LES and DNS

For most re-entry capsules, the shape of the forebody of the capsule is designed based on the blunted nose cone. A similar shape can be created using a hyperboloid of revolution that can control the nose bluntness and the half angle of the cone easily. In this study, the hypersonic aerodynamic characteristics of re-entry capsules designed with hyperbolic contours were investigated using the CFD code, FaSTAR, developed by Japan Aerospace Exploration Agency (JAXA). The CFD results showed that, using the hyperbolic contours, the drag and lift coefficients can be increased compared to those for the Hayabusa re-entry capsule without changing the shape of the capsule drastically. This suggests that shape design based on the hyperbolic contours can improve the aerodynamic characteristics of re-entry capsules.

We study the use of small counter-rotating cylinders to control the streaming flow past a larger main cylinder for drag reduction. In a water tunnel experiment at a Reynolds number of 47, 000 with a three-dimensional and turbulent wake, Particle Image Velocimetry (PIV) measurements show that rotating cylinders narrow the mean wake and shorten the recirculation length. The drag of the main cylinder was measured to reduce by up to 45%. To examine the physical mechanism of the flow control in detail, a series of two-dimensional numerical simulations at a Reynolds number equal to 500 were conducted. These simulations investigated a range of control cylinder diameters in addition to rotation rates and gaps to the main cylinder. Effectively controlled simulated flows present a streamline that separates from the main cylinder, passes around the control cylinder, and reattaches to the main cylinder at a higher pressure. The computed pressure recovery from the separation to reattachment points collapse with respect to a new scaling, which indicates that the control mechanism is viscous.

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Compressible DNS of transitional and turbulent flow in a low pressure turbine cascade 1 RAJESH RANJAN, SURESH DESHPANDE, ROD-DAM NARASIMHA, JNCASR -Direct numerical simulation (DNS) of flow in a low pressure turbine cascade at high incidence is performed using a new in-house code ANUROOP. This code solves compressible Navier-Stokes equations in conservative form using finite volume technique and uses kinetic-energy consistent scheme for the flux calculations. ANUROOP is capable of handling flow past complex geometries using hybrid grid approach (separate grid topologies for the boundary layer and rest of the blade passage). This approach offers much more control in mesh spacing and distribution compared to elliptic grid technique, which is used in many previous studies. Also, in contrast to previous studies, focus of the current work is mainly on the boundary layer flow. The flow remains laminar on the pressure side of the blade, but separates in the aft region of the suction side leading to transition. Separation bubbles formed at this region are transient in nature and we notice multiple bubbles merging and breaking in time. In the mean flow however, only one bubble is seen. Velocity profiles very near to the leading edge of the suction side suggest strong curvature effect. Higher-order boundary layer theory that includes effect of curvature is found to be necessary to characterize the flow in this region. Also, the grid convergence study reveals interesting aspects of numerics vital for accurate simulation of this kind of complex flows.

The present work experimentally investigates the dynamics of unsteady gravity currents produced by lock-release of a saline mixture into a fresh water tank. Seven different experimental runs were performed by varying the density of the saline mixture in the lock and the bed roughness. Experiments were conducted in a Perspex flume, of horizontal bed and rectangular cross section, and recorded with a CCD camera. An image analysis technique was applied to visualize and characterize the current allowing thus the understanding of its general dynamics and, more specifically, of the current head dynamics. The temporal evolution of both head length and mass shows repeated stretching and breaking cycles: during the stretching phase, the head length and mass grow until reaching a limit, then the head becomes unstable and breaks. In the instants of break, the head aspect ratio shows a limit of 0.2 and the mass of

Droplet evaporation in fluidized beds is of great interest in applications like fluidized catalytic cracking units. Although a significant number of analyses are available for modelling of droplet vaporization in a fluidized bed, very little work has been performed experimentally to measure the vapour concentration followed by numerical validation. In the present work, acetone droplet evaporation in a bubbling fluidized bed is studied experimentally as well as numerically. A liquid jet of acetone is injected into a hot bubbling fluidized bed kept well above saturation temperature of acetone. Nonintrusive Schlieren imaging, based on the difference in refractive index, is used to trace the acetone vapour concentration profile. The bubbling fluidized bed is modelled in an Eulerian framework using a simplistic porous media approach while the droplets are modelled in a Lagrangian framework. Intense interactions are observed between the evaporating droplets and hot particles during contact with re-suspension of particles. Experimental measurement and CFD results and measured vapour concentration are compared and found to be in qualitative agreement.

