MEASURED EFFECT OF STEP AXIAL LOCATION ON LABYRINTH SEAL LEAKAGE

AN advanced finite volume computer code,1,2 previously benchmarked against numerous seal measurements, was extensively used in a parametric design study of simple stepped seals. The objective was to 1) use the computer code to determine an optimized design to minimize leakage; and 2) to test it along with the baseline design. The wear-ring seal of a high-pressure pump was utilized as the baseline case. Complete details of the two designs as well as the overall investigation itself are found in Ref. 3. Both designs have a radial tooth clearance of 0.216 mm. For example, the optimized design has a land step radial height of 3.61 mm and a tooth thickness of 0.76 mm, whereas the baseline design has a step height of 0.58 mm and a tooth thickness of 0.38 mm. Turbomachine applications exhibit various degrees of axial shifting of the rotor relative to the stator over a range of operating conditions. It was found that a significant leakage effect arises from this shifting of the rotor and stator sealing surfaces. For cases with small seal shifting, a 67-79% leakage reduction can be obtained in the same allowable sealing space by using the optimized design. In addition, it was found that, for extremely low rpm, a significant shaft speed effect occurs for the optimized design for some shaft locations.