Your every video is awesome. pictorial representation and bullet points and your explanation clear all of the doubts. I always suggest people to refer your videos to clear basic concepts and CFD doubts. Thank you so much for your amazing work. Really appreciated. keep making more amazing videos. Good Luck!
I get different results using different operating densities in my simulations. My simulation is pretty simple - natural convection of air over vertical hot plate, but the results with operating density at 25°C give me crazy flows with reverse directions on upper boundary layer.
Hmmm is operating density the only thing you changed? Might be worth a quick check of the fluent manual to see what is recommended for natural comvection. I am pretty sure the results are sensitive to exactly what models you turn on (unlike forced flow which is very forgiving)
Hi! Wonderful video as always. I would like to ask you something since I'm currently dealing with a very low Reynolds and Mach flow simulation: I understood the reference density enters as a stabilizer, but as far as I can imagine it changes a forcing term in the governing equations. Is this correct? And if this is the case, is this effect recovered somehow? Thank you in advance!
Hello Dr, its a good video, I have questions in laminar mixed convection flow in the circular duct, if we use water or nanofluids as working fluid, how to set operating conditions in this case? what is the type of equations momentum and energy using in ansys fluent dimensionneless or adimensionneless? how to calculate Reynolds number if use nanofluid, I mean prperties using for calculate Reynolds number, properties of nanofluid or base fluid? I hope to answer me Dr?
Thank you, really nice .. could you address in details the main characteristics of weakly compressible model and fully compressible model for buoyant flow , and why some cfd coded like fluent doesn’t use weakly compressible why comsol does.
If you have an enclosed space or cavity, you can pick anywhere that is convenient. If you have an outlet, then pressure will be set on the boundary, so it doesn't matter what location you choose (it will be overwritten anyway)
@@fluidmechanics101 no, I mean, for a free surface flow. Say my cubic tank height is 1.0m (Y direction). Water is filled up to 0.5m. what should be the y coordinate value of the reference pressure location?
I am trying to simulate fluid flow analysis of duct in boiler. I gave mass flow rate boundary condition at inlet and pressure at outlet. But I want to maintain some pressure drop throughout the duct for example 130 pascal. So for this what should I do ?
Interesting topic. I would like to ask what the operating pressure would be in the case of a wing at given altitude, incompressible flow. Would it be the value of pressure at given altitude or still 101325 Pa ? Thank you
You want the atmospheric pressure at that particular height. You should be able to look this up or calculate it (a quick Google search should give you what you need)
there is one point confused me,which is how to define reference density .for example a natural convection of air over vertical hot plate, should i choose density of background of freestream flow or density at (tw+tf)/2 degree as reference density.(tw is hot plate temperature and tf is background of freestream temperature),because the heat transfer textbook recommends the (tw+tf)/2 as physical property temperature.
The film temperature (1/2 (tw + tf)) is for the empirical correlations. We use it to evaluate the material properties (mu, cp etc) at the correct temperature. In CFD we would use the freestream density as the reference density (so rho_f)
@@fluidmechanics101 thank you for your answer.i have another question that if the natural convection occurs between hot and cold plate in a closed domain, there is no freestream field, then how should i define the reference density.
Hi! Great explanation. I am simulating internal flow of gas in vacuum conditions ( 1.6 torr). I changed the operating pressure to 0 and when ansys asked to also change operating density to 0, I have also changed it. When I am running the calculation, I see " Absolute pressure is limited to 1". It does not have any units and I am not sure how it changes my solution. My boundary conditions involves 1. Velocity inlet 2. Thermal walls at 545K, 623K, 923K along with radiation. Currently I am doing a 2D simulation. Can you help me with this?
