Nor Azwadi Che Sidik

A Review on the Application of the Lattice Boltzmann Method for Turbulent Flow Simulation

The Lattice Boltzmann Method (LBM) is a potent numerical technique based on kinetic theory, which has been effectively employed in various complicated physical, chemical, and fluid mechanics problems. In recent years, turbulent flow simulation by using this new class of computational fluid dynamics technique has attracted more attention. In this article, a review of previous studies on turbulence in the frame of LBM is presented. Recent extensions of this method are categorized based on three main groups of turbulence simulation: DNS, LES and RANS methods.

A review on the flow structure and pollutant dispersion in urban street canyons for urban planning strategies

As a result of rapid urbanization in numerous cities around the world, the demand for transportation has increased rapidly, resulting in emission of high levels of exhaust pollutants into the atmosphere. This is a major cause of deterioration in the local air quality, with consequent escalating risk of adverse health conditions amongst urban inhabitants. Understanding dispersion of pollutants in street canyons, local urban configurations, meteorological processes, and other physical factors are essential for predicting and assessing air quality. This article presents a comprehensive review of the state-of-the-art research works relevant to the investigation of flow structures and pollutant dispersion phenomena in urban street canyons. Various factors, including building geometries, local atmospheric conditions, static and dynamic obstructions, as well as chemical reactions of exhaust pollutants, are critically discussed by taking into account field measurements, wind tunnel experiments, operational modeling techniques, and computational fluid dynamics (CFD). The most critical pollutant levels in street canyons under several physical circumstances are identified. Elements leading to discrepancies and resulting in inconsistencies of different research methods are briefly addressed and suggestions for future research are offered.

Simulation of forced convection in a channel with nanofluid by the lattice Boltzmann method

This paper presents a numerical study of the thermal performance of fins mounted on the bottom wall of a horizontal channel and cooled with either pure water or an Al2O3-water nanofluid. The bottom wall of the channel is heated at a constant temperature and cooled by mixed convection of laminar flow at a relatively low temperature. The results of the numerical simulation indicate that the heat transfer rate of fins is significantly affected by the Reynolds number (Re) and the thermal conductivity of the fins. The influence of the solid volume fraction on the increase of heat transfer is more noticeable at higher values of the Re.

Analysis of the Applicability of the Lattice Boltzmann Method in Targeting a Chaotic Flame Front Model

In this paper, we present utilization of the lattice Boltzmann method (LBM) to analyze spatiotemporal chaotic fields. To this end, the one-dimensional Kuramoto–Sivashinsky equation, which is a proper model for unstable flame front flutter, is rewritten in terms of lattice Boltzmann equation components and is then solved. After accuracy checks, we alter the computational domain size and also the control parameter of the problem, which is representative of the kinematic viscosity in real flows, to capture the symmetry-breaking phenomenon. In the next step, since the method is in fact a one-dimensional explicit mapping for the probability density functions, we adopt the targeting algorithm of chaotic fields using LBM. The results show that the method can be applied to chaotic fields with confidence.

Numerical Simulation of Wind Flow Structures and Pollutant Dispersion within Street Canyon under Thermally Unstable Atmospheric Conditions

Numerical studies were conducted to envisage the wind flow structures in street canyon for differential heated wall and Richardson numbers. Two-equation turbulence models, namely the Standard k-ε, Renormalization Group (RNG) k-ε and Realizable k-ε were applied to investigate the effect of flow structure on pollutant dispersion in a square street canyon. The obtained results demonstrate that the differentially heated wall/floor gives significant effects on the wind flow field compared with those under isothermal conditions. At low Richardson number, vortex intensification was observed for the case of ground or leeward heated wall. Meanwhile, for the case of windward heated wall, the ventilation was much reduced due to the buoyancy force that produces upward motion near the wall to form the secondary vortex. At higher Froude number (convective flows) case, the buoyancy flow has no discernible effects on the flow structures. Keywords— Street canyon; thermal flow; wind flow structures; pollutant dispersion; turbulence models

