A transient laser Doppler anemometry for measurement of rapidly changing velocities of solid bodies

A transient laser Doppler anemometry (LDA) is developed to extract the velocity history of a solid body that is transient in nature. A digital storage oscilloscope was used in place of the conventional counter to allow postprocessing of the recorded Doppler signals. By sliding a rectangular window with a length on the order of 1 μs, frequencies of the rapidly changing Doppler signals were extracted using a refined signal processing method. This method, which incorporates the chirp-Z transform algorithm to the short-time Fourier transform routine for frequency enhancement, has proved its superiority over the conventional short-time Fourier transform and the zero-crossing methods; the latter was used in the authors' previously published works. The transient LDA was then applied to record transient responses of projectiles with different masses during impact on plates of various thicknesses, and interesting impact phenomena were discovered. From these applications, it is found that this method is robust and reliable for extracting the velocity history of a solid body during a transient event.