Diffuser - Explained

How does a rear diffuser work on a car? What is the purpose of a diffuser? In this video I explain the science behind diffusers, and how they increase downforce of racing vehicles.
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[@nickspaulding1511]

I love his helmet

[@rjgaldonez5573]

me too

[@4K_Design]

Safety first

[@MrBranko81]

Hahahhah

[@JesseOrSomething]

😂😂😂

[@bablum2k3]

🤣🤣🤣🤣🤣🤣

[@EngineeringExplained]

The air under the diffuser is at a higher pressure in comparison with the air underneath the car. The pressure differential between the top and the bottom of the car is what allows it to increase downforce. The diffuser returns the air to atmospheric pressure (or close to it). No, it's not "high" pressure, but it's higher than underneath the car. Aston Martin has pressure differentials online that you can check out, showing how pressure increases in the diffuser, if you're more curious.

[@sodazman]

And that's why aftermarket diffusers don't work. Without a flat undertray the effect will be almost non-existant.

[@Mortalomena]

sodazman helps with new sport/supercars, even premium sedans etc. As they nowadays have flat underside. Doesnt really help at stock height but if yours is lowered then a diffuser can help in fuel consumption/aerodynamics etc.

[@Funkestech]

Mortalomena If you can find a way to seal the sides of the undertray the effect is even bigger, with no air leaking from the sides, it would be basically a vacuum chamber. They banned that in F1 years ago because the cars were entering the corners way too fast.

[@tikomichael]

Funke Motor exactly. The small flat piece of carbon or other material the length of the sideskirts and that sits under the sideskirts of a car (with flat side parallel with the ground and that sticks out from the sideskirts a few centimeters or so) helps to accomplish this. Basically, since this piece sticks out, it helps to keep more air out from underneath the car than just sideskirts alone. It helps to keep out air "spillover" from the face of the sideskirts; if nothing else it gives the air a longer path to take before making its way underneath the car.

[@lambosrkwl]

sodazman if well designed they could still theoretically reduce the turbulence at the rear to reduce drag

[@blinkybillski]

So you mean my cardboard fibre, diffuser from eBay, Won’t work as they say??

[@Treetop64]

One thing that could have been mentioned, and something that is often overlooked, is that as the race car moves through the air, the rear wing actually aids in the acceleration of air out from the diffuser. This in turn forces more air to move into the diffuser from the undertray, further aiding in accelerating the air in the low pressure zone under the car and creating more downforce.

[@EngineeringExplained]

The equation works well if everything is static. But since you're slowing the air down, you allow for it to occupy a larger space. As the velocity drops the pressure goes up.

[@EngineeringExplained]

The "hgih pressure" statement was a relative statement, I was a bit unclear. It's high relative to under the car, but not more than atmospheric. With the right design the top of the car should have greater pressure.

[@Oblithian]

yeah I was just thinking, "isn't this kind of backwards? you're trying to creating vacuum under the car"

[@EngineeringExplained]

Thanks, glad you enjoy the videos!

[@MrDanTrials]

Firstly, excellent video, well done! Second, am I really seeing comments that are from people genuinely interested in learning and people genuinely interested in helping them, rather than the usual childish arguments? Well done to the viewers on that one!

[@danielfargie9272]

Hi, could you explain why the pressure differential causes a suction effect. Surely air moves from high pressure to low pressure and so this would decelerate the air beneath the floor?

[@joewatkins1667]

i think he was wrong, the flow goes from high pressure to low, impossible for it to go from low to high

[@harshj11]

You are right. This video is somewhat unclear. What diffuser does is that it aids in transforming the kinetic energy to pressure energy and minimize the losses so that you get high pressure differential between the air at the bottom and air releasing from the bottom of the car. Without diffuser there would be turbulence which would increase the pressure at the bottom of the car as this turbulence will not permit transformation of high velocity to pressure.

