In many engineering machines, it is necessary to pass fluid, usually air, through rotating surfaces, such as a disc or drum. This is achieved by perforating the disc with a series of holes arranged on a pitch circle. It is vital for the machine designer to know the pressure ratio required to pass a desired mass flow rate. This characteristic is defined by determination of the discharge coefficient as a function of various parameters. Until recently, the literature describing this problem was small and covered a few particular cases. More articles are appearing and this present study seeks to add to the current level of knowledge by addressing the effect of the inclinations of the holes to the tangential direction. A rig was designed and built to perform the experiments and the data were compared with the numerical analysis performed by proprietary software STAR-CD. The results indicate that the discharge coefficient is highly affected by the rotational speed and that orientating the orifices at an appropriate angle of inclination enables the discharge coefficient to be maximized. Most of the studies in the past used the ratio of tangential speed and the ideal axial velocity to represent the discharge coefficient, but it has been revealed in this paper that incidence angle is more appropriate in correlating the effect of orifice inclination and rotation on the discharge coefficient. Both the experimental and numerical results confirm that the incidence angle plays a major role in dictating the discharge coefficient of the rotating orifices.