If I have a pipe and want to calculate a pressure drop. Let's just say I know the following...

fluid density
fluid viscosity
length of pipe
avg roughness of pipe interior
avg fluid velocity
pressure at pipe entrance

You're saying that you'd use something besides Bernoulli's equation to solve this because it doesn't apply to "pipes"?

I have to see this new equation. Please feel free to show your work.

-Mindgame

 

Oh god!

I like the new sig BTW

Bret

 

Food for thought, why is it that the gas is cooling so rapidly as to be cool enough to the touch at the end of the exhaust system. Expansion. The exhaust pulses are not a constant like that of of cetrifigul pump, they are pulses shoved down the exhaust system. Once the exhaust valve opens, the piston is still at the low end, the pressure in the cylinder escapes by expansion into the lower pressure area of the exhaust. Then the piston comes and pushes the rest of the gas out.
The whole time this is happeneing, the gases are expanding and the temperature is dropping. If you were to fire the piston only once, the gases would eventually find there way out the exhaust system.
While this expansion is taking place, the volume is increasing. The key to a well tuned exhaust system is to keep the velocity of the exhaust pulse moving as fast as it can. Since the pulse is constantly expanding, the needs of the exhaust system should be expanding also. To big and the pulse slows its forward momentum, to small and the natural expansion of the pulse will be restricted resulting in a slower exit of the whole pulse.
PV=RT works well in a closed system, this sytem is open to atmosphere so there are other things to consider. The pressure of the pulse drops quickly when the valve opens so temperature drops, but we now need to move that pulse down the line.

 

Thanks Bret.

Just a heads up for whoever might be interested...

Mr. Drucker passed away earlier this month at 95 years of age which had me thinking about some of the things he's written over the years. Thought putting one of my favorite quotes from him might get people searching a little. Extremely respectable and definitely worth a good read. If you're in management... he's a must read AFAIC.

All in all, that quote holds a lot of universal truths doesn't it?

Now back to your regularly scheduled programming........

-Mindgame

 

When I was getting my degree in Aeronautical Engineering from Purdue, I learned that the primary source of lift on a wing, or your hand, is from the Newtonian reaction forces. Bernoulli lift is a minor contributor.

Guess we can't discuss it.

 

The Bernoulli principle applies to a pipe. As velocity increases, pressure perpendicular to flow drops. A venturi is just a reduction in area to increase velocity, and reduce pressure even farther.

Steve.... we can continue the discussion...

To give Steve's point a bit of emphasis, ask yourself this question. If the airfoil shape and the resulting lift relies Bernoulli's principle, how can an airplane fly upside down?

 

Mother nature is the best math-a-magician the world has ever seen

I just read the first post or two and made that comment. It wasn't intended to come down on your post and if it appeared to, I apologize.

I, in general, find many people trying to calculate fluid dynamics with the same mind set as newtonian physics. Linear, single equation, "sum of the surface area" type attitudes. "There is a 3'' section of the otherwise 6'' diameter tube so it is like having a 3'' tube the whole way" type stuff. Volume vs Mass air flow and the corrilation/application of it is a big one. You seem to have a fair amount of experience with customers so I'm sure you've seen your share of enthusiasm and lack thereof with flow numbers. But alas, the world is full of misunderstandings. Im sure I am as misinformed in another relm of expertise as I see others in this area.


Pretty amazing how quickly she calculates integrals and derivatives isn't it?
...to think, they say girls aren't good at math/engineering. They spawned it!

Its kind of funny when my friends and I sit around talking about our experiences. Very often it ends with someone making a comment like "let me tell you- PV DEFINATELY equals MRT, they weren't kidding around!", "Conservation of energy! not a joke." The best ones always end with "so I was like 'No!...... sum of the forces.... think about it. ..no...no...God gave you a brain, use it.... sum of the forces' and then bam!" But NOTHING beats a "Yeah, Physics ALWAYS wins" to end the story

One of my friends works for Bendix, another his own speed shop/university test cell and some other high powered industries. All seem to have backgrounds in heavy duty trucking industry. Makes for some very interesting and diversified stories.

Despite areas of practice, we are all in agreement that we all should have taken more from our undergraduate classes. We were there, why the hell not learn it? Those "You'll never use this in the real world/ You'll only use 3% of this in the real world" people are cancers to our education and should be permanently banned from every university campus. Its amazing how I only use the stuff I learned well, isn't it

But enough about me, how about them Bernoulli characters! I heard those brothers were pretty smart.