[@anthonyantoine9232]

The air does technically move from higher pressure to lower pressure. That pressure gradient is from the front of the car to the rear. The air has to flow somewhere around the car. Forcing it to flow through a very constricted area under the vehicle allows the flow to speed up and thus drop in pressure due to the Venturi effect and Bernoulli's equation (and forcing it to flow over wings above the car obviously promotes higher pressures and lowers velocity, creating some drag). The air then simply slows down when expanding back to roughly atmospheric pressure (although a little bit less than atmospheric, where the front of the vehicle will see a slightly above atmospheric). The little fins at the back are to help reduce turbulence and promote the flow of the air under the car, and the same is true for undertrays and such. Also, for an added touch, wings at the rear of the vehicle will also decrease the pressure at the rear of the vehicle, allowing for a larger gradient in pressure from front to rear, thus promoting the flow velocity even more, and reducing pressure even more. This video didn't really explain what is happening very well, honestly.

[@okeuwechue9238]

Yeah, I think there's a mistake somewhere in there. Naturally, the fluid would flow from the high-pressure environment to the low-pressure environment and not the other way around; this is in keeping with the natural direction of increasing entropy.

[@fi4re]

I think y’all might be mistaken in claiming that flow can’t go from low pressure to high. Look up the Venturi effect on Wikipedia. Flow clearly goes from low pressure to high as is exits the restriction

[@blaaahhhhhhhhh1]

Everything seems good except you switched around the high/low pressure. And bernoulli's principle would conclude that at high speeds, a car would be experiencing lift due to the air particles moving faster over top the car than on bottom. However, adding a rear diffuser will allow for the air on the bottom to move at a faster rate, making for a smaller air speed difference from top the car to the bottom. Its not creating down-force, its lessening lift.

[@LTE18]

this explanation contradicts my knowledge on aerodynamics. how does a greater pressure differential helps draw air from the bottom out faster? doesn't air moves from high to low pressure? from what I read is that the high pressure at the exit of the diffuser is to help to minimise the vacuum at the rear created by flow separation near the trunk area hence lower drag. and the fins and shape are for the flow exiting without turbulence making faster flow at the bottom hence downforce please correct me if I am wrong

[@elbu2968]

+Kenneth Lee You are right. The rear end does not suck the wind out, it increases the pressure and minimizes turbulence. It does however creates an upward movement of the airflow, that indicates a lower pressure than the surrounding air. Expension of a subsonic airflow, always slows down the airspeed.

[@fitty77]

+Kenneth Lee This video, for me, does not tell the complete story. It is truth what is said. But lacks one part of the equation, that is, air is not "created" under the car. Air enters the bottom of the car by, specially, the front, and also, from the side of the car. There, you have high pressure (not atmospheric pressure, because the movement of the car, will increase it, forcing air entering under the car). So, is that pressure that is responsible for forcing air travelling at high speed under the car, and there, at low pressure. The diffuser in te rear helps stabilizing the flow in the rear. Yes it expandes the air, and yes, you will have teorethicaly, a higher pressure that underneath the car. The question is that we always assume that a venturi, does not represent any pressure drop. What is not real. So, when air comes to the diffuser, it will try to fill that volume, expanding, decreasing speed. But you still have a big pressure differential between the front, and the rear. The bigger the differential, the faster the air will travel. But the problem is that you need to stabilize the air in the rear, so when it goes out behind the car, does not represent turbulence enough that could affect the flow (and decreasing air speed under the car). So, by expanding the air and reducing it speed, and stabilizing the flow by the presence of those ducts and fins, that is achieved. And it must be achieved by means of, lets say, can interact with other aerodynamic questions that can affect the car. That vacuum question that you mention, is more a problem of air swirling around. So the diffuser must be able to direct the air straight out of the car, avoiding those swirls to happen, filling that vacuum (and why not saying it, using that vacuum to increase the capability to extract air under the car), reducing drag. Not an expert. Just my idea. ;)

[@elbu2968]

+fitty77 I think you're close to it. Pressure differential between the front and rear does not increase the airspeed, it just forces more air to flow. The speed depends on the cross section. Playing with the cross section allows for low pressure under the car. But your right the diffusor stabilizes the air to minimise drag and still allows for lower pressure that sucks the airflow up behind the car.

