Abstract
For a radial inflow turbine (RIT), leakage flow in impeller backface cavity has critical impacts on aerodynamic performance of the RIT and axial force acting on the RIT impeller. In order to control this leakage flow, different types of labyrinth seals are numerically studied in this paper based on a supercritical carbon dioxide (S-CO2) RIT. The effects of seal clearance and cavity outlet pressure are first analyzed, and the impacts of seal design parameters, including height, number and shape of seal teeth, are evaluated. Results indicate that adding labyrinth seal can improve cavity pressure and hence adequately inhibits leakage flow. Decreasing the seal clearance and increasing the height of seal teeth are beneficial to improve sealing performance, and the same effect can be obtained by increasing the number of seal teeth. Meanwhile, employing seals can reduce leakage loss and improve RIT efficiency under a specific range of cavity outlet pressure. Finally, the influences of seal types on the flow field in seal cavity are numerically analyzed, and results demonstrate that isosceles trapezoidal type of seal cavity has better sealing performance than triangular, rectangular and right-angled trapezoidal seal cavities.
Highlights
Supercritical carbon dioxide (S-CO2) Brayton cycle may be one of the most promising approaches in future power generation systems [1]
In order to control leakage flow of the impeller backface cavity and decrease the associated axial force, Computation Fluid Dynamic (CFD) simulations have been conducted for an S-CO2 radial inflow turbine (RIT)
Compared to the no-seal case, using the labyrinth seal can reduce leakage mass flow rate and axial force acting on the impeller backface (Fax) by 30.97% and 6.61% respectively
Summary
Supercritical carbon dioxide (S-CO2) Brayton cycle may be one of the most promising approaches in future power generation systems [1]. It has higher thermal efficiency, smaller size and better environmental friendliness when compared to traditional steam Rankine and air Brayton cycles. Despite these superiorities, many challenges associated with turbomachinery designs, cycle layouts, heat source and exchanger arrangements and so on need to be overcome for its areal and wide application [2]. The turbine is generally designed in a radial inflow type for small scale applications, and its performance is critical to S-CO2 cycle efficiency [3]. Due to this, improving radial inflow turbine (RIT) performance is one of the major topics in both academic researches
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