Supersonic simulation of rocket for various Mach numbers

krihamm · January 24, 2018, 09:40

Hello,

I want to perform supersonic simulations on a rocket for velocities ranging from subsonic to Mach 10. The rocket in question is approximately 15 m high. The body consists of an ogive nose and cylindrical sections with different diameters. The largest cylindrical section has a diameter of approximately 1 m. Four fins are attached to the bottom of the rocket. An enclosure has been added around the geometry.

I have created the geometry and built a - in my opinion - satisfactory mesh. I am, however, unsure about what setup settings I should use. I have run a few simulations with the following setup:

Default domain
Fluid material: ideal gas
Reference pressure: 1 [atm]
Heat transfer: total energy
Turbulence: SST
Wall function: scaleable, High speed (compressible) wall heat transfer model

Inlet
Flow regime option: supersonic
Mass and momentum option: normal speed and pressure
Rel. static pressure: 0
Normal speed: [equivalent to the Mach number I want to simulate]
Turbulence option: medium
Heat transfer: static temperature, 25 C

Outlet
Flow regime option: subsonic
Mass and momentum pressure: average static pressure
Relative pressure: 0
Pres. profile blend: 0.05

Solver control
Advection scheme: high resolution
Turbulence numerics: first order
Interpolation scheme: velocity interpolation type, trilinear (advanced options)
Compressibility control, High speed numerics (advanced options)

Does this seem like a good setup for such simulations? Is there something I have missed or should change? I am relatively new to CFX, so any input is much appreciated!

//krihamm

ghorrocks · January 24, 2018, 17:48

The rule of thumb is that above Mach 5 the gas starts to dissociate and you get plasma becoming significant. CFX cannot model plasma. So I suspect you will not be able to accurately model up to Mach 10.

The setup of the simulation will depend on what you are trying to learn from the simulation. So what is the reason you are doing this simulation?

krihamm · January 25, 2018, 02:53

I want to obtain the drag coefficient and the lift coefficient of the rocket.

Would Fluent be a better solver for higher speeds, or is Fluent also limited to Mach 5?

Quote:

Originally Posted by ghorrocks

The rule of thumb is that above Mach 5 the gas starts to dissociate and you get plasma becoming significant. CFX cannot model plasma. So I suspect you will not be able to accurately model up to Mach 10.

The setup of the simulation will depend on what you are trying to learn from the simulation. So what is the reason you are doing this simulation?

Gert-Jan · January 25, 2018, 03:16

This is rocket sience. Go to the library, grab a good book and start reading about the basics.

CFX might work up to Mach 3. I am quite sure Fluent's pressure based solver will even be worse. But you could try their density based solver. Ask this in the other forum. Alternatively, contact to ANSYS. They might know.

ASCT · November 22, 2018, 10:22

Hi,

can I know if fluent solved the supersonic and hypersonic flows?

ghorrocks · November 23, 2018, 03:16

I don't know of any CFD solver which can handle hypersonic flows. But I have not looked either, so feel free to look for yourself.

ASCT · November 24, 2018, 14:41

Hi,

I was searching online and found this cfd solver named cfd++ which claims to be accurate for almost all flows including hypersonic flows. but there is no information about how to get it. you can give a shot

http://www.metacomptech.com/index.php/features/icfd

ghorrocks · November 25, 2018, 01:59

They have a validation case on their website which shows good agreement to a Ma=6 flow. This is on the borderline of Navier Stokes supersonic flows to Hypersonics so CFX might be OK here. I have not checked the detail of what physics CFD++ has to enable hypersonic flow. Caviat Emptor.

How do you get it? Clicking on "Request Info" on there website seems like a good guess....

Jiricbeng · December 4, 2018, 04:50

Hi there,

my experience is that Fluent is much more convinient than CFX for high speed external aerodynamics (subsonic to supersonic/hypersonic). I recommend performing these simulations in Fluent - you can use far-field boundary, you can use density based solver if desired and in addition Fluent was initially developed for external flows.

Moreover Fluent is capable to even manage one transient analysis with one setup, whereas CFX must be stopped and solver setup must be switched, especially if you want to create a transient run from subsonic to supersonic regime.

I spent some time trying to analyse supersonic flows in CFX but it was clear quite soon that compared to Fluent the CFX has got several disadvantages.

ghorrocks · December 4, 2018, 04:55

Agreed, the density based solver in Fluent is far superior than CFX's pressure based solver for supersonic flows. Not sure how it goes in hypersonics, however - but it will be better than a pressure based solver.

I don't understand your comment about Fluent managing "one transient analysis with one setup", or why CFX is different to Fluent for this point.

ASCT · December 4, 2018, 05:09

Hi, I have used both fluent and cfx extensively. In my personal experience and opinion.
shock formations in flow results to discontinuous Partial derivative equations and initially Ausm(adjective upstream segregation method) was specially developed to solve these type of equations.
more over in density based solver, the energy equation is solved along with conservation of mass and momentum equations. I don't know why but most of cfd engineers prefer solving energy equation along with conservation of mass and momentum equations when energy equation is involved. note: note that unlike density based solver, segregate solver and pressure based solver solves energy equation separately.

Jiricbeng · December 4, 2018, 08:08

Quote:

Originally Posted by ghorrocks

I don't understand your comment about Fluent managing "one transient analysis with one setup", or why CFX is different to Fluent for this point.

I mean in Fluent you apply Mach number, temperature and pressure on far-field and thats all. In CFX you must apply sub/supersonic regime. Fluent does not care. Therefore Fluent is capable to analyse a simulation including transient acceleration of the rocket (transient boundary conditions applied on far-field), e.g.

t=0s, Ma=0.2
t=20s, Ma=0.5
t=40s, Ma=1.2
t=60s, Ma=2.7
etc. In one transient run, without any interuption.

