Kacper Palkus

A new design solution – the front deflector – intended to improve the performance of the outer air seals of the low-pressure turbine is analyzed in this paper using steady Reynolds-Averaged Navier-Stokes (RANS) simulations of a three-stage, state-of-the-art LPT model, including inner and outer cavities. The regions near the casing in the LPT still show potential for improvement, mainly due to flow interactions associated with the outer air seals. One recent concept for improving these areas is the front deflector. The solution is to modify the front part of the cavity. Its operating principle is to introduce an additional labyrinth for the leakage while simultaneously minimizing the front cavity volume. In the paper, several scenarios for implementing this feature are analyzed, including reducing the front-cavity volume without a static fin and adding a static fin to create an auxiliary labyrinth. Furthermore, the effects on the flow and the potential improvements in LPT efficiency associated with the solution are discussed. The former reduces front-cavity recirculation and its interaction with the mainstream; the latter reduces seal leakage when the fin length is sufficient. Across three stages, the predicted changes in LPT isentropic efficiency are on the order of 0.03–0.06%, depending on the scenario.

A new design solution improving performance of Outer Air Seals of Low Pressure Turbine is analyzed in the paper. The regions near the casing in LPT still show potential for improvements, due to effects associated with presence of Outer Air Seals. One of the recent concepts for improvement of these areas is a Front Deflector. The solution is a modification of the front part of the OAS cavity. The principle behind the concept is to provide additional labyrinth for the leakage and to reduce the front volume to minimum. In the paper, several scenarios of implementation of the deflector are analyzed. The effects associated with the solution on the flow through the outer air seal and the potential for improvement of LPT performance are discussed.

The dimensional analysis and the numerical parametric study of the typical outer air seal from a low-pressure turbine were performed in the framework of the presented paper. The most crucial variables for the flow through the outer air seal were identified and further dimensionless numbers were derived. The dependent quantities resulting from the analysis were: the axial Reynolds number (formulated with the bulk velocity, corresponding to the mass flow through the seal), the outlet swirl ratio (incorporating the exit flow angle, important for mixing) and the windage heating (related to the internal losses). Additionally, the discharge coefficient was cross-checked enabling further comparison with the available literature. The comprehensive numerical parametric study included all important contributors for the flow through the seal with a parameter operating range appropriate for engine outer air seals.