A new, highly parallelized, adaptive mesh refinement (AMR) library, equipped with an accurate immersed boundary (IB) method for solving the compressible Navier-Stokes system is presented. The library, named ADAM, is designed to efficiently exploit modern exascale GPU-accelerated supercomputers and it is implemented with a highly modular structure in order to make easy to leverage it for a wide range of CFD applications. The structured Cartesian grids at the basis of (octree) AMR approach allows to implement very high order accurate models retaining a low computational cost and high level of parallelization. The accurate IB method coupled with efficient AMR technique enables the simulation flows with complex (possibly moving and deforming) geometries. The library is applied to the simulation of a strong shock diffraction over a solid sphere and a detailed discussion concerning the physical results and the parallel performance obtained is presented.

This manuscript relates to the exploiting of the abstract calculus pattern (ACP) for the (numerical) solution of ordinary differential equation (ODEs) systems, which are ubiquitous mathematical formulations of many physical (dynamical) phenomena. We present FOODIE, a software suite aimed to numerically solve ODE problems by means of a clear, concise, and efficient abstract interface. The results presented prove manifold findings, in particular that our ACP approach enables ease of code development, clearness and robustness, maximization of code re-usability, and conciseness comparable with computer algebra system (CAS) programming (interpreted) but with the computational performance of compiled programming. The proposed programming model is also proven to be agnostic with respect to the parallel paradigm of the computational architecture: the results show that FOODIE applications have good speedup with both shared (OpenMP) and distributed (MPI, CAF) memory architectures. The present paper is the first announcement of the FOODIE project: the current implementation is extensively discussed, and its capabilities are proved by means of tests and examples.

A new immersed boundary approach for high order Weighted Essentially non-Oscillatory (WENO) schemes is proposed. The schemes is based on the main ideas from both the general immersed boundary algorithms and the level-set approach and can be easily applied to both finite difference and finite volume formulation. Although formally only second order accurate, numerical tests prove that the use of higher order approximation for the Eulerian fluxes can be very convenient to capture flow details and to obtain low uncertainty also with very coarse grids.

The starting transient of highly under-expanded supersonic jets is studied by means of very high resolution weighted essentially non oscillatory finite volume schemes, coupled with a positivity-preserving scheme in order to ensure positivity of pressure and density for high compression/expansion ratio. Numerical behaviour of the schemes is investigated in terms of grid resolution, formal accuracy and different approximated Riemann solvers. The transient flow field is also discussed.

The aim of the present paper is the analysis of simplified boundary conditions to be used in numerical simulations, to take into account blockage effects for wind tunnel experiments of large scale wind tur- bines. The goal is the development of an efficient and reliable tool to be used to correct data obtained from experiments where the blockage coefficient is high and/or the turbine is highly loaded, for which traditional correction coefficients (derived from the Glauert theory or its more recent versions) fail. Numerical simulations of the flow around a three-bladed model-scale wind turbine with horizontal axis are reported; in all test cases, the turbine diameter is comparable with test section dimensions, and therefore blockage effects are significant. The actual experiments were approximated numerically with a simplified wind tunnel geometry, that retains the symmetries of the isolated turbine simulation in a rotating frame and therefore allows steady state computations. To this end, two circular wind tunnel were tested: for the first, the radius was chosen to retain the same cross-section as the actual wind tunnel; in the second, its was set to be equal to half of the smallest cross-section dimension. The aerodynamic performances of the turbine, in terms of power and thrust coefficients, are analyzed and compared with available experimental data. Detailed analysis of the flow in the wake is also reported. Analogous simulations in an unbounded domain are also reported.

Abstract The hydrodynamic characterization of control appendages for ship hulls is of paramount importance for the assessment of maneuverability characteristics. However, the accurate numerical simulation of turbulent flow around a fully appended maneuvering vessel is a challenging task, because of the geometrical complexity of the appendages and of the complications connected to their movement during the computation. In addition, the accurate description of the flow within the boundary layer is important in order to estimate correctly the forces acting on each portion of the hull. To this aim, the use of overlapping multi-block body fitted grids can be very useful to obtain both a proper description of each particular region in the computational domain and an accurate prediction of the boundary layer, retaining, at the same time, a good mesh quality. Moreover, block-structured grids with partial overlapping can be fruitfully exploited to control grid spacing close to solid walls, without propagation of undesired clustering of grid cells in the interior of the domain. This approach proved to be also very useful in reducing grid generation time. In the present paper, some details of the flow simulation around a fully appended submarine is reported, with emphasis on the issues related to the complexities of the geometry to be used in the simulations and to the need to move the appendages in order to change the configuration of the various appendages.

