1 Copyright © 2014 by ASME
Proceedings of ASME Turbo Expo 2014
GT2014
June 16-20, 2014, Düsseldorf, Germany
ASME GT2014-25818
Investigation of Applicability of Transporting Water Mist for Cooling Turbine Blades
Ting Wang and Reda Ragab
Energy Conversion and Conservation Center
University of New Orleans
New Orleans, Louisiana, USA
ABSTRACT
This paper presents a numerical study to investigate the
feasibility of transporting water mist to the rotating blades of a
high pressure turbine. The idea of using mist film cooling to
enhance conventional air cooling has been proven to be a
feasible technique under laboratory conditions. However,
there are challenges in implementing this scheme for real gas
turbine systems. The first challenge is how to transport the
mist to the rotating blades and the second challenge is
delivering the mist to the injection holes and getting the
particles to survive within the harsh gas turbine environment.
Both a zero-dimensional mist evaporation analytical model
and a 3D computational fluid dynamics (CFD) scheme are
employed for analysis. In the CFD simulation, the Lagrangian-
Eulerian method is used along with the discrete phase model
(DPM) to track the evaporation process of each individual
water droplet.
For transporting the mist to the blades, the high-pressure
water mist is injected into the stream of cooling air extracted
from the compressor through two different passages. The first
passage passes through the rotor cover-plate cavity before
entering the blade base. The second passage passes through a
diaphragm box on the base of the second vane, then
tangentially through a cooling passage in the rotating shaft,
and eventually to the blade base. The results show that it is
feasible to transport the mist from the turbine casing to the
blade through both passages, provided that droplets with
sufficient particle diameter and mist loading are used. The
shorter passage, through the nozzle diaphragm, alleviates a lot
of challenges facing the passage through the blade cavity, and
seems to be more practical. A side benefit of transporting mist
through the internal passages is the additional cooling of the
pre-swirler and rotor cover plates. The results are encouraging
for implementing the mist cooling technique under real gas
turbine conditions
Keywords: film cooling, mist cooling, heat transfer
enhancement
NOMENCLATURE (Selected)
C
D
Aerodynamic drag coefficient.
C Vapor concentration (kg/m
3
) or Specific heat
(J/kgK)
D
10
Arithmetic Mean Diameter
D
32
Mean Sauter Diameter (ratio of droplet volume to its
surface area)
h Convective heat transfer coefficient, (W/m
2
K)
h
fg
Latent heat, (J/kg)
P Pressure, (Pa).
Re
d
Droplet Reynolds number based on slip velocity,
(ud/ν)
F Force (N)
Greek Letters
μ Dynamic viscosity (Pa-s)
ε Particle emissivity
σ Stefan-Boltzmann constant (5.67x10
-08
W/m
2
K
4
)
ν Kinematic viscosity (m
2
/s)
ρ Density (kg/m
3
)
τ Shear stress (N/m
2
) or time scale (s)
ζ Random number for stochastic tracking
Subscripts
D Drag
g Gravity
i Initial, term number, tensor index (1, 2, 3)
p Particle, droplet
S Saffman
th Thermophoretic
∞ Away from the computational cell
INTRODUCTION
Gas turbines play a vital role in today’s industrialized
society. As the demands for power increase, the power output
and thermal efficiency of gas turbines must also increase. One
method of increasing both the power output and thermal
efficiency of the engine is to increase the turbine inlet
temperature. In the modern advanced gas turbines, the turbine
inlet temperature can be as high as 1500°C. However, this