The icing of compressor blades and their protection by surface heating

Abstract

This paper describes an investigation into the feasibility of protecting compressor blades against ice accretion by the method of surface heating. Experiments with surface-heated inlet guide vanes and stator blades were performed in the icing tunnel at the Royal Aircraft Establishment. An electrically heated blade, having almost uniform surface temperature, was developed and then used to determine the effects of air velocity and icing conditions on the minimum heat flow required to prevent the formation of ice. The theoretical method, by J. K. Hardy, of calculating this heat requirement shows reasonable agreement with the experimental results. Steel, copper and copper-plated gas-heated blades with various internal passage shapes were also tested and their heat requirement compared with those of the corresponding electrically heated blades under the same external conditions. The ratio of the latter to the former heat quantity is called the thermal efficiency and is shown to be a function of internal passage shape, blade material, conductivity and dimensions, the gas flow and the external conditions. Finally, a method of estimating the pressure drop through the gas-heated blades is suggested and a worked example is included to demonstrate the method of assessing the mass flow and pressure required to anti-ice a row of inlet guide vanes by means of a compressor bleed.