Hartmut Krain

Investigations of the Flow through a High Pressure Ratio Centrifugal Impeller

In an industrial research project of German and Swiss Turbo Compressor manufacturers a high pressure ratio centrifugal impeller was designed and investigated. Performance measurements and extensive laser measurements (L2F) of the flow field upstream, along the blade passage and downstream of the impeller have been carried out. In addition to that, 3D calculations have been performed, mainly for the design point. Results have been presented by Krain et al., 1995 and 1998, Eisenlohr et al., 1998 and Hah et al.,1999. During the design period of this impeller a radial blade at the inlet region was mandatory to avoid a rub at the shroud due to stress reasons. The measurements and the 3D calculations performed later, however, showed a flow separation at the hub near the leading edge due to too high incidence. Additionally a rather large exit width and a high shroud curvature near the exit caused a flow separation near the exit, which is enlarged by the radially transported wake of the already addressed hub separation. Changes to the hub blade angle distribution to reduce the hub incidence and an adaptation of the shroud blade angle distribution for the same impeller mass-flow at the design point were investigated by means of 3D calculations first with the same contours at hub and shroud; this was followed by calculations with a major change of the shroud contour including an exit width change with a minor variation of the hub contour. These calculations showed encouraging results; some of them will be presented in conjunction with the geometry data of the original impeller design.Copyright

Improved High Pressure Ratio Centrifugal Compressor

The paper describes the development and the experimental as well as theoretical investigation of a new transonic, high specific speed centrifugal compressor rotor of 6.2:1 pressure ratio. Performance measurement results, laser measurements and calculated 3D results are shown for the new rotor and are compared with the corresponding data of a same type predecessor rotor. A 2% gain in stage efficiency and a 0.2 bar increase in stage pressure ratio are found at design speed by performance measurements. With the help of optical measurements and 3D stage calculations it is shown that the flow at the exit of the new rotor is more uniform/homogeneous. The degree of uniformity increases with decreasing pressure ratio, i.e. in the compressor part load region. Deeper insight into the internal rotor and the vaned diffuser flow is obtained from the 3D stage calculations showing less flow separation in the new rotor but significant secondary flow in the small span diffuser. The investigations are indicating that a further improvement of stage performance seems to be possible by an additional optimization of the vaned diffuser.Copyright

Analysis of the Transonic Flow at the Inlet of a High Pressure Ratio Centrifugal Impeller

In an industrial research project of German and Swiss Turbo Compressor manufacturers a high pressure ratio centrifugal impeller was designed and investigated. Performance measurements and extensive laser measurements (L2F) of the flow field upstream, inside and downstream of the rotor have been carried out. In addition to that, 3D calculations have been performed, mainly for the design point. Some earlier results have been presented by Krain et al., 1995.With four different viscous 3D-solvers, used in companies of the group, calculations for the design speed were carried out to investigate the suitability of these programs in the various design procedures.Special attention was given to the area from rotor inlet up to the splitter blades. The results for the flow field obtained with the four viscous 3D-Solvers are compared with one another and with the L2F-measurements.Copyright

Review of Centrifugal Compressor’s Application and Development

The paper historically describes the application and development of the centrifugal compressor from the very beginning of its introduction until today. It focuses on selected practical and theoretical examples that — to the author’s opinion — pushed the centrifugal’s standard from simple, low efficiency designs to its current high level status. The main events related with this development like the impact of the industrial revolution and the introduction of jet propulsion are pointed out. The implication of improved theoretical tools becoming available with raising computer capacity and the impetus of advanced measurement techniques on the centrifugal’s improvement are described. A considerable number of references offers the possibility to engross the thoughts.Copyright