Turbulence intensity measurement technique for use in icing wind tunnels

Current understanding of the ice accretion process is based largely on icing wind-tunnel tests. Wind-tunnel turbulence has been identified as having potentially important effects on the results of tests performed in icing tunnels. The turbulence intensity level in icing tunnels in the absence of the spray cloud had been previously measured and found to be quite high because of the lack of turbulence-reducing screens and because of the presence of the spray system in the settling chamber. However, the turbulence intensity level in the presence of the spray cloud had not been measured. A method for making such measurements was developed and a limited set of turbulence measurements was taken in the NASA Lewis Research Center's Icing Research Tunnel (IRT). Turbulent velocity fluctuations were measured using hot-wire sensors. Droplets striking the wire resulted in distinct spikes in the hot-wire voltage that were removed using a digital acceleration threshold filter. The remaining data were used to calculate the turbulence intensity. Using this method, the turbulence intensity level in the IRT was found to be highly dependent on nozzle air pressure, whereas other factors such as nozzle water pressure, droplet size, and cloud liquid water content had little effect.