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Proceedings ArticleDOI

A Comparison of the Noise Characteristics of a Conventional Slat and Krueger Flap

30 May 2016-

AbstractAn aeroacoustic test of two types of leading-edge high-lift devices has been conducted in the NASA Langley Quiet Flow Facility. The test compares a conventional slat with a notional equivalent-mission Krueger flap. The test matrix includes points that allow for direct comparison of the conventional and Krueger devices for equivalent-mission configurations, where the two high-lift devices satisfy the same lift requirements for a free air flight path at the same cruise airfoil angle of attack. Measurements are made for multiple Mach numbers and directivity angles. Results indicate that the Krueger flap shows similar agreement to the expected power law scaling of a conventional flap, both in terms of Strouhal number and fixed frequency (as a surrogate for Helmholtz number). Directivity patterns vary depending on the specific slat and Krueger orientations. Varying the slat gap while holding overlap constant has the same influence on both the conventional slat and Krueger flap acoustic signature. Closing the gap shows dramatic reduction in levels for both devices. Varying the Krueger overlap has a different effect on the data when compared to varying the slat overlap, but analysis is limited by acoustic sources that regularly present themselves in model-scale wind tunnel testing but are not present for full-scale vehicles. The Krueger cavity is found to have some influence on level and directivity, though not as much as the other considered parameter variations. Overall, while the spectra of the two devices are different in detail, their scaling behavior for varying parameters is extremely similar.

Topics: Krueger flap (57%)

Summary (3 min read)

NASA Ames Research Center, Moffett Field, California 94035

  • An aeroacoustic test of two types of leading-edge high-lift devices has been conducted in the NASA Langley Quiet Flow Facility.
  • The behavior of these sources must be studied to assess if NLF wing technology can simultaneously meet ERA fuel burn and noise goals.

II. Test Description

  • This experiment was performed at the NASA Langley Research Center in the Quiet Flow Facility (QFF).
  • The QFF is an anechoic, open jet wind tunnel equipped with a 2- by 3-foot rectangular nozzle.
  • The QFF is equipped with a Medium Aperture Directional Array (MADA), which is mounted on a rotating boom, allowing directional coverage of the model for a wide range of polar elevation angles (referenced to the downstream direction of the test section).
  • The azimuthal angle of the MADA can be manually varied but was not in this study.

II.A. Test Hardware

  • A pair of models were fabricated for this experiment.
  • The stowed, cruise airfoil associated with the 30P30N work provided a consistent basis for model design.
  • The as-built geometry of the conventional slat is shown in Fig. 2a.
  • Note that this figure shows a positive overlap value.
  • The Krueger flap deployment parameters function similarly, although αKrueger is defined from the stowed Krueger position and thus, has an angle reference of the local cruise airfoil pressure side profile slope at the leading edge of the Krueger cavity.

II.B. Data Acquisition and Processing

  • The employed microphone shading scheme maintains a constant beamwidth (when applying conventional beamforming) of 1 foot for the frequency band spanning from 5 kHz to 40 kHz.
  • Resultant DAMAS narrowband data were then summed into 1/3rd-octave bands as necessary.
  • The need for deconvolution is illustrated in Fig. 3, where the conventional beamforming output in Fig. 3a shows sidewall junction contamination of the leading edge noise source.
  • They are also scaled to a common 10 foot emission distance referenced from the center span point of the equivalent cruise (stowed slat/Krueger) configuration leading edge of (x, y) = (0, 0) in Fig.

III. Results - Matched Run Conditions

  • While the conventional slat and Krueger flap were evaluated at a variety of run conditions, those which had the design equivalent-mission parameters are discussed first.
  • As mentioned, the equivalent-mission parameters were evaluated to provide Krueger locations and angles to match six conventional slat configurations.

III.A. Baseline spectra

  • The first matched configuration addressed is that of the baseline conventional slat deployment.
  • Additionally, Mach 0.09 data do not always scale as expected and may be approaching a “noise floor” for the analysis.
  • The conventional slat spectra in Fig. 4a show features common to many slat noise experiments.
  • These tones are not fully understood, but since they do not appear to occur at full-scale they undesirably influence the data of interest.
  • Note that a very sharp tone is sometimes embedded in the frequency range of the trailing edge shedding peak.

