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CFD Code (cfd + code)
Selected AbstractsParallel simulation of unsteady hovering rotor wakesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2006C. B. Allen Abstract Numerical simulation using low diffusion schemes, for example free-vortex or vorticity transport methods, and theoretical stability analyses have shown the wakes of rotors in hover to be unsteady. This has also been observed in experiments, although the instabilities are not always repeatable. Hovering rotor wake stability is considered here using a finite-volume compressible CFD code. An implicit unsteady, multiblock, multigrid, upwind solver, and structured multiblock grid generator are presented, and applied to lifting rotors in hover. To allow the use of very fine meshes and, hence, better representation of the flow physics, a parallel version of the code has been developed, and parallel performance using upto 1024 CPUs is presented. A four-bladed rotor is considered, and it is demonstrated that once the grid density is sufficient to capture enough turns of the tip vortices, hover exhibits oscillatory behaviour of the wake, even using a steady formulation. An unsteady simulation is then performed, and also shows an unsteady wake. Detailed analysis of the time-accurate wake history shows that three dominant unsteady modes are captured, for this four-bladed case, with frequencies of one, four, and eight times the rotational frequency. A comparison with theoretical stability analysis is also presented. Copyright © 2006 John Wiley & Sons, Ltd. [source] A two-grid fictitious domain method for direct simulation of flows involving non-interacting particles of a very small sizeINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010A. Dechaume Abstract The full resolution of flows involving particles whose scale is hundreds or thousands of times smaller than the size of the flow domain is a challenging problem. A naive approach would require a tremendous number of degrees of freedom in order to bridge the gap between the two spatial scales involved. The approach used in the present study employs two grids whose grid size fits the two different scales involved, one of them (the micro-scale grid) being embedded into the other (the macro-scale grid). Then resolving first the larger scale on the macro-scale grid, we transfer the so obtained data to the boundary of the micro-scale grid and solve the smaller size problem. Since the particle is moving throughout the macro-scale domain, the micro-scale grid is fixed at the centroid of the moving particle and therefore moves with it. In this study we combine such an approach with a fictitious domain formulation of the problem resulting in a very efficient algorithm that is also easy to implement in an existing CFD code. We validate the method against existing experimental data for a sedimenting sphere, as well as analytical results for motion of an inertia-less ellipsoid in a shear flow. Finally, we apply the method to the flow of a high aspect ratio ellipsoid in a model of a human lung airway bifurcation. Copyright © 2009 John Wiley & Sons, Ltd. [source] The performance of natural draft dry cooling towers under crosswind: CFD studyINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2004Rafat Al-Waked Abstract The thermal performance of a natural draft dry cooling tower (NDDCT) under a crosswind has been investigated using a general-purpose CFD code. A three-dimensional study using the standard k,, turbulence model to simulate airflow in and around an NDDCT has been conducted. A parametric study has been carried out to examine the effect of crosswind velocity profile and air dry-bulb temperature on the thermal performance of an NDDCT. Two approaches have been considered in this study to quantify the crosswind effect. Firstly, simulations have been conducted at the nominal conditions and crosswind effect has been represented by thermal effectiveness parameter. Secondly, the ejected heat from the NDDCT has been maintained at a constant value (285 MW) and the crosswind effect has been represented by the change in the cooling tower approach parameter. After quantifying the effect of the crosswind on the thermal performance, windbreak walls have been introduced as a means of reducing this effect. The results in this paper show the importance of considering the crosswind velocity profile. Moreover, the introduction of windbreak walls has indicated an improvement in reducing the thermal performance losses due to the crosswind. Copyright © 2004 John Wiley & Sons, Ltd. [source] A multi-QMOM framework to describe multi-component agglomerates in liquid steelAICHE JOURNAL, Issue 9 2010L. Claudotte Abstract A variant of the quadrature method of moments (QMOM) for solving multiple population balance equations (PBE) is developed with the objective of application to steel industry processing. During the process of oxygen removal in a steel ladle, a large panel of oxide inclusions may be observed depending on the type of oxygen removal and addition elements. The final quality of the steel can be improved by accurate numerical simulation of the multi-component precipitation. The model proposed in this article takes into account the interactions between three major aspects of steelmaking modeling, namely fluid dynamics, thermo-kinetics and population balance. A commercial CFD code is used to predict the liquid steel hydrodynamics, whereas a home-made thermo-kinetic code adjusts chemical composition with nucleation and diffusion growth, and finally a set of PBE tracks the evolution of inclusion size with emphasis on particle aggregation. Each PBE is solved by QMOM, the first PBE/QMOM system describing the clusters and each remaining PBE/QMOM system being dedicated to the elementary particles of each inclusion species. It is shown how this coupled model can be used to investigate the cluster size and composition of a particular grade of steel (i.e., Fe-Al-Ti-O). © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Integration of on-the-fly kinetic reduction with multidimensional CFDAICHE JOURNAL, Issue 5 2010Kaiyuan He Abstract A reduction approach for coupling complex kinetics with engine computational fluid dynamics (CFD) code has been developed. An on-the-fly reduction scheme was used to reduce the reaction mechanism dynamically during the reactive flow calculation in order to couple comprehensive chemistry with flow simulations in each computational cell. KIVA-3V code is used as the CFD framework and CHEMKIN is employed to formulate chemistry, hydrodynamics and transport. Mechanism reduction was achieved by applying element flux analysis on-the-fly in the context of the multidimensional CFD calculation. The results show that incorporating the on-the-fly reduction approach in CFD code enables the simulation of ignition and combustion process accurately compared with detailed simulations. Both species and time-dependant information can be provided by the current model with significantly reduced CPU time. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Mathematical modelling of fire development in cable installationsFIRE AND MATERIALS, Issue 4 2001P. Van Hees In 1996 DG XII of the European Commission (Research and Development) approved a 3 year project on the fire performance of electrical cables. Within this FIPEC project, a major part of the work involved correlation and mathematical modelling of flame spread and heat release rate in cable installations. The FIPEC project has developed different levels of testing ranging from a small-scale, cone calorimeter test procedures developed for cables and materials, a full-scale-test procedure based on the IEC 60332-3, but utilizing HRR and SPR measurements, and a real scale test conducted on model cable installations. Links through statistical correlations and mathematical fire modelling between these levels were investigated and the findings are presented in this paper. These links could form the scientific foundations for standards upon which fire performance measurements can be based and for new fire engineering techniques within fire performance based codes. Between each testing level correlation, numerical and mathematical models were performed. All of the models were based on the cone calorimeter test method. The complexity of the models varied from correlation models to advanced physical pyrolysis models which can be used in CFD codes. The results will allow advanced prediction of cable fires in the future. Also a bench mark was established for the prediction of cable performance by means of data obtained from the constituent materials. Copyright © 2002 John Wiley & Sons, Ltd. [source] Critical evaluation of CFD codes for interfacial simulation of bubble-train flow in a narrow channelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2007Furkan Özkan Abstract Computational fluid dynamics (CFD) codes that are able to describe in detail the dynamic evolution of the deformable interface in gas,liquid or liquid,liquid flows may be a valuable tool to explore the potential of multi-fluid flow in narrow channels for process intensification. In the present paper, a computational exercise for co-current bubble-train flow in a square vertical mini-channel is performed to investigate the performance of well-known CFD codes for this type of flows. The computations are based on the volume-of-fluid method (VOF) where the transport equation for the liquid volumetric fraction is solved either by the methods involving a geometrical reconstruction of the interface or by the methods that use higher-order difference schemes instead. The codes contributing to the present code-to-code comparison are an in-house code and the commercial CFD packages CFX, FLUENT and STAR-CD. Results are presented for two basic cases. In the first one, the flow is driven by buoyancy only, while in the second case the flow is additionally forced by an external pressure gradient. The results of the code-to-code comparison show that only the VOF method with interface reconstruction leads to physically sound and consistent results, whereas the use of difference schemes for the volume fraction equation shows some deficiencies. Copyright © 2007 John Wiley & Sons, Ltd. [source] Theoretical analysis for achieving high-order spatial accuracy in Lagrangian/Eulerian source termsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2006David P. Schmidt Abstract In a fully coupled Lagrangian/Eulerian two-phase calculation, the source terms from computational particles must be agglomerated to nearby gas-phase nodes. Existing methods are capable of accomplishing this particle-to-gas coupling with second-order accuracy. However, higher-order methods would be useful for applications such as two-phase direct numerical simulation and large eddy simulation. A theoretical basis is provided for producing high spatial accuracy in particle-to-gas source terms with low computational cost. The present work derives fourth- and sixth-order accurate methods, and the procedure for even higher accuracy is discussed. The theory is also expanded to include two- and three-dimensional calculations. One- and two-dimensional tests are used to demonstrate the convergence of this method and to highlight problems with statistical noise. Finally, the potential for application in computational fluid dynamics codes is discussed. It is concluded that high-order kernels have practical benefits only under limited ranges of statistical and spatial resolution. Additionally, convergence demonstrations with full CFD codes will be extremely difficult due to the worsening of statistical errors with increasing mesh resolution. Copyright © 2006 John Wiley & Sons, Ltd. [source] Experimental and Numerical Studies of Fe2O3 Particle Formation Processes in a Flat Flame BurnerCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 6 2007M. Beck Abstract Particle formation processes are of interest for many industrial applications. This work focuses on investigating Fe2O3 particle formation. The particles form during thermal decomposition of an iron chloride solution in so-called spray roasting reactors. To analyze the reaction process, a laboratory reactor was designed which reproduces the conditions required for a systematic study of the particle formation process. Furthermore, a simplified particle conversion model was developed to simulate the realistic geometries and particle numbers on an industrial scale by CFD codes. [source] | |||||||||||||