[@fitty77]

+El BU Sorry, but you are wrong. So if you have a pressure differential, between the front and the rear, that is what is responsible for it's speed, both in the intake, under the car, or in the rear end. Think of it this way: if you don't have that pressure differential, the air wouldn't flow at all, and speed would be 0m/s. You say "more air to flow", and you are right there. But if the cross section is constant, in order to let more air to pass, something must happen. And as you know, flow=speed x area (or cross section). So if you have more air passing under the car, or in correct terms, a increase in flow, and the area is constant, speed must increase. Regarding the pressure differential, in a system, as it increases, the speed will also increase.

[@fitty77]

+El BU also about the cross section, in pratical terms, you don't want it to be to large, as it will lose effectivness, or to small, as it can disrupt the air flow itself. Not talking about the diffuser. Talking about ground clearence and the shape of the bottom of the car. The idea is to have the air flowing as fast as possible under the car, keep it flowless (not sure if this is even a word... lol, but english is not my language), and take care that it reaches the rear as "clean" as possible. Because when speed increases, is really hard to avoid turbulence. So the bottom must be regular, and the diffuser, will help stabilizing the flow in the rear (really don't believe that a laminar flow is achievable, but hey, try your best :) ).

[@SooperKewl]

Excellent video. So glad I discovered your series. For the F1 fans, might be nice if you did a follow-up to this that explains the double-diffuser as well as blown diffuser designs.

[@EngineeringExplained]

First, yes. Second, the diffuser fins (straight lines) are used to channel the air, so it doesn't swirl within the diffuser, and heads straight back instead.

[@KARASAWA40]

The higher pressure doesn't reduce pressure at the throat, it only lowers drag. However, greater expansion means the diffuser is steeper, so the angle change that the flow has to make is larger. This makes the radius of curvature smaller which is what decreases pressure.

[@EngineeringExplained]

Diffusers are not used for additional propulsion, in fact they do the opposite. Their purpose is to slow down the air (allow it to return to atmospheric pressure more slowly than just a cut-off) moving under the car. A nozzle does the opposite, increasing velocity by reducing pressure, thus providing propulsion.

[@gtgodbear6320]

2012? I didn't know you've been around this long and I'm subscribed. You look like my nephew that young.

[@TheKpratheep]

How does pressure increase when fluid comes out from an orifice to a larger area? Wouldn't the force be distributed among the large area and hence pressure reduces?

[@sureshraghul2715]

Pratheep Kalaiselvan yes I have the same doubt

[@ak47suki242]

The reduction in kinetic energy has to be converted into some form I.e. pressure.

[@chasemiller7974]

Air pressure is based on the amount of air molecules. When it expands to a larger area, it allows more air molecules to flow through that area and thus higher air pressure.

[@donggari]

You're almost there. The diffuser forces the air in front of it to accelerate and thus induce a pressure drop, but by doing that, it must let the air re-expand and decelerate cleanly (Bernoulli's principle). If the low pressure air did not re-pressurize exiting the underbody, the higher pressure air on top of the car would essentially fold back over itself, causing a turbulent stream and thus induce drag. The diffuser, in tandem with creating downforce, allows the air to exit cleanly.

[@EngineeringExplained]

When the exhaust is diverted to expel in the diffuser, thus increasing the effectiveness of the diffuser (more downforce).

[@frsevera]

I think you could clarify this by swapping your terminology. You talked about a liquid to start. Carry that through, and imagine that the air is liquid, measured in gpm. If you consider flow, then the body of the car is restricting flow, but increasing pressure, as happens with water. When it opens under the diffuser, a drop in pressure would create a larger demand for flow. This could create a vacuum under the tail, increasing down pressure from under. I love your attention to detail! Great videos.

[@EngineeringExplained]

The air exiting the rear diffuser has to return to atmospheric pressure, which is what the diffuser is enhancing. The flow underneath the car is very rapid, and low pressure. The diffuser basically creating a vacuum underneath the car.

[@Erlkonig24]

You explain everything I want to know about the cars in so comprehensible way that it seems so easy to remember. Thank you.