III.B. Non-dimensional analysis

  • Spectra are further scaled by test section Mach number and plotted as a function of Strouhal number in Fig.
  • Scaling by a Mach power of 4.5 provides better collapse for these spectra than for the conventional slat data, at least for the Strouhal number range above any influence of the low-frequency tones and below the blunt shedding peaks.
  • As with the conventional slat data, no common power law for tone levels is observed.
  • An alternate Strouhal definition using a length scale of the Krueger flap trailing edge thickness of 0.02 inches and the local trailing edge flow speed from RANS results10 for M = 0.17 yields the expected Strouhal number of slightly greater than 0.2 for the shedding peak.
  • Spectral collapse is also seen at frequencies beyond the band contaminated by shedding peaks.

III.C. Directivity

  • For this section, the directivities of all three αc = 27 ◦ slat angle configurations are addressed.
  • Low frequency tones are nearly omnidirectional and the broadband portion of the spectra peaks forward of the model and decreases toward its aft.
  • Krueger data in Fig. 7f show similar trends to the conventional slat, although the aft-most measurement angle is still observed to be the directivity minimum.
  • The 30 ◦ equivalent data appear to confirm this.
  • Notably, the shedding peak for this final plot has more omnidirectional behavior, only reducing at φ = 90◦.

III.D. Level comparison

  • Note that this comparison is not intended to show whether a Krueger flap is universally louder or more quiet than a conventional slat.
  • Comparison to examples from literature suggests that a reduction in noise should be observed when closing the gap,25 but also that significant spectral variability may be present.
  • As in previous work, completely sealing the gap provides a dramatic reduction in the measured slat noise.
  • Reducing the overlap first increases the spectral level slightly and then decreases it.

V. Summary and Conclusions

  • An experiment comparing the acoustic behavior of a conventional slat to an equivalent-mission Krueger flap has been conducted, and results are presented.
  • The experiment utilized a companion CFD effort to compare the conventional slat to a Krueger, which could provide the same lift at the same AoA under free stream flight for a common reference cruise airfoil.
  • This peak occurs at an equivalent full-scale frequency that is lower than it should be due to the relative thickness of the model trailing edges.
  • Nevertheless, common behavior is observed between the conventional slat and Krueger for both the contaminating sources and the desired broadband spectral components.
  • Individual parameter variations are performed on the models to assess the acoustic influence of the gap and overlap of both the conventional slat and Krueger flap.

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A Comparison of the Noise Characteristics of a
Conventional Slat and Krueger Flap
Christopher J. Bahr
, Florence V. Hutcheson
, Russell H. Thomas
NASA Langley Research Center, Hampton, Virginia 23681
Jeffrey A. Housman
NASA Ames Research Center, Moffett Field, California 94035
An aeroacoustic test of two types of leading-edge high-lift devices has been conducted
in the NASA Langley Quiet Flow Facility. The test compares a conventional slat with a
notional equivalent-mission Krueger flap. The test matrix includes points that allow for
direct comparison of the conventional and Krueger devices for equivalent-mission configu-
rations, where the two high-lift devices satisfy the same lift requirements for a free air flight
path at the same cruise airfoil angle of attack. Measurements are made for multiple Mach
numbers and directivity angles. Results indicate that the Krueger flap shows similar agree-
ment to the expected power law scaling of a conventional flap, both in terms of Strouhal
number and fixed frequency (as a surrogate for Helmholtz number). Directivity patterns
vary depending on the specific slat and Krueger orientations. Varying the slat gap while
holding overlap constant has the same influence on both the conventional slat and Krueger
flap acoustic signature. Closing the gap shows dramatic reduction in levels for both de-
vices. Varying the Krueger overlap has a different effect on the data when compared to
varying the slat overlap, but analysis is limited by acoustic sources that regularly present
themselves in model-scale wind tunnel testing but are not present for full-scale vehicles.
The Krueger cavity is found to have some influence on level and directivity, though not as
much as the other considered parameter variations. Overall, while the spectra of the two
devices are different in detail, their scaling behavior for varying parameters is extremely
similar.
Nomenclature
c = cruise airfoil chord
EPNL = Effective Perceived Noise Level
f = frequency
L
B
= 1/3
rd
-octave band SPL, dB ref 20 µPa
L
B,scaled
= 1/3
rd
-octave band SPL, scaled to one-foot slat span and 10-foot distance,
dB ref 20 µPa
L
p,scaled
= Narrowband SPL, scaled to one-foot slat span and 10-foot distance, dB ref 20 µPa
`
Krueger
= Krueger flap length
`
slat
= Conventional slat length
M = Mach number
SPL = Sound Pressure Level
St = Strouhal number
U
= Test section flow speed
x
g ap
= Slat or Krueger gap distance
x
ov erlap
= Slat or Krueger overlap distance
Research Aerospace Engineer, Aeroacoustics Branch, MS 461, Senior Member AIAA, christopher.j.bahr@nasa.gov
Senior Research Engineer, Aeroacoustics Branch, MS 461, Senior Member AIAA
Research Scientist, Applied Modeling and Simulation Branch, NAS Division, MS 258-2, Senior Member AIAA
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American Institute of Aeronautics and Astronautics

