軸方向に部分的にねじ溝を設けたシールの静および動特性に関する数値解析

（ねじ溝の長さによる影響）

抄録

Liquid annular seals with axially partial helical grooves were proposed to improve the efficiency and stability margin of pumps. Numerical analysis was carried out to investigate the effects of the axial length of the helical groove, g_la , which is measured from the seal inlet, upon the static characteristics (leakage flow rate) and dynamic characteristics (dynamic fluid forces, dynamic coefficients, and whirl frequency ratio). The leakage flow rate Q for the partially helically grooved seals was lower than that of the conventional through helically grooved seal. Under a lower range of rotor spinning velocities N, Q decreases with g_la. On the other hand, under a higher range of N, the quantitative difference in Q due to g_la becomes small as compared with that under a lower range because the reduction in Q due to the pumping effect becomes more pronounced for a larger g_la. For a small concentric whirling motion of the rotor, the radial dynamic fluid force suppressing the rotor whirling amplitude for the partially helically grooved seals was larger than that for the through helically grooved seal, and increased with decreasing g_la. The tangential dynamic fluid force suppressing the rotor whirling motion for the partially helically grooved seals was larger than that for the through helically grooved seal. The magnitude of variation in the tangential dynamic force with the whirling angular velocity for the partially helically grooved seals was larger than that for the through helically grooved seal, and increased with decreasing g_la. As a result, the partially helically grooved seals yielded larger main stiffness coefficient Km and damping coefficient C_m than the through helically grooved seal, and these coefficients increased with decreasing g_la. The partially helically grooved seals also provided lower values of the cross-coupled stiffness coefficient K_c and the whirl-frequency ratio _WFR defined as K_c /(C_mω), where ω is the angular velocity of the rotor spinning, than the through helically grooved seal under a lower range of N. The maximum value of N under which K_c and _WFR for the partially helically grooved seals become lower than those for the through helically grooved seal increased with g_la.