Sommerfeld paradox roughly says that mathematically Couette linear shear is linearly stable for all Reynolds number, but experimentally arbitrarily small perturbations can induce the transition from the linear shear to turbulence when the Reynolds number is large enough. The main idea of our resolution of this paradox is to show that there is a sequence of linearly unstable shears which approac...

In this paper, an investigation into the effect of explicit non-linear turbulence modelling on anisotropic flows is presented. Such are typified in corner separations turbomachinery. The commonly used Reynolds-Averaged Navier-Stokes (RANS) closures, which Reynolds stress tensor modelled by Boussinesq (linear) constitutive relation with mean strain-rate tensor, often struggle to predict separati...

This paper experimentally investigates the mechanism of water droplet detachment in a confined microchannel under highly inertial air flow. Experimental observations show that as the Reynolds number in the channel is increased, the droplet transitions from a nearly spherical droplet to a high aspect ratio slug. Scaling arguments are then made to address this behavior in an order of magnitude se...

Developing accurate wall functions for LES is a great challenge. This is indeed also the case also for RANS. It can be argued that it should be easier to develop accurate wall functions for LES than for RANS. In a well-resolved LES using wall functions, the task of the wall function is to give an instantaneous wall shear stress; this does probably not need to be exactly correct. Compare with in...

In the past twenty years, shear-banding flows have been probed by various techniques, such as rheometry, velocimetry and flow birefringence. In micellar solutions, many of the data collected exhibit unexplained spatio-temporal fluctuations. Recently, it has been suggested that those fluctuations originate from a purely elastic instability of the flow. In cylindrical Couette geometry, the instab...

Bernoulli pads can create a significant normal force on an object without contact. The radial outflow which creates this also imposes shear the object. Better understanding improve pad designs in order to mitigate material deformation and damage, or allow be used as shear-based cleaning implements. Here, we use computational fluid dynamics explore parameter space show power-law relationship bet...

This study numerically investigates the vortex-induced vibration (VIV) of an elastically mounted rigid cylinder by using Reynolds-averaged Navier-Stokes (RANS) equations with computational fluid dynamic (CFD) tools. CFD analysis is performed for a fixed-cylinder case with Reynolds number (Re) = 104 and for a cylinder that is free to oscillate in the transverse direction and possesses a low mass...

This paper provides a framework for estimating appropriate turbulent velocity scales in adverse pressure gradient boundary layers (APG TBLs) via study of the mean stress balance. We examine APG TBLs using relationship between Reynolds shear and stress. It is reasoned that as distance from wall increases scaling transitions one dominated by wall-shear-stress scale, uτ, to A uhyb, proposed varies...

We study the linearized stability of shear flow satisfying Navier slip boundary conditions. The Orr-Sommerfeld equation for the plane Poiseuille flow with Navier slip boundary conditions is solved numerically by the Chebyshev collocation method. Our numerical results show that slip at the boundary increases the critical Reynolds number Rc for instability. The dependence of the this critical Rey...

One of the newest of viscoelastic RANS turbulence models for drag reducing channel flow with polymer additives is studied in different flow and rheological properties. In this model, finitely extensible nonlinear elastic-Peterlin (FENE-P) constitutive model is used to describe the viscoelastic effect of polymer solution and turbulence model is developed in the k-ϵ-(ν^2 ) ̅-f framework. The geome...