Basic Experiment on Focusing Schlieren PIV Method with LED Light Source

The focusing schlieren PIV technique is being done to investigate the velocity vector, and it is considered as the useful measurement technique in the compressible flow. In this study, the LED light sources of a focusing schlieren system was used to visualize the flow fields of helium jets. And the flow vector was estimated by using PIV software as the first step. The system was constructed by an extended light source, a Fresnel lens, source and cutoff grids, focusing lens, and a CCD camera. The three source grids were prepared. The light source was designed by consisting of four LEDs. This system was used to visualize free jets from the convergent nozzle. The helium gas was used as the test gas to obtain large density gradient in low-speed flows. As the result, the density gradient could be seen though the condition was low speed. And the flow field from the nozzle was visualized by the LEDs as the extended light source. The jet at the focal plane could be seen clear, and the flow vector due to the turbulence was seen by the PIV analysis.