Development of Finite State Inflow Models for Multi-Rotor Configurations using Analytical Approach

Multi-rotor configurations require accurate inflow models for performance, aeromechanics and handling qualities analyses. Single rotor finite state inflow models have been used for performance, aeromechanics and handling qualities analyses and shown to have good correlation with experimental data. Recently, finite state inflow models based on pressure and velocity potential superposition approaches have been developed for coaxial rotor configurations. Furthermore, Pressure Potential Superposition Inflow Model (PPSIM) has been extended to arbitrary number of rotors and arrangements. In this paper, a finite state multi-rotor inflow model based on Velocity Potential Superposition Inflow Model (VPSIM) approach is developed. In addition, the developed finite state multi-rotor inflow models are compared with a high fidelity numerical model known as viscous Vortex Particle Method (VVPM) for three different configurations; a coaxial and two tandem rotor configurations with different longitudinal separation distances. Rotors induced inflow distributions in these configurations are investigated in hover and at a low speed flight condition of advance ratio equal to 0.04. Differences in the uniform, fore-to-aft and side-to-side inflow variations among the three models are found in both steady-state and transient responses to rotor load perturbations.