Page 1 of 2 12 LastLast
Results 1 to 10 of 19

Thread: ye olde chestnut

  1. #1
    Join Date
    Oct 2012
    Location
    FNQ
    Posts
    1,723
    Total Downloaded
    0

    ye olde chestnut

    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

  2. #2
    Join Date
    Jan 1970
    Location
    Canberra
    Posts
    18,474
    Total Downloaded
    0
    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

  3. #3
    Join Date
    Jan 1970
    Location
    NSW far north coast
    Posts
    17,279
    Total Downloaded
    0
    StPierre-White or whatever his name is.
    A mate sent it to me last night

    Youtube is your friend

  4. #4
    Join Date
    Jan 1970
    Location
    Central West NSW
    Posts
    13,671
    Total Downloaded
    0
    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 ~

  5. #5
    Join Date
    Jan 1970
    Location
    NSW far north coast
    Posts
    17,279
    Total Downloaded
    0
    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.

  6. #6
    Join Date
    Jan 1970
    Location
    Central West NSW
    Posts
    13,671
    Total Downloaded
    0
    Quote Originally Posted by rick130 View Post
    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.
    Yep, I'll just do a paintshop quality simulation. There isn't a lot of flow over the bonnet, where on a car there will be a lot of flow.

    Potentially the GU sets up a low pressure area under the vehicle which creates that situation.
    Cheers
    Slunnie


    ~ Discovery II Td5 ~ Discovery 3dr V8 ~ Series IIa 6cyl ute ~ Series II V8 ute ~

  7. #7
    Join Date
    Jan 1970
    Location
    Central West NSW
    Posts
    13,671
    Total Downloaded
    0
    Quote Originally Posted by rick130 View Post
    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.
    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.
    Attached Images Attached Images
    Cheers
    Slunnie


    ~ Discovery II Td5 ~ Discovery 3dr V8 ~ Series IIa 6cyl ute ~ Series II V8 ute ~

  8. #8
    JDNSW's Avatar
    JDNSW is offline RoverLord Silver Subscriber
    Join Date
    Jan 1970
    Location
    Central West NSW
    Posts
    28,805
    Total Downloaded
    0
    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

  9. #9
    Join Date
    Jan 1970
    Location
    NSW far north coast
    Posts
    17,279
    Total Downloaded
    0
    Quote Originally Posted by Slunnie View Post
    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.
    Is this a type of CFD programme??!! ye olde chestnutye olde chestnut

  10. #10
    Join Date
    Jan 1970
    Location
    NSW far north coast
    Posts
    17,279
    Total Downloaded
    0
    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

Page 1 of 2 12 LastLast

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Search AULRO.com ONLY!
Search All the Web!