A 3-D model was developed for simulating multistage turbomachinery flows using supercomputers. This average passage flow model described the time averaged flow field within a typical passage of a bladed wheel within a multistage configuration. To date, a number of inviscid simulations were executed to assess the resolution capabilities of the model. Recently, the viscous terms associated with the average passage model were incorporated into the inviscid computer code along with an algebraic turbulence model. A simulation of a stage-and-one-half, low speed turbine was executed. The results of this simulation, including a comparison with experimental data, is discussed

Adamczyk, John J.

Barnett, Mark

Beach, Tim A.

Celestina, Mark L.

Kirtley, Kevin

English

NASA Technical Reports Server

AVERAGE-PASSAGE FLOW MODEL DEVELOPMENT
N91-24338
-s3,,_3 y
John J. Adamczyk
NASA Lewis Research Center
Mark L. Celestina, Tim A. Beach, Kevin Kirtley,
Sverdrup Technology, Inc.
Lewis Research Center Group
and
Mark Barnett
United Technologies Research Center
h research effort has been underway to develop a three-dimensional model
for simulating multistage turbomachinery flows using today's supercomputers.
This model, referred to as the "average passage" flow model, describes the
time-averaged flow field within a typical passage of a bladed wheel within a
multistage configuration. To date, a number of inviscid simulations have been
executed to assess the resolution capabilities of the model. Recently, the
viscous terms associated with the "average passage" model have been incorpo-
rated into the inviscid computer code along with an algebraic turbulence
model. A simulation of a stage-and-one-half, low-speed turbine has been ex-
ecuted. The results of this simulation, including a comparison with experimen-
tal data, is the subject of this report.
h goal of computational fluid dynamics for turbomachinery is the predic-
tion of performance parameters and the flow processes which set their values.
Achieving this goal for multistage machinery is made difficult by the wide
range of length and time scales in the associated flow fields. Currently, the
procedure used in the design and off-design analysis is based on a quasi-three-
dimensional flow model whose origins can be traced to the late forties and
early fifties.
Although proven useful, this flow model has its limitations. Among these
are the inability to analyze off-design performance and unconventional machin-
ery where extrapolation of the underlying empirical data base is required.
Other problems arise whenever there are large local variations in the radial
velocity component within a blade passage. It is generally agreed that a way
of overcoming these shortcomings is the development of true three-dimensional
flow models. The "average passage" flow model under development at Lewis
Research Center is such a model. The objective of this paper is to present
the status of the development of this model for multistage turbines. This
will include several comparisons with measurements obtained from a recently
completed experimental program at the United Technologies Research Center.
247
https://ntrs.nasa.gov/search.jsp?R=19910015025 2020-03-19T18:11:31+00:00Z
SIMULATIONRESULTS
The simulation executed was the low-speed rotating rig at United Technolo-
gies Research Center. The low-speed rotating rig (LSRR) is a stage-and-one-
half turbine consisting of an inlet guide vane, a rotor, and a stator. The in-
let guide vane contains 22 blades, and the rotor and stator both contain
28 blades. The flow coefficient, _, is 0.78, and the spacing between blades,
B x, is 0.5. The LSRR grid contains 228 axial, 25 radial, and 41 circumferen-
tial points. Each blade row contains 40 axial points distributed along the
chord with 26 axial points between each blade row, the inlet and exit.
The results presented required Ii hours of Cray 2 CPU time. They repre-
sent but a small fraction of the information obtained from the simulation.
They are intended to illustrate the degree to which one can quantitatively pre-
dict performance parameters that are of interest to designers and to reveal
qualitative information identifying flow phenomena that may have an effect on
performance. These results also reflect the current state of model develop-
ment. The first series of results shows the predicted pressure distribution
on the surface of each blade row of the turbine as a function of axial chord
length and percent of span height. The span locations measured from the hub
are 1.3, 12.5, 50, 87.5, and 98.7 percent, respectively. The experimental
measurements taken at these locations are also shown. Experimental data were
also available for 25 and 75 percent of span, but were not used, since they
provided little additional information relative to the current discussion.
The results for the first vane are shown in figure I. The predicted loading
level is in good agreement with the measurements of Dring (1988). The predict-
