Download Sensitivity studies of flow parameters on the performance

International Journal on Mechanical Engineering and Robotics (IJMER)
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Sensitivity studies of flow parameters on the performance of film
cooling of a high temperature plug type valve used in a propulsion test
facility
Gautam S.M.1, Gokul.S.1, Rohith .R. Kartha1, Samik Jash2, Dileep KN2, Dr J.S Jayakumar2
1
B. tech students, Mechanical Department, Amrita School of Engineering
2
Scientist, FMTD/APRG/PRSO, VSSC/ISRO Trivandrum
3
Professor, Mechanical Department, Amrita School of Engineering
Abstract- In the present paper flow simulation of a high
temperature plug type valve, with film cooling is carried
out. The main parameter, injection angle of the film
coolant is varied to study the effect of these parameters on
the performance of the film coolant. The cooling
effectiveness is studied with respect to the adiabatic wall
temperature along the valve seat wall and further
downstream pipelines. The average exit temperatures of
the gas near the inlet plane of the convergent – divergent
nozzle are also compared to arrive at the relative
effectiveness of the film coolant. Transient thermal analysis
is also carried out for the valve seat, to understand the
effect of the film coolant on the temperature distribution of
the valve throat for the different flow case studies carried
out. From the set of parametric studies carried out
inference is arrived at for the best combination of film
coolant injection inlet pressure and injection angle.
INTRODUCTION
Film cooling is the introduction of a film of coolant gas
or liquid into the interface between a hot flowing fluid
and surface along which it flows. This is done to protect
the surface from deformation due to heating up from
high temperature mainstream flow. This technique is
employed in gas turbine vanes, nozzles, combustion
chamber exit walls etc. to make sure that the surfaces are
protected from hot mainstream gas flows. There are
usually two types of film cooling – gasfilm cooling and
liquid film cooling. The present effort deals with the
flow and thermal simulation of gaseous film cooling of
the high temperature plug valve used in a propulsion test
facility.
In aerospace/ propulsion test facilities such as wind
tunnels, heating of the working fluid, air or nitrogen, to
elevated temperature prior to its flow through the tunnel
system is required. The schematic of a typical
propulsion facility is shown in figure 1.The functional
requirement of the hot shut off valve’s (HSV) are to
isolate the high temperature heater from the pressure
regulating system upstream and tunnel system
downstream, during the heating process. The
downstream HSV (HSV 2) is the one of the most critical
system in the tunnel, that isolates the heater from the
tunnel system (refer figure 1), which is evacuated to
vacuum before the start of the blow down operation. The
shut-off valve when closed separates gases at high
temperature and high pressure from downstream
vacuum. As the valve is opened, flow starts to occur and
the tunnel blow down is initiated. The thermal design of
the hot shut off valve takes care of the above
requirements by suitable cooling system and appropriate
choice of materials for its various parts. The shut-off
valve is a plug type valve made of stainless steel. In
order to protect the valve material (especially in the
valve throat region) from high temperature of gases, film
cooling is employed, from the convergent portion of the
valve seat section. Figure 2 shows a typical plug type
valve which is used in the present study.
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ISSN (Print) : 2321-5747, Volume-2, Issue-5,2014
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International Journal on Mechanical Engineering and Robotics (IJMER)
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Figure 1: Schematic of the propulsion facility
Figure 2: Plug type valve
In the present study, CFD simulation is carried out to
find out the sensitivity of two parameters viz., injection
pressure and injection angle on the performance of film
cooling on the valve throat section. The wall
temperature along the valve body and further
downstream pipelines are compared along with the
average exit temperature of the gas and is presented in
detail in this paper. Thermal analysis for the valve seat
has also been carried out to provide a comparative
assessment of the film cooling effectiveness for the
different
flow
case
studies
carried
out
.
