Dantec and Lund University team up for high-speed combustion research
Lund University and Dantec Dynamics performs joint measurements of simultaneous time-resolved flow velocity field and flame front location in turbulent combustion.
By: Dr. Jimmy Olofsson, Application Specialist - January 24th, 2012
Simultaneous PIV (arrows) and OH PLIF (blue) data sampled with 4 kHz, in a turbulent premixed flame. Field-of-view is about 30 mm in width. The complete sequence consists of 2000 images.
Within the field of combustion research the structure and dynamics of turbulent flames are influenced by many parameters. In order to investigate flame stabilization mechanisms, the Combustion Physics division at Lund University in collaboration with Dantec Dynamics, has recently performed cutting edge flame measurements.
By applying high-end laser and imaging systems, unique high-speed film sequences with a frame rate of up to 4 kHz of simultaneous flow field (PIV) and flame front location (OH PLIF) were obtained in a turbulent, low-swirling premixed flame.
The image sequences give detailed insight in the flame-flow interaction e.g. the typical dilatation of the flow field upstream of the flame and the formation of large-scale vortices in the shear-layer that roll-up the flame and mixes burnt and unburnt gases. The goal of the project is to build a complete database for LES validation.
Special laser design for time-resolved OH PLIF
A double cavity kHz Nd:YLF laser (DualPower, Dantec Dynamics) in combination with a high-speed camera (SpeedSense 9060, Dantec Dynamics) was used to perform PIV. The laser used for OH PLIF consists of a kHz Nd:YAG laser, pumping a high-speed dye laser. The excited OH was imaged onto an intensified high-speed camera.
“The high repetition rates and thus relatively low pulse energies make ordinary dye lasers useless” says Rikard Wellander, Ph.D. candidate in physics at Lund University. “Firstly, the lasing threshold is too high in a standard dye laser. Secondly, the dye pump rate is not high enough to exchange the dye between the laser pulses.”
Rikard Wellander continues: “The kHz dye laser, with high pump flow rate and optics design, overcomes these problems and has good conversion efficiency for the rates and energy levels provided by the kHz Nd:YAG laser.”
Advanced data analysis
Previous single-shot PIV and multi-shot PLIF have given valuable information for validation but the full dynamics of the flame has never been captured before. The recent time-resolved measurements open up new possibilities for understanding the flame-flow interaction in depth.
Both an adaptive cross-correlation and an iterative correlation method (Least Squares Matching) were applied to analyze the flow field. DynamicStudio was used to combine the PIV and LIF images and to perform Proper Orthogonal Decomposition (POD) analysis of the PIV images to capture the dynamics of coherent structures.
Further data analysis will focus on conditional data - flow field changes across the flame front and flame front displacement in time - to build statistics for validation of LES and combustion models as well as for analysis of the dynamic phenomena.