Experiments for Combustion-LES Validation

Abstract

Designs of future combustors increasingly rely on numerical combustion simulations. Large-eddy simulation (LES) emerged as a method to better describe turbulence than Reynolds-averaged Navier-Stokes (RANS) approaches. Processes at the subgrid scale, however, need to be modelled. Validation using comprehensive and reliable experimental data sets is therefore a crucial part in the development of combustion-LES. Using well-defined benchmark flames and advanced laser diagnostics, different physical and chemical quantities can be precisely measured with high temporal and reasonable spatial resolution. In this contribution, quantities important to combustion-LES validation and the most frequently used laser diagnostic methods are briefly reviewed. New challenges in the field of diagnostics at high repetition rates and at walls are highlighted. In a closing chapter, some critical aspects on the comparison of experimental measurands and combustion-LES-predicted counterparts are discussed.

Review of laboratory swirl burners and experiments for model validation

“…A key ingredient to advance the modelling of turbulent swirling flames is the availability of extensive and reliable data bases of well-designed laboratory burners that may be used by modellers as platforms for model development and validation [20]. Workshops such as TNF (International Workshop on the Measurements and Computations of Turbulent Nonpremixed Flames) have been instrumental in promoting this approach through computations supported by data derived via non-intrusive laser diagnostics [21][22][23]. The complexity and multi-modal nature of swirling flows, as well as the need to access state-of-the-art diagnostics so as to resolve swirl combustion characteristics, have limited the number of research groups involved with these flows to a handful.…”

In-Nozzle Measurements of a Turbulent Opposed Jet Using PIV

“…For Reynolds Averaged Navier Stokes (RANS) simulations, only the Reynolds averaged mean quantities, Reynolds stresses and length scales must be known at the inflow and the simulations are relatively insensitive to small errors of the inlet conditions. For LES, even more detailed information is needed because the unsteady, three-dimensional, turbulent velocity field must be imposed at the inflow at each time step [3,16,24]. Therefore temporally evolving velocity profiles as well as information on the structure and shape of the turbulent eddies are required.…”

Highly-resolved LES and PIV Analysis of Isothermal Turbulent Opposed Jets for Combustion Applications

“…In particular for LES the length scale of turbulence and the Reynolds stress tensor at the inlet are required, without which the simulations will not yield any accurate results [14]. Furthermore time-resolved velocity information from state-of-the-art experiments is helpful to understand the turbulence at the computational inlet and can thereby improve the simulation quality [2,41]. Previous experimental investigations of opposed jets have for example found that the flow field near the nozzle is often not fully developed, isotropic and homogenous, and the authors referred to this state as 'young turbulence' [13,35].…”