20 research outputs found
Wall roughness induces asymptotic ultimate turbulence
Turbulence is omnipresent in Nature and technology, governing the transport
of heat, mass, and momentum on multiple scales. For real-world applications of
wall-bounded turbulence, the underlying surfaces are virtually always rough;
yet characterizing and understanding the effects of wall roughness for
turbulence remains a challenge, especially for rotating and thermally driven
turbulence. By combining extensive experiments and numerical simulations, here,
taking as example the paradigmatic Taylor-Couette system (the closed flow
between two independently rotating coaxial cylinders), we show how wall
roughness greatly enhances the overall transport properties and the
corresponding scaling exponents. If only one of the walls is rough, we reveal
that the bulk velocity is slaved to the rough side, due to the much stronger
coupling to that wall by the detaching flow structures. If both walls are
rough, the viscosity dependence is thoroughly eliminated in the boundary layers
and we thus achieve asymptotic ultimate turbulence, i.e. the upper limit of
transport, whose existence had been predicted by Robert Kraichnan in 1962
(Phys. Fluids {\bf 5}, 1374 (1962)) and in which the scalings laws can be
extrapolated to arbitrarily large Reynolds numbers
Investigation of the Unsteady Aerodynamics of Insect Flight:The Use of Immersed Boundary Method
Large-eddy simulation of a vertical axis tidal turbine using an immersed boundary method
Vertical Axis Tidal Turbines (VATTs) are an innovative way of harnessing renewable energy from tidal streams. Herein a novel numerical approach using a refined Large Eddy Simulation (LES) code to simulate the performance of a VATT is presented. The turbine blades are modelled with Lagrangian markers using the Immersed Boundary Method which offers several advantages especially concerning computational effort. Comparisons of the LES results with experimental and numerical data suggest reasonably good accuracy of the code. In addition, the stability of the method for high Reynolds number flows is also discussed
Systolic anterior motion in hypertrophic cardiomyopathy: a fluid–structure interaction computational model
Modeling the pore level fluid flow in porous media using the immersed boundary method
This chapter demonstrates the potential of the immersed boundary method for the direct numerical simulation of the flow through porous media. A 2D compact finite differences method was employed to solve the unsteady incompressible Navier-Stokes equations with fourth-order Runge-Kutta temporal discretization and fourth-order compact schemes for spatial discretization. The solutions were obtained in a Cartesian grid, with all the associated advantages. The porous media is made of equal size square cylinders in a staggered arrangement and is bounded by solid walls. The transverse and longitudinal distances between cylinders are equal to two cylinder diameters and at the inlet a fully developed velocity profile is specified. The Reynolds number based on the cylinder diameter and maximum inlet velocity ranges from 40 to 80. The different flow regimes are identified and characterised, along with the prediction of the Reynolds number at which transition from steady to unsteady flow takes place. Additionally, the average drag and lift coefficients are presented as a function of the Reynolds number