Sorry not following - please explain.
intercooler air ducts face the wrong way? (My response to 4xoverland) | Auto Expert John Cadogan
No link as it does include a few poo words
Sorry not following - please explain.
REMLR 243
2007 Range Rover Sport TDV6
1977 FC 101
1976 Jaguar XJ12C
1973 Haflinger AP700
1971 Jaguar V12 E-Type Series 3 Roadster
1957 Series 1 88"
1957 Series 1 88" Station Wagon
StPierre-White or whatever his name is.
A mate sent it to me last night
Youtube is your friend
Good video, but I disagree with elements of both.
I agree with Cadogee in that the scoop is facing the right way for many of the reasons he outlined. Pressure differentials, temps etc with low pressure under the engine.
But 3nuts is correct in that there is a low pressure area at the base of the windscreen. What Cadogee hasn't realised is that he has modelled his aero off a car and not a 4WD, where the car is very aerodynamically designed to retain lamellar flow as they all do these days, but the Landcruiser is designed as a Landcruiser and the flow off the nose detaches as it lifts over the roof leaving turbulant low pressure air at the bottom of the windscreen and over the bonnet. What will exacerbate this is the back of the bonnet scoop where it drops again but the bonnet scoop helps to fill the low pressure area which improves the drag in that area. These things are not designed in the slightest like a modern aerodynamically efficient car.
Cabin air intakes don't sit in a high pressure zone, they're also always in that low pressure area which is dropped away in the well below bonnet height. If it was in the high pressure area it would pressurize the cabin and the air would come in a 110km/h. The reason why the air flows from the low pressure zone is because the cabin air exhausts from the rear of the cabin where there is a more siginificant low pressure zone from where the air detatches at the rear of the vehicle which creates a more sensible flow without ear problems.
Out of interest from testing and thesis investigations, a Series is more aero with a tyre on the bonnet because it fills the turbulent air area but if you did that to a Disco5 it would increase the drag. Also from LandRovers design, engineering and testing white paper, the new LandRovers have a Cd value very close to the 300ZX at 0.33.. but remember, it still has a larger area than the 300ZX
Cheers
Slunnie
~ Discovery II Td5 ~ Discovery 3dr V8 ~ Series IIa 6cyl ute ~ Series II V8 ute ~
Slunnie, are you sure the base of the windscreen is a low pressure zone?
In all my reading it's a high pressure zone, and wool tuft testing a Defender (yes, you read that right) the flow was pretty laminar in the centre of the bonnet from front to near the back
However, the edges of the bonnet where it curves down to the guards and the tops of the guards was interesting, it was really disturbed and when I removed the blanking plate that is the fresh air intake/ventilation on LH drive cars the flow reversed, ie. air didn't come out, it went in.
Also, when lifting the rear of a GU bonnet with packers to see if it allowed air out to help with overheating it mase things worse, air was being pushed into the engine bay and wool tufts bore this out, it was a really strong high pressure zone at the base of the screen.
Cheers
Slunnie
~ Discovery II Td5 ~ Discovery 3dr V8 ~ Series IIa 6cyl ute ~ Series II V8 ute ~
Sorry for the low quality, but you'll get the idea. Hopefully the pictures work here as I normally host them on my website.
For the top of the bonnet you can see that the airflow detatches off the front of the bonnet and then rejoins after the front of the roof. You can see on the pressure simulation that the pressure drops and on the speed simulation that the airspeed also drops. (Simulations 2, 3, 4).
For the GU, I'm really not sure, but you can see how the slightest of tweaks to the floor will change the pressure characteristic quite significantly which will have a massive effect on the way the air flows through the engine and why a top mount intercooler can work.... and why you probably don't want to drop a low hanging LPG or long range fuel tank into it. Compare simulations 1 and 3.
Cheers
Slunnie
~ Discovery II Td5 ~ Discovery 3dr V8 ~ Series IIa 6cyl ute ~ Series II V8 ute ~
This reminds me of a discussion from nearly fifty years ago - the Citroen I drove at the time was considered to have much more realistic "real life" aerodynamic drag than any other car, simply because the self levelling suspension meant that attitude and ground clearance remained the same regardless of loading. Also helped that the bottom is smooth and aerodynamically designed, with a low pressure area for the airflow from the engine.
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
And re the GU bonnet, previous experience with cars showed that would happen, as the under bonnet region is generally considered an area of high pressure so the pressure at the base of the screen would need to be higher still to push the will tufts back under the trailng edge.
I wish I'd taken video of it all.
One of the race car guys I worked with had an XJ6 Series II Jag at one point and he said the bonnet catch failed at 100km/h and it flew up to nearly the top of windscreen height.
Their bonnets are hinged at the front.
I wish I had a pressure differential gauge at the time I was playing with all that stuff just to really see what was going on.
Airflow isn't always what it seems
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