December 2018 - Nektar-users

Hi All (( can i use two different Reynolds in the same case ))
by Moto Light 19 Dec '18

19 Dec '18

Hi All, I need to use two different Reynolds in the same case as two velocity inputs, my case is incompressible case, if I defined rho and Kinematic viscosity and change inlet speeds is it ok like OpenFoam and does not define Re like this:   rhoInf = 1.2041  Kinvis = 0.000015111 -------- <REGION REF="0">  <D VAR="u" VALUE="0.00226665" />  <D VAR="v" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0"/> </REGION> <REGION REF="1">  <D VAR="u" VALUE="0.000846216" />  <D VAR="v" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0"/> </REGION> ----------------------- and calculate real two velocities and put it in the inlet speeds, is this ok Regards,

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problem in Aerodynamic forces
by Moto Light 19 Dec '18

19 Dec '18

Hi All, My case is incompressible flow case and I am using two different velocity inlets, like: --------------------------------------------------- <REGION REF="0">  <D VAR="u" VALUE="3" /> <D VAR="v" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0"/> </REGION> <REGION REF="1">  <D VAR="u" VALUE="1" /> <D VAR="v" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0"/> </REGION> ----------------------------------------------------- Re = value Kinvis = 1./Re My characteristic length D =1 and i have a problem in the Cd calculation even in Fd drag force value, I need to know when I am using Aerodynamics filter to calculate the forces around my body, which value i have from this filter??? this filter produce forces file, when i plot 1:4 columns ((4 is the total force in X direction)), is it the force directly (( the user guide says it calculate the pressure and viscous contributions are computed in each direction )) which means it is the Fd Cd = 2*Fd / (rho*U*U*A) (( Note: for the Base cases as a Validation case using one inlet velocity value and with using velocity equal 1, I just take this forces results and multiplied by 2 it gives the write value like considering rho =1 U=1 A=1)) I am using homogeneous expansion for my mesh in the spanwise direction, also when I tried to use two different spanwise lengths, the forces output was the same How???? is Aerodynamics filter give us Fd/A ? Thanks,

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PressureOutflow boundary condtions
by 中华腾飞 19 Dec '18

19 Dec '18

Hi all! I want to give static pressure on my outlet, p0eInf is the value that i have defined in parameters . Can you help me check out my example? By the way, i don't know how to set 'WallAdiabatic' boundary conditions ,can you help me check out my example? Sometimes when i run the calculation,it will report an error called 'vacuum is generated by given data'.If i change the TimeStep , it will calculate some steps.How to explain it? Looking forward to your replay!

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nektar++ mesh
by 中华腾飞 18 Dec '18

18 Dec '18

Hi all! When i calculate my task , there is always an error called 'vacuum is generated by given data' .I have tried to check out my boundary conditions and initial conditions ,but it doesn't work. I want to check out my meshes .My meshes are generated by gmsh 3.0.6, all the elements are 'A' (tetrahedron) and about 36912. Can you give me some suggestions about my meshes or geometry?Looking forward to your reply!

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help my condition.xml
by 中华腾飞 18 Dec '18

18 Dec '18

Hi all! I will give you about my condition.xml ,I hope someone can help me to refine it. In parameters list, p0,rho0Inf,u0Inf,v0Inf,w0Inf are parameters on the first inlet called ' REF="0" ',pc,rhocInf,ucInf,vcInf wcInf are parameters on the second inlet ' REF="2" '.They are all static values. p0e is the static pressure on the first outlet called " REF="1" ' , pce is the static pressure on the second outlet called " REF="3" '. I want to use 'PressureOutlet' boundary condtions ,how to write the condtions? On the REF="4" ,i want to use the 'WallAdiabatic',how to write it? Hope you can write your answer in my condition.xml ,i will learn it as a reference! Looking forward to your reply!

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compressible flow solver
by 中华腾飞 17 Dec '18

17 Dec '18

Hi all! Can you give me an specific example in using 'PressureOutflow' and 'WallAdiabatic' boundary conditions? On the website i don't know why the values are set to zeros...

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compressible solver issues
by 中华腾飞 17 Dec '18

17 Dec '18

Hi all! I want to ask about the boundray conditions.In 3D task,the variables are only rho,rhou,rhov,rhow and E? We can't set other variables,such as p(pressure),t(temperature)? In D type boundary condtions,if i give values to variables,such as ' VAR="rho" VALUE="rhoInf" after i have defined rhoInf=1.007, it means rho=1.007? In some tutorials, they set VALUE="0",rho=0 or E=0,it seems to be impossible!

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problems in using compressible flow solver
by 中华腾飞 16 Dec '18

16 Dec '18

Hi all! I have met some problems in using compressible flow solver. When i begin to calculate ,after some steps ,it will stop and print an error on the screen called'vacuum is generated by given data'. Now, i will talk about my task. If you open the fight.geo with gmsh 3.0.6,you will see a box. You can also open the fight.msh file with gmsh which you can see the generated meshes .Inlet is on the left and outlet is on the right. I want to give total values like total temperature and total pressure on the inlet (T*=1600K,P*=1312800Pa,Ma=0.33),but when i see the tutorials about compressible flow solver,it seems that i should give values like rhoInf ,rhoInf*uInf and so on,i don't know whether my understanding is right or not .I have to calculate static values through total values and i do that .You can see my fight.xml file,the REF=0 is the boundary of inlet,and values use the parameters defined before.Then i want to give static pressure on the outlet, on the REF=1, i use the 'pressureoutflow' condition,because of no examples of this condition, i don't know how to set right values.... On the REF=2, i want to use 'walladiabatic' condition ,because of no examples of this condtion,i also don't know how to set right values... Initial condition is same to the inlet. I hope you can give me some suggestions. Looking forward to your reply!

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(no subject)
by Xu Chu 14 Dec '18

14 Dec '18

Dear all, Recently I am facing some issues in the post-processing. I use "FieldConvert -m gradient" to get velocity gradient and "FieldConvert -m meanmode" to do spatial averaging in my 3DH1D simulation. They both worked in my previous experiences. However, I found some problem recently. When I am running "-m gradient", I can not convert it to the chk format, but I can convert it directly to vtu format. with chk/fld format, the error shows "Unable to extract the data from the element tag." I am trying to understand it in the source code. But it is still not so clear to me. The other fieldconvert utilities like -vorticity works. When I use "-m meanmode", sometimes it gives me the error "Input data is not the same length as header information". It is also very confusing. Hope someone can help me out here. Merry Christmas and happy new year to all Nektarer. Xu Chu

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BiGlobal Stability Analysis of 3D Channel Flow case at Re15000
by Xu Chu 14 Dec '18

14 Dec '18

Dear Nektarers, I am running a 3D direct stability analysis test case, the Re15000 Channel Flow from the tutorial (PPF_R15000_3D, ARPACK as the solver). As I understand, this is a BiGlobal stability analysis with 2D base flow and the spanwise wavenumber Beta. It means that for a given Beta, the Eigenvalues can be calculated. What I am seeking is the Eigenvalues under different spanwise wavenumber Beta, so I turn "Beta Set To Zero" as false (as in the PPF_R15000_3D). And the solver converged showing 4 Eigenvalues with Real and Imaginary part of each, with no information of Beta. How can I find the Eigenvalues under different spanwise wavenumber Beta? Thank you very much. Best Regards, Xu

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