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Unsteady Flow and Transition Phenomena in an Axial Flow Compressor

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Henderson, AD (2006) Unsteady Flow and Transition Phenomena in an Axial Flow Compressor. PhD thesis, University of Tasmania.

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Abstract

The unsteady mid-span aerodynamics of an outlet stator row in a 1.5-stage low-speed
axial compressor is investigated experimentally and numerically. Two stator blade
rows with characteristically dierent blade proles are studied: one of standard British
C4 section and a controlled diusion (CD) blade with a circular arc leading edge
prole.
A turbulence grid placed at compressor inlet is used to generate turbulence characteristics
similar to those occurring in an embedded stage in a multi-stage axial compressor.
The stator inlet
ow is studied using hot-wire anemometry and compared
with previous measurements made in the natural low inlet turbulence conguration of
the research compressor. Increased turbulence level enhances the dispersion of inlet
guide vane (IGV) wakes. This modies the interaction between IGV and rotor blade
wakes, leading to a more circumferentially uniform
ow eld at entry to the stator
with signicantly lower periodic unsteadiness.
Laminar-turbulent transition on a C4 stator blade is studied using an array of
surface-mounted hot-lm sensors. Comparisons with measurements made at low inlet
turbulence show that the increased inlet turbulence level reduces the extent of periodic
transitional
ow on the stator blade surface. The blade element behaviour
ow
behaviour at high inlet turbulence closely resembles the low inlet turbulence case with
the stator immersed in IGV wake turbulence.
The circular arc leading edge prole of the CD stator produces rapid acceleration
and deceleration at the stator leading edge. The in
uence of this velocity spike on the
stator boundary layer development and transitional
ow behaviour is studied using
an array of surface mounted hot-lm sensors. A region of favourable pressure gradient
on the suction surface following the leading edge spike has a stabilising eect on the
boundary layer, with a large region of
ow in a laminar or transitional state. Turbulent
spots and instability phenomena in this region are examined for convection speed, growth rate and evidence of relaminarisation. In contrast, the
ow on the pressure
surface becomes turbulent near the leading edge. The study shows that compressor
blade leading edge proles have a major in
uence on boundary layer development over
the whole surface.
The eect of upstream rotor wake passing on the stability of stator blade boundary
layers is examined. The unsteady quasi-three dimensional
ow solver, UNSFLO, is
used to interpret surface hot-lm data and unsteady laminar
ow behaviour at the
leading edge of both C4 and CD stators. Rotor wake chopping is found to stabilise the
pressure surface boundary layer and destabilise the suction surface boundary layer.
Examination of hot-lm data points to the leading edge as the principal receptivity
site for transitional
ow phenomena occurring on the suction surface of both the C4
and CD blading.

Item Type: Thesis (PhD)
Keywords: Unsteady Flow Transition Boundary Layer Axial Compressor Low Speed
Date Deposited: 06 Jan 2009 04:38
Last Modified: 11 Mar 2016 05:54
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