## Issues with OpenFOAM, Pt. 1

The OpenFOAM Issue Tracking system exists to enable users to report issues. An issue exists when OpenFOAM behaves in a manner that does not meet reasonable expectations, including in design and usability. OpenFOAM is mature, quality software, whose successful development demands that issues are resolved in a timely manner. Roadmap development obstructs issue resolution, resulting in unreliable software and inefficient development. Instead, free, open source software can exploit agile development with frequent code release, as the best strategy for CFD development. Users should adopt continuous upgrade to minimize cost and to benefit the agile development strategy.

## Computational Fluid Dynamics

Fluid dynamics is concerned with the motion of fluids (liquids and gases) and the forces on them. “Computational” refers to computation of the flow and forces using numerical analysis. We define “computational fluid dynamics” as “the prediction of fluid motion and forces by computation using numerical analysis, generally extended to include heat, thermodynamics, chemistry and solids”. This definition covers a broad range of calculations for numerous scientific and engineering applications, in particular involving heat.

## Energy Equation in OpenFOAM

This article provides information on the equation describing conservation of energy relevant to fluid dynamics and computational fluid dynamics (CFD). It first assembles an equation for combined mechanical and thermal energy, i.e. total energy, in terms of material derivatives. It then presents an equation for thermal, or internal, energy. The total energy equation is then provided in terms of local (partial) derivatives, both in terms of internal energy and enthalpy. The implementation of the energy equation in solvers in OpenFOAM is then described.

## Tensor Mathematics

This article provides information on tensor mathematics, relevant to fluid dynamics and computational fluid dynamics (CFD). It describes scalars and vectors and typical algebraic vector operations. It follows with second rank tensors, their algebraic operations, symmetry, skewness and tensor invariants such as trace and determinant, higher rank tensors, co-ordinate system and change of axis. Tensor calculus is introduced (div, grad, curl and Laplacian), followed by integral theorems of Gauss and Stokes, with a physical representation of div and curl, and more.

## OpenFOAM Linux Guide

This guide provides information and example terminal commands for Linux, relevant to users of OpenFOAM. Commands are written that refer to OpenFOAM, e.g. they include OpenFOAM Linux environment variables. Those commands that refer to OpenFOAM will only function as stated, if they are executed on a machine on which OpenFOAM is installed and the user’s environment variables are set up for OpenFOAM, e.g. as described in the source download page (see Setting Environment Variables).

## Inside OpenFOAM 4.0

OpenFOAM version 4.0 is the latest major version of OpenFOAM, released on 28th June 2016. CFD Direct was by far the largest contributor to OpenFOAM 4.0, contributing the vast majority of new functionality including post-processing, numerous boundary conditions and physical models. Additionally, we contributed across all other aspects of software engineering that make OpenFOAM a mature, modern environment for CFD. This article provides the inside view of that work on the software engineering behind OpenFOAM 4.0, contributed largely during a 3 month period from April-July, 2016.