Exhaust Flow and Aero

[55chevr]

SF317-

Your threads actually make my hair hurt but dont stop.  I have to print them and reread them a couple of times but it is really eye opening. 


Joe

[Jorge]

In using a single turbo system ive seen cars use a single exhaust straight through all way to the rear of the car coming off the left side header and in other single turbo setups ive seen an x-pipe that leads to duals at the back. Which one would be a better choice? Or does it really matter? I would think that the less bends and extra tubes that get tied in would lead to a smoother exhaust flow.

[Jorge]

Meant to say less bends and "LESS TUBES"

[Old Scrambler]

When you ask a good question...........be prepared for the best answer!  This read is great............and so far I have yet to break 100 mph!

[ChrisLenahan]

I've been reading this thread and find it really gets the gray matter stirred up.  I have a lot of experience as an aircraft mechanic and have been an aircraft enthusiast for most of my life (well actually an enthusiast for just about anything that has a motor or wheels for that matter) and have read about the X-21 program and understand how is just wasn't practical on that scale.  However, I do see how it could be used on a smaller scale in LSR to clean up problem areas.  For instance the area around an intake scoop.  Suction could be used to bring the airflow into a laminar flow over and around a scoop.  Same goes for any other problem area.  For those running at very high speeds  these same suction holes could be used to increase drag at the end of a run by turning off the suction or even blowing air out to create more drag by disrupting the laminar flow over a larger portion of the body.  Of course there would be handling considerations to creating drag at high speed in this manner. Aerodynamic braking such as this may allow for higher potential speeds as less space would be need to get the vehicle stopped and allow for a longer run under power.

[Rex Schimmer]

Chris,
One of the misconceptions that is in this thread is that streamliners operate with laminar flow. If you calculate the Reynolds number for a car moving at 350 mph and one foot back from the nose  it is 19.4 x 10(to the 7 power) ( 194000000) which is way beyond the transition point value for laminar to turbulent flow. The stardard calculation for the Re is: Re= (air density)(velocity)(length)/viscosity. If you use calculate it at STP (Standard Temperature and Pressure) and use English dimensions it simplifies to: Re= 6300(Velocity ft/sec)(lenght ft). If you use this formula you can see that the Re quickly exceeds 1,000,000 within the first .06 inches of the body length.

Some things can affect the position of the transition zone, and one is the shape of the body, if the pressure gradient is negative it can assist in keeping the boundry layer thin and extend the length of the laminar flow region, which is the lowest drag regime. This is why using such shapes as the NACA 66000 shapes is good as these were designed specifically to have extended areas of laminar flow. I am not sure if suction would cause a turbulent flow regime to become laminar again. Probably a good question for "Blue".

Rex

[ChrisLenahan]

Rex,   I'm not an engineer so I'm just trying to apply logic to what I've been learning.  As I understand it turbulence creates drag and anything that can be done to decrease turbulent flow will reduce drag.  I would think every designer has to make compromises in the design of a vehicle that create drag and this may be one way around some of those compromises.  I'm definitely interested in what Blue and SuperFord have to say.  This brings me to another question,  are the horsepower gains made from a ram air system worth the increased drag created by the scoop.  I know that is not a simple question to answer and there are many variables to consider.  I'm new to LSR but really enjoying the mental stimulation all this is bringing.  Chris

[Rex Schimmer]

Chris,
I contend that most of the air flow over any 300 mph+ car is turbulent the trick is to assure that it remains attached. High drag occurs when the air becomes unattached and then generate large trailing vortex formations that cause drag.

Regarding air inlets I feel that if the inlet is sized properly to the engine air requirements at the cars estimated maximum speed and then the rest of the scoop is designed to ensure attached flow then the scoop will have a positive affect on the cars performance. I think that a properly designed and placed NACA inlet is probably the best possible design regarding drag and inlet but some cars do not allow you to put them in the proper air flow and they are not optimum.

I have posted these pics already of a scoop that I built for Steve Nelson's 4V fuel lakester. This car ran 187 in 2010 and 197 at the 2011 August Speed Week. The engine was basically the same as 2010 but I feel that the scoop did contribute to a part of the performance increase. The inlet is sized for about 115% of the engine air flow requirement at 200 mph and the general plan shape of the scoop is a NACA 66018 air foil shape. The area ratio of the inlet area to the maximum cross section area is about 8:1  so the scoop should do a good job of converting the energy of the inlet air into inlet pressure. The scoop is sealed to the body and the body is sealed to the injector inlets so there is very little air leakage. The scoop has internal turning vanes to aim the inlet air at each of the injector inlets. The opening in the top is to allow us to prime the injectors to get the motor started.

Rex

[Tman]

Rex, I love the look of that scoop, I am working on ideas for mine. Any pictures of the whole car?

[Rex Schimmer]

Tman,
This is a pic of the car several years ago, the only outward change is the addition of the scoop and I do not have a currrent pic of the car with the scoop mounted. It is a very classic "tank" exceptionally well built and great detail and finish. Steve has worked very hard to get the car where it is today and I am very proud to be associated with the car. It did set the 4V Fuel Lakester record this year, around 195 mph. The tank is from a Grumman Albatross.

Rex

[Dr Goggles]

I was talking to Steve , he said that he'd been into the salt for a long time but since his kids had grown up " we have a bit more time , and my wife and I both love it here"....I said , with reference to his wife loving the salt " and for that you are a lucky man"

He replied " indeed, I am very, very lucky man".

It is a great car, a great mix of style and business.

[SPARKY]

Steve's Lakester is inspiring!!!  we have visted several times 

[Tman]

OK, you have posted other shots of it in the past. I think I saw your modified at their pit but was chasing parts at the time and did not stop

[Scott]

Tman,
This is a pic of the car several years ago, the only outward change is the addition of the scoop and I do not have a currrent pic of the car with the scoop mounted. It is a very classic "tank" exceptionally well built and great detail and finish. Steve has worked very hard to get the car where it is today and I am very proud to be associated with the car. It did set the 4V Fuel Lakester record this year, around 195 mph. The tank is from a Grumman Albatross.

Rex

We pitted next to this Lakester at W.F. it is a very nice car.   SB

[38flattie]

Wow! That's a very nice looking lakester!