[@EngineeringExplained]

If you take a chunk of fast moving air, the molecules are far apart from each other. If you take a chunk of slow moving air, the molecules are close together. So take two equal sized volumes of fast air, and non-moving air. Since the non-moving air has molecules packed more closely together, it has a greater pressure. This is what the diffuser is doing, it's slowing down the fast moving air, and in doing so, increasing the pressure. Hope this clears things up!

[@EngineeringExplained]

Diffusers are at the rear of a vehicle. Splitters can be used at the front.

[@EngineeringExplained]

I passed thermodynamics, I understand basic pressure principles. If the car was not moving, yes, air pressure would go from high to low, however, since the car is moving, the air is being forced backward (relative to the car) and thus the pressure difference is not enough for it to move from high to low, as is the case in static examples.

[@Nickpaflas]

Your videos are excellent. I'm a 45 year old who's always been sort of interested in cars, but never know that much about them. I'm going to school on these videos. I hop you've been able to turn this into gainful employment.

[@pulcinoz]

Diffuser does not pull the low pressure flux,in the diffuser there is an adverse gradient pressure,roughly speaking the diffuser allows a recovery pressure, without it the mass flux underneath the car would be less because of the much slower freestream (btw it's more complicated).However it's a very nice explanation!! it's hard to find something good on internet...if you want to go in deep with this effect I suggest you to read this paper

[@khrazy_one6472]

It would be nice if a lot more teachers can explain concepts as clear as _you_ are able to. Learning would be so much more easier.

[@ToastedTurtleOnRye]

EXCELLENTLY explained. Lots of people understand mechanical concepts, not everyone understands how to explain them intelligibly. Well done! And thank you!

[@EngineeringExplained]

Excellent, I will share this in the description.

[@EngineeringExplained]

You can model it however you would like - car moving and air stationary, or car stationary and air moving (think wind tunnel). Regardless, the air in the diffuser will have the opportunity to slow down and increase pressure.

[@hsieh811]

Great stuff! Please compare the Pros and Cons of the use of "Rake Angle" with just flat floor + diffuser.

[@drifterKen17]

Very good performed and useful. I hate only one thing about you, that I haven't got your knowleges, although I'm nearly at your age. Well done, sir. You're keeping me be motivated. Thank you

[@EngineeringExplained]

Haha I didn't know much only a few years ago, and I feel like I know very little in the big scheme of things.

[@Beck17E]

I wanna let you know that I showed my friend this and afterwards when we went out to eat he tested your example of the styrofoam cup...

[@EngineeringExplained]

Haha, nice! :)

[@user-uq4el5bj8h]

Was he high ? Not judging, I'm not one to be a hypocrite, just asking...he was high wasnt he?.

[@dielog2211]

@@user-uq4el5bj8h your name full of kanji's RiP

[@elbu2968]

If the diffuser increases airpressure, it does not create downforce, but the opposite. I think the real purpose of the diffusor is to slow tow the airflow and increase the airpressure to the speed of the car and the normal airpressure. In doing so this prevents turbulence behind the car that would happen when the high velocity low pressure air underneath the car is released to 'open air'. The real down force comes from the low pressure underneath the car. the diffusor just releases the airflow 'gently' to the atmosphere and by so reducing the drag.

[@BcoleMC]

In the video he says that it was drawn out backwards, that is correct.

[@elbu2968]

+Baylor Mccarville The diffuser itself (rear body work) does not draw anything. It is just an airflow with constant energy (except for normal loss of energy) that is manipulated by increasing or decreasing cross section and through this, airflow velocity. This effects also the static pressure which generates the true downforce. If you want an extreme low pressure at the end of the diffusor that would 'suck' the air out, that will create extreme turbulence behind the car and increases drag. In the end, the air is not drawn out, but the car pushed down.

[@vitaliypetruk3872]

+EI BU you are correct. The explanation of diffusers in this video is incorrect.

[@EngineeringExplained]

Exhaust gases are blown into the diffuser expansion area, causing the air to expand more quickly (due to the heat), creating a greater pressure differential (and more downforce).

[@EngineeringExplained]

Convex allows for a smooth transition to a higher area section of the diffuser. If it were concave, it would be an abrupt change in area.

