Strangest Types of Rocket Nozzles

a few months ago i wanted to make shock diamonds which are inefficiencies that show up in the supersonic exhaust of rocket engines now to do this i wanted to make a really cheap liquid fuel rocket engine and it worked about as well as you could expect a plaster of paris and pvc liquid fuel rocket engine to work what ended up working super well was this super simple wish rocket with a 3d printed plastic nozzle on the end of it so in this video i'm going to use this simple setup to show you some of the strangest rocket nozzles that i've ever seen plus talk about how they work and how i tried to optimize them because i mean you don't want to be that guy with the sub-optimal wish rocket instead of just trying to throw you into the math and rocket science of all of this i'm going to try to use the analogy that i used in the last rocket video to explain the concepts of how these rocket engines work starting with a recap we have a street with a building on it and both are full of people a guy walks into the building with a pineapple pizza and let's give him a tub of ranch this time to keep it interesting and says not to get political but and then naturally everybody runs towards the door as they get closer and closer to the door they're able to move faster and faster until the guy in the door frame is able to move faster than anyone else in the room but as soon as he hits the street he starts bumping into people and going off in a random direction but let's say that's not enough they want to get as far away as fast as possible from the political pineapple ranch pizza guy so we can give them this weird hallway that gives them more and more space to get up to a running speed and gets them all going in the same direction now that pretty much covers the analogy as far as i took it last time but sadly even the best analogy tends to fall apart if it's carried too far so anyway to continue with this analogy this cone-shaped hallway isn't our only option for similar results we could slice this whole thing in half and turn it inside out and we'd end up with a spike or better known as an arrow spike arrow spikes are special because the people leaving the room push against both the spike and the people out on the street until they reach an equilibrium this way whether the crowd outside is really densely packed or really far apart the people leaving the building are as spread out as they need to be to keep running as fast as possible by the time they reach the end of this bike dropping the analogy for a second the tip of the spike usually isn't practical to maintain so they just lop it off now that would you think reduced the efficiency a lot but that gap is filled with exhaust or trapped atmosphere that's recirculating in that little spike region and sometimes they even pump in exhaust from the turbo machinery which is used to feed the engine oxidizer and fuel this little spike made out of air is where we got the name aerospike and it helps maintain efficiencies even when the spike is truncated alright there's one more strange nozzle i want to talk about today and that's going to be splitting this aerospike in half and switching the sides again now at this point this is reminding me less of rocketry and more of translate telephone where you throw a sentence into google translate you flop it around a bunch between a bunch of different languages and then what you end up with when you come back to english is just total nonsense but while this does look like a garbled mess it is a real nozzle known as an expansion deflection nozzle an expansion deflection nozzle works a lot like an aerospike in that it compensates for the conditions outside of the room but instead of being pressed inwards towards a spike the exhaust is pressed outwards towards a more conventional conical or bell nozzle but it can only compensate for those conditions so long as it doesn't expand so far that the wake closes at that point it would act more like a traditional conical or bell nozzle meaning that it can't compensate for those conditions outside the nozzle anymore all right let's take a break from the analogies for just a second and talk about designing and building the test stand first of all it needs to be safer because last time i was using a welding glove and a barbecue igniter which isn't the safest thing in the world and i also need a spot to mount an arduino and a load cell so i can take thrust measurements from the rockets [Music] [Music] [Applause] [Music] [Applause] [Music] [Applause] [Music] [Applause] [Music] with that done we can move on to everybody's favorite the math and the design of these rocket novels to start let's put some terms and some concepts over the analogy that we used earlier let's start with two of the more simple but also very important properties that we have to describe the people in and outside of the room first up being pressure which is how hard each person pushes on either the people around them or the walls and then temperature which is how energetically they move about while doing so next up is the heat capacity ratio or gamma entire videos could be dedicated to heat capacity ratio and all the intricacies of it but for the purposes of this video it might as well be a magic number that describes how pressure and temperature changes for each person as they move through the room speaking of the room let's break down each region of the rocket analogy the room itself is the combustion chamber which has a doorway which is the throat that leads to the nozzle which is the hallway which has an exit which is well the exit which leads to the street which has two main components being the exhaust the people that came from inside the room and then the people that were always out on the street or the atmospheric ambient air before i can design the physical nozzle i need to know the throat area and the exit area first let's look at what we do know the chamber pressure i'm going to set at 80 psi because any more than that i'd be a little bit worried that with the heat and whatnot that the 2-liter bottle would just pop and then the pressure at the exit if we designed this right will be about