scholarly journals Flow separation in a straight draft tube, particle image velocimetry

2014 ◽  
Vol 22 (3) ◽  
pp. 032004 ◽  
Author(s):  
P Duquesne ◽  
Y Maciel ◽  
G D Ciocan ◽  
C Deschênes
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Separation ◽  
Particle Image ◽  
Draft Tube ◽  
Image Velocimetry

scholarly journals Visualization of flow characteristics between the ribbed plates via particle image velocimetry

2019 ◽  
pp. 300-300
Author(s):  
Ilker Goktepeli ◽  
Ulas Atmaca ◽  
Sercan Yagmur
Keyword(s):  
Heat Transfer ◽  
Particle Image Velocimetry ◽  
Flow Separation ◽  
Particle Image ◽  
Reference Model ◽  
Water Channel ◽  
Flow Characteristics ◽  
Advanced Technology ◽  
Particle Image Velocimetry System ◽  
Image Velocimetry

Heat transfer is considerably influenced by flow stagnation, separation and reattachment regions due to the ribbed plates. Placing the ribs such as fins, turbulators that trigger the flow separation, enhances the heat transfer inside the channel by increasing the turbulence intensity. The flow separation is caused by disturbing the thermal and hydrodynamic development lengths. Moreover, these ribs also make an impact that increases the heat transfer by enlarging the heat transfer area. However, the ribs lead to the increment of the required pumping power in the meantime due to the increasing pressure loss in such systems. This aforementioned method is used for the heat exchangers, the solar collectors, the cooling of electronic devices. The investigation of the flow characteristics is very crucial to understand the heat transfer mechanism in the ducts for this reason. In the present paper, the flow characteristics between the plates have been experimentally researched. Particle Image Velocimetry system in the open water channel of Selcuk University Advanced Technology Research and Application Center has been used. The smooth plates have been taken as the reference model and used for the comparison with the plates having the rectangular cross-sectional ribs. The ribs with various heights of 0.1 ? h' = h/H ? 0.3 have been symmetrically placed on the internal surfaces of the plates via several spacing values of 0.5 ? S' = S/H ? 1 for varying Reynolds numbers as 10000 ? Re ? 20000. As a result, the flow characteristics have been given in terms of the contour graphics for velocity vector field, velocity components and vorticity.

On the effect of operating condition on separated-flow control by nanosecond pulse discharge actuators

2016 ◽  
Vol 232 (3) ◽  
pp. 505-516 ◽  
Author(s):  
Hai Du ◽  
Zhiwei Shi ◽  
Keming Cheng ◽  
Xuan Jiang ◽  
Zheng Li
Keyword(s):  
Particle Image Velocimetry ◽  
Shear Layer ◽  
Flow Separation ◽  
Particle Image ◽  
Barrier Discharge ◽  
Separated Flow ◽  
Separation Control ◽  
Dielectric Barrier ◽  
Flow Separation Control ◽  
Image Velocimetry

The surface dielectric barrier discharge plasma actuator driven by nanosecond pulses is recognized as an effective fluid actuator for flow separation control. The operation condition of nanosecond dielectric barrier discharge actuators for separated flow control still requires further study, particularly prioritizing the improvement of the effectiveness and reducing energy consumption in flow separation control implementation. In this study, experiments are conducted using a two-dimensional NASA SC(2)-0712 airfoil in a wind tunnel with a Reynolds number of 0.5 × 106 (25 m/s). The pressure measurement experiments show that the location of actuators affects the efficiency of separation control. Particle image velocimetry results indicate that the most efficient location of the actuator is upstream of the separation point and near the original point of the separated shear layer. Meanwhile, the particle image velocimetry results show the vorticity attaches to the airfoil wall after discharge, which suggests that the reattachment is due to the generation of large-scale vortices. These present structures result in the mixing of the shear layer with the main flow thereby delaying separation and reattaching a separated flow. This study shows the most efficient location related to the separation point. Furthermore, it indicates the reattachment of flow is attributed to the motion of vortexes coherent structure.

Numerical Investigation of Flow in a Runner of Low-Head Bulb Turbine and Correlation With Particle Image Velocimetry and Laser Doppler Velocimetry Measurements

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
David Štefan ◽  
Sébastien Houde ◽  
Claire Deschênes
Keyword(s):  
Particle Image Velocimetry ◽  
Velocity Field ◽  
Laser Doppler Velocimetry ◽  
Particle Image ◽  
Draft Tube ◽  
Laser Doppler ◽  
Doppler Velocimetry ◽  
Image Velocimetry ◽  
Low Head ◽  
Bulb Turbine

