Abstract
A strong interest in highly-efficient, small-scale propeller configurations can be recognized, especially due to the currently growing number of and usage possibilities for unmanned aerial vehicles (UAVs). Although a variety of different propulsion concepts already exist on the market or are discussed in the literature, there is still a demand for a systematic investigation to compare such configurations, in particular, small-scale propellers with a fixed pitch, which are analyzed in this work. Therefore, different configurations of small-scale propellers with a fixed pitch are analyzed in this paper. They were operated as isolated single propellers and as ducted propellers in a cylindrical wing. Furthermore, due to their flight envelope, UAVs are likely to operate at highly inclined inflow conditions and even under reverse inflow. These non-axial inflow conditions have a major influence on the flow field around a propeller. In order to investigate this influence, all analyses were performed at a range of inflow angles in relation to the propeller axis from αdisc=0° to 180°.
Highlights
Many reasons can be found for a propeller experiencing non-axial inflow.In particular, conventional unmanned aerial vehicles (UAVs) multicopter configurations with propellers on a fixed vertical axis cause highly yawed inflow conditions in horizontal flight [1,2].aircraft equipped with conventional propeller configurations can face angles of attack of up to 10◦, for example, in very slow forward flight, during side-slip and during a turning flight [3].For applications in the field of maritime vehicles, such inflow conditions are very common.Nowadays, many highly maneuverable ships are equipped with so-called azimuth thrusters
The results of the ducted propeller configuration are analyzed and compared to the results of the same propeller without a duct of previous analysis. Shown are both the experimental results and the data obtained by URANS calculations
The comparison of the ducted propeller with the open one shows that at static thrust conditions, the duct has a positive effect on the propeller efficiency
Summary
Many reasons can be found for a propeller experiencing non-axial inflow (see Figure 1). A comprehensive analysis of the occurring flow fields under different inflow angles was conducted, allowing the explanation of the load behaviors by the formation of characteristic vortex structures and flow separation regions The knowledge of this analysis could possibly be used for a mission-specific choice of propeller configurations or duct geometries for future aviation vehicles. The resulting ution on the propeller surface differs from the corresponding two-dimensional polar for this discrepancy are the occurring three-dimensional flow effects and, with the va gle of attack, the non-axial inflow velocity components. They result in additional local ntial velocities and, eventually, a variation of the local inflow velocity magnitude and g. Within non-axial infl ncreased blade vortex interaction by the deflected wake causing additional time-vary propeller
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