LES and DNS

Conocer el comportamiento del flujo alrededor de pares de cilindros circulares es de gran importancia practica en muchas areas de la ingenieria. En este trabajo se investiga numericamente la interferencia de flujo entre dos cilindros dispuestos uno detras de otro (tandem) para un numero de Reynolds Re=1.2e05. El flujo turbulento tridimensional y dependiente del tiempo alrededor de los cilindros es simulado numericamente utilizando el modelo de turbulencia SAS (Scale-Adaptive Simulation) por medio del codigo Fluent, que implementa el metodo de volumenes finitos. El solver empleado es el algoritmo SIMPLE (Semi Implicit Method for Pressure Linked Equations) con un esquema bounded second-order implicit para resolver la formulacion transitoria. La distancia de centro a centro entre los cilindros (L) varia desde 1.2 a 6 diametros (D) del cilindro, a fin de identificar los efectos de interferencia de estela debido a la proximidad entre los cilindros. La dinamica de vortices y las fuerzas a...

A fin de mejorar el diseno racional de estructuras fijas, resulta necesario estudiar la accion del flujo de aire alrededor de las mismas. Tal es el caso de los tanques y silos de almacenamiento, donde la estimacion de las acciones debidas al viento y sus consecuencias, inciden en el diseno y optimizacion estructural. En este trabajo se presenta un analisis numerico por medio de dinamica de fluido computacional (CFD) del campo de movimiento alrededor de un tanque metalico con el objetivo de obtener la distribucion de presiones de viento sobre el mismo. El estudio se realiza mediante el uso del programa comercial Ansys Fluent que implementa el metodo de volumenes finitos. La validacion del codigo se realizo mediante la reproduccion numerica del flujo alrededor de una esfera para distintos numeros de Reynolds. Seguidamente se desarrollaron modelizaciones numericas del flujo de viento actuando sobre un tanque cilindrico del que se tienen datos experimentales en tunel de viento. Los resu...

Reducing the consumption of hydrocarbon fuels within the transportation sector remains one of the most important challenges to reduce greenhouse gas emissions. Even if the development of electric vehicles is regarded as one of the preferred routes in coming years, most of the future projections agree that hybrid powertrains will continue to have a large market share in the next decades as underlined recently by Reitz et al. [1]. Therefore, improvements in internal combustion engine efficiency are essential, in addition to the fact that internal combustion engine remains an effective and low risk technology pathway for energy transition. The performance of combustion engines has significantly improved in terms of thermal efficiency, thus contributing to significantly reduced levels of CO2 and exhaust gas emissions as the result of advanced research and development for combustion systems. Engine CFD codes can be very powerful tools to support advanced combustion system development if ...

In the present study, the turbulent gas flow dynamics in a two-dimensional convergentdivergent rocket nozzle is numerically predicted and the associated physical phenomena are investigated for various operating conditions. The nozzle is assumed to have impermeable and adiabatic walls with a flow straightener in the upstream side and is connected to a plenum surrounding the nozzle geometry and extended in the downstream direction. In this integrated component model, the inlet flow is assumed a two-dimensional, steady, compressible, turbulent and subsonic. The physics based mathematical model of the considered flow consists of conservation of mass, momentum and energy equations subject to appropriate boundary conditions as defined by the physical problem stated above. The system of the governing equations with turbulent effects is solved numerically using different turbulence models to demonstrate their numerical accuracy in predicting the characteristics of turbulent gas flow in such complex geometry. The performance of the different turbulence models adopted has been assessed by comparing the obtained results of the static wall pressure and the shock position with the available experimental and numerical data. The dimensionless shear stress at the nozzle wall and the separation point are also computed and the flow field is illustrated. The various implemented turbulence models have shown different behavior of the turbulent characteristics. However, the shear-stress transport (SST) k-x model exhibits the best overall agreement with the experimental measurements. In general, the proposed numerical procedure applied in the present paper shows good capability in predicting the physical phenomena and the flow characteristics encountered in such kinds of complex turbulent flow.

