The injection of water into air (or liquids into gases in general) can be used to reduce the absorbed power of a compression process. The enthalpy raised for evaporation ideally ensures isothermal compression and reduces the power demand. During the injection, the prediction of droplet sizes, their distribution and their velocities is crucial for the resulting evaporation. This knowledge serves as a basis for the design of turbomachines. Originally developed to increase the flexibility of conventional gas turbines, this technology is now investigated to reduce the power demand of turbo compressors in general.

The reverse phase change of the condensation and the resulting drop formation occurs in steam turbines and expanders. Emerging drops may cause damage when they impinge the rotating components of the machine. This occurs in radial expanders, which are designed to use decay heat and are utilized in fuel cell systems as well as in the low-pressure stages of multistage steam turbines. The prediction of primary and secondary drop formation can be used for the design process in order to reduce impingement damage and aerodynamic losses. Besides the damage to the components done by the impingement of the droplets, they do as well wet the surfaces of components in areas with low flow rates. This leads to different local heat transmissions and heat exchanges between fluid and component surfaces, which in turn results in temperature gradients in the components and results in increased mechanical stress on the material. These stresses limit the maximum possible load gradients of power plants. The prediction of condensation, including secondary droplet formation, droplet growth, deposition and knowledge about the heat transfer, allows to influence the load gradients and thus the flexibility of power plants.

The phase change of a fluid can be used to make turbomachines more flexible. Consequently, it provides a positive contribution to the energy transition.

The interaction between the structure and the surrounding fluid can have a significant and lasting effect on the design of components, their functionality and their service life. The realistic modelling of fluid-structure interactions allows for a precise design and a reliable operation under dynamically changing conditions, being of particular use in the context of the energy revolution. Due to the required much higher flexibility of the machines with a lot more operation time in extreme part load or overload condition a deeper knowledge of the interaction between fluid flow and structure in this operating conditions is required to guarantee a reliable operation.

In order to control mass flows and volume flows, valves ensure high dissipation at high throttling. This leads to high velocity at the Vena Contracta between the valve’s exact position and its casing. The jet either attaches itself to the wall as a stable jet (Coanda effect) or is completely detached. Time-dependent flow conditions may occur between these two extremes, with high fluctuations in velocity and pressure. In interaction with the structure, a coupled observation including acoustic phenomena is required to predict the vibration behaviour of the system and, ultimately, of the valve itself.

Acoustic phenomena must also be considered in rotor-stator cavities in radial compressors. The coupling of the vibration behaviour of the structure and the fluid is an observation that can be made. It leads to a shift of the natural frequencies as well as to changes in the system’s damping. Due to the coupling, structural and acoustic modes become indistinguishable. The severity of the effect depends on the operating conditions (pressure, temperature, speed) as well as the geometry of the compressor (number of rotor blades compared to the number of guide blades, geometry of the cavity, etc.). The modelling of this system is significant for the design and operation of the centrifugal compressor.

Dry gas seals minimize leakage, especially at high pressures in compressors. The proper functioning of the seal is essential for the availability of the compressor. The fluid flows through the seal, and the rotor's internal fittings, e.g. its pockets, distribute the pressure within the gap, resulting in a balance with a gap of 1-2 micrometres. The internals provide a stimulating impulse to the system. However, this may cause the entire system to become unstable, increasing the risk of contact between the sealing elements. Contacting sealing elements, however, would cause the compressor to fail. Thus, the design of the sealing systems, including the prediction of its lifetime during operation, requires modelling which is capable of taking into account the current operating parameters.

The faculty of engineering at the UDE pools its research activities into four developed interdisciplinary focal points:

• Tailored Materials
• Human-Centered Cyber-Physical Systems
• Smart Engineering
• Energy and Resource Engineering

The Chair’s research projects are assigned to “Tailored Materials” and “Energy and Resource Engineering”. Please klick on the links above for further information on the Chair’s relevant research activities within the faculty.