It is a well-known fact and a much studied problematic that the performance of low-head hydraulic turbines is highly dependent on the runner–draft tube coupling. Around the optimal operating conditions, the efficiency of the turbine follows closely the performance of the draft tube that in turn depends on the velocity field exiting the runner. Hence, in order to predict correctly the performance of the draft tube using numerical simulations, the flow inside the runner must be simulated accurately. Using results from unique and detailed particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) measurements inside the runner channel of a bulb turbine, this paper presents an extensive study of the predictive capability of a widely used simulation methodology based on unsteady Reynolds-averaged Navier–Stokes equations with a k-epsilon closure model. The main objective was to identify the main parameters influencing the numerical predictions of the velocity field at the draft tube entrance in order to increase the accuracy of the simulated performance of the turbine. This paper relies on a comparison of simulations results with already published LDV measurements in the draft tube cone, interblade LDV, and stereoscopic PIV measurements within the runner. This paper presents a detailed discussion of numerical–experimental data correlation inside the runner channel and at the drat tube entrance. It shows that, contrary to widely circulated ideas, the near-wall predictions at the draft tube entrance is surprisingly good while the simulation accuracy inside the runner channels deteriorates from the leading to the trailing edges.

scholarly journals Investigation of Reverse Swing and Magnus Effect on a Cricket Ball Using Particle Image Velocimetry

2020 ◽  
Vol 10 (22) ◽  
pp. 7990
Author(s):  
Richard W. Jackson ◽  
Edmund Harberd ◽  
Gary D. Lock ◽  
James A. Scobie
Keyword(s):  
Boundary Layer ◽  
Particle Image Velocimetry ◽  
Flow Separation ◽  
Particle Image ◽  
Separation Bubble ◽  
Laminar Separation ◽  
Magnus Effect ◽  
Cricket Ball ◽  
Image Velocimetry ◽  
First Time

Lateral movement from the principal trajectory, or “swing”, can be generated on a cricket ball when its seam, which sits proud of the surface, is angled to the flow. The boundary layer on the two hemispheres divided by the seam is governed by the Reynolds number and the surface roughness; the swing is fundamentally caused by the pressure differences associated with asymmetric flow separation. Skillful bowlers impart a small backspin to create gyroscopic inertia and stabilize the seam position in flight. Under certain flow conditions, the resultant pressure asymmetry can reverse across the hemispheres and “reverse swing” will occur. In this paper, particle image velocimetry measurements of a scaled cricket ball are presented to interrogate the flow field and the physical mechanism for reverse swing. The results show that a laminar separation bubble forms on the non-seam side (hemisphere), causing the separation angle for the boundary layer to be increased relative to that on the seam side. For the first time, it is shown that the separation bubble is present even under large rates of backspin, suggesting that this flow feature is present under match conditions. The Magnus effect on a rotating ball is also demonstrated, with the position of flow separation on the upper (retreating) side delayed due to the reduced relative speed between the surface and the freestream.

scholarly journals Investigation of Flow Separation in a Diffuser of a Bulb Turbine

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Pierre Duquesne ◽  
Yvan Maciel ◽  
Claire Deschênes
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Separation ◽  
Particle Image ◽  
Separation Zone ◽  
Three Dimensional ◽  
Pressure Sensors ◽  
Sudden Drop ◽  
Convergence Line ◽  
Image Velocimetry ◽  
Bulb Turbine

A three-dimensional unsteady flow separation in the straight diffuser of a model bulb turbine is investigated using tuft visualizations, unsteady wall pressure sensors, and particle image velocimetry (PIV). Experimental results reveal a link between the flow separation zone extension and the sudden drop in turbine performances. The flow separation zone grows as the flow rate increases past the best efficiency operating point (OP). It starts on the bottom wall and expands azimuthally and upstream. It deviates and perturbs the flow far upstream. Despite high unsteadiness, a global separation streamline pattern composed of a saddle point and a convergence line emerges.

Experimental and Numerical Analysis of the Cavitating Part Load Vortex Dynamics of Low-Head Hydraulic Turbines

2011 ◽  
Author(s):  
Se´bastien Houde ◽  
Monica S. Iliescu ◽  
Richard Fraser ◽  
Se´bastien Lemay ◽  
Gabriel D. Ciocan ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Draft Tube ◽  
Experimental Methodology ◽  
Flow Measurements ◽  
Measured Velocity ◽  
Piv Measurements ◽  
Vortex Rope ◽  
Part Load ◽  
Image Velocimetry

The draft tube flow is a two-sided challenge for the operation of a hydraulic turbine. On one side, it is an important component for the performance of low to medium head turbines, where it can provide up to 40% of the extracted energy from the flow. On the other side, being a diffuser with a complex vorticity distribution at the inlet, vortex breakdown instability can occur at part load and generate a corkscrewed precessing vortex that can be associated with cavitation. The cavitating vortex rope, may generate undesired power output fluctuation and/or structural vibration. Therefore, draft tubes are much studied components but hard to tackle both numerically and experimentally. Within the framework of the AxialT project, the flow in the draft tube of a propeller turbine model operating at part load was studied using a combination of two-phase Particle Image Velocimetry (PIV) measurements and Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations. The paper main focus is on the experimental methodology and results. It explains how Particle Image Velocimetry measurements were implemented, validated and post-treated to provide flow measurements in the draft tube cone at part load in the cavitating and non-cavitating regimes. It also describes various image processing techniques used to extract the velocity field around the cavitating vortex rope and to estimate the location of the water-vapour interface of the cavitating region. In the spirit of feeding experimental data to numerical simulations, an analysis of measured velocity profiles just under the runner is presented. Comparison between PIV measurements and preliminary URANS simulations is also illustrated.

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