Air flow through hood scoop

[Richard Hudgins]

Originally posted by ItBites


By the way. Back on my first reply on this thread, I'd suggested the old tuft of yarn test around the scoop inlet area.

Is anyone going to try this? I'd really like to know what happens to the flow in this area.

I think speeds of 50, 100, 150, and 200 mph would give us enough data

Mr. Bites,

We have done tests on the scoop used on the JBL. It is a big ugly thing. Look here. JBL hood scoop

We did do a flow path test using oil drops to show patterns. (Please note: Oil paths are much easier to observe in real world testing than tuft testing.) Unfortunately. I do not have any photos of the results. Sorry, as photos would show the reality of what is going on with the flow.

There were a couple of test parameters that need explaining:

1. Open bottom (No “Turkey pan”)
2. Closed bottom (With turkey pan.)

The results of the test were as follows.

Case 1. Flow: The oil streams were consistent and did not divulge from the expected flow path. The pressure at the opening was (at 100 mph) 9 inches of water. ( .3251 psi) This was no doubt the internal pressure of the engine compartment. Temperature was 87f. Ambient was 71f.

Case 2. The oil streams were not consistent. Significant divergence was found at the annulus and evidence of stalling and boundary separation was apparent. The pressure at the opening was (at 100 mph) 11 inches of water. (.3974 psi) This was obviously due to flow separation and boundary layer effects due to closed annulus. Temperature was 73f. Ambient was 72f.

From these tests, it is obvious that the only real benefit is temperature. Ram air effect is negated by the flow properties and stalling of the flow at the annulus.

There are also a number of problems with boundary layer effects and the curvature of the front section. It would be quite easy to fix these problems, but then it would even less like a Cobra then the JBL does now.

Therefore, things were left as is.

Note: we did test the small scoop configuration as well. This unit provided no flow enhancement. It actually reduced pressure at the annulus. This was due to boundary layer effects. In other words, at 100 mph, the flow is over the unit due to thickness of the boundary layer, therefore giving a net reduction in pressure.

That’s all I know.