How to Create a Volute in 10 Steps

Volute geome­tries are tricky. They look simple, and design­ing a single baseline design is not that hard. However, once you are getting into the field of sim­u­la­tion-driven shape opti­miza­tion, things start to get really chal­leng­ing. New design can­di­dates need to be gen­er­ated auto­mat­i­cally within an opti­miza­tion loop, where the geome­tries are meshed auto­mat­i­cally, too. So, in this scenario, you have to make sure that all volute can­di­dates are clean and water­tight. In addition, surface patches need to be uniquely iden­ti­fied for the meshing process, and your geome­tries have to fulfill con­straints such as pre­scribed cross-sec­tional area pro­gres­sions and pack­ag­ing constraints.

In this blog post, we have compiled the 10 major steps we typ­i­cally got through to create para­met­ric models of volutes in CAESES. In some specific sit­u­a­tions and with very specific cross sections, we need to use dif­fer­ent approaches. But gen­er­ally the fol­low­ing steps work well. All screen­shots and ani­ma­tions are taken from within the CAESES GUI. Hope you’ll like it!

Step 1: Cross Section Parameterization

Every company has its own way of describ­ing cross sections. For effi­cient vari­a­tion of the shape, you usually need to define 2D para­me­ters such as inlet/​outlet size, centroid values, A/R ratos, as well as further geo­met­ric controls to fine-tune your shape. These controls can vary a lot, depend­ing on the indi­vid­ual shape you want to achieve. In the picture below, there are NURBS control point weight­ings that addi­tion­ally change the shape of the section:

Step 2: Para­me­ter Distributions

For each 2D para­me­ter of your cross section you can create func­tions that describe how the para­me­ters behave in cir­cum­fer­en­tial direc­tion. These func­tions (i.e. para­me­ter dis­tri­b­u­tions) are the ones that will be varied later on during design studies and shape optimization.

Step 3: Generate Scroll Surface

Based on the cross section def­i­n­i­tion and the cor­re­spond­ing para­me­ter dis­tri­b­u­tions, you are ready to generate the main scroll surface. In CAESES, we use either a lofted surface for this (to inter­po­late a finite set of cross sections), or meta surface tech­nol­ogy, which directly takes the 2D def­i­n­i­tions and function graphs to generate a smooth surface.

Step 4: Create Inlet/​Outlet

Depend­ing on whether you are design­ing a turbine or a com­pres­sor volute, you need to create the inlet or outlet geometry, respec­tively. Typ­i­cally, this is not a big deal and often just a ruled surface or a rather simple B‑spline geometry with a circular con­nec­tion. Of course, even if this geometry is not that complex, we intro­duce a couple of shape para­me­ters that let us control the shape, if needed.

Step 5: The Smooth Transition

This is an inter­est­ing geometry part: The tran­si­tion from the main scroll to the inlet/​outlet geometry. In CAESES, we use either the fillet surface type for this which runs from one surface to another, and which has some controls about the tan­gen­tial influ­ence. That’s often suf­fi­cient and very effec­tive. Or, we again use a meta surface which gives us more detailed control in terms of shape variations.

Step 6: Offset Surfaces for the Intersection

So far, this is not that com­pli­cated, and one can probably create every­thing within a few minutes. However, now we have to prepare the inter­sec­tion process. As a first thing, we create two offset surfaces that will inter­sect with the initial surfaces.

Step 7: Intersection

Now we need space for the tongue surface. The initial surfaces are inter­sected and trimmed with the offset surfaces so that a gap is created. We use either the CAESES’ sub­sur­faces to rep­re­sent the remain­ing parts (modeling in the UV-space of the NURBS geome­tries gives us some more controls for complex volutes), or simply BReps which handle the trimming part auto­mat­i­cally. The latter is shown below:

Step 8: Tongue Surface

Gen­er­at­ing the tongue surface is the most inter­est­ing part of the volute design process, and it took us a while to come up with a col­lec­tion for all sorts of volutes. In CAESES, we mostly use a meta surface or a lofted surfaces with deriv­a­tive infor­ma­tion and rail curves to create smooth surfaces. You typ­i­cally also want to have control while sweeping the surface, so similar to the volute cross section you can define your tongue cross section as a para­met­ric template. As a result, you have separate para­me­ter dis­tri­b­u­tions for a detailed control of the tongue shape. Some volutes have a constant-radius fillet. In theses cases we simply use the BRep’s fil­let­ing capa­bil­i­ties, where you can directly set a radius value during the inter­sec­tion process.

Step 9: Close Geometry

The inlet and outlet needs to be closed with ​“lids”, so that the entire geometry is water­tight. In addition, we can assign colors and IDs to the dif­fer­ent surface patches for iden­ti­fy­ing them later on in the meshing process.

Step 10: Check Robustness

As men­tioned in the intro­duc­tion, we do not want to create a single design, but rather a model that can be used for design opti­miza­tion. Hence, we need to check whether this model is robust during vari­a­tion, i.e., it should not break or fail to regen­er­ate. In CAESES, we can utilize the inte­grated algo­rithms for the para­me­ter studies of this auto­mated check.

More Infor­ma­tion

How do you design variable volute models? What is your expe­ri­ence when it comes to the tongue part? How robust are your models? Let us know your thoughts by com­ment­ing below. Feel free to contact us if you have any ques­tions. Finally, see the volute pages for infor­ma­tion about the volute design capa­bil­i­ties in CAESES.