22 research outputs found

    A new Eulerian Monte Carlo method for the joint velocity-scalar PDF equations in turbulent flows

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    In the field of turbulent combustion, Lagrangian Monte Carlo (LMC) methods (Pope, 85) have become an essential component of the probability density function (PDF) approach. LMC methods are based on stochastic particles, which evolve from prescribed stochastic ordinary differential equations (SODEs). They are used to compute the one-point statistics of the quantities describing the state of a turbulent reactive flow: namely, the velocity field and the reactive scalars (species mass fractions and temperature). Numerous publications document the convergence and accuracy of LMC methods. They have been used in many complex calculations (including LES), and for several years now, they have been implemented in commercial CFD codes. Nonetheless, the development of a new Eulerian Monte Carlo (EMC) method is useful and stimulating, since the competition between LMC and EMC methods could push both approaches forward. EMC methods have already been proposed by Sabel'nikov and Soulard (2006) in order to compute the one-point PDF of turbulent reactive scalars. EMC methods are based on stochastic Eulerian fields, which evolve from prescribed stochastic partial differential equations (SPDE) statistically equivalent to the PDF equation. The extension of EMC methods to include velocity still remains to be done. Thus, the purpose of this article is to derive SPDEs allowing to compute a modeled one-point joint velocity-scalar PDF. To achieve this objective, we start from existing Lagrangian stochastic models. The latter are described by SODEs, which can be considered as modeled Navier-Stokes equations written in Lagrangian variables. Then, the idea is to transform these Lagrangian SODEs into Eulerian SPDEs, in the same way one transforms the Lagrangian Navier-Stokes equations into Eulerian equations, in classical hydrodynamics. However, our case differs from the classical one. Indeed, the stochastic velocity does not respect an instantaneous continuity constraint, but only a mean one. To account for this difference between the stochastic and the physical system, one must introduce a stochastic density, different from the physical density. As a result of this procedure, we eventually obtain hyperbolic conservative SPDEs giving the evolution of a stochastic velocity, of stochastic scalars, and of a stochastic density. In addition to the main result, an alternative EMC method for the scalar PDF is also derived as a special case of the full velocity-scalar method

    Numerical investigation of a Mach 12 REST scramjet at off-design conditions

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    The description of combustion in high-speed turbulent flows where turbulent mixing, compressibility effects and chemical kinetics processes are competing, still remains a challenging issue for numerical simulations. The key features of such turbulent supersonic reactive flows are highlighted and integrated into a new Turbulence-Chemistry Interaction (TCI) closure which relies on the partially stirred reactor (PaSR) framework. The corresponding closure, hereafter denoted UPaSR model, is integrated into the Onera CFD (Computational Fluid Dynamics) code CEDRE. A Mach 12 REST (Rectangular-to-Elliptical-Shape-Transition) scramjet engine developed and tested at the University of Queensland is retained as a validation test case. Results of Reynolds Average Navier Stokes (RANS) numerical simulations based on the UPaSR concept and the QL (Quasi-Laminar) closure are presented and compared. Similar results in terms of pressure distributions were obtained. This confirmed that the essential point to cope with such scramjet engine conditions is to represent satisfactorilly the compressible flowfield. Two different strategies to evaluate the scramjet engine performance have been applied: the first one is based on a quasi-one-dimensional tool using experimental pressure distributions and the second one is based on RANS numerical simulations through the calculation of energetic efficiencies. The inlet injection scheme presented the best performance with a combustion efficiency of 78%

    Shortand medium-term results of knee replacement with modular eddoprothesis in maligant tumors of knee

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    The purpose - to evaluate the short- and medium-term results of treatment patients with knee tumors using modular endoprostheses GMRS (Stryker) and OSS (Biomet). Matherial and methods. The article presents the experience of use in clinical practice in patients with malignant tumors of the knee modular endoprosthesis (Global Modular Replacement System (Stryker) and Oncology Salvage System (Biomet). Also the results of analysis of these implant systems in primary total knee replacement in 63 patients. Results. Overall 5-year survival of patients of the study group was 87.3%, 5-year disease-free survival - 92.1%. Average follow-up was 4 years. Immediate and medium-term good and satisfactory results were achieved orthopedic in 51 (80.9%) patients; complications were noted in 5 (8.8%) cases

    On the possible mechanisms of intensification of the combustion in the channel with the supersonic stream

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    Communication to : 12th international conference on methods of aerophysical research (ICMAR 2004), Novosibirsk (Russie), 28 Juin - 1 Juillet 2004Available from INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.2004 n.230 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc
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