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1
Project Elise- Ducted propeller test
Project Elise- Ducted propeller test
::2008/07/10::
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2
Carol Moran With Kort Nozzle
Carol Moran With Kort Nozzle
::2010/08/01::
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3
Ducted propeller project by Sławek Maiden Flight
Ducted propeller project by Sławek Maiden Flight
::2014/01/05::
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4
CFD P&G SOLUZIONI AUTOGRID DUCTED PROPELLER GRID 2
CFD P&G SOLUZIONI AUTOGRID DUCTED PROPELLER GRID 2
::2009/04/02::
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5
CFD P&G SOLUZIONI  AUTOGRID DUCTED PROPELLER GRID
CFD P&G SOLUZIONI AUTOGRID DUCTED PROPELLER GRID
::2009/04/02::
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6
Coupled fluid-structure analysis (FSI) of a ducted propeller
Coupled fluid-structure analysis (FSI) of a ducted propeller
::2009/12/21::
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7
Deformación tobera - Ducted propeller deformation
Deformación tobera - Ducted propeller deformation
::2009/10/19::
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8
Project Elise- Ducted propeller test #2
Project Elise- Ducted propeller test #2
::2008/07/22::
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9
Newly invented ducted 3D rotor of wind / hydrokinetic turbine
Newly invented ducted 3D rotor of wind / hydrokinetic turbine
::2012/04/29::
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10
Movable Water Outlet of Propeller Duct
Movable Water Outlet of Propeller Duct
::2011/09/20::
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11
5 Blade Vs Change Sun 10 Blade SOUND UPGRADE
5 Blade Vs Change Sun 10 Blade SOUND UPGRADE
::2012/04/17::
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12
The Case For Ducted Fan VTOL
The Case For Ducted Fan VTOL
::2011/10/07::
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13
Propeller cavitation experiment
Propeller cavitation experiment
::2012/09/15::
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14
Ducted Fan Bixler
Ducted Fan Bixler
::2013/01/26::
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15
SUPER FAST Piasecki X 49A Helicopter for US Military
SUPER FAST Piasecki X 49A Helicopter for US Military
::2014/02/05::
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16
Solidworks 2011 - Propeller Design
Solidworks 2011 - Propeller Design
::2010/10/15::
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17
A flying ship using the Coanda effect to generate horizontal power
A flying ship using the Coanda effect to generate horizontal power
::2013/07/06::
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18
UH-8FS Personal or Racing Hovercraft
UH-8FS Personal or Racing Hovercraft
::2012/05/15::
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19
Raven EPP rc Flying wing with ducted fan
Raven EPP rc Flying wing with ducted fan
::2009/12/11::
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20
Both Coanda and helicopter propulsion air ship -- newly patented
Both Coanda and helicopter propulsion air ship -- newly patented
::2013/07/06::
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21
Piasecki Aircraft VTDP Compound Helicopter Technology
Piasecki Aircraft VTDP Compound Helicopter Technology
::2013/08/28::
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22
Ducted fan wind turbine - V-LIM
Ducted fan wind turbine - V-LIM
::2011/01/07::
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23
Carbon made Small Unmanned Aerial System (SUAS); named NEO
Carbon made Small Unmanned Aerial System (SUAS); named NEO
::2014/03/19::
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24
HYBRID (WINGLET) propellers for multicopters
HYBRID (WINGLET) propellers for multicopters
::2014/02/01::
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25
Piasecki X-49A Speedhawk flight tests
Piasecki X-49A Speedhawk flight tests
::2007/10/18::
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26
EADS E-Fan electric aircraft demonstrator
EADS E-Fan electric aircraft demonstrator
::2013/06/17::
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27
US Naval Research First Flying Platform 1955  (2X4 Cyl & counter rotating propellers)
