Experimental investigation of flow development and gap vortex street in an eccentric annular channel. Part 1. Overview of the flow structure

2014 ◽  
Vol 752 ◽  
pp. 521-542 ◽  
Author(s):  
George H. Choueiri ◽  
Stavros Tavoularis
Keyword(s):  
Laser Doppler Velocimetry ◽  
Large Scale ◽  
Particle Image ◽  
Annular Channel ◽  
Stereoscopic Particle Image Velocimetry ◽  
Entrance Region ◽  
Narrow Gap ◽  
Velocity Fluctuations ◽  
Flow Development ◽  
Image Velocimetry

AbstractFlow visualization, laser Doppler velocimetry and planar and stereoscopic particle image velocimetry were used to investigate the isothermal velocity field along an eccentric annular channel with a diameter ratio of 0.5 and an eccentricity of 0.8 for a Reynolds number of 7300. Observation of the flow development has identified three distinct regions: the entrance region, the fluctuation-growth (FG) region and the rapid-mixing (RM) region. Weak quasi-periodic velocity fluctuations were first detected in the downstream part of the entrance region, and grew into very strong ones, reaching peak-to-peak amplitudes in the narrow gap that were nearly 60 % of the bulk velocity. Two mixing layers were identified on either side of the gap, which generated a street of counter rotating vortices and thorough large-scale mixing of the fluid in the channel.

Experimental measurement of large-scale three-dimensional structures in a turbulent boundary layer. Part 2. Long structures

2011 ◽  
Vol 673 ◽  
pp. 218-244 ◽  
Author(s):  
DAVID J. C. DENNIS ◽  
TIMOTHY B. NICKELS
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
High Speed ◽  
Large Scale ◽  
Particle Image ◽  
Three Dimensional ◽  
Velocity Fluctuations ◽  
Taylor’S Hypothesis ◽  
Image Velocimetry ◽  
Streamwise Structures

Three-dimensional (3D) measurements of a turbulent boundary layer have been made using high-speed particle image velocimetry (PIV) coupled with Taylor's hypothesis, with the objective of characterising the very long streamwise structures that have been observed previously. The measurements show the 3D character of both low- and high-speed structures over very long volumes. The statistics of these structures are considered, as is their relationship to the important turbulence quantities. In particular, the length of the structures and their wall-normal extent have been considered and their relationship to the other components of the velocity fluctuations and the instantaneous stress.

scholarly journals Experimental Study by Optical and Statistical Methods of Large-Scale Velocity Fluctuations in the Flow Past a Cylinder

2019 ◽  
Vol 14 (3) ◽  
pp. 5-14
Author(s):  
S. S. Abdurakipov ◽  
K. G. Dobroselsky
Keyword(s):  
Experimental Study ◽  
Turbulent Flows ◽  
Large Scale ◽  
Particle Image ◽  
Velocity Fields ◽  
Velocity Fluctuations ◽  
Flow Past ◽  
Image Velocimetry ◽  
Flow Past A Cylinder ◽  
Proper Orthogonal

Using an optical method for measuring the velocity fields Particle Image Velocimetry (PIV) and a statistical method for analyzing coherent structures in turbulent flows Proper Orthogonal Decomposition (POD), an experimental study of the spatial structure of large-scale velocity fluctuations in the precavitational and cavitational flow past a circular cylinder with a Reynolds number of 280 000 was carried out.

Experimental Investigation of Unsteady Flow Field in the Tip Region of an Axial Compressor Rotor Passage at Near Stall Condition With Stereoscopic Particle Image Velocimetry

2004 ◽  
Vol 126 (3) ◽  
pp. 360-374 ◽  
Author(s):  
Baojie Liu ◽  
Hongwei Wang ◽  
Huoxing Liu ◽  
Hongjun Yu ◽  
Haokang Jiang ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Large Scale ◽  
Particle Image ◽  
Light Sheet ◽  
Stereoscopic Particle Image Velocimetry ◽  
Flow Section ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Image Velocimetry ◽  
Corner Vortex

Stereoscopic particle image velocimetry (SPIV) was applied to a large-scale low-speed compressor facility with the configuration of the two CCD cameras placed on each side of the light sheet to make the measurement of the vortices in the cross flow section possible and to avoid the disturbance from the light sheet containing periscope-type probe. Instantaneous velocity and vorticity distributions were successfully documented at the tip region of the rotor at near stall condition. The measurement results clearly revealed the generation and evolution of the tip leakage vortex. Comparing to design condition, the tip leakage vortex at near stall condition generates and breaks down earlier and interacts more violently with mainstream, which causes large blockage and much loss. Whether corner vortex exists or not is the primary difference between near stall and design condition. Differing from the leakage vortex, the corner vortex is composed of multiple vortices developed from the suction surface of the rotor blade. The key mechanism for the generation of the corner vortex is that the rotation of the rotor has different effect on the evolution of positive vortices and negative vortices, which makes the positive vortices dissipates faster than the negative ones, the vortices at the rotor exit therefore bear mainly negative vortices, which induces the fluids to rotate clockwise at the corner and forms the corner vortex.

