Experimental study to characterize flow dynamics and drag response of a multi-propeller system

Recent advances in unmanned aerial vehicle (UAV) technologies have given rise to a variety of drone swarm strategies, particularly useful for security and surveillance, provision of wireless connectivity, delivery of goods, and environmental monitoring. Most of the current literature on UAV swarms is concerned with control algorithms, with little focus on aerodynamics of these formation strategies. Understanding the mechanics of flow around motorized multi-propeller systems can be used as an optimization tool to achieve certain outputs, like minimizing energy expenditure in a swarm of drones. In this talk, we will focus on the dynamics of flow past a multi-propeller system, containing up to 7 propellers, with varying orientations with respect to the freestream at moderate angular velocities. Our propellers are comprised of two-blade cross-sectional shapes following 4-digit series NACA profiles, with a maximum blade twist of 45^○ at the root. The performance of an individual propeller is characterized using a load cell and motor to allow for comparison with the multi-propeller configuration. These propellers are suspended in various formations in a water tunnel where we perform 2D-2C high-resolution and high-speed particle image velocimetry (PIV).  We will use the PIV data to explore the complex vortex dynamics and the associated turbulence statistics. We will also obtain the pressure and calculate the forces experienced by each propeller to determine the optimum orientation for minimizing the total drag of this propeller system. Lastly, we will also use the time-resolved PIV to characterize the vortex shedding and the turbulent energy spectrum.