# Optimizing Bladeless Wind Turbines: Morphological Analysis and Lock-In Range Variations
## 3 Methodology  
### Prototype Design  
The blueprint for the prototype was meticulously crafted, considering multiple factors to ensure its functionality and efficacy. This prototype served as both a proof of concept and a testbed, enabling a comprehensive evaluation of the blackless wind turbine's performance based on VIV. Commencing with material selection, the design process prioritized materials possessing robustness, durability, and lightweight properties essential for operational efficiency. The structural components were designed to withstand dynamic wind forces, wich produce vibrations. Aerodynamic optimization formed a cornerstone, focusing on shaping and refining surface characteristics to facilitate the vortex generation and shedding, thereby promoting VIV. In this way, wind tunnel tests were employed to analyse and refine the turbine's aerodynamic efficiency. In the present work, the prototype used incorporates sensors and data acquisition systems to real-time monitor some critical parameters, like wind speed and vibration amplitudes. These data proved instrumental in evaluating the prototype's performance and identifying avenues for further enhancements. Derived from [35], the prototype used in this study adheres to the dimensions illustrated in Figure 3.  
Expanding the study, two additional modified models were subjected to testing alongside the original model shown in Figure 4. The original model features a cylindrical section of 28.50 mm transitioning into a convergent conical section with a \(-0.80^{\circ}\) angle. The modifications include a pure cylindrical section model (\(0^{\circ}\) angle), and another with a cylindrical section transitioning into a divergent conical section (\(0.80^{\circ}\) angle). A total of six models (Figure 4) were tested, each test under both smooth and rough surface conditions. Figure 3: Dimensioned drawing of the model used in the experiments. Figure 4 displays the six prototypes designed and manufactured to analyse the effect of geometry and roughness on the performance of BWT energy harvesters. The red surfaces represent the rough prototypes, while the transparent surfaces represent the smooth prototypes. Fabrication employed additive manufacturing via 3D printing technology using Polyethylene Terephthalate Glycol (PETG) [37]. For the smooth models, a constant diameter was maintained for each layer, whereas for the rough-surfaced ones, specific parameters (a 0.3 mm ripple thickness and a 0.80 mm spacing between ripples) were applied to each layer (Figure 5). The printing process maintained a layer thickness of 0.10 mm. While the joining part with the mast retained a consistent diameter (28.50 mm) across all prototypes, variations in mass occurred due to differing fabrication materials and geometries (convergent, straight, and divergent) as well as surface finishes (smooth and rough). Table 1 provides details of the masses of the six tested prototypes. To simplify the prototype used in the experiments, certain elements from the original model, such as coatings and casings, were omitted. Only the upper segment responsible for wind energy harvesting was tested. This segment was connected centrally (via a rib) to a 4 mm diameter fiberglass rod (200 mm long) serving as the mast, anchoring the turbine to a fixation point. The fixation involved securing 20 mm of the mast into a mandrel, further anchored to the ground. The vibration sensor, positioned 180 mm from the fixation to the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Surface/Geometry** & **Convergent** & **Straight** & **Divergent** \\ \hline Smooth & 7.33 g & 8.02 g & 8.72 g \\ Rough & 8.02 g & 8.66 g & 9.36 g \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Masses of the different prototypes tested. Figure 4: From left to right: straight geometry, convergent (original model), and divergent for the prototypes tested with smooth surfaces (transparent) and rough surfaces (red).