Effect on engine power from Coanda exhaust

[adam2003]

I have searched the thread with " Coanda" but cant find the topic

how much power does it drain from the engine as compared to non Coanda-style exhausts

[hollus]

What about adding the word "power" to the title, then, so that the next person to search like you did can actually find the right topic?

Mods?

Not sure in terms of power, but on Friday Raikkonen was 3Km/h down on top speed compared to Grosjean. Of course it could be due to setup as much as to the exhaust.

[adam2003]

What about adding the word "power" to the title, then, so that the next person to search like you did can actually find the right topic?

Mods?

Not sure ion terms of power, but on Friday Raikkonen was 3Km/h down on top speed compared to Grosjean. Of course it could be due to setup as much as to the exhaust.

I called the topic this as its about the coanda exhaust and people may want to talk more than just the power of it

[hollus]

2012 Exhaust Blowing & Coanda viewtopic.php?f=6&t=12046

[skgoa]

The answer is "none."

[Steven]

The answer is "none."

Actually, Lotus have said, both by means of Raikkonen and the team's technical director James Allison that it takes away some engine power. It's maybe not the case for all configurations, but it has to do with the length of the exhaust, and maybe also the exhaust channel wherein it exits, instead of a more free stream of air.

[marcush.]

the Coanda exhausts use a smaller exhaust tip diameter -increasing the speed of exhaust flow at the exit .This is not the optimum setup for maximum power .
But on the other hand it sure bumps the torque at lower rpm as well ..so overall it might cost the odd km/h in terminal speed if any .

[hardingfv32]

1) Opening the exhaust into a low pressure zone is helpful. Do the current Coanda exhaust configurations promote low pressure at the exhaust upening?

2) I can not say that I have noticed that the exhaust chokes down for the Coanda systems. What is the benefit of 'increasing the speed of exhaust flow at the exit'? Does it help with flow redirection?

Brian

[Dragonfly]

the Coanda exhausts use a smaller exhaust tip diameter -increasing the speed of exhaust flow at the exit .This is not the optimum setup for maximum power .
But on the other hand it sure bumps the torque at lower rpm as well ..so overall it might cost the odd km/h in terminal speed if any .

^The right explanation IMHO

[Carlos]

"I called the topic this as its about the coanda exhaust and people may want to talk more than just the power of it."
Thread Author: Adam

As the member that introduced the possibility of applying the Coanda Effect to F1 aero on this forum, several years ago. I'd like to comment on what the next refinementent to coanda exhaust aero might be. Noting the 2 photos heading the homepage Technical Insights section. Imagine the McLaren frontal sidepod down-wash wing-let positioned on the descending profile of the rear sidepod of the Lotus; conditioning airflow to aid the coanda effect. Interestingly the suggestion that the Coanda Effect ever having application F1 was ridiculed, as being as likely as time travel or a fusion reactor powering a laptop. Imagination is always in short supply.

Edit: Thanks Hollus, now I can let that small irritation evaporate. Yes that's the one, I appreciate you looking it up and thank you for making a pleasant Sunday afternoon even more enjoyable. I was just watching this a moment ago, a vintage on-board video you might find interesting, Arton Senna's Qualifying lap at the 1989 Japanese Grand Prix: http://vimeo.com/10427952

[hollus]

Very cool, Carlos. Even cooler would be if you could fish out that vintage post. Recognition where it is due, specially in this short in imagination world.

Maybe it was this one?

This is 29 pages long, and it may be familiar material -- but it may have some application or interesting value:

http://www50.dt.navy.mil/reports/CC.pdf

Just an idea -- Does the "Coanda-effect circulation control to low aspect ratio wings" have any application to underbody "flow control" or wing design? I was reading a little about it and wondered if anyone else had
an idea about possible applications.

Would the minimum radius rules allow something like that winglet in the McLaren anywhere mid sidepod? Now I don't dare to say not...

[olefud]

It seems that using the exhaust for Coanda doesn’t per se compromise power, only the flow control and enhancement to direct the exhaust. What would a substantially enhanced hot air flow from the brakes do for aero?

