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Effect of Prefilmer Edge Thickness on Spray Characteristics in Prefilming Airblast Atomizer
( Naoki Katagata ),( Toshihiro Sakaki ),( Takahiro Okabe ),( Takao Inamura ),( Koji Fumoto ),( Minori Shirota ) 한국액체미립화학회 2017 한국액체미립화학회 학술강연회 논문집 Vol.2017 No.-
A prefilming airblast atomizer is a fuel injector used in aircraft gas turbines. The atomization mechanism of the atomizer is well known. After injection, the liquid homogeneously wets the prefilmer surface, and flows down to the prefilmer edge in the form of a liquid film that is sheared by the high-speed air stream. The accumulated liquid at the prefilmer edge is sheared by the air and disintegrated into the bag-shaped liquid framed by a thicker rim. The bag-shaped part of the structure bursts into fine droplets. The rim is stretched and fragments into two elongated ligaments that disintegrate into larger droplets than those generated by bag-shaped disintegration. We focused on the effect of the prefilmer edge thickness on the breakup phenomena of the liquid film and the spray characteristics. Our previous study showed that there is a correlation between the edge thickness and the breakup length and breakup frequency. The objective of this study is to clarify the effect of the prefilmer edge thickness on the spray characteristics such as the Sauter mean diameter (SMD) and the spray generation frequency. The SMD at three prefilmer edge thicknesses (160, 500, and 2000 ㎛) under various conditions were observed using a high-speed camera and an image processing technique. The measurement position from the prefilmer edge was widely varied. The fast Fourier transformation (FFT) analysis was also conducted to evaluate the periodicity of the SMD. The experimental results showed that the SMD increases as the prefilmer edge becomes thicker. In the wake region of the edge, the FFT analysis showed that the increase in prefilmer edge thickness causes the transition of the maximal power spectrum to a lower frequency (i.e. less than 100Hz) due to the larger volume of a liquid accumulation attaching to the edge.