Detailed Analysis of the Wake of a DP Thruster Emphasizing Comparison Between LDV and SPIV Techniques

2005 ◽  
Vol 128 (2) ◽  
pp. 81-88
Author(s):  
S. El Lababidy ◽  
N. Bose ◽  
P. Liu ◽  
F. Di Felice
Keyword(s):  
Detailed Analysis ◽  
Laser Doppler Velocimetry ◽  
Particle Image ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Hydrodynamic Characteristics ◽  
Dynamic Positioning ◽  
Doppler Velocimetry ◽  
Image Velocimetry ◽  
Variable Operating Conditions

To provide experimental data on the hydrodynamic characteristics and features of dynamic positioning (DP) thrusters under variable operating conditions, wake measurements were performed on a DP thruster model using 2D laser Doppler velocimetry (LDV) and stereoscopic particle image velocimetry (SPIV). These tests were performed with and without a nozzle and over a range of advance coefficient values including the bollard pull condition. In this paper, a detailed analysis of the hydrodynamic characteristics of the wake at a plane equal to a distance of 0.5 diameters downstream from the thruster, at advance coefficient values of 0, 0.4, and 0.45 are presented for both the LDV and SPIV measurements showing a comparison between the results of each technique. The effect of the duct and of changes in the advance coefficient values is presented in this paper.

Development and Testing of an Unmanned Aerial Vehicle for Large Scale Particle Image Velocimetry

2014 ◽  
Author(s):  
Christopher Pagano ◽  
Flavia Tauro ◽  
Salvatore Grimaldi ◽  
Maurizio Porfiri
Keyword(s):  
Particle Image Velocimetry ◽  
Large Scale ◽  
Field Experiments ◽  
Particle Image ◽  
Low Cost ◽  
Surface Flow ◽  
Natural Environments ◽  
Natural Stream ◽  
Image Velocimetry ◽  
Scale Particle

Large scale particle image velocimetry (LSPIV) is a nonintrusive environmental monitoring methodology that allows for continuous characterization of surface flows in natural catchments. Despite its promise, the implementation of LSPIV in natural environments is limited to areas accessible to human operators. In this work, we propose a novel experimental configuration that allows for unsupervised LSPIV over large water bodies. Specifically, we design, develop, and characterize a lightweight, low cost, and stable quadricopter hosting a digital acquisition system. An active gimbal maintains the camera lens orthogonal to the water surface, thus preventing severe image distortions. Field experiments are performed to characterize the vehicle and assess the feasibility of the approach. We demonstrate that the quadricopter can hover above an area of 1×1m2 for 4–5 minutes with a payload of 500g. Further, LSPIV measurements on a natural stream confirm that the methodology can be reliably used for surface flow studies.

scholarly journals Turbulent drag in a rotating frame

2016 ◽  
Vol 794 ◽  
Author(s):  
Antoine Campagne ◽  
Nathanaël Machicoane ◽  
Basile Gallet ◽  
Pierre-Philippe Cortet ◽  
Frédéric Moisy
Keyword(s):  
Large Scale ◽  
Scaling Law ◽  
Stereoscopic Particle Image Velocimetry ◽  
Turbulence Theory ◽  
Water Tank ◽  
Wave Interactions ◽  
Turbulent Drag ◽  
Image Velocimetry ◽  
Weak Turbulence Theory ◽  
Large Scale Flow

What is the turbulent drag force experienced by an object moving in a rotating fluid? This open and fundamental question can be addressed by measuring the torque needed to drive an impeller at a constant angular velocity ${\it\omega}$ in a water tank mounted on a platform rotating at a rate ${\it\Omega}$. We report a dramatic reduction in drag as ${\it\Omega}$ increases, down to values as low as 12 % of the non-rotating drag. At small Rossby number $Ro={\it\omega}/{\it\Omega}$, the decrease in the drag coefficient $K$ follows the approximate scaling law $K\sim Ro$, which is predicted in the framework of nonlinear inertial-wave interactions and weak-turbulence theory. However, stereoscopic particle image velocimetry measurements indicate that this drag reduction instead originates from a weakening of the turbulence intensity in line with the two-dimensionalization of the large-scale flow.

An experimental and numerical study of the resonant flow between a hull and a wall

2021 ◽  
Vol 930 ◽  
Author(s):  
I.A. Milne ◽  
O. Kimmoun ◽  
J.M.R. Graham ◽  
B. Molin
Keyword(s):  
Vortex Shedding ◽  
Particle Image ◽  
Numerical Study ◽  
Numerical Models ◽  
Vertical Wall ◽  
Liquefied Natural Gas ◽  
Narrow Gap ◽  
Image Velocimetry ◽  
High Degree ◽  
Wave Induced

The wave-induced resonant flow in a narrow gap between a stationary hull and a vertical wall is studied experimentally and numerically. Vortex shedding from the sharp bilge edge of the hull gives rise to a quadratically damped free surface response in the gap, where the damping coefficient is approximately independent of wave steepness and frequency. Particle image velocimetry and direct numerical simulations were used to characterise the shedding dynamics and explore the influence of discretisation in the measurements and computations. Secondary separation was identified as a particular feature which occurred at the hull bilge in these gap flows. This can result in the generation of a system with multiple vortical regions and asymmetries between the inflow and outflow. The shedding dynamics was found to exhibit a high degree of invariance to the amplitude in the gap and the spanwise position of the barge. The new measurements and the evaluation of numerical models of varying fidelity can assist in informing offshore operations such as the side by side offloading from floating liquefied natural gas facilities.

Sign in / Sign up

Export Citation Format

Share Document