Is Aerodynamic Design influenced by the Animal Kingdom?

[johnny comelately]

take out the automatically and i will respectfully disagree with you

[graham.reeds]

A car's diffuser is a passive device intended solely to reduce the air speed, and hence increase the pressure, of the air flow below the car before the flow joins the freestream flow. It reduces drag and lift that way.

No. It doesn't.

Pressure *decreases* in a diffuser, increasing the airspeed. It's the low pressure trying to equalise that sucks the car to the ground.

[Giblet]

There was a pretty involved post some time back.

viewtopic.php?f=6&t=4630&p=59021&hilit= ... kin#p59021

[Just_a_fan]

Pressure *decreases* in a diffuser, increasing the airspeed. It's the low pressure trying to equalise that sucks the car to the ground.

No. The diffuser allows the air to slow down, increasing its pressure. The lowest pressure is at the point of highest speed which is the diffuser's throat.

The lowest pressure is blue, red is highest pressure. See how the pressure in the diffuser is higher (green/yellow) than in the throat (blue)

The teams do use vortices in the diffuser which causes the underside of the diffuser to experience localised lower pressure but the whole device's job to get the air back to freestream speeds.This is also why the teams try to get clean air above the diffuser so that the air above and below are as close to the same speed as possible. This maximises extraction and thus maximises the speed/lowers the pressure in the throat.

[jjn9128]

A car's diffuser is a passive device intended solely to reduce the air speed, and hence increase the pressure, of the air flow below the car before the flow joins the freestream flow. It reduces drag and lift that way.

No. It doesn't.

Pressure *decreases* in a diffuser, increasing the airspeed. It's the low pressure trying to equalise that sucks the car to the ground.

Nope just a fan was correct. In a duct when the pressure is fixed at the inlet and outlet the air must accelerate underneath for mass flow to be conserved, this is the venturi effect, the high velocity caused by the contraction results in low pressure i.e. velocity faster than freestream causes a relative vacuum. The job of the diffuser is to smoothly decelerate the airflow back to atmospheric. On a flat bottomed car you get a spike of low pressure in the contraction and a spike of low pressure at the diffuser kick (where the ramp starts) as the airflow is accelerated around the bend. You then try to maintain the low pressure along the flat part of the floor.

Where this gets confused on a Formula 1 car, is that because the surfaces are limited they want to maintain the lowest pressure they can right to the end of the diffuser. So they over expand the duct, using channels and vanes to keep the air attached, the vanes are trapeziod rather than triangular in shape to create vortices for that purpose.

On the subject of aero inspired by nature, I'm surprised nobodies posted CFD cow, producing enough lift to fly at Mach 8 .
https://blogs.mentor.com/robinbornoff/b ... bly-sonic/

[jjn9128]

Pressure *decreases* in a diffuser, increasing the airspeed. It's the low pressure trying to equalise that sucks the car to the ground.

No. The diffuser allows the air to slow down, increasing its pressure. The lowest pressure is at the point of highest speed which is the diffuser's throat.
http://i.imgur.com/ZkuQTF6.png
The lowest pressure is blue, red is highest pressure. See how the pressure in the diffuser is higher (green/yellow) than in the throat (blue)

The teams do use vortices in the diffuser which causes the underside of the diffuser to experience localised lower pressure but the whole device's job to get the air back to freestream speeds.This is also why the teams try to get clean air above the diffuser so that the air above and below are as close to the same speed as possible. This maximises extraction and thus maximises the speed/lowers the pressure in the throat.

You beat me to it.

[godlameroso]

Nice beautiful high res shot of the diffuser in action, open in new tab.



Close up.

Question what kind of flow structures are created between the wheel winglets and the diffuser gurney interaction? Who would know about this? If only there were some being that had intimate experience with interaction of overlapping flow structures.

[J.A.W.]

