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Kim, D.,Yi, S. J.,Kim, H. D.,Kim, K. C. [np] 2017 JOURNAL OF VISUALIZATION Vol.20 No.2
<P>A simple and inexpensive measurement system is suggested to measure the temperature and velocity fields simultaneously at high temperature using thermographic phosphor tracer particles. A 385-nm UV-LED and only one high-speed camera with a CMOS sensor were used for the simultaneous measurement system. The dispersion of a confined oil jet with high temperature was investigated to validate the system. The instantaneous temperature and velocity fields were obtained when silicon oil at 200 degrees C was injected into a silicon oil chamber at 25 degrees C. The decay-slope method was used for the temperature field analysis, and the velocity field was obtained by a two-frame cross-correlation algorithm. The velocity of the injected silicon oil rapidly decreased because of the change in viscosity of the silicon oil with temperature. The selection of an appropriate interrogation window size is suggested to take the moving distance of temperature-sensitive particles into account for accurate temperature measurement.</P>
Vortex generation using fin-slot structures and a submerged nozzle at a wall-injected cylinder
Kim, D.,Lee, I.,Koo, J.,Chang, H.,Kang, M. [np] 2014 JOURNAL OF VISUALIZATION Vol.17 No.1
The internal flows of solid rocket motors are not yet fully understood. Several cold-air flow experiments that simulated combustion gas flow with compressed gas wall injections have been conducted to observe the behavior of internal flows and acoustic phenomena. Direct visualization, however, has rarely been performed due to the non-transparency of the wall-injecting media. In this study, novel techniques were employed to visualize the internal flow of the cold-flow model of a solid rocket motor. The smoke, which was generated using a heated Ni-Cr wire, was used as a flow tracer, and a light penetrated through an acrylic nozzle. The head-end of the test model was made with a transparent acrylic window to record the visualized flow using a high-speed CCD camera. The results of the visualization at the nozzle entrance region showed the symmetric vortex tube structures and the transient behavior of the circumferential flow. The vortex tube generation mechanism was explained with reference to the inlet vortex phenomenon of an aircraft engine. Also, it was observed that the interaction between the adjacent vortex tubes created the circumferential flow.
Sung, H. G.,Yoo, K. H.,Kim, J. C. [np] 2014 Journal of visualization Vol.17 No.1
The proper orthogonal decomposition (POD) analysis was implemented to extract the acoustic modes from the flow field inside a swirl-stabilized combustor obtained from non-reacting large eddy simulation. The major frequencies and the spatial distribution of fluctuating pressure of dominant POD modes were presented. The first four dominant modes occupied more than 70 % of the total energy of the oscillatory flow fields. Cooling flow injection suppressed the amplitude of pressure fluctuation and tended to dissipate the high-order longitudinal acoustic modes. The dominant acoustic modes observed in the fluctuating pressure field in the case with no cooling flow injection were dissipated or shifted by the injection of cooling flow..