[A Muharib]

Hi all I am very new to using STAR CCM+ and was wondering if some one could help me with my dilemma. I have both a Hi and Low Re meshes designed to model flow through a 2x2 inline tube bank. I am modelling the turbulent flow through the 3-D system by including periodic boundaries on x, y and z directions. Essentially trying to observe the pressure, coefficient of pressure, and nusselt number around the central tube. The model description is presented below:
Model Considered -
Constant Density
Gas - Air
High y+ wall treatment
Implicit Unsteady
RANS
Reynolds Stress Model
Quadratic Pressure Strain (which is the same as SSG)
Segregated Flow and Fluid Temperature
Three Dimensional
Turbulent

Air properties:
Density = 1.0
Dynamic viscosity = 2.43902439 x10-5 (1/Reynolds number) and Re = 41,000
Specific heat = 1009
Thermal conductivity = 0.0024609756 (viscosity x specific heat)
Turbulent Prandtl Number = 1.0

Initial conditions:
Pressure = 0.0
Static temperature = 500K
Turbulence intensity = 0.03
Turbulent velocity scale = 1.0
Turbulent Viscosity ratio = 10
Velocity = 1.0

Reference Values:
Min allowable wall distance = 1.0 x 10-6
Min allowable temp = -500 k ( I know this is completely unrealistic however I am using temperature as a passive scalar so it really has no knock on effect to the density and rest of the calculation)
Max allowable temp = 5000k
Reference Pressure = 0.0

I am struggling with a few problems:

1) Defining the correct stopping criteria and time step for the implicit unsteady solver.

2) I have managed to simulate pressure differences with the simulations I have run so far, however I cannot seem to get the nusselt number plots to work correctly i.e. I get nothing.

3) I am essentially trying to model an inline tube bank, hence the periodic boundaries. I have set the y and z - periodic boundaries with a zero pressure jump. Yet the x - direction periodic boundary has been defined with a mass flow rate of 0.12 kg/s in order to drive the flow. I was wondering if this approach was correct.

Any help would be greatly appreciated. Thank you.