157 results on '"Lockard, David P."'
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2. Comparison of Measured and Simulated Acoustic Signatures for a Full-Scale Aircraft with and Without Airframe Noise Abatement
- Author
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Khorrami, Mehdi R, Ravetta, Patricio A, Lockard, David P, Duda, Benjamin, and Ferris, Ryan
- Subjects
Aerodynamics - Published
- 2019
3. Comparative Study of Active Flow Control Strategies for Lift Enhancement of a Simplified High-Lift Configuration
- Author
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Vatsa, Veer N, Duda, Benjamin, Lin, John C, Melton, Latunia P, Lockard, David P, O'Connell, Matthew D, and Hannon, Judith A
- Subjects
Aerodynamics - Abstract
Numerical simulations have been performed for a simplified high-lift (SHL) version of the Common Research Model (CRM) configuration, where the Fowler flaps of the conventional high-lift (CRM-HL) configuration are replaced by a set of simple hinged flaps. These hinged flaps are equipped with integrated modular active flow control (AFC) cartridges on the suction surface, and the resulting geometry is known as the CRM-SHL-AFC configuration. The main objective is to make use of AFC devices on the CRM-SHL-AFC configuration to recover the aerodynamic performance (lift) of the CRM-HL configuration. In the current paper, a Lattice Boltzmann method-based computational fluid dynamics (CFD) code, known as PowerFLOWQ® is used to simulate the entire flow field associated with the CRM-SHL-AFC configuration equipped with several different types of AFC devices. The transonic version of the PowerFLOWQ® code that has been validated for high speed flows is used to accurately simulate the flow field generated by the high-momentum actuators required to mitigate reversed flow regions on the suction surfaces of the main wing and the flap. The numerical solutions predict the expected trends in aerodynamic forces as the actuation levels are increased. More efficient AFC systems and actuator arrangements emerged based on the parametric studies performed prior to a Fall 2018 wind tunnel test. Preliminary comparisons of the numerical solutions for lift and surface pressures are presented here with the experimental data, demonstrating the usefulness of CFD for predicting the flow field and lift characteristics of AFC-enabled high-lift configurations.
- Published
- 2019
4. Flight-Test Evaluation of Landing Gear Noise Reduction Technologies
- Author
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Khorrami, Mehdi R, Lockard, David P, Humphreys, William M, and Ravetta, Patricio A
- Subjects
Aircraft Design, Testing And Performance ,Acoustics - Abstract
Results from the third Acoustics Research Measurements flight test, conducted under the NASA Flight Demonstrations and Capabilities project, are presented and discussed. The test evaluated landing gear and gear cavity noise mitigation technologies installed on a NASA Gulfstream G-III. Aircraft configurations with and without main landing gear treatments were flown at several flap deflections to determine the acoustic performance of the technologies for aircraft equipped with conventional Fowler flaps. With the aircraft flying an approach path and engines at “ground-idle,” extensive acoustic measurements were acquired with a phased microphone array system. Computed beamform maps were used to examine the effectiveness of the tested technologies in reducing the strength of the noise sources generated by the main landing gear. Various integration regions were devised to extract the farfield noise spectra associated with the treated and untreated landing gear configurations. Analyses of the gathered acoustic data demonstrate that significant noise reduction was achieved. How- ever, the full noise reduction potential of the technologies could not be determined because of contamination from flap inboard edge noise and other secondary sources.
- Published
- 2019
5. Assessment of Aeroacoustic Simulations of the High-Lift Common Research Model
- Author
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Lockard, David P, O'Connell, Matthew D, Vatsa, Veer N, and Choudhari, Meelan M
- Subjects
Acoustics ,Aircraft Design, Testing And Performance - Abstract
This paper presents further validation of PowerFLOWR aeroacoustic simulations of the High-Lift Common Research Model through comparisons with experimental data from a recently completed wind tunnel test. Preliminary time- averaged surface pressure and microphone array data from the experiment are in reasonably good agreement with the simulations, and the slat is shown to be a dominant noise source on this model. The simulations did not predict slat tones that were very prominent in the experiment, but they did capture the broadband component of slat noise in the low-frequency range up to 1 kHz at full scale. Future tests are planned to demonstrate slat noise reduction technology, and simulations are being used to guide this development.
