Water Pump Design: Geometry for a Shrouded Impeller

For the CFD-driven shape opti­miza­tion of water pumps with shrouded impellers, it is crucial to have an effi­cient variable geometry model with a set of relevant para­me­ters (“design vari­ables”). Let’s briefly illus­trate and outline the modeling process of a typical water pump, where the idea is to have full flex­i­bil­ity in terms of shape vari­a­tions and fine-tuning. The fol­low­ing geometry was set up in CAESES® and all ani­ma­tions were gen­er­ated in CAESES® by changing all design vari­ables at the same time. Note that the model vari­a­tions are very large in these ani­ma­tions, to make it easier to under­stand what’s actually going on (probably design­ers would not nec­es­sar­ily apply these drastic changes to an initial design). 

Merid­ional Contour

The hub and shroud contours, as well as the leading edge curve, are designed in the ZX-view. Vari­ables are created and con­nected to these curves (e.g. to the control vertices of the bspline-curves or to an angle control), so that they can be changed in auto­mated processes. Basi­cally, the entire shape can be intu­itively con­trolled and adjusted, if needed.

Camber and Thick­ness of the Blade

The camber surface of the blade is gen­er­ated using a theta function in the (m,theta)-system. This function graph is a 2D curve def­i­n­i­tion for which addi­tional design vari­ables are created and con­nected. From this function and from the leading edge contour in the merid­ional plane, one can derive the camber surface.

In a next step, the user-defined thick­ness dis­tri­b­u­tion is applied normal to the gen­er­ated camber surface. In order to control the shape, addi­tional design vari­ables are intro­duced to change the leading edge region (more ellip­ti­cal shapes vs. circular ones) and to vary the thick­ness from the leading edge to the trailing edge. In addition, the thick­ness can also be varied in radial direc­tion, i.e. while sweeping from the hub to the shroud.

Boolean Oper­a­tions and Filleting

Once the blade surface is gen­er­ated, it can be combined with the hub and shroud surfaces. In CAESES® we can use Boolean oper­a­tions to merge these geome­tries. Fillets are created at the inter­sec­tion of the blade and the remain­ing geometry. In our model, there are two fillets (one between blade & hub, and another between blade & shroud). Here is an ani­ma­tion from the top view of the final impeller:

And here is a final one, where we zoomed in:

Download PDF Summary

If you are inter­ested in some more details, then check out this PDF summary which contains addi­tional illus­tra­tions and more detailed explanations.

CFD Flow Domain

The para­met­ric flow domain of the impeller can also be auto­mat­i­cally derived from the solid model for each design variant. This domain geometry contains several colors for the dif­fer­ent patches and allows users to directly automate the down­stream meshing process.

Download Colored STL Example

The surface patches of the solid impeller are also colored dif­fer­ently, again to make it easy to ref­er­ence them and automate the meshing process. During the auto­mated vari­a­tion and opti­miza­tion, these patch iden­ti­fiers are fixed and hence the meshing is robust for each new design can­di­date. Click here to download a zipped STL example of the pump that was gen­er­ated from the geometry model in this blog post. The file comes as a multi-body STL, and the iden­ti­fiers are created by using the dif­fer­ent patch color infor­ma­tion. If you want to take a look at it, just import it into your meshing or CAE package using a standard STL import routine. 

More Infor­ma­tion

General details about pump design and opti­miza­tion with CAESES® can be found on the pumps page.

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