Experimental Investigation of Instabilizing Mechanism of Super High Pressure Pump Induced by Noncontacting Seal

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In the pump design, clearance of noncontacting seal is decreased in order to prevent the leakage flow in a high presure pump, but unstable vibration may occure by decreasing the clearance. In this study fluid force induced by the noncontacting seal and also the vibration of rotor induced by it's fluid force are analyzed.First an experimental apparatus to measure the fluid force induced by the noncontacting seal is built and instability mechanism of the fluid force are analyzed by measuring the axial and circunferencial flow components. That is, flow distribution and pressure distribution in the seal are measured for changing whirling speed and spinning speed of the rotor and the fluid force is obtained from the above measured values.Next the instability force induced by the clearance flow in the seal is theoretically obtained and nathematical model for design of seal is formulated, which is qualitatively coincident with the experimental results.It is concluded from the above analysis; (1) Fluid force increases as the whirl amplitude increases, but it decreases as the seal clearance increases. (2) Inlet swirl velocity effects very much on the stability of rotor system. Positive swirl velocity acts unstable to the rotor and negative one does stable. (3) Tangential fluid force increases as the spinning speed of the shaft increases and it effects unstable to the rotor system. (4) Axial flow velocity effect stable to the rotor system. This effect is represented as the fluid force of the radial direction. (5) Coeffecients of stiffness term K_<xx>,K_<xy> are effected much for the inlet swirl velocity compared with coeffecients of mass and damping terms. (6) The experimental results and the theoretical results obtained by infinite width approximation theory coincide qualitatively but these results have discrepancies in quantity.