A well-resolved large eddy simulation (LES) of a large-eddy breakup (LEBU) device in a spatially evolving turbulent boundary layer is performed with, Reynolds number, based on free-stream velocity and momentumloss thickness, of Re θ ≈ 4300. The implementation of the LEBU is via an immersed boundary method. The LEBU is positioned at a wall-normal distance of 0.8δ (δ denoting the local boundary layer thickness at the location of the LEBU) from the wall. The LEBU acts to delay the growth of the turbulent boundary layer and produces global skin friction reduction beyond 180δ downstream of the LEBU, with a peak local skin friction reduction of approximately 12%. However, no net drag reduction is found when accounting for the device drag of the LEBU in accordance with the towing tank experiments by Sahlin et al. (Phys. Fluids 31, 2814. Further investigation is performed on the interactions of high and low momentum bulges with the LEBU and the corresponding output is analysed, showing a 'break-up' of these large momentum bulges downstream of the LEBU. In addition, results from the spanwise energy spectra show consistent reduction in energy at spanwise length scales for λ + z > 1000 independent of streamwise and wall-normal location when compared to the corresponding turbulent boundary layer without LEBU.

Aortic dissection is a serious cardiovascular condition where tears in the aortic wall lead to blood flow in between arterial tissue layers, separating the tissue and forming a false lumen. Knowledge of the blood flow dynamics for patients with aortic dissection can inform the treatment of aortic dissection. This paper aims to present haemodynamic metrics found in aortic dissection. In this study, individual patient-specific geometry and pulsatile flow velocity data is extracted from computed tomography (CT) angiography and four-dimensional flow magnetic resonance imaging (4D flow MRI) respectively, with MRI data introduced as boundary conditions for computational fluid dynamics (CFD) simulation. Numerical simulation data shows the presence of vortical flow structures proximal to the entry tear of the false lumen. Regions of high time-averaged wall shear stress are detected and they correlate to tears in the aortic wall. The study provides quantitative indexes for optimal treatment planning.

Particle-laden turbulent flows are both technologically important and challenging to understand. This is especially true in rough-walls as opposed to smooth-wall flows, and when the particle loading becomes higher such that particles affect the turbulence-the two-way coupling regime. Depending on the Stokes number and particle volume fraction, turbulence can be suppressed or enhanced by the particles. Direct numerical simulations with the point particles were conducted in order to better understand the particle turbulence interaction. At low volume fractions, the mean force of the particles relative to the driving force of the flow is low and does not affect the turbulent flow. At higher volume fractions, particles with large Stokes number collide frequently with the rough walls behaving like a sink. Particles with smaller Stokes number have a more complicated interaction with the flow turbulence, where we observe both suppression and reappearance of turbulence over long time scales causing the mean flow to pulsate.

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