Research on visualization of transient high speed exhaust flow by FRS technique

A visualization technique based on of molecular filtered Rayleigh scattering (FRS) was studied for diagnosing the structures of transient high speed exhaust flow.The diagnostics system was composed of a narrow line width laser,a molecular/atomic absorption filter and a collection device such as ICCD(intensified charge coupled device).The absorption filter was used to modify the spectra of the Rayleigh scattering signal from the flow field illuminated by a laser sheet from a Nd : YAG (neodymium-doped yttrium aluminium garnet) pulsed laser.The laser was tuned to an absorption line of iodine vapor contained in the filter.This caused background scattering from solid particles and surface to be strongly absorbed,while much of Doppler broadened Rayleigh scattering was transmitted through the filter.FRS diagnostic system was described.FRS technique was used to diagnose transient high speed exhaust flows.The turbulence structures on the area of laser action were obtained.These demonstrate the ability of the FRS technique to diagnose supersonic flow.