Experiments on Transition to Turbulence in a Constant-Acceleration Pipe Flow

1989 ◽  
Vol 111 (4) ◽  
pp. 428-432 ◽  
Author(s):  
P. J. Lefebvre ◽  
F. M. White
Keyword(s):  
Control Valve ◽  
Linear Increase ◽  
Transition To Turbulence ◽  
Laser Doppler Velocimeter ◽  
Mean Flow ◽  
Flow Loop ◽  
Mean Velocity ◽  
Stress Sensors ◽  
Diameter Pipe ◽  
Wall Shear Stress Sensors

Experiments were conducted to study transition to turbulence in pipe flows started from rest with a linear increase in mean velocity. The data were taken at the Unsteady Flow Loop Facility at the Naval Underwater System Center, using a 5-cm diameter pipe 30 meters long. Instrumentation included static pressure, wall pressure, and wall shear stress sensors, as well as a laser Doppler velocimeter and a transient flowmeter. A downstream control valve was programmed to produce nearly constant mean flow accelerations, a, from 2 to 12 m/s2. In each of 37 runs, the time of transition to turbulence was the same throughout the pipe to within ± 30 ms, indicating a global instability. As acceleration increased, the transition Reynolds number ReD increased monotonically from 2 × 105 to 5 × 105. Other dimensionless transition parameters are also presented, the simplest and most effective of which is T* ≈ 400 ± 10 percent for the present experiments, where T* = ttr(a2/ν)1/3 and ν is kinematic viscosity.

An Experimental Investigation of Turbulent Drag Reduction in Concentric Annulus Using Particle Image Velocimetry Technique

2013 ◽  
Author(s):  
Fabio Ernesto Rodriguez Corredor ◽  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Particle Image Velocimetry ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Particle Image ◽  
Reynolds Shear Stress ◽  
Polymer Concentration ◽  
Mean Flow ◽  
Flow Loop ◽  
Mean Velocity ◽  
Image Velocimetry

Polymer drag reduction is investigated using the Particle Image Velocimetry (PIV) technique in fully developed turbulent flow through a horizontal flow loop with concentric annular geometry (inner to outer pipe radius ratio = 0.4). The polymer used was a commercially available partially hydrolyzed polyacrylamide (PHPA). The polymer concentration was varied from 0.07 to 0.12% V/V. The drag reduction is enhanced by increasing polymer concentration until the concentration reaches an optimum value. After that, the drag reduction is decreased with the increasing polymer concentration. Optimum concentration value of PHPA was found to be around 0.1% V/V. Experiments were conducted at solvent Reynolds numbers of 38700, 46700 and 56400. The percent drag reduction was found to be increasing with the increasing Reynolds number. The study was also focused on analyzing the mean flow and turbulence statistics for fully-turbulent flow using the velocity measurements acquired by PIV. Axial mean velocity profile was found to be following the universal wall law close to the wall (i.e., y+ <10), but it deviated from log law results with an increased slope in the logarithmic zone (i.e., y+ >30). In all cases of polymer application, the viscous sublayer (i.e., y+ <10) thickness was found to be higher than that of the water flow. Reynolds shear stress in the core flow region was found to be decreasing with the increase in polymer concentration.

scholarly journals Transition to turbulence in the rotating disk boundary layer of a rotor–stator cavity

2018 ◽  
Vol 848 ◽  
pp. 631-647 ◽  
Author(s):  
Eunok Yim ◽  
J.-M. Chomaz ◽  
D. Martinand ◽  
E. Serre
Keyword(s):  
Boundary Layer ◽  
Similarity Solution ◽  
Rotating Disk ◽  
Transition To Turbulence ◽  
Mean Flow ◽  
Self Similarity ◽  
Mean Velocity ◽  
Global Mode ◽  
Spatial Growth ◽  
The Mean

