American Institute of Aeronautics and Astronautics
1
The Quiet Technology Demonstrator Program: Static Test of an
Acoustically Smooth Inlet
Bryan Callender1 and Bangalore Janardan
2
GE Aviation
Cincinnati, OH
Stefan Uellenberg 3
and John Premo4
Boeing Commercial Airplane Group
Seattle, Washington
Hwa-Wan Kwan 5
and Amal Abeysinghe6
Goodrich Corporation – Aerostructures Group
Chula Vista, California
13th
AIAA/CEAS Aeroacoustics Conference
21-23 May 2007
Rome, Italy
Abstract
The QTD2 static engine test sought to provide further insight into the noise reduction technologies
demonstrated during the 2005 flight test program. One of the technologies demonstrated in the QTD2
program was the Acoustically Smooth Inlet. This technology represented a true zero splice design with the
total treated area increased relative to a typical production design. During the flight test, this inlet
demonstrated community noise reductions of over 2 EPNdB and significant reductions in forward cabin
noise. The static test was successful in identifying key design features that led to these benefits. Multiple pure
tone noise reduction was shown to be primarily attributable to increased acoustic area in the inlet.
Reductions in BPF tone related noise was shown to be mostly due to the elimination of splices of the inlet.
Finally, a detailed investigation into the effects of splices in the forward fan case region was completed.
Nomenclature
ASI = acoustically smooth inlet
BPF = Blade Passage Frequency
dB = Decibel
EPNL = Effective Perceived Noise Level
MPT = Multiple Pure Tone
Mrel = Relative Fan Tip Mach Number PNLT = Tone Corrected Perceived Noise Level
PTO = Peebles Test Operations
QTD = Quiet Technology Demonstrator
TCS = Turbulence Control Structure
1 Lead Engineer, Acoustics and Installation Aerodynamics, 1 Neuman Way, MS W26, Member AIAA.
2 Principal Engineer, Acoustics and Installation Aerodynamics, 1 Neuman Way, MS W26, Associate Fellow, AIAA.
3 Engineer, PD Noise & Emissions, P.O. Box 3707, MS 0R-MM, Member, AIAA.
4 Engineer, Aeroacoustics & Fluid Mechanics Group, P.O. Box 3707, MS 67-ML, Senior Member, AIAA.
5 Staff Engineer, Technical Support, 850 Lagoon Drive, MZ 107N.
6 Senior Engineer, Technical Support, 850 Lagoon Drive, MZ 107N.
13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) AIAA 2007-3671
Copyright © 2007 by General Electric, The Boeing Company, and Goodrich Corporation. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.
American Institute of Aeronautics and Astronautics
2
I. Introduction
ecently, a consortium of aerospace industry leaders including Boeing, GE Aviation, Goodrich and
NASA Langley Research Center completed static engine testing as part of the Quiet Technology
Demonstrator 2 (QTD2) program. The QTD2 program focused on the demonstration and characterization
of several advanced technologies for mitigation of airplane and engine noise both inside the airplane and
for the community below.
Environmental concerns such as fuel efficiency, emissions, and community noise continue to drive
aircraft engine designs to higher bypass ratios. As the bypass ratio increases, so does the relative
contribution of inlet radiated fan noise to the total aircraft system noise. As such, it is becoming
increasingly important to improve the understanding of fan inlet radiated noise source and propagation
mechanisms. Such understanding allows for more effective design of inlet acoustic treatment. Boeing
Seattle and Boeing Wichita, now Spirit Aerosystems, have sustained a continuous effort to maximize
treated area and minimize splices and acoustic discontinuities in composite inlets since the mid 1980’s.
This effort has been called Area MAXimization (AMAX). Boeing Seattle supported the effort through
funding and efforts to predict the improvements while Boeing Wichita focused on manufacturing
technologies that enabled improved acoustic area and splice minimization or elimination. Although
aspects of this technology have been applied continuously to improve production engine nacelles over
time, the first true test of the technology was the AMAX inlet tested in 2001 as part of the first QTD test
program1.
In 1986, Ganz2 used early spinning mode measurements from Joppa
3 to show that forward fan case
splices were likely responsible for increased blade passage frequency (BPF) tone levels measured on a
Boeing product. The Ganz paper was the first from Boeing that gave a physical description of the
scattering source mechanism for BPF tone increases due to splices. These results led Boeing to examine
and ultimately hardwall the forward fan case lining on selected products to improve aircraft noise
certification levels. An equivalent source model was later developed at Boeing to give a quantitative
evaluation of the scattering effects of splices. This model, named the Cargill Method, is described in a
recent work by Tester4. It shows how the highly attenuated rotor-locked field at subsonic and transonic tip
speeds can be scattered into other spinning orders where the lining suppression is greatly reduced. More
recently, Tam5 put together a model capable of evaluating more general impedance variation which was
validated against the earlier work of Tester, et al. In addition, 3-D propagation codes using the Linearized
Euler Equations (LEE) have also been applied to the problem allowing refraction effects to be captured.
