Rotor blade optimization with blade airfoil Reynolds numbers between 100 000 and 500 000 — characteristic of small single-rotor unmanned aerial vehicles (UAV) — was performed for hover using blade element momentum theory (BEMT) and demonstrated via flight tests. BEMT was used to test various airfoil profiles and rotor blade shapes using airfoil data from 2D computational fluid dynamics simulations with Reynolds numbers representative of the blade elements. Selected blade designs were manufactured and flight tested on a Blade 600X single main-rotor UAV (671 mm blade radius) to validate the theoretical results. The parameters considered during the optimization process were the rotor frequency, radius, taper ratio, twist, chord length, airfoil profile, and blade number. The best of the improved blade designs increased the figure of merit, a measure of rotor efficiency, from 0.31 to 0.68 and reduced power consumption by 54%. Reducing the rotational frequency accounted for 45% of the improvement in power consumption, while the taper ratio and blade number accounted for 25% and 17%, respectively. The blade twist and airfoil profile only had a minor effect on the power consumption, contributing 7% and 6% to the improvement. The rotor diameter and root chord were kept identical to the original rotor and hence had no contribution. The presented results could serve as useful guidelines to single-rotor UAV manufacturers and operators for increasing endurance and payload capabilities.
When the rotor blades are at a high advance ratio and/or a high thrust coefficient, the onset of dynamic stall makes accurate prediction of airloads on the rotor blades difficult. Comprehensive rotor analysis codes used in the industry rely on semi-empirical dynamic stall models to generate the aerodynamic coefficients of the blade sections undergoing dynamic stall. However, these models neglect the unsteady nature of the freestream seen by the blade sections compromising the accuracy of the analysis at high speed forward flight and high blade loading conditions. Thus, this thesis aims to investigate the impact of including the unsteady freestream effects in dynamic stall for the prediction of the airloads on the rotor blades. To study the impact of including the unsteady nature of the freestream in dynamic stall, Computational Fluid Dynamics (CFD) was used to generate the unsteady 2D dynamic stall aerodynamic data. The CFD data then served as inputs to the in-house rotor analysis code called Qoptr to generate blade airload results. The flight test data from a steady-level flight case (C T /σ = 0.129, µ = 0.24) from the UH-60A Airloads program was used for validation. The Qoptr blade airload results generated with the unsteady CFD dynamic stall data showed considerably better agreement with the flight test data than the results generated with semi-empirical dynamic stall models, especially in the sectional moment results.
When the rotor blades are at a high advance ratio and/or a high thrust coefficient, the onset of dynamic stall makes accurate prediction of airloads on the rotor blades difficult. Comprehensive rotor analysis codes used in the industry rely on semi-empirical dynamic stall models to generate the aerodynamic coefficients of the blade sections undergoing dynamic stall. However, these models neglect the unsteady nature of the freestream seen by the blade sections compromising the accuracy of the analysis at high speed forward flight and high blade loading conditions. Thus, this thesis aims to investigate the impact of including the unsteady freestream effects in dynamic stall for the prediction of the airloads on the rotor blades. To study the impact of including the unsteady nature of the freestream in dynamic stall, Computational Fluid Dynamics (CFD) was used to generate the unsteady 2D dynamic stall aerodynamic data. The CFD data then served as inputs to the in-house rotor analysis code called Qoptr to generate blade airload results. The flight test data from a steady-level flight case (C T /σ = 0.129, µ = 0.24) from the UH-60A Airloads program was used for validation. The Qoptr blade airload results generated with the unsteady CFD dynamic stall data showed considerably better agreement with the flight test data than the results generated with semi-empirical dynamic stall models, especially in the sectional moment results.
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