Progress in measuring water impingement characteristics on aircraft surfaces

Validation of trajectory computer codes, for icing analysis, requires experimental water droplet impingement data for a wide range of aircraft geometries as well as flow and icing conditions. This paper provides a summary of experimental water droplet impingement research starting with the early efforts of NACA in the 1950's. Industry requirements for additional impingement data are discussed based on results from a recent industry survey. A new research program aimed at expanding and modernizing the existing water droplet impingement data is outlined. Improved experimental and data reduction methods for obtaining water impingement data are presented. A discussion on sources of error in the experimental and data reduction methods is provided. Relative humidity is shown to have a significant effect on the repeatability of the experimental data. Recent wind tunnel test results for an MS(1)-0317 airfoil and a three element McDonnell Douglas high lift system are compared with computational results obtained with the LEWICE code. In most cases, the correlation between the analytical and experimental impingement efficiency distributions is good. The experimental and analysis results include impingement characteristics for median volumetric diameters of 11.5, 21 and 92 microns. Test repeatability for the experimental results presented ranged from 4% to 10% with respect to the average data. This represents a significant improvement compared to previous experimental results.