Annular seals are used in many turbomachineries to reduce the leakage from high to low pressure zones. In this paper, 2D CFD simulations are used to analyze the flow inside straight annular seals and convergent tapered annular seals with two different exit clearances. The working fluid used was water. The effect of the geometry and surface roughness on the seal performance was studied at different differential pressures and rotor speeds. Moreover, a new design parameter is introduced that relates the normalized axial pressure gradient to the axial wall shear stress for straight and convergent annular seals. This ratio was found to be constant at different seal geometries, exit clearances, differential pressures, and rotor speeds. This allows designers to consider the effects of various convergent tapered seal designs upon the rotordynamic characteristics of the seal without requiring individual CFD simulations.

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