US Naval Research First Flying Platform 1955 (2X4 Cyl & counter rotating propellers)
::2011/06/30::
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28
Ducted Fan Quad Flight
Ducted Fan Quad Flight
::2013/02/04::
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29
SUPER FAST Piasecki X 49A Trực thăng tốc độ cao của Mỹ
SUPER FAST Piasecki X 49A Trực thăng tốc độ cao của Mỹ
::2014/04/23::
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30
Universal Hovercraft - UH-10F Entry Level Hovercraft Racing- Plans & Kits available
Universal Hovercraft - UH-10F Entry Level Hovercraft Racing- Plans & Kits available
::2010/01/25::
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31
ROV Thrusters - Part 3 - Testing Props
ROV Thrusters - Part 3 - Testing Props
::2014/03/18::
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32
Propfan: "Back to Propellers" 1987 NASA Lewis Research Center Fuel Efficient Aircraft Propulsion
Propfan: "Back to Propellers" 1987 NASA Lewis Research Center Fuel Efficient Aircraft Propulsion
::2012/11/21::
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33
HEAVY DUTY TRANSPORT US Navy Landing Craft Air Cushion LCAC Hovercraft
HEAVY DUTY TRANSPORT US Navy Landing Craft Air Cushion LCAC Hovercraft
::2014/01/06::
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34
Multiplex Xeno with Electrical Ducted Fan makes much fun
Multiplex Xeno with Electrical Ducted Fan makes much fun
::2010/05/30::
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35
ProBoat Pro Boat Retrieval Decoy 2.4ghz Rc Boat
ProBoat Pro Boat Retrieval Decoy 2.4ghz Rc Boat
::2010/09/30::
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36
Electric ducted fan test (64mm EDF, brushless motor, 30A ESC)
Electric ducted fan test (64mm EDF, brushless motor, 30A ESC)
::2010/05/10::
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37
Kamdax Glow Ducted Fan 0,9cc engine break-in
Kamdax Glow Ducted Fan 0,9cc engine break-in
::2012/03/19::
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38
Rim Driven Propellers (RDP) or Rim Drive Propulsers and Thrusters
Rim Driven Propellers (RDP) or Rim Drive Propulsers and Thrusters
::2012/04/20::
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39
Folding propeller design which rotates
Folding propeller design which rotates 'around' the boom, for UAV and R/C planes
::2013/05/12::
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40
PROPELLER SOLUTION
PROPELLER SOLUTION
::2014/03/01::
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41
Micro Ducted Fan EDF Quadcopter Build 35 Grams With Lipo
Micro Ducted Fan EDF Quadcopter Build 35 Grams With Lipo
::2012/03/21::
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42
Retrieval Decoy 2.4 RTR by Pro Boat
Retrieval Decoy 2.4 RTR by Pro Boat
::2013/02/08::
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43
RC Jets: The BEST DUCTED FAN?
RC Jets: The BEST DUCTED FAN?
::2011/09/12::
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44
X-UAV Bobcat Rc airplane trainner EPO plane model with 70 ducted motor
X-UAV Bobcat Rc airplane trainner EPO plane model with 70 ducted motor
::2013/06/06::
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45
Ducted fan test
Ducted fan test
::2014/02/16::
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46
Sky Jeeps: Doak VZ-4, Chrysler VZ-6, & Short SC-1 VTOL Tethered Hovering Tests 1960 NASA Langley
Sky Jeeps: Doak VZ-4, Chrysler VZ-6, & Short SC-1 VTOL Tethered Hovering Tests 1960 NASA Langley
::2013/05/26::
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47
Velocity 30 Hovercraft - Silent Propeller I
Velocity 30 Hovercraft - Silent Propeller I
::2012/04/06::
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48
Surface Propeller tested on "Levi Drive Experimental LD240 600"
Surface Propeller tested on "Levi Drive Experimental LD240 600"
::2013/09/26::
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49
Tandem-Duct Aerial Demonstrator
Tandem-Duct Aerial Demonstrator
::2012/07/13::
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50
Ducted Prop Assembled
Ducted Prop Assembled
::2014/01/25::
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From Wikipedia, the free encyclopedia
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The towboat Dolphin I in a floating drydock on the Mississippi River in Algiers, Louisiana.

