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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.06.035 Byline: Ja-Ren Lin (a)(b), Taras V. Gerya (b), Paul J. Tackley (b), David A. Yuen (c), Gregor J. Golabek (b) Keywords: Planetary formation Abstract: We developed and tested an efficient 2D numerical methodology for modeling gravitational redistribution processes in a quasi spherical planetary body based on a simple Cartesian grid. This methodology allows one to implement large viscosity contrasts and to handle properly a free surface and self-gravitation. With this novel method we investigated in a simplified way the evolution of gravitationally unstable global three-layer structures in the interiors of large metal-silicate planetary bodies like those suggested by previous models of cold accretion [Sasaki, S., Nakazawa, K., 1986. J. Geophys. Res. 91, 9231-9238; Karato, S., Murthy, V.R., 1997. Phys. Earth Planet Interios 100, 61-79; Senshu, H., Kuramoto, K., Matsui, T., 2002. J. Geophys. Res. 107 (E12), 5118. 10.1029/2001JE001819]: an innermost solid protocore (either undifferentiated or partly differentiated), an intermediate metal-rich layer (either continuous or disrupted), and an outermost silicate-rich layer. Long-wavelength (degree-one) instability of this three-layer structure may strongly contribute to core formation dynamics by triggering planetary-scale gravitational redistribution processes. We studied possible geometrical modes of the resulting planetary reshaping using scaled 2D numerical experiments for self-gravitating planetary bodies with Mercury-, Mars- and Earth-size. In our simplified model the viscosity of each material remains constant during the experiment and rheological effects of gravitational energy dissipation are not taken into account. However, in contrast to a previously conducted numerical study [Honda, R., Mizutani, H., Yamamoto, T., 1993. J. Geophys. Res. 98, 2075-2089] we explored a freely deformable planetary surface and a broad range of viscosity ratios between the metallic layer and the protocore (0.001-1000) as well as between the silicate layer and the protocore (0.001-1000). An important new prediction from our study is that realistic modes of planetary reshaping characterized by a high viscosity protocore and low viscosity molten silicate and metal [Senshu, H., Kuramoto, K., Matsui, T., 2002. J. Geophys. Res. 107 (E12), 5118. 10.1029/2001JE001819] may result in the transient exposure of the protocore to the planetary surface and a strongly (up to 8% of the planetary diameter) aspherical deviation of the planetary shape during the early stages of core formation. Exposure of the protocore might happen in the early stages of iron core formation. This process may conceivably convert a large amount of potential energy into temperature increase and a transient strongly non-uniform depth of the magma ocean around the protoplanet. Our simplified model also predicts that the time for metallic core formation out of the metal-rich layer depends mainly on the dynamics of the deformation of the solid strong protocore. In nature this dynamics will be strongly dependent on the effective viscosity of the protocore, which should generally have non-Newtonian pressure-, temperature-, and stress-dependent rheology with strong thermomechanical feedbacks from gravitational energy dissipation. Author Affiliation: (a) Institute of Oceanography, National Taiwan University, Taiwan (b) Geophysical Fluid Dynamics Group, Institute of Geophysics, Department of Geosciences, ETH-Zurich, Switzerland (c) University of Minnesota Supercomputing Institute, Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN55455, USA Article History: Received 30 May 2008; Revised 25 April 2009; Accepted 21 June 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.06.014 Byline: Seiji Yasuda (a), Hitoshi Miura (b), Taishi Nakamoto (c) Keywords: Meteorites; Origin Solar System; Solar nebula Abstract: We carried out three-dimensional hydrodynamics simulations of the disruption of a partially-molten dust particle exposed to high-speed gas flow to examine the compound chondrule formation due to mutual collisions between the fragments (fragment-collision model; [Miura, H., Yasuda, S., Nakamoto, T., 2008a. Icarus194, 811-821]). In the shock-wave heating model, which is one of the most plausible models for chondrule formation, the gas friction heats and melts the surface of the cm-sized dust particle (parent particle) and then the strong gas ram pressure causes the disruption of the molten surface layer. The hydrodynamics simulation shows details of the disruptive motion of the molten surface, production of many fragments and their trajectories parting from the parent particle, and mutual collisions among them. In our simulation, we identified 32 isolated fragments extracted from the parent particle. The size distribution of the fragments was similar to that obtained from the aerodynamic experiment in which a liquid layer was attached to a solid core and it was exposed to a gas flow. We detected 12 collisions between the fragments, which may result in the compound chondrule formation. We also analyzed the paths of all the fragments in detail and found the importance of the shadow effect in which a fragment extracted later blocks the gas flow toward a fragment extracted earlier. We examined the collision velocity and impact parameter of each collision and found that 11 collisions should result in coalescence. It means that the ratio of coalescent bodies to single bodies formed in this disruption of a parent particle is R.sub.coa=11/(32-11)=0.52. We concluded that compound chondrule formation can occur just after the disruption of a cm-sized molten dust particle in shock-wave heating. Author Affiliation: (a) Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tenno-dai, Tsukuba 305-8577, Japan (b) Department of Earth and Planetary Materials Science, Tohoku University, Aramaki Aoba 6-3, Aoba, Sendai 980-8578, Japan (c) Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan Article History: Received 6 October 2008; Revised 7 June 2009; Accepted 10 June 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2009.05.012 Byline: Atit Koonsrisuk, Tawit Chitsomboon Keywords: Solar chimney; Solar tower; Solar energy; Geometric effects; Theoretical model; CFD Abstract: A solar chimney is a solar power plant which generates mechanical energy (usually in terms of turbine shaft work) from a rising hot air that is heated by solar energy. The present paper compares the predictions of performances of solar chimney plants by using five simple theoretical models that have been proposed in the literature. The parameters used in the study were various plant geometrical parameters and the insolation. Computational Fluid Dynamics (CFD) simulation was also conducted and its results compared with the theoretical predictions. The power output and the efficiency of the solar chimney plants as functions of the studied parameters were used to compare relative merits of the five theoretical models. Models that performed better than the rest are finally recommended. Author Affiliation: School of Mechanical Engineering, Institute of Engineering, Suranaree University of Technology, Muang District, Nakhon Ratchasima 30000, Thailand Article History: Received 26 July 2008; Revised 28 April 2009; Accepted 24 May 2009 Article Note: (miscellaneous) Communicated by: Associate Editor S.A. Sherif

