January 2017 - Nektar-users

Source terms and mesh generation
by Selbach, Fabian 09 Feb '17

09 Feb '17

Dear Users, which kind of mesh generator do you recommend to get a good mesh for an airfoil simulation? Actually I am using Gmsh. My next question deals with the CompressibleFlowSolver in Nektar++. Is there a possibility to get acoustical source terms during a simulation with its? Best regards Fabian

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Compressible flow simulation initiation with Blasius flat-plat boundary layer
by devabratasahoo＠campus.technion.ac.il 31 Jan '17

31 Jan '17

Hi All, Can anyone please suggest me how to initiate the case of compressible flow over an open cavity with Blasius flat-plate boundary layer. Further, my simulation getting killed even before getting initiated when I am using a mesh with above 0.1million elements. Is it because of the low-performance computing resources used? Regards, Dev

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linearised Navier-Stokes element matrix
by Martin Hess 26 Jan '17

26 Jan '17

Dear All, I would like to use the incompressible Navier-Stokes solver for parametric model order reduction. As a first step, I thought I have a look at the assembled system matrix in the steady stokes case, since I need access to these matrices in some point. What I found in the code are several layers of static condensation, but no access to the complete linearised Navier-Stokes element matrix. Could I somehow form that matrix from the available submatrices formed in CoupledLinearNS.cpp? Best, Martin Hess

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Using high oder data as Initial Condition to a low order simulation
by Mehak 20 Jan '17

20 Jan '17

Dear all, I have generated a high order data for Quasi-3D: Homogeneous in z-direction (Number of homogeneous mode =8). Now i want to use the result as a initial condition for another simulation where i have (Number of homogeneous mode =7 or less). My solution is very smooth. The simulation is crashing with the segmentation fault error. EquationType: UnsteadyNavierStokes Spatial Dim.: 3 Max SEM Exp. Order: 6 Quasi-3D: Homogeneous in z-direction Expansion Dim.: 3 Num. Hom. Modes (z): 6 Projection Type: Continuous Galerkin Advection: explicit Diffusion: implicit Integration Type: IMEXOrder2 Any input from you will be very helpful. *Thanks * *Mehak naina oberoi * *mehak.n.oberoi(a)gmail.com <mehak.n.oberoi(a)gmail.com>*

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checkpoint fields
by Asım Önder 12 Jan '17

12 Jan '17

Dear all, I've recently updated my local Nektar++ version to the latest one in the repository. In this new version, it looks like there are some changes in checkpoint filter. In particular, once in a while the code writes out chk files with a "bak0" extension. What would this extension supposed to mean? I did some research but couldn't find. I also noticed that the chk file for the same time instance is slightly larger compared to its "bak0" counterpart and to the rest of the fields, for instance: 62G config_22.chk 62G config_23.chk 62G config_24.bak0.chk 64G config_24.chk 62G config_25.chk 62G config_26.chk 62G config_27.chk 62G config_28.chk 62G config_29.chk 62G config_30.chk 62G config_31.chk 62G config_32.chk 62G config_33.chk 62G config_34.chk 62G config_35.chk 62G config_36.chk 62G config_37.chk 62G config_38.bak0.chk 64G config_38.chk It is now a little confusing, which one to keep, bak0 version or the other version, i.e. should I delete for example config_38.bak0.chk or config_38.chk? I'd appreciate any feedback on this. Best, Asim

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Using PhysDeriv() for gradient-based source terms
by Kilian Lackhove 12 Jan '17

12 Jan '17

Dear List, i am trying to implement a source term based on the gradient of an auxiliary field in the APESolver. My problem is quite general, so i in terms of the simpler ADR solver, a minimal example would look like this: du / dt + v * grad(u) = c * grad(v) with u being a transported variable, v the advection velocity and c a constant. The problem is the gradient on the right hand side. I tried computing it by using ExpList::PhysDeriv(), but since the projection is not C1-continuous, this fails at the element edges. I attached an example plot to illustrate the problem. p0/rho0 uses the left axis, the gradient the right hand side one. Do you have any suggestions on how to handle the gradient term? Is there some other method i should use? Cheers, Kilian -- Kilian Lackhove, M.Sc. Fachgebiet für Energie- und Kraftwerkstechnik L1|08 114 Technische Universität Darmstadt Jovanka-Bontschits-Straße 2 D-64287 Darmstadt Germany Tel.: +49 6151 16 - 28915 Fax: +49 6151 16 - 6555 e-mail: lackhove(a)ekt.tu-darmstadt.de

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Compressible flow solver problem
by devabratasahoo＠campus.technion.ac.il 02 Jan '17

02 Jan '17

________________________________ Hi Users, I am solving my cavity flow case at a Re= 0.3x10^7 per mtr, M=0.15, and NumModes=4. I am not using the CFL tool, instead I am taking a constant time step = 0.0001. The simulation is running fine now but the problems now remains as follows: 1) The residuals are not good at all. (pics attached below) 2) I am still not able to capture the boundary layers in this mesh though the flow in cavity is captured but it can't be accurate. (Present mesh attached below) 3) My final aim is to run the simulation at a larger RE (1X10^7 per mtr at M-0.5). (presently used solver info, parameters and expansions used are attached below) 4) I also need to run the CFL tool to get the mean flow which I can further use as base flow for the stability analysis. I am trying it out but the solution is terminating when I use CFL tool. It is working only when I use CFL=0.1. 1) Residual [cid:a9b4a5b0-2a7d-45a9-841f-f78538ca0598] 2)Present Mesh [cid:3afb70e7-e590-47be-ab01-03fe8b38b5fd] 3) Solverinfo and Parameters used [cid:5f9937c8-6fed-49f2-aa25-153f71a94bea] 4) Expansions used [cid:f4dd55b8-2b6a-4185-becc-c037ff3a5fe2] Result(Mach Contour at 1Sec) [cid:797fa64e-55db-4abc-aa5b-4e6c83a1a06f] I tried the same case at a very low Re = 7500 using Incompressible flow solver and I could capture the boundary layer but the residuals still not good. When I try running it for longer time the solution is blowing up. Can anyone please help me out with where I am going wrong? How to reduce the residual and get a converged solution? Regards, Dev

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