Together these models have provided new insights into the effects of splices on inlet noise generation and
propagation. Premo, et al6 utilize the data collected during the QTD2 Static Test to validate some of these
models.
One of the key technologies developed and demonstrated in the QTD2 program was the Acoustically
Smooth Inlet (ASI). Goodrich, in cooperation with Boeing, has continued the development of the AMAX
technologies and developed the ASI inlet specifically for the QTD2 program7. By completely eliminating
all splices and acoustic discontinuities, the ASI improves upon the AMAX inlet demonstrated in the first
QTD program and represents a true entitlement level design of inlet acoustic treatment. This is the first
full-scale, zero-splice inlet tested on a Boeing airplane. The acoustic lining design of the inlet also
differed from past designs in terms of the tuning frequency. The removal of impedance discontinuities
and increased acoustic area allowed the inlet to target the peak Noy frequencies, which provide the
dominant contribution to Perceived Noise Level (PNL), with less consideration to lower power BPF tone
noise.
The QTD2 flight test program, conducted in 2005 at Boeing’s Glasgow, MT flight test facility,
demonstrated the benefits of the ASI for both community and cabin noise8. In terms of community noise,
the flight test demonstrated over 2 EPNdB cumulative noise benefit versus a traditional inlet design with
splices. Additionally, in-cabin noise measurements showed dramatic reductions in both BPF tone levels
and buzzsaw noise during climb. The QTD2 static engine test, conducted in 2006, sought to improve the
understanding of the flight test results. Specifically, the test sought to identify the significance of the
R
American Institute of Aeronautics and Astronautics
3
individual design features of the ASI relative to a current production inlet design. This was accomplished
by applying tape to the ASI to simulate splices and hardwalled regions. Additionally, the data was used to
validate some of the recently developed numerical models for splice prediction. This paper will focus on
the far-field effects of the various ASI design features, while reference 6 will provide details of the splice
prediction tool validation.
II. Measurement Facilities
The QTD2 static engine test was conducted at GE Aviation’s Peebles Test Operations (PTO) facility
near Peebles, Ohio. PTO Test Site 4D has been used for static engine acoustic development and
certification tests since 1987. The site features a sound field arena composed of a flat concrete surface that
is fully compliant with the recommendations of SAE Standard ARP1846 9. For this test, both far-field and
near-field microphone arrays were deployed. The far-field array is located at a constant arc distance of
150’ and is centered on a point directly beneath the engine. This array consisted of 23 microphones
positioned over an angular range of 10° to 120° in 5° increments. The angle was defined from the inlet
direction. In addition, a near-field array was deployed for measurement of inlet radiated multiple pure
tone (MPT), or buzzsaw, noise. Located on a 28’ ground sideline, the near-field array included
microphones at acoustic angles ranging from 30° to 80° in 10° increments. All far-field and near-field
microphones were mounted in ground-plane stands. Figure 1 shows an overview of the test site, while
Fig. 2 shows the microphone mounting stand and orientation.
Both the far-field and near-field arrays were composed of Bruel and Kjaer model 4134 ½” condenser
microphones with model 2639 preamplifiers. The microphones and preamplifiers were powered by Bruel
and Kjaer model 2807/2829 power supplies. Microphone head calibration was completed by the Bruel
and Kjaer calibration laboratory in Atlanta, GA prior to the start of the test. Total system calibrations for
both amplitude and frequency response were completed frequently throughout the test program to avoid
any calibration drift. The total system amplitude calibration is provided by a Bruel and Kjaer model 4228
pistonphone, while a pseudo-random pink noise signal is used for calibration of the total system
frequency response. Acoustic data was acquired and post processed by GE’s Digital Acoustic Processing
System (DAPS). The raw digitized time series data was processed using a 32-second integration time and
the results were converted to one-third octave band sound pressure levels. Adjustments and corrections
that were applied to the acoustic data include barometric correction for the pistonphone calibration,
microphone head corrections, pink noise generator corrections, amplitude calibration, total system
frequency response corrections, and a free-field adjustment of 6 dB to account for pressure doubling due
to the microphone ground plane orientation. Finally, all data was corrected to reference atmospheric
conditions of 77° F and 70% relative humidity using standard atmospheric corrections10
. In the case of
narrowband spectra, which was processed to a bandwidth of 8 Hz, only the amplitude pistonphone
calibration was applied.
Atmospheric data was collected by sensors on a Portable Environmental Data System (PEDS) cart
that was positioned beyond the far-field array at a distance of approximately 170’ from the engine center
and at an inlet angle of 85°. Measured parameters included dew point for relative humidity calculation,
temperature, wind direction, and wind velocity. These measurements were all collected at a height
corresponding to the engine centerline height. The meteorological and engine parameters were recorded
on the transient Advanced Data System (ADS) at a rate of one scan per second during all acoustic
readings.
