60252 - On Sco2 Compressor Performance Maps at Variable Intake Thermodynamic Conditions 

Unconventional aero-thermodynamic phenomena affect the performance of compressors that operate with carbon dioxide (CO2) close to its thermodynamic critical point. As a consequence, whether compressor performance maps based on conventional scaling parameters, such as flow coefficient and peripheral Mach number, still posses general features remains an open question.
In this work, we show that additional dimensionless parameters are needed to ensure full similarity conditions when intake thermodynamic conditions vary. Thanks to a combina-tion of three-dimensional turbulent-flow simulations, analytical-based expressions and physical flow insights, three independent phenomena are found to differently affect compressor operation when changing the upstream total state: (i) non-ideal effects that can modify the fluid compressibility from liquid-like to gas-like and viceversa, (ii) the extent of the two-phase region within the blade channel, (iii) the resulting compressibility of the two-phase mixture. Three dimensionless parameters are introduced to separately account for such effects. The influence of these parameters on compressor performance maps is widely discussed, shedding lights on the way they act in the modification of the ideal similarity based only on the flow coefficient and the peripheral Mach number.
As a general result, two operating conditions can be regarded as similar when all the above dimensionless parameters are kept constant. These findings are expected to be relevant for the plant regulation in off-design conditions and for planning ex-perimental campaigns at different thermodynamic conditions.