I want to do a c-d nozzle simulation (supersonic flow). Let chamber pressure be 100bar. I want to simulate the nozzle at different altitudes? Do I have to change the operating conditions for this or what? And gauge pressure can be my chamber pressure right? And is pressure outlet the exit pressure of nozzle or ambient pressure? (assuming my nozzle exit plane is set as outlet baoundary )
Hi there, when I export the solution data from Fluent to Tecplot, I got a message "The sum of operating pressure and reference pressure is zero". is it anything wrong with my simulation? I use a density-based formulation with steam as the working fluid (density : ideal gas), the case is converging-diverging nozzle so the pressure gradient will much higher. I set the operating condition to 0 I don't really know what is the point of the message
Have a look at the flow field in tecplot and see if you can see any problems. If you can't see anything then you are good and can ignore the error message. If not, go back to fluent and check your case ✅
There is something wrong in equation (3). The term -2/3* µ*(∇·U)I should be inside the divergence operator to get a vector instead of a tensor of second order.
hi im trying to understand more about cfd and aftr the fundamentals list that you shared, which list i should continue or any other step i should follow?
If I want to simulate flow inside a nozzle. And the ambient press is 1bar, chamber press is 10bar and flow will be supersonic after throat but subsonic before throat. Then what should be operating press and gauge press at inlet & outlet. Basically what boundary conditions do I give for this?
You will probably find that the calculation is quite difficult to converge if you go for supersonic straight away. Try going for low chamber pressure first, less than the critical pressure ratio (say 1.2 bar). Then gradually ramp up the pressure ratio, past the critical pressure ratio (I think it's about 1.8 for air) and then all the way up to 10 bar. As this is a supersonic calc, you should follow the guidance in your CFD code manual on how to set this up. I would guess that it will tell you to set the operating pressure to 0 bar, and have your gauge pressure equal to the pressure you want. But make sure to look in your code manual!
Hello sir, can i ask you few question. How to solve liquid density temperature pressure dependent variables?Most of your point in this video were applied to gas using ideal gas law. How to deal with problem involving low marc temperature pressure dependent liquid flow. i.e the heat transfer in the high depth water tank.Please give some tips and advice.
Hi Husaini, the first thing I would try is a Boussinesq model for the density variations (you can check out my video for the Boussinesq model here: ua-cam.com/video/onKiVbKSoXw/v-deo.html . If not you can always try a compressible liquid thermodynamic model if the temperature and density changes are large. Hopefully this helps? If you can provide some more details then maybe we can work out some more helpful advice?
I have check your video before. It stated that its only valid for low temperature differences. How can i define the pressure when there is no pressure boundary (pressure inlet or outlet) in the domain?
Currently im modelling the heat transfer in the spent fuel pool water tank which has about 12m depth of water and about 450K temperature of heat source. I have set the water surface as slip condition but i cant define the hydrostatic pressure inside the water tank.
I am solving a natural convection problem in a room using Buossinsqu approx. For a very low Ma number as you know. My question is can i let the operating pressure equal to zero ? Would you recommend that Thanks a lot for your videos 👍👏
Hi there I am going to simulate a fire in tunnel by using fluent ansys and I have question about the density of air inside the tunnel howshould i define it is it incopresable ideal gas or ideal gas Hi I am going to simulate a fire in tunnel by using fluent ansys and I have question about the density of air inside the tunnel howshould i define it is it incopresable ideal gas or ideal gas
Incompressible ideal gas should be fine. This will allow the gas density to vary with temperature but not pressure, which is fine because your flow is at low Mach number. You will get the buoyancy effects you are looking for
So, for example, if I want to analyse the pressure drop of an incompressible flow in a pipe elbow, do I calculate the gauge pressure or is it the (total pressure-static pressure)=dynamic pressure or back pressure?
@@fluidmechanics101 Thank you! I already assumed it, but is there a specific wording for this kind of pressure drop ? In German it is called additional pressure drop, when you calculate it via the resistance values on the moody-diagramm...
