13th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
Leakage between rotating and stationary parts in turbomachines has a strong impact on performance and reliability. So, the demand for robust and reliable sealing solutions is high. Under challenging operating conditions, dry gas seals and aerostatic gas seals are used to avoid high leakage rates and high friction losses. Generally, an aerostatic seal is pressurized by several holes distributed over the sealing. As a result, a gap of a few micrometers between the slip ring and rotating ring arises. This operation is very similar to that of an air bearing. However, it has been shown in the past that the use of porous materials makes the flow film more stable regarding any force effects. The major difference between an aerostatic seal and an air bearing is that the porous layer of an air bearing is mounted in the housing in a fixed manner, while it is freely movable in a gas seal and thus adjusts autonomously with respect to its force equilibrium. These characteristic properties impact the entire operational behavior of a seal. In this paper a numerical investigation is undertaken to check the feasibility of an aerostatic gas seal with a porous ring. By using MATLAB, a design tool is developed to quickly calculate the pressure profile in the gap and the operational behavior of the seal. Special focus is put on the control of the permeability (pore distribution) and the geometric size of the porous material and its impact on the gap flow. The model is based on the assumption of Darcy’s law in the porous part and a laminar viscous flow field with isothermal conditions in the gap. Using a test bench, the numerical analysis is validated. In addition, the pressure distribution in the gap is shown when lifting the porous ring for different permeability distributions.