It’s sometimes overlooked that brake heat is primarily rejected as radiant energy. This is because radiant heat is rejected to the fourth power of the difference in delta absolute temp. I’ve been working on a means to substantially enhance convection cooling of the brakes which develops heated air at the brakes in a nicely controlled heated flow (incandescent particles in the stream). With much more energy in the convection cooling flow, the rotor runs cooler and the radiant cooling is diminished. This convection stream at the wheels is nicely positioned and occurs at a favorable time. My brake dyno data is with cast iron rotors, but with a few fudge factors it maybe can be guesstimated for carbon disks

If I could provide such a heated air stream, could you aero guys do anything with it?

[aussiegman]

1) Opening the exhaust into a low pressure zone is helpful. Do the current Coanda exhaust configurations promote low pressure at the exhaust upening?

2) I can not say that I have noticed that the exhaust chokes down for the Coanda systems. What is the benefit of 'increasing the speed of exhaust flow at the exit'? Does it help with flow redirection?

Brian

Again simple questions with not so simple answers.....

1) Generally, I would expect it would, or should yes, as Bernoulli's principle indicates that an increase in the velocity of any fluid or gas will be accompanied by a resulting decrease in pressure. As the air stream passes over the exhaust slot gap opening, the flow volume/area is increased as it curves downwards and so pressure should drop prior to it actually reaching the exhaust exit. You also have the effects of inducement and entrainment from the high velocity exhaust plume which should help to "pull" the airstream downwards and backwards, increasing its velocity and again resulting in a pressure drop.

2) Basically, as the exhaust plume is exiting through a smaller diameter orifice it will have greater velocity than if it exits from a larger orifice or opening for the same volume of gas over a similar time period. It's similar to blowing through a straw or an drain water pipe. Using the straw the resulting air stream will have more velocity and therefore greater directionality and energy to create the require votices to seal the diffuser area. Using the drain pipe the air stream will have less velocity and therefore less directional stability and the energy will be spread over a large area and diffused even though the same volume of gas is affected.

So, in order to get the exhaust plume to the diffuser area and provide any benefit, it has to be of sufficient velocity and directional stability to reach from the exhaust outlet to the diffuser area and then provide energy to gain a benefit. The velocity also enhances the Coanda effect prior to flow separation and allows the exhaust plume to remain attached to the guiding body work for a greater distance/time before being disturbed and diffused rendering it ineffective.

The Coanda exhausts are very complicated constructions effected by a large number of aero and mechanical effects which is why they have been constantly altered throughout the season so far.

They have to consider things like:

1) exhaust orifice diameter to control exhaust plume velocity.
2) extension of the exhaust tip into the airstream to retain flow attachment and possibly enhance the venturi effect seen at the exhaust tip /airstream interface.
3) slot gap sizing, shape and direction to ensure flow attachment
4) the system overall to maintain required airstream velocity and integrity over the distance it is required to travel

As for negatively effecting power, it could perhaps reduce high RPM power by altering restricting outright flow, the tuning of the exhaust system or otherwise compromising the systems efficiency.

There has also been various versions of exhausts primaries with multiple small "steps" placed in the primary header tubes to provide better or different pulse wave reversion tuning effects as well as the recent Helmhotz resonator type tubes (yes with necks) or more simple tuning tubes that have been seen over 2012 which all might be an attempt to regain some of the losses induced by a trying to package the Coanda exhausts.

[aussiegman]

It seems that using the exhaust for Coanda doesn’t per se compromise power, only the flow control and enhancement to direct the exhaust. What would a substantially enhanced hot air flow from the brakes do for aero?

It’s sometimes overlooked that brake heat is primarily rejected as radiant energy. This is because radiant heat is rejected to the fourth power of the difference in delta absolute temp. I’ve been working on a means to substantially enhance convection cooling of the brakes which develops heated air at the brakes in a nicely controlled heated flow (incandescent particles in the stream). With much more energy in the convection cooling flow, the rotor runs cooler and the radiant cooling is diminished. This convection stream at the wheels is nicely positioned and occurs at a favorable time. My brake dyno data is with cast iron rotors, but with a few fudge factors it maybe can be guesstimated for carbon disks

If I could provide such a heated air stream, could you aero guys do anything with it?