There may be a specific wording for it. I would just make it clear what you mean in your report / document, to avoid any confusion. Something like 'the additional pressure was calculated ( the difference between the total pressure at the inlet and outlet)'
hello sir, can i ask a few question. how to set a different ambient pressure? for example i want to set 8MPa as ambient pressure in the tank.. or does the operating pressure means the ambient pressure? Please give some tips and advice. thanks for your kind
I think you need to set 8MPa as the pressure at the outlet of your tank (with an operating pressure of 0). The CFD code will compute the pressure distribution in the tank. Alternatively, set the operating pressure to 8MPa and set the pressure at the tank outlet to 0. 👍
In fluent, it is recommended to put zero as operating density for material with ideal gas eqn as its density (for natural convection flow). do you know the reason for that?
@@fluidmechanics101 😅😅 ok ok.. Maybe, it's because if we are putting ideal gas as density then it's probably assumed that density is varying a lot and fluctuation is so large that it cancelled out the advantage of using reference pressure. So just solve original NS equation with rho*g term. But it's just my assumption and will have to search more about it. Anyway, thank you for the video!😁
![[CFD] Hexcore Meshes for CFD](http://i.ytimg.com/vi/59xfM0ayFE0/mqdefault.jpg)
![[CFD] Hexcore Meshes for CFD](/img/tr.png)
![[CFD] The Courant (CFL) Number](http://i.ytimg.com/vi/WBWY46ynRk0/mqdefault.jpg)
![[CFD] The Finite Volume Method in CFD](http://i.ytimg.com/vi/E9_kyXjtRHc/mqdefault.jpg)
![[CFD] What are Wall Functions and How do they work?](/img/n.gif)
Your every video is awesome. pictorial representation and bullet points and your explanation clear all of the doubts. I always suggest people to refer your videos to clear basic concepts and CFD doubts. Thank you so much for your amazing work. Really appreciated. keep making more amazing videos. Good Luck!
Your videos and explanations are awesome. Thank you so much for you efforts. I learned a lot from you
Very very very good speech, thank you!
Really clear explanation. Thanks a lot!
Very good speech, thank you!
We learned a new idea again :)
Thx so much
Nice talk.
Doing great work,👌👌 thank you
Perfect
I get different results using different operating densities in my simulations. My simulation is pretty simple - natural convection of air over vertical hot plate, but the results with operating density at 25°C give me crazy flows with reverse directions on upper boundary layer.
Hmmm is operating density the only thing you changed? Might be worth a quick check of the fluent manual to see what is recommended for natural comvection. I am pretty sure the results are sensitive to exactly what models you turn on (unlike forced flow which is very forgiving)
great work
Thanks 👍🏼
Hi! Wonderful video as always.
I would like to ask you something since I'm currently dealing with a very low Reynolds and Mach flow simulation:
I understood the reference density enters as a stabilizer, but as far as I can imagine it changes a forcing term in the governing equations.
Is this correct? And if this is the case, is this effect recovered somehow?
Thank you in advance!
god of fluent
Hello Dr, its a good video, I have questions in laminar mixed convection flow in the circular duct, if we use water or nanofluids as working fluid, how to set operating conditions in this case?
what is the type of equations momentum and energy using in ansys fluent dimensionneless or adimensionneless?
how to calculate Reynolds number if use nanofluid, I mean prperties using for calculate Reynolds number, properties of nanofluid or base fluid?
I hope to answer me Dr?
How do we get reference temperature and pressure in finding gas correction factor ???
Thank you, really nice .. could you address in details the main characteristics of weakly compressible model and fully compressible model for buoyant flow , and why some cfd coded like fluent doesn’t use weakly compressible why comsol does.
Great. The reference pressure concept is understood. What about the location, co-ordinates?
If you have an enclosed space or cavity, you can pick anywhere that is convenient. If you have an outlet, then pressure will be set on the boundary, so it doesn't matter what location you choose (it will be overwritten anyway)
@@fluidmechanics101 no, I mean, for a free surface flow. Say my cubic tank height is 1.0m (Y direction). Water is filled up to 0.5m. what should be the y coordinate value of the reference pressure location?
I would probably set the reference pressure to 101325pa at y=0.5 (the approximate location of the free surface)
@@fluidmechanics101 what if I set it to 1.0. will it make any difference?
