Abstracts - KTH Mechanics

164
Flowcontrol with crosswise groves in diffusor flows
R. Meyer a, W. Hage a and C.O. Paschereit b
Crosswise grooves can increase the efficiency of flows that are partially separated
due to a high pressure gradient. In the present investigation the effect and
mechanisms of such crosswise grooves are examined in detail on a simple diffuser
geometry. A diffuser with smooth walls and without areas of flow separation surely
exhibits the best efficiency. But with high pressure gradients and short overall lengths
a separation-free diffuser is however, not attainable. By the implementation of orifice
plates or crosswise grooves into the area of separated flow the efficiency of a Borda-
Carnot diffuser can be improved from 28% to 75%. Pressure measurements within a
Reynolds number range of 10,000 to 250,000 (related to the nozzle diameter) show
that the orifice plates effectively obstruct pressurization between the small and the
large cross section of the diffuser (see fig. 1). Particle Imaging Velocimetry (PIV)
measurements (see fig. 2) and CFD calculations show clearly the differences in the
flow field with and without orifice plates. In the second part of the investigation these
principles will be exploited in the context of axial compressors from turbo machines.
A large part of the compressor stage losses is caused by corner separations on the
blades and the side walls (casing and hub). By flow control with crosswise groves
these secondary flow losses should be decreased. Thus the efficiency of axial
compressors and gas turbines could be improved.
Figure 1: Efficiency of the different diffuser geometries; all dimensions in [mm]
Figure 2: PIV-measurements of two different diffusor configurations. (Re =10,000).
a German Aerospace Center (DLR), Mueller-Breslau-Strasse 8, D-10623 Berlin, Germany.
b Technical University of Berlin, Hermann-Foettinger-Institute, Mueller-Breslau-Strasse 8, D-10623
Berlin, Germany