ed pressure-surface pressure distribution is in excellent agreement with the
experimental results. For the suction surface the agreement between measure-
ment and simulation is good for the region forward of the minimum pressure
peak. Aft of the peak the agreement between experiment and simulation deterio-
rates. This deterioration is believed to be related to viscous effects (i.e.,
turbulence and transition modeling) whose modeling could be improved. Some
exploratory calculations suggest that the boundary layer aft of the suction-
surface minimum pressure is growing too rapidly and, as a result of the radial
pressure gradient, is being transported toward the hub to an extent greater
than that suggested by flow visualization studies. Improvements in the agree-
ment between simulation and experiment have been obtained by incorporating a
simple transition model in which the flow remains laminar forward of the mini-
mum pressure peak and Baldwin-Lomax turbulence model as implemented by Dawes
(1986).
Figure 2 shows the results for the first blade row, which incorporated
these changes in the tucbulence model. The improvement is obvious. The re-
maining results for the rotor and second stator incorporated the modified tur-
bulence model. Figure 3 shows the predicted and measured pressure distribu-
tion for the rotor. The predicted loading levels appear to be in good agree-
ment with meisurements, with the exceptlon of the hub and tip regi0n. The
present simulatlon does not include a Clearance region, which should account
for some of the discrepancy in the tip region The pressure dlstribution
along the pressure surface is once more in excellent agreement with the mea-
surements. At the midspan and at 25 and 75 percent (not shown) of span, the
predicted pressure distribution along the suction surface is in good agreement
with the data. At 1.3 and 12.5 percent of span, the Shction-surface pressure
coefficient is lower than that measured. As a result, the loading is lower
over the forward portion of the rotor than what has been measured. Although
248
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=|
t
|
_=
the cause of this discrepancy is, at present, unknown, one could speculate
that it may be due to an improper estimate of the magnitude and extent of the
low momentum fluid exiting the first vane.
The pressure distribution for the last vane is shown in figure 4. Once
again, the loading level is well predicted, with the exception of the 1.3 per-
cent of span location. The underpredicted suction-surface pressure coeffi-
cient at 1.3 and 12.5 percent of span suggests that the flow incidence to
these sections is underestimated. There also appears to be a shift of the pre-
dicted pressure distribution relative to the measured distribution. This
shift is believed to be caused by an overestimate of the loss generated by the
first two blade rows. With the exception of this discrepancy, the pressure
distribution on the pressure surface is in good agreement with measurements.
Similarly, the predicted suction-surface distribution at midspan agrees well
with the experimental distribution.
Currently, the results of this simulation are being reduced to a format
which will allow for the comparison with measurements of total pressure level
and flow angle. This comparison should provide additional information for
judging the accuracy of the simulation.
SUMMARY AND CONCLUSION
Given the early state of the average passage model development, the re-
sults presented in this report are very encouraging. The amount of empirical
information used in the stage-and-one-half turbine simulation is considerably
less than that required to achieve comparable results using today's quasi-
three-dimensional flow models.
249
FIRST BLADE PRESSURE DISTRIBUTIONS
FIRST VANE
PRESSURE
COEFFICIENT
8 -- 87.50% SPAN -- 98.70% SPAN
6
4
2 q
0
8 -- 1.30% SPAN
4
2
0 .50 1.00 0 .50
X/BX
Figure 1
O SUCTION SURFACE
[] PRESSURE SURFACE
-- 50.00% SPAN
1.00 0 .50 1.00
CD-89-3_411
PRESSURE
COEFFICIENT
BLADE PRESSURE DISTRIBUTIONS
FIRST BLADE ROW
10 -- 87.50% SPAN
8
6
4
2
0
10 -- 1.30% SPAN
8
6
4
2
0 .25 .50 .75 1.00 0
Fzgure
250
-- 98.70% SPAN
-- 12.50% SPAN
•25 .50 .75 1.00 0
X/BX
2
O SUCTION SURFACE
[] PRESSURE SURFACE
-- 50.00% SPAN
.25 .50 .75 1.00
CD-89-39412
BLADE PRESSURE DISTRIBUTIONS
ROTOR
PRESSURE
COEFFICIENT
10 -- 87.50% SPAN
6
4
2--
0 ] I .... _l____J
10 -- 1.30% SPAN
6
4
2 -
I I I
0 .50
-- 98.70% SPAN
I, I [ J
-- 12.50% SPAN
I I I I
.5O 1.00
X/BX
Figure 3
O SUCTION SURFACE
Q PRESSURE SURFACE
-- 50.00% SPAN
I I I ]
0 '.50 1.00
C0-89-39413
BLADE PRESSURE DISTRIBUTIONS
LAST VANE
PRESSURE
COEFFICIENT
12
10
8_
6_
4
2
0
12
10
8
I
6
4
2
87.50% SPAN
I I__l___J
-- 1.30% SPAN
__Z__I [ I
,50
-- 98.70% SPAN
I I l .... J
I I
1.00 0 .50
XIBX
Figure 4
O SUCTION SURFACE
O PRESSURE SURFACE
50.00% SPAN
I_1 I I I I
1.00 0 .50 1.00
CD-llg-3f414
251


Average-passage flow model development

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