SpinOffs

Wind power generation is rapidly growing worldwide, and with that growth, demand for wind turbine design engineers is also growing.  However, an engineer who has experience designing turbines in most applications, will often have trouble translating their hard-won skills for general turbine design, into the wind turbine design. Why? 

Valentine’s Day is February 14, and while some cynics refer to it as a “Hallmark holiday”, most people commemorate the day in some way. One of the biggest challenges is finding a card that perfectly captures the way you feel about someone, while also reflecting who you are.  Well, Concepts NREC has created some turbomachinery-themed Valentine’s Day cards for engineers. These fall into the Art end of our Art-to-Part Solution.

In my blog Flow Coefficient and Work Coefficient, I outlined the basic concept behind the flow and work coefficient. These nondimensional parameters are widely used to characterize axial and radial turbomachinery. Another widely used parameter for radial design is “specific speed”. For something with such a finite name, specific speed is perhaps the most mysterious and non-intuitive parameter in all of turbomachinery. In this blog, I'll lay the ground work for understanding specific speed.

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.

The advancement of composite material technologies over the past few decades has contributed to their widespread use in a vast array of aerospace applications. Most applications target weight reduction without compromising the strength and endurance capabilities of the metallic structures being replaced. The high-strength composite materials used in advanced applications involving elevated temperature conditions are, typically, continuous fibrous material embedded in a matrix material that acts to hold the fibers together. The fibers in the matrix material can be oriented in various directions to achieve the desired mechanical properties in any specific direction. Weight reduction is achieved by eliminating redundant fiber material for the directions in which material strength and stiffness are not required by the design.

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.

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.

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”:

Turbine inlet temperature is one of the most critical parameters in the Brayton cycle of gas turbine engines. One way to increase the cycle efficiency is to increase the turbine inlet temperature, as illustrated in Figure 1. Here, a typical Brayton cycle T-S diagram chart visualizes the impact of higher turbine inlet temperatures on higher efficiency. Indeed, the area between the solid curves through points 0-3-4-8 represents the useful power generated by the turbine. The cycle efficiency can be calculated by dividing this area by the total area below curve 3-4, being the heat input. The dash lines convey the cycle with increased turbine inlet temperature, and the new cycle efficiency is the area in 0-3’-4’-8 curves divided by the area below curve 3’-4’. It is easy to see how a higher turbine inlet temperature increases cycle efficiency. Because of pursuing higher efficiency in modern gas turbine engine design, turbine inlet temperature has been pushed to a level that most material cannot withstand without effective cooling. Figure 2 shows the increasing trend of turbine inlet temperature since the 1940’s. Since the 1970’s, the turbine inlet temperature has been above material capability through the introduction of turbine cooling techniques.

Many energy recovery, drive cycles (Organic and Steam Rankine cycles) and rocket propulsion cycles require the use of a turbine that operates at low volumetric flow and high-pressure ratio. Additional requirements include low cost, reduced weight, and reduced axial length (for robust rotor dynamics).