[@KARASAWA40]

At race car speeds, air in incompressible, the density is the same both in fast and slow air. This changes above Mach .3-Mach .5, which is out of reach of most cars. The fast air accelerates to satisfy mass conservation (m_dot = rho*V*A_cross_section). Even with rho held fixed, V varies with A, plugging V into Bernoulli yields a pressure change.

[@KARASAWA40]

accelerated by a combination of compression at the front of the car (think of the car as a solid object in a wind tunnel, even though there are no walls, there is still some "blockage" and this tends to lower pressure around the car) funneling air underneath it and curvature at the diffuser throat which reduces pressure (partial of P / partial of normal = density * V^2/radius). It's also interesting to note that guide vanes may not always be of benefit. Removing them allows vortex formation...

[@KARASAWA40]

The inlet angle can be used to increase the Bernoulli effect. The pressure drop from Bernoulli comes from the ratio of cross sectional areas, A_inlet/A_throat. One thing that may be confusing is that A_inlet/A_throat is not 1 for a perfectly flat diffuser. A_inlet would include the area of the opening in addition to the area below the stagnation line on the front face of the diffuser, while A_throat would be the area of the diffuser opening.

[@EngineeringExplained]

The pressure increases because the fluid (air - fluid not liquid) slows down. The density of the air increases within the given space, so it gains pressure.

[@KARASAWA40]

The air does not expand. Rake (what you're describing) creates a low pressure zone under the very front of the car, but the pressure will increase as you go toward the tail because the cross sectional area seen by the flow increases, which makes the air slow down. Adding a diffuser doesn't reduce the effectiveness of rake. It can actually make the low pressure zone of the front of the car stronger. The diffuser just adds a second low pressure zone at the rear of the car and also lowers drag.

[@KARASAWA40]

The area of the inlet can be exactly the same as the area before the throat. The stagnation point at the nose will automatically accelerate the air under the car. A raised leading edge only increases this effect but is not required.

[@KARASAWA40]

The throat is the location of lowest pressure. There is a favorable gradient ahead of it and an adverse gradient behind it. The air under the front section of the car will feel the effect of the throat more than the mild pressure rise in the diffuser.

[@inox1ck]

The air is forced to go up by the curved up surface that is done with a force exerted by the upper surface. If the force drives air up then an equal force pulls the surface down. Another way of explaining it is that the airflow wants to separate from the upper curved surface so it lowers the pressure on the surface dragging it down. Or another way, the wing effect the airspeed on a curved surface is accelerated compared to a flat one, thus the dynamic pressure on the curved surface is lowered.

[@KARASAWA40]

Air is always drawn to regions of low pressure. With a diffuser, the point of lowest pressure is the throat, which is where the diffuser just starts to open up. In front of the throat air is drawn back, behind the throat it is pulled forward. This helps explain why air is fast underneath the car and why it's slow in the diffuser. The other reason for fast air is the venturi effect at the front of the car. Look at the front of a Ferrari Enzo, you'll see what looks like a backwards diffuser.

[@KARASAWA40]

which is turbulent and therefore less likely to undergo flow separation than laminar flow. This produces an induced drag penalty, but may reduce pressure drag and increase downforce.

[@EngineeringExplained]

It increased the volume of the diffuser, which in turn increased the downforce. Basically it was a loophole in the rules that teams exploited and was good for a short time (and well worth it).

[@robertwinterstein6690]

Love your channel, I learn so much, thank you!!!! So if you had a 35 food long, 11.5 feet high and 8 foot wide motor home with a flat front and back with 10" ground clearance, what would be the best way to divert air into the rear radiator? The fan creates a low pressure, but it would seem there would be a low pressure already accuring there. Could you break up the air on the sides and roof and see if the low pressure from the fan will draw more air into the radiator? Thank you for taking the time to explain things in detail.

[@KARASAWA40]

A vortex is a form of flow separation, it's also turbulent and viscous so bernoulli's equation does not apply, at least not at the core. The wing and diffuser are very similar. The wing will have a pressure distribution along its length. On the curved upper surface, pressure goes down and then up. If it did not go up, planes would be very draggy and no one would use them.