In this investigation, semiempirical and numerical studies of blood flow in a viscoelastic artery were performed using the Cosserat continuum model. The large-amplitude oscillatory shear deformation model was used to quantify the nonlinear viscoelastic response of blood flow. The finite difference method was used to solve the governing equations, and the particle swarm optimization algorithm was utilized to identify the non-Newtonian coefficients (k υ and γ υ ). The numerical results agreed well with previous experimental results. c

High-speed particle image velocimetry measurements were performed at the exit of a pressurized lean-burn combustion chamber fueled with kerosene and operated at flight relevant conditions (elevated pressure and pre-heated supply air). The aim was to obtain information on the turbulent nature of the exhaust flow as this is of relevance for the modelling of aero-thermal dynamics of the combustor-turbine interface, such as heat transfer on the outlet guide vanes and turbulence induced noise. Two-component velocity data was sampled at 20 kHz along a narrow strip and used to obtain frequency spectra and correlations. Synchronously acquired chemiluminescence of the OH radical in the primary zone exhibited a notable tonal peak near 100 Hz that could also be detected in the circumferential velocity component at one operating condition

In this article, we present numerical solutions for flow over an airfoil and a square obstacle using Incompressible Smoothed Particle Hydrodynamics (ISPH) method with an improved solid boundary treatment approach, referred to as the Multiple Boundary Tangents (MBT) method. It was shown that the MBT boundary treatment technique is very effective for tackling boundaries of complex shapes. Also, we have proposed the usage of the repulsive component of the Lennard-Jones Potential (LJP) in the advection equation to repair particle fractures occurring in the SPH method due to the tendency of SPH particles to follow the stream line trajectory. This approach is named as the artificial particle displacement method. Numerical results suggest that the improved ISPH method which is consisting of the MBT method, artificial particle displacement and the corrective SPH discretization scheme enables one to obtain very stable and robust SPH simulations. The square obstacle and NACA airfoil geometry with the angle of attacks between 0°and 15°were simulated in a laminar flow field with relatively high Reynolds numbers. We illustrated that the improved ISPH method is able to capture the complex physics of bluff-body flows naturally such as the flow separation, wake formation at the trailing edge, and the vortex shedding. The SPH results are validated with a mesh-dependent Finite Element Method (FEM) and excellent agreements among the results were observed.

Airway Replicas: This study was approved by the Health Research Ethics Board (HREB) of the University of Alberta. Five adult and eleven child airway replicas were built based on segmentation of CT scans of subjects with healthy airways3. Generational airway diameters are summarized in Tables 1 and 2 as the average of equivalent circular cross-section diameters evaluated at 2 mm increments along the length of each airway segment.

Noise source characterization from far-field data in high-speed jets 1 JACQUES LEWALLE, KERWIN R. LOW, MARK N. GLAUSER, Syracuse University -We analyze pressure data from 3 microphones in the far-field coherent noise cone of a Ma=0.6 jet. 3500 individual sources are identified in the time-frequency domain, and some of their properties are extracted from the wavelet coefficients: magnitude, frequency, time of arrival. The sources' signature therefore includes the lags between the sound arrival times at the microphones. Based on a modeled mean jet velocity field, we calculate the refracted acoustic paths and propagation times from a grid of source locations to the microphones. The excellent agreement between measured and calculated lags provides a mapping between the measured lags and the approximate source locations. For our catalog of sources, we report on some statistics of source properties as a function of their location in the near-jet's shear layer and developing region beyond the end of the potential core. The ability to narrow the search (time and location) for sources in near-field data (LES or PIV) may be established on this basis.

