Flow over a step cylinder using partially-averaged Navier-Stokes equations with application towards dynamic subsea power cables

Abstract

Understanding the flow characteristics of buoyancy sections in power cable and umbilical configurations is crucial for analyzing floating offshore wind turbine systems. Buoyancy sections decouple the motions from the floater and the destination point to ensure the integrity of the system. Using accurate drag coefficients in their design is essential, as they significantly impact the overall behavior of the configuration. Therefore, Computational Fluid Dynamic (CFD) analysis is performed in the present study on a single buoyancy module attached to a power cable represented by a step cylinder configuration. The Partially-Averaged Navier-Stokes (PANS) turbulence model is applied. Its accuracy is validated against experimental findings of a wall-mounted cantilever cylinder and an infinite cylinder. The numerical results reveal that the larger diameter cylinder (LDC) section reduces the drag experienced by the smaller diameter cylinder (SDC) section near the junction. The LDC has a sharp, chamfered, and filleted edge replicating the various shapes of buoyancy modules. The edge design of the LDC affects the drag forces and flow patterns. The SDC has an 8% lower drag coefficient in the fillet edge case than the sharp edge case. The drag coefficient is 3.5% lower for the LDC in the filleted edge case than the sharp edge case. The sharp edge causes a significant separation of the fluid upstream of the SDC. However, this separation is notably reduced when the LDC has a chamfered or filleted edge. Detailed drag coefficients for buoyancy section analysis of power cable configurations have been deduced from the presented results.