α
c
= Cruise airfoil angle of attack
α
slat
= Conventional slat deployment angle
α
Krueger
= Krueger flap deployment angle
α
= Cruise airfoil free stream angle of attack
L
B,scaled
= L
B,scaled,Conventional
L
B,scaled,Krueger
δ
g ap
= Chord-normalized slat or Krueger gap distance, x
g ap
/c
δ
ov erlap
= Chord-normalized slat or Krueger overlap distance, x
ov erlap
/c
φ = MADA elevation angle, referenced to test section downstream direction
θ = Polar emission angle for slat noise source, referenced to test section upstream direction
I. Introduction
A
s commercial air traffic increases, the environmental impact of this increase must be mitigated through
reduction of the environmental footprint of individual aircraft. The NASA Environmentally Responsible
Aviation (ERA) Project is part of the agency’s continued efforts to do so, with simultaneous goals of 50%
fuel burn reduction relative to the 2005 best in fleet, 75% nitrous oxide reduction below the Committee
on Aviation Environmental Protection (CAEP) 6 standard, and 42 dB cumulative EPNL relative to the
Stage 4 requirement.
1
Natural laminar flow (NLF) wings are one technology for improving fuel burn (and
by association, reducing nitrous oxide emissions) through drag reduction.
2
Krueger flaps offer a leading-
edge high-lift device, which can shield NLF wings from insect fouling at low altitudes, in contrast to a
conventional slat. However, as the structure and deployment mechanisms of a Krueger flap differ from those
of a conventional slat, it is possible that the noise sources of the two differ.
3
The behavior of these sources
must be studied to assess if NLF wing technology can simultaneously meet ERA fuel burn and noise goals.
As part of ERA’s broader efforts, an experiment that compares conventional slat and Krueger flap acoustic
behavior was conducted and is now reported.
II. Test Description
This experiment was performed at the NASA Langley Research Center in the Quiet Flow Facility (QFF).
The QFF is an anechoic, open jet wind tunnel equipped with a 2- by 3-foot rectangular nozzle. The facility
can operate up to a Mach number of 0.17. The QFF is equipped with a Medium Aperture Directional Array
(MADA), which is mounted on a rotating boom, allowing directional coverage of the model for a wide range
of polar elevation angles (referenced to the downstream direction of the test section).
4
The azimuthal angle
of the MADA can be manually varied but was not in this study.
II.A. Test Hardware
A pair of models were fabricated for this experiment. The intent of the experiment is to compare conventional
slat and Krueger flap noise for models that could be, at least for one configuration, related for an equivalent-
mission. In this usage, equivalent-mission is defined such that both models have the same cruise airfoil profiles
and flight operations, e.g., angles-of-attack (AoA) on approach, match. This experiment and matching
process is involved in the broader objective of implementing a noise model for Krueger flaps, which is
documented by Guo et al.
5
Note that this experiment only addresses the two dimensional noise sources,
neglecting three dimensional Krueger flap bracket noise sources, which may be dominant for many flight
conditions.
6
Two models were necessary for this experiment, as the Krueger flap deploys from the pressure side of
the cruise airfoil while the conventional slat deploys from the leading edge of the cruise airfoil, leading to
different main element airfoil profiles. Additionally, the Krueger model required a pressure side cavity cut-
out to evaluate the potential influence of a notional Krueger stowage cavity on the model aerodynamics and
aeroacoustics. The Krueger model cavity could be closed with a plate matching the cruise airfoil contour.
Due to the scale of this test, the cavity was extremely simplified from what would be present on a full-scale
aircraft. Both models were equipped with static pressure ports and Kulite dynamic pressure transducers.
The aerodynamic pressure measurements allowed for sectional lift calculation and comparison with Reynolds-
Averaged Navier Stokes (RANS) simulations for validation of effective free stream AoA calculations.
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American Institute of Aeronautics and Astronautics