The QTD2 test vehicle was a GE90-115B engine, which features 22 compound swept, wide-chord
fan blades with a fan diameter of 128.3”. All pretest preparation was completed in the PTO Large Engine
Prep Building. This included installation of all test instrumentation as well as a pylon. An aeroacoustic
bellmouth was attached to the inlet lip as shown in Figure 3. The bellmouth is designed to produce similar
aerodynamic conditions over the inlet barrel to those encountered during the flight test by producing
similar boundary layer properties and fan face Mach number distributions. For all test configurations, a
American Institute of Aeronautics and Astronautics
4
Turbulence Control Structure (TCS) was attached to the engine. The TCS reduces large-scale inflow
turbulence and ground vortices that can lead to the generation of excess noise that is not present in flight.
This also provides more stable engine operation, by removing large-scale, low frequency disturbances
which can modulate the fan speed. Finally, an aft acoustic barrier wall was used to isolate the inlet
radiated fan noise from the engine exhaust noise for the configurations described in this paper. The main
portion of the barrier is 56 feet long by 34 feet high. It is designed such that the engine exhaust noise on
the acoustic measurement side of the engine is blocked from the inlet quadrant microphones. Figure 4
shows the complete static engine test setup with the TCS and the acoustic barrier wall installed.
III. Test Inlet Configurations The same fully treated ASI barrel that was flown on the 2005 flight test was utilized as the baseline
configuration for the QTD2 static engine test. Figure 5 shows a direct comparison between a current
production type inlet and the Goodrich ASI. The white dashed lines in Fig. 5(a) define the boundary of
the acoustically treated area. In addition to the two axial splices at the 3 and 9 o’clock positions of the
inlet, much of the inlet area is untreated. In comparison, the dashed lines on the ASI in Fig. 5(b) show that
the axial splices have been eliminated and the treated area has been maximized. As described in Section I,
one of the primary goals of the static test was to identify and better understand the design features
responsible for the flight test acoustic benefits. To accomplish this goal, six different test configurations
were simulated using 3M Y434 tape to represent different splices and hardwall regions. These
configurations are presented graphically in Figure 6 and described below.
Configuration 1 – Fully treated ASI.
Configuration 2 – Tape was used to simulate hardwall surfaces forward of the inlet throat and in the
forward fan case region. Two simulated axial splices were applied to the ASI inner barrel with 180°
spacing.
Configuration 3 – Tape was used to simulate hardwall surfaces forward of the inlet throat and in the
forward fan case region. The ASI inlet barrel was fully treated with no splices.
Configuration 4 – Tape was used to simulate hardwall surfaces in the forward fan case region. Tape
was used to simulate hardwall forward fan case. Acoustic lining forward of inlet throat was exposed.
The ASI inlet barrel was fully treated with no splices.
Configuration 5 –ASI was fully treated with the exception of 2 simulated splices in the forward fan
case region. Splices were located 180° apart and spanned the axial length of the forward fan case
region. These splices were approximately 33% smaller in width than those tested in Configuration 2.
Configuration 6 – ASI was fully treated with the exception of 2 simulated splices in the forward fan
case region. Splices were located 180° apart and spanned the axial length of the forward fan case
region. These splices were of equal width to those tested in Configuration 2.
Each of these test configurations is used to assess the relative impact of treated area and treatment
discontinuities compared to the fully treated ASI. Configurations 1 and 4 are used to understand the
effects of additional treated area in the forward fan case region. The benefit of adding treatment forward
of the inlet aerodynamic throat, where convective velocities are higher, is determined by comparing
configurations 3 and 4. Splice effects are investigated by configurations 1, 2, 3, 5, and 6. The effect of
splices in the inlet barrel is considered by evaluating configurations 2 and 3, while configurations 1, 5,
and 6 allow the noise impacts of forward fan case splices to be assessed. The impact of each of these
design features is discussed in detail in Section IV.
American Institute of Aeronautics and Astronautics
5
IV. Results and Discussion The QTD2 static engine test followed the 2005 flight test, which demonstrated the ability of the inlet
to provide significant reductions in inlet radiated fan noise7, 8
. Figure 7 presents data from the flight test
which shows the impact of the ASI on the tone corrected Perceived Noise Level (PNLT) relative to the
production inlet. These data, which were measured at a cutback power setting, show that the ASI provides
reductions of 3 – 5 PNdB at forward angles between 20° and 50°. These forward arc noise reductions
lead to a reduction in the duration correction used in calculation of Effective Perceived Noise Level
(EPNL). In addition to community noise reductions, Figure 8 shows the noise reductions that were
measured in the aircraft cabin region during the flight test. Microphones mounted in the forward cabin
showed significant reductions in both BPF tone noise and buzzsaw noise for the ASI relative to the
baseline inlet. More complete details of the inlet related flight test results are provided in references 7 and
8.
