100% Bluff Body Drag Reduction Theory

[Frank Lee]

OK.

yaw.

and speed.

Maybe if that thing is aimable- veer it off towards the xwind.

[pstrbrc]

Funny. I was picturing a car with a "nerf bar" sticking out about 6' in front of it.
#1. I know that if something sticks out, what? 12" behind your taillights, you need a reflector. But how far in front of your headlights can it be before, I don't know, the cop isn't gonna buy, "Hey, buddy! It's just a nerf bar! Doncha 'member seeing them on '50's hotrods?"



And, then, as Frank, with such minimalism one could not accuse him of pedantry, pointed out, the optimal location would necessarily vary with air speed and direction relative to the vehicle. You would conceivably need a system that was able to instantaneously adjust the location of your plate/rod via computer and electric or hydraulic actuators. Likely in all three axes. Oh, the magnitude of the technology needed! That would almost be as complicated as, what? micromanaging each cylinder's spark event and injector duty cycle based on instantaneous readings from knock sensors? Yer right, Frank. Couldn't be done. Nothin' to see here. Move along.











Just razzin' ya, Frank.

[Otto]

This reminds me of a "spike" appendage tested on rockets about 30 years ago, as shown in Aviation Week and Space Technology. I think it was a SLBM rocket, fairly short and squatty to fit in the submarine launch tubes. Upon deployment, the spike (which looked like a big spike or nail, with the disk head at front) moved forward on a telescoping tube or rod. The wind blast hit that, shed, and formed a sort of aerodynamic bubble in which the main rocket body traveled. Overall, it reduced drag at high speeds as the missile accelerated.

I've wondered about using such an idea on a motorcycle, which being narrower, would presumably mean a smaller disk deployed closer to the headlight. As it is, there is quite a lot of turbulence and buffeting behind a standard windscreen, due to Von Karmann vortex street effect. Trick is to shed such oscillations far enough behind the rider's helmet to keep the helmet in a protected bubble, where it is much quieter. With this device, perhaps the whole upper bike could run in the bubble wake.

Thoughts?

[Otto]

And, I wonder what difference if the body in front had a convex (leading edge of an elipse) shape with a serrated edge.

[winkosmosis]

I thought this was already well known... isn't this why conventional cab trucks are more aerodynamic than cab-over ones?

[Christ]

Originally Posted by winkosmosis

I thought this was already well known... isn't this why conventional cab trucks are more aerodynamic than cab-over ones?

You got something to back that up, or are you just being facetious?

[winkosmosis]

Originally Posted by Christ

You got something to back that up, or are you just being facetious?

I've heard that the trucks with the engine in the long nose are more aerodynamic, and I assumed that's why... because it forms a step for the air, roughly approximating a more aerodynamic shape.

Similarly, you'd expect a teardrop made from Lego blocks to be more aerodynamic than a box made of Lego blocks, even though both present the same surface area perpendicular to flow.

[Frank Lee]

apples n oranges boys

review the concept again

[Christ]

Originally Posted by winkosmosis

I've heard that the trucks with the engine in the long nose are more aerodynamic, and I assumed that's why... because it forms a step for the air, roughly approximating a more aerodynamic shape.

Similarly, you'd expect a teardrop made from Lego blocks to be more aerodynamic than a box made of Lego blocks, even though both present the same surface area perpendicular to flow.

Uh-Uh.

It's literally better for the air to form it's own bubble in front of the flat nose of the CoE truck, because there is more skin friction and shape induced drag for the same surface area on the extended nose trucks.

When the airflow "hits" the cab nose at highway speed, there becomes a bubble effect on the CoE trucks that displaces air further ahead of the cab due to air spoiling at the nose, creating it's own "teardrop-ish" shape.

The extended nose design could have something in it's favor if it were actually shaped to divert airflow from the smaller nose up over the cab and around the widest points without having to make contact with them, though.

Watching the teardrop shape, we understand that nose extensions are only necessary to an extent ahead of the primary body, and the angles at which they direct flow can be very steep compared to tail angles.

I'm trying to find a virtual image of the bubble that forms in front of a CoE in a wind tunnel, but I'm not having any luck.

Also, I found this post here:

Originally Posted by aerohead

From NASA/Freightliner research,it has been determined that a conventional tractor has no inherent advantage over a COE tractor.Both can be effectively streamlined.Presently,the lowest drag rig is a COE design.

[winkosmosis]

Originally Posted by Christ

Uh-Uh.

It's literally better for the air to form it's own bubble in front of the flat nose of the CoE truck, because there is more skin friction and shape induced drag for the same surface area on the extended nose trucks.

When the airflow "hits" the cab nose at highway speed, there becomes a bubble effect on the CoE trucks that displaces air further ahead of the cab due to air spoiling at the nose, creating it's own "teardrop-ish" shape.

The extended nose design could have something in it's favor if it were actually shaped to divert airflow from the smaller nose up over the cab and around the widest points without having to make contact with them, though.

Watching the teardrop shape, we understand that nose extensions are only necessary to an extent ahead of the primary body, and the angles at which they direct flow can be very steep compared to tail angles.

I'm trying to find a virtual image of the bubble that forms in front of a CoE in a wind tunnel, but I'm not having any luck.

Also, I found this post here:

When neither gets aerodynamic treatment like radiused edges, I think it makes sense that the conventional would be more aerodynamic than the cabover. The flat front COE might have a bubble, but the conventional has a smaller bubble, then another bubble forming a ramp between the hood and the windshield.