Aerodynamic performance and power redistribution in a variable wave-amplitude internal-flow travelling-wave turbine with an expanding passage

Conventional internal-flow travelling-wave turbines employ constant wave-amplitude plate motion in a straight passage, providing limited control over streamwise aerodynamic loading. To address this drawback, a novel coupled geometry–kinematics design integrates a streamwise-increasing plate amplitude with a linearly expanding passage. Two-dimensional unsteady compressible-flow simulations with prescribed travelling-wave kinematics are conducted to compare the proposed and conventional configurations. The proposed turbine achieves a maximum aerodynamic efficiency of 93.4% and a maximum vertical power coefficient of 0.07447 at a* = 0.225 and kh = 0.05. At the same mean amplitude, the upstream and downstream contributions to cycle-averaged vertical power change from 6.39% and 93.61% to 48.05% and 51.95%, respectively. Meanwhile, the mass-flow-weighted outlet velocity decreases from 37.01 to 23.26 m/s and the mean entropy increase decreases from 27.51 to 1.40 J/(kg·K). A moderate amplitude gradient enhances aerodynamic energy conversion by redistributing pressure work and suppressing downstream outlet acceleration and irreversible loss. Excessive amplitude variation causes negative cycle-averaged power in the downstream segment and intensifies separation and loss. The results establish an aerodynamic design principle for coordinating a moderate streamwise amplitude gradient with passage expansion to balance wave-segment loading and avoid downstream negative work, providing guidance for the aerodynamic design and performance optimization of internal-flow travelling-wave turbines.