Rear Spoiler - functional or aesthetic?

[EVer]

"Well it spoils the aerodynamics (hence the name) and therefore creates more drag "

That word "therefore" doesn't mean what you think it means. Same deal for aerodynamics. You can't spoil aerodynamics any more than you can spoil... botany. You may be able to spoil the aerodynamicist with candy...

Try this, if the spoiler spoils a flow pattern which generates drag, what happens?

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[eager2own]

"Well it spoils the aerodynamics (hence the name) and therefore creates more drag "

That word "therefore" doesn't mean what you think it means. Same deal for aerodynamics. You can't spoil aerodynamics any more than you can spoil... botany. You may be able to spoil the aerodynamicist with candy...

Try this, if the spoiler spoils a flow pattern which generates drag, what happens?

Why do this to yourself? I already told you 5-6 hours ago he would just repeat false statements like "all spoilers are designed to increase drag" as if it was fact. Which is what he will continue to do no matter how many times we and others explain that is not the case.

 

[EVer]

Why do this to yourself? I already told you 5-6 hours ago he would just repeat false statements like "all spoilers are designed to increase drag" as if it was fact. Which is what he will continue to do no matter how many times we and others explain that is not the case.

It’s more for the sake of discussion with a wider audience in a subject I enjoy, and hopefully furthering the original question, than anything with lyt. I will admit that I enjoy argument and it’s my nature to engage, but the end goal needs to be someone being convinced (that someone can be me). Clearly that won’t happen with this guy, so I’ll attempt to direct posts elsewhere.

For another data point which may be of interest, here is a link I just found. They’re trying to sell something so prepare your salt, however their analysis suggests the OEM rear deck spoiler on a model 3 reduces total drag by 2.3%, all else being equal. Many of their figures seem overly optimistic, but it’s within the realm of possibility.

https://unpluggedperformance.com/aerodynamic-study-of-tesla-model-3/

 

[frinesi2]

Are you a chatbot or something?

 

[pbojanoski]

It’s more for the sake of discussion with a wider audience in a subject I enjoy, and hopefully furthering the original question, than anything with lyt. I will admit that I enjoy argument and it’s my nature to engage, but the end goal needs to be someone being convinced (that someone can be me). Clearly that won’t happen with this guy, so I’ll attempt to direct posts elsewhere.

For another data point which may be of interest, here is a link I just found. They’re trying to sell something so prepare your salt, however their analysis suggests the OEM rear deck spoiler on a model 3 reduces total drag by 2.3%, all else being equal. Many of their figures seem overly optimistic, but it’s within the realm of possibility.

https://unpluggedperformance.com/aerodynamic-study-of-tesla-model-3/

You sound like me on a different subject a few weeks ago and others at various points and on various subjects over the last few months. It is interesting at first and you think you are helping educate others and that they will see the troll/know-it-all/computer program for what it is (sadly misinformed at best, divisive and loathsome troublemaker at worst), but ultimately the whole conversation looks like a needless argument and most tune it out, even the reasoned argument you are making.

I feel your pain. I fought the fight. I've given up since "there is no staying clean wrestling with a pig".

I love the good information though, so feel free to keep feeding us that while not feeding the pig. ?

Thanks @EVer.

 

[pbojanoski]

Are you a chatbot or something?

I was thinking troll or AI program, so we seem to be on a similar page!

 

[Ken7]

It’s more for the sake of discussion with a wider audience in a subject I enjoy, and hopefully furthering the original question, than anything with lyt. I will admit that I enjoy argument and it’s my nature to engage, but the end goal needs to be someone being convinced (that someone can be me). Clearly that won’t happen with this guy, so I’ll attempt to direct posts elsewhere.

For another data point which may be of interest, here is a link I just found. They’re trying to sell something so prepare your salt, however their analysis suggests the OEM rear deck spoiler on a model 3 reduces total drag by 2.3%, all else being equal. Many of their figures seem overly optimistic, but it’s within the realm of possibility.

https://unpluggedperformance.com/aerodynamic-study-of-tesla-model-3/

You will find out, as some of us have here, the ‘ignore’ function can be your best friend in dealing with him. It will make this forum far more enjoyable.

 

[EVer]

I feel your pain. I fought the fight. I've given up since "there is no staying clean wrestling with a pig".

I love the good information though, so feel free to keep feeding us that while not feeding the pig. ?

Thanks @EVer.

To that end, here's information pertinent to the original post (although it appears maybe @silverelan gave up), from someone smarter than I will ever be on the subject.

On the first page, I used the term "form drag." Here is a literal textbook example of automotive aerodynamics. This is the type of drag a spoiler can be extremely effective at preventing, by keeping flow attached longer. My apologies to the author, Joseph Katz, for plagiarism.

