Coherent structures and their impact on the near-bed time-averaged flow structure in a water-worked gravel-bed (WGB) and a screeded gravel-bed (SGB) are analyzed. Instantaneous velocities were measured using a particle image velocimetry system in the WGB and SGB flows in a flume with rectangular cross section. To ascertain the response of the WGB with respect to the SGB to the coherent structures, the timeand double-averaged flow, and the spatially averaged (SA) turbulence parameters, the experimental flow conditions for both the beds were kept identical. The surface gravels in the WGB were spatially organized owing to the water action. By contrast, the surface gravels in the SGB were randomly poised. These result in a higher roughness height in the WGB than in the SGB. Time series analysis for the instantaneous velocity and vorticity on a central vertical plane along the streamwise direction proves that the coherent structures in the near-bed flow zone are constituted by rapidly and slowly moving fluid streaks. Besides, the time-averaged streamwise velocity, vorticity, turbulence level, third-order correlations, and turbulent kinetic energy (TKE) budget are analyzed in the WGB and SGB. Their contours are plotted on the central vertical plane to study their spatial distributions. In addition, the SA higher-order correlations and TKE budget in the WGB and SGB are examined. A comparative study infers that the higher roughness in the WGB than in the SGB causes both the time-averaged and SA turbulence parameters in the former to be greater than those in the latter.

Near-bed turbulence structures in water-worked and screeded gravel-bed flows

Nadia Penna;Roberto Gaudio
2019

Abstract

Coherent structures and their impact on the near-bed time-averaged flow structure in a water-worked gravel-bed (WGB) and a screeded gravel-bed (SGB) are analyzed. Instantaneous velocities were measured using a particle image velocimetry system in the WGB and SGB flows in a flume with rectangular cross section. To ascertain the response of the WGB with respect to the SGB to the coherent structures, the timeand double-averaged flow, and the spatially averaged (SA) turbulence parameters, the experimental flow conditions for both the beds were kept identical. The surface gravels in the WGB were spatially organized owing to the water action. By contrast, the surface gravels in the SGB were randomly poised. These result in a higher roughness height in the WGB than in the SGB. Time series analysis for the instantaneous velocity and vorticity on a central vertical plane along the streamwise direction proves that the coherent structures in the near-bed flow zone are constituted by rapidly and slowly moving fluid streaks. Besides, the time-averaged streamwise velocity, vorticity, turbulence level, third-order correlations, and turbulent kinetic energy (TKE) budget are analyzed in the WGB and SGB. Their contours are plotted on the central vertical plane to study their spatial distributions. In addition, the SA higher-order correlations and TKE budget in the WGB and SGB are examined. A comparative study infers that the higher roughness in the WGB than in the SGB causes both the time-averaged and SA turbulence parameters in the former to be greater than those in the latter.
File in questo prodotto:
File Dimensione Formato  
Padhi et alii 2019 - Accepted manuscript.pdf

accesso aperto

Descrizione: This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Ellora Padhi, Nadia Penna, Subhasish Dey, and Roberto Gaudio, "Near-bed turbulence structures in water-worked and screeded gravel-bed flows", Physics of Fluids 31, 045107 (2019) https://doi.org/10.1063/1.5092442 and may be found at ( https://doi.org/10.1063/1.5092442). Source: American Institute of Physics.
Tipologia: Documento in Post-print
Licenza: Copyright dell'editore
Dimensione 11.01 MB
Formato Adobe PDF
11.01 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.11770/293194
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 14
  • ???jsp.display-item.citation.isi??? 14
social impact