Two-Dimensional Simulations of Turbulent Flow Past a Row of Cylinders using Lattice Boltzmann Method

Two-dimensional simulations of channel flow past an array of cylinders are carried out at high Reynolds numbers. Considering the thickness fluctuating effect on the equation of motion, a modified lattice Boltzmann method (LBM) is proposed. Special attention is paid to investigate the thickness fluctuations and vortex shedding mechanisms between 11 cylinders. Results for the velocity and vorticity differences are provided, as well as for the energy density and enstrophy spectra. The numerical results coincide very well with some published experimental data that was obtained by turbulent soap films. The spectra extracted from the velocity and vorticity fields are displayed from simulations, along with the thickness fluctuation spectrum H(k). Our results show that the statistics of thickness fluctuations resemble closely those of a passive scalar in turbulent flows.

Numerical study on phase change of water flowing across two heated rotating circular cylinders in tandem arrangement

The problems of fluid flow and heat transfer phenomena over an array of cylinders are quite prominent in fluid dynamics and industry applications. The current work focuses on fluid flow and heat transfer analysis over two heated rotating cylinders arranged in tandem. The flow of water over heated cylinders faces a phenomenon of phase change from liquid (water) to vapor phase (steam). The mechanism of this phase change is studied through a numerical simulation supplemented with verification of the code and validation. The problem is simulated when flows from two cylinders in a tandem arrangement become interacting and non-interacting. The Eulerian model is used during simulation to comprehend the multiphase phenomena. The volume fractions of both the phases such as water and vapor and heat transfer coefficients of both the cylinders have been computed and presented as findings of the problem. The mass and heat transfer mechanism is unidirectional from one phase to the other phase. The vapor fraction of each phase is to be observed and compared when three different rotations are given to the two cylinders immersed in a turbulent flow of water.

Dynamic Model of a Vortex-Induced Energy Converter

Vortex-induced energy converters (VIECs) are attracting the attention of researchers looking for energy-harvesting systems in the marine environment. These energy converters, while probably less efficient than many other specialized devices, have very few moving parts and are particularly suitable for operation in harsh environments, such as those encountered in the ocean and in offshore platforms. The principle of operation of VIECs is tapping the transverse vibration of a blunt slender body immersed in a stream, induced by unsteady flow separation (Von Karman vortex street). The simplest device is an array of cylinders: under specific conditions and with careful design, it is possible to work close to resonance and thereby to obtain large amplitudes of oscillation, which are converted into electricity by suitable devices (linear electrical generators or piezoelectric cells). The system was developed experimentally at University of Michigan, with several patents pending and scientific material published on preliminary tests. Numerical simulations of system dynamics allow to simulate more realistic operating conditions and to perform the mechanical optimization of the system in relation to a specific sea location. A model of the system was thus developed, resulting in a nonlinear dynamic mathematical formulation; this last is solved in the time domain using matlab/simulink programming. The sensitivity of the efficiency to the main design variables is investigated. The results demonstrate that the efficiency and power density are not attractive for the typical Mediterranean Sea conditions; however, as energy can be harvested over large surfaces, the system appears to deserve attention.