Combined Momentum Theory and Simple Vortex Theory Inflow Model for Multirotor Configurations

Abstract

For conventional main/tail rotor helicopters, momentum theory-based inflow models are still popular for design trade studies and flight simulations. However, simple momentum theory-based inflow models are not readily applicable in design trade studies of multirotor configuration vehicles where complex flow interactions among rotors can have a significant impact on vehicle overall performance, and hence, can impact vehicle sizing. The use of empirically corrected ad hoc inflow models is not often satisfactory. In this study, momentum theory is combined with a simple vortex theory in the development of a combined momentum theory and simple vortex theory (CMTSVT) based inflow model that is readily applicable to generic multirotor configurations. The developed model is validated against some multirotor inflow models and experimental data from the literature through comparisons of inflow predictions and performance predictions for different dual-rotor configurations. Further, inflow predictions using the proposed inflow model for a partially overlapping quad-rotor configuration are presented to illustrate the significance of rotor-on-rotor flow interactions in multirotor vehicle configurations.