As mentioned previously, the QTD2 static engine test sought to improve the understanding of the
acoustic benefits seen in the flight test. A static engine test is more appropriate to accomplish this goal
due to reduced costs, complexities, and measurement uncertainties relative to a flight test. Therefore,
static engine tests are well suited to evaluate the effects of detailed configuration changes such as those
defined in Figure 6. Based on results seen in the flight test, two primary effects are used to assess the
acoustic benefits of the ASI. These are forward arc BPF tone level reductions and buzzsaw noise
reduction. Power level metrics are defined to quantify the benefits provided in each of these areas. For
assessment of BPF tonal impacts, narrowband data from the 150’ polar array are used. The BPF tone and
harmonics are separated from the narrowband data and averaged over three repeat test conditions to
obtain averaged levels at each microphone location. The BPF tone levels are then integrated over an
angular range of 10° to 80° to obtain the forward arc BPF power level metric. Such an integrated and
averaged metric is necessary to accurately assess changes in BPF noise due to lobe patterns and subtle
shifts in directivity that are often seen in inlet radiated tonal noise repeat data.
In a similar manner, data from the 28’ sideline near-field array are used to compute an MPT power
level metric. At each microphone location, an overall MPT level is determined by extracting the MPT
content from the narrowband data and summing over a range of frequencies from zero through 2xBPF,
with the BPF and 2xBPF content excluded. After averaging for repeat test conditions, the overall MPT
levels are integrated over an angular range from 30° to 80° to obtain the MPT power level metric. This
angular range encompasses the full extent of the 28’ sideline array. This is the reason that the angular
integration range is different from that used for the BPF power level metric.
The overall effects of the ASI, relative to configuration 2, are shown by Figures 9 and 10. Recall that
configuration 1 is the fully treated ASI while configuration 2 is a simulation of an inlet containing both
splices and hardwall regions. Figure 9 shows a comparison of the BPF power level metric as a function of
relative fan tip Mach number, Mrel. The general trend of these curves is typical of inlet radiated BPF tonal
noise. Continuous increases in BPF tone levels are seen as the fan tip approaches Mrel ~ 1.0. As the fan tip
exceeds sonic speed, dramatic increases are seen as the rotor locked pressure field becomes cut-on. The
tone level continues to increase with fan speed before peaking at a Mrel of approximately 1.3. The ASI
provides reductions in BPF tone power level at all speeds between Mach 0.9 and Mach 1.4. At lower fan
speeds, this benefit ranges from 0.5 to 1.0 dB. As Mrel exceeds 1.0, the BPF benefits begin to increase.
The maximum benefit of 3.5 dB roughly corresponds to the fan speed where the BPF noise is highest.
Beyond this speed, the benefit diminishes to a level of approximately 1.0 dB.
Figure 10 shows the impact of the ASI on MPT power level as a function of relative fan tip Mach
number. First, note that these data also show trends consistent with documented buzzsaw noise behavior.
As the relative tip speed begins to exceed sonic velocity, the MPT power level increases dramatically due
to the formation of non-uniformly spaced bow shocks ahead of the blade leading edges. As these shocks
become stronger, MPT related noise continues to increase with fan speed. At Mrel values greater than
approximately 1.3, the shocks are swallowed into the blade passages, and the MPT noise radiated through
the inlet begins to diminish. Figure 10 shows that the ASI reduces the MPT related noise at all relative tip
Mach numbers between 1.0 and 1.5. The largest reductions of 4 –5 dB are seen at Mach numbers between
American Institute of Aeronautics and Astronautics
6
1.1 and 1.25. The peak MPT power level occurs at a Mach number of 1.3, where the ASI provides a
benefit of approximately 1.8 dB. Beyond this point, the benefit remains relatively constant between 1 and
2 dB.
While comparison of configurations 1 and 2 provides a measure of the overall ASI benefits, these
benefits are the result of two distinct types of design changes. These changes are increased acoustic
treatment area and the elimination of splices and associated acoustic discontinuities. Figures 9 and 10
provide evidence of both of these effects. For example, benefits associated with increased acoustic area
are generally relatively constant versus fan speed. There are certainly fan speed regimes shown in these
figures where this is the case. However, there are also regions where the benefits vary dramatically with
fan speed. Results such as these can indicate that the source generation and propagation mechanism are
being influenced by the ASI design changes. The four additional test configurations are structured to
provide insight into the relative effects of these two types of design features.
A. Treated Area Effects
The test configurations are designed to assess the impact of increasing the acoustic area in two
different regions of the inlet. The first region to be considered is the forward fan case region, which is
immediately forward of the fan face. Secondly, the region between the inlet aerodynamic throat and
forward bulkhead is considered. This region is referred to as the forward throat region, but should not be
confused with the lip treatment that was tested in the flight test. The lip treatment was part of the flight
inlet lip. Due to the use of the aeroacoustic bellmouth lip in the static test, it is not possible to test the lip
lining.
