Accession Number : ADA266226


Title :   Ventilated Oscillatory Boundary Layers


Corporate Author : SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA CENTER FOR COASTAL STUDIES


Personal Author(s) : Conley, Daniel C ; Inman, Douglas L


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a266226.pdf


Report Date : Feb 1993


Pagination or Media Count : 80


Abstract : A combination of field and laboratory experiments are made in order to expand our knowledge of naturally occurring oscillatory boundary layers. Chapter 1 describes field observations of the development of wave driven boundary layers at the fluid sediment interface. Under the crest of the wave, this development can be idealized as an identifiable sequence of three parts. The latter parts of this development are never observed to occur under the trough of the wave despite similarities in wave orbital velocity and acceleration. It is proposed that wave induced boundary ventilation, the oscillatory flow through the surface of a permeable bed, may be responsible for this apparent developmental asymmetry. In chapter 2, a laboratory study is presented of ventilated oscillatory boundary layers. These are boundary layers arising from a flow which oscillates parallel to a permeable bed which is subject to oscillating percolation of the same frequency as the bed parallel flow. Measurements of boundary layer velocities, bed stress and turbulent flow properties are presented. It is observed that suction (flow into the bed) enhances the near bed velocities and bed stress while injection (flow out of the bed) leads to a reduction in these quantities. As the ventilated oscillatory boundary layer experiences both these phenomena in one full cycle, the result is a net stress and a net boundary layer velocity in an otherwise symmetric flow. While production of turbulence attributable to injection is enhanced, the finite time required for this to occur leads to greater vertically averaged turbulence in the suction half cycle. Turbulence generated in the suction half cycle is maintained in a compact layer much closer to the bed. These effects appear to hold for Re ranging from 10(100,000) to 10(1,000,000) and for oscillations other than sinusoidal.


Descriptors :   *OCEAN WAVES , *TURBULENT BOUNDARY LAYER , *SEDIMENT TRANSPORT , *BOUNDARY LAYER FLOW , STRESSES , VELOCITY , FREQUENCY , INJECTION , ACCELERATION , WIND , TURBULENCE , OSCILLATION , AIR WATER INTERACTIONS , MIXED LAYER(MARINE) , SLOPE , SHEAR STRESSES , ASYMMETRY , SURFACES , CYCLES , SAND , TROUGHS , PERCOLATION , FLUID FLOW , BEACHES , SEDIMENTS , SUCTION , TURBULENT FLOW , BOUNDARY LAYER , VENTILATION , INTERFACES , MEASUREMENT , THICKNESS , COASTAL REGIONS


Subject Categories : Physical and Dynamic Oceanography
      Fluid Mechanics


Distribution Statement : APPROVED FOR PUBLIC RELEASE