Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9 Posted (12 years 2 months 1 week 5 days 3 hours ago) and read 6134 times:
In the photo below of the 737's wing you can see two sets of vortex generators (the small vertical rectangle plates). The inboard set is in front of the spoilers and flaps and the outboard set is in front of the aileron.
My question is....Why are the inboard set of vortex generators not in a straight line, like the outboard set? Instead they are forming a curved pattern towards the middle of the wing.
What is happening aerodynamically over the wing which has dictated the curved pattern in the vortex generator's positions? Is the center of pressure more aft in this location, perhaps?
OPNLguy From , joined Dec 1969, posts, RR:
Reply 1, posted (12 years 2 months 1 week 5 days 3 hours ago) and read 6119 times:
I'm not an aerodynamic engineer, nor do I play one on television, nor did I stay at a Holiday Inn Express last night, but I'd suspect it has to do with the positioning of the engine/pylon on the wing and the way the airflow behaves on the wing in response to it.
FredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 3, posted (12 years 2 months 1 week 5 days 2 hours ago) and read 6098 times:
You put the vortex generator wherever it is needed to reenergize the boundary layer and prevent separation. If the airflow can reach further aft without help before separation occurs , you put the vortex generator further aft.
Won't see me on the telly, nor have I slept at a Holiday Inn.
I thought I was doing good trying to avoid those airport hotels... and look at me now.
Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 4, posted (12 years 2 months 1 week 5 days 1 hour ago) and read 6095 times:
That was a very clear explanation regarding the purpose of vortex generators. So, obviously the airflow over the 737's wing can reach further back before it wants to separate from the wing area where the generators are further back. Why this is possible? I don't know. Perhaps the engine's position is relative as OPNLguy mentioned.
I guess this 707's wing really needed it's boundary layer re-energized behind the inboard engine. It has 2 rows of votex generators located there.
Sllevin From United States of America, joined Jan 2002, 3376 posts, RR: 6
Reply 5, posted (12 years 2 months 1 week 5 days 1 hour ago) and read 6080 times:
One other thing is that the role of the VG's could be for different flight regimes. Perhaps the inboard ones are primarily for separation issues during climb, whereas the outboard ones in front of the ailerons are almost certainly for very low speed/high AOA to ensure aileron effectiveness.
FBU 4EVER! From Norway, joined Jan 2001, 998 posts, RR: 7
Reply 6, posted (12 years 2 months 1 week 5 days ago) and read 6069 times:
I've flown McD/Douglas planes for many years,and none of my planes have had the need for VG's.
You find them "all over the place" on Boeings.That's poor designmanship!Just like adding additives if your hamburger patty doesn't taste right the first time!
Just like many of the early jet fighters,like the F-86D.
Broke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 7, posted (12 years 2 months 1 week 4 days 7 hours ago) and read 5994 times:
Ideal airflow across an airplane especially is called laminar. In laminar airflow, the air moves from front to back smoothly clinging to the airframe along its whole length.
If you can't get laminar airflow, the next best condition is a turbulent airflow that doesn't separate from the airframe. This isn't as good as laminar as it generates some additional drag in creating the turbulent condition.
The condition that designers want to avoid, as much as possible, is airflow separation from the airframe. What can happen is the airflow separates from the airframe and creates a negative pressure area that draws in airflow that goes forward instead of aft. This separation and reverse flow generates a considerable increase in drag and on flight controls reduces their effectivity to varying amounts depending on the amount of reverse airflow.
Generally, at each airframe's design point, the airflow is as smooth as possible and generally going from front to rear.
When an airplane is operated at speeds and altitudes that differ from the design point (for instance; take-offs, approaches, landings) you get an increase in airflow separation and reverse airflow. Vortex generators are one method (that is favored by Boeing) to restore a turbulent (vortex) airflow that is going front to rear. The vortex generator produces a small vortex (or spinning cone of air), since the vortex increases in diameter as it flows, horizontally from the generator, contact with the airframe is maintained and the flow is generally front to rear.
Douglas design teams prefer strakes and vortilerons in place of vortex generators. On the leading edge of all DC-9/MD-80/MD-90/717 airplanes is a forward pointing fairing that extends beyond the lower leading edge of the wing at about 1/3 of the span and in line with the horizontal stabilizer. It is called a vortileron and it generates a vortex that, at higher angles of attack, the vortex passes over the horizontal stabilizer increasing the efficiency of the stabilizer and elevator during low speed flight.
Douglas has strakes on engine cowls (MD-80's, MD-90's), fuselage noses (DC-9-50, MD-80, MD-90), on engine cowls (DC-8-72's and -73's, DC-10, MD-11).
The Beech 1900D is stake city, with them installed on the forward fuselage, rear fuselage, and underside of the horizontal stabilizer.
An unintended vortex generator that arose in NASCAR racing is the fairing on the top of the car roof just behind the windshield. This fairing is used to contain one of the in-car tv cameras and it was found that some body styles received an aerodynamic benefit from the fairing, where other didn't. NASCAR's solution was to put the fairing on all cars, whether they had a camera in it or not. F1 cars have a aerodynamic Tee on top of the roll bar that is also used for an in-car camera and it probably provides a vortex that increases the rear wing efficiency. All cars have the Tee, but they don't all have cameras.
Mr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 8, posted (12 years 2 months 1 week 3 days 3 hours ago) and read 5899 times:
Thank You for your info.
>Sllevin, Thanks for your thoughts on why there's two different sets of VGs on the 737's wing. Different flight regimes may very well dictate different VG postions along the wing's span.
>Broke, Thanks for your explanation about how laminar airflow is hard to maintain during certain phases of flight (takeoff, approach & landing) thus the use of Vortex Generators by some aircraft manufacturers and Strakes and Vortilerons by others.
When I think of a Laminar Airflow wing, I think of the Piper Malibu Meridian.