The application of swirl reducing features to brush seals in high shaft speed locations

Effective seals are critical to achieving high engine thermal efficiencies and low specific fuel consumption. Compliant shaft seals such as brush seals have offered improvements in seal leakage over the legacy labyrinth seals, but have been somewhat limited in application particularly at high radius and shaft speed. Hence robustness remains a challenge within these harsh environments. Brush seals are typically exposed to high pressures and often high levels of inlet swirl. This paper investigates a novel means by which the inlet flow can be conditioned, thus reducing or negating the inlet swirl that is incident on the upstream rows of the bristle pack. Grooved features are evaluated over a range of engine-representative operating conditions using computational fluid dynamics of a sector of the brush seal. The key dimensionless quantities that describe the problem are identified. Pressure, temperature, leakage flow rate, swirl level, and shaft speed are varied in a parametric study to evaluate groove efficacy and to provide useful design insights which could improve the robustness of brush seals within challenging environments. The results show that the simulated groove is effective over the majority of the engine range, except for conditions where shaft rotation dominates over inlet swirl and hence groove performance. The effect of seal clearance, either by design or due to in service wear, and larger axial velocities in the seal, is shown to be significant in reducing groove de-swirl performance. The results are very encouraging from the perspective of applying grooved front plates to brush seals, and potentially other advanced engine seal types, in order to reduce their sensitivity to inlet swirl over the expected range of high-shaft speed, high-pressure and high-temperature environments.