The transition to turbulence in the rotating disk boundary layer is investigated in a closed cylindrical rotor–stator cavity via direct numerical simulation (DNS) and linear stability analysis (LSA). The mean flow in the rotor boundary layer is qualitatively similar to the von Kármán self-similarity solution. The mean velocity profiles, however, slightly depart from theory as the rotor edge is approached. Shear and centrifugal effects lead to a locally more unstable mean flow than the self-similarity solution, which acts as a strong source of perturbations. Fluctuations start rising there, as the Reynolds number is increased, eventually leading to an edge-driven global mode, characterized by spiral arms rotating counter-clockwise with respect to the rotor. At larger Reynolds numbers, fluctuations form a steep front, no longer driven by the edge, and followed downstream by a saturated spiral wave, eventually leading to incipient turbulence. Numerical results show that this front results from the superposition of several elephant front-forming global modes, corresponding to unstable azimuthal wavenumbers $m$, in the range $m\in [32,78]$. The spatial growth along the radial direction of the energy of these fluctuations is quantitatively similar to that observed experimentally. This superposition of elephant modes could thus provide an explanation for the discrepancy observed in the single disk configuration, between the corresponding spatial growth rates values measured by experiments on the one hand, and predicted by LSA and DNS performed in an azimuthal sector, on the other hand.

Round Sudden-Expansion Flows

1986 ◽  
Vol 200 (6) ◽  
pp. 447-455 ◽  
Author(s):  
L Khezzar ◽  
J H Whitelaw ◽  
M Yianneskis
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Sudden Expansion ◽  
Vortex Rings ◽  
Mean Flow ◽  
Mean Velocity ◽  
Number Range ◽  
Laser Anemometry ◽  
Diameter Pipe ◽  
Inlet Geometry

This paper describes an experimental investigation of the water flows through one axisymmetric and two asymmetric round sudden expansions from a 48 mm to an 84 mm diameter pipe and eccentricities of the pipe axes of 0, 5 and 15 mm respectively. Flow visualization revealed the presence of vortex rings downstream of the plane of expansion for transitional Reynolds numbers (Re, based on the upstream pipe diameter and bulk flow velocity) and reattachment lengths were determined in the Reynolds number range 120–40 000 for all three cases. Detailed measurements of the three mean velocity components and corresponding fluctuations were obtained by laser anemometry for Re = 40000. Wall static pressure measurements are also presented. The results show that asymmetry of the inlet geometry strongly influences the distribution of mean and turbulence quantities downstream of the expansion and results in three-dimensional reattachment. In all three flows, the mean flow was nearly uniform and the turbulence nearly homogeneous at distances of seven diameters of the large pipe downstream of the expansion. Higher levels of turbulence were found in the asymmetric ducts with maxima twice those in the axisymmetric duct.

The Measurements of Mean Flow Angles Between an Automotive Fan and Stator

2002 ◽  
Author(s):  
Gregory A. Kopp ◽  
Robert J. Martinuzzi
Keyword(s):  
Flow Direction ◽  
Leading Edge ◽  
Laser Doppler Velocimeter ◽  
Hot Wire ◽  
Mean Flow ◽  
Mean Velocity ◽  
Flow Angle ◽  
Automotive Engine ◽  
Engine Cooling ◽  
The Mean

Measurements of the mean velocity vector were conducted to determine the exit angle from an automotive engine cooling fan module. The measurements were made at 15 locations along a radius between the hub and the band. The radius investigated was located in a plane roughly half-way between the blade trailing edge and stator leading edge. A two-component laser Doppler velocimeter and a four-wire hot-wire probe were used to measure the flow fields. It was found that the results obtained from hot-wire anemometry will have significant bias errors when used to measure the velocity vectors between the fan and the stator unless phase-averaged data are obtained with the probe re-oriented by phase. The differences between the techniques occur because the distribution of instantaneous swirl angles is bi-modal. Further, the mean flow angle is close to a local minimum in the probability density function of the swirl angle. This will act to increase errors in measurement devices whose accuracy depends on flow direction (the quantity being measured) such as five-hole probes which are used in industry.

