Hybrid Eulerian/Lagrangian 3D methods for high Reynolds number reactive flows

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 171-177).Research in advanced combustion modeling is critical to developing control strategies for optimized propulsion systems, especially with regard to stability, emissions, and power density. Examining combustion dynamics and control using numerical simulations, however, presents several challenges, given the multiscale and multiphysics nature of the underlying flows. This thesis presents progresses in combustion modeling for the numerical simulation of turbulent reactive jet flows through the design of a hybrid Eulerian/Lagrangian and massively parallel 3D numerical simulation tool. The adaptivity of the resulting software yields truly fast and accurate simulations, and a better understanding of the simulated combustion processes. The transverse jet vorticity dynamics at high Reynolds numbers are first described, and more specifically the unsteady interactions between the wall boundary layer and the jet. We then present actuation strategies that manipulate the jet penetration and spread via simple nozzle-edge perturbations. Finally, the adaptive Eulerian/Lagrangian code is used to provide a detailed understanding of flame anchoring mechanisms in transverse reactive jets.by Fabrice Schlegel.Ph.D

Fast three dimensional particle method for simulations of buoyant and reacting flows

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, June 2007.Includes bibliographical references (p. 89-91).This thesis describes progress in several areas related to three dimensional vortex methods and their application to multiphysics problems. The first is the solution of a generic scalar transport equation by advecting and diffusing the scalar gradient along a particle trajectory and onto a mesh, respectively, and recovering the scalar values using a Biot-Savart-like summation. The second is the accurate, high-resolution calculation of the velocity gradient using a fast treecode, which avoids using kinematic relations between the evolution of the gradients and the distortion of the flow map. The same tree structure is used to compute all the variables of interest and those required during the integration of the governing equations. Next, we apply our modified interpolation kernel algorithm for treating diffusion and remeshing to maintain long time accuracy. The coupling between the vorticity transport and that of a dynamic scalar, in this case the temperature or density in a gravitational field, is manifested by the generation of vorticity. We demonstrate the performance of the multiphysics algorithm by solving a number of buoyant and reacting flow problems.by Fabrice Schlegel.S.M

Contributions of the wall boundary layer to the formation of the counter-rotating vortex pair in transverse jets

Using high-resolution 3-D vortex simulations, this study seeks a mechanistic understanding of vorticity dynamics in transverse jets at a finite Reynolds number. A full no-slip boundary condition, rigorously formulated in terms of vorticity generation along the channel wall, captures unsteady interactions between the wall boundary layer and the jet – in particular, the separation of the wall boundary layer and its transport into the interior. For comparison, we also implement a reduced boundary condition that suppresses the separation of the wall boundary layer away from the jet nozzle. By contrasting results obtained with these two boundary conditions, we characterize near-field vortical structures formed as the wall boundary layer separates on the backside of the jet. Using various Eulerian and Lagrangian diagnostics, it is demonstrated that several near-wall vortical structures are formed as the wall boundary layer separates. The counter-rotating vortex pair, manifested by the presence of vortices aligned with the jet trajectory, is initiated closer to the jet exit. Moreover tornado-like wall-normal vortices originate from the separation of spanwise vorticity in the wall boundary layer at the side of the jet and from the entrainment of streamwise wall vortices in the recirculation zone on the lee side. These tornado-like vortices are absent in the case where separation is suppressed. Tornado-like vortices merge with counter-rotating vorticity originating in the jet shear layer, significantly increasing wall-normal circulation and causing deeper jet penetration into the crossflow stream.United States. Dept. of Energy. Office of Science (MICS) (Grant Number DE-FG02-98ER25355

Robust mechanistic modeling of protein ion-exchange chromatography

Mechanistic models for ion-exchange chromatography of proteins are well-established and a broad consensus exists on most aspects of the detailed mathematical and physical description. A variety of specializations of these models can typically capture the general locations of elution peaks, but discrepancies are often observed in peak position and shape, especially if the column load level is in the non-linear range. These discrepancies may prevent the use of models for high-fidelity predictive applications such as process characterization and development of high-purity and -productivity process steps. Our objective is to develop a sufficiently robust mechanistic framework to make both conventional and anomalous phenomena more readily predictable using model parameters that can be evaluated based on independent measurements or well-accepted correlations. This work demonstrates the implementation of this approach for industry-relevant case studies using both a model protein, lysozyme, and biopharmaceutical product monoclonal antibodies, using cation-exchange resins with a variety of architectures (SP Sepharose FF, Fractogel EMD SO3−, Capto S and Toyopearl SP650M). The modeling employs the general rate model with the extension of the surface diffusivity to be variable, as a function of ionic strength or binding affinity. A colloidal isotherm that accounts for protein-surface and protein-protein interactions independently was used, with each characterized by a parameter determined as a function of ionic strength and pH. Both of these isotherm parameters, along with the variable surface diffusivity, were successfully estimated using breakthrough data at different ionic strengths and pH. The model developed was used to predict overloads and elution curves with high accuracy for a wide variety of gradients and different flow rates and protein loads. The in-silico methodology used in this work for parameter estimation, along with a minimal amount of experimental data, can help the industry adopt model-based optimization and control of preparative ion-exchange chromatography with high accuracy

