Flow System to Detect Transitional Flow Based on Pulsed Doppler Ultrasound Velocity Profiles

2012 ◽  
Author(s):  
Narender Ambati ◽  
Dipankar Biswas ◽  
Francis Loth ◽  
Stanley E. Rittgers ◽  
Steven A. Jones
Keyword(s):  
Reynolds Number ◽  
Doppler Ultrasound ◽  
Critical Reynolds Number ◽  
Flow System ◽  
Ultrasound Velocity ◽  
Transition To Turbulence ◽  
Transitional Flow ◽  
Working Fluid ◽  
Pulsed Doppler Ultrasound

A flow circuit test rig has been constructed to determine the critical Reynolds number at which blood flow become turbulent. A Doppler ultrasound velocimeter was used in an in vitro flow system to measure the velocity of water inside a straight pipe in order to determine the critical Reynolds number (Re) at which the flow becomes transitional. Results using water as the working fluid demonstrated flow-transition to turbulence near Re = 2000 which is close to the expected value from literature. Future studies will utilize blood as the working fluid.

Transition to Turbulence Downstream of a Stenosis for Whole Blood and a Newtonian Analog Under Steady Flow Conditions

2021 ◽  
Author(s):  
Rayanne Pinto Costa ◽  
Blaise Simplice Talla Nwotchouang ◽  
Junyao Yao ◽  
Dipankar Biswas ◽  
David Casey ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Steady Flow ◽  
Whole Blood ◽  
Critical Reynolds Number ◽  
Blood Rheology ◽  
Transition To Turbulence ◽  
Flow Conditions ◽  
Shear Rates ◽  
The Impact

Abstract Blood, a multiphase fluid comprised of plasma, blood cells, and platelets, is known to exhibit a shear-thinning behavior at low shear rates and near-Newtonian behavior at higher shear rates. However, less is known about the impact of its multiphase nature on the transition to turbulence. In this study, we experimentally determined the critical Reynolds number at which the flow began to transition to turbulence downstream of an eccentric stenosis for whole porcine blood and a Newtonian blood analog (water-glycerin mixture). Velocity profiles for both fluids were measured under steady-state flow conditions using an ultrasound Doppler probe placed 12 diameters downstream of an eccentric stenosis. Velocity was recorded at 21 locations along the diameter at 11 different flow rates. Normalized turbulent kinetic energy was used to determine the critical Reynolds number for each fluid. Blood rheology was measured before and after each experiment. Tests were conducted on five samples of each fluid inside a temperature-controlled in-vitro flow system. The viscosity at shear rate 1000 s 1 was used to define the Reynolds number for each fluid. The mean critical Reynolds numbers for blood and water-glycerin were 470 ± 27.5 and 395 ± 10, respectively, indicating a ~19% delay in transition to turbulence for whole blood compared to the Newtonian fluid. This finding is consistent with a previous report for steady flow in a straight pipe, suggesting some aspect of blood rheology may serve to suppress, or at least delay, the onset of turbulence in vivo.

Single-Phase Heat Transfer and Pressure Drop of Water Cooled Inside Horizontal Smooth Tubes in the Transitional Flow Regime

2010 ◽  
Author(s):  
Josua P. Meyer ◽  
Leon Liebenberg ◽  
Jonathan A. Olivier
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Transition Region ◽  
Heat Exchangers ◽  
Operating Conditions ◽  
Transitional Flow ◽  
Working Fluid ◽  
Tube Heat Exchanger ◽  
Smooth Tubes

Heat exchangers are usually designed in such a way that they do not operate in the transition region. This is usually due to a lack of information in this region. However, due to design constraints, energy efficiency requirements or change of operating conditions, heat exchangers are often forced to operate in this region. It is also well known that entrance disturbances influence where transition occurs. The purpose of this paper is to present experimental heat transfer and pressure drop data in the transition region for fully developed and developing flows inside smooth tubes using water as the working fluid. The use of different inlet disturbances were used to investigate its effect on transition. A tube-in-tube heat exchanger was used to perform the experiments, which ranged in Reynolds numbers from 1 000 to 20 000, with Prandtl numbers being between 4 and 6 while Grashof numbers were in the order of 105. Results showed that the type of inlet disturbance could delay transition to a Reynolds number as high as 7 000, while other inlets expedited it, confirming results of others. For heat transfer, though, it was found that transition was independent of the inlet disturbance and all commenced at the same Reynolds number, 2 000–3 000, which was attributed to secondary flow effects.

