Scientific Technical Review

Detailed studies of propeller flows are regaining both interest and significance worldwide, as the number of their different design and applications (particularly for futuristic urban air vehicles) continues to grow. An additional distinctive characteristic of small-scale unmanned air vehicles (UAV) propellers is that they are meant to operate in a wide range of (previously considered atypical) operating conditions, including backward flight, flight in the vicinity of obstacles, hard/ground surfaces, etc. These specific requirements raise the issue of the effects of ground proximity on their aerodynamic performance. This paper computationally investigates flows around a small-scale, custom-made propeller in ground effect. Different ground distances are considered and novel thrust and power relations (dependencies) on them are proposed. In order to obtain sufficiently reliable and accurate results and capture the most significant flow features, Reynolds-averaged Navier-Stokes (RANS) equations are solved by finite volume method. In addition, interesting flow visualizations are presented. Although the obtained thrust trend correlates well with the conventionally used semi-empirical formula, more realistic estimations are obtained for small ground distances. Furthermore, the positive effects of ground vicinity on rotor aerodynamic performances are once again confirmed and quantified.

Key words: propeller, turbulence, RANS, IGE.

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