Abstract
Supercritical carbon dioxide (SCO2) is a vital working fluid in the application of power units and its high density helps to achieve a compact mechanical structure. Centrifugal compressors are of vital use in various kinds of equipment. In this paper, a SCO2 centrifugal compressor of large input power and mass flow rate is designed and numerically investigated. A thorough numerical analysis of the unsteady flow field in the centrifugal compressor is performed in ANSYS-CFX. The computation adopts hexahedral mesh, finite volume method, and the RNG k-ε two-equation turbulence model. Streamlines, temperature, pressure, and Mach number distributions at different time steps in one revolution period are covered to present the unsteady effect of turbomachinery. Meanwhile, the force on a single rotor blade is monitored to investigate the frequency components of exciting force, thus providing the foundation for vibration analysis. Moreover, the torque, output power, pressure ratio, and isentropic efficiency in the steady and the unsteady time-averaged condition are calculated and compared with the design condition to measure the validity of the design. In summary, the unsteady computation result reveals that the unsteady flow characteristics are prominent in the designed compressor and the design of impeller and diffuser meet the requirement.
Highlights
Supercritical carbon dioxide (SCO2 ) is a kind of supercritical fluid which has a critical point at around room temperature
The time step was set as 1.3333 × 10−5 s, which indicates that 20 steps were needed to pass a diffuser passage. It has been concluded by Liu Y.W. et al that, in general, unsteady simulation is recommended to compute at least 10 to 20 time steps per period
Withthe theabovementioned abovementioned boundary conditions, an unsteady numerical analysisanalysis was conducted based on the steady boundary conditions, an unsteady numerical was conducted based on simulation the steady result
Summary
Supercritical carbon dioxide (SCO2 ) is a kind of supercritical fluid which has a critical point at around room temperature. As a working fluid in a centrifugal compressor, SCO2 possesses lots of merits. Its critical condition is easy to reach and it is an environmentally friendly working fluid, which makes SCO2 safe and cheap for industrial use [2]. The most useful advantages of SCO2 are its high density, low viscosity, and large pressure increase with small enthalpy increase, which result in high efficiency, compact mechanical structure, and a larger pressure ratio with smaller input power in the centrifugal compressor [3,4,5].
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