Enhancing Resilience of Transmission Power Towers in Hurricane-Prone Regions: Integrating Turbulence and Complex Terrain Effects

Hurricanes stand as a prevalent catastrophe in topical and sub-tropical regions such as the Caribbean, consistently leading to significant disruptions in power delivery across the islands. When a hurricane strikes, the power transmission and distribution networks remain consistently vulnerable to strong winds, subjecting the components within these systems to a heightened probability of breakdown. In coastal mountainous areas such as Puerto Rico, these transmission lines are often situated in challenging-to-reach locations characterized by intricate landscapes. Here, the winds intensify on the windward side, and the variation in tower heights can introduce supplementary mechanical strains.

Within a hurricane, the concentrated destructive winds primarily arise due to the formation of significant large eddy circulations in the hurricane boundary layer (HBL). Present regulations for designing power transmission towers consider only their dimensions and solidity ratio when estimating the drag coefficient, disregarding these specific localized eddy circulations. Conversely, recent studies have revealed that within the HBL, the drag coefficient is significantly influenced by both the tower's shape and the turbulence strength within the boundary layer. This integration acknowledges the impact of the eddy circulations on the drag coefficient.

Existing design codes for power towers do not incorporate considerations for turbulence within the HBL or the intricate interplay between wind and complex terrain. This study aims to integrate these factors into the prevailing drag coefficient calculation methods utilized by the power industry to assess the mechanical load capacities of the power towers. In this study we take advantage of computational fluid dynamics (CFD) to study the interaction between the complex terrain and the power towers when exposed to hurricane winds. The study is focused on a section of the 230kV transmission line (Figure 1), located in the northern side of Puerto Rico. This specific segment was chosen due to its exposure to intense winds during Hurricane Maria, leading to the failure of a majority of the power towers during the event.

Simscale is used as the CFD simulation tool to recreate Hurricane Maria conditions. Specifically, a section composed of two power towers with a height difference of 100m (Figure 2). CAD models for the power towers in the section are created and placed into a representation of the complex terrain. Furthermore, the HBL wind profile from the WRF-LES weather simulation is used as a boundary condition in the CFD simulation, for a correct representation of the hurricane conditions. This application of CFD will enable us to investigate the drag forces acting on both power towers and formulate a drag coefficient that incorporates the turbulence intensity impacting the towers.

To validate the CFD simulation, we have developed a corresponding wind tunnel experiment that emulates a similar domain and meteorological conditions. The experiment will utilize the CCNY boundary layer wind tunnel, featuring a test section measuring 120cm x 120cm and capable of achieving a maximum wind speed of 12 m/s. Furthermore, the CAD files utilized for the CFD simulation are employed in the creation of 3D-printed models as a part of the wind tunnel experiment arrangement. This encompasses both the power towers and the complex terrain.

Subsequently, the 3D-printed power towers, situated on the complex terrain, undergo testing within the wind tunnel environment. During these tests, a 6-axis load sensor is employed to quantify the drag force experienced by the power towers. The load data acquired from these tests are then employed for comparison and validation against the results obtained from the CFD simulation. Ultimately, the drag coefficients yielded by both the simulation and the experiment are compared against the existing design criteria for power towers. This comparative analysis aids in comprehending the influence of turbulence on drag forces within hurricanes.