05-05-2012, 09:20 PM
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#1 (permalink)
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EcoModding Apprentice
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Boundary layer suction?
What do you guys think about using Boundary Layer Suction to reduce drag?
BLS uses pump to literally suck the drag-creating boundary layer:
Boundary layer suction - Wikipedia, the free encyclopedia
What would be the optimal place(s) to place the inlet holes?
Remember that most cars have a huge angles when transitioning from grill to hood to windshield to roof.
So I think the inlet holes would be better placed in over the hood and the roof and in the bellypan. Maybe also on the doors or fenders.
The vacuum pump may be wired so it turns on at certain speeds reducing its power consumption during stop and go traffic.
One patent addressed its use in the underbody:
Patent US20080252099 - Boundary Layer Suction System For A Vehicle - Google Patents
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05-05-2012, 09:28 PM
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#2 (permalink)
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Master EcoModder
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skin drag is pretty small in our world, which is what this addresses.
Form drag is HUGE.
The problem you would solve with this would probably not be measurable.
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05-05-2012, 10:47 PM
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#3 (permalink)
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And then you'd have to power the pump too as I don't think you could route "suction" from elsewhere to do the job.
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05-06-2012, 12:52 PM
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#4 (permalink)
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What I recall reading a few years ago is that NASA thought it was a good way to reduce noise.
Some say those silent black helicopters circling overhead use this technology.
Old Thread, see post #8
Fan & Propeller shapes: Sickle and Curved
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Trailing Edge Blowing blade with top skin removed. Air enters at the retainer (bottom right) and exits through turning vanes at the trailing edge (left).
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05-06-2012, 01:28 PM
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#5 (permalink)
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Quote:
Originally Posted by Frank Lee
And then you'd have to power the pump too as I don't think you could route "suction" from elsewhere to do the job.
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Ducted to the low pressure wake behind the vehicle? I don't know if the pressure difference is enough.
Seems like a pretty small gain for a lot of work, though. Do this after you have a full boat tail and a Volt style electric drive system with automatic P&G.
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05-07-2012, 11:26 PM
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#6 (permalink)
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EcoModding Apprentice
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Quote:
Originally Posted by drmiller100
skin drag is pretty small in our world, which is what this addresses.
Form drag is HUGE.
The problem you would solve with this would probably not be measurable.
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It's not about skin friction.
By sucking out the stationary boundary layer you get less flow separation thus less drag.
In practical terms you get lower drag equivalent to a more aerodynamic shape.
Quote:
Originally Posted by Frank Lee
And then you'd have to power the pump too as I don't think you could route "suction" from elsewhere to do the job.
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Beyond certain speed the power required to power the pump is overcompensated by the lower aero drag. |
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05-07-2012, 11:30 PM
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#7 (permalink)
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EcoModding Apprentice
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The drag coefficient is reduced by 20.25% using this strategy
Active Flow Control over the Car |
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05-07-2012, 11:39 PM
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#8 (permalink)
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The drag is CALCULATED/ESTIMATED to reduce drag that much... while increasing lift about the same amount?  We don't want lift.
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Beyond certain speed the power required to power the pump is overcompensated by the lower aero drag.
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What speed is that and how much power does the pump require? |
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05-08-2012, 06:01 PM
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#9 (permalink)
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EcoModding Lurker
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Take a look at Jim Hall's Chapperal cars of the 60's and later his Indy car program. The physics haven't changed.
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05-08-2012, 07:42 PM
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#10 (permalink)
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Master EcoModder
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suction
Quote:
Originally Posted by Big time
What do you guys think about using Boundary Layer Suction to reduce drag?
BLS uses pump to literally suck the drag-creating boundary layer:
Boundary layer suction - Wikipedia, the free encyclopedia
What would be the optimal place(s) to place the inlet holes?
Remember that most cars have a huge angles when transitioning from grill to hood to windshield to roof.
So I think the inlet holes would be better placed in over the hood and the roof and in the bellypan. Maybe also on the doors or fenders.
The vacuum pump may be wired so it turns on at certain speeds reducing its power consumption during stop and go traffic.
One patent addressed its use in the underbody:
Patent US20080252099 - Boundary Layer Suction System For A Vehicle - Google Patents |
You might want to check in with the folks at Georgia Tech University.I believe they have on-going research with this technology.
The affects of blown and suctioned slots is a mature science now,but for MPGs they haven't conquered the cost factor.So far it's been a net loss energy wise,absorbing more energy than is saved.Like Coanda's airplanes.
The first research in this field was demonstrated by Ludvig Prandtl.He would be your starting point.
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