- Published
- 2019
6. Measured and Simulated Acoustic Signature of a Full-Scale Aircraft with Airframe Noise Reduction Technology Installed
- Author
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Khorrami, Mehdi R, Ravetta, Patricio A, Lockard, David P, Duda, Benjamin, and Ferris, Ryan
- Subjects
Aerodynamics - Abstract
Microphone phased-array and pole-mounted microphone data gathered during the NASA Acoustics Research Measurements flight tests were used to benchmark results from companion full-scale aeroacoustics simulations. Conducted with the lattice Boltzmann solver PowerFLOW®, the simulations predicted the acoustic behavior of various tested aircraft configurations. Emphasis was placed on those flown during the third flight test - a Fowler flap-equipped Gulfstream G-III with and without noise abatement technology on the main landing gear. Direct comparisons between experimental and synthetic microphone phasedarray data were achieved by applying the same processing and deconvolution technique to both sets of data. To extend the validation of the computations to the metric used for noise certification, the Effective Perceived Noise Level, a high-fidelity digital model of the nose landing gear, which was excluded from earlier computations, was developed and integrated into the G-III aircraft geometry. The acoustic study presented here demonstrates that the simulated beamform maps and corresponding integrated farfield spectra accurately predict the locations and strengths of the prominent airframe noise sources present on the G-III aircraft.
- Published
- 2019
7. Optical Geolocation for Small Unmanned Aerial Systems
- Author
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Dolph, Chester V, McSwain, Robert G, Humphreys, William M., Jr, Lockard, David P, and Khorrami, Mehdi R
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Air Transportation And Safety ,Optics - Abstract
This paper presents an airborne optical geolocation system using four optical targets to provide position and attitude estimation for a sUAS supporting the NASA Acoustic Research Mission (ARM), where the goal is to reduce nuisance airframe noise during approach and landing. A large precision positioned microphone array captures the airframe noise for multiple passes of a Gulfstream III aircraft. For health monitoring of the microphone array, the Acoustic Calibration Vehicle (ACV) sUAS completes daily flights with an onboard speaker emitting tones at frequencies optimized for determining microphone functionality. An accurate position estimate of the ACV relative to the array is needed for microphone health monitoring. To this end, an optical geolocation system using a downward facing camera mounted to the ACV was developed. The 3D positioning of the ACV is computed using the pinhole camera model. A novel optical geolocation algorithm first detects the targets, then a recursive algorithm tightens the localization of the targets. Finally, the position of the sUAS is computed using the image coordinates of the targets, the 3D world coordinates of the targets, and the camera matrix. A Real-Time Kinematic GPS system is used to compare the optical geolocation system.
- Published
- 2019
8. Airframe noise predictions using the Ffowcs Williams-Hawkings equation
- Author
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Lockard, David P, primary
- Published
- 2022
- Full Text
- View/download PDF
9. Flight-Test Evaluation of Airframe Noise Mitigation Technologies
- Author
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Khorrami, Mehdi R, Lockard, David P, Humphreys, William M, and Ravetta, Patricio
- Subjects
Acoustics ,Aerodynamics - Abstract
A series of flight tests targeting airframe noise reduction was planned and executed under the NASA Flight Demonstrations and Capabilities project. The objectives of the tests were two-fold: to evaluate the aeroacoustic performance of several noise reduction technologies in a relevant environment and to generate a comprehensive database for advancing the state of the art in simulation-based airframe noise prediction methodologies. These technologies – an Adaptive Compliant Trailing Edge flap, main landing gear fairings, and gear cavity treatments – were integrated on a NASA Gulfstream G-III aircraft to determine their effectiveness, both on a component-level (individually) and a system-level (combined) basis. With the aircraft flying an approach pattern and the engines set at ground idle, extensive acoustic measurements were acquired using a phased microphone array system. Detailed analyses of the gathered acoustic data clearly demonstrate that significant noise reduction was achieved for the flap and main landing gear components.