The effect of additional acoustic area in the forward fan case region is assessed by comparison of
configurations 1 and 4. The treated forward fan case region of configuration 1 represents an increase in
acoustic area of approximately 16% relative to configuration 4. Analysis of the data shows that the largest
impacts were to MPT related noise, with relatively small impacts seen in BPF tonal noise. Figure 11
shows the impact on MPT power level as a function of relative fan tip Mach number. These results appear
very similar to the overall MPT effects seen in Figure 10, with the maximum benefits of 3 – 4 dB
occurring at fan speeds below the peak MPT speed. This benefit is slightly less than the overall ASI
benefit of 4 – 5 dB shown in Figure 10. At the peak MPT speed, the addition of forward fan case
treatment provides a reduction of slightly more than 1 dB. These results indicate that the addition of
treatment in the forward fan case region accounts for much of the overall MPT benefit that is shown in
Figure 10.
Configurations 3 and 4 are used to assess the impact of additional acoustic area in the inlet forward
throat region. Configuration 4 represents an increase in acoustic area of approximately 7% relative to
configuration 3. Figure 12 shows the impact of additional treatment on the MPT power level. The
addition of treatment in the forward throat region produces a relatively constant benefit of 0.5 – 1.0 dB
across the speed range.
Figures 10 – 12 each show that the MPT benefits are relatively independent of fan speed. This
indicates that the overall MPT benefits shown in Figure 10 are largely a result of the addition of acoustic
area as opposed to the elimination of splices. Figure 13 provides evidence to support this conclusion by
comparing the total MPT benefit, at the peak MPT fan speed of Mach = 1.3, with the benefits provided by
additional treated area in the forward fan case and forward throat region. Figure 13 shows that these
individual effects account for over 97% of the overall MPT benefits seen at the peak MPT speed.
In addition to MPT benefit, the addition of acoustic area in the forward throat region also provided
reductions in BPF tone levels. Figure 14 shows that the forward throat treatment reduces the BPF tonal
noise at relative fan tip Mach numbers between 0.9 and 1.1.
B. Splice Effects
The second design feature of the ASI that is considered in the QTD2 static test is the elimination of
splices and associated acoustic discontinuities. The effects of such design features on aircraft acoustics
have received a great deal of attention in recent years4-7, 11-13
. Analytical methods, such as those developed
American Institute of Aeronautics and Astronautics
7
by Tester and Tam, suggest that splices can scatter tonal energy into lower order azimuthal modes where
it may propagate more efficiently, while also being less attenuated by acoustic treatment. Additionally,
Boeing and Goodrich internal studies have also shown that splices can adversely affect fan tonal noise by
influencing both source and propagation mechanisms. These studies show that the splice count, location
and width can all influence fan tone levels in the far-field. The static test configurations are designed to
investigate the acoustic impacts of simulated splices in two different regions of the inlet. First, the effect
of splices in the inlet inner barrel region is considered. This refers to the portion of the inlet between the
forward fan case and the aerodynamic throat of the inlet. Secondly, the impact of splices in the forward
fan case region is considered.
The effect of splices in the inner barrel region of the inlet is assessed by comparison of configurations
2 and 3. Note that both configurations retain the hardwall surfaces in the forward fan case and forward
throat areas. Figure 15 shows that the presence of the two splices increases the BPF power level at all fan
tip speeds greater than Mach 1.0. The impact of the splices is greatest near the peak BPF speed, where
benefits in excess of 2 dB are seen. At lower fan speeds, the benefit ranges from 1.0 – 1.5 dB, while a
smaller benefit of 0.5 – 1.0 dB is seen at higher fan speeds. As demonstrated in the flight test, these tonal
reductions can have substantial implications on community noise certification levels. The cutback
certification condition is influenced by inlet radiated fan tone noise. Therefore, the benefits shown at the
peak BPF speed, and lower fan speeds, illustrate how the elimination of inlet splices can have positive
impacts on aircraft community noise. The reduced benefits at higher speeds may be of less significance
due to the fact that community noise is more influenced by aft radiated fan and jet noise at these speeds.
While axial splices in the forward fan case were not considered as part of configuration 2, there is
interest in the impact of these splices in order to determine if there is an increased sensitivity to splices
located closer to the fan face. Configurations 5 and 6 each simulate two axial splices in the forward fan
case of the ASI. These splices are located 180° apart at the inlet 3 and 9 o’clock positions. Configuration
6 uses a splice width equal to that of the inlet inner barrel splices (configuration 2), while configuration 5
reduces the splice width by 33% in order to understand sensitivity to splice width. Test data shows that
the addition of these splices impacts both BPF tonal noise and MPT related noise. Figure 16 shows the
effect of the two splice widths on the BPF power level relative to configuration 1. Both splice widths lead
to increased BPF power levels and a clear positive correlation is seen between the tone level increase and
the splice width. The smaller width splices generate BPF increases of up to 1.5 dB, while the nominal
width splices generate a maximum increase in excess of 3.5 dB. Recall that the nominal width splices are
equal in width to those that were applied to the inner barrel region in configuration 2. Figure 15 showed
that these inner barrel splices produced increases of approximately 2 dB. However, when this same splice
width is applied to the forward fan case region, increases in excess of 3.5 dB are seen. Since the fan case
splices represent significantly less treated area loss than the longer inner barrel splices, these results
cannot be related to any treated area effects. Therefore, Figure 16 provides sufficient evidence to
conclude that BPF tonal noise is more sensitive to the effects of splices that are located closer to the fan
face. Also, these results clearly show that there is a direct correlation between splice width and BPF tonal
noise.
