The response of wall-flow turbulence to high-frequency spanwise oscillations was investigated by direct numerical simulations a planar channel flow subjected either an oscillatory cross-flow or the motion wall. Periods oscillation, Tosc+=Toscuτ2/ν, ranging from 25 500 were studied. For 25≤Tosc+≤200 turbulent bursting process suppressed, leading sustained reductions 10% 40% in drag and comparable attenuations all three components intensities as well Reynolds shear stress. Oscillations at...

Experimental results on flow-field statistics are presented for turbulent oscillatory flow in a circular pipe the range of Reynolds numbers Re δ = U 0 δ/ν ( amplitude cross-sectional mean velocity, (2ν/ω) ½ ) Stokes layer thickness) from 550 to 2000 and parameters Λ R /δ radius pipe) 5 10. Axial radial velocity components were measured simultaneously using two-colour laser-Doppler anemometer, providing information ensemble-averaged profiles as well various turbulence different phases during...

The mechanism of turbulent drag reduction (DR) with super-hydrophobic (SH) surfaces is investigated by direct numerical simulation (DNS) and analysis the governing equations in channel flow. DNS studies were performed using lattice Boltzmann methods channels ‘idealized’ SH on both walls, comprised longitudinal micro-grooves (MG), transverse MG, or micro-posts. DRs $5\,\%$ to $83\,\%$ , $-4\,\%$ $20\,\%$ $14\,\%$ $81\,\%$ realized micro-posts, respectively. By mathematical equations, it shown...

Turbulent skin-friction drag reduction with superhydrophobic (SH) longitudinal microgrooves and riblets is investigated by direct numerical simulation (DNS), using lattice Boltzmann methods, in channel flow. The liquid/gas interfaces the SH were modelled as stationary, curved, shear-free boundaries, meniscus shape determined from solution of Young–Laplace equation. Interface protrusion angles $\unicode[STIX]{x1D703}=0^{\circ },-30^{\circ },-60^{\circ },-90^{\circ }$ investigated. For...

The stability of oscillatory channel flow to different classes infinitesimal and finite-amplitude two- three-dimensional disturbances has been investigated by direct numerical simulations the Navier–Stokes equations using spectral techniques. All were found decay monotonically a periodic steady state, in agreement with earlier Floquet theory calculations. However, before reaching this state an disturbance introduced boundary layer was seen experience transient growth accordance predictions...

The drag reduction characteristics and sustainability bounds of superhydrophobic (SH) surfaces in high Reynolds number turbulent flows are investigated using results from direct numerical simulation (DNS) scaling-law analysis. DNS studies were performed, lattice Boltzmann methods, channel at bulk numbers $Re_{b}=3600$ ( $Re_{\unicode[STIX]{x1D70F}_{0}}\approx 222$ ) $Re_{b}=7860$ 442$ with SH longitudinal microgrooves or aligned microposts on the walls. Surface microtexture geometrical...

The dynamics of subgrid-scale energy transfer in turbulence is investigated a database planar turbulent jet at Re λ ≈ 110, obtained by direct numerical simulation. In agreement with analytical predictions (Kraichnan 1976), found to arise from two effects: one involving non-local interactions between the resolved scales and disparate subgrid scales, other local near cutoff. former gives rise positive, wavenumber-independent eddy-viscosity distribution spectral space, manifested as...

A new nested-LES approach for computation of high Reynolds number, equilibrium, and non-equilibrium, wall-bounded turbulent flows is presented. The method couples coarse-resolution LES in the full computational domain with fine-resolution a minimal flow unit to retain accuracy well-resolved throughout domain, including near-wall region, while significantly reducing cost. two domains are coupled by renormalizing instantaneous velocity fields each dynamically during course simulation match...

The pressure difference across individual branches of a four-generation network branching tubes was measured with the objective obtaining general laws to describe drop in airways under conditions oscillatory flow. Fourier decomposition showed that signals consisted dominant component at excitation frequency (“fundamental”) and “first harmonic” smaller magnitude. For values ratio Re/alpha less than 200, fundamental mainly represented fluid acceleration, whereas first harmonic reflected...