SpinOffs

It is not a secret that when designing turbomachinery components there is a trade-off between the performance and durability. I challenge any aero or structural designer to highlight a geometric parameter, that when modified, is beneficial for both. Because of this trade-off, designers are often faced with the dilemma of selecting reduced performance or life when finalizing a component design. But which one should be sacrificed for the benefit of the other? This brings us to the all-important question: What is more important in turbomachinery design: performance or durability?  

In the world of aerodynamics, there are several branches and sub-branches of different types of aerodynamics. In the big picture the field of aerodynamics can be broken down into external and internal aerodynamics.   External aerodynamics is thought of external flow around an isolated body, with the typical example being flow around an aircraft wing section, or perhaps around an automobile. There is typically a far field ambient condition, with an isolated body moving through the field (or you can view it as the fluid moving over the body). Internal aerodynamics is thought of as a flow moving through some confined space or passage, with a prime example being flow through turbomachinery, such as a compressor or turbine. There are other ways to classify aerodynamic flow, such as subsonic flow (Mach No. <0.8, including low Mach No. incompressible flow, say Mach No. <0.3), transonic flow (around Mach No. = 1, say 0.8 to 1.2), supersonic flow (Mach No. > 1.2), and even hypersonic flow (Mach No. >5). Turbomachinery design encompasses the first three types of flow regimes, subsonic through supersonic. So in general, turbomachinery aerodynamics is predominately internal flow, over a range of Mach Numbers.    

It’s always interesting to look at the topics of my favorite engineering conferences and see what’s in vogue in a given year. What jumped out at me this year at the ASME TurboExpo was the hot topic of hydrogen.

Dave Schowalter, Director of Global Software Sales, introduces you to Claudio Raia, our newest team member and the Managing Director of Concepts NREC Europe. Welcome Claudio!

The compressor is generally one of the most sensitive components of an sCO2 cycle. This makes it a challenge to design a robust compressor while keeping the thermodynamic cycle close to optimal.

Low reaction stages are often used as control stages of steam turbines, ORC turbines,  drive and rocket turbopump turbines. Some of the benefits of low reaction stages vs higher reaction stages are:    Smaller radial size (and weight) for the given power and rotation speed  Compatibility with use of partial admission, which is used to accommodate low volumetric flow, with the needed low pressure gradients in the rotor blades to reduce leakage penalties  Both above factors allow increasing of nozzle and rotor blade heights  Smaller radial size provides lower disk rim speeds and disk stresses  Low reaction generally means lower axial thrust of the rotor  Velocity stage configurations are possible for low reaction designs (Curtis stage for example, Fig.1). Velocity stages allow further reduction in radial size and increasing blade heights 

In my last blog I wrote about visiting a local middle school to give a talk on ‘What is Turbomachinery, and How Does It Work?’   The quiz at the end of the talk was for the students to list all the turbomachinery in their home. I had a few examples in mind to get the list started but was impressed with how long of a list we were able to generate after the students thought about it for a while. Since then the list has grown to include 40 items.   I will present those 40 below, but first let me repeat the assignment and the ground rules to see if you can think of more:   List every piece of turbomachinery in your home. Inside and outside (in your yard is OK). Positive displacement equipment is OK to list. Don’t include turbomachinery in your cars or any vehicle or wheeled yard equipment (that’s another list…)

On occasion I’m invited to a local middle school to give a talk to one of the science classes about ‘What Is Turbomachinery, and How Does It Work?’.   I teach in several of the turbomachinery design courses we give at Concepts NREC, and while I’m comfortable in those courses, presenting at this level was different. I originally found it a challenge to come up with a good presentation that would keep the students' attention, while still providing some science education as requested by the science teacher that invited me. Derivation of the Euler turbomachinery equation was probably out. The attention getters that seemed to work best to get the conversation going included bringing our turbocharger cut-away (definitely the biggest hit of anything I brought), along with other interesting impeller samples. From there getting into the purpose of various types of turbomachinery (compressor vs turbine vs pump) and a very high level discussion of energy transfer to/from a fluid, seemed to flow. Getting them thinking about some of the physical aspects of turbomachinery operation (Just how fast is 100,000 rpm?) also seemed to keep their attention.

Here at Concepts NREC, we work on a wide range of turbomachinery components designed for fluids ranging from gases to liquids, including supercritical fluids like supercritical CO2 which have properties of both gases and liquids.   We do a lot of pump design, consulting work and education. In fact our annual course on Centrifugal and Axial Pump Design is consistently one of the most popular.   Many engineers in the gas compressor industries consider pump design plain vanilla, without the added complexities of Mach number effects, but there are reasons why our pump course is so popular – pump design can indeed be very difficult, with a number of complicating factors that are unique or especially critical to the pump industry.

A small turbine (for ORC, air liquification processes) , operating with low volumetric flows at inlet and significant pressure ratio in a single stage configuration (to reduce costs) is often associated with flow of media with transition from liquid to gas-liquid state, with operating levels of Mach numbers above 1.8 at nozzle exit, that assumes convergent-divergent nozzle geometry, and may require partial admission.