The cold dark matter and cosmological constant model (ΛCDM) has been successful at describing the observed large-scale structure. However, reported differences on smaller physical scales between simulations and observations have raised the exciting question of whether one of the two main assumptions about the dark matter, namely that it is cold with low thermal velocities and that it is collisionless, could need revising. We present a new code to investigate the collisional nature of dark matter by simulating `Self Interacting Dark Matter’. Based on the N-Body code GADGET-3 it allows us to implement dark matter interactions in a cosmological setting. We show the results of zoom simulations within cosmological boxes, as well as simulations of idealised mergers in which the bulk flow of dark matter leads to a preferred direction along which dark matter particles scatter. We also test the accuracy and speed of different implementations for the interactions. Our results suggest potential new observational probes to test the interaction properties of dark matter.