Hi all! I am solving the 2D unsteady turbulent Navier-Stokes equation with finite volume and implicit temporal discretisation in a piston-cylinder assembly. Every equation is going fine, except for the temperature one (I solve this instead of the energy equation). When I arrive at the algebraic equation: Ap*Tp=SUM(Ai*Ti)+Su ,the Su sometimes it takes negative values near the piston. I checked also the Ai coefficients and they are OK. Sp is also always negative. As a result everywhere the temperature is around 4 Kelvin, instead of around 350 that it should be. Any help will be much appreciated. Thank you for reading my problem

Probably using Artificial viscosity and Inertial Relaxation will help. Read in HELP Fluids Analyses Guide/Flotran Compressible Analyses/Solution Strategies. Also check what specific heat do you apply for the analyses.

Thank you for your response. I use constant specific heat, because I assume that the temperature will not change very much. The initial is 300 kelvin and the walls are at constant temperature of 350 kelvin. I do not understand where do I find this link: HELP Fluids Analyses Guide/Flotran Compressible Analyses/Solution Strategies. I use the hybrid scheme and the source (Su)is: dP/dt+u*dP/dx+v*dP/dy+den(old)*Temp(old)*Vol(old)/dt.