Characterization of spray-induced turbulence using fluorescence PIV

• Published in: Experiments in fluids 2018-07, Vol.59 (7), p.1-7, Article 110
• Main Authors: van der Voort, Dennis D., Dam, Nico J., Clercx, Herman J. H., Water, Willem van de
• Format: Article
• Language: English
• Subjects: Aerodynamics; Atomizing; Computational fluid dynamics; Dissipation; Droplets; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Fluid flow; Fluid- and Aerodynamics; Fluorescence; Heat and Mass Transfer; Nozzles; Particle image velocimetry; Particle size distribution; Research Article; Reynolds number; Sprayers; Tracer particles; Turbulence; Velocity distribution; Velocity measurement
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-018-2561-9

The strong shear induced by the injection of liquid sprays at high velocities induces turbulence in the surrounding medium. This, in turn, influences the motion of droplets as well as the mixing of air and vapor. Using fluorescence-based tracer particle image velocimetry, the velocity field surrounding 125–135 m/s sprays exiting a 200- μ m nozzle is analyzed. For the first time, the small- and large-scale turbulence characteristics of the gas phase surrounding a spray has been measured simultaneously, using a large eddy model to determine the sub-grid scales. This further allows the calculation of the Stokes numbers of droplets, which indicates the influence of turbulence on their motion. The measurements lead to an estimate of the dissipation rate ϵ ≈ 35 m 2 s - 3 , a microscale Reynolds number Re λ ≈ 170, and a Kolmogorov length scale of η ≈ 10 - 4 m. Using these dissipation rates to convert a droplet size distribution to a distribution of Stokes numbers, we show that only the large scale motion of turbulence disperses the droplet in the current case, but the small scales will grow in importance with increasing levels of atomization and ambient pressures.