The Open-Source CFD Toolbox OpenFOAM has very good prerequisites for a usage in CAD oriented CFD processes. This includes e.g. the strong encapsulation of the respective CFD solution capabilities into individual solvers. The solver approach simplifies using CFD as an application-specific tool: In contrast to the multi-purpose CFD systems, the designer can focus more easily on problem-specific settings for his specific area of application. The open-source structure of OpenFOAM also facilitates the adaptation of CFD methods and solution procedures, e.g. by a CFD expert to the designer's requirements in terms of model capabilities or individual workflow. On the other hand, OpenFOAM's hurdles for direct deployment into the design-related environment are the relatively complex application of the system, the comparatively poor integration into a CADand GUI-based workflow, and the intended work on a text file base. Thus, OpenFOAM appears to be generally unsuitable for widespread use in the design environment. However, in combination with additional third-party tools, used as wrappers around the actual CFD solver OpenFOAM, these deficits may be overcome: They retain the advantages of the CFD solver in the design-related environment, on the other hand reduce or even eliminate the disadvantages that arise from the direct use of OpenFOAM. These tools can then be adapted to a high degree for the individual needs of the designer. The use of OpenFOAMs solution capabilities for the designer becomes interesting especially in the case of recurring problems with similar flow conditions and objectives. However, even in the case of complex CFD problems, such as multiphase or multi-physics applications, which are to be implemented as simply and automatically as possible, OpenFOAM has particularly strong capabilities. These solution capabilities are easily expandable by CFD experts and can be made available to the designer. Different levels for automation are presented for a usage of OpenFOAM in combination with the thirdparty tool CastNet: This covers a pure template approach for solution settings without geometric association to CAD model entities as well as abstract modelling techniques. With the help of abstract modelling it is possible for certain CAD systems to fully define the CFD model in the design program and also for design changes to continue to use the existing settings and geometric references.

Modified law of the wall leading to turbulent channel flow universal velocity profiles valid down to Re τ = 395 GREGOIRE WINCKELMANS, UCL, Louvain School of Engineering, LAURENT BRICTEUX -Velocity profile modeling is revisited using the results from databases of turbulent channel flow DNS at Re τ = u τ h/ν = 2000, 950, 550, and 395. We consider the turbulent region: y + = Re τ η (with η = y/h) larger than 70). A new model for the effective turbulent viscosity, ν t = -u v / du dy , is proposed, that fits well the DNS results all the way to the channel center. The velocity profile is then obtained by integration: it corresponds to a "modified law of the wall," 1 κ log(y + + y + 0 ) -η + C, with the added classical "law of the wake," D g(η). The new -η term in the modified law of the wall is really required in such still limited Reynolds number channel flows, as an important correction to the usual log term: both terms "work together," as both are multiplied by the same 1 κ value (recall that D is not related to κ). Only at the highest Reynolds numbers does this correction become negligible. As to the y + 0 shift in the log term itself (value around 6), something also recently proposed by Spalart et al (Phys. Fluids in press), it too is required as a consequence of the ν t near wall behavior. The present velocity profile is quite universal: it fits very well, with the same value of all constants, all Re τ cases. In particular, the von Kàrmàn constant is obtained as κ = 0.37: same as Zanoun et al (Phys. Fluids 15 (10):3079, 2003), and close to 0.38 as Spalart et al.

Modified law of the wall leading to turbulent channel flow universal velocity profiles valid down to Re τ = 395 GREGOIRE WINCKELMANS, UCL, Louvain School of Engineering, LAURENT BRICTEUX -Velocity profile modeling is revisited using the results from databases of turbulent channel flow DNS at Re τ = u τ h/ν = 2000, 950, 550, and 395. We consider the turbulent region: y + = Re τ η (with η = y/h) larger than 70). A new model for the effective turbulent viscosity, ν t = -u v / du dy , is proposed, that fits well the DNS results all the way to the channel center. The velocity profile is then obtained by integration: it corresponds to a "modified law of the wall," 1 κ log(y + + y + 0 ) -η + C, with the added classical "law of the wake," D g(η). The new -η term in the modified law of the wall is really required in such still limited Reynolds number channel flows, as an important correction to the usual log term: both terms "work together," as both are multiplied by the same 1 κ value (recall that D is not related to κ). Only at the highest Reynolds numbers does this correction become negligible. As to the y + 0 shift in the log term itself (value around 6), something also recently proposed by Spalart et al (Phys. Fluids in press), it too is required as a consequence of the ν t near wall behavior. The present velocity profile is quite universal: it fits very well, with the same value of all constants, all Re τ cases. In particular, the von Kàrmàn constant is obtained as κ = 0.37: same as Zanoun et al (Phys. Fluids 15 (10):3079, 2003), and close to 0.38 as Spalart et al.

