TRX250R.ORG
Workshop => Carburetor, Intake, and Exhaust => Topic started by: 85drag250r on January 29, 2014, 07:19:41 PM
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Looking for opinions on an idea I have about putting a "textured" type surface on the inside bell /throat of a carb.
Here is my reasoning behind the idea, if you have ever looked inside a rad valve, you may have noticed a slight textured surface.
I assume Boyesen did this to help atomize the air/fuel mixture going into the engine.
Is there a reason why this "textured" surface could not be applied to the inside of a carb to start the atomization a little sooner?
If the intake port on a cylinder is supposed to be left a little rough (for better atomization), then why do the carb manufacturer make the inside of all carbs so smooth?
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there should be no roughness until after fuel has entered the picture
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sorry, i should have been more specific...lectron carb with the p/j at the begining of the carb bell.
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You want laminar flow in the carburetor so that proper air/fuel metering happens. (if its to turbulent, you wont get consistant fuel flow from the main jet)
After the carb you want turbulent flow to atomize the charge.
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the rad valve seams to be a sandblasted texture, probably done for a couple reason one to help fuel droplets atomize but also to probably give the product a nice looking finish after possible casting flaws are cleaned up.
There may be a advantage if it did create a boundary layer on the surface but I not sure much difference would be found.
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the friction created from the turbulence of the air flow is the main precipitate of fuel atomization. the higher the velocity of the air the more tuburlant the air. the important part most people dont realize is you want a highly turbulant flow for the best fuel atomization.
john
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Rsss, the "sandblast" type finish found inside the rad valve is the type of finish i want to use on the bell / throat of the carb.
John, i read a few articles on the effect of turbulence, and how important it is to an induction system. It got me to thinking, why not start the turbulence a little sooner with the carb.
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Like i said you need smooth laminar flow over the jets to produce the right air fuel mixture. If you have turbulent flow over the jet, you will get random a/f mixtures. Id say this is all on a very small scale, but regardless is the truth.
You dont want to start turbulent flow until after the carburetor.
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Like i said you need smooth laminar flow over the jets to produce the right air fuel mixture. If you have turbulent flow over the jet, you will get random a/f mixtures. Id say this is all on a very small scale, but regardless is the truth.
You dont want to start turbulent flow until after the carburetor.
again you come up with nonsense. you need to retake fluid mechanics. laminar flow is very slow (low velocity) its layered i.e. if anything there is a transitional flow through the intake and it accelerates through the venturi and get much more turbulent.
john
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Laminar flow means even distribution, which also means even pressure distribution. Since the jets work on pressure differential, you will want laminar flow to create a consistent charge that represents the air being ingested by the motor. My fluids is correct sir.
http://blog.nialbarker.com/wp-content/uploads/2010/03/laminar_turbulent_flow.gif
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You are referring to Reynolds number which incorporates many factors including surface roughness, velocity, diameter, mass if i remember correctly. Its all still related.
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This article has some very good information in it. Its not directly about carburetors, but it does talk some about laminar/turbulent flow and effect on orifice plates. Basically our jets are an orifice plate.
http://www-personal.engin.umd.umich.edu/~ratts/me379fil/handouts/viscous/Meriam_Laminar_Flow_Element.pdf
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Laminar flow means even distribution, which also means even pressure distribution. Since the jets work on pressure differential, you will want laminar flow to create a consistent charge that represents the air being ingested by the motor. My fluids is correct sir.
http://blog.nialbarker.com/wp-content/uploads/2010/03/laminar_turbulent_flow.gif
here is some elementary stuff for you to understand:
http://www.nationalcarburetors.com/carburetor.html
http://en.wikipedia.org/wiki/Laminar_flow
http://hyperphysics.phy-astr.gsu.edu/hbase/pfric.html
http://hyperphysics.phy-astr.gsu.edu/hbase/pturb.html
stop hanging around that idiot carla. you are starting to act like him.
john
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Dude you do not need to be hostile towards me. Im just a regular guy. No need to be an asshole to me.
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BTW your links support what im saying.
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This article has some very good information in it. Its not directly about carburetors, but it does talk some about laminar/turbulent flow and effect on orifice plates. Basically our jets are an orifice plate.
http://www-personal.engin.umd.umich.edu/~ratts/me379fil/handouts/viscous/Meriam_Laminar_Flow_Element.pdf
well if you read that article you would realize you are talking nonsense.
john
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how so?
