Vertical-axis wind turbines positioned along highways could harvest energy from vehicle wakes, but optimizing their design for these brief, intense flow events remains challenging. Researchers conducted a numerical study examining how blade count and rotational speed influence turbine performance when a car traveling at 32 meters per second generates the inflow.
The study tested VAWT configurations ranging from two to six blades while systematically increasing rotor speed from a baseline of approximately 64 rpm up to 2.2 times that value. Results revealed a striking performance divergence: the two-blade turbine achieved maximum energy extraction of 158.5 joules at elevated speed, representing a 24.5 percent improvement over baseline operation. Critically, this low-solidity design maintained consistent energy production across speed variations.
By contrast, rotors with more blades experienced severe performance degradation at higher speeds. Several configurations actually produced negative net energy, absorbing more power than they generated. The underlying cause was unfavorable blade-wake interactions: as rotor speed increased, blades increasingly intercepted the wake core while positioned at angles that produced torque reversal rather than extraction.
This finding contradicts intuition that more blades inherently capture more energy. The fundamental issue involves timing: vehicle wakes exist for only seconds, and the transient nature of the flow creates a narrow window for effective energy capture. With high-solidity designs, multiple blades compete for the same energetic wake core, leading to destructive interference and efficiency losses.
The research suggests that roadside turbine installations should prioritize low-solidity configurations and employ speed control strategies tuned to typical vehicle traffic patterns. Flow-guiding structures that redirect wakes toward the rotor area amplify these benefits. These findings could inform the next generation of distributed renewable energy systems in transportation corridors, where conventional wind turbines are impractical but the cumulative energy from frequent vehicle passages remains substantial.
