I have a pretty solid technical background as a college science professor. :thumbsup:
V
aerodynamics?
- Thread starter the bruce
- Start date
I have a pretty solid technical background as a college science professor. :thumbsup:
anile_eight
Go Kart Champion
- Location
- Savannah, GA
What do you hope to get out of the book?
The satisfaction of learning and not living in ignorance. Not intending on becoming an expert on aerodynamics, but interested in the application. And maybe some nice examples for my lectures and presentations. :wink:
I'd also recommend these following texts:
My thinking was if total underbody pressure is high it would cause lift. If not
the shape of the rear roof section must be the reason for the lift the Golf has.
Junker, I'm happy I have drummed up interest for car aerodynamics. :biggrin::biggrin:
I know we cannot effect that much, but at least it's interesting to get some understanding.
The only opening is the one at the end of the tube pointing perpendicular to airflow. I thought pitot tubes had an opening facing into the direction of travel. Interesting stuff.
Can you explain a bit more about the implications of these different pressure types (static, dynamic, total, stagnation, etc.) for our cars? Is my measurement appropriate for the goal of finding a suitable location for a NACA duct to drive air into the rotor hub? I should measure pressure near the wheel hub, but I've read that this area at speed is negative relative to atmospheric pressures. I've been assuming if I can find a suitable area of high pressure as a collection point, this will help with airflow to the brakes.
Interesting. We should probably get input from Anile on your question. Wouldn't one have to measure both underbody and at the roof to figure out the lift? Plus, we already know that the mkV chassis has 36-37 kg of lift at the rear (from the beginning of this thread). Are you curious about the cause, or what might be done about it? (or both :smile
.I had planned on making some measurements in the engine bay, at the radiator intake, and outside near the wipers. Personally, I'm curious about the polar bear mod and the low-profile trim mod that are both supposed to help cooling engine cooling (a problem on the VR6 with DSG). Racers have reported lower temps following the polar bear mod, but I don't think the low-profile trim mod has any empiric evidence to support it. Conceivably, it could be making things worse.
anile_eight
Go Kart Champion
- Location
- Savannah, GA
Well what I meant was more like this. The air flow (or stream lines) you can think of are going straight at the car. if it has a hole at the very front tip of it that will be total pressure. Any other holes will be static. But from what you said above it does not have a hole at the end facing into the stream lines but it has a hole perpendicular to the flow (or parallel to the ground). If that is the only thing you are measuring, then you are only measuring static pressure. Which honestly, really can't tell us much. It's like in an airplane and only have the altimeter to tell you how fast you are going. It's a little tough trying to get an idea of what you are trying to measure without actually being there.
stagnation pressure is defined to be the theoretical pressure which would exist if the flow was brought to rest adiabatically and reversibly (aka no heat added or friction) this is also an isentropic process. Total pressure is the combination of static and dynamic pressure. Static pressure is what is sounds like. It is the physical pressure on the surface which always acts perpendicular to it. Dynamic pressure is simply (1/*rho*v^2) (rho=density), you can think of it as how much energy the moving flow posses
Honestly, if you placed a duct anywhere on the front bumper, it would work out fine, it will take the ram air and take it where ever you duct it (unless the pipe is too long/too many bends). If you use the cutout next to the fogs and routed it to the rotors, would wouldn't have any problem. My only concern with the duct below the lower A-arm of the front suspension is drivability on the streets. If you are not going to do that, then don't worry about it. The wheels could create high/low pressure zone, but it will depend on the shape of the front of the wheels and if there are ducts in the well. If the front and the back cut outs (I am talking about the slits/holes etc in the face of the wheel) are symmetric front and back then there most likely would be little to no pressure drop due to the wheels. But a lot of the other style wheels would be designed to inherently draw out heat from the brakes (C4 saw blades for ex). But inherently because of the large drag increase of the tires/wheel (~20% of the overall drag of the car, yes and I researched this number on published journals), there is a lot of otherwise known as "aerodynamic crap" going on. A lot of vortecies and mixed flow. Here is one of the better articles I found: http://www.tfd.chalmers.se/~sinisa/images/stories/papers/mscThesis/2010/Sasan_Sarmast_Jan2010.pdf
You can see below. Case 1 is the wheel well being 2x volume of the wheel and Case 2 is 2.8x
There are regions of relative high and low pressure mainly due to the rotation of the wheel. This is a combination of the air's viscosity and the tread on the tires. Even if they are tucked (hence why most race cars are) air will still get in there, just less pronounced.
Interesting. We should probably get input from Anile on your question. Wouldn't one have to measure both underbody and at the roof to figure out the lift? Plus, we already know that the mkV chassis has 36-37 kg of lift at the rear (from the beginning of this thread). Are you curious about the cause, or what might be done about it? (or both :smile
I had planned on making some measurements in the engine bay, at the radiator intake, and outside near the wipers. Personally, I'm curious about the polar bear mod and the low-profile trim mod that are both supposed to help cooling engine cooling (a problem on the VR6 with DSG). Racers have reported lower temps following the polar bear mod, but I don't think the low-profile trim mod has any empiric evidence to support it. Conceivably, it could be making things worse.
that would be a very crude way to measure the lift but it could get you a little idea of what is going on if you measure the two. Well there isn't much to be done as that is primarily done by the shape of the car. If you think about it, the car looks like a very highly cambered air foil:
http://www.allstar.fiu.edu/aero/images/pic4-4.gif. You really can't do much about that unless you change the shape, it's all built in. You can try to stabilize it with front and rear aerodynamic devices which have obviously been proven.
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Wow! Thank you sir for such an erudite and clear post. The wheel-well images are very cool (and interesting).
Would you suggest I turn the tube opening to face the oncoming air stream? Would that give a more accurate measure? I thought if I was going to compare pressures in the engine bay or wheel wells (that don't have a clearly defined airstream) with pressures at the radiator opening and such I was better off comparing static pressures.
Wow! Thank you sir for such an erudite and clear post. The wheel-well images are very cool (and interesting).
Would you suggest I turn the tube opening to face the oncoming air stream? Would that give a more accurate measure? I thought if I was going to compare pressures in the engine bay or wheel wells (that don't have a clearly defined airstream) with pressures at the radiator opening and such I was better off comparing static pressures.
anile_eight
Go Kart Champion
- Location
- Savannah, GA
Yes, if you can turn it into the air stream so it will be getting ram air (total pressure) the measurements will be much more beneficial. I'm assuming you are doing this to find a region where you will be getting the highest pressure and use that to start the duct to the brakes?
Temp paint could also work. Good suggestion
I'm all about measurements :thumbsup: That's why I have this mounted on my LCA pointing at the passenger side rotor.
There is also a surface thermocouple near the banjo bolt of the passenger caliper. Each can provide data logging.
My .:R looks like a science experiment with all of these tubes and wires running into the passenger side door/window :biggrin:
You are correct: this is all about directing air for brake rotor cooling. The frontal region of the car has the advantage of more air flow, but directing ducts past the wheel wells and into the rotor hub is tough on our cars. The LCA mounted duct can remain nice and tidy behind the wheel and should be able to be configured to avoid rubbing/binding even at full steering lock. I just wanted to compare pressures at the two likely spots for a NACA duct to make sure I wasn't on a fools errand.
I will try turning each tube opening into the airflow to see how they compare in that configuration.
