Laminar Flow Vs Turbulent Flow

[Roy]

You want turbulent flow in your IC. Thats why they have all those little turbulators etc. Not only to increase the surface area/contact area between the two mediums but alos to escite the air so it bounces around and exchanges heat. Show me an intercooler that has 0.0psi pressure drop at a big number and odds are it doesnt cool the air for shit

[sh@un]

^ that's true

but apart from that, anywhere else its just costing you-

on the rest of the inlet or exhaust tract: rough walls/deliberate obstructions to induce turbulence = friction = more drag = increase in air temperature = reduction in air density = less power.

[Faid]

do you guys even know physics. at the first, i would really like to know how you are going to make the airflow laminar in you intake piping, because your turbo charger is nothing more than a centrifugal pump, it swings the air in infinite amounts of direction at a certain velocity making the flow turbulent. True is the fact that a laminar flow is desired for transport as is can handle more volume per time unit, but a good turbilant flow has the heat dissipating capacity that is desired, i know this beacause at the calcination facility in the plant where i work we turbulate the flow of liquid alumina to dissipate the heat more efficiently. also for fuel mixing capacity, a turbulant flow is more efficient. i realy want to know how you would make the flow laminar, the dynamic viscosity of a gas is so low that you need only a small deficiency's in you piping to disrupt this flow

[djr81]

Well said Faid.

All that is happening is that people have missed recognising that ALL of the flow in the induction system is turbulent. They are confusing a few concepts:

1: Flow restrictions which cause pumping losses which they are characterising as laminar/turbulent flow. Essentially the more changes of direction/diameter/shape etc etc the more pumping losses you will get in your induction system. This is true is turbulent flow as well as laminar flow.

2: Gas mixing & cylinder fill with laminar & turbulent flow. Clearly gas will mix better & exchange heat better the more turbulent it is. Cylinders will typically fill better the less turbulent the flow is.

At the end of the day with the diameters of a rtypical induction system, the large airflow invloved & the action of the turbo charger compressor ALL engine flow will be turbulent.

[Oblivion]

yeah, piping lamilar. soon as it hits the manifold you want to to tumble around as much as posible.

i think you have the idea right, but under compression in a turbo charger and intercooler you have heating and cooling of air, it is hard to get a air tumbling under 1 bar of pressure. at the rate at which air is going into and out of an engine, all that matters is how quickly and efficiently you can get air into the engine.

Having super smooth walls on air passages can actually cause a drop in flow because the air 'sticks' to the walls.

You need enough 'roughness' on the walls to allow some turbulance to assist the flow. This isn't to say that a cast finish on the inside of your head is a good thing, but something you can see a reflection of yourself in can be a bad thing.

Turbulent flow can assist in fuel mixing, and the new 2.0 Litre TFSI (Turbo Fuel Stratified Injection) Golf GTI engine features valves in the head which open and close according to the power requirements, closing when low flow is required for better velocity of air, and opening when high power is required for more volume of air.

These valves are infinitely adjustable, and actually between the plenum and the head ports.

sort of right....

smooth walls means air "doesnt" stick to them, air moves quicker against air, so having a slightly roughened surface is better for air flow.

I'm guessing a lot of you have done Engineering? Or engineering subjects??

I'm studying this stuff at the moment and all I can say is Thermo-Fluids freaking suks dog balls :(

its boring as a lesbian in a bad mood. i left to get a job.

Well said Faid.

All that is happening is that people have missed recognising that ALL of the flow in the induction system is turbulent. They are confusing a few concepts:

1: Flow restrictions which cause pumping losses which they are characterising as laminar/turbulent flow. Essentially the more changes of direction/diameter/shape etc etc the more pumping losses you will get in your induction system. This is true is turbulent flow as well as laminar flow.

2: Gas mixing & cylinder fill with laminar & turbulent flow. Clearly gas will mix better & exchange heat better the more turbulent it is. Cylinders will typically fill better the less turbulent the flow is.

At the end of the day with the diameters of a rtypical induction system, the large airflow invloved & the action of the turbo charger compressor ALL engine flow will be turbulent.

more details then alot of people will comprehend, but yes +1 for that.

i suppose it is another reason why generally larger bore engine create more torque, is that the air can move more turbulent in the chamber, before igniting...i think.

[GeeTR]

...how you are going to make the airflow laminar in you intake piping...

...people have missed recognizing that ALL of the flow in the induction system is turbulent...

I was under the impression people were talking best example, as in, if you could choose what was actually happening

Edited September 28, 2007 by GeeTR

[djr81]

I was under the impression people were talking best example, as in, if you could choose what was actually happening

Unfortunately you don't get to choose.

It doesn't make the question invalid, it just needs to be posed differently.