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how so?
you think you get laminar flow across the jets and you are wrong. you get transitional flow at best. you need the air moving very fast to keep feeding the system. LAMINAR FLOW MOVES SLOWLY!!!!
john
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Everything i have stated is fact. I dont see how you are saying its not. The smoother, less turbulent, or more laminar the flow, the better job the jets are going to do measuring the amount of fuel to mix in. If you have "more" turbulent flow over the jets, the jets wont meter in the proper amount of fuel proportional to the actual amount of air injested.
Granted this is on a very small scale, and probably doesnt make any difference if the inside of a carburetor was roughed up. This i dont know. But the facts still apply.
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you think you get laminar flow across the jets and you are wrong. you get transitional flow at best. you need the air moving very fast to keep feeding the system. LAMINAR FLOW MOVES SLOWLY!!!!
john
Yes laminar flow moves slowly. And i see what your saying. Your point is correct. What i meant was less turbulent flow the better. Your correct that no flow would be laminar in a carburator or any of the intake for that matter. I was only using laminar as a point of reference as less turbulent. I shouldnt have said that. I should have said less turbulent.
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did you guys kow that most of the air flows on the outer edges of the air horn.harry klemm told me that you could place a silver dollar very close to the carb opening without effecting flow
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Do some calculation for your reynolds number for the air velocity at the smallest area of flow through the carb. The smallest cross-section is usually at the fuel entry point into the air stream. Typical peak velocity in most carburetors easily exceeds 300 feet per second and some engines approach the sonic threshold which is over 1000 feet per second. I do not have time now to find and do the calculations for the reynolds number. My intuition tells me the flow will be well into the turbulent region.
The flow through a round cross-section is always highest in the center of the round cross-section and zero at the theoretical surface. The flow velocity goes from zero at the surface to a much higher number at the edge of the boundary layer and continues to increases as the distance from the boundary layer increases.
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here is something related to your question, interesting results
(http://www.ducati.ms/forums/attachment.php?attachmentid=48836&stc=1&d=1243848799)
(http://www.ducati.ms/forums/attachment.php?attachmentid=48844&stc=1&d=1243853667)
(http://www.ducati.ms/forums/attachment.php?attachmentid=48845&stc=1&d=1243853667)
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That appears to be an injected motor. Those diviets definitely reduce air resistance which would increase flow. Very cool
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It's even referred to as "golfballed". It doesn't appear that any of the runs had only that mod though.
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The way I read the dyno sheet is the run 046 and 127 are the same setup but 127 has the golf ball effect on the 50mm Wasp stacks and 046 has untouched 50mm wasp stacks
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81 dyno runs were made between run 46 and run 127. A lot of different changes were probably made during those runs.
There is not enough information in the dyno notes to draw any meaningful conclusion as to what caused what.
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................................Those diviets definitely reduce air resistance which would increase flow. Very cool
It has been many years since I have studied the effects that the threads on a baseball or dimples on a golf ball have on their trajectory of flight.....I think you may be making some miss-informed conclusions as to why a dimpled golf ball will usually fly further than a non dimpled ball and trying to relate how dimples would affect flow in a confined area like a port. It is my understanding that the dimples reduce the influence spin has on the ball. A non dimpled ball that has some forward spin or no spin will not fly as far as a non dimpled ball that has backward spin. Dimples will add distance and reduce the left right flight deviation to the AVERAGE drive because all drives have some degree of spin.
In a port, increasing the boundary layer thickness reduces the effective flow cross-section. Increasing the boundary layer thickness surrounding a dimpled golf ball does not have any walls or boundaries that will affect what is happening close to the golf ball. Fluid Mechanics and Gas Dynamics are complex subjects and cannot be mastered reading a few hundred pages on the subjects on the internet. High-level math and physics are prerequisites for Fluid Mechanics and Gas Dynamics.
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I have never studied the effects of the dimples. We studied this somewhat in college many years ago. My only "real world" experience was on Mythbusters.... I know not a great source. But they where able to reduce the air drag on the car by covering the car in clay and putting patterned dimples over the car. Even with the additional hundreds of pounds of clay, they increase the MPG by several miles.
Im not going to dive into the fluid dynamics on this. I dont have the time, or the memory. And i will add I could be very wrong. But it was my understanding that by creating turbulence at each dimple moved the boundary layer further from the car. . I dont have any proof/math behind this, just kinda imagining it in my head. So please dont take this as gospel.
here is a statement i found while playing around on the internet. Take it for what it is. A statement.