In applied hydrodynamics it is presently a general common task to simulate flow around complex shaped ships with moving appendages. As an example the simulation of a turning circle manoeuvre of a full-appended combatant ship is common in manoeuvrability studies. Nevertheless the accurate numerical simulation of turbulent, unsteady flow around a full appended maneuvering complex-shaped hull is a challenging task, because of the geometrical complexity of the appendages present and their relative movement, generating a very complex hydrodynamic flow.

A complementary experimental and numerical study of the interference eect for a fast catamaran is presented. Resistance, sinkage and trim are collected by towing tank experiments for Froude number in the range from 0:2 to 0:8 for several separation distances and for the monohull. Resistance coefficient curves reveal the presence of two humps, the second one strongly depending on the separation length; high interference is observed in correspondence of the second hump. To gain a deeper insight into these behaviors, a complementary analysis is carried out by a numerical campaign; simulations are performed by means of an in-house unsteady RANS solver. Verication of numerical results is provided, together with validation, which is made by the comparison with both present and other experimental data. Agreement in terms of resistance coefficient is rather good, comparison error being always smaller than 2.2%.

This paper presents the results of a large experimental and numerical campaign aimed to the analysis of the interference effect for a fast catamaran. Several separation distances are considered; data for resistance, sinkage and trim are collected by towing tank experiments for Froude number ranging from 0.2 to 0.8. Monohull tests are also carried out, the analysis of the interference and its dependency on the separation length being the main objective of the paper. Resistance coefficient curves reveal the presence of two humps, the second one strongly depending on the separation length; high interference is observed in correspondence of the second hump. It is found that the narrower is the configuration, the higher is the interference and the speed at which this maximum occurs. To gain a deeper insight into these behaviors, a complementary analysis, in terms of wave field, surface pressure and velocity field is carried out by an in-house unsteady RANS solver. Verification of numerical results is provided, together with validation, which is made by the comparison with both present and other experimental data. Agreement in terms of resistance coefficient is rather good, comparison error being always smaller than 2.2%.

The simulations of the flow around a high-speed vessel in both catamaran and monohull configurations are carried out by the numerical solution of the Reynold averaged Navier–Stokes (RANS) equations. The goal of the analysis is the investigation of the interference phenomena between the two hulls, with focus on its dependence on the Reynolds number (Re). To this aim, numerical simulations are carried out for values of Re ranging from 106 to 108 for two different values of the Froude number (Fr = 0.30, 0.45). Wave patterns, wave profiles, limiting treamlines, surface pressure and velocity fields are analyzed; comparison is made between the catamaran and the monohull configurations. Dependence of the pressure and viscous resistance coefficients, as well as of the interference factor, on the Reynolds number is investigated. Verification and validation for both resistance coefficients and wave cuts is also performed.

The results of accurate compressible Navier-Stokes simulations of aerodynamic heating of the Vega launcher are presented. Three selected steady conditions of the Vega mission profile are considered: the first corresponding to the altitude of 18 km, the second to 25 km and the last to 33 km. The numerical code is based on the mathematical model described by the Favre-Average-Navier-Stokes equations; the turbulent model chosen for closure is the one-equation model by Spalart-Allmaras. The equations are discretized by a finite volume approach, that can handle block-structured meshes with partial overlap ("Chimera" grid-overlapping technique). The isothermal boundary condition has been applied to the lancher wall. Particular care was devoted to the construction of the discrete model; as a matter of facts, the launcher is equipped with many protrusions and geometrical peculiarities (as antennas, raceways, inter-stage connection flanges and retrorockets) that are expected to affect considerably the local thermal flow-field and the level of heat fluxes, because the flow have to undergo strong variation in space; consequently, special attention was devoted to the definition of a tailored mesh, capable of catching local details of the aerothermal flow field (shocks, expansion fans, boundary layer, etc..). The computed results are reported together with uncertainty and actual convergence order, that were estimated by the standard procedures suggested by AIAA.

In this work the numerical simulations of a submarine in straight ahead motion with the appendages at several prescribed deflection angles are performed. Due to the complex geometry involved (the presence of moving appendages), these simulations are rather demanding form the point of view of both grid generation and accuracy of the numerical method. In order to analyze these aspects, the numerical solutions are computed by means of an unsteady Reynolds averaged Navier-Stokes equations solver, which is particularly effective because of the high order discretization schemes adopted. From the point of view of mesh construction, a dynamic overset grid technique is used, where each geometrical element of the whole geometry is discretized with a set of block-structured body-conformal mesh with partial overlapping (Chimera approach). In the present paper, the details of the method and numerical results for several deflection angles of the bow and stern planes are presented.