Seedless Velocimetry in Air by Vibrational Excitation and by Laser-Induced Ionization

Measurement of turbulent velocities in air flows requires high temporal and spatial selectivity. The Raman Excitation + Laser-Induced Fluorescence (RELIEF) flow tagging concept is capable of resolving turbulent structures down to 25 microns with velocity resolution on the order of 1 meter per second. With that capability, vortex filaments can be detected at scales as small as twice the Kolmogoroff scale and accurate velocity structure function scaling can be determined. For further capabilities, including the simultaneous measurement of point vector velocities, Quadrature Radar REMPI is proposed. In this case, the flow is tagged by a small laser-induced breakdown, and the motion of that breakdown region is followed using coherent microwave scattering from the free electrons contained within the region. The phase of the microwave scattering is followed in real time using quadrature detection, providing a polar plot of velocity as a function of time for each sampling event as the scattering region moves through a virtual microwave interference pattern. Copyright 2008 by Princeton University.

Seedless Velocimetry in Air by Vibrational Excitation and by Laser-Induced Ionization Conference Paper