scholarly journals Non-normal origin of modal instabilities in rotating plane shear flows

2020 ◽  
Vol 476 (2233) ◽  
pp. 20190550
Author(s):  
Sharath Jose ◽  
Rama Govindarajan
Keyword(s):  
Reynolds Number ◽  
Shear Flows ◽  
Critical Reynolds Number ◽  
Flow System ◽  
Neutral Line ◽  
Plane Couette Flow ◽  
Plane Shear ◽  
Perturbation Amplitude ◽  
Fundamental Reason ◽  
The Stability

Small variations introduced in shear flows are known to affect stability dramatically. Rotation of the flow system is one example, where the critical Reynolds number for exponential instabilities falls steeply with a small increase in rotation rate. We ask whether there is a fundamental reason for this sensitivity to rotation. We answer in the affirmative, showing that it is the non-normality of the stability operator in the absence of rotation which triggers this sensitivity. We treat the flow in the presence of rotation as a perturbation on the non-rotating case, and show that the rotating case is a special element of the pseudospectrum of the non-rotating case. Thus, while the non-rotating flow is always modally stable to streamwise-independent perturbations, rotating flows with the smallest rotation are unstable at zero streamwise wavenumber, with the spanwise wavenumbers close to that of disturbances with the highest transient growth in the non-rotating case. The instability critical rotation number scales inversely as the square of the Reynolds number, which we demonstrate is the same as the scaling obeyed by the minimum perturbation amplitude in non-rotating shear flow needed for the pseudospectrum to cross the neutral line. Plane Poiseuille flow and plane Couette flow are shown to behave similarly in this context.

Numerical study of the dimensionless characteristics and modeling experiment of a molten salt pump that transports viscous fluids

2017 ◽  
Vol 27 (9) ◽  
pp. 2131-2153 ◽  
Author(s):  
Chunlei Shao ◽  
Yang Zhao
Keyword(s):  
Reynolds Number ◽  
Molten Salt ◽  
High Speed ◽  
Critical Reynolds Number ◽  
Numerical Study ◽  
Working Fluid ◽  
High Speed Photography ◽  
Content Type ◽  
Modeling Experiment ◽  
External Characteristics

Purpose The purpose of this paper is to study the dimensionless characteristics of a molten salt pump and propose an approach to carry out the modeling experiment by using water instead of molten salts. Design/methodology/approach External characteristics of the pump were estimated by using the steady flow model and compared with the experimental results. By taking water as the working fluid, the pathlines in the volute of the model pump were validated by the results obtained of high-speed photography. According to the derived dimensionless characteristics of the molten salt pump, the modeling experimental schemes were proposed. Adopting the validated numerical simulation model, the performance of the molten salt pump was studied in detail. Findings The modeling experimental schemes designed according to the dimensionless characteristics are theoretically feasible. However, to carry out the experiment successfully, factors such as rotational speed, geometric size, flow rate and head should be taken into account. The flow in the pumps is similar under the similar operating condition and the external characteristics of the similar pump can be converted to each other. Compared with transporting water, the decline of the head and efficiency is within 5 per cent when the viscosity is lower than 0.01453 Pa · s. The pump is not suitable for running under the critical Reynolds number of 1.0 × 107. Originality/value The current work revealed the relationships among the dimensionless performances of a molten salt pump and proposed a critical Reynolds number ReQcr for the pump running.

