An IGA-BEM method for the open-water marine propeller flow problem

In this work we deal with the problem of flow around a marine propeller rotating with constant angular velocity in a stream of uniform velocity parallel with propeller's axis (open-water of operation). The flow is considered to be inviscid, incompressible and irrotational except from the wake, which an a-priori unknown force-free vortex sheet surface emanating from the trailing edge of each blade. In this setting, the problem can be formulated as a Fredholm Boundary Integral Equation of the 2nd kind with respect to the strength of normal dipoles distributed over the propeller's boundary and the wake [2]. This BIE is accompanied by conditions on the wake, namely no flow and no pressure jump across it, as well as appropriate conditions for vanishing disturbance at infinity [1]. Adopting the concept of Isogeometric Analysis (IGA), the solution of
the continuous problem is approximated via a discrete space involving a bicubic T-spline basis used for representing the propeller's boundary surface. The resulting non-linear system is solved iteratively so that the shape of the wake secures zero-pressure jump through it (wake alignment) [3]. Using an in-house developed code, the proposed IGA-BEM scheme is tested against simple (e.g., cycloid) blade shapes and its performance is compared with results available in pertinet literature.