scholarly journals Peristaltic Pumping of Blood Through Small Vessels of Varying Cross-Section

2012 ◽  
Vol 79 (6) ◽  
Author(s):  
J. C. Misra ◽  
S. Maiti
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cross Section ◽  
Amplitude Ratio ◽  
Circulatory System ◽  
Small Vessels ◽  
Peristaltic Pumping ◽  
Mean Pressure ◽  
Wall Shear ◽  
Power Law Index

The paper is devoted to a study of the peristaltic motion of blood in the micro-circulatory system. The vessel is considered to be of varying cross-section. The progressive peristaltic waves are taken to be of sinusoidal nature. Blood is considered to be a Herschel-Bulkley fluid. Of particular concern here is to investigate the effects of amplitude ratio, mean pressure gradient, yield stress, and the power law index on the velocity distribution, streamline pattern, and wall shear stress. On the basis of the derived analytical expressions, extensive numerical calculations have been made. The study reveals that velocity of blood and wall shear stress are appreciably affected due to the nonuniform geometry of blood vessels. They are also highly sensitive to the magnitude of the amplitude ratio and the value of the fluid index.

scholarly journals Time-Dependent Wall Shear Stress in a Duct with Arbitrary Cross-Section

1985 ◽  
Vol 28 (244) ◽  
pp. 2280-2287 ◽  
Author(s):  
Manabu IGUCHI ◽  
Munekazu OHMI ◽  
Fujio AKAO
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cross Section ◽  
Arbitrary Cross Section ◽  
Time Dependent ◽  
Wall Shear

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.

scholarly journals Phase Averaged Wall Shear Stress, Wall Pressure and Near Wall Velocity Field Measurements in a Whirling Annular Seal

1995 ◽  
Author(s):  
Gerald L. Morrison ◽  
Robert B. Winslow ◽  
H. Davis Thames
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Field Measurements ◽  
Wall Pressure ◽  
Mean Velocity ◽  
Annular Seal ◽  
Mean Pressure ◽  
Wall Shear ◽  
Anemometer System ◽  
Velocity Turbulence

The flow field inside a 50% eccentric whirling annular seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Flush mount pressure and wall shear stress probes have been used to measure the stresses (normal and shear) along the length of the stator. The rotor was mounted eccentrically on the shaft so that the rotor orbit was circular and rotated at the same speed as the shaft (a whirl ratio of 1.0). This paper presents mean pressure, mean wall shear stress magnitude and mean wall shear stress direction distributions along the length of the seal. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.

scholarly journals A PIV COMPARISON OF THE FLOW FIELD AND WALL SHEAR STRESS IN RIGID AND COMPLIANT MODELS OF HEALTHY CAROTID ARTERIES

2016 ◽  
Vol 17 (03) ◽  
pp. 1750041 ◽  
Author(s):  
PATRICK H. GEOGHEGAN ◽  
MARK C. JERMY ◽  
DAVID S. NOBES
Keyword(s):  
Shear Stress ◽  
Carotid Artery ◽  
Wall Shear Stress ◽  
Flow Field ◽  
Mechanical Response ◽  
Circulatory System ◽  
Rigid Boundary ◽  
Numerical Predictions ◽  
Wall Shear

Certain systems relevant to circulatory disease have walls which are neither rigid nor static, for example, the coronary arteries, the carotid artery and the heart chambers. In vitro modeling allows the fluid mechanics of the circulatory system to be studied without the ethical and safety issues associated with animal and human experiments. Computational methods in which the equations are coupled governing the flow and the elastic walls are maturing. Currently there is a lack of experimental data in compliant arterial systems to validate the numerical predictions. Previous experimental work has commonly used rigid wall boundaries, ignoring the effect of wall compliance. Particle Image Velocimetry is used to provide a direct comparison of both the flow field and wall shear stress (WSS) observed in experimental phantoms of rigid and compliant geometries representing an idealized common carotid artery. The input flow waveform and the mechanical response of the phantom are physiologically realistic. The results show that compliance affects the velocity profile within the artery. A rigid boundary causes severe overestimation of the peak WSS with a maximum relative difference of 61% occurring; showing compliance protects the artery from exposure to high magnitude WSS. This is important when trying to understand the development of diseases like atherosclerosis. The maximum, minimum and time averaged WSS in the rigid geometry was 2.3, 0.51 and 1.03[Formula: see text]Pa and in the compliant geometry 1.4, 0.58 and 0.84[Formula: see text]Pa, respectively.

Phase-Averaged Wall Shear Stress, Wall Pressure, and Near-Wall Velocity Field Measurements in a Whirling Annular Seal

1996 ◽  
Vol 118 (3) ◽  
pp. 590-597
Author(s):  
G. L. Morrison ◽  
R. B. Winslow ◽  
H. D. Thames
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Three Dimensional ◽  
Field Measurements ◽  
Wall Pressure ◽  
Mean Velocity ◽  
Annular Seal ◽  
Mean Pressure ◽  
Wall Shear ◽  
Anemometer System

The flow field inside a 50 percent eccentric whirling annular seal operating at a Reynolds number of 24,000 and a Taylor number of 6600 has been measured using a three-dimensional laser-Doppler anemometer system. Flush mount pressure and wall shear stress probes have been used to measure the stresses (normal and shear) along the length of the stator. The rotor was mounted eccentrically on the shaft so that the rotor orbit was circular and rotated at the same speed as the shaft (a whirl ratio of 1.0). This paper presents mean pressure, mean wall shear stress magnitude, and mean wall shear stress direction distributions along the length of the seal. Phase-averaged wall pressure and wall shear stress are presented along with phase-averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall, where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure, and wall shear stress are very complex and do not follow simple bulk flow predictions.

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.

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