Yu Saiki

3D Printing of Instantaneous Turbulent Flame Shapes, Experimentally Captured by 3D-Computer Tomography and Multi-Directional Schlieren Photography

Non-scanning 3D-CT(Computer Tomography) technique employing a multi-directional quantitative schlieren photographic system(top-left picture) with flash light source, has been performed to obtain instantaneous density distributions of high-speed turbulent flames(for reference, the target flame of 8 m/s exit velocity is indicated in the right-top picture). For simultaneous schlieren photography, the custom-made 20-directional schlieren camera was constructed and used. The target turbulent flame is high-speed flames, anchored on the burner of a nozzle exit of 4.2 mm diameter. The image set of 20 directional schlieren images are processed by MLEM CT-algorithm to obtain the 3D reconstruction of instantaneous density distribution. The solid models(bottom picture) of threshold density level of 0.7 kg/m3 are 3D-printed as 4 times large size for detail observations. The average exit velocity of the propane-air mixture of equivalence ratio of 1.1 is set to be 10, 8, 6 and 4 m/s (models from left to right in the bottom picture). The solid models show the complicated shape of the high speed turbulent flames. The flame structure of higher speed flame has fine scale corrugations. This corresponds to the “corrugated flamelets regime” of the Borghi & Peters diagram well.

H-TALIF measurement for wall radical quenching modelling in microscale combustion

Two-dimensional hydrogen atom (H) distribution in a CH4/air premixed flame in a narrow channel was measured using a newly-developed two-photon absorption LIF (TALIF) setup with high efficiency 205 nm laser. The wall chemical effect of SUS321 and quartz surfaces on the H distribution in a methane flame was examined. Based on the measured H atom concentration near the wall, a radical quenching model focused on the H adsorption is proposed and the initial sticking coefficient (S 0) of H on SUS321 and quartz surfaces are estimated as 0.1 and 0.01, respectively. Sensitivity analysis of CO, HRR and species distributions with varying S 0 of H, O, OH, CH3 were performed. It is found that the H adsorption should be dominant in the wall chemical effect on the methane flame.

Active control of coaxial jet mixing with manipulation of primary vortical structures by arrayed micro flap actuators

Active mixing control of a methane/air isothermal coaxial jet was achieved using micro magnetic flap actuators arranged on the inner surface of the outer annular nozzle. The spatio-temporal evolution of vortical structures and the scalar mixing were studied through the particle image velocimetry and planar laser-induced fluorescence methods. In contrast to studies on jet control using acoustic forcing, the mechanical movement of the flap directly generated large-scale intense vortices. The mixing was enhanced significantly by the vortices formed in the inner shear layer, although the control input was given to the outer shear layer. It was found that the primary vortex rings dominated the near-field mixing, while streamwise vortices were responsible for the downstream mixing. It was also demonstrated that the radial range of the inner fuel transportation could be manipulated flexibly by adjusting the shedding interval of the vortices. Especially, the mixing was enhanced most significantly when the primary vortices were most densely populated near the nozzle exit at the control Strouhal number of unity.