			Home About us Contact

Inflow Conditions (inflow + condition)

Distribution by Scientific Domains

Engineering	100%

Selected Abstracts

LES of a Confined Configuration using Oscillating Inflow Conditions

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003
Michael Düsing
In actual turbulent flow problems, in particular in gas turbine combustion chambers, flows are three dimensional, recirculating and turbulent in confined and complex geometries. Instationarities due to turbulence, combustion instabilities and oscillating inflow conditions require a highly time and spatial resolving procedure. 3D Large Eddy Simulations (LES) are therefore used in this work to study two confined coaxial air jets with oscillating velocity inflow conditions. The influences of the inflow, in particular frequency (f = 0 ÷ 1600 [Hz]) and amplitude, on the velocity are analysed. [source]

Numerical simulation of gaseous fuel injection: A new methodology for multi-dimensional modelling

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2010
Luca Andreassi
Abstract The use of natural gas (instead of liquid or solid fuels) is nowadays drawing an increasing interest in many applications (gas turbines, boilers, internal combustion engines), because of the greater attention to environmental issues. To facilitate the development of these applications, computer models are being developed to simulate gaseous injection, air entrainment and the ensuing combustion. This paper introduces a new method for modelling the injection process of gaseous fuels that aims to hold down grid requirements in order to allow the simulation also of other phenomena, like combustion or valve and piston motion, in reciprocating internal combustion engines. After a short overview of existing models, the transient jet model and the evaluation of inflow conditions are described in detail. Then a basic study of the grid effects on the jet evolution is presented. The model is updated and validated by comparing numerical results with available experimental data for two different operating conditions: a subsonic and a supersonic under-expanded case. The model demonstrates to be fast enough to be used in a multi-dimensional code and accurate enough to follow the real gas jet evolution. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Influence of reaction mechanisms, grid spacing, and inflow conditions on the numerical simulation of lifted supersonic flames

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2010
P. Gerlinger
Abstract The simulation of supersonic combustion requires finite-rate chemistry because chemical and fluid mechanical time scales may be of the same order of magnitude. The size of the chosen reaction mechanism (number of species and reactions involved) has a strong influence on the computational time and thus should be chosen carefully. This paper investigates several hydrogen/air reaction mechanisms frequently used in supersonic combustion. It is shown that at low flight Mach numbers of a supersonic combustion ramjet (scramjet), some kinetic schemes can cause highly erroneous results. Moreover, extremely fine computational grids are required in the lift-off region of supersonic flames to obtain grid-independent solutions. The fully turbulent Mach 2 combustion experiment of Cheng et al. (Comb. Flame 1994; 99: 157,173) is chosen to investigate the influences of different reaction mechanisms, grid spacing, and inflow conditions (contaminations caused by precombustion). A detailed analysis of the experiment will be given and errors of previous simulations are identified. Thus, the paper provides important information for an accurate simulation of the Cheng et al. experiment. The importance of this experiment results from the fact that it is the only supersonic combustion test case where temperature and species fluctuations have been measured simultaneously. Such data are needed for the validation of probability density function methods. Copyright © 2009 John Wiley & Sons, Ltd. [source]

LES of a Confined Configuration using Oscillating Inflow Conditions

Large eddy simulations of turbulent swirling flows in a dump combustor: a sensitivity study

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2005
P. Wang
Abstract Large eddy simulations (LES) of confined turbulent swirling flows in a model dump combustor are carried out. The simulations are based on a high-order finite difference method on a Cartesian grid, with the sub-grid scale stress tensor modelled using a scale-similarity model. The aims of this work are to study the physics of the flow and to evaluate the performance of LES method for simulation of the major features of turbulent swirling flows,the vortex breakdown, the highly anisotropic and fast-decaying turbulence structure. Influences of inflow/outflow conditions, combustor geometry, inlet swirl profile and Reynolds numbers on the vortex breakdown and turbulence structures are investigated. At very high swirl levels, the influence of the outflow conditions and the outlet geometry is fairly significant, not only at downstream near the outlet, but also at far upstream. At low Reynolds numbers, the onset of vortex breakdown is fairly sensitive to the change of Reynolds number; however, at high Reynolds numbers it is rather insensitive to the Reynolds number. Comparisons of LES results with experimental data are made. The LES results are shown to be in reasonably good agreement with the experimental data if appropriate inflow and outflow boundary conditions are imposed. Copyright © 2004 John Wiley & Sons, Ltd. [source]