2012 Exhaust Blowing & Coanda

[ringo]

So you are questioning the angle through which the exhaust can flow around the coanda channel?
It goes out 10 degrees above horizontal and tuns downward soon after.
So you are saying it's much different than the air craft.

I think the effect over the air craft examples are more extreme. They are turning through an acute angle of 90 degrees.

The F1 car's exhaust turn through an obtuse angle, an angle wider than 90.

[hardingfv32]

Bodywork has to stay clear of a conical section with a 3 degree divergence from the exhaust exit (not from the horizontal).

Yes, 3 degrees is correct and seemingly more manageable.

What about the fact that the channel is round? Wouldn't the attractive force of the Coanda Effect which acts perpendicular to the flow surface reduce to zero as the curved wall reaches 90 deg? I am assuming that we are turning the flow in one plain, McLaren's system, and not a bell mouth system.

Why isn't the floor of the channel flatter? Poor flow characteristics in corners?

Brian

[hardingfv32]

So you are questioning the angle through which the exhaust can flow around the coanda channel?

No, the quality of the attachment as the flow leaves the exhaust tip.

Brian

[shelly]

@brian: the ramp is circular and not flat just because the jet is circular. Do not think abbout planes passing through the axis of the exhaust and exit 3deg cone: think about verticel planes parallel to each other. Ifyou take a section of the jet and the circular ramp on a vertical longitudinal plane you will see that the circular shape is a consequence of wanting to keep the ramp surface near the slice of jet over it

[hardingfv32]

Yes, a compromise created by the round exhaust outlet. This also makes my research more difficult as almost all Coanda Effect surfaces are a curve flat plain (wing) as opposed to a half pipe.

Brian

[shelly]

there is something on internet also on coanda effect on round jets

[PlatinumZealot]

All it takes are the dregs from the aero space industry to create an innovative F1 car. The engineers only have to be well read to suggest putting these ideas on the cars.

I say the 10 deg angle of the floor of the McLaren exhaust channel precludes a valid implementation of the Coanda Effect.

Can you demonstrate or illustrate how it is done in the McLaren exhaust channel? In all my research I can find no illustration of a Coanda Effect system that does not have the flow axis starting at less than a 90 deg angle or less to the flow surface. Tangental to the radius of the curved surface.

Brian

Here is a section of the exhaust I modeled. I don't know but the gas really slows down right after it exits. The pressure and density increases after it leaves the channel.

[ppj13]

I am not comfortable with tying to control engine speed with a big bias towards fuel and ignition management.

Brian

I think this is key aspect to understand everything.

I'd bet they do. why not? You've got 8 PWM torque delivering devices, pulsing at a combined speed of what, 40000rpms minimum? You can't have continous variable torque, like with throttle valves, but with 1000 torque setpoints you would't care. Today's engines can cut and restore fuel really fast. I'd keep throttle valves fully open all the race to max the cooling. That's what I would do if cooling was heavily compromised with tiny coolers.

At the end of the day, that's the way tcs work, and they work well even with no fuel cut and --- engine management.

I bring this back up because nobody will model it properly until we get clear how much gas these pipes blow.

[hardingfv32]

I'd keep throttle valves fully open all the race to max the cooling. That's what I would do if cooling was heavily compromised with tiny coolers.

I am sympathetic to your view, but then why do they retain the throttle system? I am not sure I have ever heard of any SI engine not having throttles. There is a reason.

Brian

[hardingfv32]

I don't know but the gas really slows down right after it exits. The pressure and density increases after it leaves the channel.

Thanks for posting the detail view.

Can you expand on your concerns.

Why is there no demonstrated influence by the flow around the body on the exhaust flow after it clears the channel?

Brian

[shelly]

Why move the exhaust outlet farther away for all your aero targets, wings, etc. as RB has done?

Is this really about just imparting addition energy into the body flows? The body flows are doing what you want, so why not increase them with the exhaust. In that context goes it matter how far away you are from the aero targets?

Brian

Two things at once, i think.

Using coanda means force acting normal to the leading surface.

With this solution they'll:

1. move upwards facing part of this force (lift) further away from the back of the car, which should help with balance
2. exhaust gases make their way to the floor mainly on the sides, so other component of this force acts outwards (symmetrical on both sides, so basicaly compensating), instead of acting rearwards (drag), as in McLaren & Co.

I think one of the key aspects is how you make the exhust plume make the second turn, i.e. from downward back to horizontal basicall by impacting against the floor.
Fior the first turn you have coanda, and it is basically an acceleration giving you low pressure peak and narrowing of the plume. Second turn is a compression, so inherently instable and prone to losses.

The shorter the path, the tighter the angle, the stronger the compression, the higher the losses.

To achieve a smoothr tranistion you have to have a wide angle (130 deg maybe?), and that forces you to use more horizontal length to travel the same vertical height downwards, i.e. it forces to put the exhausts forward on the sidepod

Even in n_smikle pictures could be seen the scrambling of pathlines after the impact on the floor, suggesting of destabilising and unpredictable that compression could be.

Maybe the cannels o the rb8 help controlling that also?

[raymondu999]

What's the corriander effect?

A play on words ...

The question is; how much thyme would you need to fully optimise the corriander effect?

[hardingfv32]

Why is there no demonstrated influence by the flow around the body on the exhaust flow after it clears the channel?

Brian

[hardingfv32]

For those of you hoping to seal the diffuser, here is a simulation from n smikle. Please note that the flow is less than 30 m/s when hits the floor. Also this a McLaren simulation, so the outlet is much closer to the wheel. With RB you double the distance and you probably end up with less than 15 m/s. Last year you had the exhaust on the floor with a flow of 230 m/s.

Now every little bit helps, but this has now become a very small little bit!

Brian

[beelsebob]

For those of you hoping to seal the diffuser, here is a simulation from n smikle. Please note that the flow is less than 30 m/s when hits the floor. Also this a McLaren simulation, so the outlet is much closer to the wheel. With RB you double the distance and you probably end up with less than 15 m/s. Last year you had the exhaust on the floor with a flow of 230 m/s.

That looks a lot like it's making the assumption that the air around it isn't moving at all – that'll be why you're losing all your air speed