Well as you see the tutorial is just for demonstration purposes. I used for both laminar and turbulent flow few prism layers based on the wall function approach i.e. the turbulence model you choose will take care of the all y+ wall treatment. In case of real flow scenario one should use the appropriate settings like no. of prism layers and the prism layer thickness / strecthing ratio so as to completely resolve the boundary layer accordingly. Normally based on the given Reynolds number, you should calculate y+ value and then decide accordingly if you want to resolve the flow till the wall or you want to use wall-function approach. Hope this helps thanks.
Well for internal flows turbulent specification methods: 1. turbulent intensity + length scale OR 2. turbulent intensity + hydraulic diameter are recommended Only in case you don't know the turbulence values you can use K+Epsilon.
Nice comment, sure improving the Y+ or performing grid independent study and in case of turbulent flow use of different turbulence model could be the next step. Thanks
hi, I am unable to define pipe surface roughness in star ccm+. Could you tell me how to define this sourface roughness. Also what will be the surface roughness for iron pipes
Well for the pipe surface defined as wall follow these steps: pipe boundary -> Physics Conditions -> Wall Surface Specification -> choose Method -> Rough Then under: Physical Values -> you will see the parameters -> Roughness Heigth & Wall Roughness Parameter Normally surface roughness for Iron pipe - galvanized is approx: 0.15-0.20 mm Thanks and hope this helps
Thanks for this excellent video. Can you please modify this simulation to model gas-liquid (water-air) flow with the VOF multiphase model? At least can you point me to a gas-liquid pipe flow example with STAR-CCM VOF model?
You are welcome thanks for the nice feedback. Have a look at following Video tutorial using VOF model using Star-CCM+: th-cam.com/video/CRjhLEoIlO8/w-d-xo.html
@@Simulation-Engineer I did follow your VOF example with a horizontal pipe flowing air and water at the inlet with phase fractions of 0.8 and 0.2 and a mixture axial velocity of 1 m/s. I designated the pipe outlet as "pressure outlet." The pipe is initially filled 100% with water. However, the program will not run unless I specify the phase fractions of air and water at the outlet. I get the error "Please check your boundary values for "Volume Fraction" on the following boundaries:[Fluid.outlet]. I did not see how you handled this issue in your outlet boundary of your VOF example. In principle, the phase fractions at the outlet are supposed to be predicted. Any suggestions will be greatly appreciated.
Well first of all you need to patch the fluid domain based on the VOF requrement i.e air + water regions. If in your case initially the pipe is filled with water then you ues 100% water and 0% air at the outlet. This can be achieved by using explicity defining the field functions for air and water at time t=0 like i did in the dam break tutorial. As it is necessary to initialize the flow with correct VOF patch, afterwards as the simulation progresses the fluid behavior at the outlet boundary will be predicted accordingly.
hi! from 10:53, the length scale is 7% of diameter, and velocity scale is 10% of free-stream velocity in tutorial guide. why is it 7% or 10%? how can i get these percentages?
Hello, I am a student who is learning star-ccm at university. I can set the air to inlet and outlet, but I don't know how to give conditions when I change it to water. I want to set the temperature of the water and see the temperature that the water has when it goes into the outlet. Can you take a video of the lecture?
Thanks for the comment and feedback. We'll you can change the fluid under material properties and define the related quantities such as density, viscosity etc. Also you can set the inlet temperature and observe its behavior over the fluid domain.
------------------Starting local server: starccm+ -server -notokens -power -np 2 "File_Name.sim" Unable to start STAR-CCM+. Invalid file type. Check arguments and their order.-------------- Do you know a solution for this particular case?
It seems the file is missing or you are not using proper syntax to run in parallel using 2 CPUs. I would recommend running the simulation in serial mode and then switch it to parallel mode. Its also possible that you don't have power license available.
Best ever
Thanks for the feedback
Can you please explain at what basis you gave your mesh parameters (no:of prismmlayers, streching,thickness) ?
Well as you see the tutorial is just for demonstration purposes. I used for both laminar and turbulent flow few prism layers based on the wall function approach i.e. the turbulence model you choose will take care of the all y+ wall treatment. In case of real flow scenario one should use the appropriate settings like no. of prism layers and the prism layer thickness / strecthing ratio so as to completely resolve the boundary layer accordingly. Normally based on the given Reynolds number, you should calculate y+ value and then decide accordingly if you want to resolve the flow till the wall or you want to use wall-function approach. Hope this helps thanks.