The present paper is concerned with the study of variable viscosity and variable thermal conductivity on the flow and heat transfer of an electrically conducting non-Newtonian power-law fluid within a thin liquid film over an unsteady stretching sheet in the presence of a transverse magnetic field. The transformed system of nonlinear ordinary differential equations describing the problem is solved numerically. The effects of various parameters on the velocity and temperature profiles are shown through graphs and discussed. The values of the local skin-friction coefficient and the local Nusselt number for different values of physical parameters are presented through tables. PACS Nos: 47.50.-d, 47.15.gm Nous etudions ici les effets d'une viscosity et d'une conductivity thermique variables sur l'ecoulement et le transfert de chaleur d'un fluide non Newtonien conducteur a l'interieur d'un mince film liquide sur une surface instable elastique en presence d'un champ magnetique transverse. Le systeme transforme d'equations differentielles ordinaires non lineaires est alors solutionne numeriquement. Nous presentons de facon graphique et analysons les resultats illustrant les effets des differents parameters sur les profils de vitesse et de temperature. Nous presentons sous forme de tables les valeurs du coefficient local de friction de peau et du nombre local de Nusselt pour differentes valeurs des parameters physiques. [Traduit par la Redaction], 1. Introduction The study of fluid flow and heat transfer in a thin liquid film over an unsteady stretching surface has gained considerable attention due to its many theoretical and [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2009.05.007 Byline: Stefan Goppert, Rolf Lohse, Thorsten Urbaneck, Ulrich Schirmer, Bernd Platzer, Philipp Steinert Keywords: Solar storage tanks; Inlet stratifiers; Computation Abstract: The efficiency of low-flow solar systems is strongly influenced by the quality of the thermal stratification in the storage tank. The better a thermal stratification can be generated and maintained, the higher can be the yield of the solar system. Fluid mechanical charge systems are often used for this purpose, which cause, however, undesirable sucking effects. Therefore, the knowledge of the appearing fluid flows as well as the knowledge of the consequences of constructive changes are very important for the design of such charge systems. However, simulations with CFD (Computational Fluid Dynamics) are very costly and time-consuming. In this article a new and much simpler computation method is introduced making the determination of the individual fluid flows and the estimation of the effects of constructive changes possible. The computations can be carried out within short time. The comparison with CFD gives a qualitatively good agreement for a simple charge system. The results of a constructive modification of the charge system reducing the sucking effect are discussed. The remaining quantitative differences result from the discrepancies between the non-ideal behaviour of the real fluid and the model assumptions and point out improvement potentials. Author Affiliation: Department of Technical Thermodynamics, Chemnitz University of Technology, Reichenhainer Str. 70, 09126 Chemnitz, Germany Article History: Received 22 August 2008; Revised 11 May 2009; Accepted 18 May 2009 Article Note: (miscellaneous) Communicated by: Associate Editor Halime Paksoy

A collection of MATLAB classes for computing and using spherical harmonic transforms is presented. Methods of these classes compute differential operators on the sphere and are used to solve simple partial differential equations in a spherical geometry. The spectral synthesis and analysis algorithms using fast Fourier transforms and Legendre transforms with the associated Legendre functions are presented in detail. A set of methods associated with a spectral_field class provides spectral approximation to the differential operators [nabla]*, [nabla] x, [nabla], and [[nabla].sup.2] in spherical geometry. Laplace inversion and Helmholtz equation solvers are also methods for this class. The use of the class and methods in MATLAB is demonstrated by the solution of the barotropic vorticity equation on the sphere. A survey of alternative algorithms is given and implementations for parallel high performance computers are discussed in the context of global climate and weather models. Categories and Subject Descriptors: F.2.1 [Analysis of Algorithms and Problem Complexity]: Numerical Algorithms and Problems--Computation of transforms; G.4 [Mathematical Software] ; G. 1.8 [Numerical Analysis] Partial Differential Equations; J.2 [Physical Sciences and Engineering]: Earth and atmosphere science General Terms: Algorithms, Theory Additional Key Words and Phrases: Spectral transform methods, spherical, fluid dynamics, geophysical flow, high performance computing DOI: 10.1145/1391989.1404581. http://doi.acm.org/10.1145/1391989.1404581