The American Physical Society LES investigation of aircraft wake two-vortex system in low level atmospheric turbulence GREGOIRE WINCKELMANS, LOUIS DUFRESNE, LAURENT BRICTEUX, Universite catholique de Louvain (UCL) -The numerical simulation of realistic vortical aircraft wakes constitutes a challenging task, as the problem is of large size, the vortex cores are small, and the Reynolds number is very high. In particular, the vortex cores grow very little during the lifetime of the vortices. Large-eddy simulation (LES) at "essentially" infinite Reynolds number is here used: a Fourier-based pseudo-spectral method in "quasi-Euler" mode (ν set to zero and use of a high order k 16 hyperviscosity subgrid-scale model, which ensure negligible viscous core growth). The LES grid is also fine enough so as to properly capture relevant dynamics in the core region. A realistic case is simulated: circulation Γ 0 = 400 m 2 /s, spacing b 0 = 50 m, core radius r c = 2.5 m. We use a L 3 computational box of 256 3 grid points and with L = 200 m. The background atmospheric turbulence is here at low level (dissipation ϵ = 0.0001 m 2 /s 3 ) and was obtained as a pre-simulation. The vortex system engulfs the ambient turbulence, the non-linear interactions then amplify it and this eventually leads to a vortex pair where the surrounding turbulence is independent of the atmospheric background: the low level turbulence thus acts as a seed to create a "turbulent vortex pair" that then lives and decays on its own. We also observe significant axial velocities in the core region. Those results are further being used for simulations of LIDAR return signal.

The American Physical Society LES investigation of aircraft wake two-vortex system in low level atmospheric turbulence GREGOIRE WINCKELMANS, LOUIS DUFRESNE, LAURENT BRICTEUX, Universite catholique de Louvain (UCL) -The numerical simulation of realistic vortical aircraft wakes constitutes a challenging task, as the problem is of large size, the vortex cores are small, and the Reynolds number is very high. In particular, the vortex cores grow very little during the lifetime of the vortices. Large-eddy simulation (LES) at "essentially" infinite Reynolds number is here used: a Fourier-based pseudo-spectral method in "quasi-Euler" mode (ν set to zero and use of a high order k 16 hyperviscosity subgrid-scale model, which ensure negligible viscous core growth). The LES grid is also fine enough so as to properly capture relevant dynamics in the core region. A realistic case is simulated: circulation Γ 0 = 400 m 2 /s, spacing b 0 = 50 m, core radius r c = 2.5 m. We use a L 3 computational box of 256 3 grid points and with L = 200 m. The background atmospheric turbulence is here at low level (dissipation ϵ = 0.0001 m 2 /s 3 ) and was obtained as a pre-simulation. The vortex system engulfs the ambient turbulence, the non-linear interactions then amplify it and this eventually leads to a vortex pair where the surrounding turbulence is independent of the atmospheric background: the low level turbulence thus acts as a seed to create a "turbulent vortex pair" that then lives and decays on its own. We also observe significant axial velocities in the core region. Those results are further being used for simulations of LIDAR return signal.

Merging of unequal strength co-rotating vortices LOUIS DUFRESNE, JULIEN CHRISTOPHE, OLIVIER GOURGUE, GREGOIRE WINCKELMANS, Universite catholique de Louvain (UCL) -We present numerical simulation results on the 2D merging of a pair of co-rotating vortices and examine the effect of varying the circulation ratio between the two vortices. In a first step we present the results obtained for a pair of equal strength vortices (Γ 2 /Γ 1 = 1) at a Reynolds number of Re = Γ 1 /ν = 530 . A detailed quantitative analysis is made and shown to be in very good agreement with the experimental measurements of Cerretelli & Williamson (2003, JFM, 475, 41-77) for that same case. The results for vortex pairs with unequal strengths, i.e. with Γ 2 /Γ 1 < 1, also at Re = 530 , are presented next. The decomposition of the vorticity field into its symmetric and antisymmetric components, as done by Cerretelli & Williamson, shows that the structure of the anti-symmetric vorticity, in the convective merging phase, completely changes when Γ 2 /Γ 1 reaches a value of about 0.8. Above that value, both vortices undergo deformation and contribute to the apparition of anti-symmetric vorticity. They also both move towards the center of rotation while they merge. Below that value, only the weaker vortex undergoes significant deformation and thus contributes to the apparition of anti-symmetric vorticity. Furthermore, the center of that weak vortex remains almost stationary (in the proper rotating frame of reference). The stronger vortex follows the opposite behavior with only a little deformation but with a more significant relative displacement.

We present an analytical theory of turbulence based upon the procedure of successive elimination of small-scale modes that leads to gradual coarsening of the flow field and accumulation of eddy viscosity. The Reynolds number based upon the eddy viscosity, velocity and length scale of the remaining smallest scales stays O(1). The main results of the theory are analytical expressions for eddy viscosity and kinetic energy spectrum. Partial scale elimination yields a subgrid-scale representation for large eddy simulations while the elimination of all fluctuating scales is analogous to the Reynolds averaging.

