Graduate Thesis Or Dissertation

 

DNS study of Particle-bed-Turbulence Interactions in Oscillatory Flows Public Deposited

Downloadable Content

Download PDF
https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sf268951f

Descriptions

Attribute NameValues
Creator
Abstract
  • Turbulent flows over rough surfaces are encountered in many engineering and geophysical applications. Flows of this nature, due to their increasing technological interests, have been a subject of rigorous investigation in recent years. Of the particular interest to the oceanographic community is the study of turbulent oscillatory flow over rough surfaces, representative of sediment-bed in a coastal environment. In particular, formulation of predictive criteria for onset of sediment motion requires detailed knowledge of the dynamics of the near-bed turbulence structure and resultant variations in the magnitudes and time-scales of the destabilizing drag and lift forces on sediment grains. The primary objectives of this work are (i) to quantify, using high-fidelity numerical experiments, sediment grain-turbulence interactions and (ii) provide data on the temporal variations in the magnitude of drag and lift forces on sediment grains, the time-scales associated with these variations, and their correlations with the near-bed turbulence in an oscillatory flow environment. To this end, particle-resolved direct numerical simulations (DNS) are performed to investigate the behavior of an oscillatory flow field over a bed of closely packed fixed spherical particles for a range of Reynolds numbers in transitional and rough turbulent flow regime. Presence of roughness leads to a substantial modification of the underlying boundary layer mechanism resulting in increased bed shear stress, reduction in the near-bed anisotropy, modification of the near-bed sweep and ejection motions along with marked changes in turbulent energy transport mechanisms. Characterization of such resulting flow field is performed by studying statistical descriptions of the near-bed turbulence for different roughness parameters. A double-averaging technique is employed to reveal spatial inhomogeneities at the roughness scale that provide alternate paths of energy transport in the turbulent kinetic energy (TKE) budget. Spatio-temporal characteristics of unsteady particle forces by studying their spatial distribution, temporal auto-correlations, frequency spectra as well as cross-correlations with near-bed turbulent flow variables are reported. Intermittency in the forces by means of impulse is also investigated.
Resource Type
Date Available
Date Copyright
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Committee Member
Academic Affiliation
Non-Academic Affiliation
Keyword
Subject
Rights Statement
Peer Reviewed
Language
Replaces

Relationships

Parents:

This work has no parents.

Items