Hello Luqi,

Indeed, the simulation will be non-dimensional. If you non-dimensionalise the simulation w.r.t.
the inflow velocity then you will have a velocity of 1 at the inflow, otherwise it will be a factor of
your reference velocity, wherever you take it.

Remember you will have to use a non-dimensional mesh. If you opt to use a dimensional one
you will have to scale your viscosity by the reference length (nu=lref/Re).

All the best,

Guglielmo
From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> on behalf of Luqi Zhang <luqizhang2@gmail.com>
Sent: 08 April 2025 10:34
To: nektar-users <nektar-users@imperial.ac.uk>
Subject: [Nektar-users] Questions about the units of the parameters set in Nektar++.
 

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Dear Nektar++ Team,

I apologize for disturbing you again.

I'm currently having trouble setting the kinvis value and noticed that the Nektar++ User-guide sets it to <kinvis=1/Re>. Does this mean that when defining parameters in <PARAMETERS>, they need to be dimensionless , such as timestep, kinvis. 

 If so, how do I define the reference velocity and length in Session.xml for doing dimensionless? Or are they just default values?  Moreover, should u,v,p in <BOUNDARYCONDITIONS> and <InitialConditions> be dimensionless, as well?

Thank you very much for your time and support. I look forward to your response.

Best regards,

Luqi Zhang