- Published
- 2018
10. Assessment of Noise Reduction Concepts for Leading-Edge Slat Noise
- Author
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Zhang, Yang, O'Neill, Adam, Cattafesta, Louis N., III, Pascioni, Kyle, Choudhari, Meelan M, Khorrami, Mehdi R, Lockard, David P, and Turner, Travis
- Subjects
Aerodynamics ,Acoustics - Abstract
The leading-edge slat of a high-lift airfoil can be a significant noise contributor during aircraft landing. This paper summarizes the effects of several passive noise reduction devices on the 30P30N high-lift airfoil. Experiments are conducted on a two-dimensional multi-element high-lift airfoil with leading-edge slat extensions, gap filler, and cove filler in an anechoic wind tunnel to evaluate the effect of passive flow control on the acoustics generated by the unsteady flow field. Slat geometry modifications associated with the treatments alter the flow field in the region that dominates the generation of the acoustic field. Three angles of attack (a(k) = 8°, 10°, and 15.5°) and three different Reynolds numbers (Re(c) = 1.2e6, 1.5e6, and 1.71e6) are selected as the test conditions. Steady surface pressure measurements are conducted to assess the effect of the treatments on the lift and drag. Unsteady surface pressure measurements along with the far-field acoustic array measurements are performed to evaluate the changes in near- and far-field pressure fluctuations, respectively. Delay and Sum (DAS) beamforming method is applied to locate the noise sources on the model and provide integrated spectra. Implementation difficulties with the gap filler led to structural integration deficiencies that prevented a fair assessment of this technology. Among the other passive devices, the cove filler s the most effective noise reduction, along with a negligible change in the aerodynamic metrics.
- Published
- 2018
11. The Impact of Local Meteorological Conditions on Airframe Noise Flight Test Data
- Author
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Lockard, David P and Bestul, Kimberly A
- Subjects
Acoustics - Abstract
Phased microphone array measurements obtained during flight tests conducted in 2016 and 2017 are used to assess the importance of local meteorological measurements on the data. In particular, the effectiveness of atmospheric absorption corrections is evaluated under vastly different temperature and humidity conditions. The results indicate that, even under conditions with high absorption, sources can be visualized up to a frequency that is dependent on background noise levels, wind, and atmospheric turbulence. However, absolute levels were found to be problematic on days with high absorption rates, with the discrepancies most prevalent for aircraft positions further from the center of the array. Restricting the data to those days with favorable meteorological conditions generally resulted in a good collapse of the spectra, with differences less than a couple of decibels.
- Published
- 2018
12. Aeroacoustic Simulations of the High-Lift Common Research Model and Validation with Experiment
- Author
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Lockard, David P., primary, Choudhari, Meelan M., additional, and Vatsa, Veer N., additional
- Published
- 2022
- Full Text
- View/download PDF
13. Development of Slat Gap and Slat Cove Filler Treatments for Noise Reduction Assessment on the High Lift Common Research Model in the NASA LaRC 14x22
- Author
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Turner, Travis L., primary, Mulvaney, John W., additional, Lockard, David P., additional, Allen, Albert R., additional, and Brynildsen, Scott E., additional
- Published
- 2022
- Full Text
- View/download PDF
14. Effects of Porous Gap Fillers on 30P30N Leading-Edge Slat Noise. Part I: Surface Pressure and Acoustics
- Author
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Zhang, Yang, primary, Cattafesta, Louis N., additional, Choudhari, Meelan M., additional, Pascioni, Kyle A., additional, Khorrami, Mehdi R., additional, Lockard, David P., additional, and Turner, Travis L., additional
- Published
- 2022
- Full Text
- View/download PDF
15. Phased Array Characterization of Slat Noise Radiation from a High-Lift Common Research Model
- Author
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Humphreys, William M., primary, Lockard, David P., additional, and Bahr, Christopher J., additional
- Published
- 2022
- Full Text
- View/download PDF
16. On the Alleviation of Background Noise for the High-Lift Common Research Model Aeroacoustic Test
- Author
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Hutcheson, Florence V., primary, Lockard, David P., additional, and Stead, Daniel, additional
- Published
- 2022
- Full Text
- View/download PDF
17. Effects of Porous Gap Fillers on Leading-Edge Slat Noise of 30P30N. Part II: PIV Measurements
- Author
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Zhang, Yang, primary, Cattafesta, Louis N., additional, Choudhari, Meelan M., additional, Pascioni, Kyle A., additional, Khorrami, Mehdi R., additional, Lockard, David P., additional, and Turner, Travis L., additional
