Hello I have a question on
I have a question on the turbForce term in the liftDrag.C (../src/postprocessing/incompressible/liftDrag/liftDrag.C ).
In the laminar case the drag is the pressure drag + x_component of the wall shear stress . although i am not an expert in C++ , i could make out that
is approximately meu*velocityGradient*area . Am i correct ?
2. turbulent drag
In turbulent flow the wall shear stress is (according to ferziger and peric) rho*(u_tau)^2.
which equals rho*(C_meu)^0.25*k*sqrt(k)*vel_parallel_wall/(ln(n+E))
But the formulation given in liftDrag.C is totally different . first the laminar drag is found out ( even in turbulent case ) . then the turbulent drag is found ( this does not at all resemble the expression given by say ferziger , peric). then these 2 are added.
could someone tell me why this procedure is adopted and where i am wrong ? i am stuck with my comparison.
thanks a lot
Hello all, Could someone co
Could someone comment on this post ?
i am stuck with my results
thanks in advance
Hi kumar, I'm very sorry th
I'm very sorry that I can't help you, but maybe you can answer some of my questions?
- where do I get the mu field from?
- how do I have to change the code for a compressible fluid?
- where do I have to write the code?
- how can I actually use it?
- where do I find the results
Hi Kumar, the difference be
the difference between laminar and turbulent navier-stokes equations are the reynolds-stresses.
So you can simply take the laminar forces and add the forces due to the reynolds-stresses.
viscosity * velocity gradient normal to surface * area
surface vector(length equal to area) &(dot-product) reynolds stress tensor
the calculation is general, given a stress tensor which is calculated from your choice of turbulence model
Hi Anja, Let me try to answ
Let me try to answer your questions .
1. mu field
the liftDrag utility uses nu ( mu/density ). this is set in the transportProperties in your case directory.
2. Compressible fluid
since liftDrag utitlity uses nu , you may have to modify the utility itself.
3. writing the code.
The liftDrag.C ( & associated codes ) code resides in /OpenFoam-1.2/application/utilities/postProcessing/miscellaneous/liftDrag/ . This program while executing calls another program also called liftDrag.C ( & associated programs ) in ../src/postProcessing/incompressible/liftDrag/
the liftDrag.C in /miscellaneous/../ calls createNu.H . createNu.H then opens transportProperties file ( this resides in the case directory )gets nu ( mu/rho ) . You can give a different nu by either modifying the transportProperties file . however you can also modify the later part of createNu.H to say for example read a certain different value , but here again , we are still talking about nu ( NOT mu)
to modify the code . copy the code to your /applications directory and follow the instructions in user manual . also refer other wonderful posts ( search with liftDrag in openFoam )
Once you compile your program you are ready to go!
hope this helps
Hi Markus Thanks a lot for
Thanks a lot for your reply. i hope i can trouble you with one more question.
In the case of ke models the reynolds shear stress are not calculated . this means that the wall shear stress given in liftDrag utility is an approximate formulation because in the turbulent case - while using ke model - the wall shear stress is (according to ferziger and peric) rho*(u_tau)^2. which equals rho*(C_meu)^0.25*k*sqrt(k)*vel_parallel_wall/(ln(n+E)) , but the utility does not calculate this and approximates with the laminar formulation.
Am i correct ?
Hi Kumar, if you look for t
if you look for the k-eps model in src/turbulenceModels/incompressible/kEpsilon the reynolds stresses are calculated according to the boussinesq approximation common to all k-eps models.
((2.0/3.0)*I)*k_ - nut_*2*symm(fvc::grad(U_))
the turbulence viscosity nut is calculated like
nut_ = Cmu*sqr(k_)/(epsilon_ + epsilonSmall_)
with standard wall function approach to get the wall values for nut (wallViscosityI.H) with yPlusLam = 11.63
if (yPlus > yPlusLam_)
nuw[facei] *(yPlus*kappa_/log(E_*yPlus) - 1);
nutw[facei] = 0.0;
markus and pierre
Hi Markus & Pierre Thanks a
Hi Markus & Pierre
Thanks a lot for the replies
Hi all, also thanks from my s
also thanks from my side.
Hi, I want to implement the vi
Hi, I want to implement the viscous dissipation rate in my application. the term which im hopeing to get implemented is 1/2*1/Cp*(R()() & R ()())
on acount that R()() = tau/rho.
However the implementation of the dot product of R()() is not accepted.
Does anyone know how to do this?
Hi to everybody, does anybody know where this equation
nuw[facei] *(yPlus*kappa_/log(E_*yPlus) - 1);
is coming from??
Thanks in advance
Thanks again ;)
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