We present a new method for coupling fluid and particle systems that works by directly manipulating the flow field variables, mimicking the presence of solid particles rather than adding additional force terms in the governing equations as, e.g., in the traditional immersed boundary method (IBM). We demonstrate an implementation based on the open source OpenFOAM [2] package. The OpenFOAM-Interactive (OFI) presented here gives access to all internal field variables of the governing equations. This ease and facilitates complex computational and seamless data exchange and manipulation of the field variable. OFI contributes to reducing the time needed in creating the initial geometry and enables readily recreating the geometry for the basic computational fluid dynamics (CFD) simulation steps. The presented methodology is verified for a reference simple problem (i) obstruction to flow with bluff bodies. The verified methodology is then applied as an example to demonstrate a realistic problem of heat transfer to a gas through particle bed [1]. The particle bed is created “on the fly” with OFI, this will facilitate studying fluid behavior over different particle configurations in particle beds (i.e. porosity variation) more efficiently in future.