Critical Reynolds Number in Constant-Acceleration Pipe Flow From an Initial Steady Laminar State

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Charles W. Knisely ◽  
Kazuyoshi Nishihara ◽  
Manabu Iguchi
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Pipe Flow ◽  
Laser Doppler Velocimetry ◽  
Critical Reynolds Number ◽  
Transition To Turbulence ◽  
Doppler Velocimetry ◽  
Constant Acceleration ◽  
Laminar State ◽  
Steady Laminar

The transition to turbulence in a constant-acceleration pipe flow from an initial laminar state was investigated in a custom-made apparatus permitting visual access to the water flow in the pipe. The apparatus allowed both laser Doppler velocimetry measurements and flow visualization using a tracer. The experiment was carried out by accelerating the flow from a steady laminar state to a steady turbulent state. The relation between the critical Reynolds number for transition to turbulence and the acceleration was found to be similar to that in a constant-acceleration pipe flow started from rest. In addition, with increased acceleration, the turbulent transition was found to be delayed to higher Reynolds numbers using flow visualization with simultaneous laser Doppler velocimetry measurements.

A Theory of Transitional and Turbulent Flow of Non-Newtonian Slurries Between Flat Parallel Plates

1971 ◽  
Vol 11 (01) ◽  
pp. 52-56 ◽  
Author(s):  
Richard W. Hanks ◽  
Maheshkumar P. Valia
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Critical Reynolds Number ◽  
Frictional Resistance ◽  
Newtonian Fluids ◽  
Transitional Flow ◽  
Parallel Plates ◽  
Bingham Plastic ◽  
Turbulent Transition ◽  
Large Width

Abstract A theoretical model is developed which Permits prediction of velocity profiles and frictional prediction of velocity profiles and frictional resistance factors for the isothermal flow of Bingham plastic non-Newtonian slurries in laminar, transitional, and turbulent flow between that parallel walls, in rectangular ducts of large width-to-height ratios, or in concentric annuli with radius ratios approaching unity. The theory is tested with available frictional resistance data for a range of Hedstrom numbers from 10(4) to 10(8) and a set of theoretical design curves of friction factor vs Reynolds number is developed. The model indices that for certain ranges of Hedstrom number (the non-Newtonian index) turbulence is suppressed relative to Newtonian flow behavior, whereas for other ranges of Hedstrom number, the converse is true. Introduction The handling of non-Newtonian fluids in turbulent motion is an important operation in many modern technological processes. Despite this fact, however, little has been done to develop models which are comparable to those available for Newtonian turbulent flow. In particular, a model of the transitional flow regime is notably lacking. Recently, a theory of laminar-turbulent transition for non-Newtonian slurries flowing in pipes and parallel plates was presented. A theory of parallel plates was presented. A theory of transitional and turbulent flow of Newtonian fluids in pipes and parallel plate ducts has also recently been developed. This theory permits the analytic calculation of the friction factor-Reynolds number curves as a continuous function of Reynolds number from the critical Reynolds number of laminar turbulent transition to any condition of turbulent flow. In this paper these two theories will be combined in order to develop a theory for the transitional and turbulent flow of non-Newtonian slurries in parallel plate ducts, rectangular ducts of large width-to-height ratio, or concentric annuli with radius ratios approaching unity. THEORETICAL ANALYSIS The rheological model which will be used to represent the non-Newtonian slurry behavior is the linear Bingham plastic model, ..............(1) ............(2) For this model the laminar flow curve is given by ..............(3) where q = 2v/b, b is one-half the distance between the plates, w = b(−dp/dz) is the wall shear stress, and D = o/ w. The end of the laminax flow, region is determined by the equations ........(4) .........(5) where N Rec = 4bp vc/ p is the critical Reynolds number, Dc is the critical transitional value of D and N He -16bp o/ p is the Hedstrom number expressed in terms of the hydraulic diameter for parallel plates. parallel plates. The calculation of the transitional flow field for this type of fluid will be based upon the model developed by Hanks for Newtonian fluids. SPEJ P. 52

scholarly journals Coronary sinus fow measured by pulsed Doppler ultrasound is a powerful indicator of coronary blood supply – a pig heart in vitro study.