Aerodynamic characteristics of wind barriers on two Croatian viaducts were experimentally studied in the CRIACIV boundary layer wind tunnel. Effects of wind incidence angle on flow field characteristics behind the wind barrier were reported. Mean velocity fields and vorticity fields were determined using the Particle Image Velocimetry (PIV). Freestream velocities were measured using the hot-wire velocimetry and the Pitot tube. Results indicate a possibility of wind-induced instability of high-sided vehicles at larger vertical incidence angles, especially in the traffic lane close to trailing edge of the bridge, as velocity fluctuations and mean freestream velocities approach the road surface when increasing the vertical incidence angle. Removing elements from the wind barrier can result in very large local velocities immediately downstream from the barrier. Variations in horizontal incidence angle do not seem to affect flow field characteristics significantly.

Multiphase flows in pipes are widely used in oil and gas industries to transport solid-liquid or gas-solid mixtures. Erosion caused by solid particles impact and friction becomes a major challenge for equipment maintenance and safety, especially at pipeline singularities such as elbows. In this work, a CFD study on wall erosion in a 90 • standard elbow is performed using a multi-fluid approach, also called Euler/Euler, for poly-dispersed fluid-particle flows. A model is proposed for the erosion prediction by taking into account particle agitation obtained from the Euler-Euler approach. A good agreement with experiments is observed. Then, effect of different particle turbulence models on the erosion rate are investigated.

This study investigated the distribution and dynamics of the Turbulent Kinetic Energy (TKE) around a group of three tandem piers using a combination of numerical simulations and experimental measurements. The Volume of Fluid (VOF) method, coupled with the k-ε turbulence model, was implemented in ANSYS FLUENT to replicate the free-surface flow conditions. An experimental validation was conducted using Acoustic Doppler Velocimetry (ADV) to assess the model's capability at capturing the turbulence characteristics. While the model effectively reproduced the near-bed turbulence, it consistently underestimated the TKE magnitudes across the flow domain, particularly in regions of strong vortex-induced turbulence. Discrepancies emerged in the confined regions between the piers, where the velocity profiles were overestimated at the surface and underestimated near the bed and mid-depth, impacting the TKE predictions. Despite these inconsistencies, the general pattern of the TKE distribution aligned with the experimental trends, though the absolute values remained underestimated due to the inherent limitations of the k-ε model. The model's performance in less turbulent regions demonstrated improved accuracy, reinforcing its applicability for moderate turbulence simulations. To further examine the interaction between vortex structures and the TKE, velocity distributions were analyzed at three specific depths (z/h = 0.15, 0.4, and 0.62). The findings showed the critical role of vortex shedding in TKE generation and dissipation, with notable variations in the turbulence intensity influenced by structural confinement effects. This study offers a novel, high-resolution evaluation of the k-ε model's ability to predict TKE distributions around tandem piers, using spatially detailed comparisons with the experimental data. Unlike previous studies that broadly acknowledged the model's limitations, this work systematically identifies the specific regions, particularly vortex-dominated zones, where its predictive accuracy significantly degrades.

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.

The study focuses on fluid–structure interactions (FSI) between a turbulent, gusty fluid flow, and a membrane structure. Lightweight structures are particularly vulnerable to wind gusts and can be completely destroyed by them, making it essential to develop and evaluate numerical simulation methods suited for these types of problems. In this work, a thin-walled membrane in the shape of a hyperbolic paraboloid (hypar) is analyzed as a real-scale example. The membrane structure is subjected to discrete wind gusts of varying strength from two different directions. A partitioned FSI approach is employed, utilizing a finite-volume flow solver based on the large-eddy simulation technique and a finite-element solver developed for shell and membrane structures. A recently proposed source-term formulation enables the injection of discrete wind gusts within the fluid domain in front of the structure. The study aims to assess the impact of wind gusts on the resulting deformations and the induced stresses in the tensile material, with a particular focus on the influence of different wind directions. The corresponding article https://doi.org/10.1063/5.0232369 is in Open Access.