A well-studied model, the 30P30N, was selected for the reference conventional slat model.
7
The stowed,
cruise airfoil associated with the 30P30N work provided a consistent basis for model design. The cruise
airfoil chord was reduced from c = 18 inches to c = 16.7 inches in an effort to reduce the turning of the QFF
test section jet flow induced by these high-lift models. This reduction also matched the conventional slat
model’s main element chord to that of previous high-lift model studies in the QFF.
8
A photograph of the
Krueger model installation is shown in Fig. 1a, with a schematic of the conventional slat installation and
measurement setup shown in Fig. 1b.
(a) Krueger installation photograph (b) Measurement locations (slat)
Figure 1. High-lift model installation and acoustic instrumentation in QFF. Note that the origin for
φ is determined by the center of rotation of the MADA boom, not the slat.
The conventional slat design used in this experiment has some differences when compared to the baseline
slat from the recent BANC Workshop series. Some cove modifications were included in the design, which
were based on changes to the model in recent work with slat cove fillers.
9
Further minor modifications were
incorporated for practical machining purposes. The as-built geometry of the conventional slat is shown in
Fig. 2a. As with previous high-lift studies in the QFF, the model was fabricated with a stowed flap to
mitigate open jet turning effects.
8
This significantly reduces the achievable lift of the installed model, but
allows the noise generation mechanisms of the leading edge device to be studied independently of the flap
noise.
The Krueger flap used in this work was designed through an extensive RANS campaign documented
in a companion paper by Akaydin et al.
10
as part of a slat noise study. The overall study also includes
computational efforts by Housman and Kiris.
11
Summarizing the design process, a chain of Computational
Fluid Dynamics (CFD) simulations was used to link the conventional slat configuration within the QFF to
the Krueger flap configuration within the QFF. First, the conventional slat model was simulated in the QFF
open jet flow for two cruise airfoil AoAs, α
c
= 27
and α
c
= 33
. These corresponded to the two main
element airfoil AoAs used in previous work.
8
The simulations were conducted for slat deployment angles
of α
slat
= 10
, α
slat
= 20
, and α
slat
= 30
, all with a stowed flap. A series of simulations were then run
in free air for these three slat deployment angles with the flap deployed. The lift and pressure coefficient
profiles about the slat and leading edge region of the model were compared between the installed and free
air simulations to find the free air equivalent AoAs for the two installed AoAs. The free air equivalent of the
QFF-installed α
c
= 27
was found to be α
= 2
, while that for the QFF-installed α
c
= 33
was found to
be α
= 4.5
. Note that matching only the slat aerodynamics and neglecting the leading edge region of the
model led to respective equivalent free air AoAs of α
= 4.5
and α
= 8
, consistent with the previous
QFF slat noise study.
8
A Krueger flap was then designed to match the overall model lift at these free air AoAs with a deployed
trailing flap. The as-built geometry of this Krueger flap is shown in Fig. 2b. The Krueger deployment details
for the QFF-installed configuration (gap, overlap, angle) were then determined via a final set of CFD runs
for a stowed trailing flap configuration in the open jet facility. Table 1 summarizes these details for the
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American Institute of Aeronautics and Astronautics

