Video Blade Design Tutorial

With CAESES® 4.0, there is a lot of new and cool stuff for tur­bo­ma­chin­ery blade design. This post will give you a brief intro­duc­tion into the fully-para­met­ric design of an impeller blade, as you can typ­i­cally find them in tur­bocharg­ers and pumps. We have added some com­ple­ment­ing infor­ma­tion right below the tutorial video since not every­thing is covered in all details (we didn’t want to blow it up it up to a block­buster length…).

Pre­req­ui­sites

Here comes a rec­om­men­da­tion for a higher fun factor: If you are seri­ously inter­ested in setting up your own blade model in CAESES®, then check out the meta surface and feature def­i­n­i­tion tuto­ri­als (PDF) that are shipped with CAESES®. There are also several videos that com­ple­ment these tuto­ri­als, e.g. the one for features and a basic volute design which illus­trates the general meta surface concept.

Some of the features that are used in the video will be released with version 4.0.3. Anyway, there you go — we hope it will help you to get started with blade design in CAESES®:

Merid­ional Contours

Alright, let’s get started with some comments. First of all, we create the 2D hub and shroud contours in the y‑plane of CAESES®. There is a new button for this blade view so that you can switch back at any point in time. The leading edge and trailing edge guide curves are simple con­nec­tions of hub and shroud curve posi­tions. The trailing edge guide will be used to cut off the blade in the end. In our video example, we use a smooth fspline curve where you can set start and end tangent angle. This is nice and easy to use for design studies later on. One little detail: select­ing a curve and then creating a point imme­di­ately creates the point on the selected curve and you can move it along the curve by using the created curve domain parameter. 

Camber Surface

Basi­cally, you can use any kind of camber def­i­n­i­tion in order to create a camber surface. This camber surface will be the input for applying thick­ness in the next step. CAESES® comes with a handy camber def­i­n­i­tion that you can directly use without any deeper knowl­edge. CAESES® offers the pos­si­bil­ity to define camber data in the (m’,beta) or (m’,theta) system. If you set up 2D curves for this, then simply do it in the global xy-system of CAESES®. It gets auto­mat­i­cally inter­preted the correct way later on, i.e. beta/​theta, by choosing the system at the stream section. The stream section is the curve that takes all the input (hub and shroud infor­ma­tion, leading and trailing edge as well as camber data plus a radius location) and creates a curve in the 3D space — our 3D camber curve. BTW: the stream section is also used in the context of blade design for axial turbines and compressors.

So back to our 2D camber infor­ma­tion. In the video, the camber value at the leading edge ​“Value A” (or also called ​“Value at Start”) can be changed for a single section. In the first run, this value is kept constant in radial direc­tion, e.g. 0.3 which cor­re­sponds to 30 degrees. Note that we always use nor­mal­ized rep­re­sen­ta­tions (easier to visu­al­ize!) and we scale it up at a later stage by using factors. The picture below shows camber data for 1 section: 

The next picture shows a stream section curve that gets gen­er­ated from such camber data: 

Now, we want to create a surface. The section para­me­ter ​“Value A” is then con­trolled in radial direc­tion by a smart function graph — yep, this is the fun part of CAESES®: Intro­duce graphs for any section para­me­ter. Again, the graph is quickly created in the xy-system of CAESES®: 

You can use any kind of curve type to create such a graph. It is modeled in the xy-system but gets inter­preted later on as shown in the picture above (in this case: x=R=radius range, y=value A). Simply set such a graph at the curve engine instead of using the constant value. Hold on, curve engine? The curve engine object in CAESES® links together the stream section and all the user function graphs. This is basi­cally all we need to smoothly sweep in radial direc­tion, which is great team work of the curve engine and the meta surface: 

Applying Thick­ness

CAESES® uses a so-called offset curve to apply thick­ness to the camber surface. Of course, we want to control the thick­ness char­ac­ter­is­tics at the leading and trailing edge in radial direc­tion. Hence, we have a user-defined 3D curve that gets con­trolled by function graphs. The job of creating a surface is again done by a curve engine plus a meta surface. Here is the single 3D curve that is used for our intel­li­gent graph-based sweep: 

The shape of the leading edge can be con­trolled in the same way, i.e. we can have a circular or a more ellipse-like shape, there is a simple ​“ellipse factor” for this purpose. The thick­ness dis­tri­b­u­tion and the 3D curve gen­er­a­tion are wrapped in a feature def­i­n­i­tion so that users are able to still cus­tomize and manip­u­late it. In our example, we run along the camber surface, create a surface curve and apply thick­ness in normal direc­tion. Let’s take a quick look into it: 

This thick­ness def­i­n­i­tion is shipped with CAESES® and can be readily used, e.g. as a ref­er­ence for own designs. We think it is quite nice already: a smooth thick­ness dis­tri­b­u­tion where its values, tangent angles and the ellipse factor can be con­trolled in radial direc­tion. What else do you need? Finally, here comes the para­met­ric blade surface: 

Solid Impeller

As a last step, we create the periodic blade surfaces and a solid body. For this purpose, we have prepared another fancy feature that can be readily used with just a single-click, and which is also shown in the video. The feature takes the blade, hub and shroud infor­ma­tion plus the trailing edge guide, and then uses so-called ​“BReps” inter­nally. These BReps are able to perform Boolean Oper­a­tions and trimming. If needed, this feature could also generate hub and blade fillets.

Inter­ested in trying out CAESES® for your appli­ca­tion? Then download and install our free version today! It is fully free for com­mer­cial work, and you can directly start setting up your own intel­li­gent model :-) 

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