Note: Surprisingly, in Fluent I have better experience with Pressure based solver pressure-velocity coupled than with Density based solver even for supersonic cases.

ghorrocks · December 4, 2018, 17:01

I suspect the accelerating rocket use case has a quite limited user base. I don't think that will be a limitation for many users

January 24, 2018, 09:40	Supersonic simulation of rocket for various Mach numbers	#1
krihamm New Member Join Date: Nov 2017 Posts: 27 Rep Power: 8	Hello, I want to perform supersonic simulations on a rocket for velocities ranging from subsonic to Mach 10. The rocket in question is approximately 15 m high. The body consists of an ogive nose and cylindrical sections with different diameters. The largest cylindrical section has a diameter of approximately 1 m. Four fins are attached to the bottom of the rocket. An enclosure has been added around the geometry. I have created the geometry and built a - in my opinion - satisfactory mesh. I am, however, unsure about what setup settings I should use. I have run a few simulations with the following setup: Default domain Fluid material: ideal gas Reference pressure: 1 [atm] Heat transfer: total energy Turbulence: SST Wall function: scaleable, High speed (compressible) wall heat transfer model Inlet Flow regime option: supersonic Mass and momentum option: normal speed and pressure Rel. static pressure: 0 Normal speed: [equivalent to the Mach number I want to simulate] Turbulence option: medium Heat transfer: static temperature, 25 C Outlet Flow regime option: subsonic Mass and momentum pressure: average static pressure Relative pressure: 0 Pres. profile blend: 0.05 Solver control Advection scheme: high resolution Turbulence numerics: first order Interpolation scheme: velocity interpolation type, trilinear (advanced options) Compressibility control, High speed numerics (advanced options) Does this seem like a good setup for such simulations? Is there something I have missed or should change? I am relatively new to CFX, so any input is much appreciated! //krihamm

November 23, 2018, 03:16		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I don't know of any CFD solver which can handle hypersonic flows. But I have not looked either, so feel free to look for yourself. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

November 25, 2018, 01:59		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	They have a validation case on their website which shows good agreement to a Ma=6 flow. This is on the borderline of Navier Stokes supersonic flows to Hypersonics so CFX might be OK here. I have not checked the detail of what physics CFD++ has to enable hypersonic flow. Caviat Emptor. How do you get it? Clicking on "Request Info" on there website seems like a good guess.... __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

December 4, 2018, 04:55		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Agreed, the density based solver in Fluent is far superior than CFX's pressure based solver for supersonic flows. Not sure how it goes in hypersonics, however - but it will be better than a pressure based solver. I don't understand your comment about Fluent managing "one transient analysis with one setup", or why CFX is different to Fluent for this point. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

December 4, 2018, 17:01		#13
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I suspect the accelerating rocket use case has a quite limited user base. I don't think that will be a limitation for many users __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

January 24, 2018, 17:48		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	The rule of thumb is that above Mach 5 the gas starts to dissociate and you get plasma becoming significant. CFX cannot model plasma. So I suspect you will not be able to accurately model up to Mach 10. The setup of the simulation will depend on what you are trying to learn from the simulation. So what is the reason you are doing this simulation?

January 25, 2018, 03:16		#4
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,827 Rep Power: 27	This is rocket sience. Go to the library, grab a good book and start reading about the basics. CFX might work up to Mach 3. I am quite sure Fluent's pressure based solver will even be worse. But you could try their density based solver. Ask this in the other forum. Alternatively, contact to ANSYS. They might know.

November 22, 2018, 10:22		#5
ASCT New Member sree charan teja Join Date: Oct 2018 Posts: 8 Rep Power: 7	Hi, can I know if fluent solved the supersonic and hypersonic flows?

November 24, 2018, 14:41		#7
ASCT New Member sree charan teja Join Date: Oct 2018 Posts: 8 Rep Power: 7	Hi, I was searching online and found this cfd solver named cfd++ which claims to be accurate for almost all flows including hypersonic flows. but there is no information about how to get it. you can give a shot http://www.metacomptech.com/index.php/features/icfd

December 4, 2018, 04:50		#9
Jiricbeng Senior Member Jiri Join Date: Mar 2014 Posts: 218 Rep Power: 13	Hi there, my experience is that Fluent is much more convinient than CFX for high speed external aerodynamics (subsonic to supersonic/hypersonic). I recommend performing these simulations in Fluent - you can use far-field boundary, you can use density based solver if desired and in addition Fluent was initially developed for external flows. Moreover Fluent is capable to even manage one transient analysis with one setup, whereas CFX must be stopped and solver setup must be switched, especially if you want to create a transient run from subsonic to supersonic regime. I spent some time trying to analyse supersonic flows in CFX but it was clear quite soon that compared to Fluent the CFX has got several disadvantages.

December 4, 2018, 05:09		#11
ASCT New Member sree charan teja Join Date: Oct 2018 Posts: 8 Rep Power: 7	Hi, I have used both fluent and cfx extensively. In my personal experience and opinion. shock formations in flow results to discontinuous Partial derivative equations and initially Ausm(adjective upstream segregation method) was specially developed to solve these type of equations. more over in density based solver, the energy equation is solved along with conservation of mass and momentum equations. I don't know why but most of cfd engineers prefer solving energy equation along with conservation of mass and momentum equations when energy equation is involved. note: note that unlike density based solver, segregate solver and pressure based solver solves energy equation separately.

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