We present dye visualizations of the flow generated by a sphere rolling along a solid surface in a quiescent fluid at low Reynolds numbers. Recent experimental and numerical studies of this configuration (Stewart et al. 2008, 2010) have shown a transition from steady to periodic flow at a Reynolds number Re (based on the sphere diameter and rolling speed) near 100. The unsteady flow involves th...

Vector fields are a common concept for the representation of many different kinds of flow phenomena in science and engineering. Topology-based methods have shown their convenience for visualizing and analyzing steady flow but a counterpart for unsteady flow is still missing. However, a lot of good and relevant work has been done aiming at such a solution. We give an overview of the research don...

Initial results of an ongoing Navier-Stokes Computational Fluid Dynamics study of horizontal axis tidal current turbine hydrodynamics are presented. Part of the underlying motivation is assessing the effects of the Reynolds number on turbine performance and loads in steady and unsteady flow regimes. The study aims at a) providing initial verification and validation of Navier-Stokes CFD for stea...

Unsteady inviscid flow models of wings and airfoils have been developed to study the aerodynamics of natural and man-made flyers. Vortex methods have been extensively applied to reduce the dimensionality of these aerodynamic models, based on the proper estimation of the strength and distribution of the vortices in the wake. In such modelling approaches, one of the most fundamental questions is ...

Water-hammer is a transient condition which may occur in a network as a result of rapid or slow valve closures, pump failures, changes in turbine loading, etc. It creates high and low pressure waves which travel along the system and decay as a result of wall shear stress. Comparison o experimental and theoretical results revealed the failure of steady or quasi-steady models in correctly predict...

We present a combined theoretical and computational analysis of three-dimensional unsteady finite-Reynolds-number flows in collapsible tubes whose walls perform prescribed high-frequency oscillations which resemble those typically observed in experiments with a Starling resistor. Following an analysis of the flow fields, we investigate the system’s overall energy budget and establish the critic...

Laminar-turbulent transition in a 3-D boundary layer under controlled simultaneous forcing of unstable steady and unsteady crossflow waves is investigated by means of direct numerical simulations. The flow configuration reproduces the accelerated 3-D flat-plate boundary layer of the ”Querstr ömungsprinzipexperiment”of the DLRG öttingen [1]. The superposition of high-amplitude steady and unstead...

magnetic field effect on unsteady natural convection heat transfer of cu–water nanofluid in a square porous cavity was studied numerically in here. at first, initial temprature of the cavity was and vertical walls were at temprature . suddenly the right wall's tamprature was changed to and the horizontal walls were adiabatic. the effective parameters in this study were ra , ha, and . which appe...

Preconditioners for hyperbolic systems are numerical artifacts to accelerate the convergence to a steady state. In addition, the preconditioner should also be included in the artificial viscosity or upwinding terms to improve the accuracy of the steady state solution. For time dependent problems we use a dual time stepping approach. The preconditioner affects the convergence rate and the accura...