- Published
- 2022
- Full Text
- View/download PDF
18. Aeroacoustic Simulations of a Nose Landing Gear with FUN3D: A Grid Refinement Study
- Author
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Vatsa, Veer N, Khorrami, Mehdi R, and Lockard, David P
- Subjects
Acoustics ,Fluid Mechanics And Thermodynamics - Abstract
A systematic grid refinement study is presented for numerical simulations of a partially-dressed, cavity-closed (PDCC) nose landing gear configuration that was tested in the University of Florida's open-jet acoustic facility known as the UFAFF. The unstructured-grid flow solver FUN3D is used to compute the unsteady flow field for this configuration. Mixed-element grids generated using the Pointwise (Registered Trademark) grid generation software are used for numerical simulations. Particular care is taken to ensure quality cells and proper resolution in critical areas of interest in an effort to minimize errors introduced by numerical artifacts. A set of grids was generated in this manner to create a family of uniformly refined grids. The finest grid was then modified to coarsen the wall-normal spacing to create a grid suitable for the wall-function implementation in FUN3D code. A hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) turbulence modeling approach is used for these simulations. Time-averaged and instantaneous solutions obtained on these grids are compared with the measured data. These CFD solutions are used as input to a FfowcsWilliams-Hawkings (FW-H) noise propagation code to compute the farfield noise levels. The agreement of the computed results with the experimental data improves as the grid is refined.
- Published
- 2017
- Full Text
- View/download PDF
19. Evaluation of Methods for In-Situ Calibration of Field-Deployable Microphone Phased Arrays
- Author
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Humphreys, William M, Lockard, David P, Khorrami, Mehdi R, Culliton, William G, and McSwain, Robert G
- Subjects
Statistics And Probability ,Acoustics ,Communications And Radar - Abstract
Current field-deployable microphone phased arrays for aeroacoustic flight testing require the placement of hundreds of individual sensors over a large area. Depending on the duration of the test campaign, the microphones may be required to stay deployed at the testing site for weeks or even months. This presents a challenge in regards to tracking the response (i.e., sensitivity) of the individual sensors as a function of time in order to evaluate the health of the array. To address this challenge, two different methods for in-situ tracking of microphone responses are described. The first relies on the use of an aerial sound source attached as a payload on a hovering small Unmanned Aerial System (sUAS) vehicle. The second relies on the use of individually excited ground-based sound sources strategically placed throughout the array pattern. Testing of the two methods was performed in microphone array deployments conducted at Fort A.P. Hill in 2015 and at Edwards Air Force Base in 2016. The results indicate that the drift in individual sensor responses can be tracked reasonably well using both methods. Thus, in-situ response tracking methods are useful as a diagnostic tool for monitoring the health of a phased array during long duration deployments.
- Published
- 2017
20. Noise Simulations of the High-Lift Common Research Model
- Author
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Lockard, David P, Choudhari, Meelan M, Vatsa, Veer N, O'Connell, Matthew D, Duda, Benjamin, and Fares, Ehab
- Subjects
Acoustics - Abstract
The PowerFLOW(TradeMark) code has been used to perform numerical simulations of the high-lift version of the Common Research Model (HL-CRM) that will be used for experimental testing of airframe noise. Time-averaged surface pressure results from PowerFLOW(TradeMark) are found to be in reasonable agreement with those from steady-state computations using FUN3D. Surface pressure fluctuations are highest around the slat break and nacelle/pylon region, and synthetic array beamforming results also indicate that this region is the dominant noise source on the model. The gap between the slat and pylon on the HL-CRM is not realistic for modern aircraft, and most nacelles include a chine that is absent in the baseline model. To account for those effects, additional simulations were completed with a chine and with the slat extended into the pylon. The case with the chine was nearly identical to the baseline, and the slat extension resulted in higher surface pressure fluctuations but slightly reduced radiated noise. The full-span slat geometry without the nacelle/pylon was also simulated and found to be around 10 dB quieter than the baseline over almost the entire frequency range. The current simulations are still considered preliminary as changes in the radiated acoustics are still being observed with grid refinement, and additional simulations with finer grids are planned.