I am trying to simulate fluid flow analysis of duct in boiler. I gave mass flow rate boundary condition at inlet and pressure at outlet. But I want to maintain some pressure drop throughout the duct for example 130 pascal. So for this what should I do ?
Interesting topic. I would like to ask what the operating pressure would be in the case of a wing at given altitude, incompressible flow. Would it be the value of pressure at given altitude or still 101325 Pa ? Thank you
You want the atmospheric pressure at that particular height. You should be able to look this up or calculate it (a quick Google search should give you what you need)
Hey thankyou so much
U r awesome
Thanks 😊
there is one point confused me,which is how to define reference density .for example a natural convection of air over vertical hot plate, should i choose density of background of freestream flow or density at (tw+tf)/2 degree as reference density.(tw is hot plate temperature and tf is background of freestream temperature),because the heat transfer textbook recommends the (tw+tf)/2 as physical property temperature.
The film temperature (1/2 (tw + tf)) is for the empirical correlations. We use it to evaluate the material properties (mu, cp etc) at the correct temperature.
In CFD we would use the freestream density as the reference density (so rho_f)
@@fluidmechanics101 thank you for your answer.i have another question that if the natural convection occurs between hot and cold plate in a closed domain, there is no freestream field, then how should i define the reference density.
If you take the temperature of the cold surface and then evaluate the density at the cold plate temperature that will probably work
perfekt...
Hi! Great explanation.
I am simulating internal flow of gas in vacuum conditions ( 1.6 torr). I changed the operating pressure to 0 and when ansys asked to also change operating density to 0, I have also changed it. When I am running the calculation, I see " Absolute pressure is limited to 1". It does not have any units and I am not sure how it changes my solution.
My boundary conditions involves
1. Velocity inlet
2. Thermal walls at 545K, 623K, 923K along with radiation.
Currently I am doing a 2D simulation.
Can you help me with this?
I want to do a c-d nozzle simulation (supersonic flow). Let chamber pressure be 100bar.
I want to simulate the nozzle at different altitudes? Do I have to change the operating conditions for this or what? And gauge pressure can be my chamber pressure right?
And is pressure outlet the exit pressure of nozzle or ambient pressure? (assuming my nozzle exit plane is set as outlet baoundary )
Hi there, when I export the solution data from Fluent to Tecplot, I got a message "The sum of operating pressure and reference pressure is zero". is it anything wrong with my simulation? I use a density-based formulation with steam as the working fluid (density : ideal gas), the case is converging-diverging nozzle so the pressure gradient will much higher. I set the operating condition to 0
I don't really know what is the point of the message
Have a look at the flow field in tecplot and see if you can see any problems. If you can't see anything then you are good and can ignore the error message. If not, go back to fluent and check your case ✅
There is something wrong in equation (3). The term -2/3* µ*(∇·U)I should be inside the divergence operator to get a vector instead of a tensor of second order.
😂 i can always rely on you to find my typos! Thanks!
hi im trying to understand more about cfd and aftr the fundamentals list that you shared, which list i should continue or any other step i should follow?
I would have a look at the turbulence models next. K epsilon is probably the best one to start with, then look at k omega SST 👍
@@fluidmechanics101 thanks for advice, ill do that:)
If I want to simulate flow inside a nozzle. And the ambient press is 1bar, chamber press is 10bar and flow will be supersonic after throat but subsonic before throat. Then what should be operating press and gauge press at inlet & outlet. Basically what boundary conditions do I give for this?
You will probably find that the calculation is quite difficult to converge if you go for supersonic straight away. Try going for low chamber pressure first, less than the critical pressure ratio (say 1.2 bar). Then gradually ramp up the pressure ratio, past the critical pressure ratio (I think it's about 1.8 for air) and then all the way up to 10 bar. As this is a supersonic calc, you should follow the guidance in your CFD code manual on how to set this up. I would guess that it will tell you to set the operating pressure to 0 bar, and have your gauge pressure equal to the pressure you want. But make sure to look in your code manual!
