Numerical Study of Unsteady Effects in Combustion Systems by Means of Coupled Explicit Algebraic Reynolds Stress Model (earsm) and Explicit Algebraic Scalar Flux Model (easfm)

The swirl flow plays a central role in combustion systems. It is important to capture all phenomena associated with it. In particular, lean partially premixed combustion in gas turbine combustion chamber is often associated with hydrodynamic instabilities, known as processing vortex core (PVC). Therefore an unconfined swirl flow with a precessing vortex core is being studied in presented work by means of simulations and experiments. The ability of explicit algebraic formulation to capture such flow and mixing properties by using economical cost requared for engineering design purposes is demonstrated. The experiment has been carried out by Schneider [3] and the first time dependent numerical investigation, based on Reynolds stress models, has been presented by Maltsev [2] and with LES by Wegner [5]. Introduction For many industrial and engineering purposes statistical modeling will continue to be the main approach to represent the effects of turbulent processes in CFD for technical flows regardless of recent progress in Large Eddy Simulation (LES) and novel development of statistical closures at a level higher than the first order. While first order model provide excellent predictions for many flows of engineering interest, there are many applications for which predicted flow properties differ greatly from corresponding measurements, e.g. flows with sudden changes in vean strain rate, flows over cuvature surface, flows with secondary motions, unsteady effect in combustion systems etc. In contrast to the first order models the second order models allow to take into account many effects included to above named flows. Unfortunatelly, the number of additional transport equations for turbulent quantities of the flow field (Reynolds stress tensor) and the scalar field (scalar flux vector) increased dramatically to 7+3 for second order models from 2+0 for k ε − models and gradient assumption. Compomise between first and second order models is the nonlinear models, which have strong binding to the cflibration of model coefficients by nonlinear terms e.g. CLS model has 7 model coefficients. This can be overcome by the algebraic formulation resulting from the full Reynolds stress models. Therefore these models save the simplest of models of first level and allow to describe many effects as models of second level. Governing Equation The turbulent mean flow of a viscous, incompressible fluid is governed by the Reynolds-averaged continuity and Navier-Stokes equations