How to compile FLUENT 64-bit UDFs using Visual Studio Express 2010 and the 7.1 SDK
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Installing VS Express 2010 and SDK.
The 2010 Express Edition and the SDK will allow you to compile 64-bit UDFs for FLUENT by first opening the SDK Command prompt window and starting FLUENT.
The following two programs are needed to be installed:

Microsoft Visual Studio 2010 Express Edition (http://www.microsoft.com/visualstudio/eng/products/visual-studio-2010-express)
Microsoft Windows SDK for Windows 7.1 and .NET Framework 4 (http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=4422)
If you get the following error installing the SDK for Windows 7.1,

A problem occurred while installing selected Windows SDK components. Installation of the ?icrosoft Windows SDK for Windows 7? product has reported the following error: Please refer to SamplesSetupHTMLConfigDetails.htm document for further information.

Try the following fix:

Uninstall Microsoft Visual C++ 2010 x64 Redistributable, or Microsoft Visual C++ 2010 x86 Redistributable depending on the Version of the SDK you are installing prior to SDK installation. The he SDK reinstalls both packages when selecting the appropriate options in the setup.
Other known issues:

Visual C++ compiler installation fails when the Windows SDK 7.1 is installed, repaired, or modified after Visual Studio 2010 SP1 has been installed

If the Visual C++ Compilers checkbox is selected when Windows SDK 7.1 is installed, repaired, or modified after Visual Studio 2010 SP1 has been installed, the SDK installer attempts to install an older version of compilers. One of the following messages may be displayed:

Installation of the ?icrosoft Windows SDK for Windows 7 Compilers for x86? product has reported the following error: Fatal error during installation.
or

Installation of the ?icrosoft Windows SDK for Windows 7 Compilers for x64? product has reported the following error: Fatal error during installation.
To resolve this issue:

Condition 1: If the Visual C++ Compilers checkbox is selected when the Windows SDK 7.1 is installed, repaired, or modified after Visual Studio 2010 SP1 has been installed, the error may be encountered and some selected components may not be installed.

Workaround: Clear the Visual C++ Compilers checkbox before you run the Windows SDK 7.1 installation, repair, or modification.

Condition 2: If the Visual C++ Compilers checkbox is selected when the Windows SDK 7.1 is installed, repaired, or modified after Visual Studio 2010 has been installed but Visual Studio 2010 SP1 has not been uninstalled, the error may be encountered.

Workaround: Uninstall Visual Studio 2010 SP1 and then rerun the Windows SDK 7.1 installation, repair, or modification.

If all these fail and you still get a compiler installation error, then download this patch: Microsoft Visual C++ 2010 Service Pack 1 Compiler Update for the Windows SDK 7.1

Compiling a source .c file in FLUENT

1. The UDF and the FLUENT .cas file must be in the same folder. Folder names, FLUENT .cas and .dat files must not have any spaces.

2. For Windows Vista, 7 and 8 then the folder must have full permissions allowed.

3. Starting FLUENT using the SDK 7.0 Command Prompt Window

4. Open up the SDK Command Window. This is required to set the compiler environment variables.

5. Change directory (CD) to your working directory (your working directory is the directory where your case, data file and udf is located). Make sure the directory contains no spaces in the name.

6. Launch FLUENT 14.x