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Liquid
Wimdy

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Itās not just that the leaves will break down on their own (and enrich the soil while theyāre at it!). During the winter, all sorts of insects use leaf litter for shelter, and theyāre the first food available to larvae in early spring. Leaves also insulate the plants under them during the winter, which is important if youāre in an area prone to frost heaving.
One of the best thing you can do for native pollinators in your area is Leave the Leaves!
My mom stopped raking her leaves when she found out about this but her neighbor used his leaf blower to clear out her yard the first year she decided to try. So she started posting a Leave the Leaves sign in the yard each year with an explanation about why itās good and two winters later only one house still rakes their lawn each year.
Weāve seen a dramatic increase in the biodiversity in the neighborhood since. We have birds that we havenāt seen since we moved into the city from living rurally and those birds are starting to nest in the trees and gardens in spring. The swallows and bats are back at night. The single woodpecker we would only occasionally see visits daily and even has a friend that has joined it. We have more squirrels and rabbits and shockingly fewer moles and voles. We heard an owl outside last fall.
Leave the leaves indeed.
You guys liked my firefly post?
Leave your leaves!!!
Outraged by the Jan. 6 Capitol riot, a wilderness survival trainer spent years undercover climbing the ranks of right-wing militias. He didn
Outraged by the Jan. 6 Capitol riot, a wilderness survival trainer spent years undercover climbing the ranks of right-wing militias. He didnāt tell police or the FBI. He didnāt tell family or friends. The one person he told was a ProPublica reporter.
This is such a wild story like holy shit dude
ālet it be known that homosexuals are not cowardsā š¤ āa faggot is doing this to themā
Holy fuck I just read this whole damn article and it is G R I P P I N G. I strongly recommend giving it a read if you get a chance
You should read this.
m1=116.9 m2=71.1 m3=46.9 (solar masses) v1x=-1.583 v1y=0.51 v2x=-3.148 v2y=-1.294 v3x=3.912 v3y=-0.717 (km/s) x1=-27.0 y1=18.0 x2=6.0 y2=-34.0 x3=-30.0 y3=-13.0 (AU from center) Music: Prelude in E Minor ā Chopin
stooges three

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King of the table
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This is so fucking funny
good morning
I think I have an infestation
it's been a long week... pass the yaoi!
every time i see this thumbnail i want to hatewatch the video but i. i refrain.
AH YES. LAMINAR FLOW. THE FLOW CONDITION WHICH OCCURS AT LOW REYNOLDS NUMBERS. A THING WHICH YOU FAMOUSLY WANT IN A ROCKET ENGINE.
i've watched a few of this guy's videos and they all make me really mad because he has such an incredibly vibes-based understanding of engineering. literally the peak "maker youtuber" type of guy where he has access to all sorts of fancy manufacturing toys but only designs via trial and error. the type of guy who thinks that conceptual understandings are all that matter and the math is just boring details that you don't have to worry about.

