Analysis of a finite state coaxial rotor inflow model

Abstract

An Active-Receiving Rotor Inflow Model (ARRIM) developed from potential flow theory has been shown in the literature to predict experimentally observed coaxial rotor inflow and its impact on rotor power variation with rotor thrust in hover. However, discrepancies have been noticed between the coaxial rotor forward flight performance predictions based on inflow computed using ARRIM and experimental data. In order to gain further understanding of the reasons for the observed discrepancies, the present study is aimed at a detailed analysis of rotor inflow predictions from ARRIM and compare the results with a high fidelity simulation model. Towards this, the ARRIM is implemented in FLIGHTLABR and its inflow distribution in forward flight is analysed and compared with the inflow distribution obtained using the Vortex Particle Model from the literature. It is found that while the mean inflow predictions from the ARRIM and the Vortex Particle Model are somewhat similar, the fore-to-aft inflow gradient predictions are significantly different. At higher advance ratios, side-to-side inflow gradient differences are also found between the two models.