Window screen grille block?

[California98Civic]

Seems to me instrx and d0sitmatr agree that screen will block air. They disagree about the effectiveness of design ideas and whether the idea is even worthwhile. Earlier on this thread jthistle suggested a test. Good idea too. I have a question. If we doubled and trippled-up screens to create greater and greater blockage, wouldn't that also gradually bring down the beneficial effects of venting at slow speeds or at lights? Thanks.

[Frank Lee]

Originally Posted by instarx

So I think I will stick to the engineering formulas that say as the vehicle's speed increases, the screen (vertical, slanted, whatever) will block a greater and greater proportion of the incoming air. How much screen, how many layers, or how small a mesh size are just engineering details to be worked out. But the idea of using mesh as a variable air block material is a good one.

This has been my experience in making vent screens for snowmobiles.

[instarx]

Originally Posted by California98Civic

I have a question. If we doubled and trippled-up screens to create greater and greater blockage, wouldn't that also gradually bring down the beneficial effects of venting at slow speeds or at lights? Thanks.

Well, some, but probably not much. Remember that the air moving through the mesh at stoplights is moving slowly and therefore there isn't much resistance from the mesh. You could of course carry it to extremes and block too much air.

[jthistle]

The trick will be finding the balance between high speed blockage and low speed air flow. I have decided to follow up on my own test design. I found a cheap air speed meter on amazon and I purchased several steel mesh sheets with varying open areas. I should have results by this weekend.

I think there is something here. Have you ever had a fan in a window with a screen that gets starved when there is a gust of wind.

[California98Civic]

Originally Posted by jthistle

I should have results by this weekend.

I have been converted: testing is cool. Seems like you'd want part of the test designed to allow air to seek the lower resistance route and go around your screens, no? If the air has nowhere else to go, it will surely go through the mesh, no? I'll look forward to results. Thanks.

[justjohn]

The idea of an air block that is "invisible" at low speeds is of course awesome.

However, everyone seems to think this is going to work marvelously and that seems a little counter-intuitive to me. What about all the drag you are adding?

[metroschultz]

I believe the idea is similar to running water over a window screen into a bucket.
Put the screen over your bucket.
Run your garden hose at a slow rate for a few minutes and observe.
Most, if not all, of the water goes through the screen into the bucket.
Turn your hose on full and observe.
Most of the water, but not all, goes over the screen onto the ground.
Turn the bucket at an angle and the full power water stream will almost completely bypass the bucket, while the low power stream still goes through the screen into your bucket. The greater the angle the greater the amount of water bypassing the bucket.
One of the simpler laws of hydrodynamics. Fluid does not like to turn corners and at higher flow or pressure rate the effect is more pronounced. I forget the formulas.
Also one of the hydrodynamic laws that can be directly applied to air flow, since air is a fluid and the difference is viscosity.

[mort]

Originally Posted by justjohn

The idea of an air block that is "invisible" at low speeds is of course awesome.

However, everyone seems to think this is going to work marvelously and that seems a little counter-intuitive to me. What about all the drag you are adding?

I have to agree with this. The added drag of shapes like window screen will be awful. Screens are almost as bad as radiators for drag.

-mort

[justjohn]

Originally Posted by metroschultz

I believe the idea is similar to running water over a window screen into a bucket.
Put the screen over your bucket.
Run your garden hose at a slow rate for a few minutes and observe.
Most, if not all, of the water goes through the screen into the bucket.
Turn your hose on full and observe.
Most of the water, but not all, goes over the screen onto the ground.
Turn the bucket at an angle and the full power water stream will almost completely bypass the bucket, while the low power stream still goes through the screen into your bucket. The greater the angle the greater the amount of water bypassing the bucket.
One of the simpler laws of hydrodynamics. Fluid does not like to turn corners and at higher flow or pressure rate the effect is more pronounced. I forget the formulas.
Also one of the hydrodynamic laws that can be directly applied to air flow, since air is a fluid and the difference is viscosity.

Yes, I have basic college level physics so I understand the principals. I don't doubt for a second that more air will be deflected at higher speeds.

What I doubt is that you will make up for the increased drag of forcing air through a screeen.

[Phantom]

I would figure that drag would be about the same as a sold grill block or slightly less. The reason is that at high speed the air that gets stopped creates a stagnation point forcing air away from the grill, by doing this less air entered the engine bay reducing the drag created by the turbulence in the engine bay. So the real question is, "Does the small increase in surface area and drag created by the screen decrease the drag created in the engine bay more/less/or by the same amounts?"