- Published
- 2017
21. Assessment of Slat Extensions and a Cove Filler for Slat Noise Reduction
- Author
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Zhang, Yang, primary, Cattafesta, Louis N., additional, Pascioni, Kyle A., additional, Choudhari, Meelan M., additional, Khorrami, Mehdi R., additional, Lockard, David P., additional, and Turner, Travis, additional
- Published
- 2021
- Full Text
- View/download PDF
22. Development and Calibration of a Field-Deployable Microphone Phased Array for Propulsion and Airframe Noise Flyover Measurements
- Author
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Humphreys, William M., Jr, Lockard, David P, Khorrami, Mehdi R, Culliton, William G, McSwain, Robert G, Ravetta, Patricio A, and Johns, Zachary
- Subjects
Acoustics - Abstract
A new aeroacoustic measurement capability has been developed consisting of a large channelcount, field-deployable microphone phased array suitable for airframe noise flyover measurements for a range of aircraft types and scales. The array incorporates up to 185 hardened, weather-resistant sensors suitable for outdoor use. A custom 4-mA current loop receiver circuit with temperature compensation was developed to power the sensors over extended cable lengths with minimal degradation of the signal to noise ratio and frequency response. Extensive laboratory calibrations and environmental testing of the sensors were conducted to verify the design's performance specifications. A compact data system combining sensor power, signal conditioning, and digitization was assembled for use with the array. Complementing the data system is a robust analysis system capable of near real-time presentation of beamformed and deconvolved contour plots and integrated spectra obtained from array data acquired during flyover passes. Additional instrumentation systems needed to process the array data were also assembled. These include a commercial weather station and a video monitoring / recording system. A detailed mock-up of the instrumentation suite (phased array, weather station, and data processor) was performed in the NASA Langley Acoustic Development Laboratory to vet the system performance. The first deployment of the system occurred at Finnegan Airfield at Fort A.P. Hill where the array was utilized to measure the vehicle noise from a number of sUAS (small Unmanned Aerial System) aircraft. A unique in-situ calibration method for the array microphones using a hovering aerial sound source was attempted for the first time during the deployment.
- Published
- 2016
23. Autonomous Slat-Cove-Filler Device for Reduction of Aeroacoustic Noise Associated with Aircraft Systems
- Author
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Turner, Travis L, Kidd, Reggie T, Lockard, David P, Khorrami, Mehdi R, Streett, Craig L, and Weber, Douglas Leo
- Subjects
Acoustics - Abstract
A slat cove filler is utilized to reduce airframe noise resulting from deployment of a leading edge slat of an aircraft wing. The slat cove filler is preferably made of a super elastic shape memory alloy, and the slat cove filler shifts between stowed and deployed shapes as the slat is deployed. The slat cove filler may be configured such that a separate powered actuator is not required to change the shape of the slat cove filler from its deployed shape to its stowed shape and vice-versa. The outer contour of the slat cove filler preferably follows a profile designed to maintain accelerating flow in the gap between the slat cove filler and wing leading edge to provide for noise reduction.
