A local, un-structured, re-meshing technique capable of handling large body-motion in rotating machinery

In this paper we propose a simple, unstructured mesh generation technique that is capable of handling the large and complex blade motion that is encountered in certain rotating machines, such as vertical axis wind turbines or cycloidal propellers. The technique is characterised by localised re-meshing and interpolation, so as to keep the mesh generation cost and interpolation error as low as possible

The role of mesh generation, adaptation, and refinement on the computation of flows featuring strong shocks

Within a continuum framework, flows featuring shock waves can be modelled by means of either shock capturing or shock fitting. Shock-capturing codes are algorithmically simple, but are plagued by a number of numerical troubles, particularly evident when shocks are strong and the grids unstructured. On the other hand, shock-fitting algorithms on structured grids allow to accurately compute solutions on coarse meshes, but tend to be algorithmically complex. We show how recent advances in computational mesh generation allow to relieve some of the difficulties encountered by shock capturing and contribute towards making shock fitting on unstructured meshes a versatile technique

UnDiFi-2D: an Unstructured Discontinuity Fitting code for 2D grids

International audienceUnDiFi-2D, an open source (free software) Unstructured-grid, Di scontinuity Fi tting code, is presented. The aim of UnDiFi-2D is to model gas-dynamic discontinuities in twodimensional (2D) flows as if they were true discontinuities of null thickness that bound regions of the flow-field where a smooth solution to the governing PDEs exists. UnDiFi-2D therefore needs to be coupled with an unstructured CFD solver that is used to discretize the governing PDEs within the smooth regions of the flow-field. Two different, in-house developed, CFD solvers are also included in the current distribution. The main features of the UnDiFi-2D software can be summarized as follows: Programming Language UnDiFi-2D is written in standard Fortran 77/95; its design is highly modular in order to enhance simplicity of use, maintenance and allow coupling with virtually any existing CFD solver; Usability, Maintenance and Enhancement In order to improve the usability, maintenance and enhancement of the code also the documentation has been carefully taken into account. The git distributed versioning system has been adopted to facilitate collaborative maintenance and code development; Copyrights UnDiFi-2D is a free software that anyone can use, copy, distribute, change and improve under the GNU Public License version 3. The present paper is a manifesto of the first public release of the UnDiFi-2D code. It describes the currently implemented features, which are the result of more than a decade of still ongoing CFD developments. This work is focused on the computational techniques adopted and a detailed description of the main characteristics is reported. UnDiFi-2D capabilities are demonstrated by means of examples test cases. The design of the code allows to easily include existing CFD codes and is aimed at ease code reuse and readability

Esercizi di Gasdinamica

Pubblicazione didattica riguardante esercizi del corso di Gasdinamic

Esercizi di gasdinamica - Seconda edizione

Il libro può essere utilizzato nei corsi universitari che affrontano le tematiche dei flussi compressibili, è suddiviso in sette capitoli. In particolare, i primi cinque capitoli sono dedicati agli esercizi i) sui flussi quasi-unidimensionali stazionari, ii) sull’applicazione della teoria delle caratteristiche, iii) sui flussi unidimensionali non stazionari (flussi in piccole perturbazioni, espansioni, urti e problema di Riemann), iv) sugli schemi numerici dei flussi compressibili (schemi upwind alle differenze finite e schemi ai volumi finiti alla Godunov), v) sui flussi bidimensionali (teoria di Ackeret, espansioni, urti obliqui, interazioni, flussi su profili ed ali). Il sesto capitolo contiene una miscellanea di esercizi non riconducibili ai temi dei capitoli precedenti (strato limite compressibile e flussi transonici). Infine, l’ultimo capitolo propone degli esercizi di ricapitolazione. Tutti gli esercizi sono forniti di risposta, mentre per alcuni esercizi particolari viene fornito lo svolgimento. Infine, il libro è corredato dalle tabelle dei flussi compressibili necessarie per la soluzione degli esercizi

Shock fitting: classical techniques, recent developments, and memoirs of Gino Moretti

This book describes the revolutionary capabilities of new shock fitting algorithms; a great improvement in computational fluid dynamics (CFD) for high-speed numerical simulations. Shock fitting methods provide a solution to the current difficulties and inaccuracies in shock-capturing approaches. This work traces the evolution of shock-fitting methods, from the pioneering methods based on the structured grids (boundary and floating shock-fitting) to recent developments on unstructured grids, illustrating algorithmic details, significant applications and potential developments.  Also, to celebrate the centenary birth of the father of shock-fitting techniques, the book also includes a tribute to Gino Moretti, as well as his unpublished manuscript. This book will appeal to professionals, researchers, and graduate students in the field of CFD

Detached eddy simulation of a supersonic flow over an open cavity

A supersonic flow over an open cavity is numerically studied using the RANS and DES approaches. The results analysis and the comparison with experiments show that the DES approach is able to captured correctly the unsteady phenomenology. On the contrary, the RANS approach shows all its limitations providing only steady state solutions

Comparative study of stagnation point anomalies by means of shock-capturing and shock-fitting unstructured codes

The two-dimensional, hypersonic (M?=17.605), laminar flow (Re?=376930) past the forebody of a circular cylinder has been simulated by means of a vertex-centred CFD code using linear triangular elements. Two different approaches have been used to simulate the strong detached bow shock: shock-capturing on anisotropically refined meshes and shock-fitting. Concerning the boundary layer mesh, the distribution of gridpoints has been kept constant, while three different connectivity patterns have been examined. When looking at wall quantities such as pressure, skin friction and heat transfer these appear to be more heavily affected by the boundary layer mesh than by the numerical model used to simulate the detached shock wave

Numerical simulation of flows with shocks through an unstructured shock-fitting solver

A new floating shock-fitting technique featuring the explicit computation of shocks by means of the Rankine-Hugoniot relations has been implemented in an unstructured solver. This paper briefly illustrates the algorithmic features of this orginal technique and the results obtained in the computation of the hypersonic flow past a circular cylinder