[@KARASAWA40]

Yes and no. Expanding area increases pressure and does act like propulsion, but the diffuser is still producing downforce by imparting upward momentum into the air, which means downward momentum is being transferred to the car. Divide the diffuser in two. The entrance is responsible for downforce, the tail is for reducing drag.

[@airj17]

Think u got this wrong. air exiting the diffuser is of less pressure and higher velocity than the air undercarriage. Boyle's law - For a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional.

[@shi01]

+airj17 Boiyle's law only works for a static system. A closed chamber or something similar. You don't have that in this case here.

[@BcoleMC]

If you listen closely he'll say, "this is just backwards" so it's the opposite of what he said, but he meant for that to happen. You are correct.

[@KelvinTan133]

There's nothing to do with volume and Boyle's Law. We're speakin of a high and low pressure effect on an object aka venturi effect. It is correctly explained in this video, the undercarriage has lower pressure and higher velocity, and at the exit of diffuser, pressure is high and velocity drops (don't argue, this is basic physics). Hence the lower pressure below (undercarriage) causes the higher pressure above the vehicle to push the whole car to the floor. This concept works similarly to an aerofoil wing of aircrafts.

[@EngineeringExplained]

It would be negligible if anything, also there would be a greater pressure on the front (air resistance).

[@KARASAWA40]

are fixed. Because of this, the area that the flow passes through get smaller. By conservation of mass: m_dot = density*area*velocity, so speed goes up. By Bernoulli, speed going up means pressure goes down. The opposite happens during diffuser expansion.

[@Madvilllain]

Because you have that pressure gradient, with a greater pressure at the back end of the car, does that push the car forward as well?

[@kevn009]

i think the air that travels from under the car and into the diffuser has the same speed, therefore when it expands it creates a low pressure area that sucks in more air. the pressure under the diffuser wil be atmospheric, but further towards the end and not at the entrance. the ventury effect of higher pressure in a bigger area just applies when the direction of the air is towards the smaller area, creating a sort of bottle neck effect.

[@shawnoswald9854]

This video is confusing! Isn't the air at the rear of the car LOW PRESSURE? Shouldn't it create a vacuume and downforce like an upside down wing? High pressure released creates low pressure. Think of a balloon where the pressure is higher inside then when released it is now low pressure. Am I missing something ?

[@shi01]

shawn oswald Well, the pressure is still lower than on the upside of the diffusor. So it still creates downforce. But the pressure raises when the air streams along the underside of the undertray to the back of the car.There's a very intresting video of the Windtunnel of Sauber F1 here watch?v=KC0E0wU6inU and around the 23 minute mark of the video you can see a picture that shows where the car is producing it's downforce. The picture shows the car actually from the underside. The intresting part is, and that's often not mentioned, a diffusor influence also the very begining of the undertray and creates downforce there because it helps to suck air under the car and immediatly accelerate it, which leads to a pressure drop.

[@zakarioze]

shawn oswald You are missing something. That something is fluid (air) velocity.

[@indigocolossus]

The diffuser doesn't create downforce. It accelerates the air under the car, so the underbody, if no relative air leak, can create downforce.

[@TheQaked]

+Indigo Colossus thank i was still confused, then thought of this idea and wasn't sure if i was right.

[@FerrariMC_1947]

I love these videos!! You do such a great job at explaining this stuff so clearly, even despite the various complexities involved. We've gotta figure out how to capitalize on your videos/knowledge!! Keep up the great work!

[@KARASAWA40]

It depends. The lighter a vehicle, the less speed is required to generate significant downforce, because less downforce will have more effect. There is also the secondary benefit of diffusers, which is reduced drag. Even for relatively low drag road cars, the few counts gained from a diffuser or diffuser like profile makes an impact on fuel savings. For high performance low speed focused cars, large vortex producing diffusers can be a valuable source of downforce at the cost of drag.

[@vineeshkumarkv1]

If there isn't divider, air flow might be turbulent at the rear side and it offer much pressure than a laminar air flow. It create even higher pressure drops, thus higher down force is achieved, then what is the significance of creating a laminar flow there?

