Design of a test rig for the investigation of water separation in two-phase annular flow

At the Institute of Aerospace Thermodynamics, a test rig was built that is capable of generating two-phase flow conditions with air velocities of up to Ma = 0.25 and liquid water mass fractions of up to 30% in order to investigate water separation processes for future aircraft propulsion systems such as the Water-Enhanced Turbofan (WET) or the Flying Fuel Cell (FFC). The resulting annular flow is characterized by moist air and water droplets in the core region and a wall film at the pipe wall, which suggests the use of separation lips in combination with an upstream vane swirler. This configuration enables water separation at high flow velocities and low available space, which are the key requirements for the aforementioned technologies. In this paper, the design of the test rig is presented. This includes the generation and sensitivity analysis of the inlet conditions, as well as the measuring principles and an uncertainty analysis of the two target quantities, Water Recovery Factor (WRF) and Darcy friction factor (fD), which represents pressure losses. The results indicate a sufficiently developed turbulent velocity profile in the test section and high repeatability. Preliminary two-phase flow results show that the configuration yields WRF values of over 94% for all operating points, which demonstrate the test rig's capability to perform well in these critical conditions. This, however, results in increased pressure losses, indicating the trade-off between the target quantities. Therefore, the presented university test rig serves as a foundation for future basic research and geometric optimization studies.