Scaling of analog LDPC decoders in sub-100nm CMOS processes

International audienceAnalog implementations of digital error control decoders, generally referred to as analog decoding, have recently been proposed asan energy and area competitive methodology. Despite several successful implementations of small analog error control decoders, little is currently known about how this methodology scales to smaller process technologies and copes with the non-idealities of nano-scale transistor sizing. A comprehensive analysis of the potential of sub-threshold analog decoding is examined in this paper. It is shown that mismatch effects dominated by threshold mismatch impose firm lower limits on the sizes of transistors. The effect of various forms of leakage currents is also investigated and minimal leakage current to normalizing currents are found using density evolution and control simulations. Finally, the convergence speed of analog decoders is examined via a density evolution approach. The results are compiled and predictions are given which show that process scaling below 90nm processes brings no advantages, and, in some cases, may even degrade performance or increase required resources

Reduction of trace mineral supplementation on performance and mineral status of fattening pigs

International audienceExcreted Cu and Zn can accumulate in the upper soil layer and harm its fertility. Thus, managing dietary contents in pig diets should reduce such risk. However, a limited supply of these essential trace elements to pig requires a better knowledge. This study aimed to evaluate the effect of three levels and two sources of Cu and Zn on performance and mineral status of fattening pigs. Four dietary treatments were compared including a negative control (NC) corresponding to the basal growing and finishing diets, without Zn and Cu supplementation (5 and 29 mg/kg Cu and Zn respectively); an intermediate level (O1) supplemented with Cu and Zn oxides (Cu2O and ZnO; CoRouge® and Hizox®, Animine, France), which provided on average 7.4 mg/kg Cu and 47.5 mg/kg Zn; two diets were supplemented with oxides (O2) or sulphates (PC, positive control) at maximal EU regulation levels (25 and 120 mg/kg for total Cu and Zn, respectively). Ninety-six pigs (24.3±3.3 kg BW) were allocated to one of the four experimental treatments and raised in individual pens during 14 weeks (up to 110.3±8.9 kg). Animal performance were measured and samples of plasma (at d1, d41 and d90), bones and liver (at slaughter) were collected. Every third week, samples of faeces were obtained to determine the dynamic of Cu and Zn excretion. Over the whole experimental period feed intake, body weight and feed conversion ratio were not affected by the level nor the source of Cu and Zn. Plasma Cu was not affected neither by treatment nor period, whereas plasma Zn increased with period but did not differed between treatments. Hepatic Cu increased (P<0.05) with dietary content, and a tendency for increase of bone Zn with dietary content (P<0.10) was observed. Faecal Cu and Zn decreased significantly (P<0.01) with dietary content. Although it seems possible to reduce dietary Cu and Zn without affecting performance, these results require to be validated in commercial farms with more challenging health constraints

Effects of reducing copper and zinc supplementation on the performance and mineral status of fattening pigs

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Effet de la réduction des niveaux de supplémentation en cuivre et zinc des aliments sur les performances et le statut minéral des porcs à l’engraissement

International audienceIn the perspective of reducing environmental impacts, this study aimed to assess impacts of reduced dietary copper (Cu) and zinc (Zn) supplementation on the growth performance and mineral status of fattening pigs. Ninety-six pigs weaned at 21 days of age were assigned one of four dietary treatments: a diet with no Cu or Zn supplementation (WS, 5 mg Cu and 29 mg Zn per kg feed); a diet supplemented with Cu and Zn oxides at an intermediate level (OINT, 7.4 mg Cu and 47.5 mg Zn per kg feed); and two diets supplemented with Cu and Zn oxides (OREG) or Cu and Zn sulphates (SREG) at levels reaching the maximum levels authorized in theEuropean Union (25 mg Cu and 120 mg Zn per kg feed). The pigs were raised in individual pens until slaughter. Over the entire experimental period, growth performance was not influenced by the dietary Cu and Zn content, nor by the Cu and Zn source used for supplementation. Plasma Cu and Zn contents were not influenced by the treatments. Liver Cu content increased (P < 0.05) as dietary Cu content increased. Bone Cu and Zn contents and bone physical characteristics were not influenced by the dietary treatments. As expected, faecal Cu and Zn contents decreased (P < 0.01) as dietary Cu and Zn contents decreased. Thus, excretionof Cu and Zn in faeces could be decreased by decreasing dietary supplementation of these elements for fattening pigs, without influencing growth performance or mineral status. However, these results need to be validated on commercial farms with group housing and more diverse sanitary conditions