Supersonic nozzle simulation in Ansys Fluent - part 1

[@gabrielflcsantos]

Hello Professor, This is a really nice simulation. Did you use Excell to generate the MOC values? It would be nice to have a video about the MOC too. Thanks, miss UNB. :)

[@shravanmishra4429]

Many many thanks. What is NPR(nozzle pressure ratio)? and What is NPR in this simulation?

[@kunalpansari6538]

How we can see the normal shock in your tutorial

[@chemicalpropulsionlaborato499]

This video shows the flow close to isentropic (without a normal shockwave), so it could be validated with a simple quasi-one-dimensional analytical model. If you are interested to obtain a normal shockwave please create appropriate flow conditions reducing chamber pressure or increasing exit pressure.

[@kunalpansari6538]

@@chemicalpropulsionlaborato499 can you please provide the geometry and the boundary conditions of convergent divergent nozzle

[@chemicalpropulsionlaborato499]

@@kunalpansari6538 Here you go: 1 1 0 11.61693 0 1 2 3.84016 11.61693 0 1 3 4.38788 11.61198 0 1 4 4.93543 11.59715 0 1 5 5.48262 11.57243 0 1 6 6.02928 11.53784 0 1 7 6.57522 11.49339 0 1 8 7.12028 11.43908 0 1 9 7.66426 11.37495 0 1 10 8.20699 11.301 0 1 11 8.74831 11.21727 0 1 12 9.28802 11.12378 0 1 13 9.82595 11.02056 0 1 14 10.36194 10.90764 0 1 15 10.8958 10.78507 0 1 16 11.42736 10.65287 0 1 17 11.95644 10.5111 0 1 18 12.48288 10.35981 0 1 19 13.00651 10.19903 0 1 20 13.52714 10.02883 0 1 21 14.04462 9.84925 0 1 22 14.55877 9.66036 0 1 23 15.06942 9.46222 0 1 24 15.57642 9.25489 0 1 25 16.07959 9.03844 0 1 26 16.57877 8.81295 0 1 27 17.0738 8.57847 0 1 28 17.56451 8.3351 0 1 29 18.05075 8.08291 0 1 30 18.53236 7.82198 0 1 31 19.00918 7.5524 0 1 32 26.04915 3.48787 0 1 33 26.11762 3.44916 0 1 34 26.18677 3.41169 0 1 35 26.25659 3.37548 0 1 36 26.32706 3.34053 0 1 37 26.39814 3.30687 0 1 38 26.46982 3.27449 0 1 39 26.54207 3.2434 0 1 40 26.61487 3.21363 0 1 41 26.6882 3.18518 0 1 42 26.76203 3.15806 0 1 43 26.83633 3.13227 0 1 44 26.91109 3.10783 0 1 45 26.98628 3.08475 0 1 46 27.06188 3.06302 0 1 47 27.13785 3.04266 0 1 48 27.21418 3.02368 0 1 49 27.29084 3.00608 0 1 50 27.3678 2.98987 0 1 51 27.44504 2.97504 0 1 52 27.52254 2.96162 0 1 53 27.60027 2.9496 0 1 54 27.67821 2.93898 0 1 55 27.75632 2.92977 0 1 56 27.83458 2.92197 0 1 57 27.91298 2.91559 0 1 58 27.99147 2.91062 0 1 59 28.07005 2.90707 0 1 60 28.14867 2.90494 0 1 61 28.22732 2.90423 0 1 62 28.26674 2.90493 0 1 63 28.28644 2.90581 0 1 64 28.30612 2.90703 0 1 65 28.32577 2.90861 0 1 66 28.34539 2.91053 0 1 67 28.36497 2.9128 0 1 68 28.38451 2.91542 0 1 69 28.404 2.91839 0 1 70 28.42344 2.9217 0 1 71 28.44281 2.92536 0 1 72 28.46211 2.92936 0 