Intro­duc­tion to PFF (Pro­peller Free Format)

For the exchange of pro­peller geometry data, CAESES® offers the pos­si­bil­ity to import and export files using a format that is called PFF (Pro­peller Free Format). We support the PFF format since these files are widely used by ship and pro­peller design com­pa­nies as well as clas­si­fi­ca­tion soci­eties. This short blog post gives you an intro­duc­tion to this file format, e.g. to be able to generate your own PFF files that can be read into CAESES®. There is also a PFF file avail­able for download at the end of this post. Note that we support only a subset of a specific PFF version, and some of the attrib­utes that are not directly related to actual geometry are simply ignored by CAESES®. If you use a dif­fer­ent PFF version or you need more attrib­utes to be con­sid­ered, just let us know. Alter­na­tively, you can also write your custom import/​export by using features. 

Header Section

In the header section, there is some infor­ma­tion about the name of the pro­peller and the date when the file was exported. CAESES® searches for the pro­peller diameter (see below) in the first step, so that these header comments can be neglected. In the second block of PFF files appears a line “*( Pro­peller Geometry (Standard)” which is followed by a company name, a person in charge, and another date entry that you can use e.g. as a ​“last edit” date. Again, this is not taken into account by CAESES® but usually part of the PFF file.

Now comes the pro­peller infor­ma­tion: As you can see from the picture above, in the third block you find the pro­peller and hub diam­e­ters (every­thing always in mm), an optional scaling factor for the given values, the area ratio and a blade mass. The second part of this block contains some general infor­ma­tion about moments and shaft power. Note that CAESES® ignores area ratio, blade mass, moments and shaft power in the current release so that only the sub­stan­tial geo­met­ric quan­ti­ties are con­sid­ered. The next lines in the header contain the number of blades, a material flag (also ignored), number of radii i.e. sections and number of points per section (“No.CordPart”). Finally, the pro­peller ori­en­ta­tion is given where the clock­wise rotation (when looking from behind) is indi­cated by a ​“1”, and ​“0” defines the counter-clock­wise rotation. 

Section Data

After the header section with more general infor­ma­tion, the profile data needs to be provided. When you write 2D sec­tional data into a PFF file, you have to start the line with “* r/​R”, see the fol­low­ing picture for an example:

What you can find is the nor­mal­ized radius, the real radius and a chord length. Impor­tant: The x‑coordinates (“Station”) of the profile run from 0 to 1, i.e. they are nor­mal­ized wrt. the chord length. By using the increas­ing x‑stations, the coor­di­nates for the profile run from leading edge to trailing edge. They are followed by the cor­re­spond­ing y‑values for suction and pressure side, respec­tively. We do not dig into pro­peller design details here, probably most of you know about things such as chord lengths, camber and thick­ness values, rake, skew and pitch. The term ​“Dis­tLeaEdge” in the PFF file is related to the skew of the profile. See the fol­low­ing illus­tra­tion for more infor­ma­tion about the dif­fer­ent terms:

After a section is finished and a new radius is coming up, it again starts with “* r/​R”. The whole block with all 2D profile data ends with an indi­ca­tor in two lines:

Footer Section

There can be more geometry infor­ma­tion in a PFF file — just as a side note and to let you know. However, CAESES® supports only the geometry parts that are described in this blog post, i.e. 2D section data. 

Solid CAD Model from a PFF File

So what else can you do with such file data? We have recently devel­oped a method to create a solid CAD geometry from a given PFF file with just one single click (press an import button). If you are inter­ested in it, feel free to get in touch with us.

More Infor­ma­tion

The PFF import allows CAESES® users to visu­al­ize the cross-sections and change the point data inter­ac­tively (e.g. to correct them manually etc.). The manip­u­lated pro­peller can be exported again into the same or a new PFF file. Alter­na­tively, the imported data can be used as a starting point for a para­met­ric pro­peller model, too. See the marine section for more infor­ma­tion about pro­peller modeling.

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