Auto­mated Gen­er­a­tion of Para­met­ric Pro­peller Models

In pro­peller modeling, often a very similar design approach is applied. Typ­i­cally, the blade is described based on a set of func­tions for rake, skew, pitch, etc. and a profile section def­i­n­i­tion. Addi­tional para­me­ters, such as the number of blades and the pro­peller diameter, are then used to create the final pro­peller model. In this blog post, we’ll take a quick look into an auto­mated workflow for the fast and flexible design of pro­peller CAD models that are also suited for auto­mated shape opti­miza­tion with CFD (Com­pu­ta­tional Fluid Dynamics). The pro­ce­dure is entirely auto­mated and can be broken down into the fol­low­ing sub steps:

Create a Pro­peller Model from Existing Data

If existing pro­peller data is stored in a stan­dard­ized manner, such as offset tables at dif­fer­ent radii and discrete data for the design func­tions, a para­met­ric pro­peller model can be derived auto­mat­i­cally in a few steps. For the example and the pictures in this blog post, the Pro­peller Free Format (PFF) was chosen as an input format. CAESES allows you to load existing pro­peller geometry that is stored in the PFF format and auto­mat­i­cally convert it into a flexible, robust CAD model. If other formats are used in a company, there is the option to use feature def­i­n­i­tions for custom import routines.

Extract­ing Camber and Thick­ness Distributions

Let’s assume we have an imported point cloud of the 2D pro­peller sections as shown in the previous picture. Pre­lim­i­nary para­met­ric sections are then created as inter­po­la­tion curves at all given radii. Circles are inscribed into each profile curve to deter­mine both camber and thick­ness as a function of chord.

Fairing is auto­mat­i­cally applied to the camber dis­tri­b­u­tion to ensure a smooth shape espe­cially around the leading and trailing edge region. The result­ing camber and thick­ness dis­tri­b­u­tions are then inter­po­lated by two surfaces, to have a con­tin­u­ous def­i­n­i­tion with regards to the full pro­peller radius, i.e, also in between of the single sections.

The radial func­tions for all para­me­ters are inter­po­lated with NURBS curves. Each of the result­ing curves is addi­tion­ally para­me­ter­ized to allow the designer flexible mod­i­fi­ca­tions. If needed, any user defined curve can be used to replace the auto­mat­i­cally created function.

3D Pro­peller Model Generation

For the local section profile, the inter­po­la­tion surfaces for camber and thick­ness can be inter­sected at any radius to provide the local chord-wise dis­tri­b­u­tions. The thick­ness is offset normal from the camber line, the leading edge region receives an addi­tional fairing and the trailing edge is closed. The chord length, maximum camber position, maximum camber, maximum thick­ness position and maximum thick­ness are adjusted accord­ing to the design functions.

Pitch, rake and skew are taken into account when gen­er­at­ing the blade via CAESES’ generic blade func­tion­al­ity. The number of blades, pro­peller diameter, hub radius and exten­sion can be set to complete the definition.

Variable Radius Fillet

A fillet is created at the blade root with a variable radius. The dis­tri­b­u­tion function might be either fully cus­tomized or based on the thick­ness of the root profile, e.g., 2/​3rd and 1/​3rd of the profile thick­ness on the pressure and suction side, respectively.

Export Formats

CAESES gives you a set of standard export formats, such as IGES, STEP, STL or Para­solid. For pro­pri­etary formats, the script­ing envi­ron­ment of CAESES can be used again.

Solid with Boundary Conditions

In case a CFD analysis will be con­ducted, a solid pro­peller geometry includ­ing a shaft and a closed tip can be created in CAESES with a few clicks. Bound­aries and refine­ment regions are set as needed for the specific CFD code. Finally, a com­pu­ta­tional domain can be exported, either for the single blade or for the entire propeller.

More Infor­ma­tion

If you would like to learn more about pro­peller modeling in CAESES, please see the marine section.

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