EXPERIMENTAL INVESTIGATION OF FLOW RESPONSE TO STATIONARY DISTURBANCE IN ROTATING-DISK FLOW

2019 ◽  
Vol XVI (2) ◽  
pp. 13-22
Author(s):  
Muhammad Ehtisham Siddiqui
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Three Dimensional ◽  
Rotating Disk ◽  
Careful Analysis ◽  
Laboratory Frame ◽  
Transition To Turbulence ◽  
Turbulent Regime ◽  
Mean Velocity ◽  
Layer Flow

Three-dimensional boundary-layer flow is well known for its abrupt and sharp transition from laminar to turbulent regime. The presented study is a first attempt to achieve the target of delaying the natural transition to turbulence. The behaviour of two different shaped and sized stationary disturbances (in the laboratory frame) on the rotating-disk boundary layer flow is investigated. These disturbances are placed at dimensionless radial location (Rf = 340) which lies within the convectively unstable zone over a rotating-disk. Mean velocity profiles were measured using constant-temperature hot-wire anemometry. By careful analysis of experimental data, the instability of these disturbance wakes and its estimated orientation within the boundary-layer were investigated.

The structure of a highly decelerated axisymmetric turbulent boundary layer

2021 ◽  
Vol 929 ◽  
Author(s):  
N. Agastya Balantrapu ◽  
Christopher Hickling ◽  
W. Nathan Alexander ◽  
William Devenport
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Shear Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Large Scale ◽  
Convection Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean

Experiments were performed over a body of revolution at a length-based Reynolds number of 1.9 million. While the lateral curvature parameters are moderate ( $\delta /r_s < 2, r_s^+>500$ , where $\delta$ is the boundary layer thickness and r s is the radius of curvature), the pressure gradient is increasingly adverse ( $\beta _{C} \in [5 \text {--} 18]$ where $\beta_{C}$ is Clauser’s pressure gradient parameter), representative of vehicle-relevant conditions. The mean flow in the outer regions of this fully attached boundary layer displays some properties of a free-shear layer, with the mean-velocity and turbulence intensity profiles attaining self-similarity with the ‘embedded shear layer’ scaling (Schatzman & Thomas, J. Fluid Mech., vol. 815, 2017, pp. 592–642). Spectral analysis of the streamwise turbulence revealed that, as the mean flow decelerates, the large-scale motions energize across the boundary layer, growing proportionally with the boundary layer thickness. When scaled with the shear layer parameters, the distribution of the energy in the low-frequency region is approximately self-similar, emphasizing the role of the embedded shear layer in the large-scale motions. The correlation structure of the boundary layer is discussed at length to supply information towards the development of turbulence and aeroacoustic models. One major finding is that the estimation of integral turbulence length scales from single-point measurements, via Taylor's hypothesis, requires significant corrections to the convection velocity in the inner 50 % of the boundary layer. The apparent convection velocity (estimated from the ratio of integral length scale to the time scale), is approximately 40 % greater than the local mean velocity, suggesting the turbulence is convected much faster than previously thought. Closer to the wall even higher corrections are required.

Laser Velocimeter Measurements in Highly Turbulent Recirculating Flows

1984 ◽  
Vol 106 (2) ◽  
pp. 173-180 ◽  
Author(s):  
W. H. Stevenson ◽  
H. D. Thompson ◽  
R. R. Craig
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Quantitative Description ◽  
Sudden Expansion ◽  
Laser Doppler Velocimeter ◽  
Bias Error ◽  
Mean Velocity ◽  
One Dimensional ◽  
Numerical Predictions ◽  
Velocity Bias

This paper presents the results of an extensive study of subsonic separated flows using a laser Doppler velocimeter. Both a rectangular rearward facing step and cylindrical (axisymmetric) sudden expansion geometry were studied. The basic objectives were to resolve the question of whether a velocity bias error does, in fact, occur in LDV measurements in highly turbulent flows of this type and, if so, how it may be eliminated; map the velocity field (mean velocity, turbulence intensity, Reynolds stress, etc.) including the entire recirculation zone; and compare experimental results with numerical predictions based on the k-ε turbulence model. Measurements were carried out using a one-dimensional LDV operating in forward scatter with signal processing by means of a commercial counter-type processor. Results obtained show that velocity bias does occur in turbulent flows and that it can be overcome by proper data acquisition procedures. The results also indicate that the important mean velocity and turbulence quantities can be obtained with reasonable accuracy using a one-dimensional LDV system. Although the k-ε turbulence model provides a good qualitative picture of the flow field, it does not yield a completely adequate quantitative description. Results obtained here illustrate the discrepancies to be expected and provide a basis for further model development.