[@KARASAWA40]

Getting back to atmospheric pressure is impossible because of viscous losses. The F1 is also going to generate a wake from the wings and various other lift devices, not to mention the open tires. You can get a rough idea of the draft strength from the drag coefficient since this is related to the momentum defect left in the air by the vehicle, which is one of the things that creates the draft. The F1 is probably going to leave a much stronger wake than a regular car.

[@brendanhood2624]

so if it is returning the pressure behind the car back to atmospheric or close to, it would reduce the draft effects of a vehicle behind (as the pressure from behind the car is almost back to atmospheric). What sort of difference would the draft be between the formula 1 and say two of your integra's following each other for example?

[@Danhor7]

An air plane wing has the opposite arrangement but exact same effect. The flat bottom of a wing shields the higher pressure under the wing from entering the low pressure area above the trailing edge.

[@mohitsn519]

No mate..I searched your channel n downloaded most of d videos...Actually i wanted some knowledge about turbomachines like turbines,compressors,pumps,fans,etc...Both axial n radial (centrifugal).... Anyways thanks 4 uploading wonderful videos .....I really like dem!

[@EngineeringExplained]

Though I agree it would be awesome, unfortunately it wouldn't be safe. The FIA has been exceptionally strict since Senna's death, and they've been successful at preventing driver deaths.

[@jdmcommute]

What do you think about some small vortex generators on the underside of a front wind splitter just before the axial line of the front A arms to help keep the high flow of air moving underneath the flat bottom of the car rather than run into suspension linkage while increasing the boundry layer until it reaches the rear diffuser? Do you think its a good addition?

[@RunNscar3d]

Its the same with air plane wings. You create a high pressure on the bottom of the wing and low on the top. The air on top of the wing has to move faster. The wing will always travel the same way as the low pressure which is up. Thats why cars have spoilers for down force, to counteract that high pressure zone on the bottom of the car.

[@jsjohnsmithy]

Thanks. any ideas on the inlet angle of the diffuser. i Know the difference made by different diffuser angle but not on the inlet angle.

[@KimiMotoVlog]

you need a larger volume of air to feed the larger expansion chamber at the rear. where would you get this larger volume of air? of course from the front. and in the process of 'feeding' the rear diffuser with more air, you inadvertently speed up the speed in that region (front) causing even lower pressures. of course you can scoop up air from other parts of the car to feed the diffuser (as in EBDs and Double Diffusers in F1). but to simply answer your question, more air is needed for the rear.

[@Benny46drift]

I did a diffuser for my R32 Skyline but didn't add the dividing fins... will his make a massive amount of difference overall?

[@bo093]

How about those drag cars? Bumper cut and holes in them. Does that reduce drag? They say about removing the parachutes effect.

[@qx4n9e1xp]

Thank youn handsome man. You have passed down your intellect well. Very well actually. Good job.

[@meganemb]

The Citroen DS3 as a small diffuser. Does it makes a considerable difference on the performance with a small diffuser on a daily driving?

[@ACamaroGuy]

On a stock car, will the shark fin looking rear diffuser work? Does the underside of the car have to be flat? Will it work with turbulent air underneath a stock car that does not have body panels creating a flat surface?

[@modernpanther]

Hmm, does the faster moving air underneath the car have to contend with a back-pressure of sorts introduced by a higher pressure area of the diffuser, thereby inihibiting flow?

[@EngineeringExplained]

Sort of, except the air is forced back, since the car is moving so fast, rather than "wanting" to go to a high pressure area. The diffuser allows the "high" pressure area to exist, creating an imbalance - which in turn makes the bottom of the car a vacuum.

[@mrtorotek]

if they get more downforce doesnt it means they can go faster round corners ? or is it due to such downforces and rapid loss of 'vacuum' on the sides of the car, this makes it less controllable in corners ?

[@GubenkovED]

Although diffuser increases pressure behind the car (in comparison with pressure under the car), but pressure would be even more without diffuser because of turbulence. And this would lead to slower flow under the car. Correct me, please, if I was wrong.