1 73 28.48135 2.93371 0 1 74 28.5005 2.93839 0 1 75 28.51956 2.94341 0 1 76 28.53853 2.94878 0 1 77 28.5574 2.95447 0 1 78 28.57617 2.96051 0 1 79 28.59483 2.96687 0 1 80 28.61338 2.97357 0 1 81 28.74912 3.02388 0 1 82 28.88487 3.07403 0 1 83 29.02062 3.12403 0 1 84 29.15636 3.17387 0 1 85 29.29211 3.22356 0 1 86 29.42786 3.27309 0 1 87 29.56361 3.32246 0 1 88 29.69935 3.37168 0 1 89 29.8351 3.42074 0 1 90 29.97085 3.46964 0 1 91 30.10659 3.51839 0 1 92 30.24234 3.56697 0 1 93 30.37809 3.6154 0 1 94 30.51384 3.66366 0 1 95 30.64958 3.71177 0 1 96 30.78533 3.75972 0 1 97 30.92108 3.8075 0 1 98 31.05683 3.85513 0 1 99 31.19257 3.90259 0 1 100 31.32832 3.94989 0 1 101 31.46407 3.99703 0 1 102 31.59981 4.04401 0 1 103 31.73556 4.09082 0 1 104 31.87131 4.13747 0 1 105 32.00706 4.18396 0 1 106 32.1428 4.23028 0 1 107 32.27855 4.27644 0 1 108 32.4143 4.32243 0 1 109 32.55004 4.36826 0 1 110 32.68579 4.41392 0 1 111 32.82154 4.45941 0 1 112 32.95729 4.50474 0 1 113 33.09303 4.5499 0 1 114 33.22878 4.59489 0 1 115 33.36453 4.63972 0 1 116 33.50027 4.68437 0 1 117 33.63602 4.72886 0 1 118 33.77177 4.77318 0 1 119 33.90752 4.81732 0 1 120 34.04326 4.8613 0 1 121 34.17901 4.90511 0 1 122 34.31476 4.94874 0 1 123 34.4505 4.99221 0 1 124 34.58625 5.0355 0 1 125 34.722 5.07861 0 1 126 34.85775 5.12156 0 1 127 34.99349 5.16433 0 1 128 35.12924 5.20693 0 1 129 35.26499 5.24935 0 1 130 35.40074 5.2916 0 1 131 35.53648 5.33367 0 1 132 35.67223 5.37557 0 1 133 35.80798 5.41729 0 1 134 35.94372 5.45883 0 1 135 36.07947 5.5002 0 1 136 36.21522 5.54139 0 1 137 36.35097 5.5824 0 1 138 36.48671 5.62323 0 1 139 36.62246 5.66388 0 1 140 36.75821 5.70436 0 1 141 36.89395 5.74465 0 1 142 37.0297 5.78477 0 1 143 37.16545 5.8247 0 1 144 37.3012 5.86444 0 1 145 37.43694 5.90401 0 1 146 37.57269 5.9434 0 1 147 37.70844 5.9826 0 1 148 37.84418 6.02162 0 1 149 37.97993 6.06045 0 1 150 38.11568 6.0991 0 1 151 38.25143 6.13757 0 1 152 38.38717 6.17585 0 1 153 38.52292 6.21394 0 1 154 38.65867 6.25185 0 1 155 38.79441 6.28957 0 1 156 38.93016 6.3271 0 1 157 39.06591 6.36444 0 1 158 39.20166 6.40159 0 1 159 39.3374 6.43856 0 1 160 39.47315 6.47533 0 1 161 39.6089 6.51192 0 1 162 39.74464 6.54831 0 1 163 39.88039 6.58452 0 1 164 40.01614 6.62053 0 1 165 40.15189 6.65635 0 1 166 40.28763 6.69197 0 1 167 40.42338 6.7274 0 1 168 40.55913 6.76264 0 1 169 40.69488 6.79768 0 1 170 40.83062 6.83253 0 1 171 40.96637 6.86718 0 1 172 41.10212 6.90164 0 1 173 41.23786 6.9359 0 1 174 41.37361 6.96996 0 1 175 41.50936 7.00382 0 1 176 41.64511 7.03748 0 1 177 41.78085 7.07095 0 1 178 41.80204 7.07616 0 2 1 0 0 0 2 2 0 11.61693 0 3 1 0 0 0 3 2 41.80204 0 0 4 1 41.80204 0 0 4 2 41.80204 7.07616 0