Basically all you need to remember is this:

If you need to exchange heat or mix gases then the more turbulent the flow the better the mixing/exchange will be (broadly).

If you need to transport gas (ie flow it somewhere) the fewer restrictions & smoother the flow path the lower the pumping loss will be. Broadly that is, I don't want to get into arguments about boundary layer effects.

[GeeTR]

Broadly that is, I don't want to get into arguments about boundary layer effects.

Well the thread creation was kinda silly and theoretical anyway (no offense Rick) What better time to get into a boundary effect, fluid dynamics discussion

[djr81]

Well the thread creation was kinda silly and theoretical anyway (no offense Rick) What better time to get into a boundary effect, fluid dynamics discussion

Go right ahead! Just make sure your start from first principles so everyone can enjoy it...

Edited September 28, 2007 by djr81

[ztuned]

transition is the best. i learnt it from fluid mechanics ol

[Rekin]

haha im doing a unit of thermo-fluids also.

Maybe if i didnt sleep through the lectures i might have understood this discussion.

Ill come back to this thread and have another read after i studied for the exam

[FATGTS-R]

Turbulent flow can assist in fuel mixing, and the new 2.0 Litre TFSI (Turbo Fuel Stratified Injection) Golf GTI engine features valves in the head which open and close according to the power requirements, closing when low flow is required for better velocity of air, and opening when high power is required for more volume of air.

These valves are infinitely adjustable, and actually between the plenum and the head ports.

That thinking was used by Nissan back in 1986. The first breed of RB engines, the RB20 redtop (12 port head) from the R31 had the exact same thing.

There was a sandwich plate between the head and the intake runers that had basically little throttle butterflies that would close off 6 of the 12 ports at low engine speeds to increase velocity and obviously open up at higher engine speeds.

Interestingly, Nissan ditched that idea in all following engines. It worked reasonably well at factory levels but is seen as a restriction when higher levels of power are wanted and hence most people remove them.

[benl1981]

What FATGTSR is saying. Toyota had a similar TVIS system on the 4AGE and I think the 3SGE. At low engine speed (below 4400rpm) I think 4 ports were closed to increase gas velocity into enigne. People removed it but actually found they lost low down power and gained nothing up high.

Edited September 28, 2007 by benl1981

[Faid]

Well fluid dynamics is a complex head ache, i recently did my PhD research in pneumatics and fluid dynamics. I studied the boundry effects that gasses display under pressure and high velocity and tried to make quick reaction pneumatic devices work more efficiantly. so thats why i know that trying to make a gas flow laminar is basicly impossible, you better off trying to shit in a coke botle . Laminar flow is good for transport purpouses, but if you just take a look at the pricaple of entropy your better off leaving it as is. evry system goes for the biggest amount of chaos, and lets face it gasses are most prone to go chaotic. for thermodynamic property's a turbulent flow is more desired. your better off in a mixing pool when you try to cool air down. the air that "sticks" to the intercooler get cooled, but if the flow was laminar, the airflow on the inside would stay hot, and also heat is like a battery, the moment there is a thermal potential difference, it begins to create flow, so even if you would get it laminar before the cooler, the heat dissapation of the cooler would on itslef create turbulance in the flow. that is just some theory. be happy to lecture you guys on fluid dynamics when im in aussie next month

[xRHETTx]

http://en.wikipedia.org/wiki/Reynolds_number

As the other engineers/engineering students have said before, there won't be any "laminar" flow anywhere near your cars intake/cylinders/exhaust etc.

Just reduce the pressure drop as much as possible through your piping by making it as straight and short as possible, with the largest piping that still gives you resonable response.

[T04GTR]

dont get confused in thinking turbulant air wont flow. the engine doesnt suck the air. its pushed in. the more its moving the more evan the cyliner filling.

[Roy]

Take the power of your car...guess the intake flow, and calculate the velocity in the intake pipes? Allowing for the compression factor im guessing the pipe velocity is going to be two parks of fark all so you get what you get with regards to the type of flow????

[Rekin]

asked my thermo-fluids lecturer at university on which is best for engine; laminar or turbulent flow.

He told me if its fuel injected it doesnt matter what type because the fuel spray is atomised...

[Yawn]

^ Haha, what?

Edited October 2, 2007 by Yawn

[PX29]

At the end of the day, one would ultimately want laminar flow though the inlet and outlet piping. This kind of flow would get the air from turbo to plenum with the least amount of energy. This laminar gaseous flow obviously isnt possible under the given conditions and hence all you can do is reduce the pressure drop ie larger piping, smoother transitions, bigger cooler etc, but with this you will get a laggier throttle response.

The scope of thermodynamics extends far beyond uni engineering units..!! (though this is the basics)

Edited October 4, 2007 by PX29