Control of Hemorrhage in Critical Femoral or Inguinal Penetrating Wounds—An Ultrasound Evaluation

2006 ◽  
Vol 21 (6) ◽  
pp. 379-382 ◽  
Author(s):  
Michael Blaivas ◽  
Stephen Shiver ◽  
Matthew Lyon ◽  
Srikar Adhikari
Keyword(s):  
Flow Velocity ◽  
Abdominal Aorta ◽  
Femoral Artery ◽  
Iliac Artery ◽  
Common Femoral Artery ◽  
Body Armor ◽  
Mean Flow ◽  
Mean Velocity ◽  
Flow Measurements ◽  
Ultrasound Evaluation

AbstractIntroduction:Exsanguination from a femoral artery wound can occur in sec-onds and may be encountered more often due to increased use of body armor. Some military physicians teach compression of the distal abdominal aorta (Abdominal Aorta) with a knee or a fist as a temporizing measure.Objective:The objective of this study was to evaluate if complete collapse of the Abdominal Aorta was feasible and with what weight it occurs.Methods:This was a prospective, interventional study at a Level-I, academ-ic, urban, emergency department with an annual census of 80,000 patients. Written, informed consent was obtained from nine male volunteers after Institutional Research Board approval. Any patient who presented with abdominal pain or had undergone previous abdominal surgery was excluded from the study. Subjects were placed supine on the floor to simulate an injured soldier. Various dumbbells of increasing weight were placed over the distal Abdominal Aorta, and pulsed-wave Doppler measurements were taken at the right common femoral artery (CFA). Dumbbells were placed on top of a tightly bundled towel roughly the surface area of an adult knee. Flow measurements at the CFA were taken at increments of 20 pounds. This was repeated with weight over the proximal right artery iliac and distal right iliac artery to eval- uate alternate sites. Descriptive statistics were utilized to evaluate the data.Results:The mean velocity through the CFA was 75.8 cm/ sec at 0 pounds. Compression of the Abdominal Aorta ranging 80 to 140 pounds resulted in no flow in the CFA. A steady decrease in mean flow velocity was seen starting with 20 pounds. Flow velocity decreased more rapidly with compression of the prox- imal right iliac artery, and stopped in all nine volunteers by 120 pounds of pressure. For all nine volunteers, up to 80 pounds of pressure over the distal iliac artery failed to decrease CFA flow velocity, and no subject was able to tolerate more weight at that location.Conclusion:Flow to the CFA can be stopped completely with pressure over the distal Abdominal Aorta or proximal iliac artery in catastrophic wounds. Compression over the proximal iliac artery worked best, but a first responder still may need to apply upward of 120 pounds of pressure to stop exsanguination.

Multiphase Flow Loop Testing of Autonomous Inflow Control Valve for Light Oil

2021 ◽  
Author(s):  
Soheila Taghavi ◽  
Ismarullizam Mohd Ismail ◽  
Haavard Aakre ◽  
Vidar Mathiesen
Keyword(s):  
Multiphase Flow ◽  
Oil Recovery ◽  
Flow Behavior ◽  
Control Valve ◽  
Flow Loop ◽  
Negative Effects ◽  
Total Recovery ◽  
Light Oil ◽  
Control Devices ◽  
Model Oil