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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An ideal scheme for the solution of multidimensional non-linear systems of partial differential equations governing fluid motion has not been found yet despite years of research effort and many scientific contributions. In the context of finite volume approximations based on flow dependent schemes, discussion is opened as to whether upwind or multidimensional upwind schemes are preferable for solving 2D problems. In this work we consider the use of upwind and multidimensional upwinding techniques for 2D shallow water flows, in particular, to the simulation of dam break flows. The basis of the two numerical methods is stated and the particular adaptation to the shallow water system is described. As test cases, laboratory experimental data supplied by partners of the Working Group on Dam Break Flow Modelling (CADAM) are used.

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.

Compressible DNS study of separation bubbles for flow past a low pressure turbine blade 1 RAJESH RANJAN, SURESH DESHPANDE, RODDAM NARASIMHA, JNCASR -A representative low pressure turbine blade T106A is subjected to a direct numerical simulation (DNS) study for low Reynolds Number (Re = 51831 based on inflow velocity and axial chord) and angle of incidence (45.5 deg from the axial chord). The DNS code used here solves the compressible Navier-Stokes equations and uses a semi-kinetic energy preserving scheme. A hybrid grid is used for the computational domain, with a very fine wall-bounded boundary layer grid near the surface of the blade and an unstructured grid for rest of the domain. Total grid size for the current simulation is around 160 million. In the mean flow, a long but shallow separation bubble is found near the trailing edge. However, the instantaneous flow reveals a train of bubbles at this location. These instantaneous bubbles continually break and merge in time. The presence of these separation bubbles make the flow very complicated, as the bubbles are responsible for tripping the otherwise laminar flow to a transitional state. Skin friction and heat transfer coefficient are also computed over the blade to understand the effect of these bubbles on parameters of engineering importance.

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.

Fil: Aguirre, Cesar Augusto. Provincia de Entre Rios. Centro de Investigaciones Cientificas y Transferencia de Tecnologia a la Produccion. Universidad Autonoma de Entre Rios. Centro de Investigaciones Cientificas y Transferencia de Tecnologia a la Produccion. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Centro de Investigaciones Cientificas y Transferencia de Tecnologia a la Produccion; Argentina. Universidad Nacional de Entre Rios. Facultad de Ciencias Agropecuarias; Argentina

When two liquid bodies with different density come in contact in non-equilibrium conditions, a flow is caused, known as gravity or density current. In the environment, as well as in the industrial framework, this kind of flow is very common and the scientifictechnical interest of the investigation on it is very high. The paper of and the book of Ungarish (2009b) give excellent reviews on the state of the art of the topic, while a huge collection of artificial, as well as natural, gravity currents and a qualitative description of their key features is given in the book of . The investigation on gravity currents dates back to several decades ago (first important works are those of Von Prandtl, 1952 and, nevertheless many aspects still need a better understanding. These aspects should be investigated in order to widen the knowledge on the considered phenomenon and are generally related to the geometry of the fluid domain and the use of particular fluids, like e.g. mixtures of liquid and sediments. Early studies on gravity currents were based on analytical and experimental methods and were concerned with 2D gravity currents: i.e. gravity currents whose description can be made in a vertical x-z plane. The seminal work of Benjamin (1968) formulates a fundamental theory, based on the perfect-fluid hypothesis and simple extensions of it (like the classical theory of hydraulic jumps), which gives a relationship between the thickness of the gravity current and the velocity of the front. The Benjamin's theory is a milestone and analytical investigations on gravity currents, even the most recent (

Speleogenesis is one of the most essential studies at speleological science. it examines how caves are formed and developed as the fundamental knowledge to comprehend cavity phenomena. These phenomena occasionally occur in karstic landscape where Karakal-Japyryk Natural Reserve, as part of carboniferous limestone in Tien-Shan Mountain is located. Several factors such as climatic, geologic, and biologic factors hold a certain role in speleogenetic process. One of the key roles from geological factor is the presence of geological structures e.g. bedding plane and joint which initiates cavity development.This paper tends to examine the speleogenetic process happens at Karakal-Japyryk Reserve. The speleogenetic process can be described using speleomorphological approach combined with measured stratigraphy and structural study to reconstruct the process happening. Measurement and drawing of cave dimension was also conducted to obtain a visualization of the cave. This study was particular...