WRF-bLES-Pyplume (PyPlume) is a generalized python-based library that has been
developed to automate the computations of the plume characteristics, mean state,
and turbulence characteristics of the plume and flow fields using the data generated
from the bplume-WRF-LES model [4]. The implementation of the Pyplume framework
for idealistic and realistic boundary conditions have been presented in this manuscript.
Details of the model development, model formulation, and model implementation
and the Pyplume software in python are presented. A Case study for the release of
heated Co2
plumes into the neutral atmosphere is presented. The LES data, Pyplume
generated data and the Pyplume library are available on github. The Pyplume library
is compatible for all versions of WRF-LES and the library can be used to extract the
turbulence fields to conduct an analysis of data generated by WRF-LES

Fluid-particle momentum transfer modelling is a key issue for the simulation of gas-solid fluidized beds. In the literature, many empirical correlations can be found for the prediction of the drag force but these correlations are generally not satisfactory for all the flow conditions found in fluidized bed: dilute and dense regime, low and high particle Reynolds number values, mono-or polydisperse solid mixture. Up to now, in dense particulate flows, the validation of such correlations were performed only by comparison with experiments using mean pressure drop, fluidization or settling velocity measurements and analytical solutions in some limit cases (Stokes flow). Nowadays, the development of particle resolved numerical techniques, like Lattice Boltzmann Method (LBM), allows to perform Direct Numerical Simulation (DNS) of the flow across dilute and dense particle arrays. Such simulations allow to compute directly the forces acting on the particles which may be used to validate or develop drag force correlations. In the present paper, we show that the simple drag correlation proposed by [6], and already used extensively for circulating and dense fluidized bed simulation, is in very good agreement with the particle-resolved immersed boundary-method results of Tenneti et al. (2011)[15] and with the boddy-fitted DNS results of Massol . An extension of the correlation is also proposed for poly-disperse mixture based on the LBM results of Beetstra et al. (2007)[1].

The interaction between an incident shock wave and a Mach-6 undisturbed hypersonic laminar boundary layer over a cold wall is addressed using direct numerical simulations (DNS) and wall-modeled large-eddy simulations (WMLES) at different angles of incidence. At sufficiently high shock-incidence angles, the boundary layer transitions to turbulence via breakdown of near-wall streaks shortly downstream of the shock impingement, without the need of any inflow free-stream disturbances. The transition causes a localized significant increase in the Stanton number and skin-friction coefficient, with high incidence angles augmenting the peak thermomechanical loads in an approximately linear way. Statistical analyses of the boundary layer downstream of the interaction for each case are provided that quantify streamwise spatial variations of the Reynolds analogy factors and indicate a breakdown of the Morkovin's hypothesis near the wall, where velocity and temperature become correlated. A modified strong Reynolds analogy with a fixed turbulent Prandtl number is observed to perform best. Conventional transformations fail at collapsing the mean velocity profiles on the incompressible log law. The WMLES prompts transition and peak heating, delays separation, and advances reattachment, thereby shortening the separation bubble. When the shock leads to transition, WMLES provides predictions of DNS peak thermomechanical loads within ±10% at a computational cost lower than DNS by two orders of magnitude. Downstream of the interaction, in the turbulent boundary layer, WMLES agrees well with DNS results for the Reynolds analogy factor, the mean profiles of velocity and temperature, including the temperature peak, and the temperature/velocity correlation.

Two-dimensional shear flow over a rotating circular cylinder is investigated using lattice Boltzmann method. Simulations are performed at a fixed blockage ratio (B = 0.1) while the Reynolds number, nondimensional shear rate (K ) and absolute rotational speed range as 80 ≤ Re ≤ 180, 0 ≤ K ≤ 0.2 and -2 ≤ β ≤ 2, respectively. To verify the simulation, the results are compared to previous experimental and numerical data. Quantitative information about the flow variables such as drag and lift coefficients, pressure coefficient and vorticity distributions on the cylinders is highlighted. It is found that, generally, with the increment in |β|, the absolute value of time average lift coefficient increases and time average drag coefficient decreases, and beyond a certain magnitude of β, the vortex shedding vanishes. It is also revealed that the drag coefficient decreases as the Reynolds number increases while the effect of the Reynolds number on lift is almost negligible. At the end, correlations for drag and lift coefficients (C D , C L ) are extracted from the numerical data.