If you want to get deeper into the aerodynamics, there are two types of flow around an object: laminar and turbulent. Laminar flow has less drag, but it is also prone to a phenomenon called "separation." Once separation of a laminar boundary layer occurs, drag rises dramatically because of eddies that form in the gap. Turbulent flow has more drag initially but also better adhesion, and therefore is less prone to separation. Therefore, if the shape of an object is such that separation occurs easily, it is better to turbulate the boundary layer (at the slight cost of increased drag) in order to increase adhesion and reduce eddies (which means a significant reduction in drag). Dimples on golf balls turbulate the boundary layer.
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Also i read that there where other mods on those dyno pulls. I knew that looked like to much gain to be true. Would be interesting to see what if any gain there would be with just the intakes designed like that. You would think someone would already be doing it.
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Post by Daniel Jones
A lot of people confuse turbulent flow with pressure separation. They are two
separate phenomenon. You can have attached flow or separated flow. Separated
flow generally has much more drag. You can also have a laminar or turbulent
boundary layer. A laminar boundary layer generally has less drag but can be
only maintained over slender bodies, like airfoil sections (and then only
sometimes) which unless some sort of active means of boundary layer control
(e.g. suction) is employed. For low drag on a shape that will not sustain
a laminar boundary layer, you want to eliminate separation. As it turns out,
inducing turbulence is a great way to do this. The profile drag of an object
can be spilt into two components:
Cd = Cdf + Cdp
where
Cd = profile drag coefficient
Cdp = pressure drag coefficient due to flow separation
Cdf = skin friction drag coefficient due to surface roughness
in the presence of laminar/turbulent flow
The drag which comprises the Cdf component is caused by shear stress induced
when air molecules collide with the surface of a body. A smooth surface will
have a low Cdf. Also, the Cdf is lower for laminar flow and higher for
turbulent flow. Cdp, on the other hand, is caused by the fore-and-aft pressure
differential created by flow separation. Usually, Cdp is lower for turbulent
flow and higher for laminar flow. In many cases, inducing turbulence will
dramatically decrease the pressure drag component, decreasing the overall drag.
Airplanes use this trick all the time.
Back in the 19th century, when scientists were just beginning to study the
field of aerodynamics, an interesting observation was made with respect to
the drag of a cylinder. Since a cylinder is symmetric front-to-back (and
top-to-bottom), their early theories predicted it should have no drag (or
lift). If you plot the (theoretical) pressure distribution along the
surface of the cylinder (remembering that pressure acts perpendicular to a
surface) and decompose it into horizontal (drag) and vertical (lift)
components, you'll find that the pressure on the front face of the cylinder
(from -90 to +90 degrees) and the pressure on the rear face ( from +90 to
+270 degrees) are equal in magnitude but opposite in direction, exactly
cancelling each other out. Therefore, there should be no drag or lift.
However, if you actually measure the pressure distribution, you'll find
there are considerably lower pressures on the rear face, resulting in
considerable drag. This difference between predicted and observed drag
over a cylinder was particularly bothersome to early aerodynamicists who
termed the phenomenon d'Alembert's paradox. The problem was due to the
fact that the original analysis did not include the effects of skin
friction at the surface of the cylinder. When air flow comes in contact
with a surface, the flow adheres to the surface, altering its dynamics.
Conceptually, aerodynamicists split airflow up into two separate regions,
a region close to the surface where skin friction is important (termed the
boundary layer), and the area outside the boundary layer which is treated
as frictionless. The boundary layer can be further characterized as
either laminar or turbulent. Under laminar conditions, the flow moves
smoothly and follows the general contours of the body. Under turbulent
conditions, the flow becomes chaotic and random.
It turns out that a cylinder is a very high drag shape. At the speeds
we're talking about, a cylinder has a drag coefficient of between 0.4 and
1.17. An efficient shape like a symmetric airfoil (that is aligned
with the airflow, i.e. is at 0 degrees angle of attack) may have a Cd of
0.005 to 0.01. Think about what this means. An airfoil that is 40 to 80
inches tall may have approximately the same drag as a 1 inch diameter
cylinder.
Luckily, there are easy ways of reducing a cylinder's drag. Another thing
the early aerodynamicists noticed was that as you increased the speed of
the air flowing over a cylinder, eventually there was a drastic decrease in
drag. The reason lies in different effects laminar and turbulent boundary
layers have on flow separation. For reasons I won't get into here, laminar
boundary layers separate (detach from the body) much more easily than
turbulent ones. In the case of the cylinder, when the flow is laminar,
the boundary layer separates earlier, resulting in flow that is totally
separated from the rear face and a large wake. As the air flow speed is
increased, the transition from laminar to turbulent takes place on the front
face. The turbulent boundary layer stays attached longer so the separation
point moves rearward, resulting in a smaller wake and lower drag. In the
case of the cylinder, Cd can drop from 0.4 to less than 0.1.
