Re: Pressure Inlet
the function defineRho() expects lattice values. To convert a physical pressure to a lattice value, there is a function in the LBconverter called rhoFromPhysicalPressure, just have a look at the doxygen documentation:
Also when looking at e.g. the cylinder2D example the inflow velocity is slowly increased in the function setBoundaryValues(), you could try that for the pressure too. Setting large gradients without smooth transition can lead to numerical instabilities.