An Analytical Study of Icing Similitude for Aircraft Engine Testing. Revision

Abstract : An analytical study was conducted of the requirements for achieving similitude for icing as test conditions were varied. The application is aimed at engine icing tests conducted in ground spray rig facilities. The analysis considers the changes in the icing test conditions, including static temperature, static pressure, liquid water content, droplet size, and flow velocity, that are required to achieve similitude if any of the conditions are changed. The analysis uses a math model of icing scaling which has been validated by experimental data collected at the AEDC icing research tunnel. The requirements for similitude were analyzed for changes in both temperature and pressure. Expressions to describe the influence of test condition changes on the value of the scaling parameter were developed. The effect of icing caused by free-stream static temperature changes and temperature rise through a generic high-bypass turbofan engine was studied. The icing test points listed for compliance testing for aircraft icing certification under guidelines given in the Federal Aviation Administration Advisory Circular (AC) 20-73 were used as test points for the analyses.