Investigation of Hierarchical Structure of Turbulent Premixed Flames by High Spatial Resolution Time-Resolved Laser Diagnostics and GRID DNS

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In this study, hierarchical structure of turbulent premixed flames have been investigated to develop effective control schemes for turbulent combustion observed in many engineering applications such as gas turbines. Three-dimensional direct numerical simulations (DNS) of hydrogen/air and methane/air turbulent premixed flames were conducted by taking into account a detailed or reduced kinetic mechanism and temperature dependence of thermal and transport properties. From DNS of high Reynolds number turbulent premixed flame, hierarchical structure of flame front in inertial subrange of turbulence was clarified, and a new subgrid-scale turbulent combustion model was proposed based on the hierarchical structure of the flame front and the scale separation of turbulence characteristic lengths. Furthermore, hierarchical structure in the local flame element is shown by DNS of high-intensity turbulent premixed flames. Three-dimensional DNS of methane/air turbulent premixed flame, which is the fi … More rst DNS in the world, revealed local extinction mechanism of turbulent premixed flame. To investigate the hierarchical structure of turbulent premixed flame experimentally, high spatial resolution, time-resolved laser diagnostics such as dual-plane time-resolved stereoscopic PIV, simultaneous CH-OH PLIF and stereoscopic PIV measurement and CH double-pulsed PLIF have been developed. The dual-plane time-resolved stereoscopic PIV gives all of velocity and velocity-gradients components on a cross section in turbulence up to 26.7 kHz. The simultaneous CH-OH PLIF and stereoscopic PIV measurement leads to the direct comparison between experiments and DNS. The CH double-pulsed PLIF allows a direct measurement for displacement speed of local flame element. The results of these laser diagnostics were compared with those of DNS and the characteristics of flame structure in turbulence were discussed. To develop effective control schemes of turbulent combustion, flame structure of a noise-controlled swirl-stabilized turbulent combustor has been investigate by the laser diagnostics, and the relation between combustion noise and three-dimensional flame structure has been clarified in a view point of the acoustic sound source. For active controls of turbulent combustion field, a diode-laser absorption sensor was developed and the performance of the sensor was investigated in the noise-controlled swirl-stabilized turbulent combustor. Less