Nomenclature
Figure 3: Computational domain for the analysis of the Plug type valve
p
Pressure
𝑑𝑖
Diameter of each injection hole (mm)
r
(mm)
Radius of shut off valve at the point of injection
𝑡𝑖
Equivalent thickness (mm
Re
Reynolds Number
m*
Mass flow rate of the main stream flow(kg/s)
µ
R
Ideal gas constant
T
Temperature
i
specific internal energy
𝐶𝑣
specific heat at constant volume
COMPUTATIONAL DOMAIN:
2
Kinematic viscosity (N.s/𝑚 )
d
Diameter of shut off valve (with throat as area
of cross section) (mm)
f
Friction factor
Pr
Prandtl Number
Nu
Nusselt Number
h
Convection coefficient (W/𝑚2 𝐾)
k
Thermal conductivity (W/m. 𝐾)
ρ
Density
t
Time
u
Velocity
u
x component of velocity
v
y component of velocity
The plug type valve is already described in figure 2. The
hot gases enters the valve from the top , takes a 900 turn
and leaves from the right side of the valve as shown by
arrows in the figure. The downstream of the valve
interfaces with the tunnel pipelines, to the settling
chamber and finally to the convergent divergent nozzle.
The plug of the valve seats in the valve seat and
provides the required valve sealing. The valve seat is the
most critical part of the valve and hence requires an
effective cooling strategy. The film cooling in the
present configuration is provided in the convergent
section of the valve seat, so as to keep the entire seat at a
lower temperature. The flow inside the valve is
essentially a 3 – dimensional flow due to the 900 turn.
However, the present analysis, the focus is to study the
relative effect of injection pressure and injection angle
on the film cooling effectiveness. Hence the analysis
domain is simplified with axisymmetric flow
assumption. The computational domain is shown in
figure3.
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Figure 4: Meshed domain of the computational domain
This geometrywas created in AutoCad. The valve seat
domain was preceded by a 0.5 m long pipeline, with the
same diameter as the valve inlet. The outlet of the valve
is connected to a transition piece which is connected to a
0.5 m long outlet pipeline. The convergent – divergent
nozzle is kept at the end of the pipeline, to avoid any
ambiguity of boundary condition at outlet. It should be
noted here; that in the actual facility the pipelines in the
downstream of the valve is connected to a settling
chamber before the C–D nozzle. In the present analysis,
to reduce the computational domain only 0.5 m long
outlet pipeline is taken.The film cooling injection in the
present valve configuration is done along 64 holes,
equally distributed along the 3600 circumferentially at a
radial location of 90 mm in the convergent side of the
valve throat/seat. Due to the axisymmetric
computational domain, the film cooling injection is
converted to an equivalent annular injection area as
shown below. The equivalent thickness(t) of the annular
injection passage is determined by equation 1.
64 ∗ 𝜋
𝑑𝑖
2
4
= 2𝜋𝑟𝑡𝑖
…(1)
(2)
(3)
(4)
(5)
(6)
ɸ is dissipation function
The terms SMx and SMy are source terms of
momentum, which show the combined effect of body
forces.The term Si is the energy source term.
In this case SMx and SMy are 0.
The standard k-ε turbulence model was used in the
analysis, with standard coefficients.
The equivalent thickness,𝑡𝑖 was found out to be 0.8 mm.
BOUNDARY CONDITIONS
The meshing was done using Hypermesh software.
Quadrilateral mesh was used to discretize the
computational domain. Figure 4 shows the meshing for
the entire computational domain. Suitable biasing was
done towards the wall and near the film cooling inlet
location. Finer meshing was given near the valve throat
area and in the region of convergent – divergent nozzle
The boundary conditions for the domain are specified in
figure 5. The main inlet is given as pressure inlet (P01 =
30 bar, T01 = 1600 K), along with the assumption of
zero v -velocity. The film cooling inlet is also given as
pressure inlet (P02 = [30 + ∆] bar, T02 = 300 K). The
outlet is taken as supersonic outlet. The y derivative
along the axis line is taken as zero. No – slip boundary
condition is taken at the wall. Adiabatic wall boundary
is also
GOVERNING EQUATIONS:
The governing equations in conservative form for two
dimensional compressible flow and heat transfer of
fluids are given below:
Figure 5: Boundary conditions in the computational domain
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International Journal on Mechanical Engineering and Robotics (IJMER)
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Figure 6:Static Pressure contours for injection angle 0 degree and pressure 30.1 bar assumed.
