Dry gas seals (DGS) are widely used in turbomachinery applications. They are recently being also recommended for sealing novel super critical CO2 turbomachinery space. However, these seals can render interesting behavior under certain operating conditions which needs to be carefully monitored so that intended level of dynamic characteristics can be achieved. The ability of these seals to maintain low leakage by riding at small clearances makes them an attractive solution where secondary flows need to be minimized. To understand the significance of some of the key design features of these seals, in this work an analysis on a gas lubricated spiral groove dry gas seal is presented. Equations in polar coordinates governing the compressible flow through the DGS gap and a numerical method to solve such non-linear partial differential equation is presented. The resulting sets of equations are solved for hydrodynamic pressure distribution and the axial separation force and the film stiffness at the rotor-stator interface is calculated. A detailed study on key spiral groove features is then performed to investigate the effect of spiral angle, groove depth, groove pitch and dam width ratio on the hydrodynamic pressure generation capacity, film stiffness and hence on overall performance of the DGS. Another important phenomenon that can occur in DGS under high operating pressure is the sonic transition. It is shown that choked flow under such conditions can take place over the dam section of the seal which manifests itself into large local pressure and temperature variations and can result into dynamic instabilities.

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