As an emerging energy conversion technology, the supercritical carbon dioxide (SCO₂) Brayton cycle offers advantages, including a compact structure and high efficiency. As a core component of the power cycle, the performance of pressurization equipment significantly impacts the cycle’s thermal efficiency. SCO₂, as a working fluid in a state between gas and liquid phases, allows for the selection of pumps for liquid pressurization or compressors for gas pressurization. In the context of SCO₂ power cycles, current domestic and international research on SCO₂ pressurization primarily focuses on centrifugal compressors, with limited attention paid to the feasibility and performance of centrifugal pumps. This study compares the structural design principles of centrifugal pumps and centrifugal compressors, analyzes the challenges posed by the supercritical state of the working fluid to the selection and design of pressurization equipment, and identifies key difficulties in the design and numerical simulation of SCO₂ centrifugal pumps. Additionally, the feasibility of centrifugal pumps as pressurization equipment for SCO₂ power cycles is evaluated, along with the design and operational considerations that must be addressed. Future investigations into three-dimensional flow phenomena will serve as a critical reference for the design of supercritical CO₂ centrifugal pumps.

The high-density nature of supercritical carbon dioxide (S-CO₂) allows for compact centrifugal compressor designs, where small absolute tip clearances result in relatively large normalized clearance ratios. This increases leakage flow at the impeller outlet, altering the velocity distribution, especially compared to air compressors. Steady-state simulations were conducted to investigate different relative tip clearances (CR=0%, 3.33%, 6.66%, and 10%). The results show that due to size effects, the types and distributions of secondary flows and vortices within the impeller vary significantly with tip clearance, affecting the jet-wake distribution at the impeller exit and the stall region in the diffuser. When the relative tip clearance exceeds a certain threshold, some secondary flow becomes trapped in the clearance, moving towards the impeller outlet and forming a low flow velocity region on the shroud side. Additionally, when the relative clearance is small, the wake region is primarily affected by channel and separation vortices. As the relative tip clearance increases, the secondary flow in the channel weakens, while the leakage flow intensifies, causing the leakage vortex to extend and dominate at higher blade heights, at the same time, the separation vortex to be formed near the suction side at mid to high positions. Consequently, the core region of the wake at the impeller outlet shifts from the hub side to the casing side, and the reverse flow region in the diffuser shifts from below 20% span (near the hub) to above 80% span (near the shroud).

The compression power consumption of the working fluids in the near-critical region is low. However, there is currently no research on the common characteristics of near-critical region compression for different types of working fluids. This paper takes H₂O, CO₂, and R134a as research subjects, and based on the common characteristics of the physical properties of working fluids in the near-critical region, a 1D common design method and performance prediction model for near-critical compressors are proposed. Meanwhile, 3D models of centrifugal compressors are established based on the 1D design results. The 3D numerical simulations results show that there is about a 4% error between the numerical simulation results and the 1D performance prediction. Therefore, a slip factor model and a flow correction coefficient are introduced to account for the impact of rotating speed and mass flow rate changes on the loss models. At the same time, the friction loss coefficient and through-flow loss coefficient are corrected based on the viscosity of different working fluids. After optimization, the error under off-design conditions between the numerical simulation results and the 1D performance prediction results is maintained within 1.2%, demonstrating the advantage of the new model in predicting the near-critical compression performance of different working fluids.

Controllable speed casing (CSC) represents an innovative development in casing treatment technology, wherein the traditional stationary casing is reconfigured into two components: a rotatable ring and a stationary ring. Initial position (IP) of the rotatable ring is a critical parameter affecting the operational effectiveness of CSC. This study investigates the influence of varying IP of the rotatable ring on the aerodynamic performance and flow stability of a high-load compressor stage, with terminal position (TP) fixed at the rotor tip trailing edge. The results reveal that positioning the rotatable ring near the rotor tip trailing edge leads to moderate improvements in stability by controlling the secondary flow at the trailing edge. However, when IP coincides with the region where the tip leakage vortex and induced vortex breakdown, CSC disrupts the upstream flow, increasing the blockage of low-energy fluid, thereby precipitating an early stall in the compressor. Conversely, positioning IP at the rotor leading edge enables CSC to effectively manage tip leakage flow, facilitating the deflection of the tip leakage vortex away from the adjacent blade pressure surface. This adjustment mitigates the blocking effect within the blade tip passage, thereby significantly enhancing the compressor’s flow stability. Under these optimal conditions, CSC achieves a substantial 45.11% improvement in stable operating margin of the compressor.

The opposing jet technique has the potential to provide superior aerothermal protection for long-term high-speed flight in the atmosphere. However, the single-hole opposing jet has certain limitations, including a high requirement for jet injection pressure and inadequate maneuverability. To overcome this, a novel multi-hole opposing jet concept has been proposed, comprising a primary hole located at the stagnation point and multiple secondary holes located downstream. The findings indicated that a secondary hole positioned inside the primary jet recirculation vortex can inhibit primary jet flow reattachment and mitigate peak reattachment heat flux. A smaller secondary hole could impede the lift-off effect of the downstream vortex, facilitating efficient heat reduction at various jet injection pressures. The side-by-side and staggered multi-hole opposing jet configurations were established, which demonstrated an efficacy in reducing the peak heat flux by 11.7% statistically compared to a single-hole injection at the same mass flow rate. When an incoming angle of attack was presented, the multi-hole arrangement exhibited a further peak heat flux reduction of 12.2% by statistical analysis. The results underscore the effectiveness of multi-hole configurations with low-pressure injection in reducing heat and enhancing maneuverability, while demonstrating stronger engineering applicability than traditional combined thermal protection systems without structural compromises or flow instability risks.