Boundary-layers integral analysis - Heated airfoils in icing conditions

Abstract

Under icing conditions, it is necessary to heat and control the temperature of the airfoil surface at leading edge region to prevent ice formation. The thermal anti-ice system balances mainly the evaporative cooling effects, which are caused by the coupled heat and mass convection transfer, imposed by the air flow loaded with supercooled water droplets and the runback water flow around the airfoil. The most dificult and important parameter for accurate estimation of airfoil surface temperatures and water runback mass flow rates is the local convective heat transfer coefficient. This paper presents an integral analysis of momentum and thermal boundary-layers applied to heated airfoils operating in icing conditions. The objectives are to implement two different mathematical models, assess the effects of the model assumptions on the results accuracy and compare the numerical results obtained with reliable experimental data. One boundary-layer model assumes isothermal and non-permeable surface with presence of a abrupt laminar-turbulent transition. These are common assumptions adopted by previous workers. The other model, proposed by present authors in previous works, considers the boundary-layers over a non-isothermal and permeable surface with a smooth laminar-turbulent transition region. The onset and length of laminar-turbulent transition may be estimated by classic empirical correlations or just imposed. All numerical results are compared with classic and recent experimental data of two different thermal anti-iced airfoils operating in icing tunnel. Copyright © 2008 by Guilherme A. L. Silva, Otavio M. Silvares and Euryale J. G. J. Zerbini.