While Figure 16 provides data that shows the noise impact correlates with splice width and that there
is increased sensitivity to splices located closer to the fan face, it also reveals another interesting effect in
regard to the fan case splices. Note that these splices appear to affect the tone levels at a limited range of
speeds. The effects of the smaller splices are confined to speeds between Mach 1.0 and 1.2, while the
effects of the nominal width splices extend to Mach 1.3. These effects are in contrast to the inlet splices,
which affected the tone levels at all speeds between Mach 0.9 and 1.4. The inlet splices also showed the
maximum impact to occur near the peak BPF level, while the fan case splices create the largest impacts at
speeds below the peak BPF. The net effect of the increased sensitivity to the fan case splices and the
localized speed range impact is that the peak BPF power level is effectively shifted to a lower fan speed.
Such an effect could have implications for the cutback certification condition, where efforts are made to
trade aircraft altitude and power setting in a manner to minimize noise. This procedure, referred to a
delayed or optimized cutback, typically results in a cutback fan speed that occurs below the peak BPF
American Institute of Aeronautics and Astronautics
8
speed. Therefore, increases in BPF power level to the left of the peak, as shown by Figure 16, could have
significant implications for cutback noise. Of course, cutback optimization is highly specific to the details
of the engine/aircraft system performance and noise characteristics.
In addition to the BPF impacts seen in Figure 16, the forward fan case axial splices also produced
increased MPT related noise. These results are shown in Figure 17. First, note that fan case splices were
not represented by configuration 2. Therefore, these effects were not part of the results shown in Figure
10. Figure 17 shows that there is a positive correlation between MPT noise and fan case splice width.
However, the results seen in Figure 17 are somewhat different from the BPF impacts seen in Figure 16.
For example, Figure 16 showed that the larger splice widths produced significantly larger BPF increases
than did the smaller splice widths. In contrast, Figure 17 shows that the smaller splice width account for
much of the MPT noise increases, with only a slightly greater increase seen for the larger splice widths.
While the exact cause of these trends is not clear from the far-field data, some conclusions can be drawn
in regard to the implications. Recall that Figure 11 shows that the addition of acoustic treatment to the
forward fan case region results in MPT power level reductions as high as 4 dB at certain speed ranges.
Figure 17 indicates that the addition of splices to this treatment could potentially compromise much of
this improvement. The implication is that in order to fully realize the potential MPT benefits of forward
fan case treatment, efforts should be made to eliminate or minimize splices in the treatment.
V. Summary and Conclusions
The QTD2 static engine test validated the flight test conclusions in regard to the benefits of the
acoustically smooth inlet with reductions in both BPF and MPT related tonal noise being demonstrated.
In addition, the static test provided further insight and understanding to the specific design features that
contributed to these benefits. Two distinct types of design changes were considered in the static test.
These were the effects of increased acoustic area and the effects of eliminating splices. Measurements
showed that the addition of acoustic treatment to the forward fan case region and the forward throat
region primarily impacted MPT related noise. Peak benefits of 4 dB in MPT power level were
demonstrated for the addition of 16% treated area in the forward fan case region. Reductions as high as 1
dB were seen when treatment was added to the forward throat region. Investigation of splice effects
showed that the largest impacts were seen in BPF related tone noise. The elimination of splices in the
inlet inner barrel region produced peak reductions in excess of 2 dB in the BPF power level metric.
Detailed investigation of forward fan case splices revealed several interesting effects. First, conclusive
evidence was provided to show that there is an increased sensitivity of BPF tone noise to splices that are
located closer to the fan face. This was shown by direct comparison of the same splice width. When
located in the inlet inner barrel, these splices produced increases of 2 dB in BPF power level. However,
when the same width splice was applied in the forward fan case region, increases in excess of 3.5 dB were
measured. Furthermore, it was shown that fan case splices seem to affect the BPF power level over a
more limited range of power setting than inlet splices. The result of this can be a shift of the peak BPF
power level to a lower speed range. Finally, the fan case splices were also shown to impact MPT power
levels. Each splice width was shown to produce MPT power level increases of 2 – 3 dB. This data
indicated that care needs to be taken to minimize or eliminate splices in the forward fan case region to
avoid compromising potential MPT noise benefits.