 

To a small extent, Bernoulli (conservation of energy in fluids) plays a part but I'm in agreement that the conservation of momentum and Newton's 3rd law are of primary importance.

Anyone remember reading about Einstein's aerofoil design? A little too much Bernoulli and not enough Newton.

The right angle of attack will lift an inverted airplane too.

-Mindgame

 

Thoughts:

I'll admit to NOT being an aero engineer, just an ME, but I was fortunate enough to fly a number of aircraft inverted, some at fairly high speeds thanks to "Uncle". If the airfoil was symmetrical or close to it, it took about the same angle of attack (AOA) to fly inverted as upright. Look at some pics of Blue Angels or T'Birds with lead flying inverted and wingman upright. If the airfoils weren't symmetrical, it took more AOA inverted. Newton or Bernoulli?

Flying chase a few tens of feet off the wing of another aircraft, especially when practicing stalls or high-g turns, both of which demand lots of lift from a given indicated airspeed (AKA molecules/second passing/hitting the wing), one wonders why the Newtonian reaction gives up at maybe 30-35 deg AOA. Should it not be even stronger there as you expose more of the bottom of the airfoil to the impacting molecules than you did with 2-3 degrees AOA? Also as you camber the wing with leading edge and/or trailing edge flaps, you can fly slower (or pull more gs at higher speed) without increasing AOA. In this case more top surface is exposed to impacing molecules. Doesn't that go counter to Newtonian reaction forces?

I'm not denying the Newtonian reaction forces, but the Bernoulli stuff seems to explain more accurately my obsevations. When you deploy speed brakes or dive brakes, Newtonian reaction is most definitely at work.

Just how does a propellor generate thrust? How does the underbody shape of a downforce racecar generate downforce by Newtonian reaction? If one flattens the underbody without changing the topside, the downforce lessens drastically. Bernoulli or Newton?

I don't pretend to know all the answers, but then again, all we can do is try to explain how Mother Nature works without changing how she works. If I may quote myself this once,

"Too many folks get hung up on the math without having the gut understanding of what's really going on. Math is a tool used to explain things, but it doesn't change how things are. Mother Nature isn't a mathematician she's a practicing physicist, and one tough broad." - OldSStroker

Not trying to be a Richard here, in spite of how it may read.

Jon

 

Your quote seems to imply that you will take your SOP ruminations over math and physics, in which case you are right there is no point in a discussion.

For the rest, here's a relevant page:
http://mb-soft.com/public2/lift.html

I've been around pilots and airplanes all my life, and I've observed that being a good pilot doesn't necessarily bring with it any understanding of the physics of flight.

This isn't necessarily a bad thing. A friend who was a combat flight instructor in the Navy told me that the guys who understood something about why planes fly were usually the worst pilots.

 

my head hurts....

woah

 

I thought Bernulli and Newton both co-existed.
While bernuilli is doing his thing, Newton is doing his.

F is equal to MA, and that whole equation of bernulli's is also happening.

I never realized it was one or the other

 

I don't think anyone's saying they don't coexist. It's all a matter of, which takes precedence?.

I mentioned the conservation of momentum because it's going to play a part. Air flowing over an airfoil, whether that surface be concave or convex, will follow the curvature. If airflow follows downwards and air momentum is downwards then there will be an equal upward momentum (reaction). Call it "lift" if you want.

At the front of the wing the air is seperated and somewhere near the peak of the "hump" the streamlines crowd together creating a low pressure area. So there's Bernoulli. Ideal gas laws make Bernoulli difficult to apply, at least at my limited level of understanding, but I believe it still does to some extent.

Steve,

You being the aero expert here, would you care to answer some of Jon's questions? They're definitely valid as I see it.

I remember reading a few papers in college about spinning ***** written by physicist. After all was said and done I left the lessons completely confused. It became quite obvious to me, after looking at the illustrations showing a counter-clockwise rotation (overhead) curveball that moven towards 3rd base that the author had never thrown a curve ball or kicked a soccerball off center such to impart a spin. Same thing when I first read up on the subject of lift and drag. Lots of conflicting opinions.

-Mindgame

 

Since his is questions seem to be an argument against the claim that "Bernoulli doesn't exist" and nobody made such a claim, I figured no answers were needed.

The claim I have made is "You are wrong in saying that wing/hand lift is entirely or even primarily due to Bernoulli."

Plus I was trying to avoid totally hijacking this thread, but I guess it's too late for that...

It has been 15 years since I did any of this stuff so I would not dare try and explain things in any detail myself. The page I posted above gives answers to many of his questions. Most of his questions are phrased such that I bet you can get a lot of good hits in Google as well.

