Simultaneous dual-plane CH PLIF, single-plane OH PLIF and dual-plane stereoscopic PIV measurements in methane-air turbulent premixed flames

Simultaneous dual-plane CH planar laser induced fluorescence (PLIF), single-plane OH PLIF and dual-plane stereoscopic particle image velocimetry (PIV) measurement has been developed to investigate three-dimensional structures of methane-air turbulent premixed flame. Dual-plane CH PLIF system consists of two independent conventional CH PLIF measurement systems and laser beams from each laser system are led to parallel optical pass using the difference of polarization, and CH PLIF is conducted in two parallel two-dimensional cross-sections. Dual-plane stereoscopic PIV was established by using the difference of wavelength. The dual-plane CH PLIF and stereoscopic PIV are combined with single-plane OH PLIF. The laser sheet for single-plane OH PLIF is located at the center of two planes for CH PLIF and stereoscopic PIV. The separation between each plane is set to about 170 μm. The spatial resolution of PIV is set to 175 μm (about three times Kolmogorov length scale) × 175 μm × 210 μm and is same as that of general direct numerical simulations (DNSs) of turbulence. This simultaneous measurement can provide three-dimensional flame front, three velocity components and nine velocity derivatives. The measurement is conducted in methane-air swirl-stabilized turbulent premixed flames of Reλ=63.1, 95.0 and 115.0. Various complicated three-dimensional flame structures such as the handgrip and spire structures, which have been shown by previous three-dimensional DNSs, are observed in high Reynolds number turbulent premixed flames. Magnitude of strain rate, which is evaluated from nine velocity derivatives, shows high value in unburnt region except for the region engulfed by burnt gas. These results show that the simultaneous dual-plane CH PLIF, single-plane OH PLIF and dual-plane stereoscopic PIV measurement is useful for investigating the characteristics of turbulent premixed flames.