Experimental investigation of flow past arrays of propellers using multi-plane, time-resolved, 2D-2C PIV

The expansions in the unmanned aerial vehicles (UAVs) technology have given rise to implementations of drone swarm strategies for a variety of applications, such as environmental monitoring, security, and surveillance to name a few. With fewer safety guidelines for drone swarms compared to formation flight with crewed aircraft, the opportunity has expanded in exploring tighter formation strategies for these vehicles. Thus, understanding the mechanics of flow around multi-propeller and vertical take-off and landing systems is an essential optimization tool to achieve certain outputs, like minimizing energy expenditure for a long-distance mission of multiple drones. In this talk, we focus on the dynamics of flow past multi-propeller systems, containing 5 propellers packed closely in a V-formation. We employ propellers comprised of two-blades with cross-sectional shapes following NACA 6430, with a maximum blade twist of 45° at the root. The performance of a single propeller is first characterized in a water tunnel with the axis of the propeller oriented vertically and the freestream in horizontal direction. Arrays of these propellers are then suspended in the water tunnel where we perform 2D-2C high-resolution, high-speed PIV at three horizontal planes: one below, one above and one at the height of the propellers. We use the PIV data to explore the interactions between the propellers, complex vortex dynamics, and the associated turbulence statistics. PIV data is used in conjunction with the Navier-Stokes equations to extract some flow field information in the third (vertical) direction. We also obtain the pressure fields and estimates of drag forces experienced by propellers. Lastly, we use the time-resolved PIV to characterize vortex shedding.