Institute of Applied Mechanics > About us > Departments > Division of Fluid Dynamics > Research > Numerical investigation of dynamic effects in the flow around airfoil employed

Unsteady flow effects play in machines such as pumps, compressors and turbines a major role. Of particular importance are fluctuations with large amplitude, such as those caused by detachment at partial load. The fluctuations are of varying load on the components connected by fluid forces and can thus in the case of resonance lead to vibration problems. In the deep part load Fehlanströmung occur through the leading edge separation, which are not stable, but circulate in the machine. The rotational speed of the vortex areas is generally less known than the rotational speed of the impeller, but not for interpretation. This phenomenon is called thus rotating chopping (rotating stall). The frequency of the rotating stall is to be determined on the basis of the possible vibrational excitation of great importance and can be either in the experiment, or even with the help of modern simulation techniques. The Institute is being investigated with the aid of computational fluid dynamics (CFD), the part-load performance of a pump. Treatment of the turbulence plays a crucial role. Classical turbulence modeling is only suitable for flows with separation. Methods such as LES (Large Eddy Simulation) that turbulent structures are fully or partially resolved, are due to the enormous computational effort is currently not yet suitable for use in pump currents. However, there are new hybrid developments, such as DES (Detached Eddy Simulation), the applied currents with a classical turbulence model and LES detached areas with similar approaches to calculate. The advantage of this method lies in a drastic reduction in the number of grid points compared to an LES calculation for the total fluid volume. Nevertheless, this method requires high-performance computers to create in reasonable computational times (in days) results. As part of the project first hybrid models for the calculation of turbulent flows are validated. After the evaluation of simple test cases in the literature documented the suitability of the model for the simulation of rotating stall is studied. It detailed measurements at a pump for comparisons. In further studies, the influence of the inflow-outflow conditions and the frequency and the start of the rotating stall are examined. This spiral casing with a view to minimizing the rotor stator interaction designed and optimized. The efficiency is also considered as the most important design criterion. The flow conditions are taken into account by typical built-in suction line as diffusers or elbows. The result will be demonstrated that it can be done through the use of CFD is an important contribution to the prediction of possible vibration problems in runners.

Kontakt

Dipl.-Ing. Andreas Lucius, Raum 120, Tel. 05323 72-3715

Publikationen A. Lucius, G. Brenner: “Unsteady CFD Simulations of a Pump in Part Load Conditions Using a Hybrid LES RANS Model”, to appear in Conference on Modelling Fluid Flow, Budapest 2009A. Lucius, G. Brenner: “3D time accurate simulations of a centrifugal compressor” to appear in 20th International Conference on Parallel Computational Fluid Dynamics, Lyon 2008