The project “Efficient Swirl Generators for Multi‑Wave Compressors” (FlexASU, 03SFK300‑2) was carried out within the second phase of the SynErgie programme. It was funded by the Institute for Aerodynamics (ISA) and involved a consortium of industry and academia: MAN Energy Solutions, Linde AG, the Technical University of Berlin, RWTH Aachen, and the Technical University of Munich. The work built on a test rig that had been established during SynErgie I at the Institute for Jet Propulsion of the University of the Bundeswehr Munich. The consortium met regularly through seminars and workshops, and the project ran from the completion of SynErgie I through the full duration of SynErgie II, covering the design, manufacture, and experimental evaluation of new swirl‑generator concepts.

The scientific focus was to enlarge the loss‑free operating range of swirl generators, which are the primary control devices in air‑separation plants. Conventional swirl generators use a single, symmetric blade with open tips. Their performance deteriorates when the redirect angle becomes too large, leading to flow separation, high pressure losses, and reduced compressor efficiency. The team introduced a two‑segment blade concept with a variable geometry skeleton. By sealing the gap between the front and rear blade segments, the new design achieved a clear performance advantage over the open‑tip configuration. Experiments showed that a fully sealed gap yielded the best results, while a partially sealed gap produced intermediate performance. The optimal distribution of redirect work was found to be close to equal between the two blade segments; an uneven split caused a noticeable increase in flow losses.

A further innovation was the replacement of open blade tips with a hub (Nabenkörper). This modification increased the swirl intensity at the same blade spacing, but introduced additional aerodynamic losses at low redirect angles due to the hub’s struts. Consequently, the hub‑based design is best suited for compressors that operate frequently at partial load, a regime increasingly important for demand‑side management in power systems with high shares of renewable energy. The new swirl‑generator configurations therefore provide a more flexible and economical solution for air‑separation plants that must adapt to fluctuating energy prices.

The experimental programme also advanced measurement techniques. In addition to the five‑hole probe already used in SynErgie I, the team introduced an oil‑film method to capture near‑wall flow characteristics. An oil‑removal mechanism was installed to prevent oil deposition on optical sensors, thereby expanding the usable measurement portfolio. These developments not only improved the accuracy of the current study but also laid the groundwork for future research and student projects, enhancing ISA’s capacity to secure third‑party funding.

Overall, the project delivered a set of validated swirl‑generator designs that extend the loss‑free operating envelope, improve partial‑load performance, and support the integration of variable renewable energy into the electricity grid. The results have been disseminated through peer‑reviewed publications and presentations at international conferences, ensuring that the scientific community and industry partners can benefit from the advances achieved.