Role of Plaque Morphology in Altering the Flow Characteristics in Diseased Coronary Artery

2012 ◽  
Author(s):  
Carlos Moreno ◽  
Kiran Bhaganagar
Keyword(s):  
Coronary Artery ◽  
Nonlinear Response ◽  
Flow Characteristics ◽  
Proximal Region ◽  
Patient Specific ◽  
Plaque Morphology ◽  
Mean Velocity ◽  
Peak Location ◽  
The Mean

Patient specific simulations of a single patient based on an accurate representation of the plaque in a diseased coronary artery with 35% stenosis are performed to understand the effect of inlet forcing frequency and amplitude on the wall shear stress (WSS). Numerical simulations are performed with unsteady flow conditions in a laminar regime. The results have revealed that at low amplitudes, WSS is insensitive to forcing frequency and is it in phase with Q. The maximum WSS is observed at the proximal region of the stenosis, and WSS has highest negative values at the peak location of the stenosis. For higher pulsatile amplitude (a > 1.0), WSS exhibits a strong sensitivity with forcing frequencies. At higher forcing frequency the WSS exhibits nonlinear response to the inlet forcing frequency. Furthermore, significant differences in the mean velocity profile are observed during maximum and minimum volumetric flow rates.

scholarly journals Role of LA strain assessed by speckle tracking echocardiography in predicting patients who develop POAF after a coronary artery bypass surgery

2021 ◽  
Vol 42 (Supplement_1) ◽  
Author(s):  
V Rukmani Prabha ◽  
N Rajeshwari ◽  
J Jenifer
Keyword(s):  
Coronary Artery ◽  
Coronary Artery Bypass ◽  
Left Atrial ◽  
Speckle Tracking ◽  
Speckle Tracking Echocardiography ◽  
Artery Bypass ◽  
Coronary Risk Factors ◽  
Global Strain ◽  
The Mean

Abstract Objectives To evaluate the correlation between left atrial dysfunction assessed by speckle tracking echocardiography and development of postoperative atrial fibrillation (POAF) in patients undergoing coronary artery bypass grafting. To determine the role of coronary risk factors in development of POAF. Method Patients undergoing CABG from January 2019 till June 2020 in Apollo institute, fulfilling the inclusion and exclusion criteria were included.Total of 200 patients were followed.They were subjected to LA strain and strain rate analysis by speckle tracking. Results The incidence of POAF in our study was 24% (n=48). The mean age of this study population was 59.13 years. The patients who developed POAF were older (68.5±9.048 vs 58.39±9.74 years, p value=0.05) than those with no POAF. POAF occurred in 2 phases. the highest proportion of POAF occurrence noticed on postoperative day 2. Among the total POAF cases 79.% occurred within the first 48 hours and 20.8% occurred later (p=0.001). Among the 48 patients who developed POAF, 5 of them developed recurrence during their hospital stay. They had reverted to sinus rhythm following anti-arrhythmic medication for a duration of >24 hours, but went on to develop recurrence of AF at a later. 4 among them reverted to sinus rhythm at discharge while 1 continued to remain in AF at discharge.The duration of hospital stay for patients with POAF group was 10.4 days compared with 10.04 days for those without POAF. Similarly the post-operative stay in the hospital was 7.4 days for the POAF group and 7.04 days for the NO POAF.There was no added economic impact secondary to AF.Comparing the values of left atrial volume index of both the groups it was derived that the mean LAVI value of the POAF group was 26.84+3.654 ml/m2 and that for the NO POAF group was 26.6+3.037ml/m2. Though the patients with POAF had larger LA volume, the chi square test analysis did not yield any clinically significant relationship between LAVI and POAF in our study (p=0.3). The mean LA global strain for the patients with POAF was 29.73+3.695%. And for the patients with no POAF was 36.3+4.854%. LA global strain was reduced in patients who developed POAF (P<0.001) which indicated a strong correlation between LA strain and POAF. Conclusion There is significant correlation between Global Left Atrial Strain and POAF in patients undergoing CABG (P<0.001).There is no significant correlation between patient factors like age, BMI, and the conventional coronary risk factors with POAFThere is no significant correlation between the conventional echocardiographic parameters like LA diameter, LAVI, LVDD, LVSD, LVEF and transmitral flow velocities with POAF. To conclude, preoperative speckle tracking assessment of LA has a strong predictive role in determining the occurrence of POAF in patients undergoing Coronary artery bypass grafting surgery. FUNDunding Acknowledgement Type of funding sources: None.