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

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.

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.

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.

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.

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.

Prediction Technologies (WaPT) -A turbulent two-vortex system (T-2VS) at statistical equilibrium is first obtained. This is done by putting two vortices with analytical circulation distribution in a weak homogeneous isotropic turbulence field (obtained by LES), and then further running the LES. The system goes unstable and a turbulent equilibrium is obtained after some transient. This is believed to be representative of the state reached by the wake behind a real aircraft, when it is fully rolled up. The T-2VS is also characterized (vortex circulation profile, turbulence, etc.), which provides useful information to support further modeling and theory. Next, that T-2VS wake is put in near ground proximity, and a wall-resolved LES at Re Γ = Γ/ν = 2.0 10 5 is carried out: this is ten times larger than the published works on wake vortices interacting with a ground. As the T-2VS comes down, it goes in ground effects (IGE), and then strongly interacts with the ground and rebounds. The physics of the interaction with the ground are analyzed (also relatively to previous works where the 2VS was made of 2D analytical vortices with white noise added), and diagnostics are obtained: vortex rebound and trajectory, vortex global circulation decay, state of the vortices long after rebound (also an equilibrium).

Prediction Technologies (WaPT) -A turbulent two-vortex system (T-2VS) at statistical equilibrium is first obtained. This is done by putting two vortices with analytical circulation distribution in a weak homogeneous isotropic turbulence field (obtained by LES), and then further running the LES. The system goes unstable and a turbulent equilibrium is obtained after some transient. This is believed to be representative of the state reached by the wake behind a real aircraft, when it is fully rolled up. The T-2VS is also characterized (vortex circulation profile, turbulence, etc.), which provides useful information to support further modeling and theory. Next, that T-2VS wake is put in near ground proximity, and a wall-resolved LES at Re Γ = Γ/ν = 2.0 10 5 is carried out: this is ten times larger than the published works on wake vortices interacting with a ground. As the T-2VS comes down, it goes in ground effects (IGE), and then strongly interacts with the ground and rebounds. The physics of the interaction with the ground are analyzed (also relatively to previous works where the 2VS was made of 2D analytical vortices with white noise added), and diagnostics are obtained: vortex rebound and trajectory, vortex global circulation decay, state of the vortices long after rebound (also an equilibrium).

Numerical flux functions for solving the Euler equations using exact and/or approximate solutions of the Riemann problem of gasdynamics are discussed. Under certain restrictive conditions, schemes using these flux functions produce systems of equations which can exhibit a single degree of freedom. In some instances, the solutions represented by this degree of freedom are unstable to perturbations. This local instability can seriously degrade the temporal convergence of numerical schemes. This point is demonstrated by numerical example.

Fil: Aguirre, Cesar Augusto. Provincia de Entre Rios. Centro de Investigaciones Cientificas y Transferencia de Tecnologia a la Produccion. Universidad Autonoma de Entre Rios. Centro de Investigaciones Cientificas y Transferencia de Tecnologia a la Produccion. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Centro de Investigaciones Cientificas y Transferencia de Tecnologia a la Produccion; Argentina. Universidad Nacional de Entre Rios. Facultad de Ciencias Agropecuarias; Argentina

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.

Naturally occurring plumes such as wildland fires [17], smoke plumes [18], volcanic plumes [16], and dust storms are all examples of buoyancy-driven turbulent flows at geophysical scales in which the active scalar, such as temperature, density, or concentration dominates the flow physics.

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

This NRC Decadal Survey white paper, provided by the thermal protection technology community, is a general assessment of the current capability of thermal protection systems (TPS) with respect to the scientific exploration of Venus as well as anticipated TPS requirements in support of future Venus missions 1,3,5. The paper begins with a brief history of

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].