α
c
= 27
experiments. Fig. 2c defines the deployment parameters for the conventional slat model. Note that
this figure shows a positive overlap value. Negative overlap indicates the slat trailing edge is downstream
of the main element leading edge. The Krueger flap deployment parameters function similarly, although
α
Krueger
is defined from the stowed Krueger position and thus, has an angle reference of the local cruise
airfoil pressure side profile slope at the leading edge of the Krueger cavity.
Table 1. Krueger deployment settings for equivalent-mission conventional slat settings. For all baseline
conventional slat angles, δ
g ap
= 3.08% and δ
ov erlap
= 2.66%.
slat angle Krueger angle Krueger gap Krueger overlap
α
slat
α
Krueger
δ
g ap
δ
ov erlap
10
131
1.12% 0.20%
20
127
1.12% 0.20%
30
124
1.54% 0.78%
(a) Conventional slat (b) Krueger flap (c) Slat deployment parameters
Figure 2. High-lift device shapes and deployment parameter definitions for the conventional slat.
The conventional slat angle α
slat
is defined as the total rotation about the slat trailing edge from
the stowed orientation, with an effective reference of the model chord line. The Krueger flap angle
α
Krueger
is also defined this way, with an effective reference of the local airfoil surface slope at the
Krueger cavity leading edge.
II.B. Data Acquisition and Processing
Acoustic data were acquired using the MADA at elevation angles of φ = 73
, 90
, 107
, 124
, and 140
,
always on the model pressure side. These values correspond to a variety of emission angles, depending on the
test section speed, ambient conditions and the model AoA. The emission angles for an example acquisition
are summarized in Table 2, although these relations could vary by a degree or so depending on ambient
conditions. Emission angles were computed using the retarded angle relationships of Amiet,
12
prior to being
re-referenced to the test section upstream direction. Note that the φ = 73
relationship is not shown, and
the data are not presented in this paper. At this angle, uncertainty in the shear layer position for various
configurations leads to greater variability in the shear layer correction,
13
and the results become difficult to
assess.
The MADA consists of 41 B&K model 4138,
1
/8-inch microphones projecting from an acoustically treated
frame. The array pattern is an extension of the Small Aperture Directional Array,
8, 14
adding an additional
irregular ring of microphones. The employed microphone shading scheme maintains a constant beamwidth
(when applying conventional beamforming) of 1 foot for the frequency band spanning from 5 kHz to 40 kHz.
Data were acquired at a sampling rate of 200,000 samples/sec for 60 seconds, yielding 1464 non-overlapping
data blocks with a length of 8192 samples each. All channels were filtered with a passband between 300
Hz and 90 kHz. A Hamming window was applied to each block of data prior to the calculation of narrow-
band auto- and cross-spectra. The resultant spectral frequency resolution from this sampling rate and block
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American Institute of Aeronautics and Astronautics

Table 2. Relationships between MADA elevation (φ) and slat emission (θ) angles for varying Mach number,
model AoA of 27
in QFF test section. φ is referenced as given in Fig. 1, while θ is referenced to the upstream
direction in the test section with origin located at the center span of the equivalent cruise airfoil profile.
θ
φ M = 0.09 M = 0.11 M = 0.13 M = 0.15 M = 0.17
140
54.0
53.8
53.7
53.6
53.5
124
71.7
71.4
71.1
70.8
70.6
107
89.8
89.6
89.4
89.2
89.0
90
107.4
107.5
107.6
107.6
107.7
length is 24.4 Hz. The data were then processed using the DAMAS algorithm.
15
To accelerate processing,
7 adjacent spectral bins were summed in the computed cross-spectral matrix prior to processing, yielding
narrowband DAMAS results for 585 frequencies for every test point. Steering vectors were computed for
the center bin frequencies of these narrowband summation bounds. These steering vectors accounted for
free shear layer refraction, atmospheric attenuation and instrumentation directivity.
16
DAMAS was run
for 500 iterations in a varying two-dimensional sweep pattern, and integrated levels were tracked to ensure
convergence. Resultant DAMAS narrowband data were then summed into 1/3
rd
-octave bands as necessary.
The summation region for calculating integrated levels was specified around the model leading edge such
that slat/Krueger noise sources were isolated from other facility and model/facility interaction noise sources.
The need for deconvolution is illustrated in Fig. 3, where the conventional beamforming output in Fig. 3a
shows sidewall junction contamination of the leading edge noise source. Fig. 3b, which shows acoustic levels
referenced to the MADA center, demonstrates the ability of deconvolution to isolate the acoustic sources of
interest from extraneous installation noise sources. Note that the scale of the experiment with respect to
the array precludes the isolation of individual components of the slat such as the gap and cove.
For subsequent spectral plots, the integrated levels are scaled to a per-foot slat span from the full width
of the integration bounds. They are also scaled to a common 10 foot emission distance referenced from the
center span point of the equivalent cruise (stowed slat/Krueger) configuration leading edge of (x, y) = (0, 0) in
Fig. 3. While somewhat non-intuitive, this point is a common geometric reference between the conventional
slat and Krueger flap models.
ow
-20 -10 0 10 20
y (inches)
-10
0
10
20
30
x (inches)
46
51
56
61
66
L
B
sidewalls
summation bounds
cruise airfoil footprint
(a) Conventional beamforming
-20 -10 0 10 20
y (inches)
40
45
50
55
60
L
B
(b) DAMAS output
Figure 3. 20 kHz 1/3
rd
-octave band MADA output for the Krueger flap configuration shown in
Fig. 1a. Data are acquired at a Mach number of M = 0.17 and a MADA elevation angle of φ = 124
.
Flow is from bottom-to-top of the plots. The footprint of the equivalent cruise model for both the
conventional slat and Krueger is denoted with the magenta boundary. The summation region is
denoted with the white boundary. Test section sidewalls are denoted with black lines.
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American Institute of Aeronautics and Astronautics

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Cites background from "A Comparison of the Noise Character..."

