Numerical Computation of Flow around a Helicopter by Coupling Structured and Unstructured Grid Methods

Abstract

The objective of this study is to develop a new CFD solver by combining the structured and unstructured grid methods so that the tip vortices can be predicted accurately for the realistic geometry of a helicopter. Flow around a helicopter has unique features caused by the rotor and a variety of equipment on the helicopter fuselage surface such as hoist crane and landing gear. There are difficulties in CFD analysis for rotorcraft, particularly in accurately capturing of rotor tip vortices and solving flow around a complicated geometry. Generally, structured grid method is suitable for capturing tip vortices, while unstructured grid method can solve flow around complicated geometry. In this study, two validations are conducted to show effectiveness of this coupled CFD solver. The first validation is related to a steady flow around ROBIN fuselage (Mach # 0.062). Computational results are compared with both experimental data and existing CFD results. The results show that the coupled CFD solver can predict surface pressure distributions in good agreement with experimental data and existing CFD results. The second validation is related to an unsteady flow around ROBIN fuselage with a rotor (µ = 0.15, C_T = 0.0064). Results show that coupled CFD solver can predict periodical surface pressure also in good agreement with experimental data and existing CFD results. Furthermore, the vortex structure predicted has a good agreement between the coupled and existing structured grid CFD solvers. Finally, the coupled CFD solver is applied to a flow around the Eurocopter 135 model to demonstrate its capability for a realistic complicated helicopter geometry.