It seems that Blender graphics software supports the Biovision Hierarchy Animation format (.bvh) and as such it should be possible to convert .blend files and save them as .bvh files. You can download Blender for free and try it yourself.
Convert Blender 3D data file to Biovision Hierarchy Animation file.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert blend to bvh on Windows
A very popular free program used for work with 3D graphics
Convert from blend file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.