Thermofluid design and analysis of centrifugal compressors for a 50 MWe concentrated solar power supercritical CO₂ Brayton power cycle

Brayton power cycles employing supercritical CO₂ (sCO₂) as the working fluid are attracting growing interest for use in concentrated solar power (CSP) plants. The primary motivation is to enhance the efficiency of the power block and reduce overall system costs by utilising the high efficiency, compact layout, and reduced turbomachinery size achievable with sCO₂. This study presents the design and simulation of three centrifugal compressors for a 50 MWe CSP sCO₂ Brayton power cycle. To accomplish this, a one-dimensional (1-D) mean line design methodology was developed for preliminary design and optimisation purposes. The methodology employs Latin Hypercube Sampling combined with an exhaustive search strategy to systematically explore the design space and identify optimal compressor configurations based on isentropic efficiency. A 1-D mean line simulation model was then developed to perform design point and off-design performance predictions. The model was validated using data from literature and thereafter used to simulate each of the designed compressors over a range of mass flow rates at the design rotational speed. Further validation was done using 3-D computational fluid dynamics (CFD) simulations conducted at the design point, as well as 90% and 105% mass flow conditions. The results of the 1-D simulation model and the 3-D CFD show good agreement. The findings reveal that compressors with lower rotor tip diameter ratios and meridional velocity ratios generally exhibit higher efficiencies, although values below 0.7 result in excessive diffusion within the blade passages. Optimal flow and work coefficients were found to depend on the specific thermodynamic requirements of each compressor stage. The final high-pressure compressor (HPC) design achieved the highest isentropic efficiency and the low-pressure compressor (LPC) the lowest. Skin friction was identified as the predominant aerodynamic loss mechanism within the rotor. The exhaustive search mean line preliminary design approach provided valuable insights into the influence of different parameters on the performance of each of the machines, while the good agreement between the 1-D and 3-D CFD models provides confidence in the prediction capability of the mean line approach. The methodology applied here can be improved further by incorporating the parasitic work into the preliminary design tool, as well as an equation of state (EOS) capable of handling two-phase flow. To further optimize compressor performance the effects of blade profile and entropy generation can also be examined in more detail.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• De Villiers, Caroline Michelle

Advisors dc:contributor.advisor

• Laubscher, Ryno
• Rousseau, Pieter
• Pretorius, Johannes

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135733

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135733