This work reports a numerical experiment designed to address the 4 th and 9 th questions posed by S.B. Pope (New Journal of Physics, 2004) concerning the respective merits of physical and numerical (or implicit) Large Eddy Simulation (LES and MILES), in the simulation of high speed non-reacting and reacting air/H 2 jets typical of scramjet engines. Numerical simulations are performed at resolutions ranging from 32 × 32 × 128 to 256 × 256 × 1024, using a 5 th order WENO scheme. Physical LES are carried out with the Smagorinsky and the Selective Structure Function subgrid models associated to molecular diffusion. Implicit LES are performed with and without molecular diffusion. In the nonreacting case, the Smagorinsky model is too dissipative, even with a low value of the constant, C s = 0.1. The Selective Structure Function leads to better results, but does not show any superiority compared to MILES, whatever the grid resolution. In the reacting case, a molecular viscous cut-off in the simulation is mandatory to set a physical width for the reaction zone in MILES-Euler, hence to achieve grid-convergence.

Anotace: Tento článek se zabývá výzkumem mechanických vlastností (síly ve střihu) u pouzdra s kulovými vývody (BGA) s a bez výplně mezi pouzdrem a nosnou deskou (underfill) na substrátech FR4 a Al2O3. BGA pouzdro zapájené na FR4 (ENIG) dosahovalo větší hodnoty střihové síly než BGA zapájené na keramickém substrátu s vodivou tlustou vrstvou. Výsledky experimentů byly použity pro validaci virtuálního modelu a simulací v programu ANSYS Workbench. Tyto simulace budou použity pro predikci termomechanického namáhání BGA pouzder zapájených na keramickém substrátu a organickém substrátu FR4.

The development of aerospace technology in the future depends on supersonic and hypersonic vehicles. As the national defense and military strength become more and more crucial for national growth, communication, security and stability, the high-efficiency thrust vectoring nozzle, which can significantly enhance the maneuverability and stability of supersonic and hypersonic vehicles, has always been the focus of research for military powers. This thesis paper presents a numerical study on the flow characteristics and performance of baffled shock two dimensional vector nozzle. The baffled shock vector nozzle is a type of fluidic thrust vectoring nozzle that uses secondary injection to deflect the primary flow and generate a vector angle. Fluidic thrust vectoring technology is regarded as a key technology for the development of very low detectable vehicles because of its advantages such as fast response, light weight and good stealth performance. The main objectives of this study are to investigate the effects of various parameters such as slot interval distance, slot width, injection angle, nozzle pressure ratio, secondary flow pressure ratio and outflow Mach number on the deflection angle, thrust coefficient, thrust efficiency and secondary flow ratio of the nozzle. The numerical simulations are carried out using k−epsilon turbulence model, which is validated by comparing with experimental data. The results show that the nozzle performance can be improved by optimizing the slot interval distance and width, increasing the injection angle, adjusting the nozzle pressure ratio and secondary flow pressure ratio, and controlling the outflow Mach number. The results also reveal the complex flow phenomena inside the nozzle, such as shock wave interactions, flow separation and reattachment, and boundary layer effects. The study provides a comprehensive understanding of the flow characteristics and performance of baffled shock two dimensional vector nozzle and offers some guidance for its design and optimization.

A consistent dual-mesh hybrid LES/RANS framework for turbulence modeling has been proposed recently (H. Xiao, P. Jenny, A consistent dual-mesh framework for hybrid LES/RANS modeling, J. Comput. Phys. 231 (4) (2012)). To better enforce componentwise Reynolds stress consistency between the LES and the RANS simulations, in the present work the original hybrid framework is modified to better exploit the advantage of more advanced RANS turbulence models. In the new formulation, the turbulent stresses in the filtered equations in the under-resolved regions are directly corrected based on the Reynolds stresses provided by the RANS simulation. More precisely, the new strategy leads to implicit LES/RANS consistency, where the velocity consistency is achieved indirectly via imposing consistency on the Reynolds stresses. This is in contrast to the explicit consistency enforcement in the original formulation, where forcing terms are added to the filtered momentum equations to achieve directly t...

