editorial ...downloads.hindawi.com/journals/mse/2011/304983.pdfpredict airﬂow and gas diﬀusion...

Hindawi Publishing CorporationModelling and Simulation in EngineeringVolume 2011, Article ID 304983, 3 pagesdoi:10.1155/2011/304983

Editorial

Advances in Computational Fluid Dynamics and Its Applications

Guan Heng Yeoh,1, 2 Chaoqun Liu,3 Jiyuan Tu,4 and Victoria Timchenko2

1 Australian Nuclear Science Technology Organisation (ANSTO), Locked Bag 2001, Kirrawee, Sydney, NSW 2233, Australia2 School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, NSW 2052, Australia3 Center for Numerical Simulation and Modeling, Department of Mathematics, The University of Texas at Arlington, Arlington,TX 76019-0408, USA

4 School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, P.O. Box 71,Bundoora, Melbourne, VIC 3083, Australia

Correspondence should be addressed to Guan Heng Yeoh, [email protected]

Received 14 October 2011; Accepted 17 October 2011

Copyright © 2011 Guan Heng Yeoh et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Computational fluid dynamics, better known by CFD, iscertainly very prevalent in many fields of engineeringresearch and application. There is no doubt that we arecertainly witnessing a renaissance of computer simulationtechnology where the ever-changing landscape is as a resultof the rapid evolution of CFD techniques and models andthe decreasing computer hardware costs accompanied byfaster computing times. In spite of the many significantachievements, there remains much concerted developmentand advancement of CFD to meet the increasing demandsbolstered from various emerging industries such as biomedi-cal and bioengineering, uncharted areas in process, chemical,civil, and environmental engineering as well as traditionallyrenowned high-technology engineering areas in aeronauticsand astronautics and automotive. In this special issue,we believe that significant coverage on the advances andapplications of CFD has been achieved via the selectedtopics and papers which incidentally represent a good paneladdressing the many different aspects of CFD in this specialissue. Of course, we realise that these selected topics andpapers are not an exhaustive representation. Nevertheless,they still represent the rich and many-faceted knowledge thatwe have the great pleasure of sharing with the readers. Wecertainly would like to thank the numerous authors for theirexcellent contributions and patience in assisting us. Moreimportantly, the tiresome work of all referees on reviewingthese papers is very warmly acknowledged.

This special issue contains sixteen papers. The advancesand wide applications of CFD in each of the papers aredetailed in the following.

In the first paper, “New findings by high-order DNS forlate flow transition in a boundary layer,” C. Liu et al. present asummary of new discoveries by direct numerical simulation(DNS) for late stages of flow transition in a boundary layer.Based on the new findings, ring-like vortex is found to bethe only form existing inside the flow field and the resultof the interaction between two pairs of counter-rotatingprimary and secondary streamwise vortices. Following firstHelmholtz vortex conservation law, the primary vortex tuberolls up and is stretched due to the velocity gradient. In orderto maintain vorticity conservation, a bridge must be formedto link twoΛ-vortex legs. The bridge finally develops as a newring. This process proceeds to form a multiple ring structure.U-shaped vortices are not new but existing coherent vortexstructure. U-shaped vortex, which is a third level vortex,serves as a second neck to supply vorticity to the multiplerings. The small vortices can be found on the bottom ofthe boundary layer near the wall surface. It is believed thatthe small vortices, and thus turbulence, are generated by theinteraction of positive spikes and other higher level vorticeswith the solid wall.

In the second paper, “Implicit LES for supersonic micro-ramp vortex generator: new discoveries and new mechanisms,”Q. Li and C. Liu present the application of an implicitlylarge eddy simulation (ILES) via fifth-order WENO schemeto study the flow around the microramp vortex genera-tor (MVG) at Mach 2.5 and Reθ = 1440. A numberof new discoveries on the flow around supersonic MVGhave been made including spiral points, surface separationtopology, source of the momentum deficit, inflection surface,

2 Modelling and Simulation in Engineering

Kelvin-Helmholtz instability, vortex ring generation, ring-shock interaction, 3D recompression shock structure, andinfluence of MVG decline angles. A new 5-pair-vortex-tubemodel near the MVG is given based on the ILES observation.The vortex ring-shock interaction is found as the newmechanism of the reduction of the separation zone inducedby the shock-boundary layer interaction.

In the third paper, “An initial investigation of adjoint-based unstructured grid adaptation for vortical flow simula-tions,” L. Li presents a CFD method utilizing unstructuredgrid technology to compute vortical flow around a 65◦

delta wing with sharp leading edge, specially known as thegeometry of the second international vortex flow experiment(VFE-2). The emphasis of this paper is to investigate theeffectiveness of an adjoint-base grid adaptation methodfor unstructured grid in capturing concentrated vorticesgenerated at sharp edges or flow separation lines of liftingsurfaces flying at high angles of attack. Earlier vortical flowsimulations indicated that the vortex behaviour has beenfound to be highly dependent on the local grid resolutionboth on body surface and space. The basic idea of theadjoint-based adaptation method has been to construct anew adaptive sensor in a grid adaptation process with theintent to allocate where the elements should be smaller orlarger through the introduction of an adjoint formulation torelate the estimated functional error to local residual errorsof both the primal and adjoint solutions.

