Gas-phase velocity field measurements in sprays without particle seeding

A laser-based technique is presented that can be used to measure the instantaneous velocity field of the continuous phase in sprays and aerosols. In contrast to most well established laser-based velocity measurement techniques, this method is independent of particle seeding and Mie scattering. Instead of that it is based on gaseous flow tracers and laser-induced fluorescence (LIF). Inhomogeneous tracer gas distributions, which are created by an incomplete, turbulent mixing process, are exploited for flow tracing. The velocity field can be measured close to the droplets, because frequency-shifted LIF is separated from Mie scattering by optical filters. Validation tests and results from a water spray in air are given. Accuracy and spatial resolution are discussed in detail.