ABSTRACT The aim of our work is to improve the understanding of flow distribution and determine the optimum set of hydraulic design parameters that favour the drilling fluid circulation, with both computations and experiments. Once a new bit design has been defined according to these criteria, field tests will be done for a final validation. This paper deals with a modelling of the turbulent flow occurring around a PDC bit. Numerical simulations have been done to study and quantify the influence of parameters such as flow rates, nozzles sizes, locations and inclinations, on the fluid behaviour. Comparisons with theory and experiments done on the same bit, including laser velocimetry data allowed us to check the accuracy of the computer code. All these studies have revealed complex flows with various main structures such as eddies, counter currents, low circulation zones and impact points. To improve the fluid distribution along the bit and especially along the cutting edges, we have searched the most fitted design parameters which could avoid negative hydraulic structures. In that way, we are now able to design a more efficient bit.