"The discussion on the flow field created by bodies moving through air is incomplete without mentioning the far-field effects caused by this motion. The track of disturbed flow left behind a body moving through an otherwise undisturbed fluid is called a wake. Typical examples for wake flows include the vortex wakes visible behind airplanes flying in humid air, of the dust clouds which continue to roll behind a truck, long after it has passed by. In the following examples, let us highlights some of the features of a wake flow, and establish its relevance to vehicle aerodynamics.
The concept of flow separation behind bluff bodies was introduced early as Fig 2.3. This local disturbance in the flow pattern behind the vehicle actually causes momentum loss (or form drag) which extends behind the vehicle and is described schematically by Fig 2.16. Suppose we measure the velocity distribution, at various heights z, in the symmetry plane ahead of the vehicle at point A. Then, if the measurement is taken at a reasonable distance ahead of the vehicle (e.g., more than one car length) the velocity profile indicates a near uniform velocity distribution. Now, if the same measurement is made behind the vehicle, even at a relatively large distance of 10 to 20 body lengths, then a velocity deficiency will be detected, as shown at point B. If the flow separates behind a bluff body, then such a wake will result, and in the wake area the flow seems to be dragging behind the vehicle. The energy of dragging this wake behind results in drag, whereas an ideal body with completely attached flow may not have such a wake (and also no form drag)."

 

[frinesi2]

To that end, here's information pertinent to the original post (although it appears maybe @silverelan gave up), from someone smarter than I will ever be on the subject.

On the first page, I used the term "form drag." Here is a literal textbook example of automotive aerodynamics. This is the type of drag a spoiler can be extremely effective at preventing, by keeping flow attached longer. My apologies to the author, Joseph Katz, for plagiarism.

"The discussion on the flow field created by bodies moving through air is incomplete without mentioning the far-field effects caused by this motion. The track of disturbed flow left behind a body moving through an otherwise undisturbed fluid is called a wake. Typical examples for wake flows include the vortex wakes visible behind airplanes flying in humid air, of the dust clouds which continue to roll behind a truck, long after it has passed by. In the following examples, let us highlights some of the features of a wake flow, and establish its relevance to vehicle aerodynamics.
The concept of flow separation behind bluff bodies was introduced early as Fig 2.3. This local disturbance in the flow pattern behind the vehicle actually causes momentum loss (or form drag) which extends behind the vehicle and is described schematically by Fig 2.16. Suppose we measure the velocity distribution, at various heights z, in the symmetry plane ahead of the vehicle at point A. Then, if the measurement is taken at a reasonable distance ahead of the vehicle (e.g., more than one car length) the velocity profile indicates a near uniform velocity distribution. Now, if the same measurement is made behind the vehicle, even at a relatively large distance of 10 to 20 body lengths, then a velocity deficiency will be detected, as shown at point B. If the flow separates behind a bluff body, then such a wake will result, and in the wake area the flow seems to be dragging behind the vehicle. The energy of dragging this wake behind results in drag, whereas an ideal body with completely attached flow may not have such a wake (and also no form drag)."

Great information - form drag is the term I was looking for (guess I should have read your page 1 post a little closer ?). I'm a mechanical engineer who never did particularly well in fluid dynamics but I've been reading up on racecar aerodynamics with the goal of designing a lower-drag body for a Formula Vee car that will hopefully have a minimal wake to make it harder to draft. Most of my information is from Competition Car Aerodynamics by Simon McBeath.


Also, here's a topical XKCD:

 

[silverelan]

Thanks @EVer, so if I'm to understand what was quoted out of Joseph Katz's book, the bluff style body that the MME (or even a Prius) has uses the spoiler in order to keep the air attached to the body for longer. A more fluid shaped body like a Tesla doesn't need one and their small decklid spoilers deflects air away from the trunk lid to reduce the amount of air that reattaches at the back of the vehicle.

If I totally missed the point or am off-base, please let me know. I really appreciate the feedback and the chance to learn something new!

 

[EVer]

Thanks @EVer, so if I'm to understand what was quoted out of Joseph Katz's book, the bluff style body that the MME (or even a Prius) has uses the spoiler in order to keep the air attached to the body for longer. A more fluid shaped body like a Tesla doesn't need one and their small decklid spoilers deflects air away from the trunk lid to reduce the amount of air that reattaches at the back of the vehicle.

If I totally missed the point or am off-base, please let me know. I really appreciate the feedback and the chance to learn something new!

Generally, except I would not say that a decklid spoiler prevents air from reattaching at the back of the vehicle. The wake is getting pulled by the vehicle (which is incidentally how drafting works), but isn't "attached" in the sense of a fluid moving over a body. It really just changes the geometry, shaping the body to delay and thus minimize separation, which is more significant over a sudden discontinuity like the edge of a roofline or trunk.

Here is a view* of two similarly shaped cars, but one with a rear end intended to minimize a wake. This is in my estimation what the roof spoiler on the Mach E is trying to accomplish, although less effectively less obtrusively.

*without knowing the conditions I can't call it a comparison. This is for illustration only.

 

[zhackwyatt]

Your so funny. There is a difference between a rooftop spoiler on a sedan, and a rooftop spoiler on a crossover body like the Mach-E.

Have you ever said in your life "I don't know" or "I am wrong"? I bet not.

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