SIMULATION RESULTS
For finding the sensitivity of the injection angle on the
performance of the film coolant in the present valve
configuration, the injector angle is varied from 0° to
1000 to the flow axis. Analysis was done forsame
injector pressure of 30.1 bar. The inlet pressure was
defined as 30.0bar and 1600 K as inlet temperature for
all the case studies. Five case studies are done assuming
injector angle to be 0°, 30°, 60°, 90° and 100° to the
flow axis. The film cooling inlet is assumed to be at 300
K temperature at the inlet.
Figure 6 shows the static pressure contour for the
injection angle of 0° to the flow axis. The static
temperature contour in the domain is shown in figure 7.
The area weighted average temperature near the inlet
plane of the C–D nozzle is calculated to be 1483 K. The
mass flow rate for the main inlet is calculated to be 2.95
kg/s, while the mass flow rate for the film coolant inlet
is 0.36 kg/s for the given flow conditions (specified
pressures at the inlet).
Figure 8 shows the comparison plots for the velocity
vectors near the injection point for different injection
angles. It is seen for 00 injection angle, since the film
cooling injection flow is against the main flow direction
a strong recirculation exists ahead of the injection point.
A strong vortex is also seen near the injection point. As
the injection angle is increased the flow becomes more
in line to the main flow, and the recirculation zone near
the injection point disappears for injection angle greater
than 600.
Table 1 and table 2 gives in brief, the results of the flow
simulation carried out for different injection angles. The
mass flow rate of film coolant from the injector
increases initially from 0.36 kg/s (for 0 0 injector angle)
to 0.54 kg/s (for 600 injector angle) before reducing to
0.31 kg/s(for 1000 injector angle). This variation of
coolant mass flow rate for the same inlet pressure of
main flow and film coolant flow can explained from
figure 8, which shows the presence/ absence of
recirculation zone near the injector inlet. As a
consequence, the local pressure at the film coolant inlet
region would vary resulting in varying mass flow rates.
In this case studies also, like in the previous parametric
study of varying injection pressure; a higher film coolant
mass flow may be desirable from standpoint of valve
seat cooling. However, this results in a lower flow
average temperature further downstream of the valve,
which is not desirable from the perspective of a blow
down type wind tunnel test facility. The selection of the
injection angle thus depends on the combination of
valve cooling requirement and allowable reduction in
the gas temperature in the facility, due to this film
coolant gases.
Figure 7: Static temperature contour for 0 degree angle and 30.1 bar pressure
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International Journal on Mechanical Engineering and Robotics (IJMER)
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Figure 8: Velocity vector near the injection point for 00,
300, 600, 900 and 1000 injection angle and a constant
30.1 bar injection pressure
Table 1: Area-weighted average Temperature, near the
inlet plane of the nozzle for 30.1 bar injection pressure
Table 2 : Simulation results for different injection angle
with the flow axis for 30.1 bar injection pressure
Figure 9: Comparison plot for Static Temperature vs horizontal length along wall for 30.1 bar injection pressure
The comparison plots for different injection angle for
temperature drops suddenly and then increases as we
static temperature along the wall is given in figure 9.
move away from the point of injection. Because of the
Static temperature is shown to be decreasing with the
presence of strong recirculation zone for the 00film
increase in pressure along the axis, but along the wall
cooling injection angle, it is seen that the wall
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International Journal on Mechanical Engineering and Robotics (IJMER)
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temperature is much lower even in the upstream region
of the injection.
Thermal analysis has been carried out for the valve seat,
to understand the effect of the film coolant on the
temperature distribution of the valve throat for the
different flow case studies carried out. The material of
construction for the valve seat is assumed to be SS304.
