Two coupled turbines are used to harness wave energy using a pair of fluidic diodes (FDs). A better FD should have a higher diodicity defined as the ratio of pressure drop in reverse to forward flow direction. The reverse flow occurs when the wave pushes air out of the system, and one diode-linked turbine gets power, while the forward flow gives power to the other diode-linked turbine. In this article, an FD is proposed and studied numerically by solving three-dimensional Reynolds Navier–Stokes equations. The FD shape is optimized using a surrogate-based optimization technique. The result shows that the optimized diodicity is increased by 185% because the reduction in the throat diameter of the model facilitated a higher resistance to the reverse direction. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.