Research on characteristics of fluid-induced vibration for short labyrinth seals

Short seal (e.g. shroud seal) is a key component for the safe and reliable operation of a turbine unit. This paper sets up the three dimensional numerical model of a short labyrinth seal and analyzes its characteristics of the fluid-induced force. Results show that the tangential fluid-induced force increases almost linearly as the rotational speed increases. The sign of the radial fluid-induced force changes as the rotational speed increases. For higher inlet pressure, a more dramatic increase can be found for both the tangential and radial fluid-induced force. A transition speed range was found that the magnitude of the radial fluid-induced force at higher inlet pressure became less than that at lower inlet pressure. For each seal cavity, the peak pressure location had a shift away from the minimum clearance location as the rotational speed increased. This shift also existed in the axial direction. The effect of the rotational speed on the fluid-induced force became more remarkable for the longer seal with many cavities. Both the radial and tangential fluid-induced force increased with the increasing preswirl ratio. However, the two forces decreased with the increasing preswirl ratio when the inlet total pressure was kept as a constant value. In the end, the critical preswirl ratio which corresponds to zero tangential fluid-induced force was calculated, and results show that a smaller magnitude of the preswirl ratio will be needed to offset the effect of rotational speeds at higher inlet pressures. The inlet preswirl generated a majority of the tangential force for short seals.