Evaluation of a Water Channel-Based Platform for Characterizing Aerostat Flight Dynamics: A Case Study on a Lighter-Than-Air Wind Energy System

Abstract

Aerostat development and testing costs often suffer from a lack of scalability. In particular, it very difficult to fabricate an inexpensive lighter-than-air system that can be evaluated in a lab environment, since the maximum allowable mass of the aerostat becomes prohibitively low for small length scales. This paper presents an evaluation of a novel water channel-based platform for assessing the flight dynamics of aerostats at a very small scale, in a lab environment, for a very low cost. Altaeros Energies' buoyant airborne turbine (BAT) is used as a case study to demonstrate the effectiveness of the proposed approach. Specifically, we identify important dynamic scaling properties and show how the water channel experiments are run to match these properties closely in the water channel vs. full-scale settings. We then show how the water channel results can be used in concert with a simulation model to predict the performance of the full-scale system. The ultimate result is a design which, after an inexpensive evaluation process, can proceed to a larger-scale prototype stage with a high degree of confidence in its success.

A case study in experimentally-infused plant and controller optimization for airborne wind energy systems

“…8 shows a heading offset that corresponds to the BAT operating under the initial set of design parameters. This behavior was in fact observed in full-scale flight under improper ballasting configurations, as described in [17] and [16]. It is therefore encouraging that the experimentallyinfused optimization employed in this work was able to identify and rectify this known problem.…”

“…For the case study described herein, this was accomplished by 3d printing 1/100-scale ABS plastic models that were subsequently tethered and flown in the UNC Charlotte 1m × 1m water channel. The experimental setup is an extension of earlier work by one of the co-authors to study passive flight properties at University of Michigan in conjunction with Altaeros Energies, which is described in [15] and [16]. These references demonstrate the dynamic equivalence between key properties of the labscale and full-scale systems, where a more comprehensive equivalence study based on dimensional analysis is a topic of current investigation.…”

“…These references demonstrate the dynamic equivalence between key properties of the labscale and full-scale systems, where a more comprehensive equivalence study based on dimensional analysis is a topic of current investigation. The present experimental setup expands upon the setup of [15] and [16] through the incorporation of closed-loop control. Fig.…”

“…For the specific case study considered in this paper, we isolated our optimization to two very important system parameters, namely the center of mass position, x cm , and the trim pitch angle, θ sp , which have been shown in [15] and [16] to dramatically influence flight performance. Because experiments were run at 1/100-scale, in a water channel environment, it was important to consider non-dimensional parameters in the optimization.…”

“…The proposed technique, referred to as experimentally-infused optimization retains the simplicity of the dynamic model used for numerical optimization, reconciling differences between the model and reality through lab-scale experiments. Furthermore, the use of 3d printing technology to test 1/100-scale models in the water channel enables accurate characterization of important system characteristics (such as added mass effects, net buoyancy, and scaled inertial properties, along with general stability and damping characteristics) at orders of magnitude lower cost than a full-scale prototype, as further detailed in [15] and [16]. This paper presents a case study of experimentally-infused optimization on the Altaeros BAT, which focuses on two non-dimensional (and therefore scalable between the water channel and full-scale) parameters that are tightly interconnected, namely the trim pitch angle and the center of mass position.…”