Establishment of the Wake Behind a Disk

1964 ◽  
Vol 86 (4) ◽  
pp. 869-880 ◽  
Author(s):  
Thomas Carmody
Keyword(s):  
Shear Stress ◽  
Ambient Pressure ◽  
Continuous Distribution ◽  
Flow Characteristics ◽  
Graphical Form ◽  
Stress Distributions ◽  
Mean Velocity ◽  
Pressure Distributions ◽  
Energy Relationships ◽  
The Mean

An air-tunnel study of the establishment of the wake behind a disk at a Reynolds number of approximately 7 × 104 was undertaken. On the basis of the measured data, such a wake is fully established, that is, similarity profiles of the flow characteristics are formed, within 15 diameters of the disk, and approximately 95 percent of the transfer of energy from the mean motion to the turbulence motion takes place within 3 diameters of the disk, in the region of the mean standing eddy. The measured mean ambient-pressure and mean total-pressure distributions, mean velocity distributions, turbulence-intensity and shear-stress distributions, and the mean streamline pattern are presented in graphical form, as are the quantitative balances of the integrated momentum and mean-energy relationships. A stream function consisting of a continuous distribution of doublets is introduced to extend the radial limit of understanding of the flow characteristics to a very large if not infinite radius. Considerable attention is given to the problem of obtaining and interpreting turbulence shear-stress data immediately downstream from the point of flow separation. The applicability of a local diffusion coefficient or virtual viscosity of the Boussinesq or Prandtl type for relating the turbulence shear stress to the radial gradient of mean axial velocity is discussed. The Bernoulli sum and the energy changes along individual streamlines investigated in an associated study are incorporated herein to obtain a quantitative estimate of the local errors involved in the turbulence-shear-stress measurements.

LDV and PIV Velocity Results in a Thermosiphon

2003 ◽  
Author(s):  
J. Kulman ◽  
D. Gray ◽  
S. Sivanagere ◽  
S. Guffey
Keyword(s):  
Large Scale ◽  
Single Phase ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Laser Doppler Velocimeter ◽  
Mean Velocity ◽  
Developed Turbulence ◽  
The Mean ◽  
Good Agreement

Heat transfer and flow characteristics have been determined for a single-phase rectangular loop thermosiphon. The plane of the loop was vertical, and tests were performed with in-plane tilt angles ranging from 3.6° CW to 4.2° CCW. Velocity profiles were measured in one vertical leg of the loop using both a single-component Laser Doppler Velocimeter (LDV), and a commercial Particle Image Velocimeter (PIV) system. The LDV data and PIV data were found to be in good agreement. The measured average velocities were approximately 2–2.5 cm/s at an average heating rate of 70 W, and were independent of tilt angle. Significant RMS fluctuations of 10–20% of the mean velocity were observed in the test section, in spite of the laminar or transitional Reynolds numbers (order of 700, based on the hydraulic diameter). These fluctuations have been attributed to vortex shedding from the upstream temperature probes and mitre bends, rather than to fully developed turbulence. Animations of the PIV data clearly show these large scale unsteady flow patterns. Multiple steady state flow patterns were not observed.

Axisymmetric Flow in a Motored Reciprocating Engine

1978 ◽  
Vol 192 (1) ◽  
pp. 213-223 ◽  
Author(s):  
A. D. Gosman ◽  
A. Melling ◽  
J. H. Whitelaw ◽  
P. Watkins
Keyword(s):  
Laser Doppler Anemometry ◽  
Axisymmetric Flow ◽  
Flow Characteristics ◽  
Small Scale ◽  
Mean Velocity ◽  
Inlet Velocity ◽  
Reciprocating Engine ◽  
Laminar And Turbulent Flow ◽  
Flow Through ◽  
The Mean

A study was made of axisymmetric, laminar and turbulent flow in a motored reciprocating engine with flow through a cylinder head port. Measurements were obtained by laser-Doppler anemometry and predictions for the laminar case were generated by finite-difference means. Agreement between calculated and measured results is good for the main features of the flow field, but significant small scale differences exist, due partly to uncertainties in the inlet velocity distribution. The measurements show, for example, that the mean velocity field is influenced more strongly by the engine geometry than by the speed. In general, the results confirm that the calculation method can be used to represent the flow characteristics of motored reciprocating engines without compression and suggest that extensions to include compression and combustion are within reach.

scholarly journals Experimental Study of Mean Flow Characteristics in the Near Field of Wedge-Shaped Swirling Jets

2020 ◽  
Vol 5 (10) ◽  
pp. 1199-1203
Author(s):  
Md. Mosharrof Hossain ◽  
Muhammed Hasnain Kabir Nayeem ◽  
Dr. Md Abu Taher Ali
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Flow Characteristics ◽  
Velocity Profiles ◽  
Mean Flow ◽  
Mean Velocity ◽  
Potential Core ◽  
Swirling Jets ◽  
The Mean ◽  
Sinusoidal Flow

