Vortex Generators & Climb Performance
Thread Starter
Joined: May 2005
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From: Australia
Vortex Generators & Climb Performance
Morning all,
Just wondering if/how vortex generators improve climb performance?
As I understand it vortex generators delay separation on the aerofoil by mixing the lower energy air in the boundary layer with some nice fresh air above it. This delays the transition and separation on the aerofoil = less induced drag (or is that parasite drag)?
Is it this reduction in drag which improves the climb performance of a VG equipped aircraft?
Just wondering if/how vortex generators improve climb performance?
As I understand it vortex generators delay separation on the aerofoil by mixing the lower energy air in the boundary layer with some nice fresh air above it. This delays the transition and separation on the aerofoil = less induced drag (or is that parasite drag)?
Is it this reduction in drag which improves the climb performance of a VG equipped aircraft?
Joined: Sep 2002
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From: La Belle Province
If you're talking about Vgs on the wing, chances are they won't be doing much to help climb performance.
I can think of three functions for VGs, two of which are vaguely related, and one might help climb performance.
1. Shock stabilisation. A row of VGs in front of an aileron, say, or just as a row on the wing upper surface, may act to 'hold' a shock location, preventing it from wandering fore and aft, which might cause handling issues. Most versions of the BAe Hawk have one or two VG rows on the upper surface of the outboard wing for reasons such as these.
2. Stall characteristics. By acting as you described - mixing the laminar and turbulent BLs, so re-energising the BL and delaying separation, better stall characteristics and a lower stall speed may be obtained. While this may imporve some aspects of performance, it probably won't affect climb performance (which is usually optimal at much higher speeds, hence the use of 'overspeed' takeoff procedures)
3. Control of separation drag. Vgs on a 'boat-tailing' fuselage may act to re-energise the fuselage BL and delay separation until nearer the aft end. Since base drag is almost always worse than profile drag, this will usually improve fuselage drag overall, and THAT may slightly improve climb (though it's more noticeable at cruise, I wager, and may actually be there for handling not performance issues, dependent on the type)
Of course, any purist aerodynamicist will turn his or her nose up at the idea of fitting VGs; much as pilots regard the spoiler lever with some disdain, add-on fixes are in some ways an admission that we didn't get things right the first time....
I can think of three functions for VGs, two of which are vaguely related, and one might help climb performance.
1. Shock stabilisation. A row of VGs in front of an aileron, say, or just as a row on the wing upper surface, may act to 'hold' a shock location, preventing it from wandering fore and aft, which might cause handling issues. Most versions of the BAe Hawk have one or two VG rows on the upper surface of the outboard wing for reasons such as these.
2. Stall characteristics. By acting as you described - mixing the laminar and turbulent BLs, so re-energising the BL and delaying separation, better stall characteristics and a lower stall speed may be obtained. While this may imporve some aspects of performance, it probably won't affect climb performance (which is usually optimal at much higher speeds, hence the use of 'overspeed' takeoff procedures)
3. Control of separation drag. Vgs on a 'boat-tailing' fuselage may act to re-energise the fuselage BL and delay separation until nearer the aft end. Since base drag is almost always worse than profile drag, this will usually improve fuselage drag overall, and THAT may slightly improve climb (though it's more noticeable at cruise, I wager, and may actually be there for handling not performance issues, dependent on the type)
Of course, any purist aerodynamicist will turn his or her nose up at the idea of fitting VGs; much as pilots regard the spoiler lever with some disdain, add-on fixes are in some ways an admission that we didn't get things right the first time....
Thread Starter
Joined: May 2005
Posts: 49
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From: Australia
Thanks for the info Mad (Flt) Scientist. I was thinking along the lines that climb performance is really dictated by the amount of excess power/thrust as opposed to the maximum CL of the wing. Hence the question.
Cheers
Cheers