Flow and pollutant dispersion in a densely built-up area of Seoul, Korea, are numerically examined using a computational fluid dynamics (CFD) model coupled to a mesoscale model [fifth-generation Pennsylvania State University--National Center for Atmospheric Research Mesoscale Model (MM5)]. The CFD model used is a Reynolds-averaged Navier--Stokes equations model with the renormalization group k - [epsilon] turbulence model. A one-way nesting method is employed in this study. MM5-simulated data are linearly interpolated in time and space to provide time-dependent boundary conditions for the CFD model integration. In the MM5 simulation, four one-way nested computational domains are considered, and the innermost domain with a horizontal grid size of 1 km covers the Seoul metropolitan area and its adjacent areas, including a part of the Yellow Sea. The NCEP final analysis data are used as initial and boundary conditions for MM5. MM5 is integrated for 48 h starting from 0300 LST 1 June 2004 and the coupled CFD-MM5 model is integrated for 24 h starting from 0300 LST 2 June 2004. During the two-day period, a high-pressure system was dominant over the Korean peninsula, with clear conditions and weak synoptic winds. MM5 simulates local circulations characterized by sea breezes and mountain/valley winds. MM5-simulated synoptic weather and near-surface temperatures and winds are well matched with the observed ones. Results from the coupled CFD-MM5 model simulation show that the flow in the presence of real building clusters can change significantly as the ambient wind speed and direction change. Diurnally varying local circulations mainly cause changes in ambient wind speed and direction in the present simulation. Some characteristic flows--such as the double-eddy circulation, channeling flow, and vertical recirculation vortex--are simulated. Pollutant dispersion pattern and the degree of lateral pollutant dispersion are shown to be complicated in the presence of real building clusters and under varying ambient wind speed and direction. This study suggests that because of the sensitive dependency of urban flow and pollutant dispersion on variations in ambient wind, time-dependent boundary conditions should be used to better simulate or predict them when the ambient wind varies over the period of CFD model simulation.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2009.01.017 Byline: E. Papanicolaou, V. Belessiotis Keywords: Underground thermal storage; Charging; Variable inlet temperature Abstract: The flow and heat transport phenomena developing in a real-scale, underground hot-water storage tank intended for central solar systems and made of concrete walls are studied numerically and experimentally. The cubic tank with a volume of 8m.sup.3 has been equipped with two linear diffusers extending over its entire width. For the numerical computations, charging of the tank at a constant flow rate and three different inlet-temperature histories was considered. One of these corresponded to a simple constant value, a second one to solar-collector heating and the third one to electric heating. In the last case experimental data were also obtained. The charging process was simulated by dynamic models based on the multinode and plug-flow approaches, as well as two-dimensional (2D) computational fluid dynamics (CFD), for which both low-Re k-I[micro] and two-layer turbulence models were used.The distinct features of the flow and temperature fields for each charging mode as obtained from the models have been analyzed and compared to each other. For the electric heating case, preliminary comparisons between models and experiments were made, showing good qualitative agreement, while quantitative agreement was achieved only for parts of the entire transient process. The effects of turbulence-model choice and water-surface heat losses were also demonstrated and found to be important factors in the modeling procedure. Author Affiliation: 'Demokritos' National Center for Scientific Research, Solar and other Energy Systems Laboratory, Patr. Grigoriou & Neapoleos, 15310 Aghia Paraskevi, Attiki, Greece Article History: Received 16 May 2007; Revised 15 January 2009; Accepted 22 January 2009 Article Note: (miscellaneous) Communicated by: Associate Editor Yogi Goswami

A computational model is presented for simulating the development of the dust cloud that can be entrained into the air when a helicopter is operated close to the ground in dusty conditions. The physics of this problem and the associated condition known as brownout, where the pilots lose situational awareness as a result of their vision being occluded by dust suspended in the flow around the helicopter, are very complex. The approach advocated here involves an approximation of the full dynamics of the coupled particulate--air system. Away from the ground, the model assumes that the suspended particles remain in near equilibrium under the action of aerodynamic forces. Close to the ground, this model is replaced by an algebraic sublayer model for the saltation and entrainment process. The model is used to analyze the differences in the geometry and extent of the dust clouds that are produced by single main rotor and tandem-rotor configurations as they decelerate to land and shows that the location of the ground vortex and the size of any regions of recirculatory flow, should they exist, play a primary role in governing the extent of the dust cloud that is created by the helicopter. DOI: 10.2514/1.41999

Unsteady solutions for the aerodynamic coefficients of a thin airfoil in compressible sub- or supersonic flows were studied. The lift, the pitch moment, and the pressure coefficients were obtained numerically for the following motions: the indicial response (unit step function) of the profile, that is, a sudden change in the angle of attack; a thin profile penetrating into a sharp edge gust (for several gust velocity ratios); a thin profile penetrating into a one- minus-cosine gust, that is, a typical gust used in commercial aircraft design; the oscillating airfoil; and the interaction of the profile with a convected (from convection phenomenon) vortex passing under the profile, a phenomenon known in the literature as blade vortex interaction or, for a profile case, airfoil--vortex interaction. The present work uses a numerical approach based on vortex singularity. The numerical model was created through the profile discretization in uniform segments, and the compressible flow vortex singularity was used. The results available in the literature are based on approximated exponential equations or computed via computational fluid dynamics. Thus, the purpose of this method is to obtain results as accurate as those from approximated equations and significantly faster than those done via computational fluid dynamics. DOI: 10.2514/1.40610

The application of active flow control for high-lift multi-element wing sections is investigated. A computational fluid dynamics procedure is used to simulate the interactive flow in conjunction with distributed flow control. Favorable nonlinear interactions using flow control on a conventional wing section and an advanced airfoil lead to major aerodynamic performance improvements at representative takeoff and landing conditions. This study demonstrates that judicious application of flow control at select locations on the individual wing elements may lead to near inviscid lift levels in the linear lift range and substantial gains in maximum lift. DOI: 10.2514/1.41236

This article is the second of two companion papers which document the concept and the application of a coupled computational fluid dynamics system which was designed to incorporate the prediction of laminar--turbulent transition into a hybrid Reynolds-averaged Navier--Stokes solver. Whereas the first part deals with the description of the transition prediction methodology and the sensitivities of the coupled system, the second part documents its practical application. The complete coupled system consists of the Reynolds-averaged Navier--Stokes code, a laminar boundary-layer code, and a fully automated local, linear stability code. The system predicts and applies transition locations due to Tollmien--Schlichting and crossflow instabilities using the [e.sup.N] method based on the two-N-factor approach. The coupled system was designed to be applied to three-dimensional aircraft configurations which are of industrial relevance. The application of the coupled system to a wing--body configuration with a three-element wing consisting of slat, main wing, and flap is described and documented in this paper. The prediction of the laminar-- turbulent transition lines was done in a fully automatic manner. It is shown that complex aircraft configurations can be handled without a priori knowledge of the transition characteristics of the specific flow problem. DOI: 10.2514/1.39738

