Dear Prof Spencer and dear Prof Moxey, Thank you very much for your kind and prompt reply. I am glad to know about this implementation. I successfully compiled the development branch of the code on Cray-XC40 and tried it for the example test case (' ChanFlow_m8_Flowrate.xml') and then channel flow-2D and it works. As soon as I try to use it for case-3DH1D, the simulation starts but does not proceed, it stuck just after writing the initial file at 0th timestep, I even ran the simulation for ~40 CPU-hrs. The simulation proceeds only when processors are less than or equal to 2 but after that (>2), it stuck. I tried to debug it and found out that it stuck at "MeasureFlowrate" function in *./solvers/IncNavierStokesSolver/EquationSystemsVelocityCorrectionScheme.cpp* specifically at: m_comm->AllReduce(flowrate, LibUtilities::ReduceSum); however, this implementation looks correct, but I don't know whats wrong here. In addition, the 3DH1D simulation with <=2 processors crashes, therefore, I checked the outputs of few variables and found out that "m_flowrateArea" is wrong in this case. The Lx*Ly*Lz= 4Pi*2*1.333Pi, therefore "m_flowrateArea" for the 3D case, it should be 8.37, but code's output is 128 while for 2D case, its correct (i.e. 2). This, "m_flowrateArea"=128 is the result of Ly*HomModesZ (should be Ly*Lz?). Moreover, the "flowrate" from the function turns out to be negative for the 3DH1D case during the very first step and I guess it also causes the crashing. While it is positive and remains constant in 2D case during the entire run. Do you have any suggestions which I can try and also please correct me if I am doing or understanding it in a wrong way. Snippet of parameter.xml file: <!-- xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx --> <CONDITIONS> <SOLVERINFO> <I PROPERTY="SolverType" VALUE="VelocityCorrectionScheme"/> <I PROPERTY="EQTYPE" VALUE="UnsteadyNavierStokes"/> <I PROPERTY="AdvectionForm" VALUE="Convective"/> <I PROPERTY="Projection" VALUE="Galerkin"/> <I PROPERTY="TimeIntegrationMethod" VALUE="IMEXOrder1"/> <I PROPERTY="HOMOGENEOUS" VALUE="1D"/> <I PROPERTY="DEALIASING" VALUE="ON"/> <I PROPERTY="USEFFT" VALUE="FFTW" /> <I PROPERTY="SPECTRALHPDEALIASING" VALUE="True" /> </SOLVERINFO> <PARAMETERS> <P> TimeStep = 0.00001 </P> <P> NumSteps = 1000000 </P> <P> IO_CheckSteps = 500 </P> <P> IO_InfoSteps = 1 </P> <P> Kinvis = 1.0/180.0 </P> <P> Flowrate = 15.0 </P> <!--For Re_tau=180 and Re_b=2700 (based on H) --> <P> IO_FlowSteps = 1 </P> <P> HomModesZ = 64 </P> <P> LZ = 4.0*PI/3.0 </P> </PARAMETERS> <VARIABLES> <V ID="0"> u </V> <V ID="1"> v </V> <V ID="2"> w </V> <V ID="3"> p </V> </VARIABLES> <BOUNDARYREGIONS> <B ID="0"> C[1] </B> <B ID="1"> C[2] </B> <B ID="2"> C[3] </B> </BOUNDARYREGIONS> <BOUNDARYCONDITIONS> <REGION REF="0"> <D VAR="u" VALUE="0" /> <D VAR="v" VALUE="0" /> <D VAR="w" VALUE="0" /> <N VAR="p" USERDEFINEDTYPE="H" VALUE="0" /> </REGION> <REGION REF="1"> <P VAR="u" VALUE="[2]" /> <P VAR="v" VALUE="[2]" /> <P VAR="w" VALUE="[2]" /> <P VAR="p" VALUE="[2]" /> </REGION> <REGION REF="2"> <P VAR="u" VALUE="[1]" USERDEFINEDTYPE="Flowrate" /> <!--Cross section for Q = outlet. --> <P VAR="v" VALUE="[1]" /> <P VAR="w" VALUE="[1]" /> <P VAR="p" VALUE="[1]" /> </REGION> </BOUNDARYCONDITIONS> <FUNCTION NAME="FlowrateForce"> <E VAR="ForceX" VALUE="1" /> <!--Flow is in the X-Direction, so explicitly defined --> <E VAR="ForceY" VALUE="0" /> <E VAR="ForceZ" VALUE="0" /> </FUNCTION> <FUNCTION NAME="InitialConditions"> <F VAR="u" FILE="TurbChFl_3DH1D_83.rst" /> <!--Initialize with fully developed turbulent flow --> <F VAR="v" FILE="TurbChFl_3DH1D_83.rst" /> <F VAR="w" FILE="TurbChFl_3DH1D_83.rst" /> <F VAR="p" FILE="TurbChFl_3DH1D_83.rst" /> </FUNCTION> </CONDITIONS> <!-- xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx --> Thanks you very much! Sandeep On 29 May 2018 at 00:48, Sherwin, Spencer J <s.sherwin@imperial.ac.uk> wrote:

HI Sandeep,

I think Dave has implemented this type of feature but I do not know if it is in Master or a branch? I am cc’ing Dave for who is best able to comment.

Cheers, Spencer.

On 27 May 2018, at 14:25, Sandeep Pandey <spandey.ike@gmail.com> wrote:

Hello all,

I am a newbie to Nektar++ and I validated turbulent channel flow DNS with the standard DNS database. For now, the flow was driven by the constant pressure gradient. As a next step, I want to drive flow with such forcing so that I have constant mass flux at every time step. The forcing should take the following form to achieve the constant mass flux:

*dpdx(time)= dpdx(time-1) -[ 0.3*(massFlowRef (time=0) - 2*massFlow (time) + massFlow(time-1) ) / (Ly*Lz*dt)]*

where; *massflow *should be volume integrated value.

Does anyone has already implemented such forcing? Or does anyone any idea? I am familiar with ./library/SolverUtils/Forcing, but any hint in the specific direction will be very useful to me.

Thanks and have a nice weekend! Sandeep _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/nektar-users

Spencer Sherwin FREng, FRAeS Head, Aerodynamics, Professor of Computational Fluid Mechanics, Department of Aeronautics, Imperial College London South Kensington Campus, London, SW7 2AZ, UK s.sherwin@imperial.ac.uk +44 (0)20 7594 5052 http://www.imperial.ac.uk/people/s.sherwin/