What is Open Source?
If you were to go out on the street and ask ten different people what OpenSource software is, you would most likely get ten different answers. The official definition, from The Open Source Initiative, can be found on Wikipedia.One perspective, from an engineer's standpoint: "Open-source software ... is computer software that is ... provided under a software license that permits users to study, change, and improve the software."
For any decision, especially those related to significant cost and safety impacts, to rely on the analysis based on the results from a software package, the engineer or decision maker needs a mechanism whereby the validity of the algorithms and their implementation can be verified easily. This aspect is all the more important in the case of CFD, where several assumptions and simplifications are made in the process of breaking down the problem, into a set of parameters that can be computed with the available resources. Other factors resulting in the increased interest in CFD, other than the boom in computing power in recent years, is the cost and feasibility of setting up the facilities to realistically experiment and study complicated physical phenomenon.
Granted, not all of us are going to go digging around in the code to determine that a particular piece of software actually cranks out viable results; however, the fact that there are a large number of other users who ARE validating and improving the code provides us with a greater sense of confidence than taking some commercial entity's word for it. There are of course technical paper's and validation studies done using the commercial codes.
Other than the cost savings, there is another peripheral benefit that is often overlooked : the user community can be quite diverse, not to mention vast. Through forums and mailing lists, a good deal of support and assistance can be accessed without having to navigate through a corporate "Help" desk. These communities are often comprehensive sources of answers to specific questions. The kind of support, usually found in OpenSource Software, is often purely a function of 'getting things done' and 'gaining knowledge', sans the set commercial limitations.
Of course, in parallel, commercial software giants like ANSYS and Altair have made their own powerful impact on the industry and have become conventional, albeit 'reliable' solutions. They have comprehensive after-sales support and often hire well qualified professionals, including PhD's as application engineers, to solve the problems of their clients. Many of them are also active in developing new and probably more customized solutions in collaborations with Universities and the Industry as well. There are plenty of industries and users satisfied with being end users, as it serves their purpose well.
The objective of this wiki section is to provide a comprehensive reference for harnessing the power of OpenSource and to make an informed decision of the best kind of package that will provide the most efficient/comprehensive solution to the problem being faced.
Cost and Licensing Considerations
Note that there's nothing in the definition of OpenSource software about its cost. Fortunately, many of the OpenSource solutions now available for engineering applications also happen to be free of any licensing fees (although this is not always the case). Some of the OpenSource software that is available for free is restricted to personal-use; you are not allowed to use it in your commercial engineering practice. Yet many of the best tools we have encountered are not hindered by restrictive licenses. Still, one must be aware of such restrictions to avoid ethical violations or possible legal problems.
One's focus will naturally be upon Free and Open software. But, this particular category may not provide a viable solution for every circumstance. Therefore, as necessity dictates, the engineer should swerve off the path to explore some possibilities that are not free, or that may involve restrictive licenses. The goal is to identify the most cost-effective tools for engineering applications. And, of course, part of the cost that must be considered is the time one must invest in learning how to use the software. It lies in the engineer's purview to understand the software and make informed decisions about which kind of tool to use.