A careful study is conducted to assess the numerical mesh resolution requirements for the accurate computation of sonic boom ground signatures produced by complete aircraft configurations. The details of the ground signature can depend heavily on the accurate prediction of the pressure distribution in the near field of the aircraft. It is, therefore, important to accurately describe the geometric details of complete configurations (including the wing, fuselage, nacelles, diverters, etc.) and to precisely capture the propagation of shock and expansion waves at large distances from the aircraft. Unstructured, adaptive mesh technologies are ideally suited for this purpose as they use mesh points only in the appropriate locations within the flowfield. In this work, we consider a supersonic business jet configuration that was tested at the NASA Langley Research Center. Near-field data were measured at several locations underneath the flight track. The propagation of these near-field signatures from different altitudes can be shown to result in near N-wave ground booms. To examine the effect of both nacelles and empennage, results for three test cases are presented. These test cases represent the complete configuration, the configuration without the nacelles, and the configuration without the nacelles and empennage. Inviscid solution-adaptive unstructured meshes with up to 7.2 million nodes and 42.1 million tetrahedra are used to calculate the pressure distributions at several locations below each configuration where comparisons with experimental data are performed. All near-field pressure distributions are propagated to the ground (from an altitude of 50,000 ft) to predict the ground boom and the perceived noise level of the ground signature. Both the near-field overpressures and ground boom signatures are compared between experimental data and computational fluid dynamics simulation, and the results show good agreement in all cases. The minimum number of mesh nodes and elements and the levels of refinement needed for the accurate computations of near-field pressure distribution and ground boom signature are discussed for each of the three cases. DOI: 10.2514/1.34367

In this paper, we present the conjugate heat transfer analysis in a 167-kVA dry-type transformer using the parallel version of the Computational Fluid Dynamics code Fluent 6.0. The renormalization group [kappa]-[epsilon] model is proposed to compute the turbulent aspect of the convective airflow inside the transformer metal tank for Air Natural/Air Natural cooling conditions. An experimental approach was used to assess Joule losses in the low-/ high-voltage windings and eddy-current losses in the magnetic core. The resulting mathematical model was solved using 14 compute nodes on a distributed machine. Index Terms--Computational fluid dynamics (CFD) analysis, dry-type power transformers, heat transfer, indirect power measurement, parallel processing.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.chb.2008.07.010 Byline: Sarah Manlove, Ard W. Lazonder, Ton de Jong Abstract: This paper looks across three experimental studies that examined supports designed to assist high-school students (age 15-19) with cognitive regulation of their physics inquiry learning efforts in a technology-enhanced learning environment called Co-Lab. Cognitive regulation involves the recursive processes of planning, monitoring, and evaluation during learning, and is generally thought to enhance learning gains for students. The research synthesis described in this paper examined the usage effects of a support tool called the process coordinator (PC) on learning outcomes. This tool incorporated goal-lists, hints, prompts, cues, and templates to support the cognitive regulation skills of students during a fluid dynamics task. Students were asked to produce two learning outcomes of their investigations: system dynamics models and lab reports. Results from the three studies indicated trends in frequent use of the PC for planning activities, but low usage for monitoring and evaluation. Correlational analysis revealed two trends with regard to how these regulative activities impacted learning outcomes. First, consistent positive correlations were apparent between regulative activities and lab report scores of students and second, consistent negative correlations between the use of supports and model quality scores. Trends with regard to how task complexity, time, and student prior experience impacted these findings are also presented with suggestions for future research. Author Affiliation: University of Twente, Faculty of Behavioral Sciences, Department of Instructional Technology, P.O. Box 217, 7500 AE Enschede, The Netherlands

The article presents a new model, which is used for the theoretical analysis of the vibrations that are produced from the multiple particle-plate impact. The study of these vibrations has been shown to be extremely effective in recovering the different particle sizes present in the carrier fluid.

The effects of placing a slot through a two-dimensional Wortmann FX 63-137 airfoil in ground effect were examined using computational fluid dynamics. The geometric shape of the slot was varied in three different ways: the width of the slot (w/c = 0.02, 0.04, and 0.06), the angle of the slot with respect to the airfoil's chord line (d = 20, 30, and 40), and the position of the slot along the chord line, (x/c = O. 15, 0.20, and 0.25). In addition, the airfoil was tested at five different angles of attack: -3, 0, 5, 10, and 15 deg. The commercially available software Gambit 2.3.16 was used to create the computational grids. FLUENT 6.2.16 with the renormalized group k-e turbulence model was then used to simulate the flow. Pitch stability of the slotted airfoil was examined and results indicated that increasing the angle of attack of the slotted airfoil while in ground effect had a reduced increase in lift when compared with the lift generated by the baseline Wortmann FX 63-137 airfoil. Results also showed that the slot could be used to reduce center-of-pressure movement along the chord of the airfoil for the range of angles of attack investigated, thus improving the overall pitch stability of the airfoil. The slot geometry that produced a minimal center-of-pressure fluctuation was located at 20 % of the chord length from the leading edge with a width of 2 % and an angle of 20 deg between the slot and a line normal to the chord line. DOI: 10.2514/1.31246

The generation of a tabular aerodynamic model for design-related flight dynamics studies, based on simulation generated data, is considered. The framework described accommodates two design scenarios. The first emphasizes the representation of the aerodynamic nonlinearities and is based on sampling. The second assumes an incremental change from an initial geometry, for which a high-fidelity model from the first scenario is available. In this case, data fusion is used to update the model. In both cases, Kriging is used to interpolate the samples computed using simulation. A commercial jet test case, using DATCOM as a source of data, is computed to illustrate the sampling and fusion. Future application using computational fluid dynamics as the source of data is considered. DOI: 10.2514/1.39626

