Improvements in turbine performance are increasingly driven by the need to control leakage both in the main gas path as well as in the secondary air flow system. Seals for static to static interfaces have a wide usage in gas turbine for component interface locations and are becoming more important as engines reach higher temperature targets and compressor pressure ratios. Both flex and honeycomb seals have been used for many years during other OEM seal service upgrades. These seals are designed to be capable of sustaining low leakage operation whilst achieving long lifetimes. To determine the sealing capability of honeycomb and flex seals an advanced hydraulically actuated rig was designed and constructed. A series of leakage performance tests were carried out that accurately simulate engine conditions, including pressure and relative axial and radial movements. The results of these tests are compared against previously presented data on standard membrane seals. Compared to the membrane seal, the flex seal has approximately 60% lower equivalent clearance when tested with uneven (triangular) grooves. This reduction was due to the bending of the seal and subsequent closing of the seal gap under pressure. The flex and membrane seal performed similarly well under more nominal conditions. The honeycomb seal achieved a consistently low leakage under all pressure loadings. All three sealing types have their place in the required technology mix which is essential when aiming for maximized engine performance and lifetime.

Tight sealing lines are vital in large gas turbines (GT) to achieve high performance and efficiency. Leakage including rim purge air can sum up to 30% of the total cooling and leakage air consumption of a gas turbine. Leakage through static strip seals contributes about 1/3 to all leakage air. Considering the seal design as on drawings, sealing quality is generally influenced by the seal type, sealing groove curvature and the sealing groove roughness. In addition the sealing quality depends strongly on the geometric deviation of the groove compared to ideal design. This is caused by manufacturing deviations or relative movements of the grooves during operation of the parts containing the sealing. In the article at hand, different seal designs and pertinent sealing quality is discussed. More in detail, it is discussed the geometric relation of seal, groove and misalignment to predict the seal position relative to its groove confinements. The risk of seal clamping can be judged and adaptation of seal or groove geometry can be derived. The effect of leakage increase due to misalignment is investigated by a test matrix varying seal length and curvature radius of groove as well as radial misalignment.

Current research and development efforts in the field of heavy-duty gas turbines focus on increasing engine efficiencies, lowering combustor emissions and extending inspection intervals. To achieve further improvements in these development fields, it is crucial for gas turbine manufacturers to continuously build up knowledge on leakage air inside different components of gas turbines. Leakage air can by nature be hardly predicted and is usually only estimated indirectly in real engines. Therefore, investigations on representative test rigs remain a fundamental method for quantifying air leakages more accurately. This article deals with a specific air leakage, which can occur between two firmly pressed rigid surfaces. One challenge for the engineers is to predict the leakage for new surfaces but also used surfaces with fretting corrosion and wear marks as a function of the contact force. In this perspective, air mass flow measurements were performed in a leakage test rig for different contact geometries, pressure ratios and compression levels between the surfaces. The purpose of the analysis is to determine the potential effect of the roughness, length, curvature and contact forces of the pressed surfaces on the leakage amount. The presented measurement procedure and results contribute to the extension of the leakage characteristic database for generic gas turbine components.