From Dick Shevell AIAA paper : Aerodynamic Bugs: Can CFD Spray Them Away? AIAA Paper 83-2063, August 1983 DC-10 wind tunnel tests showed a significant loss in maximum lift
coefficient in the flap deflected configurations, with landing slat
extension, compared to predictions. This resulted in a stall speed
increase of about 5 knots in the approach configuration. The initial
wing stall occured behind the nacelles and forward of the inboard
ailerons. The problem was traced by flow visualization techniques to
the effects of the nacelle wake at high angles of attack and the
absence of the slat in the vicinity of the nacelle pylons. The
solution was developed in the NASA Ames Research Center 12 ft.
pressurized tunnel and turned out to be a pair of strakes mounted
forward on each side of the nacelles in planes about 45 degrees above
the horizontal. The final strake shape was optimized in flight tests.
The strakes are simply large vortex generators. The vortices mix the
nacelle boundary layer air with the free stream and reduce the
momentum loss in the wake. The vortices then pass just over the upper
surface of the wing, continuing this mixing process. The
counterrotating vortices also create a downwash over the wing region
unprotected by the slat, further reducing the premature stall. The
effect of the strakes is to reduce the required takeoff and landing
field lengths by about 6%, a very large effect.
An example of condensation vortex generated by the nacelle strake (from behind the wing)
This was one of the best flights I have had on SQ22 / SQ21. Yen Ping, Kok Mun and MJ and the rest of their
cabin crew not only provided wonderful service but these 3 sort of out anticipated me and made this trip
one of the best ever. I got some interesting photos of the condensation vortex that is promoted by the nacelle
strake (more later) on the engine housing.
Our SQ 22 Flight Path
Looking from Terminal 3 Gate B7
SQ 22 taxi
A flock of birds were flying over the water drain
Changi birds close
Runway turn - waiting for incoming flights to land
For a couple of years, I have been fascinated by the appearance, structure and disappearance of what I call
condensation vortices. They appear along the engine housing and off the tip of the wing stabilizers. One of the
flight crew referred to the housing plate as a
NacelleStrake. Here is
initial vortex formation - you can see the initiation of the vortex at the Nacelle Strake
Closer view of the initiation at the Nacelle Strake
Mark Stock apparently (according to Nafees) is a computational fluid dynamics colleague and made this video
of vortex behavior. One of the delights of Facebook is making connections such as Mark - which help me
to better understand condensation vortices associated with nacelle strakes on A340 and 777 aircraft.
Altitude: 33m Condensation vortices from engine housing and wing stabilizer