An Investigation on the Discharge Coefficient of Compound Orifices in Rotating Disks

Abstract

In the modern multi-shaft gas turbine engines, orifice is an important throttling element and the discharge coefficient of rotating orifices may vary considerably depending on the operating conditions, the geometry and surrounding environment. The influences of the rotating number and the pressure ratio on the rotating orifices flow characteristics are investigated in the present study. Besides, the effects of confined space, wall inclination angle (a) and the angle between the axis of orifice and the disk wall normal (ß) are also analyzed statistically. It is found that the rotating number has a significant effect on the discharge coefficient. As the rotating number increases from 0 to 0.6, the discharge coefficient reduces by about 47.88%. When rotating number is 0.74 and pressure ratio is 1.10, the discharge coefficient can be improved by 16.88% with a changes from 90° to 180°. The parameter, ß, affects discharge coefficient slightly in rotating condition. However, the maximum discharge coefficient is achieved with ß=0° in the static condition. The results also show that, a confined space weakens the effect of rotation, and changes the air flow direction in the inlet chamber, which also has a positive impact on the discharge coefficient. In the current research, it is found that there is a significant difference between the traditional empirical formulas used in the literature and the fitting result. By modifying the incidence angle and taking account of the influence of the angle of inclination, the maximum error was reduced from 56.79% to 3.16%