A. Nauert

Simultaneous PIV/PH-PLIF, Rayleigh thermometry/OH-PLIF and stereo PIV measurements in a low-swirl-flame

The diagnostic techniques for simultaneous velocity and relative OH distribution, simultaneous temperature and relative OH distribution, and three component velocity mapping are described. The data extracted from the measurements include statistical moments for inflow fluid dynamics, temperature, conditional velocities, and scalar flux. The work is a first step in the development of a detailed large eddy simulation (LES) validation database for a turbulent, premixed flame. The low-swirl burner used in this investigation has many of the necessary attributes for LES model validation, including a simplified interior geometry; it operates well into the thin reaction zone for turbulent premixed flames, and flame stabilization is based entirely on the flow field and not on hardware or pilot flames.

Conditional velocity measurements by simultaneously applied laser Doppler velocimetry and planar laser-induced fluorescence in a swirling natural gas/air flame

Abstract By applying joint velocity/scalar measurements, conditional mean axial and radial velocity components are determined in the vicinity of the turbulent flame front of a premixed swirling natural gas/air flame. Two velocity components are measured by laser Doppler velocimetry (LDV) simultaneously with planar laser-induced fluorescence (PLIF) monitoring the hydroxyl radical (OH). The spatial OH distribution is used to tag the instantaneous position of the flame front and can be thereby used to derive conditional velocities. From these measurements the turbulent flux of the mean progress variable is determined which is an important quantity to model premixed flames. One important finding is that for this rather complex but technically realistic geometry, at some locations in the flame brush conditional axial and radial velocities show different behaviour. Thus gas expansion effects can dominate axially whereas in radial direction turbulent fluctuations determine the direction of turbulent transport.

Advanced Laser Diagnostics for Understanding Turbulent Combustion and Model Validation

This contribution is not an original publication but a report of cumulative work that was carried out within the framework of SFB 568. The work was published in different archival journals and figures and text passages have been taken from different journal articles as indicated by the references. The aim of this report is to present experiments in projects B1 and B3 for improving our understanding in turbulent combustion with a focus of turbulent flow and scalar fields as well as their mutual interactions. The report is restricted to generic gaseous turbulent flames that feature different characteristics important to practical applications. The methods presented here are feasible to study boundary conditions, flow and scalar fields and are based all on interactions between laser light and matter. Following a brief introduction, two target flames are discussed in Sect. 4.2. Sections 4.3 and 4.4 exemplify flow and scalar measurements. Section 4.5 discusses combined scalar/flow measurements that can significantly improve our understanding of turbulence-chemistry interactions. In Sect. 4.6 new developments based on high-repetition-rate imaging are highlighted. These diagnostics complement methods at low repetition rate commonly used to generate an understanding by statistical moments and probability density functions. High repetition rate imaging techniques presently are an emerging field. Although the most recent developments achieved in the funding period of the Collaborative Research Center are included to this report, near-future progress in this field will lead to even more interesting insights into combustion phenomena.

Imaging Studies of Swirl-Stabilized Premixed Flames

Swirl-stabilized flames have been studied using imaging techniques, for LES code validation. Rapid framing PLIF has been combined with simultaneous PIV. Rapid imaging of chemiluminescent emission provided information on dynamic events such as flash-back.