Title page for ETD etd-05122011-155823

Type of Document Dissertation
Author Ohanian, Osgar John
URN etd-05122011-155823
Title Ducted Fan Aerodynamics and Modeling, with Applications of Steady and Synthetic Jet Flow Control
Degree PhD
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Inman, Daniel J. Committee Chair
Kochersberger, Kevin Bruce Committee Member
Kurdila, Andrew J. Committee Member
Mason, William H. Committee Member
Wilson, Sam B. Committee Member
  • non-dimensional
  • micro air vehicle
  • UAV
  • MAV
  • unmanned aerial vehicle
  • aerodynamic modeling
  • flow control
  • synthetic jets
  • rotor
  • shrouded propeller
  • ducted fan
Date of Defense 2011-05-04
Availability unrestricted
Ducted fan vehicles possess a superior ability to maximize payload capacity while minimizing vehicle size. Their ability to both hover and fly at high speed is a key advantage for information-gathering missions, particularly when close proximity to a target is essential. However, the ducted fan’s aerodynamic characteristics pose difficulties for stable vehicle flight and therefore require complex control algorithms. In particular, they exhibit a large nose-up pitching moment during wind gusts and when transitioning from hover to forward flight.

Understanding ducted fan aerodynamic behavior and how it can be altered through flow control techniques are the two prime objectives of this work. This dissertation provides a new paradigm for modeling the ducted fan’s nonlinear behavior and new methods for changing the duct aerodynamics using active flow control. Steady and piezoelectric synthetic jet blowing are employed in the flow control concepts and are compared.

The new aerodynamic model captures the nonlinear characteristics of the force, moment, and power data for a ducted fan, while representing these terms in a set of simple equations. The model attains excellent agreement with current and legacy experimental data using twelve non-dimensional constants.

Synthetic jet actuators (SJA) have potential for use in flow control applications in UAVs with limited size, weight, and power budgets. Piezoelectric SJAs for a ducted fan vehicle were developed through two rounds of experimental designs. The final SJA design attained peak jet velocities in the range of 225 ft/sec (69 m/s) for a 0.03” x 0.80” rectangular slot.

To reduce the magnitude of the nose-up pitching moment in cross-winds, two flow control concepts were explored: flow separation control at the duct lip, and flow turning at the duct trailing edge using a Coandă surface. Both concepts were experimentally proven to be successful. Synthetic jets and steady jets were capable of modifying the ducted fan flow to reduce pitching moment, but some cases required high values of steady blowing to create significant responses. Triggering leading edge separation on the duct lip was one application where synthetic jets showed comparable performance to steady jets operating at a blowing coefficient an order of magnitude higher.

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