@@fluidmechanics101 Hey, thanks for this.
What is the cfd code manual?
Try the theory guide for ANSYS fluent, ANSYS CFX or the documentation if you are an OpenFOAM user. Not sure what it is called for Star CCM
Hello sir, can i ask you few question. How to solve liquid density temperature pressure dependent variables?Most of your point in this video were applied to gas using ideal gas law. How to deal with problem involving low marc temperature pressure dependent liquid flow. i.e the heat transfer in the high depth water tank.Please give some tips and advice.
Hi Husaini, the first thing I would try is a Boussinesq model for the density variations (you can check out my video for the Boussinesq model here: ua-cam.com/video/onKiVbKSoXw/v-deo.html . If not you can always try a compressible liquid thermodynamic model if the temperature and density changes are large. Hopefully this helps? If you can provide some more details then maybe we can work out some more helpful advice?
I have check your video before. It stated that its only valid for low temperature differences. How can i define the pressure when there is no pressure boundary (pressure inlet or outlet) in the domain?
Currently im modelling the heat transfer in the spent fuel pool water tank which has about 12m depth of water and about 450K temperature of heat source. I have set the water surface as slip condition but i cant define the hydrostatic pressure inside the water tank.
I am solving a natural convection problem in a room using Buossinsqu approx. For a very low Ma number as you know. My question is can i let the operating pressure equal to zero ? Would you recommend that
Thanks a lot for your videos 👍👏
You can let it equal zero but it is probably better to set it to atmospheric pressure (101325 Pa)
Hi there
I am going to simulate a fire in tunnel by using fluent ansys and I have question about the density of air inside the tunnel howshould i define it is it incopresable ideal gas or ideal gas
Hi
I am going to simulate a fire in tunnel by using fluent ansys and I have question about the density of air inside the tunnel howshould i define it is it incopresable ideal gas or ideal gas
Incompressible ideal gas should be fine. This will allow the gas density to vary with temperature but not pressure, which is fine because your flow is at low Mach number. You will get the buoyancy effects you are looking for
So, for example, if I want to analyse the pressure drop of an incompressible flow in a pipe elbow, do I calculate the gauge pressure or is it the (total pressure-static pressure)=dynamic pressure or back pressure?
For internal incompressible flows, total pressure at the inlet - total pressure at the outlet is what you are looking for 👍
@@fluidmechanics101 Thank you! I already assumed it, but is there a specific wording for this kind of pressure drop ?
In German it is called additional pressure drop, when you calculate it via the resistance values on the moody-diagramm...
There may be a specific wording for it. I would just make it clear what you mean in your report / document, to avoid any confusion. Something like 'the additional pressure was calculated ( the difference between the total pressure at the inlet and outlet)'
Yes, you're right! Thank you again. It's a masters thesis, I'm even quoting your talks in my literature😂
hello sir, can i ask a few question. how to set a different ambient pressure? for example i want to set 8MPa as ambient pressure in the tank.. or does the operating pressure means the ambient pressure? Please give some tips and advice. thanks for your kind
I think you need to set 8MPa as the pressure at the outlet of your tank (with an operating pressure of 0). The CFD code will compute the pressure distribution in the tank. Alternatively, set the operating pressure to 8MPa and set the pressure at the tank outlet to 0. 👍
thanks for your helps.. I'll try.. 👍👍👍
In fluent, it is recommended to put zero as operating density for material with ideal gas eqn as its density (for natural convection flow). do you know the reason for that?
I wish i understood more of the fluent manuals recommendations. But my guess is as good as yours 😅
@@fluidmechanics101 😅😅 ok ok..
Maybe, it's because if we are putting ideal gas as density then it's probably assumed that density is varying a lot and fluctuation is so large that it cancelled out the advantage of using reference pressure. So just solve original NS equation with rho*g term. But it's just my assumption and will have to search more about it.
Anyway, thank you for the video!😁
Man is there anything you haven't answered lol