It has been observed that delta wings placed in a transonic freestream can experience a sudden movement of the vortex breakdown location as the angle of incidence is increased. The current paper uses computational fluid dynamics to examine this behavior in detail. The study shows that a shock/vortex interaction is responsible. The balance of the vortex strength and axial flow and the shock strength are examined to provide an explanation of the sensitivity of the breakdown location. Limited experimental data are available to supplement the computational fluid dynamics results in certain key respects, and the ideal synergy between computational fluid dynamics and experiments for this problem is considered. DOI: 10.2514/1.38792

A reaction-drive rotor configuration including an ejector nozzle is studied to determine possible exhaust-jet velocity reduction for the purpose of noise suppression. A vortex-wake rotor model is compared with an experimental rotor test, determining the model validity for a hovering rotor. A two-dimensional computational fluid dynamic model of an ejector flow is compared with an experimental ejector-nozzle test to determine the appropriate grid coarseness and turbulence model relevant to lift and drag predictions supporting the hovering-rotor aerodynamic model. The reaction-drive-rotor tip-jet-ejector nozzle geometry is sized by the analysis method put forward here, implementing coupled rotor aerodynamic, reaction-drive tip-jet-ejector thermodynamic, and computational fluid dynamic models. A performance version of the proposed analysis method is developed to characterize this rotor configuration over a range of blade collective pitch angles operating in a hovering-flight condition. DOI: 10.2514/1.39423

In this paper, we present the extension of the spacetime expansion discontinuous Galerkin to handle ideal and viscous magnetohydrodynamics (MHD) equations. The local time-stepping strategy that this scheme is capable of allows each cell to have its own time step whereas the high order of accuracy in time is retained. This may significantly speed up calculations. The diffusive flux is evaluated through a so-called diffusive generalized Riemann problem. The divergence constraint of the MHD equations is addressed, and a hyperbolic cleaning method is shown that can be enhanced by utilizing the local time-stepping framework. MHD problems such as the Orszag-Tang vortex or the magnetic blast problem are performed to challenge the capabilities of the proposed space-time expansion scheme. Index Terms--Magnetohydrodynamics (MHD).

A tropical cyclone bogus data assimilation (BDA) scheme is built in the Weather Research and Forecasting three-dimensional variational data assimilation system (WRF 3D-VAR). Experiments were conducted (21 experiments with BDA in parallel with another 21 without BDA) to assess its impacts on the predictions of seven Atlantic Ocean basin hurricanes observed in 2004 (Charley, Frances, Ivan, and Jeanne) and in 2005 (Katrina, Rita, and Wilma). In addition, its performance was compared with the Geophysical Fluid Dynamics Laboratory (GFDL) hurricane initialization scheme in a case study of Hurricane Humberto (2007). It is indicated that hurricane initialization with the BDA technique can improve the forecast skills of track and intensity in the Advanced Research WRF (ARW). Among the three hurricane verification parameters [track, central sea level pressure (CSLP), and maximum surface wind (MSW)], BDA improves CSLP the most. The improvement of MSW is also considerable. The track has the smallest, but still noticeable, improvement. With WRF 3D-VAR, the initial vortex produced by BDA is balanced with the dynamical and statistical balance in the 3D-VAR system. It has great potential for improving the hurricane intensity forecast. The case study on Hurricane Humberto (2007) shows that BDA performs better than the GFDL bogus scheme in the ARW forecast for the case. Better definition of the initial vortex is the main reason for the advanced skill in hurricane track and intensity forecasting in this case.

Steady and unsteady viscous flow simulations of a full-scale, semispan, and full-span model of the F-16XL-1 aircraft are performed with three different computational fluid dynamics codes using a common unstructured grid. Six different flight conditions are considered. They represent Reynolds and Mach number combinations at subsonic speeds, with and without sideslip. The steady computations of the flow at these flight conditions are made with several Reynolds-averaged Navier-Stokes turbulence models of different complexity. Detached-eddy simulation, delayed detached-eddy simulation, and an algebraic hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation model are used to quantify unsteady effects at the same flight conditions. The computed results are compared with flight-test data in the form of surface pressures, skin friction, and boundary-layer velocity profiles. The focus of the comparison is on turbulence modeling effects and effects of unsteadiness. The overall agreement with flight data is good, with no clear trend as to which physical modeling approach is superior for this class of flow. The Reynolds-averaged Navier-Stokes turbulence models perform well in predicting the flow in an average sense. However, some of the flow conditions involve locally unsteady flow over the aircraft, which are held responsible for the scatter between the different turbulence modeling approaches. The detached-eddy simulations are able to quantify the unsteady effects, although they are not consistently better than the Reynolds-averaged Navier-Stokes turbulence models in predicting the flow in an average sense in these flow regions. Detached-eddy simulation fails to predict boundary-layer profiles consistently over a range of flow regimes, with delayed detached-eddy simulation and hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation models offering a remedy to recover some of the predictive capabilities of the underlying Reynolds-averaged Navier-Stokes turbulence model. Nonetheless, the confidence in the predictive capabilities of the computational fluid dynamics codes with regard to complex vortical flowfields around high-performance aircraft of this planform increased significantly during this study.

In this paper, an efficient and accurate method based on the preconditioned advection upstream splitting method (AUSM) scheme is studied. Turkel's preconditioning method in conjunction with the second-order finite-volume monotone upwind schemes for conservation laws (MUSCL)-type AUSMDV (a mixture of AUSMD and AUSMV where 'D' and 'V' denote a flux-difference splitting-biased scheme and flux-vector-splitting-biased one, respectively) and AUS[M.sup.+]-up schemes based on the primitive variables is used to solve Navier-Stokes equations. These two schemes used in computational fluid dynamics with or without preconditioning methods are compared. The surface pressure distributions are compared with those calculated from a central difference scheme. The preconditioning method used in this paper obtains an improved convergence, stability, and the capability for the calculation of the low Mach number flows and transonic flows. The preconditioning high-resolution scheme strengthens the capability of identifying discontinuities and reducing the numerical dissipation. The present method that combines the multigrid algorithm further accelerates the convergence. Flow-independent convergence rates of the method are also observed from the numerical results for the low Mach number flows.