atmospheric pressure and that that's it actually that's all we know so now i have two options i could try to teach myself some thermochemistry which no or i could hand this off to someone smarter than me so i need to give some important parameters like chamber pressure fuel oxidizer and oxidizer fuel ratio to either a chemical engineer or the much much much cheaper option which is nasa's cea program which will spit out the same numbers for free so now we have a lot of parameters and a couple equations which i'll link in the description but i have this mass flow rate equation which i can finagle into a throat area equation which is made up of variables that i can either calculate or i already have from nasa's cea and then the mass flow rate which i can measure first up is the specific gas constant which i'm a little surprised that i couldn't find on cea which it's either there and i'm dumb or they just didn't calculate it all the way for you but it's just r bar which is the universal gas constant divided by the molar mass of the exhaust next we could calculate the temperature and pressure at the throat but nasa's cea already does that for us so with that we already have everything we need to calculate the area of the throat from there we could find all the conditions at the exit of the nozzle to find the exit area or we could just use the expansion ratio calculated by nasa's cea i mean why even design rocket engines if you could just have a computer that does it for you all of that math was for this little hole this is the area of the throat of our nozzle and if it's not just right to bring the exhaust up to mach 1 then the rocket won't function properly this is about 20 square millimeters but on nasa's web page for bush rockets they recommend 3 8 of an inch this is probably to keep you from blowing up a 2 liter bottle but let's test these and see how they do now that we know that the throat of the rocket is working let me explain everything i know about optimizing aero spikes and expansion deflection nozzles nothing i don't know anything about optimizing those engines but here's what i'm going to do i'm going to hold the throat areas constant across all of the nozzles and i'm going to use lessons that i've learned from optimizing conical nozzles and apply them best i can to the geometries that i've laid out in the analogy so in fusion 360 i whipped up a bell nozzle a toroidal aerospike a linear aerospike and an expansion deflection nozzle and the two different kinds of aero spikes got me thinking if there's a circular bell nozzle why not a linear one so i made what i'm calling a cowbell nozzle that's probably just gonna tear itself apart and while i was designing things that were probably just going to blow up i designed a triangular aerospike and a square arrow spike along with a nozzle that i'm hoping will spin the exhaust a lot like the fuel injector that i made in a previous video and finally i'll also be testing the linear and the toroidal aerospike at 0 50 75 and 100 truncated with the nozzles printed it's finally time to test them and clearly we'll be outside to do that because it wouldn't really be safe indoors [Music] anyway like i was saying i don't see any real issue with testing this indoors as long as i'm in a spot with good ventilation behind a barrier wearing eye protection and hearing protection do [Music] [Music] do [Music] foreign the first thing that i noticed is that we're still making shock diamonds which isn't all that surprising because the nozzles would have to be all but perfect not to now what i did find surprising was that the swirl nozzle first of all didn't just explode but it also had shock diamonds meaning that that spinning exhaust was also supersonic i was also super surprised to see shock diamonds and the cowbell nozzle even though it had less thrust than just a cap with a hole in it with the toroidal arrow spikes we can see very uniform exhaust with no shock diamonds plus in the 50 truncated version we can see a dark void that makes up the arrow of the arrow spike and a boundary or a shear layer where that hot fast-moving exhaust is shearing past the slow-moving air in the room but as we start truncating the spike past 75 percent we start seeing a single shock diamond along with irregular flow and a loss of thrust meanwhile the triangular and the square arrow spike seemed to work great for something i just made up and then i must have done something terribly wrong while designing the expansion deflection nozzle because it's almost like the wake closed and then it got crushed in by the atmosphere as soon as it leaves the nozzle and trying to fix it i basically just made it want to explode overall there was a large variation of thrust for each nozzle because it mostly depended on the mixture of fuel and air and how well it burned well anyway it is time to finally fly these things and i've got to say this might be my best work of engineering yet [Music] [Applause] [Music] now [Music] [Music] so [Music] [Music] [Music] [Music] with the variations in burn time it's hard to declare a real winner here but on average a cap with the throat area that we calculated can produce about 10 percent more thrust than the nasa recommended size and when we make a nozzle that can expand from that throat we get about 10 percent more with only a slight increase in the chance of it exploding speaking of explosions you should never mess around with this unless you're an adult and you're willing to take responsibility for your own safety otherwise you could lose skin privileges pretty quickly now there's more burning hot dogs in just a second but i wanted to remind you that if you like this video just do everything that makes the algorithm like it too and subscribe if you want to see more engineering videos specifically the next one will probably be on robotics and thank you for watching [Music] [Music] you

Channel: Sciencish

Views: 248,574

Rating: 4.9358821 out of 5

Keywords: Sciencish, Scienceish, Science-ish, Aerospike, Rocket Engine, Rocket, Nozzle types, Airospike, Whoosh Rocket, woosh rocket, 3D printing

Id: quWKqcBXUjo

Length: 16min 58sec (1018 seconds)

Published: Fri Feb 26 2021