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F1_eng wrote:

speedsense wrote:

F1_eng wrote:Averaging volumetric inlet air flow and assuming 100% vol eff @ 18,000 rpm, the average speed in a 60mm dia exhaust would be around 140mph

Try this study on a rotary engine... the air flow through the intake and the exhaust is supersonic....

Can you elaborate on your point please?
As far as my knowledge goes, this type of flow condition wouldn't yield a possible supersonic flow situation but you may have a special case in mind?

It must be a special case. I've done an a lot of Fluid Dynamics and that situation raises some red flags.

Scotracer wrote:

F1_eng wrote:

speedsense wrote:
Try this study on a rotary engine... the air flow through the intake and the exhaust is supersonic....

Can you elaborate on your point please?
As far as my knowledge goes, this type of flow condition wouldn't yield a possible supersonic flow situation but you may have a special case in mind?

It must be a special case. I've done an a lot of Fluid Dynamics and that situation raises some red flags.

Here at autosport tech forum http://forums.autosport.com/index.php?s ... &p=3914661 another discussion brough the supersonic issue. In the above link you will see that in a SR71 flying mach 3 the engine intake is designed to bring the flow subsonic. Why in hell would someone want supersonic in an ICE?

The shocks you'd get with supersonic flow entering an engine would be...interesting to watch.

Scotracer wrote:The shocks you'd get with supersonic flow entering an engine would be...interesting to watch.

Supersonic air flow into an IC engine?
I do not think so, we are talking about 19th century technology here after all.

Scotracer wrote:

F1_eng wrote:

speedsense wrote: Try this study on a rotary engine... the air flow through the intake and the exhaust is supersonic....

Can you elaborate on your point please?
As far as my knowledge goes, this type of flow condition wouldn't yield a possible supersonic flow situation but you may have a special case in mind?

It must be a special case. I've done an a lot of Fluid Dynamics and that situation raises some red flags.

4 rotor Mazda motor on a WSC car at redline (sorry I won't quote the tach number), 1998 year... the only car(engine) you could hear five miles away at Daytona 24 at 3am....
BTW, this was not an observation but a statement from the engine builder that flowed and measured the intakes on a dyno... the high pitched sound and decibels are because the air flow has become supersonic.

autogyro wrote:

Scotracer wrote:The shocks you'd get with supersonic flow entering an engine would be...interesting to watch.

Supersonic air flow into an IC engine?
I do not think so, we are talking about 19th century technology here after all.

I was mocking the idea. Having supersonic flow into an ICE is a baaaaad idea.

Scotracer, i think you are talking a load of rubbish im afraid.

physics tells me that the flow can't be super-sonic and yo tell me an engine builder says it is.

great

F1_eng wrote:Scotracer, i think you are talking a load of rubbish im afraid.

physics tells me that the flow can't be super-sonic and yo tell me an engine builder says it is.

great

It depends how you have the inlet conditions. They could have the pipe configuration to create a supersonic flow within the intake; a de Laval nozzle allows such a thing. Not that you'd want to do such a thing.

Which could condition can never work for a real IC engine

At atmospheric conditions, you'd be right. I'm just simply pondering what would happen to the engine if it were achieved.

It would be very unpredictable since most flow equations that are used for general purposes don't apply to supersonic flow. But i think choking of the flow and excessive heating due to friction would take place before supersonic flow can be achieved in an intake manifold.

Sooooo ????

Have we got some CFD expert in the forum to run us a simple model of half a water drop shaped `thing` with a diffuser in an air stream with different temperatures from bottom to the top or something like that?

It would be nice to have a baseline to start discusing about this.

Remember density is all arround in fluids mechanics equations, like Navier-Stokes.

I've never done mach number flows before, but i can try a little thing. Don't expect anything much, or anytime soon though.
A shock wave will dramatically increase in pressure and density at the wavefront ie if the flow manages to reach sonic, an intake manifold would be destroyed.
Only one to really look at this and i guess it's with the CFD.

by the way (slightly off-topic), the intakes on fighter aircraft like the F-15 have inlet ramps that allow control of where the shock wave entering the intake will form. the oblique shocks that follow can easily give a compression ratio of 4:1 simply via compression through the shock waves themselves.

ringo wrote:I've never done mach number flows before, but i can try a little thing. Don't expect anything much, or anytime soon though.
A shock wave will dramatically increase in pressure and density at the wavefront ie if the flow manages to reach sonic, an intake manifold would be destroyed.
Only one to really look at this and i guess it's with the CFD.

I think air inside of some turbochargers can approach transonic flows at the edge of the compressor blade tips. But on a large scale of a Whole intake It would be difficult to know what should size of the throat of the nozzle due to all the effects. Especially since the car is moving at such low velocities when compared to a fighter jet/bomber It's hard to know what is needed.