Abstract To increase the production and recovery of marginal, mature, and challenging oil reservoirs, developing new inflow control technologies is of great importance. In cases where production of surrounding reservoir fluids such as gas and water can cause negative effects on both the total oil recovery and the amounts of energy required to drain the reservoir, the multiphase flow performances of these technologies are of particular significance. In typical cases, a Long Horizontal Well (LHW) will eventually start producing increasing amounts of these fluids. This will cause the Water Cut (WC) and/or Gas Oil Ratio (GOR) to rise, ultimately forcing the well to be shut down even though there still are considerable amounts of oil left in the reservoir. In earlier cases, Inflow Control Devices (ICD) and Autonomous Inflow Control Devices (AICD) have proven to limit these challenges and increase the total recovery by balancing the influx along the well and delaying the breakthrough of gas and/or water. The Autonomous Inflow Control Valve (AICV) builds on these same principles, and in addition has the ability to autonomously close when breakthrough of unwanted gas and/or water occurs. This will even out the total drawdown in the well, allowing it to continue producing without the WC and/or GOR reaching inacceptable limits. As part of the qualification program of the light-oil AICV, extensive flow performance tests have been carried out in a multiphase flow loop test rig. The tests have been performed under realistic reservoir conditions with respect to variables such as pressure and temperature, with model oil, water, and gas at different WC's and GOR's. Conducting these multiphase experiments has been valuable in the process of establishing the AICV's multiphase flow behavior, and the results are presented and discussed in this paper. Single phase performance and a comparison with a conventional ICD are also presented. The results display that the AICV shows significantly better performance than the ICD, both for single and multiphase flow. A static reservoir modelling method have been used to evaluate the AICV performance in a light-oil reservoir. When compared to a screen-only completion and an ICD completion, the simulation shows that a completion with AICV's will outperform the above-mentioned completions with respect to WC and GOR behavior. A discussion on how this novel AICV can be utilized in marginal, mature, and other challenging reservoirs will be provided in the paper.

Abstract WMP66: Cerebrovascular Hemodynamics of Mechanical Circulatory Support Device Patients

Stroke ◽  
2017 ◽  
Vol 48 (suppl_1) ◽  
Author(s):  
Kara R Melmed ◽  
Konrad H Shlick ◽  
Brenda Rinsky ◽  
Shlee S Song ◽  
Patrick D Lyden
Keyword(s):  
Continuous Flow ◽  
Mechanical Circulatory Support ◽  
Left Ventricular ◽  
Total Artificial Heart ◽  
Circulatory Support ◽  
Normative Values ◽  
Mean Flow ◽  
Mean Velocity ◽  
Ventricular Assist ◽  
Cerebrovascular Hemodynamics

Background: Multiple types of mechanical circulatory support (MCS) devices are commonly used in heart failure patients. These devices carry risk for neurologic complications, specifically cardioembolic stroke. Alterations in blood flow play a role in the pathophysiology, however there is limited data regarding cerebrovascular hemodynamics in MCS patients. We used transcranial Doppler (TCD) to define hemodynamics of commonly used MCS devices. Methods: We retrospectively examined charts from 2/2013 through 6/2016 for patients with MCS who underwent TCD, and obtained the following: peak systolic,end-diastolic velocities, mean flow velocities, pulsatility indices (PI) and number of high-intensity transient signals (HITS). Waveform morphologies were compared between devices. Results: Of 1,796 TCDs studies screened, 62 TCD studies were from 32 MCS patients. Of these, 21 were on extracorporeal membrane oxygenation (ECMO), 15 had a left ventricular assist device (LVAD), 18 had total artificial heart (TAH), and 2 had intra-aortic balloon pumps (IABP). Waveforms in patients supported by ECMO demonstrated continuous flow without clear systolic peaks. The averaged mean MCA velocity was 57.57 (SD= 21.00) cm/sec and mean PI is 0.35 (0.17). LVAD averaged mean MCA velocity was 57.57 (14.38) cm/sec and mean PI of 0.45 (0.28). PIs were low in patients with continuous-flow LVADs. Impella patients had morphologically distinct pulsatile waveforms compared to other types of VADs. IABP had averaged mean velocity of 56.21 (14.78) cm/sec and mean PI of 0.77 (0.15). These waveforms demonstrated pronounced diastolic upstrokes not present in other devices. In TAH patients, mean MCA velocity was 73.69 (33.00) cm/sec and PI of 0.86 (0.40). Emboli detection was performed in 46 studies, and HITS were detected in 29 (63%). Of these 15 (51%) were administered 100% oxygen which suppressed >50% HITS in 10 (67%) patients. Conclusion: Patients supported by MCS devices produce unique and characteristic waveforms on TCD studies. Further studies will describe normative values in this special population. HITS were not universally present and intermittently suppressible by oxygen, suggesting some may be gaseous in nature. Risk of stroke in patients with MCS and HITS is under study.

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