The simultaneous replacement of a diseased aortic valve, aortic root and ascending aorta with a composite graft equipped with a prosthetic valve is a nowadays standard surgical approach, known as the Bentall procedure: the Valsalva sinuses of the aortic root are sacrificed and the coronary arteries are reconnected directly to the graft. In practice, two different composite-material prostheses are largely used by surgeons: a standard straight graft and the Valsalva graft with a bulged portion that better reproduces the aortic root anatomy. The aim of the present investigation is to study the effect of the graft geometry on the the flowfield as well as on the stress concentration at the level of coronary-root anastomoses during the cardiac cycle. An accurate three-dimensional numerical method, based on the immersed boundary technique, is proposed to study the flow inside moving and deformable geometries. Direct numerical simulations of the flow inside the two prostheses, equipped with a bileaflet mechanical valve with curved leaflets, under physiological pulsatile inflow conditions show that, when using the Valsalva graft, the stress level near the coronary-root anastomoses is about half that obtained using the standard straight graft.

This paper provides some recent developments of an immersed boundary method for solving flows of industrial interest at arbitrary Mach numbers. The method is based on the solution of the preconditioned compressible Favre-averaged Navier - Stokes equations closed by the k-ω low Reynolds number turbulence model. A flexible local grid refinement technique is implemented on parallel machines using a domain-decomposition approach and an edge-based data structure. Thanks to the efficient grid generation process, based on the ray-tracing technique, and the use of the METIS software, it is possible to obtain the partitioned grids to be assigned to each processor with a minimal effort by the user. This allows one to by-pass the very time consuming generation process of a body-fitted grid.

This paper provides some recent results obtained in the development of Immersed Boundary (IB) methods at the Politecnico di Bari: in particular, the development and testing of one such method—using a versatile Moving Least Squares approach, coupled with a very efficient solver for solving fluid-structure interaction problems in incompressible laminar flows—will be addressed. Such a method allows one to solve complex three-dimensional solid-fluid interaction problems within reasonable computer times. The solver is validated versus: the free fall of a sphere within a fluid at rest and jellyfish propulsion. Such results demonstrate the accuracy, efficiency, and versatility of the proposed method.