another vortex generator paper

[aerohead]

I compared the aerodynamic power at 73-mph and 55-mph.The higher speed requires 2.3 X more horsepower to overcome air drag.
If the BSFC of the Toyota's powerplant was constant,then we'd expect the engines fuel requirement for air drag to increase this 2.3 X factor,since it mirrors the power.
Rolling resistance would increase arithmetically as it's basically a linear relationship up to 100-mph or so.
38-39 mpg at 73 is pretty sweet! The EPA numbers were figured at more like 50-mph.

[cyclopathic]

Also the tractor trailer aerodynamics are quite different from modern hatchbacks. They are tall and narrow, and have high % of airflow on the sides. Hatchbacks like Prius C have more air flowing over the top. Mitsubishi Mirage even have A-pilars spread out and uses windshield rain grooves to redirect flow over the roof. Observing C in the drizzle tells similar story, but may be not to the same extend.

If you think getting 38 MPG at 73mph is sweet, regular Gen3 Prius was getting about that much at 80-85mph going up 4% slope on I-40 in NM, abait at higher elevation and warmer temperatures. Just another testimony to efficiency of longer body and Kammback design.

I am seeing more and more new cars (Toyota, Subaru, GM) which incorporate VGs into trailing edge of undertail belly panel. Are they really helpful or they just easy to mold?

[aerohead]

Originally Posted by cyclopathic

Also the tractor trailer aerodynamics are quite different from modern hatchbacks. They are tall and narrow, and have high % of airflow on the sides. Hatchbacks like Prius C have more air flowing over the top. Mitsubishi Mirage even have A-pilars spread out and uses windshield rain grooves to redirect flow over the roof. Observing C in the drizzle tells similar story, but may be not to the same extend.

If you think getting 38 MPG at 73mph is sweet, regular Gen3 Prius was getting about that much at 80-85mph going up 4% slope on I-40 in NM, abait at higher elevation and warmer temperatures. Just another testimony to efficiency of longer body and Kammback design.

I am seeing more and more new cars (Toyota, Subaru, GM) which incorporate VGs into trailing edge of undertail belly panel. Are they really helpful or they just easy to mold?

My opinion is that these are just a styling gimmick.The strakes add reinforcement to the otherwise flimsy valance panel,providing some structural stiffening to prevent flutter caused by the wake.
I've seen Lincoln Continentals and Town Cars who's rear bumper facias would 'tremble' at highway speeds,revealing aeroelastic deformations caused by the wake turbulence/vorticity.
Automakers can change this area each year (along with the nose) at very low cost,giving buyers the impression that their 'new' car is 'different' from the previous year model.
You'll never see airplanes,airships,or submarines do this.

[cyclopathic]

Just burned a tank full 414mi at 73mph average, 43.6 MPG going 95 south. This may be not a good indicator as there was enough traffic esp trucks to get the benefits of drafting and need to turn off cruise.

[cyclopathic]

Originally Posted by aerohead

My opinion is that these are just a styling gimmick.The strakes add reinforcement to the otherwise flimsy valance panel,providing some structural stiffening to prevent flutter caused by the wake.
I've seen Lincoln Continentals and Town Cars who's rear bumper facias would 'tremble' at highway speeds,revealing aeroelastic deformations caused by the wake turbulence/vorticity.
Automakers can change this area each year (along with the nose) at very low cost,giving buyers the impression that their 'new' car is 'different' from the previous year model.
You'll never see airplanes,airships,or submarines do this.

So you think they incorporate them into diffusers just for structural rigidity?

[rumdog]

And looks too. Looks functional but most are too steep that i have seen.

[aerohead]

Originally Posted by cyclopathic

So you think they incorporate them into diffusers just for structural rigidity?

*The ABS thermo-formed sheeting has no structural rigidity by itself and would flap like a bed sheet on a clothes line without some sort of corrugation to stiffen it.
*The automakers appear to be borrowing from 'real' racing diffusers to create a styling cue gimmick with a low cost cheap plastic part which can be changed each year like a woman's handbag, along with the car's front fascia, which changes each year as well; so a buyer will feel like their 'new' car is actually 'different' from the previous year model.
*Carr's wind tunnel research showed zero requirement for strakes to be included on a diffuser in order to ensure it's performance for fuel economy.
*Racing diffusers are for downforce/high-speed stability.

[gone-ot]

Never confuse "aerodynamic" goals with "racing" goals (ha,ha).