2016 ◽  
Vol 18 (2) ◽  
pp. 190 ◽  
Author(s):  
Xiao-Zhi Zheng ◽  
Jing Wu ◽  
Jie Hua
Keyword(s):  
Coronary Artery ◽  
Doppler Ultrasound ◽  
Blood Supply ◽  
Coronary Sinus ◽  
Coronary Artery Occlusion ◽  
Artery Occlusion ◽  
Pulsed Doppler ◽  
Operating Characteristics ◽  
Pulsed Doppler Ultrasound

Aims: To evaluate the correlation between the coronary sinus fow and the infusion volume in the coronaries and assess the performance of coronary sinus fow in predicting coronary artery occlusion in an isolated pig heart. Material and methods: The coronary sinus fow was measured in 16 isolated pig hearts by pulsed Doppler ultrasound. The correlation between the coronary sinus fow and the infusion volume in different coronary artery was analyzed, and the performance of coronary sinus fow in predicting different coronary artery occlusion was deducted. Results: There were no statistically signifcant differences between the coronary sinus fow and the infusion volume in different coronary artery (p>0.05). The correlations between the coronary sinus fow and the infusion volume in left anterior descending coronary artery (LAD), left circumfex coronary artery (LCX), LAD and LCX, and LAD, LCX and right coronary artery (RCA) were all higher than 0.85 (p<0.01), and those of RCA, LAD and RCA, and LCX and RCA were between 0.6 and 0.8 (p<0.05). The areas under the receiver operating characteristics curve (AUC) were all higher than 0.90 (p<0.05) in predicting any two coronaries occlusion (<50% and 100%) and three coronaries occlusion (<50%) with a >85% sensitivity and specifcity. Excepting RCA mild occlusion (<50%), AUCs in predicting one coronary occlusion (<50% and 100%) were between 0.7 and 0.9, with >80% sensitivity and specifcity. Conclusions: The coronary sinus fow measured by pulsed Doppler ultrasound can effectively and exactly refect the infusion volume in coronaries, which is a powerful indicator of coronary blood supply.

scholarly journals Experimental investigation of transitional flow in a toroidal pipe

2013 ◽  
Vol 738 ◽  
pp. 463-491 ◽  
Author(s):  
J. Kühnen ◽  
M. Holzner ◽  
B. Hof ◽  
H. C. Kuhlmann
Keyword(s):  
Reynolds Number ◽  
Oscillatory Flow ◽  
Flow Instability ◽  
Measurement Techniques ◽  
Stereoscopic Particle Image Velocimetry ◽  
Transition To Turbulence ◽  
Transitional Flow ◽  
Mean Flow ◽  
Steel Sphere ◽  
Curved Pipes

AbstractThe flow instability and further transition to turbulence in a toroidal pipe (torus) with curvature ratio (tube-to-coiling diameter) 0.049 is investigated experimentally. The flow inside the toroidal pipe is driven by a steel sphere fitted to the inner pipe diameter. The sphere is moved with constant azimuthal velocity from outside the torus by a moving magnet. The experiment is designed to investigate curved pipe flow by optical measurement techniques. Using stereoscopic particle image velocimetry, laser Doppler velocimetry and pressure drop measurements, the flow is measured for Reynolds numbers ranging from 1000 to 15 000. Time- and space-resolved velocity fields are obtained and analysed. The steady axisymmetric basic flow is strongly influenced by centrifugal effects. On an increase of the Reynolds number we find a sequence of bifurcations. For $\mathit{Re}= 4075\pm 2\hspace{0.167em} \% $ a supercritical bifurcation to an oscillatory flow is found in which waves travel in the streamwise direction with a phase velocity slightly faster than the mean flow. The oscillatory flow is superseded by a presumably quasi-periodic flow at a further increase of the Reynolds number before turbulence sets in. The results are found to be compatible, in general, with earlier experimental and numerical investigations on transition to turbulence in helical and curved pipes. However, important aspects of the bifurcation scenario differ considerably.

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