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Background
The problems of sediment erosion and second-
ary (unwanted) flow in Francis turbines is
simultaneous in nature. Depending upon the
type of flow phenomena in particular regions
and operating conditions, the sediment particles
having certain geometric and material properties
create distinct erosion patterns in those regions.
The erosion on the other hand, deteriorates the
surface morphology, aggravating the flow. The
combined effect of these two problems contributes
to more losses, vibrations, fatigue problems and
failure of the turbine. This PhD deals with the
regions around guide vanes (GV), where the flow
is highly unsteady due to leakages through the
clearance gap, horseshoe vortices, rotor-stator-
interaction and turbulence supported by high
velocity and acceleration. A small clearance is
present between guide vane and cover plates
to adjust the angle corresponding to the certain
operating condition. When the sediment particles
carried by the flow passes through this gap as a
leakage from the pressure side to the suction side
of the vane, the facing walls are heavily eroded.
This erosion increases the gap size and eventually,
aggravates the flow. This PhD is a part of a project
called SEDIPASS which is being coordinated by
NTNU.Moreover, it isa jointPhDprogrambetween
Kathmandu University (KU) and NTNU.
Objectives
a)Numerical and experimental investigation of
the leakage flow through the clearance gap of
guide vanes in high head Francis turbines
I. Numerical and PIV experiment of existing 1 GV
cascade rig including clearance gaps
II: Design and development of 3 GV cascade rig
for TTL in KathmanduUniversity and conduct the
PIV experiments in that rig
b)Guide vane design optimization to reduce the
secondary flow and its consequent effects on
turbine erosion in sediment laden hydropower
projects.
Flow through a
clearance gap of GV
cascade rig
Erosion in GV of
Jhimruk HP, Nepal
Department of Energy and
Process Engineering
2015-2018
Secondary Flow and
Sediment Erosion in
Francis Turbines
Supervisor:
Ole G. Dahlhaug
Co-supervisor:
Hari P. Neopane
Sailesh Chitrakar
PHD THESIS
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