The German Aerospace Center (DLR), together with the Zittau/Görlitz University of Applied Sciences and the Technical University of Dresden, has developed a method that simulates the flow of steam in turbomachinery with high precision and 10 times faster than before. This enables scientists to predict the processes in a turbine much more precisely and provides manufacturers with sound data for the further development of their systems. Space researchers also use the calculation methods; they can use them to better understand and simulate the processes on comets, moons and exoplanets. The method has been declared the new international standard by the IAPWS (The International Association for the Properties of Water and Steam).

Water has very different properties depending on temperature and pressure. In order to numerically predict the processes in the three-dimensional environment of a turbine, the behavior must be calculated for millions of points in space at any given time. Over the past six years, scientists at the DLR Institute of Propulsion Technology, in cooperation with the Zittau/Görlitz University of Applied Sciences and the TU Dresden, have developed a highly accurate calculation method that is 300 times faster than previous models. This makes it possible for the first time to simulate the properties of water vapor in complex processes.

"In order to develop this new, very accurate and at the same time very fast algorithm, we started from the IAPWS calculation equations and solved them using efficient interpolation methods and special variable transformations. This resulted in interpolation tables that map the properties of water vapor very accurately," says Prof. Hans-Joachim Kretzschmar from the Zittau/Görlitz University of Applied Sciences, who designed the new interpolation method (spline-based table look-up, SBTL) together with Matthias Kunick. Such precise simulations are an important basis for the further development of turbines. Manufacturers can test the properties and behavior of prototypes in the computer simulation, which shortens the development time and significantly reduces development costs.

Numerical fluid dynamics

A new feature of the process is the connection to a CFD (Computational Fluid Dynamics) database. Before the calculation, the possible states of the water or steam are narrowed down with the help of this database, for example for the parameters pressure and temperature. This means that not all possible aggregate states have to be calculated, but only the relevant ones.

"Water or steam is a very versatile medium, so simulations in the complex three-dimensional environment of a turbine are extremely difficult and time-consuming," says project manager Prof. Francesca di Mare from the DLR Institute of Propulsion Technology. With the help of numerical fluid dynamics, very precise, realistic information can be obtained about the three-dimensional and highly transient processes in a turbine.

The method is already being used successfully in the Siemens Power and Gas Division. This drastically accelerates dynamic and stationary simulations of power plant processes without compromising on the quality of the calculations.

"In stationary simulations, we have been able to more than double the calculation speed in some cases," says Ingo Weber, Head of Tool Development for Stationary Power Plant Simulation in the Energy Solutions division of Siemens Power and Gas. calculation methods are also used in space research. It is not only industry that needs highly accurate calculation methods for the behavior of steam. Water, in the form of steam, liquid water or ice, is one of the most important substances on Earth and in our solar system. Planetary researchers can use the calculation method to better understand the processes of the icy moons Titan or Europa or the vapor atmospheres of hot planets such as early Venus or certain exoplanets.

"Water occurs in many different forms in our solar system. If you want to model the processes, it is not enough to simply assume that water vapor is an ideal gas. What's important here are codes that can calculate the processes quickly and accurately," says Dr. Jens Biele, deputy project manager of the Philae comet probe. From idea to international standard. "Six years ago, we started with the idea of linking high-precision algorithms with a CFD database," says di Mare, looking back. Due to the complexity of water, this link was long considered a major challenge in specialist circles. The method is so accurate and reliable that it has been declared the new international standard for calculating the properties of water vapor and water in computational fluid dynamics and complex transient process simulations by the International Association for the Properties of Water and Steam (IAPWS). The IAPWS is an international association of twelve national organizations that research the properties of water in all possible aggregate states. "By developing this innovative process, DLR has further established itself as a pioneer in virtual product technology," says Reinhard Mönig, Head of the Institute of Propulsion Technology. "DLR is thus supporting industry in solving general technical problems and creating the basis for efficient product development. "The new simulation method is the product of cooperation between scientists from three institutions. The high-precision thermodynamic algorithms were developed by Kretzschmar and Kunick at the Department of Technical Thermodynamics at the Zittau/Görlitz University of Applied Sciences in cooperation with Prof. Uwe Gampe from the Dresden University of Technology. The algorithms were optimized for the highly complex application in the 3D numerical simulation of turbomachinery in close cooperation with the DLR, where a group led by Prof. di Mare implemented them in the TRACE program system.

Text: German Aerospace Center (DLR) (Original text': here)