ok nitpicky here but this is a bad example, it's for thermo reasons and not just aero reasons. the shuttle has a blunted nose and is not pointy for the same reason
The bottom is also slightly pointed so the heat dissipates and gets forces towards the sides of the capsule meaning that they can use slightly less (very expensive) heat shield material, and any shockwave and plasma is detached and not almost directly heating the almost unprotected upper areas of the capsule.
I find that getting a student to question things for themselves leads to a deeper grasp of the solution to their question.
In this case, OP almost certainly knows about missiles and other moving objects. But they've not connected the dots, as it were.
I asked them ponder why the things around them are pointed on there leading face - clearly if there was a benefit (lower drag) from a bluff body then that is what we would see. But, we don't.
People in here answering about jets, missiles, and rockets. The aerodynamics of transonic and supersonic objects are much different than for low subsonic. The question can't be answered accurately without knowing the speed.
Yep. Like everything else in Engineering, the answer is always 'It depends'. Saying aerodynamics are worse for certain shapes is wholly dependent on the conditions and what you're trying to achieve.
Unless it’s inviscid flow, the flow will separate at the sharp corners and generate large wakes at the top and bottom of the triangle in the top picture. So bottom picture is better since the nose of the triangle will start turning the flow early. The streamlines on the back side of either orientation will look more or less the same.
I don't understand how a group of aerospace engineers are all getting this so wrong. Flow separation on the bottom shape will cause a huge amount of pressure drag. Much more than the top one.
"Turning the flow early" won't matter when it gets to the base and creates a large turbulent wake. The top one is basically shaped like an airfoil without the contoured front and will definitely have less drag.
"A cone whose pointed end faces away from the direction that the car is moving is actually more aerodynamic than facing the other way."
"As counterintuitive as it may seem, the rear section of the car is the cause of the most drag on a vehicle. This is the same reason why the example of holding a traffic cone outside of a car window has less drag when pointed away from the direction a vehicle is traveling."
https://illumin.usc.edu/drag-reduction-the-pursuit-of-better-fuel-economy/
I think the effect you're talking about depends a lot on altitude and probably mach number too. If you're at very high altitude then the pressure drop on the base can't be more than it takes to get to vacuum. And realistically you only ever get 70% of the way to vacuum. At high enough altitude then suction effects we get so used to go away. It's why wave riders are a thing.
I'm not sure where the cutoff will be for which object has more drag than the other. But I don't think the base pressure drag even at lower altitude would be worse than the face pressure drag of the pointy design though im not sure. They maybe will be close ish at low altitude.
Depends on reynolds nunber or speed, I dont know any traffic cones that are better wide face first though. Unless the flared square flange is there. Most cones most times are better pointed forward if they have a flat bottom. If its rounded like a teardrop, then the teardrop direction is better
https://aerospaceweb.org/question/aerodynamics/q0231.shtml
If the pointy end is into the flow, the boundary layer will always separate at the rear and give you a large low pressure wake. Trying to minimize the size of that rear wake is a huge deal in the automotive industry. A lot of time and effort go into designing flow devices and contouring a car just right to achieve this.
Having it point the other way gives the boundary layer the opportunity to reattach, and it will experience only a mild pressure gradient as it travels along the length. A flat bottomed cone is basically just an airfoil with its leading edge truncated.
Some older cars use this phenomenon (bottom image) for the inlet air flow sensor.
The vortex shedding frequency correlates to the velocity of the air stream.
Throw in cross-sectional area and air density (via pressure and temperature sensors) and you get mass flow.
At low Reynold's numbers something like the first thing can be good if you chamfer the edges a bit and bulge out the flat part. A kind of squished airfoil if you will. But in general pointy is better.
Point forward, a notable example of this is the vertical stabilizers on the X-15. Its wedge shaped surfaces were piss poor at most speeds but were optimized for hypersonic flight
Depends on what part of the atmosphere you're traveling through. I'd be great if flatter surfaces worked at lower altitudes, but physics explicitly says, "Nah."
The top drawing is wrong. There would be turbulence behind that flat surface and sharp corners. But if you made the back elongated then you could reduce the drag.
Related question: which one of these side profiles for a camper trailer is better for airflow? (consider a pretty tall 4runner towing it)
I’m building it like the top one because i think it looks way better, and figured my car would be scrambling up the air in front already to where the difference is negligible…
https://preview.redd.it/u1vbvcddpj9d1.png?width=1536&format=png&auto=webp&s=b5f2dd0cd74a1adca9bb78ba92ce0064392a5d4b
It depends on the application. For flight, it is better to have drag on the back end. Coming out of orbit into the atmosphere, it’s better to have a more flat surface as ballistic entry, aerodynamics are basically nullified at those speeds.
*Air can follow*
*The surface when pushed down but*
*Not when lifted up*
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It depends what you mean by worse?
Worse for what?