- Published
- 2016
24. Overview of Aeroacoustic Testing of the High-Lift Common Research Model
- Author
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Lockard, David P., primary, Turner, Travis L., additional, Bahr, Christopher J., additional, and Hutcheson, Florence V., additional
- Published
- 2021
- Full Text
- View/download PDF
25. CFD Simulations of Landing and Takeoff CRM High-Lift Configurations
- Author
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Vatsa, Veer N., primary, Lin, John C., additional, Pack Melton, LaTunia G., additional, Lockard, David P., additional, and Ferris, Ryan, additional
- Published
- 2021
- Full Text
- View/download PDF
26. Investigation of the 30P30N Slat Flow Field with Passive Control Devices Using Particle Image Velocimetry
- Author
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Zhang, Yang, primary, Richardson, Ross, additional, Cattafesta, Louis N., additional, Choudhari, Meelan M., additional, Pascioni, Kyle A., additional, Khorrami, Mehdi R., additional, Lockard, David P., additional, and Turner, Travis L., additional
- Published
- 2021
- Full Text
- View/download PDF
27. Computational Investigation of Conventional and Active-Flow-Control-Enabled High-Lift Configurations
- Author
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Vatsa, Veer N., primary, Lin, John C., additional, Melton, Latunia P., additional, Lockard, David P., additional, and Ferris, Ryan, additional
- Published
- 2021
- Full Text
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28. Assessment of Slat Noise Predictions for 30P30N High-Lift Configuration From BANC-III Workshop
- Author
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Choudhari, Meelan and Lockard, David P
- Subjects
Acoustics - Abstract
This paper presents a summary of the computational predictions and measurement data contributed to Category 7 of the 3rd AIAA Workshop on Benchmark Problems for Airframe Noise Computations (BANC-III), which was held in Atlanta, GA, on June 14-15, 2014. Category 7 represents the first slat-noise configuration to be investigated under the BANC series of workshops, namely, the 30P30N two-dimensional high-lift model (with a slat contour that was slightly modified to enable unsteady pressure measurements) at an angle of attack that is relevant to approach conditions. Originally developed for a CFD challenge workshop to assess computational fluid dynamics techniques for steady high-lift predictions, the 30P30N configurations has provided a valuable opportunity for the airframe noise community to collectively assess and advance the computational and experimental techniques for slat noise. The contributed solutions are compared with each other as well as with the initial measurements that became available just prior to the BANC-III Workshop. Specific features of a number of computational solutions on the finer grids compare reasonably well with the initial measurements from FSU and JAXA facilities and/or with each other. However, no single solution (or a subset of solutions) could be identified as clearly superior to the remaining solutions. Grid sensitivity studies presented by multiple BANC-III participants demonstrated a relatively consistent trend of reduced surface pressure fluctuations, higher levels of turbulent kinetic energy in the flow, and lower levels of both narrow band peaks and the broadband component of unsteady pressure spectra in the nearfield and farfield. The lessons learned from the BANC-III contributions have been used to identify improvements to the problem statement for future Category-7 investigations.
- Published
- 2015
29. Aeroacoustic Simulations of a Nose Landing Gear Using FUN3D on Pointwise Unstructured Grids
- Author
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Vatsa, Veer N, Khorrami, Mehdi R, Rhoads, John, and Lockard, David P
- Subjects
Acoustics ,Fluid Mechanics And Thermodynamics - Abstract
Numerical simulations have been performed for a partially-dressed, cavity-closed (PDCC) nose landing gear configuration that was tested in the University of Florida's open-jet acoustic facility known as the UFAFF. The unstructured-grid flow solver FUN3D is used to compute the unsteady flow field for this configuration. Mixed-element grids generated using the Pointwise(TradeMark) grid generation software are used for these simulations. Particular care is taken to ensure quality cells and proper resolution in critical areas of interest in an effort to minimize errors introduced by numerical artifacts. A hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) turbulence model is used for these simulations. Solutions are also presented for a wall function model coupled to the standard turbulence model. Time-averaged and instantaneous solutions obtained on these Pointwise grids are compared with the measured data and previous numerical solutions. The resulting CFD solutions are used as input to a Ffowcs Williams-Hawkings noise propagation code to compute the farfield noise levels in the flyover and sideline directions. The computed noise levels compare well with previous CFD solutions and experimental data.
- Published
- 2015
30. An Assessment of Flap and Main Landing Gear Noise Abatement Concepts
- Author
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Khorrami, Mehdi R, Humphreys, William M., Jr, and Lockard, David P
- Subjects
Acoustics ,Aerodynamics - Abstract
A detailed assessment of the acoustic performance of several noise reduction concepts for aircraft flaps and landing gear is presented. Consideration is given to the best performing concepts within the suite of technologies that were evaluated in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel using an 18 percent scale, semi-span, high-fidelity Gulfstream aircraft model as a test bed. Microphone array measurements were obtained with the model in a landing configuration (flap deflected 39 degrees and the main landing gear deployed or retracted). The effectiveness of each concept over the range of pitch angles, speeds, and directivity angles tested is presented. Comparison of the acoustic spectra, obtained from integration of the beamform maps between the untreated baseline and treated configurations, clearly demonstrates that the flap and gear concepts maintain noise reduction benefits over the entire range of the directivity angles tested.