Firstly, I have been led to believe the thermal energy (temperature) of the air stream is less critical than its kinetic energy (velocity) for use in this situation, which is the creation of a vortex at the diffuser interface that is primarily to seal the low pressure diffuser area. I think it is important to that this is what the exhaust blown diffusers and Coanda exhaust are actually trying to do, that is seal the diffuser area from pressure and turbulence influences such as tyre squirt which is a BIG factor to increase its efficiency.

The Coanda exhausts are simply trying to do replicate the same effect as the hot/cold blowing engine mapping from previous years. The hot/cold simply refers to the method of creating the gas stream and does not materially effect the outcome or effect. That said, gas density and therefore gas temperature (heat energy) is a factor that is apparently and least partially considered .

While the hot gases have more thermal energy, again for this application it the gases velocity that induces the vortices and both air stream are reportedly moving at similar velocities. This is what I think was explained to me, but happy to be educated otherwise.

The difficulty would be that the air stream may not have enough kinetic energy (velocity) to be useful and that it may not be consistent enough with variations being quite high as vehicle speed would dictate air velocity and as the car was slowed during braking application, I would imagine the lower kinetic energy air stream would provide less stable vortex and reduce the sealing of the diffuser. It could also make the car very sensitive if the threshold where the system was and was not effective was at an inconvenient point in operation.

This type of airflow, even though the air temp and thermal energy could be quite high, would be a long way from the hot or cold blowing of the diffuser as the air stream velocity is no longer governed by engine mapping and operation but only by vehicle speed and some convection effects.

Even though its called "hot blowing", the air temp is not (i believe) the desired effect but a result of producing a very high velocity air stream. To achieve "hot blowing" of the diffuser, the ECU overfuels or injects excess fuel on throttle lift off while retarding the ignition to reduce torque. This gives the exhaust plume much more velocity (kinetic energy) than under cold blowing conditions which more simply disconnects the throttle input signal from the pedal and effectively opens the throttle to 100% and cuts fuel and spark (giving zero or near zero torque) but still provides an air stream flowing through the engine that as between 60% and 75% depending on who you talk to of the exhaust velocity when compared to that seen during more normal engine operation.

The current Coanda exhaust are trying to re-create this hot/cold blown diffuser vortex to seal the diffuser as well it seems as trying to increasing flow (energy) over the top of the diffuser to reduce the risk of airflow separation at the diffuser or under the car.

This also goes to explain the strange engine and throttle maps as well as to odd wording of the FIA regulations which are intended to maintain throttle input to torque demand rather than allowing the dislocation of the throttle input to torque demand and production like 5.5.3.

5.5.3 The maximum accelerator pedal travel position must correspond to an engine torque demand equal to or greater than the maximum engine torque at the measured engine speed.
The minimum accelerator pedal travel position must correspond to an engine torque demand equal to or lower than 0Nm


Its also why the FIA require that the torque demand map must be monotonically increasing vs. accelerator position as per 5.5.5

5.5.5: At any given engine speed the driver torque demand map must be monotonically increasing for an increase in accelerator pedal position.

[aussiegman]

Sorry for the third post in a row, however I have a question for other to consider as I am in two minds about its possible effectiveness.

As the desired effect of the Coanda exhausts is for the exhaust plume to follow the contour of the body work to be directed to the right area of the diffuser and then create a vortex to seal it from the surrounding air streams, theoretically a less turbulent air stream should maintain its flow stability and direction better than more turbulent air and result in it arriving at the diffuser with more energy.

Rather than reducing the orifice size at the exhaust, could using a flow straightener (which would effectively reduce the area of the orifice) such as those used in wind tunnels, fire hoses and decorative, large scale water displays, like those in the foyer of the Burj Al-Arab in Dubai and the forecourt of the Bellagio in Las Vegas, to reduce flow turbulence and increase exhaust plume integrity and result in a more energetic air stream and therefore more efficient vortex creation and better sealing of the diffuser area?? Of would the use of a flow straightener cause other unforeseen problems??