Extrapolated shock fitting for two-dimensional flows on structured grids

Over the years the development of structured-grid shock-fitting techniques faced two main problems: the handling of a moving discontinuity on a fixed background grid and the capability of simulating complex flow configurations. In the proposed work, the authors present a new shock-fitting technique for structured-grid solvers that is capable of overcoming the limitations that affected the different approaches originally developed. The technique presented here removes the tight link between grid topology and shock topology, which characterizes previous shock fitting as well as front tracking methods. This significantly simplifies their implementation and more importantly reduces the computational overhead related to these geometrical manipulations. Interacting discontinuities and shocks interacting with a solid boundary are discussed and analyzed. Finally, a quantitative investigation of the error reduction obtained with the approach proposed via a global grid convergence analysis is presented

Numerical Simulation of Shock Boundary Layer Interaction Using a Shock Fitting Technique

The unstructured shock-fitting algorithm originally proposed in Ref. [3] has been further developed to make it capable of dealing with shock-wave/boundary-layer interactions (SWBLIs). This paper illustrates the algorithmic features of the technique and its application to 2D flow-configurations featuring different SWBLIs, including the transonic turbulent flow past a symmetrical airfoil and a laminar oblique-shock reflection

A new shock-fitting technique for 2-D structured grids

In the past years, the development of structured shock-fitting techniques dealt with two main problems: the handling of a moving discontinuity on a fixed background grid and the capability of simulating complex flow configurations. In the proposed work, the authors present a new shock fitting technique for structured solvers able to overcome the limitations that affected the approaches originally developed, such as the boundary shock-fitting and the floating shock fitting. Specifically, the technique presented herein removes the strong link between grid topology and shock position, which characterizes boundary shock-fitting methods, and reduces significantly the expensive coding effort for implementing floating shock-fitting methods. In particular, three different test-case, which also deal with mutually interacting discontinuities, are deeply discussed and analyzed. Finally, a global grid-convergence analysis has been performed to quantitatively measure discretization errors and order-of-convergence of the proposed numerical approach

An Unstructured Shock-Fitting Technique For Three-Dimensional Flows With Shock Interactions

The numerical simulation of hypersonic flows past blunt bodies by means of shockcapturing (S-C) solvers is characterized by some critical challenges, including: stagnation point anomalies, spurious numerical oscillations, the carbuncle phenomenon and the reduction of the order of accuracy of the solution in the entire region downstream of a captured shock worsen the solution quality. This paper describes an updated version of the unstructured shock-fitting (S-F) algorithm for three-dimensional flows. In particular, we present a comparison between the results obtained computing hypersonic flows on blunt bodies using both the S-C and S-F techniques on nearly identical tetrahedral meshes, with a special interest on the grid-convergence properties of the two different shock-modeling options

A shock-fitting technique for 2D/3D flows with interactions using structured grids

A novel shock-fitting algorithm is proposed in this paper. This technique has been designed to overcome the limitations that affected the originally developed shock-fitting approaches based on structured meshes: the handling of a moving discontinuity on a fixed background grid and the capability of simulating complex flow configurations. The present algorithm has been applied to high speed flows past three-dimensional bodies, such as a circular cylinder and a compression corner, providing high quality results with respect to the most common shock-capturing approaches

UnDiFi-2D: An unstructured discontinuity fitting code for 2D grids

UnDiFi-2D, an open source (free software) Unstructured-grid, Discontinuity Fitting code, is presented. The aim of UnDiFi-2D is to model gas-dynamic discontinuities in two-dimensional (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. Program summary: Program title: UnDiFi-2D CPC Library link to program files: https://doi.org/10.17632/5hwssmc2mx.1 Licensing provisions: GNU General Public License, version 3 Programming language: Fortran; developed and tested with Intel Fortran Compiler v. 18.0.3 and GNU gfortran. External routines: The code depends on several libraries and third-party packages which are detailed in the corpus of the text. Nature of problem: Numerical computation of flows with discontinuities. Solution method: Shock-fitting technique. Additional comments including restrictions and unusual features: • At present, UnDiFi-2D is validated for inviscid steady and unsteady two-dimensional flows without changes in the number of discontinuity lines and interaction points. • UnDiFi-2D implements a shock-fitting algorithm and can be coupled with unstructured cell-vertex solvers, with an Arbitrary Lagrangian-Eulerian (ALE) formulation. • UnDiFi-2D project adopts git [1], a free and open source distributed version control system. A public repository dedicated to UnDiFi-2D project [2] has been created on github [3], a web-based hosting service for software development projects using git versioning system. Finally, a comprehensive documentation is provided in the form of user manual developed in Pandoc [4]. References: [1] Git, a free and open source distributed version control system, http://git-scm.com. [2] UnDiFi-2D documentation, https://github.com/UnDiFi/UnDiFi-2D. [3] Github, a web-based hosting service for software development projects using git versioning system, https://github.com. [4] M. Dominici, TUGboat 35(1) (2014) 44-50