Separation and relaminization at the circular arc leading edge of a controlled diffusion compressor stator
Perkins, SCT and Henderson, AD, Separation and relaminization at the circular arc leading edge of a controlled diffusion compressor stator, Proceedings of ASME Turbo Expo 2012, 11-15 June, Copenhagen, Denmark, pp. 69384.1-12. ISBN 9780791844670 (2012) [Refereed Conference Paper]
This paper investigates the influence of Reynolds Number
and incidence on boundary layer development at the leading
edge of a controlled diffusion (CD) stator blade with circular
arc leading edge profile. Steady flow measurements were made
inside a large scale 2D compressor cascade at Reynolds numbers
of 260,000 and 400,000 for a range of inlet flow angles
corresponding to both positive and negative incidence. Detailed
static pressure measurements in the leading edge region show
the time-mean boundary layer development through the velocity
overspeed and following region of accelerating flow on the
suction surface. Separation bubbles at the leading edge of the
pressure and suction surfaces trigger the boundary layer to undergo
an initial and rapid transition to turbulence. On the pressure
surface, the bubble forms at all values of incidence tested,
whereas on the suction surface a bubble only forms for incidence
greater than design. In all cases the bubble length was seen to
reduce significantly as Reynolds number is increased. These
trends are supported by surface flow visualization results. Quasiwall
shear stress measurements from hot-film sensors were interpreted
using a hybrid threshold peak-valley-counting algorithm
to yield time-averaged turbulent intermittency on each blade surface.
These results in combination with raw quasi-wall shear
stress traces show evidence of boundary layer relaminarization
on the suction surface, downstream of the leading edge velocity
overspeed in the favorable pressure gradient leading to peak suction.
The relaminarization process is observed to become less
effective as Reynolds number and inlet flow angle are increased.
The boundary layer development is shown to have a large influence
on the total blade pressure loss. At negative incidence, loss
was seen to increase as Reynolds number is decreased, and in
contrast at positive incidence, the opposite trend was displayed.