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Iām not very familiar with engineering so Iām curious as to just why a laminar flow rocket engine is such a terrible idea. You donāt have to explain, but if you wanted to give an explanation Iād be interested in hearing!
okay hi anon idk what your base of knowledge is with any fluid mechanics or rocketry stuff so I'm writing this for a very general audience with no experience. hopefully i won't xkcd average familiarity myself.
Part 1 LAMINAR VS TURBULENT FLOW AND WHAT THE HELL IS A BOUNDARY LAYER
Laminar flow is a flow condition that describes how a fluid is moving in relation to a surface. It means all the fluid is moving more or less with the bulk flow, and there's no rapid changes in velocity anywhere. The flow speed changes gradually from zero at whatever surface the fluid is moving over¹, to the free-stream velocity at some distance away from the surface.
Through a pipe, it looks roughly like this. Parallel streamlines all moving in one direction all niceys. The area between the surface and the free-stream region is the boundary layer, and it's the primary source of energy loss in fluid systems. Laminar flow occurs at relatively low flow velocities² along very smooth surfaces. If you try to push the fluid too fast, you start getting turbulence.
Turbulent flow is when a bunch of tiny vortices start forming along the molecular-scale imperfections on a surface. You get a region of flow where the fluid is swirling and disorganized, full of tiny eddies which change very dynamically from instant to instant.
It's usually sketched out looking something like this, but in actuality is it's fairly fractal; you can observe vortices at basically every scale in a turbulent flow. From how disordered and messy the flow is, you might think that it's less "efficient". However, this isn't actually the case! With about a heap of "it depends", turbulent flow tends to have less energy loss than laminar flow!
As it turns out, those tiny little vortices are really efficient at transferring velocity between regions of the fluid. You still have to have a boundary layer between the surface and the free-stream velocity, but the velocity can change much more easily without fluid getting dragged by viscous forces. This means the boundary layers in a turbulent flow are typically much thinner, and this kind of flow is fairly desirable in a lot of engineering applications.
Laminar flow is definitely used in a few applications. For example, wind tunnels can't have any turbulence over the test section because it'll mess up your experiment. However, the main reason laminar flow has such a grasp on the engineeringtuber zeitgeist is because it looks pretty. And it does look pretty! You can make a hose that spits out a glassy, static-looking stream off water that's perfectly clear and looks cool as hell in a youtube thumbnail.
¹ Zero velocity on a surface is called a "no slip condition", and it's a pretty important thing in fluid mechanics. Every surface will have some amount of adhesion (stickiness) with the fluid, so it can't have any velocity directly at the interface.
² Actually the quantity we're concerned with here is called the Reynolds number, not velocity. The Reynolds number adjusts the flow speed for the viscosity of the fluid, its density, and the size of the object its interacting with. This lets us compare flows in very different substances, like water and air.
Part 2 HOW DOES A ROCKET ENGINE WORK ACTUALLY
A rocket engine is, fundamentally, a device for turning very angry chemicals into a high speed stream of gas.
An injector injects a liquid fuel and oxidizer³ into the combustion chamber, which burn violently producing a bunch of hot, high pressure gas. The propellants have to be separate until they enter the engine (otherwise what you have is a bomb)ā“, so the purpose of the injector is to mix the propellants together while they're inside the combustion chamber. There's a number of different ways injector designs accomplish this, but most of them involve smashing together two streams going in opposite directions. This creates a very fine mist of propellant which burns very quickly. If a rocket engine has poor mixing, the propellants will burn quite slowly, and much of the combustion will occur outside of the engine. In the best case, this results in a loss of efficiency, in the worst case, it'll result in the combustion instability and the rocket flaming out altogether.
As the high temperature, high pressure combustion products travel down the rocket engine, the combustion chamber starts to constrict. The constriction causes the flow speed to increase, like putting your finger on the nozzle of a garden hose. The flow speed keeps increasing until it reaches the speed of sound, and at that point it can't be accelerated any faster. This condition is called choked flow,āµ and it occurs in the narrowest part of the nozzle, called the throat.
In order to accelerate the exhaust stream to supersonic speeds, the flow is now expanded instead of constricted, in a part of the rocket engine called the nozzle. In supersonic flow regimes, the Bernoulli's principle you're familiar with (or maybe not) flips, and flow gets faster when its expanded.ā¶ By the time it reaches the end of the nozzle, it's going many times the speed of sound. The average velocity of the exhaust is what determines the efficiency of your rocket engine, so this is optimized to be as fast as possible.
³ Not every rocket engine uses a liquid fuel and a liquid oxidizer, but that's not important to understanding here. Anything you can stick in a pressure vessel and burn can be a rocket fuel.
ā“ Monopropellants are a single liquid sitting in the tank, but they usually require some catalyst to burn so they don't explode. And they still do sometimes.
āµ You can think of the speed of sound in a gas as the speed at which "information" can travel through a gas, since pressure waves like sound are the only way one region of gas can be effected by neighboring regions. As the flow travels through the constriction, the gas has to be pushed along by the pressure from the gas behind it. When you reach the speed of sound, that pressure wave can't move any faster than the gas, so the upstream gas can't accelerate the downstream gas.
ā¶ The math here is actually quite helpful! Without going into too much detail, the energy of a gas flow is proportional 1+ĪM², where Ī is a constant related to the molecular properties of the gas, and M is the speed of the fluid divided by the speed of sound, aka the Mach number. This term shows up in a lot of gas dynamics equations, and since it's a quadratic term with two roots, basically every equation has two solutions: a supersonic one and a subsonic one. The two solutions tend to have flipped behavior, so a lot of stuff in supersonic flows is backwards from how it works in subsonic flows.
Part 3 THE PUNCHLINE
Remember when I said laminar flow requires smooth, symmetrical flow? As you might of noticed, at no point is that the flow condition in a rocket engine! In fact, every one of those components I discussed benefits from turbulent flow!
The injector is, perhaps, the most obvious. Chaotic, swirly flows are ideal for mixing propellants as fast as possible. You need that turbulent small scale motion to drive that mixing, otherwise you're relying on diffusionā· which is very slow. This benefits the combustion chamber as well, as the turbulence more evenly distributes the temperature and prevents hot spots. Uneven combustion can greatly stress the structure of the engine, and cause really undesirable combustion instability.
As the flow travels through the choke and the nozzle, it's moving very very fast. Laminar boundary layers in supersonic flows aren't exactly feasible since you're just moving so damn fast, but as I mentioned earlier, they're not even more efficient. The huge boundary layers you get in laminar flow slow down the fluid a lot, which is really not something you want in a rocket engine. Any energy loss is a loss in efficiency, so thin, turbulent boundary layers are fairly desirable.
A "laminar flow rocket engine" is an idea that just sounds so absurd to anyone who has spent actual time doing aerospace engineering. And if you look at it, it's not even really shaped like a rocket engine? There's no expansion nozzle! The flow is limited to Mach 1 at the most, and there's no way its even getting that fast if you're going for laminar flow. And what the fuck is that injector???? There's so much surface area! That'll result in huge pressure losses and it'll melt if you try to operate at any type of substantial temperature. It's just. Bizarre all around.
ā· If you've ever watched tea or dye or something slowly spread itself through a container of water without mixing it, that's diffusion. It does not happen on rocket engine timescales.
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Starbirds also had some evasive maneuvers concerning their early accessā¦