  • ...Similarly for the Krueger device, sealing the gap between its trailing edge and the main wing can eliminate the high speed flow in the gap and the noise sources associated with the flow, one of the major sources of Krueger noise [14], [23], [24]....

    [...]


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04 May 2004
TL;DR: The Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) method removes beamforming characteristics from output presentations and appears to dramatically increase the value of arrays to the field of experimental acoustics.
Abstract: Current processing of acoustic array data is burdened with considerable uncertainty. This study reports an original methodology that serves to demystify array results, reduce misinterpretation, and accurately quantify position and strength of acoustic sources. Traditional array results represent noise sources that are convolved with array beamform response functions, which depend on array geometry, size (with respect to source position and distributions), and frequency. The Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) method removes beamforming characteristics from output presentations. A unique linear system of equations accounts for reciprocal influence at different locations over the array survey region. It makes no assumption beyond the traditional processing assumption of statistically independent noise sources. The full rank equations are solved with a new robust iterative method. DAMAS is quantitatively validated using archival data from a variety of prior high-lift airframe component noise studies, including flap edge/cove, trailing edge, leading edge, slat, and calibration sources. Presentations are explicit and straightforward, as the noise radiated from a region of interest is determined by simply summing the mean-squared values over that region. DAMAS can fully replace existing array processing and presentations methodology in most applications. It appears to dramatically increase the value of arrays to the field of experimental acoustics.

342 citations


Journal ArticleDOI
Abstract: A comparison is made between several shear layer refraction theories to determine their relationship to one another and to determine which parameters are important for an open jet wind tunnel shear layer correction. For sound transmission through a parallel sheared flow, the shear layer thickness is found to be unimportant at Mach numbers typical of open jet tunnels. The effect of reflected waves, although more significant, can usually be ignored, allowing a correction which is independent of source type and frequency. The shear layer shape (plane or cylindrical) can be important and the correction corresponding to the actual shear layer shape should be used. The numerical solutions of the Lilley equation for the limiting cases of a thick and a thin shear layer are found to agree with the algebraic expressions given for these limiting cases.

312 citations


Proceedings ArticleDOI
01 Jan 1998
Abstract: An overview of the development of two microphone directional arrays for aeroacoustic testing is presented. These arrays were specifically developed to measure airframe noise in the NASA Langley Quiet Flow Facility. A large aperture directional array using 35 flush-mounted microphones was constructed to obtain high resolution noise localization maps around airframe models. Complementing the large array is a small aperture directional array, constructed to obtain spectra and directivity information from regions on the model. Both arrays are employed in acoustic measurements of a 6 percent of full scale airframe model consisting of a main element NACA wing section with a 30 percent chord half-span flap. Representative data obtained from these measurements are presented, along with details of the array calibration and data post- processing procedures.

165 citations


Journal ArticleDOI
Abstract: A detailed computational study of a high-lift configuration was conducted to understand the source mechanism behind a dominant acoustic tone observed in recent experiments on slat noise The unsteady Reynolds-averaged Navier-Stokes computations focused on accurate simulation of the local flowfield of a slat with a blunt trailing edge At a slat deflection angle of 30 deg relative to the main element, the simulations revealed the presence of strong vortex shedding behind the slat trailing edge The resulting flow unsteadiness produced large-amplitude acoustic waves propagating away from the trailing-edge region The local spatial resolution of the computed solution was sufficiently fine to capture both the near-field structure and propagation direction of the generated sound The calculated shedding frequency is in good agreement with the measured acoustic frequencies obtained at NASA Langley Research Center's Low Turbulence Pressure Tunnel In contrast, computational results at a slat deflection angle of 20 deg indicated that the shedding process was severely damped, and, therefore, in agreement with the corresponding acoustic measurements during the experiment There was no evidence of a strong acoustic source near the trailing edge at this lower slat deflection

154 citations


Frequently Asked Questions (1)
Q1. What have the authors contributed in "A comparison of the noise characteristics of a conventional slat and krueger flap" ?

In this paper, the authors compare the acoustic behavior of a conventional slat to an equivalent-mission Krueger flap.