Maximilian Passmann

A one-dimensional analytical calculation method for obtaining normal shock losses in supersonic real gas flows

The calculation of isentropic flow and normal shock waves of real gases are important, especially in the preliminary design of turbo-machinery and test rigs. In an ideal gas, the relations for one-dimensional isentropic flow and normal shock waves are well known and can be found in standard textbooks. However, for fluids exhibiting strong deviations from the ideal gas assumption universal relations do not exist due to complex equations of state. This paper presents a analytical method for the prediction of isentropic real gas flows and normal shock waves, based on the Redlich-Kwong (RK) equation of state. Explicit expressions based on a series expansion for describing isentropic flow of Novec™ 649 are compared to Refprop data and ideal gas equations. For moderate pressures the RK method is in very good agreement with the Refprop data, while the ideal gas equations fail to predict the real gas behaviour. The same observations are made for normal shock calculations, where both real gas methods yield very close results. Especially the predicted stagnation pressure losses across a shock wave are in excellent agreement.

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

Reduction of Turbine Blade Tip Leakage Losses and Excitation Forces by Passive Tip Injection

The reduction of turbine blade-tip losses by means of passive tip injection was theoretically investigated. The analysis employed an analytical expression of the blade-tip discharge coefficient. The resulting blade-tip excitation forces (i. e. Thomas-Alford forces) were explicitly evaluated for unshrouded turbines with and without passive tip injection. It was found, that the Thomas-Alford coefficient for cross-force can substantially increase when the blade-tip gap was reduced. This observation can directly be explained on the basis of viscous flow effects through the gap, and it was in excellent agreement with available literature data. Due to passive tip injection, a slight decrease of the blade-tip excitation cross-force was obtained. The potential of the reduction of the cross-force due to passive tip injection was found to be comparable to the corresponding tip loss reduction.Copyright