Diesel (surrogate) fuel spray experimentation at controlled elevated temperature and pressure conditions is intended to provide a more fundamental understanding of diesel spray combustion than can be achieved in engine experiments. This level of understanding is needed to develop the high-fidelity multi-scale CFD models that will be used to optimize future engine designs. Experimental and numerical work is often combined within scientific research projects in order to enhance the development and validation of numerical CFD models. Surrogate fuel spray data needed for detailed model development and validation requires extensive characterization of all of the boundary conditions that will be used as model inputs [1] [2] [3]. There are several spray chamber facilities around the world, suitable for experiments at high temperature and pressure conditions, but because of the uniqueness of each facility there are uncertainties about the differences in their operation. These uncertainties need to be clarified because modelers cannot compare and match experimental data as long as differences between facilities are not well investigated and understood. This observation has led to the start of the Engine Combustion Network [4], initiated by Sandia National Laboratories and IFP-EN. The aim of the ECN group is to implement comparative studies mainly using constant-volume pre-combustion vessels. The ECN group has agreed to perform experiments at the same injector-and ambient conditions, thereby leveraging the expertise of each participant, and enabling direct comparison between different facilities. The aim of the combined ECN work is to generate a combined database at engine relevant conditions. It is anticipated that the data set developed will become a focal point for model validation and further advanced diagnostics. This collaborative effort will generate a highquality data set to be used for advanced computational model development at relevant engine conditions. ECN participants are expected to measure the boundary conditions (specified in Table 1) of the ambient gas properties and the injector, this to understand uncertainties among the different institutes. The ECN approach in order to better understand each facility, and to minimize uncertainties, is to directly compare results at these standardized experimental conditions. Once these boundary conditions are better understood and defined, variation in parameters beyond those specified for Spray A can proceed with higher confidence. At the Eindhoven University of Technology a high pressure and high temperature constant volume combustion vessel facility with comparable dimensions and operating range as the other participants is present [5]. The Eindhoven Combustion Technology Group joined the ECN group in order to increase the accuracy of the setup and to contribute to the aim of generating a high-quality dataset of fuel spray measurements. The pre-burn combustion vessel setup is used to implement ECN spray A conditions, targeting the same ambient gas properties, surrogate diesel fuel and injector hardware. The first step within the project is to implement the required ECN hardware and to accurately measure the particular setup temperature and pressure boundary conditions. The used approach and the obtained results are presented in this paper following the directions as presented in [6].

Past experience with ramjet engines suggests that combustion instabilities and associated flow oscillations may also occur in scramjet engines, although the problem has not been recognized and explored yet. The present work investigated thermoacoustic instabilities inside an ethylene-fueled scramjet combustor with a recessed-cavity flameholder. Detailed characterization was made of flame oscillation and acoustic motion using high-speed photography and pressure measurements. The effects of fuel/air equivalence ratio, fueling scheme, and simulated flight conditions on the stability characteristics in the engine flowpath were examined systematically. In addition, an analytical analysis based on the acoustic and convective feedback loops among the precombustion shock, fuel injection, and distributed flame was established to help understand and correlate the observed oscillation phenomena. The oscillation frequencies fall in a range of 100-400 Hz, with the upper bound dictated by the shockflame coupling mechanism and the lower bound by the injector-flame interaction.

The gas entrainment in a hollow cone spray submitted to variable density is studied experimentally in order to better understand the effect on mixture formation. Particle image velocimetry on fluorescent tracers, associated with a specific processing of the instantaneous velocity fields have been applied to obtain measurement in the close vicinity of the spray edge. In the ''quasi-steady'' region of the spray, important effect of the ambient density on the mass flow rate of entrained gas ð _ m e Þ have been pointed out. The axial evolution of _ m e is in good agreement with an integral model that takes the momentum exchange between phases into account.

This paper presents a general overview of the ACHEON Project (EU FP7 Level 0 -Transport including Aeronautic). This project presents a novel dynamically controllable Coanda jet using two fluid streams to produce the angular deflection of the jet as a function of their momentum. A control system with electrostatic plasma is used to produce an effective and more precise control of the system. This paper presents the general guidelines of the project which is going to start and presents expected results.

Este trabajo se enfoca en estudiar por medio de simulaciones numericas el flujo alrededor de dos cilindros circulares en tandem considerando su proximidad con el suelo. Los cilindros se encuentran inmersos en un flujo con capa limite del suelo para un numero de Reynolds subcritico Re=10000. Para modelar el flujo turbulento tridimensional y dependiente del tiempo se utiliza el modelo de turbulencia SAS (Scale-Adaptive Simulation) por medio del codigo Fluent. La interferencia entre los cilindros y con el suelo se analiza para distintas separaciones entre cilindros y distintas proximidades con el suelo. Se examinan los coeficientes de sustentacion, de arrastre, y el comportamiento del desprendimiento de vor-tices. Los resultados son comparados con resultados de cilindros en tandem de ensayos experimentales y simulaciones numericas disponibles en la literatura, como asi tambien con el caso de un cilindro solo cercano al suelo.