...On the subject of aero inspired by nature, I'm surprised nobodies posted CFD cow, producing enough lift to fly at Mach 8 .
https://blogs.mentor.com/robinbornoff/b ... bly-sonic/

Actually, the speed needed for cow 'lifting-body flight' is noted as very much closer to ~ Mach 0.8..

Mach 8 energetics in air - would most likely result in a badly overdone beef roast bolide..

[godlameroso]

A car's diffuser is a passive device intended solely to reduce the air speed, and hence increase the pressure, of the air flow below the car before the flow joins the freestream flow. It reduces drag and lift that way.

No. It doesn't.

Pressure *decreases* in a diffuser, increasing the airspeed. It's the low pressure trying to equalise that sucks the car to the ground.

Nope just a fan was correct. In a duct when the pressure is fixed at the inlet and outlet the air must accelerate underneath for mass flow to be conserved, this is the venturi effect, the high velocity caused by the contraction results in low pressure i.e. velocity faster than freestream causes a relative vacuum. The job of the diffuser is to smoothly decelerate the airflow back to atmospheric. On a flat bottomed car you get a spike of low pressure in the contraction and a spike of low pressure at the diffuser kick (where the ramp starts) as the airflow is accelerated around the bend. You then try to maintain the low pressure along the flat part of the floor.

Where this gets confused on a Formula 1 car, is that because the surfaces are limited they want to maintain the lowest pressure they can right to the end of the diffuser. So they over expand the duct, using channels and vanes to keep the air attached, the vanes are trapeziod rather than triangular in shape to create vortices for that purpose.

Overexpansion, I assume you mean the way the diffuser fans out at the trailing edge? By curving the air it takes a longer path than a direct line and creates a virtual increase in surface area. The keels in the diffuser help this, while also "straightening" airflow. More interesting is the sides of the diffuser and how that airflow interacts with the winglets on the uprights. That along with the central section are the most critical areas of the diffuser, big time is waiting to be found in that area, and maximizing flow to that area from upstream(more flow into the floor via mid wing, tighter coke bottle).

[godlameroso]

The odd thing is by your response you clearly didn't read my post carefully. It is not about which force vector the lift is in. In fact the force vector can be sideways for all I care.

The airflow vector determines how the surface in question displaces air, what you should care about if the topic is aerodynamics.

The point I was trying to make is that even though they look vaguely similar, the 2 things (bird wing tips and the wing tips on the inside of and F1 car front wing) are designed to do opposite jobs. The goal of the toucans wings are to produce the highest L/D ratio to enable the most optimal flight characteristics. The drag is reduced by reducing the vortex causing adverse pressure gradient the most at the wing tips.

Research shows bird wings are not overly concerned with drag. The wing tips do different things through the stroke, active aero puts all man made objects to shame. In some configurations drag is increased where lift is favored, in some configurations drag is decreased, in others flow is guided to the tail to improve efficiency, in others negative lift is induced, and others still stalling is induced.

On the other hand, the inside of the F1 front wing has a completely different job (AGAIN THIS HAS NOTHING TO DO WHETHER THE FORCE VECTOR IS UP OR DOWN OR EVEN SIDEWAYS). This job is to create a vortex and this vortex is used to control wake further back in the car. F1 cars are not drag sensitive and usually an increase in downforce far exceeds an increase in drag as far as lap times are concerned. Therefore encouraging and controlling the formation of this vortex is paramount to the performance of an F1 car.

An F1 front wing has a variety of jobs to do all of which bird wings can do, and in a more efficient manner. Active aero trumps fixed aero always.

The vortex created by the inside of the F1 wing creates a lot of drag, something that the toucan is trying to avoid. Hence the opposite job.

I almost get the feeling you think birds have fixed wings, I hope you don't think that.

I think you misunderstand many here. No one is saying we can't learn from animals and their evolutionary traits. What people are trying to express to you is simply that just because something looks similar does not mean that there is automatically some parallel to the animal kingdom.

What I'm trying to tell you is that when the function and geometry are the same, and serve the same function(vortex formation and flow control), well they're clearly exploiting the same concept.

