Leakage performance evaluation of cloth seal

Official URL: https://risc01.sabanciuniv.edu/record=b2553620 _(Table of contents)

Turbomachinery sealing technology is concerned with the crucial tasks of maintaining pressurized regions, leakage control, cooling control, purge flow, and axial force balance. Thus, advances in sealing technology have considerable impact on overall turbomachinery performance, decreasing operational costs, fuel consumption, and NOx emmisions. Cloth seals as a new stationary seal have been used as an alternative to thick metal shim seals to reduce leakage rate and increase wear life. The cloth seal includes one or more metallic-cloth fibers (cloth weave) and a thin metal shim. Measuring actual cloth seal leakage proves difficult with challenging turbine operating conditions. Modeling the flow through the complex weave voids among each warp and shute fiber involves a very complex flow structure, extensive effort, and high CPU time. Therefore, a bulk porous medium flow model with flow resistance coefficients is applied to the model cloth seal weave fibers. CFD analyses need leakage data depending on the pressure load to calibrate flow resistance coefficients. A test rig is built to measure leakage of cloth weave with respect to the pressure load and weave orientation in four directions. The Sutherland-ideal gas approach is utilized to determine the flow resistance coefficients for Dutch twill metallic-cloth fibers as a function of pressure load. Moreover, equations to calculate the porosity of plain and twill weave are developed and compared with available data. Literature reviews indicate that available published data about cloth seal leakage performance are not adequately detailed to derive a closed-form equation defining the relationship between seal design parameters and cloth seal leakage performance. In an effort to fill this gap, the effect of geometric parameters under varying pressure load on the cloth seal leakage performance has been investigated in this study. In order to reduce the number of parameters to a manageable size, some of the parameters are fixed and excluded from the experimental design based on the studies in the literature. The remaining eight parameters are included in the screening experiments. Their levels are determined to cover typical application ranges. Parameters, which have a major impact on leakage rate, are determined in the screening experiments, and analyzed in the main experiments. A closed-form equation is derived based on the data and presented in this study. Leakage rate trends with respect to levels of each parameter are examined. In order to conduct leakage tests of screening and main experiment designs, several cloth seal designs are manufactured, and another custom test rig has been designed.