In five supine normal subjects breathing spontaneously, we studied the effects of high-frequency chest wall oscillation (HFCWO), which was achieved by oscillating the pressure in an air-filled cuff wrapped around the lower thorax. Oscillations of 3.5 and 8 Hz (in randomized order) were applied for 15 minutes each at both maximal (mean of 90 to 102cm H,O) and half-maximal peak tolerable cuff pre...

Bubbly cavitating flow generated by the normal oscillation of a wall bounding a semi-infinite domain of fluid is computed using a continuum two-phase flow model. Bubble dynamics are computed, on the microscale, using the Rayleigh–Plesset equation. A Lagrangian finite volume scheme and implicit adaptive time marching are employed to accurately resolve bubbly shock waves and other steep gradients...

Direct numerical simulation (DNS) is used to study the effect of individual (hemispherical) and distributed roughness on supersonic flat plate boundary layers. In both cases, roughness generates a shear layer and counter–rotating pairs of unsteady streamwise vortices. The vortices perturb the shear layer, resulting in trains of hairpin vortices and a highly unsteady flow. Mach 3.37 flow past a ...

Amplification of deterministic disturbances in inertialess shear-driven channel flows of viscoelastic fluids is examined by analysing the frequency responses from spatiotemporal body forces to the velocity and polymer stress fluctuations. In strongly elastic flows, we show that disturbances with large streamwise length scales may be significantly amplified even in the absence of inertia. For fl...

Λ-vortex plays a critical role in the boundary layer transition process. In this paper, the mechanism of Λ-shaped rotational core formation is studied by DNS. The Blasius velocity profile is found to be the vorticity resource. The aggregation of vorticity (vortex filaments) is caused by the 2-D T-S wave. The mechanism of clustering of spanwise vorticity by 2-D T-S wave to form vortex tubes is s...

Streamwise and spanwise flow pattern over three rounded contour bumps with different flow control strategies employed have been experimentally investigated in a Mach 1.3 freestream. Surface oil flow visualisation, Schlieren photography and particle image velocimetry measurements were used for flow diagnostics. Experimental data showed that in a Mach 1.3 freestream over the baseline plain bump, ...

Highly-swept blades are used in automotive cooling systems, the fans of modern ultra-high by-pass ratio engines and counter-rotating open rotors, part order to reduce noise emission. The present work investigates effect sweep on free-field emission from trailing edge an isolated airfoil analytically, as a first step towards more complete approach dedicated rotating blades. Firstly, Amiet–Schwar...

It is shown how well-chosen perforations in a wall flow can locally reduce skin friction drag by modifying the generation of bursts boundary layer. For this purpose, detailed hot wire layer experimental investigation past perforated plate, complemented with large eddy simulations, carried out and compared to smooth case. The plate obtained an array flush-mounted circular cavities. These cavitie...

We analyse the inter-scale transfer of energy for two types plane Poiseuille flow: P4U exact coherent state Park and Graham (2015) turbulent flow in a minimal channel. For both flows, dominant energy-producing modes are streamwise-constant streaks with spanwise spacing approximately 100 wall units. Since viscous dissipation these scales is not sufficient to balance production, nonlinear terms r...

A short series of experiments was conducted with the aim of assessing the possible effect of tunnel blockage on spanwise correlation lengths measured in the near-wake of a circular cylinder. The results indicate that increasing blockage acts to increase spanwise correlation. This finding has important implications for the conduct and reporting of both physical and numerical experiments on bluff...