Authors: Lucas Lopes, Luís Eça, Fernando Marques da Silva, Fernando Oliveira

An experimental investigation of vortex shedding mitigation in circular cylinders using helical strakes with a controlled gap from the surface was carried out. While conventional attached strakes effectively suppress vortex-induced vibrations (VIV), they introduce significant drag penalties. The spaced-strake concept aims to maintain wake decoherence while reducing this aerodynamic cost. Wind tunnel experiments were conducted on a smooth baseline cylinder and three configurations with gaps relative to the cylinder surface of 20%, 40%, and 60% of the strake height. Aerodynamic forces and surface pressures were measured to assess wake behavior. Results show that spaced strakes significantly reduce lift fluctuations while decreasing drag penalties as the gap increases. Pressure data indicate enhanced momentum exchange and partial base-pressure recovery, especially for the largest gap. Overall, spaced helical strakes offer an effective compromise between drag reduction and VIV suppression.

Lucas Lopes¹ | Luís Eça¹ | Fernando Marques da Silva² | Fernando Oliveira²
1 Instituto Superior Técnico, Universidade de Lisboa
2 Laboratório Nacional de Engenharia Civil (LNEC)