SpinOffs

In my previous blog post, “How the Design of a Wind Turbine Differs from other Types of Turbines”, I showed that the very small pressure drop across the rotor makes wind turbine design different from other types of turbines. This blog will focus on the best method to design a wind turbine rotor based on the fact that only kinetic energy is available to extract from the wind.

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.

Have you ever needed to know the exact geometry of a compressor that has been running for years in your process plant? Perhaps you need to analyze how it would perform if the process fluid had to be changed to meet new government regulations. Or maybe there has been damage to the impeller and a complete mechanical analysis is required before a new one can be put into service. Eventually, everything, even well-designed turbomachinery, needs to be replaced or upgraded.

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.

It’s a straightforward question, but many turbomachinery engineers can’t easily explain the physics behind blade twist. Some shorter high-pressure turbine (HPT) blades appear nearly 2D in shape (little or no twist). Blade twist is more commonly seen in taller turbine blades, which should give an immediate clue as to origin of blade twist.

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. 

Gas turbines (or GTs) are important in the power generation sector due to their high efficiency, cleaner emissions and faster startup than old coal-powered plants. These power generators can range from small, local power supplies to huge units, large enough to power a city.  Even with the surge in renewable energy sources, there will always be a need for power when the sun goes down, on a windless day or when power peaks are expected. GTs fill this power gap. GTs are very power dense, meaning they can produce a lot of power in a relatively small footprint. This is very useful in a city, offshore, or where vast landmasses are unavailable. 

Frequently, there is a need to reconstruct 2D and 3D geometry from reported or measured surface data points. In most cases, the provided surface data include significant amounts of noise for various reasons, including quality of the scanned blade, deviations produced by the measurement system, curve digitization errors, data digital rounding and truncation, and errors in reporting the data.  This noise hampers quality surface reconstruction and masks the understanding of the design intent of the profiles.  It also affects the accurate representation of the geometry, manufacturing complexity, and aero performance which forms the basis on which a design engineer can execute any design improvements.

Computational fluid dynamic analysis (CFD) has become a standard part of the turbomachinery design process. Within Concepts NREC’s Agile Engineering Design System, FINE/Turbo, from our Partner NUMECA International, is the tool used to accomplish aerodynamic analysis of designs by applying standard methods of three-dimensional analysis. However, arriving at a converged CFD solution in any CFD program can sometimes be a challenge.