In the fourth paper, “Assessment of turbulence models forflow simulation around a wind turbine airfoil,” F. Villalpandoet al. present the investigation of flows over a NACA 63–415 airfoil at various angles of attack. With the aim ofselecting the most suitable turbulence model to simulateflow around ice-accreted airfoils, this work concentrates onassessing the prediction capabilities of various turbulencemodels on clean airfoils at the large angles of attack thatcause highly separated flows to occur. CFD simulationshave been performed employing the one-equation Spalart-Allmaras model, the two-equation RNG k-ε and SST k-ωmodels, and Reynolds stress model.

In the fifth paper, “Computation of ice shedding trajec-tories using cartesian grids, penalization, and level sets,” H.Beaugendre et al. present the modelling of ice sheddingtrajectories by an innovative paradigm based on Cartesiangrids, penalization, and level sets. The use of Cartesiangrids bypasses the meshing issue, and penalization is anefficient alternative to explicitly impose boundary conditionsso that the body-fitted meshes can be avoided, makingmultifluid/multiphysics flows easy to set up and simulate.Level sets describe the geometry in a nonparametric wayso that geometrical and topological changes due to physicsand in particular shed ice pieces are straightforward tofollow. The capabilities of the proposed CFD model aredemonstrated on ice trajectories calculations for flow aroundiced cylinder and airfoil.

In the sixth paper, “Aerodynamic optimization of anover-the-wing-nacelle-mount configuration,” D. Sasaki and K.Nakahashi present the CFD investigation of an over-the-wing-nacelle-mount airplane configuration which is knownto prevent the noise propagation from jet engines toward

ground. Aerodynamic design optimization is conducted toimprove aerodynamic efficiency in order to be equivalent toconventional under-the-wing-nacelle-mount configuration.The nacelle and wing geometry are modified to achieve highlift-to-drag ratio, and the optimal geometry is comparedwith a conventional configuration. Pylon shape is alsomodified to reduce aerodynamic interference effect. Thefinal wing-fuselage-nacelle model is compared with the DLRF6 model to discuss the potential of over-the-wing-nacelle-mount geometry for an environmental-friendly future air-craft.

In the seventh paper, “New evaluation technique for WTGdesign wind speed using a CFD-model-based unsteady flowsimulation with wind direction changes,” T. Uchida et al.present the development of a CFD model called RIAM-COMPACT, based on large eddy simulation (LES), that canpredict airflow and gas diffusion over complex terrain withhigh accuracy and simulates a continuous wind directionchange over 360 degrees. The present paper proposes atechnique for evaluating the deployment location of windturbine generators (WTGs) since a significant portion ofthe topography in Japan is characterized by steep, complexterrain thereby resulting in a complex spatial distribution ofwind speed, in which great care is necessary for selecting asite for the construction of WTG.

In the eighth paper, “Comparisons between the wakeof a wind turbine generator operated at optimal tip speedratio and the wake of a stationary disk,” T. Uchinda et al.present the investigation that the wake of a wind turbinegenerator (WTG) operated at the optimal tip speed ratio iscompared to the wake with its rotor replaced by a stationarydisk. Numerical simulations are conducted with a largeeddy simulation (LES) model. The characteristics of thewake of the stationary disk are significantly different fromthose of the WTG. The velocity deficit at a downstreamdistance of 10D (D being the rotor diameter) behind theWTG is approximately 30 to 40% of the inflow velocity. Incontrast, flow separation is observed immediately behind thestationary disk (≤2D), and the velocity deficit in the far wake(10D) of the stationary disk is smaller than that of the WTG.

In the ninth paper, “Experimental and numerical sim-ulations predictions comparison of power and efficiency inhydraulic turbine,” L. Castro et al. present the CFD simu-lations performed to principal components of a hydraulicturbine: runner and draft tube. On-site power and mass flowrate measurements have been conducted in a hydroelectricpower plant (Mexico). Mass flow rate has been obtainedusing Gibson’s water hammer-based method. Inlet boundaryconditions for the runner have been obtained from aprevious simulation conducted in the spiral case. Computedresults at the runner’s outlet are used to conduct thesubsequent draft tube simulation. Numerical results from therunner’s flow simulation provide data to compute the torqueand the turbine’s power. Power-versus-efficiency curves arebuilt.

In the tenth paper, “Simulating smoke filling in big hallsby computational fluid dynamics,” W. K. Chow et al. presentthe use of CFD in addressing the key hazard due to smokefilling within the enclosure in the event of a fire. This aspect

Modelling and Simulation in Engineering 3

primarily concerns the many tall halls of big space volumethat have been and to be built in many construction projectsin the Far East, particularly Mainland China, Hong Kong,and Taiwan. On the basis of the CFD simulations, it can beanticipated that better understanding of the smoke fillingphenomenon and design of appropriate smoke exhaustsystems can be realised.

