Para­met­ric Model of the TU Berlin TurboLab Stator

Effi­cient Geometry for TurboLab Stator Optimization

Some time ago, we were asked whether we can provide a variable and robust CAD model for the TU Berlin TurboLab Stator test case. This stator is installed in a mea­sure­ment rig at the TU Berlin (Germany), and it was designed on a rep­re­sen­ta­tive stator geometry as used in modern jet engine com­pres­sors. This means that the design has been inves­ti­gated quite a lot, and hence the per­for­mance of the stator is well known (e.g. pressure losses across dif­fer­ent oper­at­ing con­di­tions). With a suitable and flexible CAD model, one is able to run opti­miza­tions on this case in order to reduce the pressure losses even further. Since this is an ideal and inter­est­ing appli­ca­tion for CAESES®, we decided to create such a setup. 

The CAD Model

Our goal was to provide a variable stator geometry includ­ing a variable endwall con­tour­ing (EWC) para­me­ter­i­za­tion that can be readily used for this opti­miza­tion task. The model should be ready for meshing and CFD without any addi­tional user inter­ac­tion. This means that we also had to take care of the para­met­ric periodic bound­aries, includ­ing fixed def­i­n­i­tions for the inlet and outlet (e.g. coloring or assign­ing patch names). We were able to come up with an initial para­met­ric CAESES® model in a few hours. Basi­cally, the shape of the stator can be designed with many degrees of freedom, and any kind of complex free-form shape is feasible as long as new design can­di­dates fulfill a set of given geometry con­straints. Check out this PDF which gives a detailed descrip­tion of the design require­ments. The main task was to consider these indi­vid­ual spec­i­fi­ca­tions. Here is a short overview of the stator’s man­u­fac­tur­ing constraints:

• The number of blades is fixed to 15
• The axial chord of the blade needs to be kept constant
• Minimum thick­ness require­ments for leading and trailing edge
• Thick­ness and distance con­straints for two inner holes for fixing the blade
• Mounting con­straints in terms of the plate dimensions
• Radii reduc­tion limits for EWC.

All these con­straints need to be addressed in the CAD model, to be able to generate feasible design can­di­dates during opti­miza­tion runs.

The final CAD model in CAESES® gets con­trolled by a set of para­me­ters for the blade and for the EWC. Most of the para­me­ters are linked to dis­tri­b­u­tion func­tions for the section profile, such as camber or thick­ness, that are allowed to vary radiall direc­tion. When gen­er­at­ing new design can­di­dates by changing the model para­me­ters, most of the geo­met­ri­cal con­straints are auto­mat­i­cally ful­filled. For this purpose, we embedded internal opti­miza­tion routines that take care of some of the con­straints. For instance, the posi­tions for the two inner holes (to fix the blade) get auto­mat­i­cally opti­mized for each design in an internal loop. 

Model Vari­a­tions

The fol­low­ing ani­ma­tions show quick changes to a set of para­me­ters. The changes are rather large, just to give you an imme­di­ate idea of the the para­me­ter effects. Note that the outlet angle is actually fixed in this bench­mark test case i.e. you would not change the related para­me­ters (however, our model contains this as an option, which is also visible in the ani­ma­tions). The first 3 ani­ma­tions show a single-para­me­ter vari­a­tion, while the last ani­ma­tion was created with 7 para­me­ters. All ani­ma­tions were created within CAESES®.

Inter­ested in the Model?

We think that this test case is a really great bench­mark, and we decided to share this model with other parties that seri­ously intend to conduct an opti­miza­tion for this TurboLab stator. Feel free to get in touch with us if you are inter­ested in it — we are eager to see what you can squeeze out of it :-) Note that CFD-based shape opti­miza­tions with this model can be carried out by using the opti­miza­tion strate­gies from CAESES®, in com­bi­na­tion with your sim­u­la­tion tool of choice. Alter­na­tively, you can make use of your own opti­miza­tion tools where CAESES® runs in batch mode to generate new geome­tries. If you want to bring in your own ideas to this model, you can simply modify the blade and EWC para­me­ter­i­za­tion — every­thing is open in our setup, and free to edit.