Vritual gurney flap

[Mikey_s]

MC,

The comments are intended to be constructive ciriticism, but I'm far from expert in this area, I'm not an aero guy (just a simple chemist I'm afraid!), but my sense it that the NACA duct is typically used on (fighter) aircraft where the airspeed is rather high and therefore needs to be slowed down in order to be used... If this device is for the rear wing and is on the endplate I guess (and it is only a guess) that you probably don't need to worry about messing up laminar flow along the remainder of the endplate.

Furthermore, your drawing shows you taking the air from the bottom of the duct only, rather than the entire back end - I guess this would need some optimisation, in any case - somehow the device needs to be fed with air so someone with an aero background would need to consider the best way to extract air from the flow - I guess the balance needs to be between d/f generated versus drag penalty.

I was just thinking (not necessarily a good thing!!) about another means to achieving more d/f... - If i understand the Gurney flap concept well it works by developing a low pressure area at the trailing edge of the wing which essentially pulls the airstream on the low pressure side of the wing back on, preventing stall at high angles of attack.

i read an article in New Scientist some years back about a fighter jet concept which used quite the opposite to what you suggest, but with a view to achieving the same thing... It used a porous (perforated) surface on the low pressure (top) side of the wing and sucked air into the wing creating an even lower pressure surface and thus keeping the airflow attached at high angles of attack. How about reversing your venturi/duct and perforating the low pressure surface of the wing (doesn't need to be all over, just near the trailing edge) so that the airflow remains attached - i.e make it a sucker rather than a blower... what do you think of that?

[kilcoo316]

The duct alone will never give the required pressure ratio to make the thing work [well, you might be able to fill the boundary layer wake, but that would be it]. You'd need a pump of some form.



Having perforations on the suction surface of a wing (both sucking and blowing) has been something that has been extensively explored in aviation aerodynamics as a means of controlling shock induced seperation on passenger aircraft. The problem is one of maintenance - the pores/holes get blocked, with an F1 car exposed to dust particles in the air, flies etc etc etc - then I would guess the problem would be just as pronouced.


Vortex generators have been investigated, I know Renault did work on them about 4 years ago , and they managed to move the seperation point on the wing back about 15%, now whether they ever implemented it on the race cars I don't know - but I know the work was done.

[Reca]

Well, if the inlet (duct) is bigger than the outlet (slot) than it would pressurise inside the wing because air would enter it in greater amount than it would exit, right? Duct feeding more air in than what slot is capable of letting out. That's what I had in mind from the beginning.

That would be great, if that was true ram jet engines wouldn’t need supersonic flow to give a reasonable compression ratio in the inlet and start to work.
Problem is that true it’s not so at subsonic freestream velocity we need to fit compressors to increase the pressure of the freestream flow and we have to steal energy from the gasses out of combustors via turbines to make those compressors work.

In subsonic it’s up to the conditions at the outlet (pressure, speed, area etc etc) to decide how much air will enter in a duct. If the outlet allows less mass flow than the inlet could take (to make it simple, assuming everything else is equal, if outlet area is smaller than inlet area), the freestream flow “knows” it well before arriving at the inlet, so it will slow down from freestream velocity to the velocity that corresponds to the mass flow allowed by the outlet’s conditions. If you make that slow down to happen in the right way you can actually gain a bit of pressure converting the dynamic pressure in static, but we are talking about a limited gain (example, dynamic pressure in standard atmosphere at 250 km/h is about 3k Pa while static pressure is over 100k Pa so also converting all the dynamic in static you gain less than 3%)

That means that in a F1 car it’s mostly the diffuser that decides how much air is going to pass under the car no matter what you do at the front of the car (ie, if the diffuser is crap it’s pointless to have a huge mouth... FW24 anyone ? Remember it when people say that an higher nose will allow more air under the car...).
Just like are mostly the sidepods outlets, and not the intakes, that decide how much air is going to enter in the sidepods and pass thru the radiators. (remember it when people say that a car with smaller inlets requires less cooling...)
Just like it’s mostly the amount of air required by the engine, and not the size of the air intake, that decides out much air is going to enter in the airbox.

As kilcoo said, as a passive system it would never work. As an active system it could work but it wouldn’t be probably worth it.

Please, please, if this is a mechanism that could be used in F1, I suggest we destroy this thread and Manchild burn all the notes he has. The last thing race cars would tolerate would be a huge change in downforce! Overtaking would be a thing of the past.

I think that if that mechanism had some merit for F1, we would have no hope for people to forget it Ciro, blowing or suction of the b.l. are quite basic concepts anybody with a bit of interest in aeronautics is aware of and any aeronautical/aerospace engineer, as many guys working in F1 are, knows it pretty much since the second/third day at Uni, no chance to remove it from their minds
Anyway, I think there’s one thing that could reassure you :

3.10.4 Any bodywork behind the rear wheel centre line which is more than 600mm above the reference plane, and between 75mm and 480mm from the car centre line, must lie in an area when viewed from the side of the car that is situated between the rear wheel centre line and a point 350mm behind it. When viewed from the side of the car, no longitudinal cross section may have more than two closed sections in this area.