In the eleventh paper, “Numerical simulations for a typicaltrain fire in china,” W. K. Chow et al. present the useof CFD in addressing the fire safety in passenger trainsdue to big arson and accidental fires since railway is thekey transport means in China including the Mainland,Taiwan, and Hong Kong. The predicted results such as theair flow, temperature distribution, smoke layer height, andsmoke spread patterns inside a train compartment are usefulfor working out appropriate fire safety measures for trainvehicles and determining the design fire for subway stationsand railway tunnels.

In the twelfth paper, “Simulation of pharyngeal airwayinteraction with air flow using low-Re turbulence model,”M. R. Rasani et al. present the CFD simulation of theinteraction between a simplified tongue replica with expi-ratory turbulent air flow. A three-dimensional model witha low-Re SST turbulence model is adopted. An ArbitraryEulerian-Lagrangian description for the fluid governingequation is coupled with the Lagrangian structural solvervia a partitioned approach, allowing deformation of thefluid domain to be captured. Numerical simulations confirmexpected predisposition of apneic patients with narrowerairway opening to flow obstruction and suggest muchsevere tongue collapsibility if the pharyngeal flow regime isturbulent compared to laminar.

In the thirteenth paper, “CFD-guided development oftest rigs for studying erosion and large-particle damage ofthermal barrier coatings,” M. A. Kuczmarski et al. presentthe use of CFD to accelerate the successful developmentand continuous improvement of combustion burner rigs formeaningful materials testing. Rig development is typicallyan iterative process of making incremental modificationsto improve the rig performance for testing requirements.Application of CFD allows many of these iterations to bedone computationally before hardware is built or modified,reducing overall testing costs and time, and it can providean improved understanding of how these rigs operate. Thispaper focuses on the study of erosion and large-particledamage of thermal barrier coatings (TBCs) used to protectturbine blades from high heat fluxes in combustion engines.The steps used in this study—determining the questions thatneed to be answered regarding the test rig performance,developing and validating the model, and using it topredict rig performance—can be applied to the efficientdevelopment of other test rigs.

In the fourteenth paper, “Investigation of swirling flowsin mixing chambers,” J. J. Chen and C. H. Chen presentthe CFD investigation of the three-dimensional momentumand mass transfer characteristics arising from multiple inletsand a single outlet in micromixing chamber. The chamberconsists of a right square prism, an octagonal prism, or acylinder. Numerical results have indicated that the swirling

flows inside the chamber dominate the mixing index. Particletrajectories demonstrate the rotational and extensional localflows which produce steady stirring, and the configuration ofcoloured particles at the outlet section expressed at differentReynolds numbers (Re) represented the mixing performancequalitatively. Effects of various geometric parameters andRe on the mixing characteristics have been investigated.An optimal design of the cylindrical chamber with 4 inletsis found. At Re > 15, more inertia causes more powerfulswirling flows in the chamber, and the damping effect ondiffusion is diminished, which subsequently increases themixing performance.

In the fifteenth paper, “Numerical computation andinvestigation of the characteristics of microscale synthetic jets,”A. Lee et al. present the CFD investigation of a syntheticjet generated as a result of the periodic oscillations of amembrane in a cavity. A novel moving mesh algorithm tosimulate the formation of jet is presented. The governingequations are transformed into the curvilinear coordinatesystem in which the grid velocities evaluated are then fedinto the computation of the flow in the cavity domain thusallowing the conservation equations of mass and momentumto be solved within the stationary computational domain.Numerical solution generated using this moving meshapproach is compared with experimental measurement.Comparisons between numerical results and experimentalmeasurement on the streamwise component of velocityprofiles at the orifice exit and along the centerline of thepulsating jet in microchannel as well as the location ofvortex core indicate that there is good agreement, therebydemonstrating that the moving mesh algorithm developedis valid.

In the sixteenth paper, “Recent efforts for credible CFDsimulations in china,” L. Li et al. present the initiation ofa series of workshops on credible CFD simulations similarto activities in the West such as ECARP and AIAA DragPrediction Workshops. Another major effort in China isthe ongoing project to establish a software platform forstudying the credibility of CFD solvers and performingcredible CFD simulations. The platform, named WiseCFD,has been designed to implement a seamless CFD processand to circumvent tedious repeating manual operations. Aconcerted focus is also given on a powerful job manager forCFD with capabilities to support plug and play (PnP) solverintegration as well as distributed or parallel computations.Some future work on WiseCFD is proposed and alsoenvisioned on how WiseCFD and the European QNET-CFDKnowledge Base can benefit mutually.

Guan Heng YeohChaoqun Liu

Jiyuan TuVictoria Timchenko

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