Analysis of Finger Seal Lift Pads

Abstract

Analyses were performed on finger seal pads having a pressure drop across the pad at right angles to the direction of runner velocity. The film was tapered; the clearance could decrease in both the pressure flow and velocity directions. A substantial load could be carried solely due to the pressure flow; however, the bearing exhibited negative stiffness without film convergence in the velocity flow direction. This is in marked contrast to a full circular bearing or ring seal, where pressure flow alone produces a significant stiffness as long as the clearance converges in the flow direction. The performance of three different pad configurations has been evaluated: aspect ratios L/B of 0.5, 1 (square pad), and 2. Design examples pertaining to each aspect ratio were studied for a gas turbine seal. Results show that lowest leakage, highest load carrying capacity, and highest stiffness are attained for the wide-pad configuration, L/B = 0.5. This paper presents a detailed study of the pad; additional analysis needs to be done for the inclusion of the finger and many other considerations for designing a complete seal.