Numerical and experimental studies have been performed to show the potential for drag reductions of an array of discrete three-dimensional shock control bumps. The bump contour investigated was specifically designed by means of computational-fluid-dynamics-based numerical optimization for wind-tunnel testing on a modern transonic airfoil. The experimental investigations focused on turbulent flow at a Reynolds number of 5 million and were carried out at the Transonic Wind Tunnel Gottingen. Drag reductions of around 10% in the drag-rise region were found in the experiment even though the results were influenced by wind-tunnel interference effects. A detailed numerical study of the wind-tunnel environment reproduced the influence of the wind-tunnel walls on the bump performance and gave good agreement to the experimental results.

The present investigation focuses on assessing the predictive capabilities of state-of-the-art computational fluid dynamics for a generic fan-in-wing configuration by comparison with experimental data. The objective is to reproduce a short take off and landing or a transition-flight situation without ground effect. A rotating fan is placed in the wing plane, inside of the wing's rear part and close to the root section. The obtained experimental data include force measurements, surface pressure measurements, flowfield mapping using particle image velocimetry and wool-tufts visualization. A structured mesh of the entire configuration with minimum geometrical simplifications is used to perform unsteady Reynolds-averaged Navier-Stokes computations. The area surrounding the rotor blades is set up as sliding mesh to simulate the rotation. Because of the abrupt deflection of the flow by the fan, an unsteady recirculation area is generated above the rotor blades resulting in a highly distorted inflow. The blocking of the freestream by the jet exiting the fan's nozzle creates a back pressure affecting the internal aerodynamics. The jet rolls up in a counter-rotating vortex pair with considerable impact on the wing's aerodynamic performance. Time-averaged unsteady results over one fan revolution show a good agreement with the experimental data. The major turbulence phenomena are well predicted by the simulation.

This paper investigates the potential of polynomial chaos methods, when used in conjunction with computational fluid dynamics, to quantify the effects of uncertainty in the computational aerodynamic design process. The technique is shown to be an efficient and accurate means of simulating the inherent uncertainty and variability in manufacturing and flow conditions and thus can provide the basis for computationally feasible robust optimization with computational fluid dynamics. This paper presents polynomial chaos theory and the nonintrusive spectral projection implementation, using this to demonstrate polynomial chaos as a basis for robust optimization, focusing on the problem of maximizing the lift-to-drag ratio of a two-dimensional airfoil while minimizing its sensitivity to uncertainty in the leading-edge thickness. The results demonstrate that the robustly optimized designs are significantly less sensitive to input variation, compared with nonrobustly optimized airfoils. The results also indicate that the inherent geometric uncertainty could degrade the on-design as well as the offdesign performance of the nonrobust airfoil. This leads to the further conclusion that the global optimum for some design problems is unreachable without accounting for uncertainty.

Nine organizations participated in the Cranked-Arrow Wing Aerodynamics Project International study and have contributed steady and unsteady viscous simulations of a full-scale semispan model of the F-16XL aircraft. Three different categories of flight Reynolds/Mach number combinations are computed and compared with flight-test measurements for the purpose of code validation and improved understanding of the flight physics. Steady-state simulations are done with several turbulence models (of different complexity, with no topology information required) that overcome Boussinesq-assumption problems in vortical flows. Detached-eddy simulation and its successor, delayed detached-eddy simulation, are used to compute the time-accurate flow development. Common structured and unstructured grids as well as individually adapted unstructured grids were used. Although discrepancies are observed in the comparisons, overall reasonable agreement is demonstrated for surface pressure distribution, local skin friction, and boundary velocity profiles at subsonic speeds. The physical modeling, be it steady or unsteady flow, and the grid resolution both contribute to the discrepancies observed in the comparisons with flight data, but at this time, how much each part contributes to the whole cannot be determined. Overall, it can be said that the technology readiness of computational fluid dynamics simulation technology for the study of vehicle performance has matured since 2001, such that it can be used today with a reasonable level of confidence for complex configurations.

The objective of the Cranked-Arrow Wing Aerodynamics Project International was to allow a comprehensive validation of computational fluid dynamics methods against the Cranked-Arrow Wing Aerodynamics Project flight database. A major part of this work involved the generation of high-quality computational grids. Before the grid generation, an airtight geometry of the F-16XL aircraft was generated by a cooperation of the Cranked-Arrow Wing Aerodynamics Project International partners. Based on this geometry description, both structured and unstructured grids have been generated. The baseline structured (multiblock) grid (and a family of derived grids) has been generated by the National Aerospace Laboratory. Although the algorithms used by the National Aerospace Laboratory had become available just before the Cranked-Arrow Wing Aerodynamics Project International and thus only a limited experience with their application to such a complex configuration had been gained, a grid of good quality was generated well within four weeks. This time compared favorably with that required to produce the unstructured grids in the Cranked-Arrow Wing Aerodynamics Project International. The baseline all-tetrahedral and hybrid unstructured grids have been generated at NASA Langley Research Center and the U.S. Air Force Academy, respectively. To provide more geometrical resolution, trimmed unstructured grids have been generated at the European Aeronautic Defence and Space Company's Military Air Systems, University of Tennessee at Chattanooga SimCenter, Boeing Phantom Works, Royal Institute of Technology, and the Swedish Defence Research Agency. All grids generated within the framework of the Cranked-Arrow Wing Aerodynamics Project International will be discussed in the paper. Both results obtained on the structured grids and the unstructured grids showed a significant improvement in agreement with flight-test data in comparison with those obtained on the structured multiblock grid used during the Cranked-Arrow Wing Aerodynamics Project.

