Many reacting flows are inherently three dimensional and temporally evolving. High-speed 3D imaging measurements are required to capture the dynamics of key processes such as localized extinction and re-ignition in turbulent combustion. To meet that need, we have combined multi-kHz rate tomographic particle image velocimetry (tomo-PIV) and laser-induced fluorescence (LIF) imaging. Tomo-PIV provides a 3D measurement of all three velocity components, enabling us to determine key fluid dynamic quantities, such as strain rate and vorticity. Laser-induced fluorescence provides 2D and 3D measurements of select species. In one approach to 3D LIF measurements, we have combined a Sandia-built 100 kHz burst-mode laser and an acousto-optic modulator to rapidly raster scan the laser sheet across a probe volume and record LIF images on a high-speed CMOS camera. Simultaneous high-speed 3D velocity and species measurements provide a more complete picture of the dynamics of turbulence-chemistry interactions than was previously available. (See Figures 1 and 2, below)
Figure 1 Time sequence of simultaneous tomographic particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) measurements at 10 kHz in a turbulent partially premixed DME/air jet flame. Blue surfaces are isosurfaces of the compressive strain rate for Uo = -15 x 103 s-1. Velocity vectors are shown in the same plane as the OH PLIF images (1 out of 16 in-plane vectors displayed). Source: Coriton, B.; Steinberg, A. M.; Frank, J. H., High-speed tomographic PIV and OH PLIF measurements in turbulent reactive flows. Exp. Fluids 2014, 55, 1743.
Figure 2 (a) Temporal evolution of the 3D formaldehyde distribution at the base of a lifted jet flame recorded using laser-induced fluorescence excited by a 100 kHz burst-mode laser with the laser beam raster scanned using an acousto-optic modulator. (b) Temporal evolution of 3D formaldehyde and velocity field. Source: Frank, J.H., Advances in imaging of chemically reacting flows. J. Chem. Phys., 2021, 154 (4), 040901. Results based on experiments from: Zhou, B.; Li, T.; Frank, J. H.; Dreizler, A.; Bohm, B., Simultaneous 10 kHz three-dimensional CH2O and tomographic PIV measurements in a lifted partially-premixed jet flame. Proc. Combust. Inst. 2021, 38, in press.
Li, T.; Zhou, B.; Frank, J. H.; Dreizler, A.; Böhm, B., High-speed volumetric imaging of formaldehyde in a lifted turbulent jet flame using an acousto-optic deflector. Exp. Fluids 2020, 61, 112.