Turbulence
Intesity Measurements Tecnique for Use in Icing
Wind Tunnels
C.M. Henze and M.B. Bragg
University of Illinois, Urbana, Illinois 61801
ABSTRACT
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 to 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 calulate the turbulence intensity. Using this method, the
turbulence intesity 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.