A ducted propeller, also known as a Kort nozzle, is a propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and is especially used on heavily loaded propellers or propellers with limited diameter. It was developed by Luigi Stipa (1931) and Ludwig Kort (1934). The Kort nozzle is a shrouded propeller assembly for marine propulsion. The hydrodynamic design of the shroud, which is shaped like a foil, offers advantages for certain conditions over bare propellers.

Advantages are increased efficiency at lower speeds (<10 knots), better course stability and less vulnerability to debris. Downsides are reduced efficiency at higher speeds (>10 knots), course stability when sailing astern, and increase of cavitation. Ducted propellers are also used to replace rudders.

History[edit]

Luigi Stipa [1] and later Ludwig Kort (1934)[2] demonstrated that an increase in propulsive efficiency could be achieved by surrounding the propeller with a foil-shaped shroud in the case of heavily loaded propellers. A "Kort Nozzle" is referred to as an accelerating nozzle and is generally a MARIN 19A profile or a MARIN 37 profile.

Advantages and disadvantages[edit]

Kort nozzles or ducted propellers can be significantly more efficient than unducted propellers at low speeds, producing greater thrust in a smaller package. Tugboats and fishing trawlers are the most common application for Kort nozzles as highly loaded propellers on slow moving vessels benefit the most. Nozzles have the additional benefits of reducing paddlewheel-effect (e.g. the tendency of a right-hand wheel to back to the left) and reduce bottom suction while operating in shallow water.

The additional shrouding adds drag, however, and Kort nozzles lose their advantage over propellers at about ten knots (18.5 km/h).

Kort nozzles may be fixed, with directional control coming from a rudder set in the water flow, or pivoting, where their flow controls the vessel's steering.

Shrouding of this type is also beneficial to navigation in ice fields since it protects the propeller tips to some extent. However, ice or any other floating object can become jammed between the wheel and nozzle, locking up the wheel. Fouled wheels in Kort nozzles are much more difficult to clear than open wheels.

A research paper by Bexton et al. (2012)[3] concluded that ducted propellers were the likely cause of fatal injuries of seals in the northeastern Atlantic. The authors hypothesized that the seals were drawn through the nozzle and past the rotating propeller blades, incurring curvilinear lacerations to skin and muscle tissue. This type of injury has come to be known as a "corkscrew" injury. The authors also comment that other animals, including harbour porpoises, have been seen to exhibit similar injuries.

Types[edit]

There are two types of ducts; accelerating and decelerating. With accelerating ducts, the inflow velocity and efficiency of the propeller is increased. This is the type that is used on heavily loaded propellers or propellers with limited diameter. As Ludwig Kort performed extensive research on this type, it is often called a "Kort nozzle".

With the second type, the inflow velocity is reduced, whereby pressure is increased, reducing cavitation. This is called a pump-jet, especially in combination with fixed blades or stators.

NACA 4415.

MARIN has done extensive research on ducted propellers. Many of the used profiles are based on the NACA airfoils of which the NACA 4415 has very good characteristics. Most commonly used are nozzle 19A and 37 of the MARIN series. These have a rounded trailing edge to ease fabrication and increase efficiency sailing astern. Initially, the propellers of the Wageningen B-series were used, later the Kaplan-type with a wider blade tip.

Physics[edit]

Circulation around accelerating and decelerating nozzle
Circulation around nozzles.svg

dT = Thrust
dL = Lift

pu: Negative pressure
po: Positive pressure

In a Kort nozzle, the inflow velocity is increased, reducing pressure. This lowers thrust and torque of the propeller. At the same time, a circulation occurs, resulting in an inward aimed force, that has a forward component. The duct therefore has a positive thrust. This is normally larger than the thrust reduction of the propeller. The small clearance between the propeller and duct reduces tip vortex, increasing efficiency.

As drag increases with increasing speed, eventually this will become larger than the added thrust. Vessels that normally operate above this speed are therefore normally not fitted with ducts. When towing, tugboats sail with low speed and heavily loaded propellers, and are often fitted with ducts. Bollard pull can increase up to 30% with ducts.

With decelerating ducts, the circulation opposite of the Kort nozzle, resulting in a negative thrust of the duct. This type is used for high speed vessels with increased exposure to cavitation and vessels that want to reduce noise levels, such as warships.

See also[edit]

References[edit]

Bibliography[edit]

External links[edit]

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