Development and Application of a MHz Frame Rate

The ability to capture the unsteady dynamics of high speed compressible flows requires the use of ultra fast imaging diagnostics. Application of particulate based scattering techniques in high speed flows requires the use of high power, nanosecond duration, pulsed illumination sources such as Nd:YAG lasers in order to record high quality images. Furthermore, the temporal bandwidth of the measurements must be at least several hundreds of kHz while the spatial scale must be at least on the order of the large-scale structures present in the flow. High spatial and temporal bandwidth flow field measurements are not simultaneously available with high accuracy due to the combined constraints imposed by high sensitivity digital image sensors and limited pulse repetition rates of solid-state lasers, respectively. In this work we describe the development of a MHz repetition rate, high resolution, quantitative flow measurement system. The imaging system is comprised of a MHz repetition rate pulse-burst mode laser built in-house and a commercial MHz framing rate charged coupled device (CCD) camera. The laser is capable of producing a wide range of inter-pulse spacings (0.5 to 20 ?s) with individual pulse energies exceeding 75 mJ at 532 nm. The camera, having a single optical input, is comprised of an internal image splitter unit and four individual intensified, frame-straddling, 1280 x 1024 pixel, CCD camera modules. The combined laser and camera system provides imaging frame rates ranging from 2 MHz down to 50 kHz. Results from the application of the MHz rate imaging systems to obtain Digital Particle Image Velocimetry (DPIV) data from a supersonic nozzle flow will be presented.