In this work, the governing partial differential equations (continuity and Cauchy's momentum equations) describing the flow of power-law type non-Newtonian fluids across a semicircular cylinder (oriented with its curved surface in the upstream direction) have been solved numerically. In particular, consideration has been given to the delineation of the critical Reynolds numbers denoting the onset of flow separation from the surface of the cylinder and the onset of the laminar vortex shedding regime. This information is germane to establish the scaling of the macroscopic characteristics like drag coefficient and Strouhal number on the governing parameters, namely, Reynolds number and power-law index. The present results clearly suggest that the transitional Reynolds numbers show a strong dependence on the type (shear-thinning and shear-thickening) of fluid behavior as well as on the severity of the shear-dependence of the viscosity. With reference to the behavior seen in Newtonian fluids, the flow remains not only attached to the surface up to higher Reynolds numbers, but shear-thinning behavior also delays the onset of the laminar vortex shedding regime. As expected, shear-thickening fluids, of course, display the opposite characteristics.

This paper presents a general overview of the ACHEON Project (EU FP7 Level 0-Transport including Aeronautic). This project presents a novel dynamically controllable Coanda jet using two fluid streams to produce the angular deflection of the jet as a function of their momentum. A control system with electrostatic plasma is used to produce an effective and more precise control of the system. This paper presents the general guidelines of the project which is going to start and presents expected results.

Free Stream Turbulence is usually disregarded as a governing parameter in the assessment of aerodynamic forces. However, an effect is noticeable on the aerodynamic coefficients if turbulence is added at the inlet. In this work, the performance of different sub-grid scale (SGS) models of large-eddy simulation (LES) is investigated against their capability to describe the separation bubble of a blunt plate under a turbulent inlet. This is aimed at starting a broader research on the actual role of turbulence on the aerodynamic behaviour. Together with the Smagorinsky, the dynamic and the WALE SGS models, also the URANS k-ε and k-SST have been compared. The results show that whether URANS is able to accurately describe the undisturbed case, it gives a wrong turbulent inlet in the other one. Although the LES technique can improve the accuracy of this complex configuration, the choice of a suitable averaging time strongly affects the validation of the model. It was found that the role of the SGS eddies is not preponderant. Then a complex system of equations may lead to instability of the solver and prohibitive time step requirements. Among the SGS models investigated, the Smagorinsky SGS model, using a damping function to tackle the near-wall behaviour, qualifies then as a good candidate for further, more complex, geometries

The paper proposes a new concept of flight, including in the first phase of the flight, a vertical take-off, using the propulsion forces from an on-board rocket engine. The en-route phase of the flight, when moving horizontal, as the first part of the approach for landing, are conducted more similar with a rotary-wing flight. Also, the UAV sustentation comes from his aero dynamical shape. Especially designed to overcome the air resistance, the aerial vehicle has an appropriate design of the fuselage, which comply with a Coandă aerodynamic profile. Landing is assisted with the help of the same rocket engine, used for take-off. Up today, in our efforts to optimize the design of this VTOL-UAV, we made a first experimental model at a reduced scale. Moreover, aerodynamic researches have been conducted on it, in a wind tunnel, to enable optimal aerodynamic design of this new type UAV. Brief, the proposed aerial vehicle may be characterized as a mixture between a Coandă UAV and a reaction ...

Recent developments in the electronics industry have introduced a multi-stack ball grid array (BGA) to meet the growing consumer demand for both high-performance and smaller-sized chip packages. This study focused on the preliminary study of the Package-on-Package (PoP) underfill process using a material dam method. High viscosity type of underfill material is considered for the underfill process. In the current experimental work, L path-dispensing method was chosen due to its advantages, as reported in the previous work. The material dam method was used to prevent underfill from moving backwards and flowing out from the dispensing region. The material dam was built surrounding the PoP package. The effectiveness of the underfill process was analyzed based on the cycle time and lateral lapping, which are significant factors in material selection. The experimental results revealed that slow underfill flow may cause the quickly harden of material while the dispensing process is still running. This situation restricts the underfill flow and creates voids in the PoP package. The material dam method successfully enhanced the underfilling process for layers 3 and 4 stacked-package. This study is expected to provide the preliminary underfill process of stacking the PoP package and is useful as a reference for the engineer in the microelectronics industry. .