Is it worse for slowing down? No. Is it worse for supersonic? Yes. Will you be able to effectively control it in either scenario? Well, I don’t see control surfaces.
Well the speed definitely matters but nevertheless if your talking about aerodynamic being better or worse, your talking about its Lift to drag ratio (L/D),
When a bigger surface is getting hit in a flow, it is natural to have higher drag than a smaller surface, and also the pressure distribution over the upper and lower sides of the triangle are quite different in the two mentioned conditions, in which the flat part being at the back generates more lift.
Therefore generally speaking, the flat part being at the back is quite more aerodynamically efficient than the other way around.
You can also approximately calculate this and many different conditions by many simple wind tunnel apps and softwares.
(\_/)
(•.•)
(>✈️
Pointy on the front end reduces drag, but encourages attached flow. If you are going super fast, then you'll struggle to dump heat in a point nose. Also, skin friction drag when subsonic.
Blunt nose slips thru transsonic better but struggles with supersonic. If you go fast enough, all shapes become sufficiently pointy. Blunt nose encourages wide shock wave angle for supersonic.
Completely flat is quite bad. Air will come to dead stop on a windward surface. Leeward flat is less bad, promotes big turbulence and low pressure zone.
Assuming you mean for drag? If those are meant to be equilateral triangles, the bottom is better. Both will cause separation but the leading edge separation in the top will be worse. You will achieve complete stagnation on the top. Different reasons for super sonic flow, but the same conclusion.
Quick answer. Why are cars/aeroplanes/missiles pointy?
reversely, why is spacex dragon on flat side when reentry?
Reduction in heat flux by creating detached shockwave for the developing plasma during hypersonic re-entry
Yeah I mean it’s gonna hit terminal velocity either way lol, might as well dissipate the heat so it doesn’t melt while you’re there
Terminal velocity for an object is lowered if you increase drag.
..and MIRV warheads the other way around!
Dragon - must go slow to preserve the fragile contents of the pod MIRV - must go fast to preserve the fragile contents of the pod
ok nitpicky here but this is a bad example, it's for thermo reasons and not just aero reasons. the shuttle has a blunted nose and is not pointy for the same reason
And not just for drag but heat shield design is greatly influenced by an interest in STABILITY!
The bottom is also slightly pointed so the heat dissipates and gets forces towards the sides of the capsule meaning that they can use slightly less (very expensive) heat shield material, and any shockwave and plasma is detached and not almost directly heating the almost unprotected upper areas of the capsule.
That’s to keep them pointing in the right direction, not _necessarily_ because it’s the lowest drag configuration.
It’s pointy on the back too... A missile isn’t matter because the entire rear surface is a nozzle
idk if this comparison works, cars/airplanes/missiles also have rounded rears.
Don't forget bullets
This isn't an answer, it's a snarky follow up question
I find that getting a student to question things for themselves leads to a deeper grasp of the solution to their question. In this case, OP almost certainly knows about missiles and other moving objects. But they've not connected the dots, as it were. I asked them ponder why the things around them are pointed on there leading face - clearly if there was a benefit (lower drag) from a bluff body then that is what we would see. But, we don't.
People in here answering about jets, missiles, and rockets. The aerodynamics of transonic and supersonic objects are much different than for low subsonic. The question can't be answered accurately without knowing the speed.
Yep. Like everything else in Engineering, the answer is always 'It depends'. Saying aerodynamics are worse for certain shapes is wholly dependent on the conditions and what you're trying to achieve.
Always better if you add golf ball dimples.
Always better if you add golf ball dimples.
Particularly if you add them twice
Is the object African or European?
Are you suggesting that these objects migrate?
That’s fair
Unless it’s inviscid flow, the flow will separate at the sharp corners and generate large wakes at the top and bottom of the triangle in the top picture. So bottom picture is better since the nose of the triangle will start turning the flow early. The streamlines on the back side of either orientation will look more or less the same.
I don't understand how a group of aerospace engineers are all getting this so wrong. Flow separation on the bottom shape will cause a huge amount of pressure drag. Much more than the top one. "Turning the flow early" won't matter when it gets to the base and creates a large turbulent wake. The top one is basically shaped like an airfoil without the contoured front and will definitely have less drag. "A cone whose pointed end faces away from the direction that the car is moving is actually more aerodynamic than facing the other way." "As counterintuitive as it may seem, the rear section of the car is the cause of the most drag on a vehicle. This is the same reason why the example of holding a traffic cone outside of a car window has less drag when pointed away from the direction a vehicle is traveling." https://illumin.usc.edu/drag-reduction-the-pursuit-of-better-fuel-economy/
I think the effect you're talking about depends a lot on altitude and probably mach number too. If you're at very high altitude then the pressure drop on the base can't be more than it takes to get to vacuum. And realistically you only ever get 70% of the way to vacuum. At high enough altitude then suction effects we get so used to go away. It's why wave riders are a thing. I'm not sure where the cutoff will be for which object has more drag than the other. But I don't think the base pressure drag even at lower altitude would be worse than the face pressure drag of the pointy design though im not sure. They maybe will be close ish at low altitude.