A novel technique was proposed for evaluating a local heat source in film power capacitors by adopting a minimized analysis model. It is impossible to analyze directly the distributions of heat source in a capacitor element because of tiny scale of aluminum foil and polypropylene film compared to the length of capacitor element. To overcome such a multi-scale problem, here, we proposed a local heat source approximation technique (LHSA) by adopting the time-harmonic analysis of electroquasistatic (EQS) conduction law. To evaluate the dielectric losses in polypropylene film, the complex permittivity was introduced for calculating the effective conductivity subjected to the sinusoidal electric field. These numerical results show that the main heat source originated from the dielectric materials not the metal electrodes in film power capacitors. Finally, the computational fluid dynamic (CFD) solver was adopted by considering the conduction, natural convection, and thermal radiation effects. The results from the proposed method were compared to and were in good agreement with those from the experiments with five sample capacitors of 6600/3800 V, 60 Hz, and 100 kvar. Index Terms--Complex permittivity, computational fluid dynamics (CFD), electroquasistatics (EQS), film power capacitors, local heat source, loss tangent, multi-scale problems, polypropylene films, power dissipation.

For several applications including strong hydrodynamics constraints (like in a circuit breaker), Finite Element solvers are not suitable for fluid dynamical modeling. For these applications, the coupling between the Computational Fluid Dynamics and the electromagnetism modeling is not easy. In this context, a magnetodynamic formulation is developed using the Finite Volume Method to address specific issues in multiphysics involved in circuit breaker modeling. The principles of Finite Volume Method, their using for the electromagnetism modeling, and multiphysics coupling method are described. Problems are expressed within current based T-[T.sub.o]-[phi] formulation which differs drastically from other developments given in the context of Finite Volume Method. Finally a circuit breaker simulation is carried out within a magnetostatic formulation. Index Terms--Circuit breaker, finite volume method, magneto-hydrodynamic, plasma.

In this paper, the authors present an extended survey on the evolution and the modern approaches in the thermal analysis of electrical machines. The improvements and the new techniques proposed in the last decade are analyzed in depth and compared in order to highlight the qualities and defects of each. In particular, thermal analysis based on lumped-parameter thermal network, finite-element analysis, and computational fluid dynamics are considered in this paper. In addition, an overview of the problems linked to the thermal parameter determination and computation is proposed and discussed. Taking into account the aims of this paper, a detailed list of books and papers is reported in the references to help researchers interested in these topics. Index Terms--Computed fluid dynamic, electrical machines, finite-element analysis (FEA), lumped-parameter thermal network (LPTN), thermal model, thermal parameter identification.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.10.004 Byline: Jack J. Lissauer (a), Olenka Hubickyj (a)(b), Gennaro D'Angelo (a), Peter Bodenheimer (b) Keywords: Jovian planets; Jupiter; interior; Accretion; Planetary formation; Planet-disk interaction Abstract: We model the growth of Jupiter via core nucleated accretion, applying constraints from hydrodynamical processes that result from the disk-planet interaction. We compute the planet's internal structure using a well tested planetary formation code that is based upon a Henyey-type stellar evolution code. The planet's interactions with the protoplanetary disk are calculated using 3-D hydrodynamic simulations. Previous models of Jupiter's growth have taken the radius of the planet to be approximately one Hill sphere radius, R.sub.H. However, 3-D hydrodynamic simulations show that only gas within [approximately equal to]0.25R.sub.H remains bound to the planet, with the more distant gas eventually participating in the shear flow of the protoplanetary disk. Therefore in our new simulations, the planet's outer boundary is placed at the location where gas has the thermal energy to reach the portion of the flow not bound to the planet. We find that the smaller radius increases the time required for planetary growth by [approximately equal to]5%. Thermal pressure limits the rate at which a planet less than a few dozen times as massive as Earth can accumulate gas from the protoplanetary disk, whereas hydrodynamics regulates the growth rate for more massive planets. Within a moderately viscous disk, the accretion rate peaks when the planet's mass is about equal to the mass of Saturn. In a less viscous disk hydrodynamical limits to accretion are smaller, and the accretion rate peaks at lower mass. Observations suggest that the typical lifetime of massive disks around young stellar objects is [approximately equal to]3Myr. To account for the dissipation of such disks, we perform some of our simulations of Jupiter's growth within a disk whose surface gas density decreases on this timescale. In all of the cases that we simulate, the planet's effective radiating temperature rises to well above 1000K soon after hydrodynamic limits begin to control the rate of gas accretion and the planet's distended envelope begins to contract. According to our simulations, proto-Jupiter's distended and thermally-supported envelope was too small to capture the planet's current retinue of irregular satellites as advocated by Pollack et al. [Pollack, J.B., Burns, J.A., Tauber, M.E., 1979. Icarus 37, 587-611]. Author Affiliation: (a) NASA Ames Research Center, Space Science and Astrobiology Division, MS 245-3, Moffett Field, CA 94035, USA (b) UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA Article History: Received 16 August 2008; Revised 10 October 2008; Accepted 23 October 2008

A 3D computational fluid dynamics model with a reduced detailed chemical kinetics of the combustion of diesel and methane fuels is developed while considering turbulence during combustion to simulate the mixture flow, formation, and combustion processes within diesel and diesel/methane dual fuel engines having swirl chambers. The combustion characteristics of the pilot injection into a small prechamber are also investigated. Modeled results were validated by a group of corresponding experimental data. The spatial and temporal distributions of the mixture temperature, pressure, and velocity under conditions with and without liquid fuel injection and combustion are compared. The effects of engine speed, injection timing, and the addition of carbon dioxide on the combustion process of dual fuel engines are investigated. It is found that in the absence of any fuel injection and combustion, the swirl center is initially formed at the bottom-left of the swirl chamber, and then moved up with continued compression in the top-right direction toward the highest point. The swirling motion within the swirl and main combustion chambers promotes the evaporation of the liquid pilot and the combustion processes of diesel and dual fuel engines. It was observed that an earlier autoignition can be obtained through injecting the pilot fuel into the small prechamber compared with the corresponding swirl chamber operation. It is to be shown that reduced engine emissions and improved thermal efficiency can be achieved by a two-stage homogenous charge compression ignition combustion. [DOI: 10.1115/1.2981175] Keywords: dual fuel engine, swirl chamber, small prechamber, autoignition