Transient thermal analysis is carried for time duration of
40 seconds (typical blow down operation time in a wind
tunnel facility). The heat transfer coefficient for the
thermal analysis is calculated from standard pipe flow
correlation where Nusselt number is a function of
Reynolds number and Prandtl number. The correlation
used is given as,Nusselt Number, Nu is calculated as,
𝑓/8(𝑅𝑒 − 1000)𝑃𝑟
𝑁𝑢 =
𝑓
for a constant 30.1 bar injection pressure. As was seen
from the wall temperature plots (figure 11) , the
presence of strong recirculation zone for the 0 0 film
cooling injection angle, results in a cooling effect even
in the upstream region of the injection, compared to the
other cases with higher injection angles. The lowest
maximum temperature is seen for the 300 injection
angle. Table 4 gives in brief the results of the thermal
analysis carried out
(7)
2
1 + 12.7(√ )((𝑃𝑟)3 − 1)
8
where, the friction factor is 𝑓 = (0.791𝑙𝑛𝑅𝑒 − 1.64)−2
The Reynolds Number was found out for different case
studies from the calculated mass flow rates using,
Figure 10: Thermal Analysis for no injection
𝑅𝑒
=
4 𝑚̇
𝜋𝜇𝑑
(8)
The heat transfer coefficient is calculated from the
Nusselt number using,
𝑁𝑢
ℎ𝑑
=
𝑘
(9)
The calculated values of heat transfer coefficient for
different injection angles is given in table 3. Proper
temperature corrections for the gas properties are taken.
The outer wall of the valve seat is assumed adiabatic.
The gas temperature along the flow axis is taken as the
adiabatic wall temperature obtained from the flow
simulation results.
Figure 11: Thermal Analysis for 30 degree injection
angle and 30.1 bar injection pressure
Table 3:Heat transfer coefficients calculated for
different injection angle thermal
analysis is carried out for the valve seat without any film
cooling. Figure 10 shows the temperature contour in the
valve seat for no injection condition. The maximum wall
temperature is 761 K at the end of 40 seconds. The
location of the maximum temperature is near the
minimum flow area of the valve seat. Figures
11,12,13,14 show the temperature contour in the valve
seat for different injection angles of 0 0, 300,600 and 900 ,
Figure 12: Thermal Analysis for 0 degree injection angle
and 30.1 bar injection pressure
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International Journal on Mechanical Engineering and Robotics (IJMER)
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CONCLUSION
In the present study, CFD simulation was carried out to
analyze the effect of film cooling on the throat section of
a plug type valve. A sensitivity study was also carried
out to investigate the effect of film coolant for different
angles of injection (00, 300, 600, 900and 1000to the flow
axis). A comparative assessment of the film cooling
effectiveness of the present valve configuration for the
two parameters studied (injection pressure and angle of
injection). Transient thermal analysis was also carried
out for the valve seat, to understand the effect of the film
coolant on the temperature distribution of the valve
throat for the different flow case studies carried out.
Figure 13: Thermal Analysis for 60 degree injection
angle and 30.1 bar injection pressure
From the set of parametric studies carried out, it was
seen that a film cooling inlet pressure of 30.1 bar with
an injection angle of 300 gives the lowest temperature of
the valve seat.
REFERENCES
[1] Goldstein R.J., Stone L.D. (1997), Row of Holes
Film Cooling of Curved walls at Low injection
angles. ASME Journal of Turbomachinery, Vol
119, pp 574-579.
[2] Eckert E.R.G ,Goldstein R.J. , Ramsaey
J.W.(1968),Film Cooling with injection through
holes Adiabatic wall temperatures downstream of
a Circular hole. ASME Journal of Engineering for
Power,Vol 90, pp 384-393.
Figure 14: Thermal Analysis for 90 degree injection
angle and 30.1 bar injection pressure
Table 4: Thermal analysis results for different injection
angles
[3] Ammari H.D., Hay N., Lampard D. (1990), The
Effect of Density Ratio on the Heat Transfer
coefficient from a Film Cooled Flat Plate. ASME
Journal of Turbomachinery, Vol 112, pp 444-450.
[4] Leylek J.H, Zerkle R.D.(1994),Discreet Jet Film
Cooling: A comparison of comparison of
Computational Results with Experiments. ASME
Journal of Turboachinery ,Vol 116, pp 358-368.
[5] Malalaseekera
W,
Veersteg
H.(2007),An
Introduction to Computational Fluid Dynamics The
Finite Volume Method (2nd Edition), Pearson
Education Limited.
[6] Chiang.S.T
,
Hoffmann
K.A.,
(2000),
”Computational Fluid Dynamics”(Fourth Edition),
Vol.I, Engineering Education System.
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