Fluid Flow Characteristics of a Co-Flow Fluidic Slot Jet Thrust Augmentation Propulsion System

Abstract

The UAV industry is booming with investments in research and development on improving UAV systems. Current UAV machines are developed according to the quadcopter design which consists of a rotary propulsion system providing lift needed for flight. This design has some flaws; namely safety concerns and noise/vibration production both of which come stem from the rotary propulsion system. As such, a novel propulsion system using slip stream air passed through high performance slot jets is proposed and an analysis of the fluid characteristics is presented in this report. The test section for the experiment is developed using 3D printed ABS plastic airfoils modified with internal cavities where pressurized air is introduced and then expelled through slot jets on the pressure side of the airfoils. Entrainment processes develop in the system through high momentum fluid introduction into a sedentary secondary fluid. Entrainment is governed by pressure gradients and turbulent mixing and so turbulent quantities that measure these processes are extracted and analyzed according to the independent variable’s effects on these quantities. Pitot probe testing extracted one dimensional fluid information and PIV analysis is used to characterize the two-dimensional flow aspects. High slot jet velocities are seen to develop flows dominated by convection pushing momentum mixing downstream reducing the mixing in the system while low slot jet speeds exhibit higher mass fluxes and thrust development. Confinement spacing is seen to cause a decrease in flow velocity and thrust as the spacing is decreased for high speed runs. The most constricted cross sectional runs showed high momentum mixing and developed combined self-similar flow through higher boundary layer interactions and pressures, but this also hurts thrust development by minimizing secondary flows. The Angle of Attack of the assembly proved to be the most important variable. Outward angling showed the influence of coanda effects but also demonstrated the highest bulk fluid flow with turbulence driven momentum mixing. Inward angling created combined fluid flow downstream with high momentum mixing upstream driven by pressure. Minimal mixing is seen when the airfoils are not angled, and high recirculation zones occur along the boundaries. The optimal setup is seen when the airfoils are angled outwards where the highest thrust and bulk fluid movement is developed driven by the turbulent mixing induced by the increasing cross sectional area of the system.