That's why I'm not comparing a cow to an F1 car, or something stupid like that. But an animal that actually deals with air flow, at relevant velocities. 30-380kmh

[godlameroso]

the Junkers corrugated skin gave drag an order of magnitude greater than was thought at the time
(as did a lot of other stuff eg 'bracing' wires of biplanes)
Junkers was famously wrong
(the skin was for structural benefits but only the Thorp light aircraft has attempted it since)

because of insufficient Reynolds Number similarity (wind tunnels being aerodynamically smaller than real world)
the extent of Re similarity needed only emerges after decades of poor design due to insufficient similarity

adequate Re similarity takes years, costs billions, and becomes inadequate a few years after it's provided
costly after-build modifications to the F/A 18 E/F and the T45 were needed for this reason


nature's flyers operate at very low Re Nos and are full of design that is specific to very low Re numbers

The wingspan of some birds is easily wider than an F1 car, so the Re numbers are similar enough. Although I agree that to get an accurate picture one needs to use lower Re numbers as the wings are full of microstructures and have very complex interactions with overlapping flow-fields.

[jjn9128]

Actually, the speed needed for cow 'lifting-body flight' is noted as very much closer to ~ Mach 0.8..

Mach 8 energetics in air - would most likely result in a badly overdone beef roast bolide..

yes lift at mach 0.8 the cfd plot is at mach 8.

[jjn9128]

Overexpansion, I assume you mean the way the diffuser fans out at the trailing edge? By curving the air it takes a longer path than a direct line and creates a virtual increase in surface area. The keels in the diffuser help this, while also "straightening" airflow. More interesting is the sides of the diffuser and how that airflow interacts with the winglets on the uprights. That along with the central section are the most critical areas of the diffuser, big time is waiting to be found in that area, and maximizing flow to that area from upstream(more flow into the floor via mid wing, tighter coke bottle).

By over-expansion I mean the difference between a concave (when viewed from below) and convex or planar diffuser. F1 use a concave/bell shaped diffuser to expand the air hard in the initial kick, normally though this would separate because the boundary layer can't keep up with the pressure gradient. So they need the vanes and strakes to maintain a low pressure along the length of the diffuser, which flattens the pressure gradient, but also means you have a lower base pressure behind the car - i.e. it's more draggy than is ideal. A more efficient way is a planar or convex diffuser - like those used in Le Mans, Indycar, Formula E, anywhere they get overtaking.

[Just_a_fan]

An F1 front wing has a variety of jobs to do all of which bird wings can do, and in a more efficient manner.

I look forward to seeing the data to back up that assertion.

[godlameroso]

Overexpansion, I assume you mean the way the diffuser fans out at the trailing edge? By curving the air it takes a longer path than a direct line and creates a virtual increase in surface area. The keels in the diffuser help this, while also "straightening" airflow. More interesting is the sides of the diffuser and how that airflow interacts with the winglets on the uprights. That along with the central section are the most critical areas of the diffuser, big time is waiting to be found in that area, and maximizing flow to that area from upstream(more flow into the floor via mid wing, tighter coke bottle).

By over-expansion I mean the difference between a concave (when viewed from below) and convex or planar diffuser. F1 use a concave/bell shaped diffuser to expand the air hard in the initial kick, normally though this would separate because the boundary layer can't keep up with the pressure gradient. So they need the vanes and strakes to maintain a low pressure along the length of the diffuser, which flattens the pressure gradient, but also means you have a lower base pressure behind the car - i.e. it's more draggy than is ideal. A more efficient way is a planar or convex diffuser - like those used in Le Mans, Indycar, Formula E, anywhere they get overtaking.

Are you saying the concave vs convex diffuser the former is more prone to instabilities than the concave as the concave follows a more aggressive kink? That's why the central section is so critical, Williams gained .4 seconds just putting strakes in that area to help clean up the airflow.