Parametric investigation of aerodynamic interaction between two rotors and a flat plate at low Reynolds number

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University of Alabama Libraries

This research studies the rotor wake interaction of small rotors on the surface of a flatplate. The generic model is a simplification of the rotor wake and wing interaction that can exist for small-UAV tiltrotors. Most prior rotor-wing interaction research focuses on large tiltrotor configurations. Compared to these counterparts, the disk loading and Reynolds number in this work are significantly smaller by one to two orders of magnitude. The goal is to better understand the aerodynamic interaction between the rotor thrust and plate download force using experimental, analytical, and numerical tools. Throughout this work, the far-field disk loading and Reynolds number ranged between 25 –45 N/m2 and 57,000 – 80,000, respectively. Rotor thrust, download force on the flat plate, and plate surface pressure were measured in single-rotor/plate interaction and dual-rotor/plate interaction, while only rotor thrust was acquired in dual-rotor interaction. The force measurement results show both rotor thrust and download force increase as rotor-plate distance is reduced and rotor disk coverage is increased in single-rotor/plate interaction and dual-rotor/plate interaction. The increase on rotor thrust is advantageous while download force increase is disadvantageous. The increase on download force is greater than the augmented thrust. In dual-rotor interaction, rotor thrust loss increases as rotor-rotor distance is reduced. Measured pressure contours on the plate surface supports the use of the cylindrical control volume in developing analytical models to estimate download force. Also, pressure contours reveal the nonuniformity of the vertical velocity in the downstream wake, which is an assumption and limitation with momentum theory. Lastly, a smoke visualization technique was used to measure the trajectory of the tip vortex in single-rotor/plate interaction and observe the flow pattern of the upstream wake in dual-rotor interaction. The visualization results were employed in the analytical modeling. The experimental results were compared to numerical simulations using a commercial software, RotCFD package. To facilitate the design on small-UAV tiltrotors, where the wake impinges on the wing,empirical equations derived from ground effect, momentum theory and the acquired experimental data to estimate rotor thrust and download force are developed for single-rotor/plate interaction. Furthermore, two wake models—actuator disk theory and smoke visualization, combined with image vortices and momentum theory—are adopted to estimate rotor thrust and download force in rotor-wing interaction. The analytical models capture the rotor thrust and download force trends in rotor-wing interaction and can be extended to arbitrary rotor disk coverage, rotor height, and other rotor wake models in rotor-wing interaction. The analytical models on rotor thrust are independent from rotor diameter to wing chord ratio, while the empirical equations and the analytical models on download force are dependent on this ratio.

Electronic Thesis or Dissertation
Aerospace engineering