Free‐surface gravity flows and capillary wicking provide examples of flow structures with fluid partially ducted at “free” surfaces by external forces. “Wall‐less” electromechanical flow structures are developed which have a similar nature, but with polarization forces providing the orientation at free surfaces. Like their mechanical counterparts, these have the ability to ingest liquid or expel vapor through their walls. The structures consist of electrodes running in the flow directionzwith slowly varying cross sections in a plane transverse to the flow. A formulation is given of the long‐wave nonlinear (principal mode) dynamics, with use made of energy functions to represent a broad class of possible mechanical and electrical structure geometries. Based on the considerable analogy shown between electromechanical and gravity flows, conservative flow transitions and shock conditions are described. The role played by gravity waves in conventional free‐surface flows is taken by polarization waves. Three types of experiments illustrate the significance of the model: (i) standing and traveling wave resonances, (ii) critical flow transition, and (iii) fluid pendulum oscillations. Quantitative checks on the small‐amplitude wave dynamics, and on the nonlinear steady dynamics as well as qualitative observations on the behavior of an electrohydraulic jump, are reported.