Numerical Simulation of Airfoil Aerodynamic Penalties and Mechanisms in Heavy Rain

Zhenlong Wu,M Ismail,Yihua Cao

doi:10.1155/2013/590924

Abstract

Numerical simulations that are conducted on a transport-type airfoil, NACA 64-210, at a Reynolds number of2.6×106and LWC of 25 g/m3explore the aerodynamic penalties and mechanisms that affect airfoil performance in heavy rain conditions. Our simulation results agree well with the experimental data and show significant aerodynamic penalties for the airfoil in heavy rain. The maximum percentage decrease inCLis reached by 13.2% and the maximum percentage increase inCDby 47.6%. Performance degradation in heavy rain at low angles of attack is emulated by an originally creative boundary-layer-tripped technique near the leading edge. Numerical flow visualization technique is used to show premature boundary-layer separation at high angles of attack and the particulate trajectories at various angles of attack. A mathematic model is established to qualitatively study the water film effect on the airfoil geometric changes. All above efforts indicate that two primary mechanisms are accountable for the airfoil aerodynamic penalties. One is to cause premature boundary-layer transition at low AOA and separation at high AOA. The other occurs at times scales consistent with the water film layer, which is thought to alter the airfoil geometry and increase the mass effectively.

Highlights

The aerodynamic penalty of aircraft flight through heavy rain has been deemed to be a critical cause in many severe aviation accidents
Investigation of rain effect on aircraft flight was begun with the wind tunnel test, and the earliest was conducted by Rhode in 1941 [4]
In 1987, Hansman and Criag compared the aerodynamic performance degradation of NACA 64-210, NACA 0012, and Wortman FX 67-K170 airfoils under the low Reynolds numbers in heavy rain conditions and explored the various mechanisms underlying by forcing boundarylayer to transition [5]

Summary

Introduction

The aerodynamic penalty of aircraft flight through heavy rain has been deemed to be a critical cause in many severe aviation accidents. In 1992, Bezos et al determined the severity of rain effect, the aerodynamic penalty over a range of rain intensities, and the importance of surface tension interactions of water as a scaling parameter [9] Thompson and his team examined another NACA 4412 airfoil in moderate rain in wind tunnel. They primarily placed emphasis on the correlation of surfacefilm behavior including rivulet formation [10]. Comparisons with different flow patterns showed the aerodynamic degradation depended on the location of rivulet formation and the diameter of these rivulets The latter factor was found to be more important to aerodynamic performance

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Conclusion