Performance improvement of a turbine pre-swirl system using impellers to achieve high pressure energy and low entropy increase

An essential component of the turbine rotors' high-temperature thermal protection is the pre-swirl system. However, the low-radius pre-swirl system typically has inadequate air supply pressure, which hinders high-temperature turbine blades' ability to operate reliably. To address this key problem, this study proposes improving the pre-swirl system by implementing an impeller structure. The goal is to increase the system's air supply pressure energy, guarantee a steady and adequate supply of cooling medium for high-temperature blades, and ultimately ensure their long-term dependable operation. The evolution mechanism and intrinsic correlation between air supply pressure and entropy increase in the pre-swirl system are first systematically derived using the theory of fluid mechanics. The main problem of increasing air supply pressure energy is addressed by a targeted performance optimization strategy. A high-speed pre-swirl system test bench is then set up, and using a combination of numerical simulations and experimental testing, a methodical comparison of the flow properties and temperature drop laws of the pre-swirl models with and without impellers is conducted. The results demonstrate that the impeller structure can efficiently lower the flow resistance in the system's rotor region, considerably raise the air supply pressure, and improve the cooling effect of the blades when the flow ratio and rotational speed are fixed. In particular, the experiment shows that the model with an impeller has an average dimensionless rotor entropy increase that is 44.0% lower than that of the model without an impeller when the rotational Mach number is 0.70. Additionally, the average rotor pressure ratio of the model with an impeller is 9.01% higher than that of the model without an impeller. Interestingly, the impeller has the greatest impact on reducing the flow loss of the supply hole; upon its installation, the supply hole's dimensionless entropy increase drops by up to 70.5%. By inhibiting the relative circumferential Mach number of the airflow from rising with the radius, the impeller successfully lowers the relative Mach number at the supply hole's inlet, inhibiting the entropy increase in the hole's constituent parts, according to the mechanism analysis. In the end, a greater air supply pressure energy is obtained, giving high-temperature blades a more dependable thermal protection guarantee.