An Evaluation of Finite-State Dynamic Inflow for Usage in Design

Abstract

In an effort to evaluate the accuracy of the finite-state dynamic inflow of Peters and He for use in rotor design, comparisons between dynamic inflow-based calculations and measured test data are presented for a wide variety of single rotor configurations and operating conditions. The quantities compared include rotor performance parameters, blade flap bending moments, blade airloads, and blade pitch angles. The dynamic inflow calculations are performed using the U. S. Army's Rotorcraft Comprehensive Analysis System (RCAS). Rotor performance calculations are mostly accurate prior to stall, except for rotor torque calculations from an individual blade pitch control (IBC) phase sweep. Blade airloads calculations do exhibit the correct dominant features including those from blade tip vortices, but the calculated amplitudes of the wake-induced loading are significantly less than the test data; this leads to significantly lower amplitudes in the flap bending moment response and is problematic for calculating half peak-to-peak values in conditions with significant blade-wake interactions. Blade collective and cyclic pitch angles are reasonably accurate in edgewise flight. Some practical, but not necessarily well-known, aspects of dynamic inflow are also discussed; this includes convergence characteristics with the number of inflow states and providing a formula for determining the number of inflow states.