Abstract

Due to the increasing use of unmanned air vehicles (UAVs) for civil and military purposes, accurate evaluation of this kind of aircraft is becoming a fundamental aim during their development. Particularly, propellers are often the most critical elements influencing a UAV’s performance and noise emission. Therefore, selecting the appropriate tools for modeling the behavior of this element becomes crucial, especially at the design stages, evaluating both their accuracy and cost. In this paper, we will test the suitability of different tools for numerical modeling and perform an experimental campaign to validate the numerical results.

Particularly, from the computational point of view, the performance of a typical propeller will be evaluated for various values of the advance ratio and various rotational speeds at hover, paying special attention to the thrust and thrust coefficient. Various modeling approaches will be analyzed in this sense, including low-order Blade Element Momentum Theory (BEMT) evaluation, Reynolds Averaged Navier-Stokes (RANS) methodologies (both stationary using a moving reference frame and transient), and transient Detached Eddy Simulations (DES), to analyze the turbulent structures arising in these devices. Noise emission will be evaluated at the most significant working conditions by applying a Ffowcs-William & Hawkings approach to the computed unsteady results and a simplified Farassat formulation to the BEMT results. These numerical calculations will be carried out using open-source software such as OpenFOAM and libAcoustics in the case of CFD modeling or in-house codes for low-order models.

Regarding experimental validation measurements, the hovering propeller’s thrust and far-field acoustic measurements will be performed in an anechoic chamber. The experimental setup will also be mounted in a wind tunnel for forward flight tests and to validate the performance results at different advance ratios. Furthermore, rapid prototyping is a necessary part of the development process for small propellers; thanks to progress in additive manufacturing (AM), this could even become the preferred way to manufacture in-house spares. In this paper, we will also assess the suitability of Fused Deposition Modeling — one of the most popular AM techniques — for manufacturing research propeller prototypes by comparing the propulsive and acoustic performance of a commercial propeller against its 3D-printed version.

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