AlfaRomeo 159 HeadLight AeroDynamics.
 

Hi,

I Drive Alfa159 Diesel. And I'm reading what ever I found to reduce the fuel usage. I want to ask you our car has terrible Cd ( 0.33 ) As you can see from the pictures, there is a hole under the bonnet. And bonnet has a seal behind my fingers in the picture. Air is blowing the gap between bonnet & front bumper. It cannot move the bumper so it moves the bonnet up, and the bonnet start to shake even with 60mph. Also the lock mechanism is in the middle. I want to make the flow connect with upper stream. If I make holes to the bonnet. before the Bonnet Seal, it should help the flow merge with the upper stream, and don't blow in the headlight section. Or secondly, I could delete the back of the lamps, so the flow enters the engine section. And I make a manifold to collect the flow, and direct it to wheel arch or under the car or again a bonnet hole. Can you give me some advice. I could not cover the headlight with transparent plastics. In Turkey, we are not there yet. We use the most expensive fuel in the world, we get angry about it, but we cannot take action, I'm afraid.
Thank you.

Welcome!
You actually do not need to cover the headlights. Just seal all the holes around the headlights so no air can flow through. The stagnant air has the same effect as a clear cover; the raised pressure causes the air ahead to flow aside and over.

Also look at blocking part of the lower grill (I run a full lower grill block on my Insight all year round).
If you reduce the amount of air that flows in there, that will lower the under hood pressure just like plugging the holes between the lamps does.
I believe my lower grill block improves my economy by 5 to 10% during winter.

Need to add:
Monitor your air intake temperature if you block a substantial part of the front.
I bought a cheap in/out thermometer and put the outer sensor in the air intake nozzle.
Only once did I see the temperature raise to alarming levels (@ 40°C while stuck in a traffic jam during a heat wave), and I could then reduce it by switching off the A/C for a while.

I've blocked the all lower grill, it helps me get quicker warmup & maybe a little bit more MPG. Also I have an airdam & vortex generator. Now I'm doing 59MPG acording to computer past 300miles. but I think I will get 50mpg(impr) max brim to brim. I'will try what you said. I'm open for anything else by the way for headlights anti-blowing design.

Those are other pictures of the lamp design of the car. You say, cover the gap between the individual lamps?

It looks like one solid unit, seems you only have to block the area between the unit and the bodywork.

59 mpg is absolutely brilliant! I struggle to get that with my Insight, with its smaller engine, aerodynamical shape and hybrid system. I feel humbled. ;)
Even 50 mpg is very good for a 159.

50mpg(impr) is with Cruise Control @ 90km 15*C-25*C outside no-rain. But it's good engine, and I'm hypermiling as I can. Light on the throttle, no brakes using as possible.longer,lighter accelerations vs. And for avoiding traffic. I get up 30 min earlier than before. But in the traffic I get mostly 35MPG :(

block
 

Just for safety's sake,you might want to inspect the engine bay just behind the headlights and see if there are any electronic components with heat sinks which might rely on air leaking through the headlights for heat rejection.

Good point.

https://i.chzbgr.com/maxW500/7273776640/h1B594B6C/

Good point indeed. I'll check & put some photos here soon.

Those are the pictures of the lights and behind. I don't see anything need heating or cooling behind the lights assembly.

The air flow is not as bad as you think, IMHO.
you can see a rubber profile on top/behind the headlights, that the bonnet rests on.
Air flow through there will be minimal.

I don't understand what you meant, I'm sorry, can you mark the picture where is minimal air flow. I think there is non air flow through lights or the case of the headlights.

by "minimal" I mean "only a very small amount".
As said before, The 159 headlights create an area with higher pressure, aerodynamically making it seem like they are enclosed in glass like other brands.

It means that there is little or nothing to be gained by changing the headlight units.

Ohh! I see now. But does it better to make flow away, than build up some pressure?

Pressure is what moves air aside. The advantage of having a high pressure area ahead of your head;lights, or car in general, is that it moves the air aside without any surface friction.
That's why a blunt nose is more aerodynamical than a sharp one, at least at speeds well below the speed of sound.

If the lamp units were in a smoothly curved area then covering them over would help, but the hood and side pannels fold sharply away so that does not matter here.

better?
 

The headlights are in a very favorable pressure gradient regime,with air attacking all around the lights location.And with enough surrounding radii,and stagnant air pooling inside the headlight bucket,the surrounding free flow should just glance off the area without separation.
I suspect that the air is already displacing into streamlines well in advance of the nose anyway.
Most wind tunnel photos reveal this Prandtl line of discontinuity as the air attempts to avoid sharp accelerations.