scholarly journals Pulsatile flow in circular tubes of varying cross-section with suction/injection

1994 ◽  
Vol 35 (3) ◽  
pp. 366-381 ◽  
Author(s):  
Peeyush Chandra ◽  
J. S. V. R. Krishna Prasad
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Cross Section ◽  
Pulsatile Flow ◽  
Normal Velocity ◽  
Fluid Exchange ◽  
Circular Tubes ◽  
Permeable Walls ◽  
Wall Shear

AbstractWe consider here pulsatile flow in circular tubes of varying cross-section with permeable walls. The fluid exchange across the wall is accounted for by prescribing the normal velocity of the fluid at the wall. A perturbation analysis has been carried out for low Reynolds number flows and for small amplitudes of oscillation. It has been observed that the magnitude of the wall shear stress and the pressure drop decrease as the suction velocity increases. Further, as the Reynolds number is increased, the magnitude of wall shear stress increases in the convergent portion and decreases in the divergent portion of a constricted tube.

Turbulent combined oscillatory flow and current in a pipe

1998 ◽  
Vol 373 ◽  
pp. 313-348 ◽  
Author(s):  
C. R. LODAHL ◽  
B. M. SUMER ◽  
J. FREDSØE
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Cross Section ◽  
Oscillatory Flow ◽  
Combined Flow ◽  
The Mean ◽  
Wall Shear ◽  
A Current

This work concerns the combined oscillatory flow and current in a circular, smooth pipe. The study comprises wall shear stress measurements, and laser-Doppler-anemometer velocity and turbulence measurements. Three kinds of pipes were used, with diameters D=19 cm, 9 cm, and 1.1 cm, enabling the influence of the parameter R/δ to be studied in the investigation (R/δ ranging from about 3 to 53), where R is the radius of the pipe, and δ is the Stokes layer thickness. The ranges of the two other parameters of the combined flow processes, namely the current Reynolds number, Rec, and the oscillatory-flow boundary-layer (i.e. the wave–boundary layer) Reynolds number, Rew, are: Rec=0−1.6×105, and Rew=0−7×106. The transition to turbulence in the combined flow case occurs at a current Reynolds number larger than the conventional value, ca. 2×103, depending on Rew, and R/δ. A turbulent current can be laminarized by superimposing an oscillatory flow. The overall average value of the wall shear stress (the mean wall shear stress) may retain its steady-current value, it may decrease, or it may increase, depending on the flow regime. The increase (which can be as much as a factor of 4) occurs when the combined flow is in the wave-dominated regime, while the oscillatory-flow component of the flow is in the turbulent regime. The component of the wall shear stress oscillating around the mean wall shear stress can also increase with respect to its oscillatory-flow-alone value. For this to occur, the originally laminar oscillatory boundary layer needs to become a fully developed turbulent boundary layer, when a turbulent current is superimposed. This increase can be as much as O(3–4). The velocity profiles across the cross-section of the pipe change near the wall when an oscillatory flow is superimposed on a current, in agreement with the results of the wall shear stress measurements. The period-averaged turbulence profiles across the cross-section of the pipe behave differently for different flow regimes. When the two components of the flow are equally significant, the turbulence profile appears to be different from those corresponding to the fundamental cases; the level of turbulence increases (only slightly) with respect to those experienced in the fundamental cases.

Flow and Thermal Fields in a Pendant Droplet Moving on Lyophobic Surface

2010 ◽  
Author(s):  
Basant Singh Sikarwar ◽  
K. Muralidhar ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Reynolds Number ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Wall Shear Stress ◽  
Transfer Coefficient ◽  
Maximum Shear Stress ◽  
Computational Domain ◽  
Wall Shear

Clusters of liquid drops growing and moving on physically or chemically textured lyophobic surfaces are encountered in drop-wise mode of vapor condensation. As opposed to film-wise condensation, drops permit a large heat transfer coefficient and are hence attractive. However, the temporal sustainability of drop formation on a surface is a challenging task, primarily because the sliding drops eventually leach away the lyophobicity promoter layer. Assuming that there is no chemical reaction between the promoter and the condensing liquid, the wall shear stress (viscous resistance) is the prime parameter for controlling physical leaching. The dynamic shape of individual droplets, as they form and roll/slide on such surfaces, determines the effective shear interaction at the wall. Given a shear stress distribution of an individual droplet, the net effect of droplet ensemble can be determined using the time averaged population density during condensation. In this paper, we solve the Navier-Stokes and the energy equation in three-dimensions on an unstructured tetrahedral grid representing the computational domain corresponding to an isolated pendant droplet sliding on a lyophobic substrate. We correlate the droplet Reynolds number (Re = 10–500, based on droplet hydraulic diameter), contact angle and shape of droplet with wall shear stress and heat transfer coefficient. The simulations presented here are for Prandtl Number (Pr) = 5.8. We see that, both Poiseuille number (Po) and Nusselt number (Nu), increase with increasing the droplet Reynolds number. The maximum shear stress as well as heat transfer occurs at the droplet corners. For a given droplet volume, increasing contact angle decreases the transport coefficients.

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).

Evolution of wall shear stress with Reynolds number in fully developed turbulent channel flow experiments

2019 ◽  
Vol 4 (7) ◽  
Author(s):  
Pierre-Alain Gubian ◽  
Jordan Stoker ◽  
James Medvescek ◽  
Laurent Mydlarski ◽  
B. Rabi Baliga
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Wall Shear ◽  
Flow Experiments

scholarly journals Developing Pulsatile Flow in a Deployed Coronary Stent

2005 ◽  
Vol 128 (3) ◽  
pp. 347-359 ◽  
Author(s):  
Divakar Rajamohan ◽  
Rupak K. Banerjee ◽  
Lloyd H. Back ◽  
Ashraf A. Ibrahim ◽  
Milind A. Jog
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Pulsatile Flow ◽  
Thrombus Formation ◽  
Three Dimensional ◽  
Tissue Growth ◽  
Coronary Stent ◽  
Stress Distributions ◽  
Hemodynamic Parameters ◽  
Wall Shear

A major consequence of stent implantation is restenosis that occurs due to neointimal formation. This patho-physiologic process of tissue growth may not be completely eliminated. Recent evidence suggests that there are several factors such as geometry and size of vessel, and stent design that alter hemodynamic parameters, including local wall shear stress distributions, all of which influence the restenosis process. The present three-dimensional analysis of developing pulsatile flow in a deployed coronary stent quantifies hemodynamic parameters and illustrates the changes in local wall shear stress distributions and their impact on restenosis. The present model evaluates the effect of entrance flow, where the stent is placed at the entrance region of a branched coronary artery. Stent geometry showed a complex three-dimensional variation of wall shear stress distributions within the stented region. Higher order of magnitude of wall shear stress of 530dyn∕cm2 is observed on the surface of cross-link intersections at the entrance of the stent. A low positive wall shear stress of 10dyn∕cm2 and a negative wall shear stress of −10dyn∕cm2 are seen at the immediate upstream and downstream regions of strut intersections, respectively. Modified oscillatory shear index is calculated which showed persistent recirculation at the downstream region of each strut intersection. The portions of the vessel where there is low and negative wall shear stress may represent locations of thrombus formation and platelet accumulation. The present results indicate that the immediate downstream regions of strut intersections are areas highly susceptible to restenosis, whereas a high shear stress at the strut intersection may cause platelet activation and free emboli formation.

Sign in / Sign up

Export Citation Format

Share Document