Measurement of Film Effectiveness for Cylindrical and Row Trenched Cooling Holes at Different Blowing Ratios

This study was performed to investigate the effects of cylindrical and row trenched cooling holes with alignment angle of 0° and 90° at different blowing ratios on the film-cooling performance adjacent the endwall surface of a combustor simulator. The film-cooling blowing ratios varied from 1.25 to 3.18. In this study, a three-dimensional representation of a Pratt and Whitney gas turbine engine was simulated and analyzed with a commercial finite volume package FLUENT 6.2.26. The analysis has been carried out with Reynolds-averaged Navier–Stokes turbulence model on internal cooling passages. This combustor simulator was combined with the interaction of two rows of dilution jets, which were staggered in the streamwise direction and aligned in the spanwise direction. Film cooling was placed along the combustor liner walls. In comparison with the baseline case of cooling holes, the application of row trenched hole near the endwall surface doubled the performance of film-cooling effectiveness.

The use of thermal lattice Boltzmann numerical scheme for particle-laden channel flow with a cavity

In this article, particle-laden flow in a channel with heated cavity has been investigated. Calculations were performed using a point force scheme for particle dynamics, while the process of fluid renewal was modeled using the double-population thermal lattice Boltzmann method. Point-particle formulation accounts for the finite-size dispersed phase and the forces acting on the particles were modeled through drag force correlations. Two-way interactions of solid-fluid calculation were considered by adding an external force term for feedback that forced particles in the evolution of fluid distribution function. The method was first validated with steady state flow in a channel with cavity in the presence and absence of a heat source. It was then applied to mixed convection flow laden with particles at various Grashof numbers. The particle dispersion characteristics were examined in detail, where the particle removal rate from cavity upon cavity aspect ratio was emphasized. The effect of the Reynolds number on particle distribution was further investigated numerically by varying the speed of inlet flow into the channel.

Numerical Analysis on Natural Convection Heat Transfer of a Heat Sink with Cylindrical Pin Fin

As technology advancement progressed in this information age or commonly known as digital age, thermal management has equally improved to keep up with demands from the electronic sector. Hence, heat sink study has become more and more prominent. Natural convection holds advantages since it is maintenance free and has zero power consumption. The purpose of this research is to study the heat transfer performance of heat sink with parametric variations of number and height of pin fin at temperature 308K, 323K, 338K, 353K and 368K. In addition, effect of porosity ranges from 0.524 to 0.960 on thermal resistance was investigated as well. Study found that heat transfer coefficient increases as temperature difference between heat sink and ambient increases. Thermal resistance decreases when porosity increases until it reaches the minimum and subsequently increases. The optimum porosity shown in this study is around 88%.

Numerical Investigation of Turbulent Magnetic Nanofluid Flow inside Straight Channels

A numerical study using computational fluid dynamics method with an approach of single phase has been presented in order to determine the effects of the concentration of the nanoparticles and flow rate on the convective heat transfer and friction factor in turbulent regime flowing through three different straight channels (straight, circular and triangular) with different Reynolds number (5000 ≤ Re ≤ 20000) using constant applied heat flux. The nanofluid was used consist of Fe3O4 magnetic nanoparticles with average diameter of (13nm) dispersed in water with four volume fraction (0, 0.2, 0.4, 0.6%). The results revealed that as volume fraction and Reynolds number increase Nusselt number increase and the heat transfer rate in circular cross section tube is better than that in square and triangular cross section channels.

Formation and Breakup Patterns of Falling Droplets

Some interface front patterns of falling droplets are studied via direct numerical solution of the full Navier–Stokes equations governing the system of droplets and the ambient surrounding media as a single-fluid model. We focus on the mutual interactions of the effects of characterizing nondimensional parameters on the formation and break-up of large cylindrical droplets. The investigation of droplet cross sections and deformation angles shows that for moderate values of the Atwood number, increasing the Eötvös number explicitly increases the deformation rate in formation and breakup phenomena. Otherwise, increasing the Ohnesorge number basically amplifies the viscous effects.