Finite State Coaxial Rotor Inflow Model Enhancements Using VVPM-Extracted Influence Coefficients

Abstract

An analytical coaxial rotor inflow model has been developed in the literature by combining pressure fields of individual rotors. In such a pressure potential superposition inflow model (PPSIM), real flow phenomena such as viscous effects, flow swirls, and wake distortions are neglected. To capture real flow effects, inflow distribution predictions from the viscous vortex particle method (VVPM) are used to correct PPSIM influence coefficients (L-matrix). It is found that cosine–sine coupling is significant during hover and low advance ratios, especially on the lower rotor. Most correction terms are found to be insensitive to the thrust coefficient ratio between the upper and lower rotors. For ease of implementation, the curve-fitted correlation of each L-matrix correction element and wake skew function is found. Inflow states computed from PPSIM with curve-fitted L-matrix corrections are close to VVPM results, with an average difference of 6%.