Turbomachinery designers are under pressure to improve all aspects of turbomachinery performance. That applies not only to aircraft engine developers, who sometimes seem to garner the most attention in the news, but to designers of most other machine types as well. While fuel burn and efficiency targets are most often discussed, these targets must be balanced with a number of other competing and often opposing considerations, such as operating range, reliability, cost, time to market, etc.
Engineering simulation now plays a key role in turbomachinery development. This has come about because of significant improvements in engineering software and computing speed. Many turbomachinery companies were early adopters of simulation; they played a significant role in shaping software development to their needs and validating it for their applications. Experiment and testing still play an important role, but often only when a design is sufficiently evolved, or in situations where fundamental information is missing. So simulation and testing complement one another.
One can assess simulation software from a number of vantage points, but two that I like are fidelity and productivity. Fidelity usually comes first, in that we are concerned that predictions match reality. That is how software development has generally proceeded over the years. Developers have worked on improving turbulence models since the beginning of CFD, and continue to do so. Much progress has been made, with a vast array of physical models now available for both fluids and structural simulation. Numerical schemes have been developed in concert to facilitate solving the (usually) continuum equations in which these models reside. Powerful computers enable us to solve large problems. There is always more to do, with challenging, complex physics areas remaining to be conquered, but for many applications we are in pretty good shape as far as fidelity is concerned.
Productivity is the other important aspect. Equipped with productive simulation software, engineers can make a real impact. A good example appears in the ANSYS Advantage article “Pumped” ( see also the authors’ recorded presentation) in which the Denmark-based company Grundfos reports on the benefits they have realized from simulation productivity. There are many relevant examples, spanning the full range of physics and applications applicable to turbomachinery engineers. One is the development of a turbocharger compressor.
Modern turbochargers must operate over a very wide range of speeds and operating conditions. That is a big challenge on the aerodynamics side, where the usual process for a compressor designer is to construct a “map.” This map consists of a number of lines, each representing a different rotational speed and indicating the pressure rise delivered by the compressor over a range of flow rates. Each line runs from stall (at the left) to choke (at the right). Lines are also required indicating efficiency or power requirements. Each line consists of a number of simulation points — the more the better, but something like 10 points per line will often suffice. With several speed lines the number of simulations really add up. The adequacy of the design is not evaluated by looking at one point, but rather at several critical points across the map. So the designer needs not only to run a lot of simulations, but must process them as well, for multiple design configurations. Of course there are the mechanical aspects to consider as well: stress and vibration (because durability is another requirement), small package size, cost of production, and low inertia (to minimize the dreaded “turbo lag”).
Clearly, with the extensive simulation requirements outlined above, productivity is vital. That leads me to ANSYS 17.0, our latest product release, where productivity-improving enhancements have been made that impact virtually all steps in the simulation process. Some are general in nature, including “region-based volume meshing,” which is beneficial for complex geometries such as turbomachinery scrolls and housings, and improved high-performance computing scalability. Others are turbo-specific, like streamlined compressor performance mapping and transient blade row simulation for asymmetric geometries (e.g., an impeller in a scroll).
The improvements are too numerous to list or describe here. However, more will be revealed in a webinar on February 17th. Please join us to learn how ANSYS 17.0 can help you reach new levels of simulation productivity.