Carbon capture and storage could significantly reduce carbon dioxide (CO2) emissions. One of the major limitations of this technology is the energy penalty for the compression of CO₂ to supercritical conditions. To reduce the power requirements, supercritical carbon dioxide compressors must operate near saturation where phase change effects are important. Nonequilibrium condensation can occur at the leading edge of the compressor, causing performance and stability issues. The characterization of the fluid at these conditions is vital to enable advanced compressor designs at enhanced efficiency levels but the analysis is challenging due to the lack of data on metastable fluid properties. In this paper, we assess the behavior and nucleation characteristics of high-pressure subcooled CO2 during the expansion in a de Laval nozzle. The assessment is conducted with numerical calculations and corroborated by experimental measurements. The Wilson line is determined via optical measurements in the range of 41-82 bar. The state of the metastable fluid is characterized through pressure and density measurements, with the latter obtained in a first-of-its-kind laser interferometry setup. The inlet conditions of the nozzle are moved close to the critical point to allow for reduced margins to condensation. The analysis suggests that direct extrapolation using the Span and Wagner equation of state (S-W EOS) model yields results within 2% of the experimental data. The results are applied to define inlet conditions for a supercritical carbon dioxide compressor. Full-scale compressor experiments demonstrate that the reduced inlet temperature can decrease the shaft power input by 16%.

Rocket engine turbopump inducers can suffer from cavitation instabilities, dramatically limiting performance and life of the turbomachinery components. An unrestricted inducer geometry, representative of the Space Shuttle main engine low-pressure oxidizer pump inducer, is defined and serves as a platform for characterization of the cavitation dynamics. Experiments demonstrate rotating cavitation, alternate blade cavitation, and cavitation surge. Borrowing ideas from the modeling and assessment of rotating stall in aeroengine compressors, a previously established traveling wave energy analysis is applied. At flow coefficients higher than design, a single cell cavity occurs rotating at supersynchronous frequencies between 1.2 and 1.5 times rotor frequency. Optical measurements corroborate the findings and underlying mechanisms; the onset of rotating cavitation is governed by the interaction of the blade cavity with the leading edge of the adjacent blade. This leads to a change of incidence, which causes sheet cavity breakoff with periodic growth and collapse of cavities, yielding the apparent supersynchronous rotation of the cavities around the annulus. The paper breaks new ground in diagnostics of inducer dynamic behavior during rotating cavitation, alternate blade cavitation, and cavitation surge. The details of the unrestricted inducer geometry are provided for advancement of international research on rocket engine cavitation dynamics.