Equivalent Sand Grain Roughness Correlation for Aircraft Ice Shape Predictions 2019-01-1978

A new approach, based on the physics of ice accretion, is proposed to calculate the equivalent sand grain roughness (ESGR) correlation (ESGR) for aircraft ice shapes. This new approach derives a correlation based on two dimensionless numbers: the first by re-defining the Stanton number to the parameters that control the in-flight icing, correlated by a numerical sensitivity study performed for a specific icing suite; the second based on the thermodynamic heat balance considering the latent heat of freezing and the energy that the air can absorb. The correlation was calibrated using 14 2D experimental ice shapes for a NACA 0012 airfoil of 21 inches chord (MVD 20µm and LWC 1.0g/m³ with accretion time 6min and TAS 67.06m/s and LWC 0.55g/m³ with accretion time 7min and TAS 102.82m/s). Seven TAT were run ranging from -2.22 to -26.11ºC covering rime, glaze and mixed ice regimes. The correlation is validated against 41 2D experimental ice shapes obtained from 5 airfoils: the GLC 305; a commercial transport airfoil; NACA 23014; NACA 0015 and NACA 0012. A large range of icing conditions were covered. The results of this validation exercise show 90% of the predicted ice shapes are visually in excellent or good agreement. The advantage of the proposed equivalent sand grain roughness correlation to calculate the ice roughness is that the correlation is calibrated with only a few cases for a given icing simulation suite. This is possible because the correlation depends on only two dimensionless numbers related to the in-flight icing physics simulation.