SpinOffs

If there’s one thing good about sitting in snarled traffic in Boston, it’s that you get to see some very original bumper stickers. The most recent bumper sticker I saw was probably the strangest one, no doubt created by some engineering professor who doesn’t see that the glass is half full, but that it has a safety factor of 2! Nevertheless, the bumper sticker stated the obvious when one thinks about it: ENTROPY HAPPENS! And then, to emphasize the point, the artist has the letters slowly “evaporating,” demonstrating graphically that entropy proceeds from order to chaos.

Temperature envelopes in the turbomachinery industry are constantly increasing as the state of the art evolves in pursuit of better performance. This means engineers need to design compressors with higher and higher exit temperatures, and turbines and nozzles with continuously increasing inlet temperatures. This rise in temperature greatly impacts the selection criteria for materials used. 

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.

Extending the operating range of centrifugal compressors has been a highly sought-after goal for several decades. In fact, the potential benefits have motivated researchers to develop and put into practice many pieces of technology, including full span inlet guide vanes (IGV’s), complex multistage systems with interstage bleed, passive casing treatment, and many others.

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. 

In the mid 1980’s, while serving in the Canadian Air Force, I had the good fortune, on one of my many adventures, to fly into Sondrestrom Air Base in Greenland. The Base is at the head of a beautiful fjord, so the scenery during the flight to Sondrestrom was magnificent. We arrived in the early summer on a beautiful clear day. I got out of the plane and wandered around the base while the aircraft was being serviced. One feature that caught my eye was all of the bright yellow ropes and stanchions that were strung from building to building. I couldn’t figure out what they were for, so I stopped one of the locals and asked, “Why the Yellow Ropes?”  Now, for those who are not students of the geography of Greenland, Sondrestrom is north of the Arctic Circle, and, apparently, the weather is not always as bright and clear as it was that day! As a matter of fact, one of the meteorological phenomena in the area was virtually instantaneous whiteouts, caused by snowstorms funneling up the fjord. Several people had been caught out between buildings and become disoriented during a blinding storm, a dangerous thing during the long darkness of winter. To eliminate this danger, they had put up the yellow ropes to safely guide people to their destination.

Space launch vehicles can exhibit self-excited longitudinal oscillations, also known as “Pogo” — so named because the phenomenon vibrates the rocket up and down in a manner similar to bouncing on a pogo stick. The vibrations severely impair the astronauts’ ability to pilot or respond to emergencies and can cause structural failure of the vehicle. NASA first became aware of the disastrous consequences from Pogo during the Gemini-Titan program. The issue continued to plague the agency through the Saturn V Moon launch missions.

Perhaps the most common type of diffuser in turbomachinery is the conical diffuser. This diffuser is found at the exit of every volute as the geometry transitions to the exit flange. This conical diffuser must be sized appropriately to maximize machine performance across the desired flow range and can have a large impact on the end footprint and performance of the turbomachine.

The 2018 ASME Turbo Expo in Lillestrøm, Norway was, as always,  a smorgasbord of papers and presentations on the latest and greatest ideas in turbomachinery and gas turbines. Two of our favorites were from Mark R. Anderson and Felipe F. Favaretto, Concepts NREC employees. Coincidence? I think not. Felipe presented, “Development of a Meanline Model for Preliminary Design of Recirculating Casing Treatment In Turbocharger Compressors”: