Lab-Scale Experimental Characterization and Dynamic Scaling Assessment for Closed-Loop Crosswind Flight of Airborne Wind Energy Systems

Abstract

This paper presents the experimental validation and dynamic similarity analysis for a lab-scale version of an airborne wind energy (AWE) system executing closed-loop motion control. Execution of crosswind flight patterns, achieved in this work through the asymmetric motion of three tethers, enables dramatic increases in energy generation compared with stationary operation. Achievement of crosswind flight in the lab-scale experimental framework described herein allows for rapid, inexpensive, and dynamically scalable characterization of new control algorithms without recourse to expensive full-scale prototyping. We first present the experimental setup, then derive dynamic scaling relationships necessary for the lab-scale behavior to match the full-scale behavior. We then validate dynamic equivalence of crosswind flight over a range of different scale models of the Altaeros Buoyant airborne turbine (BAT). This work is the first example of successful lab-scale control and measurement of crosswind motion for an AWE system across a range of flow speeds and system scales. The results demonstrate that crosswind flight can achieve significantly more power production than stationary operation, while also validating dynamic scaling laws under closed-loop control.

Electricity in the air: Insights from two decades of advanced control research and experimental flight testing of airborne wind energy systems

“…27, 3D printed models are tethered and flown under closed-loop control in a water channel. The use of the water channel, rather than a wind tunnel, enables achievement of dynamic similarity with regard to all dimensionless variables except for Reynolds number, which still exhibits a significant difference between the two scales (see Cobb, Deodhar, & Vermillion, 2018;Deodhar et al, 2017). Under scenarios where fluid dynamic coefficients remain consistent between the two testing environments, dynamic similarity under open-and closed-loop flight has in fact been confirmed in Cobb et al (2018) and Deodhar et al (2017).…”

“…The use of the water channel, rather than a wind tunnel, enables achievement of dynamic similarity with regard to all dimensionless variables except for Reynolds number, which still exhibits a significant difference between the two scales (see Cobb, Deodhar, & Vermillion, 2018;Deodhar et al, 2017). Under scenarios where fluid dynamic coefficients remain consistent between the two testing environments, dynamic similarity under open-and closed-loop flight has in fact been confirmed in Cobb et al (2018) and Deodhar et al (2017). In other scenarios, where exact dynamic similarity is unachievable, the water channel framework provides a mechanism for refining and validating a dynamic model, which can subsequently be extrapolated to full-scale flight.…”