SpinOffs

As discussed in my previous blog post, Flank Milling, How Hard Can it Be?, turbomachinery blades are commonly designed as ruled surfaces, with the goal of making manufacturing easier and faster with flank-milling.  While some non-ruled surfaces can be acceptably flank-milled, the programming and machining process for flank-milling is generally more dependable with ruled data. However, the ruled data should be well conditioned, and several pitfalls should be avoided during the design and construction process.

As an engineer, you probably have at least some familiarity with the story of how two bicycle mechanics, named Orville and Wilbur Wright, invented controlled-powered flying machines at Kitty Hawk, NC. While I knew the basic story, I learned a lot more reading David McCullough’s book “The Wright Brothers,” which, I highly recommend. I could not help but make the connections to what we, in the turbomachinery industry, owe to these dedicated and industrious brothers. Their groundbreaking flight, pictured below, on December 17, 1903,  is often cited as the birth of modern aviation.

Below is a 4 minute video blog from Mark Anderson, Concepts NREC's Chief Technology Officer, on the geometry of radial compressors. In it, he details the various parts of the compressor wheel, including the inducer, splitters, backsweep, etc. He also looks at open and closed (shrouded) impellers and the pros and cons of each design.

Click on the image below to launch the full-size video.

Gifts for Engineers can usually be segmented into a few categories: Things you have to put together, science fiction, gaming, new technology, and witty phrases printed on stuff. A Google search of the term "Best Gifts for Engineers" will quickly validate this claim.

As an engineer in the rotating machinery world, it is my job to design things that work for a very long time. To help ensure this, we have evolved the best analytical tools to calculate the stresses and deflection of the parts we have so carefully designed. But sometimes, we lose track of what matters. We know that material strength, weight, stiffness, toughness, thermal conductivity and thermal growth all matter. They are in a material database, so they must.

Most turbomachines need to operate across a range of fluid flow rates and speeds. This is obvious in transportation applications where gas turbine engines and turbochargers need to operate at all of the speeds, altitudes and temperatures that the vehicles they power will encounter. In industrial and refrigeration applications, turbomachines need to have a wide operating range to make them appealing to end users who want efficiency under many operating conditions.

Below is 3 minute video blog from Mark Anderson, Concepts NREC's Chief Technology Officer, on splitter design for radial compressors. Click on the small thumbnail image below to launch the full-size video.

I think we can all agree that designing turbomachinery is hard. There are just so many moving parts (pun intended) in the design process, and they are all interconnected.  When you change the blade shape, it changes the aerodynamics, and could impact manufacturability. Everything you change has a cascading effect across many different areas, because all of the areas are linked; just like a Rubik's^® cube! Only, in turbomachinery design, you are not always trying to get all of the sides to be one color. Heck, even a 3-year old can do that. 

Ideally, the exit flow angle for an impeller should be the same as the exit blade metal angle. However, the exit flow angle deviates from the blade guidance at the impeller exit due to the finite number of blades. Correctly predicting flow deviation is a critical task in meanline and through-flow modeling because the exit flow angle is directly related to the work input and the pressure rise across the impeller.

Many gas turbines with radial compressors utilize a radial-to-axial inlet duct upstream of the first compressor stage. Aside from the fact that flow in the duct generates aerodynamic losses, the flow profiles at the duct exit, delivered to the inlet of the first impeller, also affects the performance of the compressor.