In this investigation experiment was carried out in 80 mm diameter swirling pipe jet, where swirl was generated by attaching wedge-shaped helixes in the pipe. All measurements were taken at Re 5.3e4. In the plain pipe jet the potential core was found to exist up to x/D=5 but in the swirling jet there was no existence of potential core. The mean velocity profiles were found to be influenced by the presence of wedge-shaped helixes in the pipe. The velocity profiles indicated the presence of sinusoidal flow field in the radial direction existed only in the near field of the jet. This flow field died out after x/D=3 and the existence of jet flow diminished after x/D=5.

scholarly journals The Role of Forcing and Eddy Viscosity Variation on the Log-Layer Mismatch Observed in Wall-Modeled Large-Eddy Simulations

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Rey DeLeon ◽  
Inanc Senocak
Keyword(s):  
Flow Rate ◽  
Eddy Viscosity ◽  
Degree Of Freedom ◽  
Channel Flows ◽  
Momentum Balance ◽  
Mean Velocity ◽  
Turbulent Channel Flows ◽  
The Mean ◽  
Viscosity Variation

We investigate the role of eddy viscosity variation and the effect of zonal enforcement of the mass flow rate on the log-layer mismatch problem observed in turbulent channel flows. An analysis of the mean momentum balance shows that it lacks a degree-of-freedom (DOF) when eddy viscosity is large, and the mean velocity conforms to an incorrect profile. Zonal enforcement of the target flow rate introduces an additional degree-of-freedom to the mean momentum balance, similar to an external stochastic forcing term, leading to a significant reduction in the log-layer mismatch. We simulate turbulent channel flows at friction Reynolds numbers of 2000 and 5200 on coarse meshes that do not resolve the viscous sublayer. The second-order turbulence statistics agree well with the direct numerical simulation benchmark data when results are normalized by the velocity scale extracted from the filtered velocity field. Zonal enforcement of the flow rate also led to significant improvements in skin friction coefficients.

Heat Transfer Augmentation for Air Jet Impinged on Rough Surface

1997 ◽  
Author(s):  
W. M. Chakroun ◽  
S. F. Al-Fahed ◽  
A. A. Abdel-Rehman
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Flow Characteristics ◽  
Mean Velocity ◽  
Potential Core ◽  
Transfer Data ◽  
Nusselt Numbers ◽  
Air Jet ◽  
Rough Plate ◽  
The Mean

An experimental investigation of heat transfer from round air jet impinging normally from below on flat square plates was performed. Smooth and rough plates were used to collect heat transfer data as well as velocity and turbulence intensity profiles. The heat transfer data have been collected for Reynolds numbers ranging from 6500 to 19000. The nozzle-to-plate distances ranged from 0.05 to 15 to cover both the potential core of the jet and the far region. The study was made to investigate the effect of roughness on the local and average heat transfer values and on the fluid characteristics. The roughness was composed of cubes of 1mm dimension distributed uniformly along the plate. The local and average Nusselt numbers for the rough plate showed an increase ranging from 8.9% to 28 % over those obtained for the smooth plate. Roughness was seen to have a strong effect on the flow characteristics, it affected the mean velocity as well as the turbulence intensity of the flow. The mean velocity profiles for the smooth case at r/D = 1 and r/D = 2.5 had steeper near-wall velocity gradient compared with the rough case. Roughness caused an increase in the turbulence intensity of the flow.

scholarly journals Investigation of the influence of nonbreaking waves on the turbulence using PIV methods within laboratory modelling of the upper layer ocean dynamics

2021 ◽  
Vol 2127 (1) ◽  
pp. 012014
Author(s):  
D A Sergeev ◽  
A A Kandaurov ◽  
Yu I Troitskaya
Keyword(s):  
Wind Wave ◽  
Flow Characteristics ◽  
Wave Interaction ◽  
Ocean Dynamics ◽  
Mixing Processes ◽  
Mean Velocity ◽  
Laboratory Modelling ◽  
Entire Depth ◽  
The Mean ◽  
Weak Wind

Abstract The influence of nonbreaking waves on the mixing processes in the upper layer of the ocean during wind-wave interaction was investigated under the conditions of laboratory modeling at the Thermostratified Wind Wave Tank (TSWiWaT) of IAP RAS. Experiments of three types were performed. In the first experiment, shear flow in water was induced using a weak wind to avoid the excitation of surface waves. In the second experiment, in the absence of wind, only a long smooth surface wave was generated using an underwater paddle wavemaker. The third type of experiment combined the conditions of the previous two, i.e. at the same time the wave generator was working and the wind was blowing. In all experiments, the underwater flow characteristics were measured using the PIV method. Vertical profiles of the mean velocity and fluctuations for two components were obtained. It was shown that the presence of waves leads to an increase in the average drift current, as well as, more importantly, on the level of fluctuations over the entire depth of the recorded profile by more than 3 times. This was observed for horizontal and vertical turbulent velocity components both.

