Inlet Flow distortion and Lip Separation in Ducted Fans used in VTOL UAV Systems

00 - Keynote Lectures

This paper describes a novel ducted fan inlet flow conditioning concept that will significantly improve the performance and controllability of ducted fan systems operating at high angle of attack. High angle of attack operation of ducted fans is very common in VTOL (vertical take off and landing) UAV systems. The new concept that will significantly reduce the inlet lip separation related performance penalties in the edgewise/ forward flight zone is named "DOUBLE DUCTED FAN" (DDF). The current concept uses a secondary stationary duct system to control "inlet lip separation" related momentum deficit at the inlet of the fan rotor occurring at elevated edgewise flight velocities. The DDF is self-adjusting in a wide edgewise flight velocity range and its corrective aerodynamic effect becomes more pronounced with increasing flight velocity due to its inherent design properties. Most axial flow fans are designed for an axial inlet flow with zero or minimal inlet flow distortion. The DDF concept is proven to be an effective way of dealing with inlet flow distortions occurring near the lip section of any axial flow fan system, especially at high angle of attack. In this present paper, a conventional baseline duct without any lip separation control feature is compared to two different double ducted fans named DDF CASE-A and DDF CASE-B via 3D, viscous and turbulent flow computational analysis. Both hover and edgewise flight conditions are considered. Significant relative improvements from DDF CASE-A and DDF CASE-B are in the areas of vertical force (thrust) enhancement, nose-up pitching moment control and recovery of fan through-flow mass flow rate in a wide horizontal flight range.


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Cengiz Camci, professor of aerospace engineering, Pennsylvania State University.

Cengiz has worked at Pennsylvania State University since 1986 and currently diretcs his research activities n his "Turbomachinery Aero-heat Laboratory". Following his doctoral degree (awarded by the Von Karman Institute for Fluid Dynamics) in 1985, Cengiz has been an invited lecturer at the VKI Lecture Series and a mission consultant at the ATO/AGARD RTO Research Technology Organisation. His research interests include aerothermodynamics of turbomachinery, analytical and experimental fluid dynamics, heat transfer in air breathing propulsion systems, turbine cooling, ducted fan aerodynamics for VTOL UAV systems and san erosion of helicopter rotor blade tips.
Cengiz has received three best paper awards from the ASME Heat Transfer Division, Fluids Engineering Division and IGTI Education Committee throughout his career and became a fellow of ASME in 2007. He completed many research programmes sponsored by NSF, NASA, DOE, AGTSR, General Electric (GE), Pratt&Whitney (P&W), Solar Turbines, Siemens Energy, Sikorsky Aircraft Company (SAC) and United Technologies Research Center (UTRC). He has also published more that 140 papers in his research areas.