I'm using OpenFOAM to run a CFD study of thermal comfort within a hall. I'm using OpenFOAM v1912 and BouyantBoussinesq(Simple&Pimple)Foam solver. eI have 6 inlets and outlets each with specific flow rates. I specified the flow rates accordingly at the inlet using flowrateinletvelocity BC and at the outlet using flowrateouletvelocity BC. Based on the height, I computed (p-rgh)/rho and fixed it at one of the outlets.
My mesh quality is good (Non-Orthogonality less than 50). The dimension of my hall is 30m *30m *4.5m. It was okay so far when I was doing the simulation for small halls, but I'm facing this problem at the moment.
This happens each time I start the simulation, at the beginning of iterations, p rgh iteration (1st step) reaches 1000 or 2000. The final residual is very high (greater than zero). After the cumulative value (continuity error) begins to rise and becomes greater than 1. The value of Pressure ranges from 1e18 to -1e18 (Two extreme values) even after after 1 or 2 time steps, then the simulation blows off.
I have tried the following options
1)potentialFoam initialization
2)Mesh quality check
3)Defining pressure at all the outlets
4)Using prefcell and prefpoint in fvsolutions to define the pressure in fvsolutions.(if I use this I get continuity error at the start of simulation)
5)Both steady state and transient analysis
6) keeping URF very low and also reltor for pressure to 0.0 in fvsolutions
7)first order and 2nd order fvschemes
7)nNonOrthogonal correction raised to 20.
8) I have turned off turbulence.
9)simplifying the geometry.
At the outlet boundaries, use following BCs:
U: advective or zeroGradient
p_rgh: fixedValue (uniform 0)
Sartaj Tanweer Thanks but yours is a basic reply. First as per my model, I need to fix the flow rates at all the outlets. 2nd) p_rgh should be greater than zero if I need to fix my pressure to be zero at the desired height.
Ijaz Fazil Syed Ahmed Kabir
1. As per my understanding, you shouldn't fix the flow rate at all the outlet boundaries. Flow rate at the outlet boundaries will be decided by flow dynamics.
2. In OpenFOAM, p_rgh is defined as "p - rho*g*h". Therefore, p_rgh does not vary with height, and will be same at all the outlet boundaries. It will depend only on the location (coordinates) of pRef.
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