You don't have to rely on high speeds to cause the bondary layer to "trip"
from laminar to turbulent. Small disturbances in the flow path can do the
same thing. A golf ball is a classic example. The dimples on a golf ball
are designed to promote turbulence and thus reduce drag on the ball in
flight. Trip strips are employed on wings for the same reason. If you look
closely, you'll notice that some Indy and F1 helmets have a boundary layer
trip strip to reduce buffeting. It seems odd but promoting turbulence can
reduce buffeting by producing a smaller wake.
Another consequence of skin friction on a cylinder is that you can generate
substantial lift with a spinning cylinder. By spinning a cylinder you can
speed up the flow over the top and slow down flow under the bottom, resulting
in a lift producing pressure differential. In aerodynamics, this is known as
the Magnus effect.
The speed at which a laminar boundary layer becomes turbulent is determined by
the Reynolds number, which is defined as:
Re_x = (Rho * V * X)/Mu
where:
Re_x = Reynolds number at location x (a dimensionless quantity)
Rho = freestream air density
V = freestream flow velocity
x = distance from the leading edge
Mu = freestream viscosity, a physical property of the gas (or liquid)
involved, varies with temperature, at standard conditions mu is
approximately 3.7373x10E-07 slug/(ft*sec) for air.
The location along the body at which the flow transitions from laminar to
turbulent determines the critical Reynolds number. Below this number, the
flow is laminar, above it's turbulent. Since the Reynolds number varies
linearly with the location along the body and with velocity, the faster you
go, the farther forward the transition point moves. At cruising speed on a
typical jet airliner, only a small region near the leading edge may be
laminar. Slow speed gliders with very slender (but still with rounded, blunt,
leading edges) may maintain laminar flow over most of the wing surface but
this is not the case for most practical aircraft. Note that glider wings
are typically designed with very short chord lengths (x distances) to help
promote laminar flow. A laminar boundary layer is desirable when there is no
pressure separation but when there is, a turbulent boundary layer can yield
less drag. Technically speaking, separated flow is not turbulent, even though
it is random and chaotic (and very draggy). Be aware that the laminar and
turbulent concepts apply only to the boundary layer, which may be a few inches
(or less) thick. Beyond the boundary layer, flow is treated as frictionless
(inviscid).
A couple of guys at work (then McDonnell Aircraft, now Boeing), tufted a 1987
Mustang LX from the center of the roof to the taillights. They were trying to
use vortex generators to increase the flow attachment on the rear glass. Vortex
generators are devices which are put in the flow field to intentionally induce
turbulent flow. They are often used on aircraft to re-attach and direct flow
(especially over control surfaces). Their vortex generators were based on
aircraft designs and they used a hang glider airspeed indicator on a pole to
measure the boundary layer thickness across the roof. They made the vortex
generators two inches tall to be conservative (the boundary layer was
approximately one inch thick and a rule of thumb is to make the generators 1.5
time the boundary layer thickness). They didn't see an improvement in coast
down times, but the tufts did appear a little better behaved with the vortex
generators. They believe the turn at the back of the roof may be too sharp to
permit attached flow. They also noted that much of the clean wing flow
appeared to be coming from around the sides of the car.
Dan Jones
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Drag reduction by riblets
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http://torroja.dmt.upm.es/pubs/2011/rgm_jj_philtrans11.pdf
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its hard to make sense of them runs. appears it started as a stock bike in the first run and last run had open mufflers, race ecu, 50mm stacks, power commander. no two runs appear to be the same configuration of parts. unless im missing something but i dont see how they could make any conclusion how much the dimples helped or hurt.
i never investigated the dimples on goflballs but i thought it just somehow reduced the drag and there for the ball flew further. perhaps reducing the surface friction. i dont know if a intake mouth would work on the same principles but maybe so
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i found this which explains why the dimple ball goes farther. in simple terms i guess it just reduces the drag , atleast to a certain speed then maybe the drag increases agian. hell i dont really understand all this chit but thats what it looks like. maybe the dimples on the air horns make a turbulent boundry layer ? thats the only thing i can figure. in them dyno graphs it appears to me they changed several things each run. unless im missing something. i would like to see nothing changed other than the air horns with/without dimples
check out from about half way where it says flight of the ball in air. http://www.physics.hku.hk/~phys0607/lectures/chap05.html