Planar Doppler Velocimetry for Low-Speed Flows

Planar Doppler velocimetry (PDV) was investigated for low-speed flow applications. The method relies on measuring the Doppler shifts in the frequency of laser light scattered from particles in a flow using an iodine vapor cell as a sharp-cutoff spectral filter. While previous PDV systems have often used pulsed lasers, continuous wave (cw) lasers are shown here to have advantages for low speed flow. Two sets of experiments were conducted using a cw laser source; one examining the uncertainty in the measurement of the laser frequency, and the other examining the accuracy of Doppler frequency measurements on the surface of a rotating wheel. The experiments demonstrated a measurement accuracy of 0.2 m/s in a laboratory system.