[@KARASAWA40]

Why does air need to be compressible to allow movement? Density is fixed, but the shape of the control volume isn't. An object moving through air will cause pressure to change at certain regions, yes. At the front of the car there is high pressure due to stagnation. This high pressure can be responsible for pushing air under the car. The point of highest pressure is on a special streamline called the dividing streamline. Streamlines above go up, those below go down. The streamlines at the ground

[@Rueda888]

The diffuser strakes are not used to make the flow go straight without turbulence. In fact, what they do is to create vortices that take the high energy air from the floor and move it to the boundary layer on the diffuser, thus increasing the energy of the boundary layer and preventing flow separarion (that's why we can build diffusers with large angles of inclination).

[@bananabottles]

your cup-and-straw example is basically the same as using your thumb on a regular gardening hose to increase the pressure and speed of the exiting water.

[@jonathanshin7558]

I heard that as the slant angle decreases below approx 15 degrees, is when downforce is increased?

[@Deathincart]

how fast would you have to be going in a street car for a diffuser to start making a difference. I have a 2016 bmw 228i and was considering getting one and wondered if it could have any real benefit other than just looks

[@KARASAWA40]

Very good videos, though I think a couple of things were off. In your first example, pressure would not increase in the cup, it would remain constant. The air being drawn through the straw would decrease in pressure as it flowed in from outside the cup as per the Bernoulli equation (perhaps add to video through annotation). For the car, the expansion in the diffuser is only for drag reduction, it's not related to turbulence, but simply raising air pressure behind the car. Underbody air is...

[@buubised]

hmm interesting... i was thinking of the re-amemiya rear carbon diffuser for fc3s, so it creates vacuum under the car, but do i need to make the downforce in the front end bigger also to not get understeer?

[@leech2827]

does Bernoulli principle apply on moving car? if so isn't that the air flow on top of car faster than air flow under the car, wouldn't that create a higher air pressure under the car and lifting the car?

[@swayingGrass]

Which will be higher from the ground, front side or rear side if the first (stop) it's flat?

[@Jron45the_pimp]

So, the air under the car wants to move faster to get to the high pressure at the back, and when the air moves faster there is less pressure under the car giving downforce elements a greater effect. Do I understand this correctly?

[@Danhor7]

You're almost there. There is a major component missing in your equation and that is the pressure differential between the top of the car and the bottom. Same principal that causes lift on a wing. The wing or car displaces air as it travels through it and there is higher pressure on the leading edge than the trailing edge. A diffuser takes advantage of this low pressure area by shielding it from the higher pressure air above the car and allowing the free flow draw of air from under the car.

[@ThePEagle]

Does it also have the effect of reducing the effect of low pressure at the back of the car by pouring air from the bottom ? Thanks for the video btw.

[@TheWolfpackcdn]

hmm, what I dont understand is that in the 1st drawing(to the left), shouldn't there be increasing pressure since molecules collide more often?

[@mattsimmons6717]

Please help! I understand the purpose of it, but why is it that shape, as in why is the actual diffuser that shape at the rear of the car?

[@Oblithian]

...So a vortex generator (like a trip) on the underside, before the curve, would negate the effects of a diffuser?

[@pascalmpower7944]

The dynamic of diffuser will also effect the cd. Depends the shape, there is cars like F1 using diffuser to gain down force. The greater pressure the diffuser have, the better cd from the front and sides. Just like the turbochargers or wind tunnel. Greater out let, greater in let by ratio.

[@bizmorphic]

what I think about a diffuser is it helps in moderating the effect of rearwing downforce that's why it is used in cars like lambo to avoid the pitching condition please correct me if I'm wrong

[@wgfvideos3768]

This is actually more useful to my hvac trade rather then my sport sedan. Lol but hey the looks are great 👍

[@somesoul.]

Holy man you really improving so much

[@griffsrearmountturbothemod1623]

I have just fabricated a nice splitter on my early muscle car too settle it at high speed.would you do a indepth vid on benefits etc. Much appreciated....

[@randomtoyotadude8952]

How fast do you(the car) need to drive before defuser is funtional for a "normal" car(not on a track)???

[@KINGsizeWINNER]

Great video. But how do car roof diffusers work if there is no pressure formation since there is no road above the car to squeeze the air between. Are roof diffusers bogus?