Aerodynamic aspects of the sealing of gas-turbine rotor-stator systems

The sealing characteristics of a shrouded rotor-stator system have been studied using flow visualization, pressure, and concentration measurements. Seven shroud geometries, incorporating axial clearance, radial clearance, or mitered seals, have been tested for a range of clearance ratios and rotational Reynolds numbers up to Reθ = 1.2 × 106. For all axial clearance seals, the superimposed airflow rate necessary to prevent the ingress of external fluid into the rotor-stator wheel space increased with rotational speed and with seal clearance. Owing to a “pressure inversion effect,” where the pressure in the wheel space increased rather than decreased with rotational speed, the increase of sealing flow rate with rotational speed for two of the radial clearance seals was less than that for the other seals. As expected, the mitered seal had a performance intermediate between the purely axial clearance seals and the radial clearance seals exhibiting the pressure inversion effect. The tests referred to above were conducted in a quiescent environment. In parts 2 and 3, the effect of an external axial flow of air at the periphery of the system is studied.