American Institute of Aeronautics and Astronautics
9
References
1) Bartlett, P., Humphreys, N., Phillipson, P., Lan, J., Nesbitt E., and Premo, J., “The Joint Rolls-
Royce/Boeing Quiet Technology Demonstrator Programme,” AIAA-2004-2869.
2) Ganz, U. W., Strout, F. G., , “Evaluation of High Fan Tone Noise Levels in Static Testing,” Boeing Internal
Paper NOIS-B8310-C86-229RES, October 24, 1986.
3) Joppa, P. D., “An Acoustic Mode Measurement Technique,” AIAA/NASA 9th
Aeroacoustic Conference,
Williamsburg, VA, October 15, 1984.
4) B.J. Tester, N.J. Baker, A.J. Kempton and M.C. Wright, “Validation of an Analytical Model for Scattering
by Intake Liner Splices”, AIAA 2004-2906, 2004.
5) Tam, C.K.W., Webb, J.C., “Dispersion-Relation-Preserving Finite Difference Schemes for Computational
Acoustics,” J. Comp. Phys. 107, 1993, pp. 262-281.
6) Premo, Breard, Lan, Chien, Abeysinghe and Callender “Predictions of the Inlet Splice Effects from the
QTD2 Static Test,” AIAA-2007, 2007.
7) Yu, J., Nesbitt, E., Kwan, H., Uellenberg, S., Chien, E., Premo, J., “Quiet Technology Demonstrator 2
Intake Liner Design and Validation,” AIAA-2006-2458.
8) W. Herkes, R. Olsen and S. Uellenberg, “The Quiet Technology Demonstrator Program: Flight Validation of
Airplane Noise-Reduction Concepts,” AIAA-2006-2720, 12th AIAA/CEAS Aeroacoustics Conference (27th
AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006.
9) SAE Standard ARP1846, “Measurement of Far Field Noise From Gas Turbine Engines During Static
Operation,” February 1990.
10) SAE Standard ARP866A, “Standard Values of Atmospheric Absorption as a Function of Temperature and
Humidity”, March 1975.
11) Gantie, F., Batard, H., Baker, N., and Schwaller, P., “Zero Splice Intake Technology and Acoustic
Benefits”, AIAA-2006-2455, Cambridge, MA, 2006.
12) Tester, B., DeMercato, L., “Far-field Directivity of Rotor-Alone Tones Radiated from Fan Intakes with
Splices Liners for Different Intake Shapes, with Flow”, AIAA-2006-2456, Cambridge, MA, 2006.
13) Tam, C., Ju, H., Chin, E., “Scattering of Acoustic Duct Modes by Axial Liner Splices”, AIAA-2006-2459,
Cambridge, MA, 2006.
American Institute of Aeronautics and Astronautics
10
20
30
35
40
4550
55 60
6570
75
8090
95
100
105
110
115
120
150 foot arc
System (PEDS) Cart
85
25
10
15
NOT TO SCALE
20
30
35
40
4550
55 60
6570
75
8090
95
100
105
110
115
120
Portable Environmental Data
85
25
10
15
Acoustic Barrier
28’ Sideline Array-20
30
35
40
4550
55 60
6570
75
8090
95
100
105
110
115
120
System (PEDS) Cart
85
25
10
15
NOT TO SCALE
20
30
35
40
4550
55 60
6570
75
8090
95
100
105
110
115
120
Portable Environmental Data
85
25
10
15
Acoustic Barrier
TCS
20
30
35
40
4550
55 60
6570
75
8090
95
100
105
110
115
120
150 foot arc
System (PEDS) Cart
85
25
10
15
NOT TO SCALE
20
30
35
40
4550
55 60
6570
75
8090
95
100
105
110
115
120
Portable Environmental Data
85
25
10
15
Acoustic Barrier
28’ Sideline Array-20
30
35
40
4550
55 60
6570
75
8090
95
100
105
110
115
120
System (PEDS) Cart
85
25
10
15
NOT TO SCALE
20
30
35
40
4550
55 60
6570
75
8090
95
100
105
110
115
120
Portable Environmental Data
85
25
10
15
Acoustic Barrier
TCS
Figure 1. Test Setup for Inlet Noise Phase of QTD2 Static
Engine Test. Peebles Site 4D.
Figure 2. Ground Plane Microphone.
Figure 3. Test Vehicle Fitted with Aeroacoustic Bellmouth Lip.
Figure 4. Static Test Setup with TCS Dome and Acoustic Barrier
Wall Installed
TCS Acoustic Barrier
American Institute of Aeronautics and Astronautics
11
Figure 5. Comparison of Typical Production Type Inlet with Goodrich Acoustically Smooth Inlet Design
c
e f
a
1
Fan Face
d
4
Fan Face
b
2Fan Face
5
Fan Face
3
Fan Face
6Fan Face
c
e f
a
1
Fan Face
a
1
Fan Face
d
4
Fan Face
d
4
Fan Face
b
2Fan Face
b
2Fan Face
5
Fan Face
5
Fan Face
3
Fan Face
3
Fan Face
6Fan Face
6Fan Face
Figure 6. QTD2 Static Test Inlet Configurations
American Institute of Aeronautics and Astronautics
12
Figure 7. Flight Test Data Showing Forward Arc PNLT Benefits
for Cutback Power Condition.
