A Comparison of Steady and Pulsatile Flow in Symmetrically Branched Tubes

1982 ◽  
Vol 104 (1) ◽  
pp. 66-68 ◽  
Author(s):  
F. J. Walburn ◽  
P. D. Stein
Keyword(s):  
Reynolds Number ◽  
Secondary Flow ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Area Ratio ◽  
Secondary Velocity

The purpose of this study was to compare the characteristics of flow in the region of symmetrical bifurcations having branch-to-trunk area ratios of 0.4, 0.8 and 1.2 during steady and pulsatile flow. Flow was visualized with neutrally bouyant particles. Secondary flow was not observed in the branches during either steady or pulsatile flow when the branch-to-trunk area ratio was 0.4. Secondary velocity patterns were not observed in the branches with branch-to-trunk area ratios of 0.8 and 1.2 during pulsatile flow, although they were observed during steady flow. It may be inaccurate, therefore, to characterize pulsatile flow at an instantaneous Reynolds number on the basis of steady flow at the same Reynolds number.

Hydrodynamic Effects on Particle Deposition in Microchannel Flows at Elevated Temperatures

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Zhibin Yan ◽  
Xiaoyang Huang ◽  
Chun Yang
Keyword(s):  
Reynolds Number ◽  
Steady Flow ◽  
Deposition Rate ◽  
Pulsatile Flow ◽  
Heat Exchangers ◽  
Particle Deposition ◽  
Elevated Temperatures ◽  
Solution Temperature ◽  
Particulate Fouling ◽  
Hydrodynamic Effects

Particulate fouling and particle deposition at elevated temperature are crucial issues in microchannel heat exchangers. In this work, a microfluidic system was designed to examine the hydrodynamic effects on the deposition of microparticles in a microchannel flow, which simulate particle deposits in microscale heat exchangers. The deposition rates of microparticles were measured in two typical types of flow, a steady flow and a pulsatile flow. Under a given elevated solution temperature and electrolyte concentration of the particle dispersion in the tested flow rate range, the dimensionless particle deposition rate (Sherwood number) was found to decrease with the Reynolds number of the steady flow and reach a plateau for the Reynolds number beyond 0.091. Based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, a mass transport model was developed with considering temperature dependence of the particle deposition at elevated temperatures. The modeling results can reasonably capture our experimental observations. Moreover, the experimental results of the pulsatile flow revealed that the particle deposition rate in the microchannel can be mitigated by increasing the frequency of pulsation within a low-frequency region. Our findings are expected to provide a better understanding of thermally driven particulate fouling as well as to provide useful information for design and operation of microchannel heat exchangers.

Comparison of Steady and Pulsatile Flow Near the Ventral and Dorsal Walls of Casts of Human Aortic Bifurcations

1984 ◽  
Vol 106 (1) ◽  
pp. 79-82 ◽  
Author(s):  
O. J. Deters ◽  
F. F. Mark ◽  
C. B. Bargeron ◽  
M. H. Friedman ◽  
G. M. Hutchins
Keyword(s):  
Secondary Flow ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Direction ◽  
Flow Patterns ◽  
Laser Doppler Anemometer ◽  
Common Features ◽  
Fluid Velocities ◽  
Pulsatile Flows ◽  
The Common

Steady and pulsatile flows were passed through casts of human aortic bifurcations and, by means of a laser Doppler anemometer, fluid velocities were measured at selected sites near the ventral and dorsal walls. At these sites, in the vicinity of the bifurcation, the influence of secondary flow is significant and therefore an appreciation of the phasic variation of secondary flow patterns is important. Results are presented comparing the flow direction in both steady and pulsatile flow at sites in three casts. The common features of the flow at these sites were the persistence of the flow direction during the accelerating and decelerating phases of the pulsatile cycle, and the consistently smaller angle (measured from the inlet centerline) of the pulsatile flow direction as compared to the angle of the flow direction in steady flow.

Entry Flow in a Circular Tube of Aortic Arch Dimensions

1984 ◽  
Vol 106 (4) ◽  
pp. 351-356
Author(s):  
K. O. Lim ◽  
J. S. Kennedy ◽  
C. M. Rodkiewicz
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Secondary Flow ◽  
Flow Pattern ◽  
Aortic Arch ◽  
Steady Flow ◽  
Circular Tube ◽  
Boundary Layer Separation ◽  
Curved Tube ◽  
Separation Zones

Steady flow within a uniform circular curved tube formed by two 90-deg elbows was studied as a function of ψ, the angle between the planes of curvature of the two elbows. Boundary layer separation was found at two locations. The sites of these separation zones were observed to be essentially independent of ψ while the Reynolds number at which separation was first detected was found to decrease as ψ increased. The relation between separation and the pathogenesis of atherosclerosis is discussed. Secondary flow pattern was found to depend on ψ and in some instances on Reynolds number as well.