[kilcoo316]

Reca - it wouldn't be a problem meeting that rule - the section would be closed - but like a U on its side....

uhm, a bit like this
_
|_


if you know what I mean... the inside surface will still 'close' the cross section.

[manchild]

No problem Mikey_s, I'm not aero guy either. I'm only presenting wild ideas here so that pros and rest of the non-pros could say what they think about it.

My sketch is just a sketch so it only appears that only lower part of duct would feed the wing. I've drawn duct as high as wing because I had in mind that it needs to feed wing as much as possible (trough whole wing cross section). If you insist I'll make additional sketch but I think there is no need for it.

NACA ducts have long history in motor racing too including F1. BAR had them last year right and they are not solely used on fighter planes but almost on all types of aircrafts.

The NACA duct or NACA scoop is a common form of low-drag intake design, originally developed by the National Advisory Committee for Aeronautics in 1945. When properly implemented, it allows fluid to be drawn into an internal duct, often for cooling purposes, with a minimal disturbance to the flow. The design was originally called a "submerged inlet," since it consists of a shallow ramp with curved walls recessed into the exposed surface of a streamlined body, such as an airplane. It is especially favored in racing car design.

Prior submerged inlet experiments showed poor pressure recovery due to the slow-moving boundary layer entering the intake. This design is believed to work because the combination of the gentle ramp angle and the curvature profile of the walls creates counter-rotating vortices which deflect the boundary layer away from the intake and draws in the faster moving air, while avoiding the form drag and flow separation that can occur with protruding inlet designs. This type of flush inlet generally cannot achieve the larger ram pressures and flow volumes of an external design, and so is rarely used for the jet engine intake application for which it was originally designed. However it is common for engine and ventilation intakes.

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About proposed idea... can you pros agree about which direction of air (outlet/slot position) would be most useful?

[zac510]

I recall there is at least 10 of them on the Ferrari F40

[manchild]

Here it is Mikey_s, I've done it anyway.

Hope it is now more understandable how NACA duct would feed whole wing cross section.



It could be even done Renault style (like Honda Monza update)

[kilcoo316]

The blade interior would need to be something like:



But I'll stress again, you need a pressure ratio to perform vectoring of 5+, and a specific mass flow rate 1.2 x mean mass flow rate [that'll be kg/s.m^2] to fill the boundary layer effectively.

I doubt the two ducts would provide the mass flow, and I know they won't even begin to provide the compression necessary.

[manchild]

kilcoo, would one big additional NACA duct below original one or several smaller ones on each endplate provide enough pressure? Is that possible at all or impossible regardless on capacity of ducts?

[kilcoo316]

Providing the mass flow may be possible.

The pressure rise is simply impossible, as I said a few pages back the most you can do is double the pressure coefficient [in inviscid flow at a stagnation point].


But you need a pressure ratio of around 5 or more to do real effective TVC - so you need a pump.


To put it in perspective - you'd need a 2 stage axial compressor to acheive that kind of pressure ratio.



edit: the PR of 5-10 is for nozzle applications - I'll see if I can find a more suitable comparision if I've time later. But, I'd imagine it would still be something similar.

[manchild]

Would one-way valve just after duct change anything?

Regarding pump... wouldn't air pump be considered as movable aero?

[zac510]

Surely it may be easier to run a hydraulic line up through a hollowed endplate to a couple of solenoids inside the element to change the wing shape.

Very illegal though

[Reca]

kilcoo, would one big additional NACA duct below original one or several smaller ones on each endplate provide enough pressure? Is that possible at all or impossible regardless on capacity of ducts?

Basic rule of thermodynamics : “there are no free lunches”. You not only are asking for a free lunch you even want to get paid to eat...

[manchild]

I'm trying to understand this correctly but I see two possible meanings:

1. I'm expecting kilcoo to do my math while I get the glory (which isn't the truth since I lost any patent right the very moment I've put my idea online).

2. I'm expecting airflow and aerodynamic shapes to do impossible things.

Which one is it Reca?

[kilcoo316]

Would one-way valve just after duct change anything?

Regarding pump... wouldn't air pump be considered as movable aero?

A valve wouldn't change a thing.


Uhm the pump might be movable.... but if you can somehow mount it within the wheel...


Others suggested a feed from the exhaust - you would have the required mass flow and pressure for sure.... if you could get a pipe large enough through the endplate and could get a light enough substance to carry it without overheating.


Fluidic TVC and nozzle control isn't used on aircraft, despite having an easily accessible flow of compressed air [from the engine core itself] - they simply don't perform as well as mechanical nozzles at the moment (and I don't know if that is ever going to change).


As Reca says - those damn free lunches are hard to find!