatile flow in stenotic arteries. Regarding, the effect of non-Newtonian modeling, it was found to be more significant in wall shear stress measurements than in velocity profiles. In addition, the appearance of recirculation zones in the 50% stenotic model was observed during systole, and a low TAWSS and high OSI were detected downstream of the stenosis which, in turn, are risk factors for plaque formation. Finally, the turbulence intensity measurements allowed to distinguish regions of recirculating and disturbed flow.

A MEMS surface fence sensor for wall shear stress measurement in turbulent flow areas

2001 ◽  
pp. 1448-1451 ◽  
Author(s):  
T. von Papen ◽  
H. D. Ngo ◽  
E. Obermeier ◽  
M. Schober ◽  
S. Pirskawetz ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Stress Measurement ◽  
Wall Shear ◽  
Wall Shear Stress Measurement

Numerical investigation of semifilled-pipe flow

2021 ◽  
Vol 932 ◽  
Author(s):  
Julian Brosda ◽  
Michael Manhart
Keyword(s):  
Shear Stress ◽  
Free Surface ◽  
Wall Shear Stress ◽  
Turbulent Flow ◽  
Pipe Flow ◽  
Flow Characteristics ◽  
Streamwise Vorticity ◽  
Reynolds Stresses ◽  
Data Set ◽  
Wall Shear

This study describes turbulent flow in a semifilled pipe with a focus on its secondary currents. To the authors’ knowledge, we provide the first highly resolved data-set for semifilled-pipe flow using direct numerical simulation. The flow parameters range from $Re_\tau =115$ , just maintaining turbulence, to moderate turbulent flow at $Re_\tau =460$ . Some of the main flow characteristics are in line with previously published results from experiments, such as the velocity-dip phenomenon, the main secondary flow and the qualitative distribution of the Reynolds stresses in the core of the flow. We observe some flow phenomena which have not yet been reported in the literature so far for this type of flow. Among those is the inner secondary cell in the mixed corner between the free surface and the pipe's wall, which plays a major role in the distribution of the wall shear stress along the perimeter. We observe that the position and extension of the inner vortex scale with the wall shear stress and those of the outer vortex scale with outer variables. For the first time, we present and discuss distributions of the complete Reynolds stress tensor and its anisotropy which gives rise to the generation of mean streamwise vorticity in a small region in the mixed corners of the pipe. Mean secondary kinetic energy, however, is generated at the free surface around the stagnation point between the inner and outer vortices. This generation mechanism is in line with a vortex dynamics mechanism proposed in the literature.

Analysis of Flow Patterns in a Patient-Specific Aortic Dissection Model

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Z. Cheng ◽  
F. P. P. Tan ◽  
C. V. Riga ◽  
C. D. Bicknell ◽  
M. S. Hamady ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Aortic Dissection ◽  
Turbulent Flow ◽  
Thoracic Aorta ◽  
Turbulence Intensity ◽  
Patient Specific ◽  
Type B ◽  
Type B Dissection ◽  
Wall Shear

Aortic dissection is the most common acute catastrophic event affecting the thoracic aorta. The majority of patients presenting with an uncomplicated type B dissection are treated medically, but 25% of these patients develop subsequent aneurysmal dilatation of the thoracic aorta. This study aimed at gaining more detailed knowledge of the flow phenomena associated with this condition. Morphological features and flow patterns in a dissected aortic segment of a presurgery type B dissection patient were analyzed based on computed tomography images acquired from the patient. Computational simulations of blood flow in the patient-specific model were performed by employing a correlation-based transitional version of Menter’s hybrid k-ε/k-ω shear stress transport turbulence model implemented in ANSYS CFX 11. Our results show that the dissected aorta is dominated by locally highly disturbed, and possibly turbulent, flow with strong recirculation. A significant proportion (about 80%) of the aortic flow enters the false lumen, which may further increase the dilatation of the aorta. High values of wall shear stress have been found around the tear on the true lumen wall, perhaps increasing the likelihood of expanding the tear. Turbulence intensity in the tear region reaches a maximum of 70% at midsystolic deceleration phase. Incorporating the non-Newtonian behavior of blood into the same transitional flow model has yielded a slightly lower peak wall shear stress and higher maximum turbulence intensity without causing discernible changes to the distribution patterns. Comparisons between the laminar and turbulent flow simulations show a qualitatively similar distribution of wall shear stress but a significantly higher magnitude with the transitional turbulence model.

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