scholarly journals Laboratory experiments for intense vortical structures in turbulence velocity fields

2007 ◽  
Vol 19 (5) ◽  
pp. 055101 ◽  
Author(s):  
Hideaki Mouri ◽  
Akihiro Hori ◽  
Yoshihide Kawashima
Keyword(s):  
Laboratory Experiments ◽  
Velocity Fields ◽  
Vortical Structures ◽  
Turbulence Velocity

Characteristics of Large Vortical Structures in the Shallow Wake Flow With a Gap Near the Bed

2018 ◽  
Author(s):  
Monsif Shinneeb ◽  
Ram Balachandar
Keyword(s):  
Bluff Body ◽  
Velocity Fields ◽  
Wake Flow ◽  
Identification Algorithm ◽  
Vortex Identification ◽  
Reference Case ◽  
Vortical Structures ◽  
Gap Flow ◽  
Vortex Size ◽  
Proper Orthogonal

PIV measurements were made to investigate the turbulent wake flow generated by a vertical sharp-edged flat plate suspended in a shallow channel flow with a gap near the bed. The purpose of this study is to investigate the behaviour of large vortical structures in the wake flow. The investigation focused on the horizontal velocity field in the mid-distance between the bottom bed and the top free surface. Two different gap heights between the channel bed and the bottom edge of the bluff body was studied. These two cases were compared to the no-gap flow case which is considered as a reference case. The Reynolds number based on the water depth was 45,000. The large vortical structures were exposed by analyzing the PIV velocity fields using the proper orthogonal decomposition (POD) method. Only few modes were used for the POD reconstruction of the velocity fields to recover ∼50% of the turbulent kinetic energy. A vortex identification algorithm was then employed to quantify the number, size, circulation, and direction of rotation of the exposed vortices. A statistical analysis of the distribution of number, size, and strength of the identified vortices was carried out to explore the characteristics of the vortical structures. The results revealed that the number of vortical structures increased as a result of the gap flow with a corresponding decrease in the vortex size and strength. This behaviour is attributed to the production of new vortices and the enhancement of the tearing process.

Effects of vortex-induced velocity on the development of a synthetic jet issuing into a turbulent boundary layer

2019 ◽  
Vol 870 ◽  
pp. 651-679 ◽  
Author(s):  
Tim Berk ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Velocity Field ◽  
Momentum Transfer ◽  
Momentum Flux ◽  
Cross Flow ◽  
Measured Data ◽  
Velocity Fields ◽  
Synthetic Jet ◽  
Vortical Structures ◽  
The Cross ◽  
Induced Velocity

A synthetic jet issuing into a cross-flow influences the local velocity of the cross-flow. At the jet exit the jet is oriented in the wall-normal direction while the cross-flow is oriented in the streamwise direction, leading to a momentum transfer between the jet and the cross-flow. Streamwise momentum transferred from the cross-flow to the jet accelerates the pulses created by the jet. This momentum transfer continuous up to some point downstream where these pulses have the same velocity as the surrounding flow and are no longer blocking the cross-flow. The momentum transfer from the cross-flow to the jet leads to a momentum deficit in the cross-flow far downstream of the viscous near field of the jet. In the literature this momentum-flux deficit is often attributed to viscous blockage or to up-wash of low-momentum fluid. The present paper proposes and quantifies a third source of momentum deficit: a velocity induced opposite to the cross-flow by the vortical structures created by the synthetic jet. These vortical structures are reconstructed from measured data and their induced velocity is calculated using the Biot–Savart law. The three-dimensional three-component induced velocity fields show great similarity to the measured velocity fields, suggesting that this induced velocity is the main contributor to the velocity field around the synthetic jet and viscous effects have only a small influence. The momentum-flux deficit induced by the vortical structures is compared to the measured momentum-flux deficit, showing that the main part of this deficit is caused by the induced velocity. Variations with Strouhal number (frequency of the jet) and velocity ratio (velocity of the jet) are observed and discussed. An inviscid-flow model is developed, which represents the downstream evolution of the jet in cross-flow. Using the measured data as an input, this model is able to predict the deformation, (wall-normal) evolution and qualitative velocity field of the jet. The present study presents evidence that the velocity induced by the vortical structures forming a synthetic jet plays an important role in the development of and the velocity field around the jet.

scholarly journals THE DISSIPATION OF WAVE ENERGY BY TURBULENCE

1980 ◽  
Vol 1 (17) ◽  
pp. 52
Author(s):  
Yu Kuang-ming
Keyword(s):  
General Theory ◽  
Wave Energy ◽  
Laboratory Experiments ◽  
Velocity Fields ◽  
Mixing Length ◽  
Two Dimensional ◽  
Two Dimensional Flow ◽  
The Mean ◽  
Vertical Gradients ◽  
Horizontal Area

This paper first gives a brief review of the existing research works on the laws governing the dissipation of rave energy by turbulence. Starting from the general theory of turbulent motion and the writer's suggestion in regard to the mixing length of water particles in two-dimensional flow and making use of the principle of dimensional analysis and the trochidal rave theory, a formula has been derived to compute the mean dissipation per unit time and per unit horizontal area of wave energy due to turbulence. The formula takes the horizontal and vertical gradients of both the horizontal and vertical velocity fields into consideration. Coefficient in the formula has been determined through laboratory experiments.

Vortex force decomposition in the tip region of impulsively-started flat plates

2014 ◽  
Vol 756 ◽  
pp. 758-770 ◽  
Author(s):  
Jochen Kriegseis ◽  
David E. Rival
Keyword(s):  
Particle Tracking Velocimetry ◽  
Three Dimensional ◽  
Velocity Fields ◽  
The Body ◽  
Flat Plates ◽  
Impulsive Motion ◽  
Vortical Structures ◽  
Low Aspect Ratio ◽  
Force Moment ◽  
Force Decomposition

AbstractAn investigation into the influence of seemingly analogous kinematics (plunge versus tow) for rapidly accelerating, low-aspect-ratio plates has been performed. The instantaneous forces and velocity fields were obtained simultaneously using a six-component force/moment sensor together with a three-dimensional particle tracking velocimetry (3D-PTV) system. Despite identical effective shear-layer velocities and effective angles of attack, the force histories are found to vary between the two aforementioned cases (plunge versus tow) once the impulsive motion is complete, as originally reported on by Kriegseis et al. (J. Fluid Mech., vol. 736, 2013, pp. 91–106). In order to uncover the cause for this curious discrepancy between the two analogous cases a vortex force decomposition is implemented. It is shown that the interplay between growth and orientation of the vortical structures significantly affects vortical hydrodynamic impulse and vortex force, and thus the net lift on the body.

scholarly journals Vortex tubes in turbulence velocity fields at Reynolds numbersReλ≃300–1300

2004 ◽  
Vol 70 (6) ◽  
Author(s):  
Hideaki Mouri ◽  
Akihiro Hori ◽  
Yoshihide Kawashima
Keyword(s):  
Velocity Fields ◽  
Turbulence Velocity ◽  
Vortex Tubes

scholarly journals Large-scale lognormal fluctuations in turbulence velocity fields

2009 ◽  
Vol 21 (6) ◽  
pp. 065107 ◽  
Author(s):  
Hideaki Mouri ◽  
Akihiro Hori ◽  
Masanori Takaoka
Keyword(s):  
Large Scale ◽  
Velocity Fields ◽  
Turbulence Velocity
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