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++. This email from luqizhang2@gmail.com originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list<https://spam.ic.ac.uk/SpamConsole/Senders.aspx> to disable email stamping for this address. 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