Great
Thanks
Hie,
While selecting inlet Turbulent specification why K+Esp isn't selected?
Well for internal flows turbulent specification methods:
1. turbulent intensity + length scale
OR
2. turbulent intensity + hydraulic diameter
are recommended
Only in case you don't know the turbulence values you can use K+Epsilon.
Could you slice it in half on the x-y plane and make that wall symmetric?
Sure as long as the geometry is symmetrical you can do it for any shape.
Compare of different Y+ settings and the pipe flow / pressure drop would be the next step.
Nice comment, sure improving the Y+ or performing grid independent study and in case of turbulent flow use of different turbulence model could be the next step. Thanks
hi, I am unable to define pipe surface roughness in star ccm+. Could you tell me how to define this sourface roughness. Also what will be the surface roughness for iron pipes
Well for the pipe surface defined as wall follow these steps:
pipe boundary -> Physics Conditions -> Wall Surface Specification -> choose Method -> Rough
Then under:
Physical Values -> you will see the parameters -> Roughness Heigth & Wall Roughness Parameter
Normally surface roughness for Iron pipe - galvanized is approx:
0.15-0.20 mm
Thanks and hope this helps
Also remember for steel pipes, when nothing more is precised, surface roughness of about 0.05 mm is 1st good approximation.
Thanks for this excellent video. Can you please modify this simulation to model gas-liquid (water-air) flow with the VOF multiphase model? At least can you point me to a gas-liquid pipe flow example with STAR-CCM VOF model?
You are welcome thanks for the nice feedback. Have a look at following Video tutorial using VOF model using Star-CCM+:
th-cam.com/video/CRjhLEoIlO8/w-d-xo.html
@@Simulation-Engineer I did follow your VOF example with a horizontal pipe flowing air and water at the inlet with phase fractions of 0.8 and 0.2 and a mixture axial velocity of 1 m/s. I designated the pipe outlet as "pressure outlet." The pipe is initially filled 100% with water. However, the program will not run unless I specify the phase fractions of air and water at the outlet. I get the error "Please check your boundary values for "Volume Fraction" on the following boundaries:[Fluid.outlet]. I did not see how you handled this issue in your outlet boundary of your VOF example. In principle, the phase fractions at the outlet are supposed to be predicted. Any suggestions will be greatly appreciated.
Well first of all you need to patch the fluid domain based on the VOF requrement i.e air + water regions. If in your case initially the pipe is filled with water then you ues 100% water and 0% air at the outlet. This can be achieved by using explicity defining the field functions for air and water at time t=0 like i did in the dam break tutorial. As it is necessary to initialize the flow with correct VOF patch, afterwards as the simulation progresses the fluid behavior at the outlet boundary will be predicted accordingly.
What are the variables used for calculating the turbulence intensity?
Turbulent Intensity is calculated as:
I = sqrt((3/2*(v_t)^2)/U^2)
where,
I - turbulent intensity
v_t - turbulent velocity scale
U - free-stream velocity
Why use the k-epsilon solver for turbulent flow?
It's just for the demonstration purposes for the tutorial. Any turbulence model can be used related to specific application, Thanks
@@Simulation-Engineer thank you
hi! from 10:53, the length scale is 7% of diameter, and velocity scale is 10% of free-stream velocity in tutorial guide. why is it 7% or 10%? how can i get these percentages?
Thanks for the feedback, well normally these scales are used to estimate the turbulent properties for CFD simulations.
Hello, I am a student who is learning star-ccm at university.
I can set the air to inlet and outlet, but I don't know how to give conditions when I change it to water.
I want to set the temperature of the water and see the temperature that the water has when it goes into the outlet. Can you take a video of the lecture?
Thanks for the comment and feedback. We'll you can change the fluid under material properties and define the related quantities such as density, viscosity etc. Also you can set the inlet temperature and observe its behavior over the fluid domain.
------------------Starting local server: starccm+ -server -notokens -power -np 2 "File_Name.sim"
Unable to start STAR-CCM+. Invalid file type. Check arguments and their order.-------------- Do you know a solution for this particular case?
It seems the file is missing or you are not using proper syntax to run in parallel using 2 CPUs. I would recommend running the simulation in serial mode and then switch it to parallel mode. Its also possible that you don't have power license available.
@@Simulation-Engineer in which file direction should be, the server working directory?
It should be in your license directory.
Also try this command might help:
starccm+ -np 2 -rsh ssh file.sim -server