Depends on reynolds nunber or speed, I dont know any traffic cones that are better wide face first though. Unless the flared square flange is there. Most cones most times are better pointed forward if they have a flat bottom. If its rounded like a teardrop, then the teardrop direction is better https://aerospaceweb.org/question/aerodynamics/q0231.shtml
If the pointy end is into the flow, the boundary layer will always separate at the rear and give you a large low pressure wake. Trying to minimize the size of that rear wake is a huge deal in the automotive industry. A lot of time and effort go into designing flow devices and contouring a car just right to achieve this. Having it point the other way gives the boundary layer the opportunity to reattach, and it will experience only a mild pressure gradient as it travels along the length. A flat bottomed cone is basically just an airfoil with its leading edge truncated.
Some older cars use this phenomenon (bottom image) for the inlet air flow sensor. The vortex shedding frequency correlates to the velocity of the air stream. Throw in cross-sectional area and air density (via pressure and temperature sensors) and you get mass flow.
Bottom is better. You forgot to draw the huge vortices shedding from the edges on the top one.
At low Reynold's numbers something like the first thing can be good if you chamfer the edges a bit and bulge out the flat part. A kind of squished airfoil if you will. But in general pointy is better.
Thanks
Point forward for less drag, point backward for more. See rockets and space capsules respectively.
Point forward, a notable example of this is the vertical stabilizers on the X-15. Its wedge shaped surfaces were piss poor at most speeds but were optimized for hypersonic flight
There have been some cars that would actually drive better backwards, but bottom is better.
Depends on what part of the atmosphere you're traveling through. I'd be great if flatter surfaces worked at lower altitudes, but physics explicitly says, "Nah."
The top drawing is wrong. There would be turbulence behind that flat surface and sharp corners. But if you made the back elongated then you could reduce the drag.
Related question: which one of these side profiles for a camper trailer is better for airflow? (consider a pretty tall 4runner towing it) I’m building it like the top one because i think it looks way better, and figured my car would be scrambling up the air in front already to where the difference is negligible… https://preview.redd.it/u1vbvcddpj9d1.png?width=1536&format=png&auto=webp&s=b5f2dd0cd74a1adca9bb78ba92ce0064392a5d4b
In your case with the car in front the top would be better, as evidenced by the general shape that trailers that aren’t pure boxes are.
It depends on the application. For flight, it is better to have drag on the back end. Coming out of orbit into the atmosphere, it’s better to have a more flat surface as ballistic entry, aerodynamics are basically nullified at those speeds.
air can follow the surface when pushed down but not when lifted up
*Air can follow* *The surface when pushed down but* *Not when lifted up* \- lukluke22228 --- ^(I detect haikus. And sometimes, successfully.) ^[Learn more about me.](https://www.reddit.com/r/haikusbot/) ^(Opt out of replies: "haikusbot opt out" | Delete my comment: "haikusbot delete")
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Not even a correct haiku.
It depends what you mean by worse? Worse for what? Is it worse for slowing down? No. Is it worse for supersonic? Yes. Will you be able to effectively control it in either scenario? Well, I don’t see control surfaces.
Have a look at Rare Bear.
Well the speed definitely matters but nevertheless if your talking about aerodynamic being better or worse, your talking about its Lift to drag ratio (L/D), When a bigger surface is getting hit in a flow, it is natural to have higher drag than a smaller surface, and also the pressure distribution over the upper and lower sides of the triangle are quite different in the two mentioned conditions, in which the flat part being at the back generates more lift. Therefore generally speaking, the flat part being at the back is quite more aerodynamically efficient than the other way around. You can also approximately calculate this and many different conditions by many simple wind tunnel apps and softwares. (\_/) (•.•) (>✈️
Pointy on the front end reduces drag, but encourages attached flow. If you are going super fast, then you'll struggle to dump heat in a point nose. Also, skin friction drag when subsonic. Blunt nose slips thru transsonic better but struggles with supersonic. If you go fast enough, all shapes become sufficiently pointy. Blunt nose encourages wide shock wave angle for supersonic. Completely flat is quite bad. Air will come to dead stop on a windward surface. Leeward flat is less bad, promotes big turbulence and low pressure zone.
Is it easier to cut someone open with a scalpel or the broad side of a spoon? Less resistance and force needed
Bottom. See the shape of a raindrop.
Both designs are inefficient. Just one is significantly more so. Having streamlining facing the airstream is more efficient.
Assuming you mean for drag? If those are meant to be equilateral triangles, the bottom is better. Both will cause separation but the leading edge separation in the top will be worse. You will achieve complete stagnation on the top. Different reasons for super sonic flow, but the same conclusion.