Abstract:

Labyrinth seals are commonly used in rotating machines such as pumps, compressors, turbines and food processing machinery. They are typically selected in applications where there is high relative speed between rotating components and there is a requirement to limit the flow of fluid. In its simplest form, a labyrinth seal consists of a series of radial fins forming a restriction to an annular flow of fluid. Labyrinth seals work by throttling the flow through successive openings in series. In each throttle, static pressure difference accelerates the flow and some of the kinetic energy associated with the flow is dissipated by turbulence induced by the intense shear stress and eddy motion in the next chamber.

Care must be taken in the design of labyrinth seals. If the cavity following the radial fin is too small the flow will pass straight through without expanding and without the subsequent pressure drop. Despite careful labyrinth design and specification of a labyrinth seal parameters, flow will inevitably be carried straight over from one fin to another. In order to reduce this effect, steps can be incorporated into a labyrinth seal design and a wide range of labyrinth variants are possible. Methods available for quantifying the leakage through a labyrinth seal include empirical, analytical and numerical computational fluid dynamics (CFD) techniques.

This Data Item:

• introduces a variety of seal configurations relevant to rotating machinery;
• assists engineers in the selection of a labyrinth seal for a specific rotating flow application;
• provides methods and recommendations for the flow performance assessment and design of straight-through and stepped labyrinth seals by means of quantifying the leakage flow rates;
• introduces methods for quantifying the leakage flow rates in staggered and radial labyrinth seals.