One of the most common geophysical phenomena, lightning, involves a variety of physical processes, starting from plasma physics to atmospheric physics. The Master thesis concerns the process of electrification in thunderclouds which leads to lightning. Although commonly observed in nature, this process is still poorly understood. However, its believed that the two major mechanisms by which this occurs, are, first, the convection of positive space charge with updrafts and second, the electrification due to collisions between graupel and ice particles. This work focuses on the second mechanism. Within this study, we develop a simple numerical model, where particles of ice and graupel are traced in an externally provided, simplified velocity field, laminar and turbulent. For the case of graupel, we assume that in the core of a thunderstorm cloud, the magnitude of its terminal velocity is equal to that of the updraft velocity. Thereby, the graupel particles remained on average, suspended in the flow, and small ice particles were advected, passing by and colliding with the graupel. We observed the accumulation of ice particles in regions of small vorticity, such that the local concentrations of the particles resembled eddy-like structures. This picture is very much dependent on the characteristic size of the eddies. Based on the recorded collision rate for laminar and turbulent flow, we conclude that turbulence does indeed enhance the collision count.