Simulating the burning behaviour of swirling flames
In several industrial applications there is a high demand for reliable predictive models for turbulent swirling flames. One example is the development of new low emission gas turbines using LPP ("Lean Premixed Prevaporized") combustion systems.
The here fore developed model consists of two parts. In one part the Navier Stokes equations for compressible flows are solved with a finite volume method to calculate the hydrodynamic fields. Additionally, to model the strong interaction between turbulence and chemistry in detail the transport equation for the joint probability density function (JPDF) of velocity and scalars is solved in the second part. Due to the high dimensionality of the transport equation this is done with a particle Monte Carlo method. Chemical kinetics are taken into account with reduced chemical reaction mechanisms, which have been developed using the ILDM method ("Intrinsic Low-Dimensional Manifold").
This model is applied to a simple but, nevertheless, realistic test case in which a statistically stationary confined swirling premixed methane-air flame is investigated.
The picture above shows the characteristic axial velocity field of the investigated system. The area of negative axial velocity in the centre of the chamber (internal recirculation zone) at the position of the jump in the diameter is used to stabilize the flame. In this region hot exhaust gases are used to ensure a stable burning behaviour of the flame.
A typical temperature profile is shown in the picture below. One can see a sudden rise of temperature in the region of the internal recirculation zone indicating the position of the flame front.
(Stefan Lipp, Ulrich Maas, Institute for Technical Thermodynamics, Universitšt Karlsruhe, Peter Lammers, HLRS)