scholarly journals Boundary-layer evolution over long wind farms

2021 ◽  
Vol 925 ◽  
Author(s):  
Antonio Segalini ◽  
Marco Chericoni
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Wind Farms ◽  
Internal Boundary Layer ◽  
Internal Boundary ◽  
Inertial Subrange ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
The Mean

The structure of the internal boundary layer above long wind farms is investigated experimentally. The transfer of kinetic energy from the region above the farm is dominated by the turbulent flux of momentum together with the displacement of kinetic energy operated by the mean vertical velocity: these two have comparable magnitude along the farm opposite to the infinite-farm case. The integration of the energy equation in the vertical highlighted the key role of the energy flux, and how that is balanced by the growth of the internal boundary layer in terms of energy thickness with a small role of the dissipation. The mean velocity profiles seem to follow a universal structure in terms of velocity deficit, while the Reynolds stress does not follow the same scaling structure. Finally, a spectral analysis along the farm identified the leading dynamics determining the turbulent activity: while behind the first row the signature of the tip vortices is dominant, already after the second row their coherency is lost and a single broadband peak, associated with wake meandering, is present until the end of the farm. The streamwise velocity peak is associated with a nearly constant Strouhal number weakly dependent on the farm layout and free stream turbulence condition. A reasonable agreement of the velocity spectra is observed when the latter are normalised by the velocity variance and integral time scale: nevertheless the spectra show clear anisotropy at the large scales and even the small scales remain anisotropic in the inertial subrange.

Abstract 1122‐000014: Effects of Patient‐Specific Blood Properties and Inflow Conditions on Hemodynamics in Cerebral Aneurysms

2021 ◽  
Vol 1 (S1) ◽  
Author(s):  
Yuya Uchiyama ◽  
Hiroyuki Takao ◽  
Soichiro Fujimura ◽  
Takashi Suzuki ◽  
Yuma Yamanaka ◽  
...  
Keyword(s):  
Cfd Simulation ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Parent Artery ◽  
Computational Domain ◽  
Cfd Simulations ◽  
Mean Velocity ◽  
Visual Evaluation ◽  
The Mean ◽  
Inflow Conditions

Introduction : Computational Fluid Dynamics (CFD) simulation is an effective tool to investigate pathologies and clinical outcomes of cerebral aneurysms from the hemodynamic perspective. However, simulation conditions such as the blood properties and boundary conditions are usually referred to in the literature do not consider patient‐specific values. In this study, we measured blood properties and extracted the inflow conditions from four‐dimensional digital subtraction angiography (4D‐DSA) images for patients who underwent flow diverter (FD) deployment. Then, we conducted CFD simulations considering the deployed FD geometry to investigate the effect of patient‐specific conditions on aneurysmal hemodynamics. Methods : We took whole blood samples of five patients with intracranial aneurysms just before the surgery and measured the blood density and viscosity with a densitometer and a falling needle rheometer. The patients underwent 4D‐DSA imaging, from which we calculated the patient‐specific inflow velocity of each patient using an in‐house flow extraction program. We used in‐house virtual FD deployment software to reproduce the FD geometry for each patient. We then defined the computational domain including the FD geometry. Four CFD simulations were performed for each of the five patients: (1) a steady CFD simulation under a referred Newtonian blood model and previously published inflow conditions as a basic simulation pattern (2) a CFD simulation including the patient‐specific non‐Newtonian blood properties only, (3) a CFD simulation including the inflow conditions only, and (4) a CFD simulation including both the patient‐specific blood properties and inflow conditions. We calculated the mean velocity in the aneurysm normalized by the mean velocity in the parent artery and the wall shear stress (WSS) of the aneurysm. We compared the results of the four CFD simulations and calculated their differences based on the values for the basic simulation pattern. Results : Based on the visual evaluation, the flow structures of the four CFD simulation patterns differed only slightly from each other, but a quantitative comparison revealed that there were large differences in the hemodynamic parameters. For the velocity, there was an average 14.2% difference with the steady CFD simulation results when the patient‐specific blood properties are considered, and an average 35.8% difference when the patient‐specific inflow conditions are considered. There was an average 60.7% difference when both the patient‐specific blood properties and inflow conditions are taken into account. For the WSS, there was an average 8.75% difference when including the patient‐specific blood properties and an average 66.8% difference in including the patient‐specific inflow conditions. There was an average 69.3% difference in including both conditions are considered. It appeared that the effect of including patient‐specific inflow conditions was more substantial than that of including the patient‐specific blood properties, and most robust when both conditions were included. Conclusions : The hemodynamics obtained from CFD simulations with the deployed FD appears to strongly depend on both the blood properties and the inflow conditions. This result implies that CFD simulations with the referred conditions may not accurately reproduce the hemodynamics. It was confirmed that patient‐specific conditions should be included in CFD simulations.

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