Flow Structures at the Proximal Side-to-End Anastomosis. Influence of Geometry and Flow Division

1995 ◽  
Vol 117 (2) ◽  
pp. 224-236 ◽  
Author(s):  
P. E. Hughes ◽  
T. V. How
Keyword(s):  
Reynolds Number ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Critical Reynolds Number ◽  
Flow Patterns ◽  
Time Dependent ◽  
Flow Structures ◽  
Proximal Side ◽  
Flow Division ◽  
Distal Artery

Flow structures were visualized in transparent polyurethane models of proximal side-to-end vascular anastomoses, using planar illumination of suspended tracer particles. Both the effects of geometry and flow division were determined under steady and pulsatile flow conditions, for anastomosis angles of 15, 30, and 45 degrees. The flow patterns were highly three-dimensional and were characterized by a series of vortices in the fully occluded distal artery and two helical vortices aligned with the axis of the graft. In steady flow, above a critical Reynolds number, the flow changed from a laminar regime to one displaying time-dependent behavior. In particular, significant fluctuating velocity components were observed in the distal artery and particles were shed periodically from the occluded artery into the graft. Pairs of asymmetric flow patterns were also observed in the graft, before the onset of the time-dependent flow regime. The critical Reynolds number ranged from 427 to 473 and appeared to be independent of anastomosis angle. The presence of a patent distal artery had a significant effect on the overall flow pattern and led to the formation of a large recirculation region at the toe of the anastomosis. The main structures observed in steady flow, such as vortices in the distal artery and helical flow in the graft, were also seen during the pulsatile cycle. However, the secondary flow components in the graft were more pronounced in pulsatile flow particularly during deceleration of the flow waveform. At higher mean Reynolds numbers, there was also a greater mixing between fluid in the occluded arterial section and that in the graft.

Performance Evaluation of Divided Intake Ducts: Effect of Area Ratio and Inlet Reynolds Number

2003 ◽  
Vol 30 (5) ◽  
pp. 525-541 ◽  
Author(s):  
Sanjeev Bharani ◽  
S.N. Singh ◽  
V. Seshadri ◽  
R. Chandramouli
Keyword(s):  
Reynolds Number ◽  
Performance Evaluation ◽  
Area Ratio

scholarly journals Incidence Angle and Pitch-Chord Effects on Secondary Flows Downstream of a Turbine Cascade

1992 ◽  
Author(s):  
A. Perdichizzi ◽  
V. Dossena
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Oil Flow ◽  
Secondary Velocity ◽  
Secondary Flow Field

This paper describes the results of an experimental investigation of the three-dimensional flow downstream of a linear turbine cascade at off-design conditions. The tests have been carried out for five incidence angles from −60 to +35 degrees, and for three pitch-chord ratios: s/c = 0.58,0.73,0.87. Data include blade pressure distributions, oil flow visualizations, and pressure probe measurements. The secondary flow field has been obtained by traversing a miniature five hole probe in a plane located at 50% of an axial chord downstream of the trailing edge. The distributions of local energy loss coefficients, together with vorticity and secondary velocity plots show in detail how much the secondary flow field is modified both by incidence and cascade solidity variations. The level of secondary vorticity and the intensity of the crossflow at the endwall have been found to be strictly related to the blade loading occurring in the blade entrance region. Heavy changes occur in the spanwise distributions of the pitch averaged loss and of the deviation angle, when incidence or pitch-chord ratio is varied.

End-Wall Film Cooling Through Fan-Shaped Holes With Different Area Ratios

2006 ◽  
Vol 129 (2) ◽  
pp. 212-220 ◽  
Author(s):  
Giovanna Barigozzi ◽  
Giuseppe Franchini ◽  
Antonio Perdichizzi
Keyword(s):  
Secondary Flow ◽  
Mass Flow ◽  
Film Cooling ◽  
Three Dimensional ◽  
Wide Band ◽  
Lateral Spreading ◽  
Area Ratio ◽  
Adiabatic Effectiveness ◽  
Flow Effects ◽  
End Wall

The present paper reports on the aerothermal performance of a nozzle vane cascade, with film-cooled end walls. The coolant is injected through four rows of cylindrical holes with conical expanded exits. Two end-wall geometries with different area ratios have been compared. Tests have been carried out at low speed (M=0.2), with coolant to mainstream mass flow ratio varied in the range 0.5–2.5%. Secondary flow assessment has been performed through three-dimensional (3D) aerodynamic measurements, by means of a miniaturized five-hole probe. Adiabatic effectiveness distributions have been determined by using the wide-band thermochromic liquid crystals technique. For both configurations and for all the blowing conditions, the coolant share among the four rows has been determined. The aerothermal performances of the cooled vane have been analyzed on the basis of secondary flow effects and laterally averaged effectiveness distributions; this analysis was carried out for different coolant mass flow ratios. It was found that the smaller area ratio provides better results in terms of 3D losses and secondary flow effects; the reason is that the higher momentum of the coolant flow is going to better reduce the secondary flow development. The increase of the fan-shaped hole area ratio gives rise to a better coolant lateral spreading, but appreciable improvements of the adiabatic effectiveness were detected only in some regions and for large injection rates.

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

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