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The Oriented-Eddy Collision (OEC) model treats turbulent flow as a non-Newtonian fluid where the average behavior of turbulence is modeled as a collection of interacting fluid particles which have inherent orientation. The model is derived from the two-point velocity correlation transport equation, and has the form of a collection of Reynolds-stress transport equations, with one set of transport equations for each representative eddy direction. The addition of eddy orientation information adds important physics to the model and allows the model to represent structural (two-point) information about the turbulence. This structural information is sufficient to allow the model to capture the effect of external forces and imposed mean strains (such as rapid distortion theory) exactly. The only physical effects that must be empirically modeled are those that are due to turbulence-turbulence interactions, referred to as eddy collisions. The performance of the model in a number of canonical flow situations is presented.

This work investigates how a highly (super)hydrophobic surface can be used to reduce turbulence-generated drag and noise on a towed streamer cable. The work is done by analyzing full-scale drag and flow noise measurements taken on a commercial seismic streamer in combination with direct numerical simulations of turbulence-generated flow noise. The main findings are that viscous drag and flow noise can be significantly reduced on a seismic streamer that is coated to make the surface highly hydrophobic. In an ocean towing test, a 4% reduction of drag on a streamer section was measured. In a separate test on a commercial seismic vessel, a reduction in the flow noise level of nearly 50% (6 dB) for frequencies below 10 Hz was found. Based upon an analysis of numerical simulation data, it is suggested that the reduction in drag and noise can be attributed to a reduced level of shear stress and change in the kinematic structure of the turbulence, both of which occur in the immediate vicinity of the highly hydrophobic surface.

Direct numerical simulations (DNSs) are used to investigate the drag-reducing performance of superhydrophobic surfaces (SHSs) in turbulent channel flow. SHSs combine surface roughness with hydrophobicity and can, in some cases, support a shear-free air–water interface. Slip velocities, wall shear stresses and Reynolds stresses are considered for a variety of SHS microfeature geometry configurations at a friction Reynolds number of Reτ ≈ 180. For the largest microfeature spacing studied, an average slip velocity over 75% of the bulk velocity is obtained, and the wall shear stress reduction is found to be nearly 40%. The simulation results suggest that the mean velocity profile near the superhydrophobic wall continues to scale with the wall shear stress but is offset by a slip velocity that increases with increasing microfeature spacing.

The objective of this study is to assess and quantify the effect of a superhydrophobic surface coating on turbulence-generated flow noise. The study utilizes results obtained from high Reynolds-number full-scale flow noise measurements taken on a commercial seismic streamer and results from low Reynolds-number direct numerical simulations. It is shown that it is possible to significantly reduce both the frictional drag and the levels of the turbulence generated flow noise even at very high Reynolds-numbers. For instance, frequencies below 10 Hz a reduction in the flow noise level of nearly 50% was measured. These results can be attributed to a reduced level of shear stress and change in the kinematic structure of the turbulence, both of which occur in the immediate vicinity of the superhydrophobic surface.

These surfaces have been shown to provide drag reduction in laminar and turbulent flows. In this work, direct numerical simulation is used to investigate the drag reducing performance of superhydrophobic surfaces in turbulent channel flow. Slip velocities, wall shear stresses, and Reynolds stresses are determined for a variety of superhydrophobic surface microfeature geometry configurations at friction Reynolds numbers of Re180, Re395, and Re590. This work provides evidence that superhydrophobic surfaces are capable of reducing drag in turbulent flow situations by manipulating the laminar sublayer. For the largest microfeature spacing, an average slip velocity over 80% of the bulk velocity is obtained, and the wall shear stress reduction is found to be greater than 50%. The simulation results suggest that the mean velocity profile near the superhydrophobic wall continues to scale with the wall shear stress and the log layer is still present, but both are offset by a slip velocity that is primarily dependent on the microfeature spacing. © 2010 American Institute of Physics. doi:10.1063/1.3432514