Karsten Hasselmann

Measurements and Visualization of the Flow in a Turbine Blade Tip Gap With Passive Jet Injection

Results of detailed measurements of the flow in a turbine blade tip are presented. The blades of the linear cascade were made by means of 3D-printing technology. Different clearances and the impact of a passive jet injection on the gap flow were investigated. The resulting velocity profiles in the gap were measured by means of a miniaturized Pitot-probe. To gain qualitative insights into the flow details, surface oil flow visualizations were performed. This classical method was extremely helpful for obtaining and interpreting occurring flow structures. The effect of an additional passive blade tip injection was investigated in detail and compared with the results obtained for plain blade tips without an additional injection. It was found that the overall flow structure was not greatly affected by the additional jet injection. But in case of moderate or large tip clearances, a local reduction of the tip leakage flow was achieved. The surface oil flow visualizations indicated a complex interaction of the jet with the gap flow. Such vortex interactions are well known in case of gas turbine film cooling technologies, but here rather similar observations were made in case of a confined flow configuration, too.Copyright

A Modular Low-Speed Wind Tunnel With Two Test Sections and Variable Inflow Angle

A modular low-speed wind tunnel system was designed and developed. Due to the modular concept, the wind tunnel permitted open-jet operation, cascade testing or closed-circuit operation. The closed-circuit wind tunnel had two test sections, and it had a high quality test-section with variable flow angle that is particular valuable for airfoil or blade testing. Physical calibration of the wind tunnel facility validated the design rules and CFD methods used and demonstrated that these techniques can be employed successfully for future wind tunnel designs. A detailed study of the thermal behavior of the closed-circuit wind tunnel was conducted. A feedback control method based on a PI control law was developed and tested for the wind tunnel speed.Copyright

Performance Predictions of Axial Turbines for Organic Rankine Cycle (ORC) Applications Based on Measurements of the Flow Through Two-Dimensional Cascades of Blades

The Organic-Rankine-Cycle (ORC) offers a great potential for waste heat recovery and use of low-temperature sources for power generation. However, the ORC thermal efficiency is limited by the relatively low temperature level, and it is, therefore, of major importance to design ORC components with high efficiencies and minimized losses. The use of organic fluids creates new challenges for turbine design, due to real-gas behavior and low speed of sound. The design and performance predictions for steam and gas turbines have been mainly based on measurements and numerical simulations of flow through two-dimensional cascades of blades. In case of ORC turbines and related fluids, such an approach requires the use of specially designed closed cascade wind tunnels. In this contribution, the specific loss mechanisms caused by the organic fluids are reviewed. The concept and design of an ORC cascade wind tunnel are presented. This closed wind tunnel can operate at higher pressure and temperature levels, and this allows for an investigation of typical organic fluids and their real-gas behavior. The choice of suitable test fluids is discussed based on the specific loss mechanisms in ORC turbine cascades. In future work, we are going to exploit large-eddy-simulation (LES) techniques for calculating flow separation and losses. For the validation of this approach and benchmarking different sub-grid models, experimental data of blade cascade tests are crucial. The testing facility is part of a large research project aiming at obtaining loss correlations for performance predictions of ORC turbines and processes, and it is supported by the German Ministry for Education and Research (BMBF).Copyright

Development of a Cost-Efficient Test Rig for Turbine Loss Education

A large number of approaches have been made to predict the total pressure loss coefficients and flow deviation angles to the geometry of turbine cascades and the incoming flow. Students feel typically uncomfortable when faced with turbine loss coefficients during their education, and it is challenging to fully understand turbine losses only by means of theory. The integration of a turbine cascade facility into academic courses might be useful but such test facilities are expensive or not available for a large number of engineering schools. To overcome this issue, a cost-efficient test rig for measurements of the flow through a two-dimensional cascade of turbine blades was designed. This test rig enabled the measurement of the flow through a blade cascade and the formation of wakes. The effect of the inlet flow angle on the cascade performance was investigated easily by students. Based on own measurements, the students were able to apply the most prominent approaches for determining loss coefficients. Furthermore, they compared their results with literature data and predictions of available correlations. By doing that, the importance of blade spacing and Reynolds number level on profile loss coefficients became more transparent and invited to further studies.© 2014 ASME