A comparison of theoretical and experimental rotordynamic coefficients for helically grooved annular gas seals

Abstract

Experimental results for the rotordynamic coefficients and leakage characteristics of helically grooved annular gas seals are presented. The effects of speed, inlet pressure, pressure ratio, clearance, fluid pre-rotation, and groove angle are investigated. The experimental results are then compared to a theoretical code which attempts to predict the rotordynamic and leakage characteristics of a compressible helically grooved cylindrical seal. The experimental results confirmed two important characteristics concerning helically grooved seals. Results showed that there is excellent stability at a range of inlet pressures, speeds, clearances, and groove angles. The results show decreasing stability with increasing groove angle at low speeds and less sensitivity to groove angle at high speeds. The results also showed reduced leakages and relatively insensitive to groove angle. In general, the theoretical code could not predict the experimental results, especially in terms of the magnitude of the results. However, there was some correct theoretical prediction of trends versus groove angle.