[@yunusemre-ur8fw]

@@chemicalpropulsionlaborato499 sir thanks a lot? i really wonder which point exactly is the starting one for the diverging section of the nozzle

[@unforgotable1]

Hi, i am having trouble in displaying mach contour. It is in data file quantities but after calculation it doesn't show up under velocity contour types. Thanks in advance.

[@MohamedSayed-re3il]

If I created a fluid domain with this nozzle, what would be the outlet, the end of the nozzle or the end of the fluid domain???

[@chemicalpropulsionlaborato499]

In this simulation, the end of the nozzle coincides with the end of the computational domain. So, it's the same line.

[@MohamedSayed-re3il]

@@chemicalpropulsionlaborato499 Thanks bro.

[@dhrumil7654]

How did u set gauge pressure?

[@chemicalpropulsionlaborato499]

in boundary conditions

[@khalidnazzal782]

Hi! Is this a bell nozzle?

[@chemicalpropulsionlaborato499]

Hello. Yes, the nozzle geometry was previously calculated by the method of characteristics.

[@khalidnazzal782]

@@chemicalpropulsionlaborato499 Many thanks for your prompt response

[@ianm1898]

hi, I face an unique case if I simulate a nozzle, it will converge with 500 iteration, but when I attach a long square behind it(2m x0,5 m), this will cause to divergen do you know why? I have mesh it with very small mesh and hexahedral shape(facesplit technic)

[@chemicalpropulsionlaborato499]

Hello. Thank you for your question. Simulation of the surroundings around the nozzle is different from just the nozzle simulation because it involves a relatively significant air volume with a small velocity. The convergence of such a simulation is usually very slow. I recommend making a volume of at least 25x25 diameters of the nozzle and put the "pressure outlet" boundary conditions with zero pressure gradient on the border.

[@fadetv360]

good day sir. What will I do if the material to be used in the simulation is not air, which is a potassium nitrate and dextrose mixture?

[@chemicalpropulsionlaborato499]

In this case, you need to simulate these propellants' combustion, or at least a mixture flow of the combustion products. I'm planning to make a video about this topic in the future.

[@fadetv360]

@@chemicalpropulsionlaborato499 Thank you sir. Noted

[@fadetv360]

@@chemicalpropulsionlaborato499 Is it okay to just use air as fluid, then change the properties in the references values using the properties of the potassium nitrate and dextrose mixture?

[@chemicalpropulsionlaborato499]

@@fadetv360 Unfortunately, no. The error will be significant.

[@fadetv360]

@@chemicalpropulsionlaborato499 okay then I'll wait for your video then. Thanks

[@sriramswain3864]

I will be glad if I could get the MOC code for getting both the chamber and nozzle size. can you get me please?

[@chemicalpropulsionlaborato499]

Hello. The code makes part of the intellectual property of my University and can't be provided, sorry.

[@danbalan998]

Helloo Professor! I have to design a supersonic nozzle for a supersonic wind tunnel for my bachelor degree. Can you recommend me a good tutorial or something? Is MOC the best option to do it?

[@chemicalpropulsionlaborato499]

Hello. Probably yes, the best way is to use the method of characteristics.

[@danbalan998]

Do you have any suggestion how to learn to do it?

[@chemicalpropulsionlaborato499]

@@danbalan998 JD Anderson in his book "Fundamentals of Aerodynamics" gives a perfect explanation about this method, and about supersonic wind tunnel design.

[@danbalan998]

@@chemicalpropulsionlaborato499 thank you!!

[@MohamedSayed-re3il]

Hi, you didn't put any value for pressure outlet, I guess you kept as 0. May I ask why you did this? Aren't you supposed to put the value of the pressure at the exit of the nozzle.

[@chemicalpropulsionlaborato499]

Thank you for asking, this question is important. The outlet pressure gauge is equal to 0 because the flow is expected to be supersonic everywhere, except a thin boundary layer. So, the flow characteristic lines are directed outside of the nozzle and the outlet pressure has no influence on the flow structure in the nozzle. In such flow configuration the ambient pressure is defined in the "Operating Conditions" tab in Fluent, but not by the gauge pressure value.

[@MohamedSayed-re3il]

@@chemicalpropulsionlaborato499 To be honest I am very confused. You have set the pressure at the exit of the nozzle to be 0, which means that the pressure at the exit of the nozzle much smaller than the ambient pressure (1atm), isn't this should generated a nozzle with overexpansion flow behaviour with flow separation and shock waves present in the nozzle? Although you haven't included a flow domain but I can see there is no any flow separation in your nozzle. How did this happen, because if the pressure at the exit of the nozzle much smaller than the ambient pressure, this should results in overexpansion flow.

[@chemicalpropulsionlaborato499]

@@MohamedSayed-re3il Probably, you did not understand the concept of the pressure gauge. It defines not absolute pressure, but a relative one. So, when you set 0 pressure gauge it means that you define a zero pressure gradient between the ambient pressure (defined in the "Operating Conditions" section) and the nozzle exit section. Is it more clear now?

[@MohamedSayed-re3il]

@@chemicalpropulsionlaborato499Not relly, I know guage pressure = absolute pressure - atmospheric pressure. However when we calculate the pressure at the exit of the nozzle using the equation of Pe/Pt= (1+( γ-1/2 )Me^2)(-γ/γ-1), the value found is it called guage pressure or absolute pressure?

[@MohamedSayed-re3il]

To be honest I have become more confused. You put your operating condition pressure to be 101325 pa which is 1 atm. I assumed you were simulating your nozzle at altitude of see level. If this the case, then operating conditions should be 0 because at see level guage pressure is zero. I said this because all pressure in fluent are only guage pressure.