With the recent increase of the rotational speed of hard disk drives, nanoparticle contamination can cause serious problems including thermal asperity. We designed a comb-shaped clamp and spacer to improve the efficacy of the recirculation filter in the operation of the hard disk drive (HDD). We calculated flow characteristics by a commercial computational fluid dynamics (CFD) code for six cases of the comb-shaped clamp and spacer. The calculation results showed that the outward velocity was the highest when the comb-shape angle was 45[degrees]. We measured temporal variations of particle concentration during the operation of the HDD by experiments. Considering the decay rate and the percent clean-up of particle concentration, we found the case of 45[degrees] to be the best design. Index Terms--Clamp/spacer, hard disk drive, nanoparticle contamination, recirculation filter.

The transonic aerodynamics of an advanced, over-the-wing nacelle, subsonic transport configuration are assessed using both Euler and Navier-Stokes computational fluid dynamics and results are compared to a similar configuration with an under-the-wing nacelle installation and a similar wing-body configuration. The over-the-wing nacelle configuration is designed with a novel inboard wing channel section between the nacelle and the fuselage that produces favorable aerodynamic interference and reduces the overall drag. Qualitative observations and quantitative drag computations are performed for the three configurations at a cruise Mach number of 0.78. It was found that, at the cruise point, the inboard wing channel section of the over-the-wing nacelle configuration effectively produces a favorable pressure distribution but that the overall drag, compared to the under-the-wing nacelle configuration, is higher. This excess drag, however, was found to be largely localized in the nacelle interior. Euler and Navier-Stokes computational fluid dynamics solutions were obtained for additional Mach numbers to assess the transonic drag-rise characteristics. The computational fluid dynamics solutions showed that the over-the-wing nacelle configuration has higher drag at lower Mach numbers than the under-the-wing nacelle configuration but experiences a milder overall drag rise and has lower drag at higher Mach numbers.

This study evaluates the potential benefits that fixed but deployable trailing-edge flaps may have on a low-twist hovering rotor using a blade-element method combined with two-dimensional and three-dimensional computational fluid dynamics. Low blade twist is beneficial in terms of forward-flight performance, which, combined with a deployable flap, could also offer good hover performance, resulting in an overall better design in comparison with a plain twisted blade. To evaluate this concept, a parametric study of flap configurations was conducted using a simple blade-element method based on computational-fluid-dynamics-generated two-dimensional aerodynamics. This simple model indicated that up to 6 deg of blade twist could be recovered at high rotor thrust by using an optimized flap configuration. Performance improvements were also obtained for outboard slotted-flap configurations. The optimum slotted-flap designs were also evaluated using three-dimensional computational fluid dynamics, which confirmed that an inboard flap combined with a low-twist (-7deg) rotor blade matched the performance of a plain blade with -13deg of twist. A blended-flap configuration was also applied and evaluated. This simpler design demonstrated the equivalent performance of a clean rotor with 10 deg of blade twist, providing further evidence of the potential of the fixed inboard flap concept.

This paper focuses on the numerical research of the influence of polymer (polyoxymethylene) on the arc behavior during arc-motion process. The mathematical model of 3-D air-arc plasma considering the ablation of sidewalls is built based on magnetic hydrodynamics. The mass-fraction equation is introduced to the model on the basis of traditional mass, momentum, and energy-balance equations. The influence of wall ablation on the thermodynamic and transport properties of air-polymer mixtures is considered in this paper. The distributions of temperature field, pressure field, and mass fraction in the arc chamber are calculated. The simulation results indicate that the vapor concentration behind the arc column is higher than that in front of the arc column because of the existence of 'vortex' in the arc chamber. The use of polymers could accelerate arc movement and reduce the probability of occurrence of back-striking. Using polymers can also increase arc voltage, which can be explained by the change of electrical conductivity for air-polymer vapor mixtures. Index Terms--Arc behavior, arc simulation, low-voltage breaker, wall ablation.

Classic thermal management solutions for microelectronics are becoming inadequate and there is an increasing need for fundamentally new approaches. Electrohydrodynamic ionic wind pumps, also known as electrostatic fluid accelerators (EFA), have the potential for becoming a critical element in electronics thermal management solutions. As the EFA field continues to evolve, developing new EFA-based technologies will require accurate models that can help predict pump performance metrics, such as air velocity profile, back pressure, and cooling effectiveness. Many previous modeling efforts only account for electrostatic interactions. For truly accurate modeling, however, it is important to include effects of fluid dynamics and space charge diffusion in charge transport. The modeling problem becomes especially challenging for the design and optimization of EFA devices with greater complexity and smaller dimensions. This paper presents a coupled-physics finite element model (FEM) using a complete EFA charge transport model including charge diffusion and fluid dynamic effects. A cantilever EFA structure is modeled and analyzed for forced convection cooling. Numerical modeling predicts maximum air velocities of approximately 4 m/s and a maximum convection heat transfer coefficient of 280 W/([m.sup.2]K) for the cantilever EFA structure investigated. Preliminary experimental results for a microfabricated cantilever EFA device for forced convection cooling are also discussed Index Terms--Electrohydrodynamics, hydrodynamics, numerical analysis, cooling, Microelectromechanical devices.