LARGE-SCALE TURBULENCE STRUCTURES OVER AN IMMOBILE GRAVEL-BED INSIDE THE SURF ZONE

2003 ◽  
Author(s):  
Javier L. Lara ◽  
Inigo J. Losada ◽  
Edwin A. Cowen
Keyword(s):  
Large Scale ◽  
Surf Zone ◽  
Gravel Bed ◽  
Turbulence Structures ◽  
Scale Turbulence

Evolution of the turbulence structure in the surf and swash zones

2010 ◽  
Vol 644 ◽  
pp. 193-216 ◽  
Author(s):  
IN MEI SOU ◽  
EDWIN A. COWEN ◽  
PHILIP L.-F. LIU
Keyword(s):  
Large Scale ◽  
Surf Zone ◽  
Early Stage ◽  
Vertical Plane ◽  
Turbulence Energy ◽  
Breaking Wave ◽  
Turbulence Structure ◽  
Grid Turbulence ◽  
Mean Flow ◽  
Scale Turbulence

The velocity field and turbulence structure within the surf and swash zones forced by a laboratory-generated plunging breaking wave were investigated using a particle image velocimetry measurement technique. Two-dimensional velocity fields in the vertical plane from 200 consecutive monochromatic waves were measured at four cross-shore locations, shoreward of the breaker line. The phase-averaged mean flow fields indicate that a shear layer occurs when the uprush of the bore front interacts with the downwash flow. The turbulence characteristics were examined via spectral analysis. The larger-scale turbulence structure is closely associated with the breaking-wave- and the bore-generated turbulence in the surf zone; then, the large-scale turbulence energy cascades to smaller scales, as the turbulent kinetic energy (TKE) evolves from the outer surf zone to the swash zone. Smaller-scale energy injection during the latter stage of the downwash phase is associated with the bed-generated turbulence, yielding a −1 slope in the upper inertial range in the spatial spectra. Depth-integrated TKE budget components indicate that a local TKE equilibrium exists during the bore-front phases and the latter stage of the downwash phases in the outer surf zone. The TKE decay resembles the decay of grid turbulence during the latter stage of the uprush and the early stage of the downwash, as the production rate is small because of the absence of strong mean shear during this stage of the wave cycle as well as the relatively short time available for the growth of the bed boundary layer.

scholarly journals Large-scale turbulence structures in a laboratory-scale boundary layer under steady and gusty wind inflows

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
W. J. Li ◽  
Y. Zhang ◽  
B. Yang ◽  
J. W. Su ◽  
Y. W. Zhang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Laboratory Scale ◽  
Turbulence Structures ◽  
Scale Turbulence

Experimental and numerical study of mixing characteristics of a rectangular lobed mixer in supersonic flow

2015 ◽  
Vol 119 (1216) ◽  
pp. 701-725 ◽  
Author(s):  
J.-H. Feng ◽  
C.-B. Shen ◽  
Q.-C. Wang ◽  
J. Lei
Keyword(s):  
Total Pressure ◽  
Large Scale ◽  
Pressure Ratio ◽  
Velocity Ratio ◽  
Interfacial Area ◽  
Small Scale ◽  
Trailing Edge ◽  
Turbulence Structures ◽  
Scale Turbulence ◽  
Total Pressure Ratio

AbstractA combined experimental and computational study on a rectangular lobed mixer is performed. A series of simulations based on a steady Reynolds-averaged Navier-Stokes Simulation (RANS) are conducted to analyse the mixing mechanisms of large-scale streamwise structure shed by the trailing edge of lobed mixer, with emphasis being placed on the effect of turbulence modeling and inflow conditions. The simulations are validated in respect of velocity and scalar distribution against the data obtained through Particle Image Velocimetry (PIV) and Nanoparticle-based Planar Laser Scattering (NPLS) technique. The computational results predicted by the SSTk–ω turbulence model show better agreement with the experimental data. But the small-scale turbulence structures are not captured accurately by these turbulence models. The convoluted shear layer shed from trailing edge is stretched and rotated by the large-scale streamwise vortices, forming an unstable ‘pinching-off’ structure, which increases the interfacial area. And at the interface of two streams, a large number of small-scale turbulence structures are formed, which contribute a lot to the mixing enhancement along with the increased interfacial area. The streamwise vorticity decays more rapidly with the decrease of velocity ratio and total pressure ratio of two streams. The scalar thickness which reflects the mixing rate of two streams increases with the decreasing velocity ratio and total pressure ratio.

scholarly journals Towards Prediction and Control of Large Scale Turbulent Structure Supersonic Jet Noise

2009 ◽  
Author(s):  
Robert H. Schlinker ◽  
Ramons A. Reba ◽  
John C. Simonich ◽  
Tim Colonius ◽  
Kristjan Gudmundsson ◽  
...  
Keyword(s):  
Large Scale ◽  
Deterministic Model ◽  
Near Field ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Shear Layers ◽  
Instability Wave ◽  
Turbulent Structures ◽  
Turbulence Structures ◽  
Scale Turbulence

In this paper, we report on progress towards developing physics-based models of sound generation by large-scale turbulent structures in supersonic jet shear layers generally accepted to be the source of aft-angle noise. Aside from obtaining better engineering prediction schemes, the development and optimization of long term jet noise reduction strategies based on controlling instability wave generated large-scale turbulence structures in the shear layer can be more successful if based on predictive flow-noise models, rather than on build and test approaches alone. Such models, if successful, may also provide a path by which laboratory scale demonstrations can be more reliably translated to engine scale. Results show that the noise radiated by large-scale structures in turbulent jet shear layers may be modeled using a RANS based PSE method and projected to the far-field using a Kirchhoff surface approach. A key enabler in this procedure is the development of near-field microphone arrays capable of providing the pressure statistics needed to validate the instability wave models. Our framework provides, for the first time, a deterministic model that will allow understanding and predicting noise radiated by large-scale turbulence.

scholarly journals Role of large-scale advection and small-scale turbulence on vertical migration of gyrotactic swimmers

2019 ◽  
Vol 4 (12) ◽  
Author(s):  
C. Marchioli ◽  
H. Bhatia ◽  
G. Sardina ◽  
L. Brandt ◽  
A. Soldati
Keyword(s):  
Vertical Migration ◽  
Large Scale ◽  
Small Scale ◽  
Scale Turbulence
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