A vortex embedding method for free wake analysis of helicopter rotor (original) (raw)

A method is described to compute flow over llelicopter ,rotor blades. The method utilizes a compressible potential flow field with embedded vortex sheets. It is fully compressible, with the ability to capture shocks in transonic cases, and is able to treat the wake as free with no external inputs. Also, the wake is treated in a general, unified way as a surface that moves through the flow field with no constraints imposed by the computation .. The method is quite different from others being developed. In other approaches the wake is typically treated as a collection of separate filaments. Also, other compressible approaches typically break the computational region into a set of small regions near each blade where the compressible flow equations are solved, and an outer region where the wake is computed. These approaches do not appear to be adequate for modern rotor blades because the physical wake from each blade usually does not break up into a set of well-defined vortex filaments, and also because it can approach quite close to other blades. The vortex embedding technique has been implemented in a computer code, HELIX I. In validation studies involving comparisons between results computed with HELIX I and experiments there has been very good agreement for the prediction of pressure distributions on blade surfaces, even in transonic cases with significant shocks. Also, the rotor wake geometry was also well predicted, for both two and four blade rotors. Successful prediction of the initial tip vortex descent rate (ki) is especially notable because previous methods have difficulty doing so.