My short answers are:

This is a demonstration of Bernoulli lift, which is a part of the total lift. This scenario is discussed in the article I posted. Doesn't have any relevance to the original claim that the lift is entirely or even mostly due to Bernoulli.

Here I'm relying on the article I posted. According to it, at high AOA you lose Bernoulli lift due to flow separation. Again has no relevance to the original claim that the lift is entirely or even mostly due to Bernoulli.

I didn't study flaps and slats, but it seems like leading edge flaps are reducing Newtonian lift while increasing Bernoulli lift. Seems like trailing edge flaps would increase both. No relevance to the original claim that the lift is entirely or even mostly due to Bernoulli.

The same way a wing produces lift. That doesn't get us anywhere does it?

Doesn't seem like the underbody shape could generate a Newtonian downforce. No relevance to the original claim that the lift on a hand/wing is entirely or even mostly due to Bernoulli.

Sounds like Bernoulli to me. And sounds like another completely irrelevant question.



The original claim, in case anybody got lost in all the red herring:
For those that don't want to read the article, here's the most important part wrt the above claim:

For a 747 at 33000 ft, 550 mph, 20o AOA:
Lift due to reaction forces: 489,000 lb
Lift due to Bernoulli effect: 103,000 lb

And from the summary:

 

Steve,

No personal offense to you is intended. I read/studied your link. I also read this by it's author:

http://mb-soft.com/public/publicme.html

I highly recommend that other readers of this thread take the time to read both. It is important to consider the source of what we place our faith and belief in. Well, it is to me anyway.

Steve, I would suggest that observing pilots while not flying with them in edge-of-the envelope maneuvers may not be the best way to determine their understanding of the physics of flight. Birds don't take aero, but they do a pretty good job or they perish.I think they have a gut feeling for the physics of flight.

I was a USAF fighter pilot flight instructor. Part of my job was to teach other pilots to be flight instructors. My observations of many pilots who went through our courses did not necessarily agree with your friend, the Navy instructor. I'm sure he and I could have an interesting discussion over a couple of beers.

My observation of hundreds of pilots I flew with or instructed was that the person's background in aeronautics ("guys who understood something about why planes fly") wasn't what determined how good they were as pilots. It was a combination of things, Job One being the ability to think, and Job Two being the ability to "juggle more than one ball at a time" (multitask in PC-speak). Flying, like creating art, isn't in your hands or the paint or the keyboard...it's in you head.

Actually, I only took exceptions to "Public Services' Author" ideas of how the world works. His is one opinion, but there are others. Obviously I put more credence in some of the others. I haven't yet accepted this nameless individual as the supreme authority of "how the world works" (HTWW). Neither should anyone blindly accept my view of HTWW without substantitive agreement from folks more knowledgable than I. Most of my views of HTWW came from studying others views as well as lots of observation. Newton is one of my favorites. Orville and Wilber are two others. C. Johnson is another, as is Joe Katz, and a bunch of others I believe know a lot about HTWW.

Steve, you haven't convinced me that "Public Services' Author" has a better handle on things than a lot of other folks' collective thoughts. It appears you believe him, which is your choice.

FWIW, my "SOP ruminations"(cud chewing?) often came with 4-6 gs squashing my seat of the pants. I suppose that could influence one. I've watched the very stiff wings of a 38 ft span fighter curl up 6-8 inches at the wing tip at 450 mph and 5 gs on a 30,000 lb aircraft (150,000 lbs lift) with a fog of condensation covering most of the top of the wing, and seen the same wing at an AOA of about 8-10 degrees less in straight and level flight produce only a enough lift (30,000 lbs) to hold up the aircraft.

I uderstand Newtonian physics, at least at the ME level, and I understand enough trig to figure how much area of the wing was presented to the relative wind in both cases. I can't find 5 times or even 2 times as much area for Newtonian reaction. My conclusion about the condensation was that there was a LOT less air pressure above the wing than below it. You've see the Angels or T'Birds, I'm pretty sure. You've observed the same thing with F-18s or F-16s, haven't you? If you haven't you should. It's a blast, and may make you think again about why and HTWW.

Oh yeah, my point of observation was from approximately 15 feet behind and 5 feet below the tailpipe of the aircraft in front of me. That is something one doesn't take lightly nor forget. Being part of the experiment is actually better than just observing it, IMO, which is NEVER humble.

Anyhoo, it matters little how you or I explain Ma Nature; Nature exists and functions in her own way. Typical woman! Men (of which I'm one) just think we run the world.

Back to the topic, perhaps?