Frequency
Sou
nd
Pre
ssu
re L
evel, d
B
BuzzsawReduction
Blade PassageTone Reduction
BaselineFully Treated
400 Hz
10 dB
Frequency
Sou
nd
Pre
ssu
re L
evel, d
B
BuzzsawReduction
Blade PassageTone Reduction
BaselineFully Treated
400 Hz400 Hz
10 dB10 dB
Figure 8: Flight Test Data Showing Forward Cabin Benefits in
BPF and MPT Noise.
1.41.31.21.11.00.9
5 dB
BPF Power Level (10°-80°)
Relative Fan Tip Mach Number
Config 2
Config 1
1.41.31.21.11.00.9
5 dB
BPF Power Level (10°-80°)
Relative Fan Tip Mach Number
Config 2
Config 1
Config 2
Config 1
Figure 9. Overall Static Test Impact of ASI on Forward
Radiated BPF Power-levels
MPT Power Level (30°-80°)
1.0 1.1 1.2 1.3 1.4 1.5
Relative Fan Tip Mach Number
Config 2
Config 1
5 dB
MPT Power Level (30°-80°)
1.0 1.1 1.2 1.3 1.4 1.5
Relative Fan Tip Mach Number
Config 2
Config 1
Config 2
Config 1
5 dB
Figure 10. Overall Static Test Impact of ASI on Forward
Radiated MPT Power-levels
American Institute of Aeronautics and Astronautics
13
5 dB
MPT Power Level (30°-80°)
1.0 1.1 1.2 1.3 1.4 1.5
Relative Fan Tip Mach Number
Config 4
Config 1
5 dB
MPT Power Level (30°-80°)
1.0 1.1 1.2 1.3 1.4 1.5
Relative Fan Tip Mach Number
Config 4
Config 1
Config 4
Config 1
Figure 11. Forward Fan-case Area Effect on Forward Radiated
MPT Power-levels
5 dB
Config 4
Config 3
MPT Power Level (30°-80°)
1.0 1.1 1.2 1.3 1.4 1.5
Relative Fan Tip Mach Number
5 dB
Config 4
Config 3
MPT Power Level (30°-80°)
1.0 1.1 1.2 1.3 1.4 1.5
Relative Fan Tip Mach Number Figure 12. Throat Area Effect on Forward Radiated MPT
Power-levels
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Fwd Fan Case (Fig. 11) Fwd Throat (Fig. 12) Overall (Fig. 10)
MP
T P
ow
er
Level B
en
efi
t (d
B)
1.2 dB
0.5 dB
1.8 dB
Figure 13. Contribution of Forward Fan Case and Forward
Throat Treatment to Overall Peak MPT Benefit.
Mon Feb 26 2007 22:35:29
5 dB
1.41.31.21.11.00.9
BPF Power Level (10°-80°)
Relative Fan Tip Mach Number
Config 4
Config 3
Mon Feb 26 2007 22:35:29
5 dB
1.41.31.21.11.00.9
BPF Power Level (10°-80°)
Relative Fan Tip Mach Number
Config 4
Config 3
Figure 14. Throat Area Effect on Forward Radiated BPF Power-
levels
American Institute of Aeronautics and Astronautics
14
5 dB
1.41.31.21.11.00.9
BPF Power Level (10°-80°)
Relative Fan Tip Mach Number
Config 3
Config 2
5 dB
1.41.31.21.11.00.9
BPF Power Level (10°-80°)
Relative Fan Tip Mach Number
Config 3
Config 2
Config 3
Config 2
Figure 15. Forward Inlet Splice Effect on Forward Radiated
BPF Power-levels
Q
Q
Q
Q
Q
Q
5 dB
Config 5
Config 1
Config 6
Q
1.41.31.21.11.00.9
BPF Power Level (10°-80°)
Relative Fan Tip Mach Number
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
5 dB
Config 5
Config 1
Config 6
Q
1.41.31.21.11.00.9
BPF Power Level (10°-80°)
Relative Fan Tip Mach Number Figure 16. Forward Fan-case Axial Splice Effect on Forward
Radiated BPF Power-levels
5 dB
Config 5
Config 1
Config 6MPT Power Level (30°-80°)
1.0 1.1 1.2 1.3 1.4 1.5
Relative Fan Tip Mach Number
5 dB
Config 5
Config 1
Config 6MPT Power Level (30°-80°)
1.0 1.1 1.2 1.3 1.4 1.5
Relative Fan Tip Mach Number Figure 17. Forward Fan-case Axial Splice Effect on Forward
Radiated MPT Power-levels