- Published
- 2015
31. Comparison of Computational and Experimental Microphone Array Results for an 18%-Scale Aircraft Model
- Author
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Lockard, David P, Humphreys, William M, Khorrami, Mehdi R, Fares, Ehab, Casalino, Damiano, and Ravetta, Patricio A
- Subjects
Acoustics ,Aerodynamics - Abstract
An 18%-scale, semi-span model is used as a platform for examining the efficacy of microphone array processing using synthetic data from numerical simulations. Two hybrid RANS/LES codes coupled with Ffowcs Williams-Hawkings solvers are used to calculate 97 microphone signals at the locations of an array employed in the NASA LaRC 14x22 tunnel. Conventional, DAMAS, and CLEAN-SC array processing is applied in an identical fashion to the experimental and computational results for three different configurations involving deploying and retracting the main landing gear and a part span flap. Despite the short time records of the numerical signals, the beamform maps are able to isolate the noise sources, and the appearance of the DAMAS synthetic array maps is generally better than those from the experimental data. The experimental CLEAN-SC maps are similar in quality to those from the simulations indicating that CLEAN-SC may have less sensitivity to background noise. The spectrum obtained from DAMAS processing of synthetic array data is nearly identical to the spectrum of the center microphone of the array, indicating that for this problem array processing of synthetic data does not improve spectral comparisons with experiment. However, the beamform maps do provide an additional means of comparison that can reveal differences that cannot be ascertained from spectra alone.
- Published
- 2015
32. Characterization of Flap Edge Noise Radiation from a High-Fidelity Airframe Model
- Author
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Humphreys, William M., Jr, Khorrami, Mehdi R, Lockard, David P, Neuhart, Dan H, and Bahr, Christopher J
- Subjects
Acoustics - Abstract
The results of an experimental study of the noise generated by a baseline high-fidelity airframe model are presented. The test campaign was conducted in the open-jet test section of the NASA Langley 14- by 22-foot Subsonic Tunnel on an 18%-scale, semi-span Gulfstream airframe model incorporating a trailing edge flap and main landing gear. Unsteady surface pressure measurements were obtained from a series of sensors positioned along the two flap edges, and far field acoustic measurements were obtained using a 97-microphone phased array that viewed the pressure side of the airframe. The DAMAS array deconvolution method was employed to determine the locations and strengths of relevant noise sources in the vicinity of the flap edges and the landing gear. A Coherent Output Power (COP) spectral method was used to couple the unsteady surface pressures measured along the flap edges with the phased array output. The results indicate that outboard flap edge noise is dominated by the flap bulb seal cavity with very strong COP coherence over an approximate model-scale frequency range of 1 to 5 kHz observed between the array output and those unsteady pressure sensors nearest the aft end of the cavity. An examination of experimental COP spectra for the inboard flap proved inconclusive, most likely due to a combination of coherence loss caused by decorrelation of acoustic waves propagating through the thick wind tunnel shear layer and contamination of the spectra by tunnel background noise at lower frequencies. Directivity measurements obtained from integration of DAMAS pressure-squared values over defined geometric zones around the model show that the baseline flap and landing gear are only moderately directional as a function of polar emission angle.
- Published
- 2015
33. Influence of Spanwise Boundary Conditions on Slat Noise Simulations
- Author
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Lockard, David P, Choudhari, Meelan M, and Buning, Pieter G
- Subjects
Acoustics ,Fluid Mechanics And Thermodynamics - Abstract
The slat noise from the 30P/30N high-lift system is being investigated through computational fluid dynamics simulations with the OVERFLOW code in conjunction with a Ffowcs Williams-Hawkings acoustics solver. In the present study, two different spanwise grids are being used to investigate the effect of the spanwise extent and periodicity on the near-field unsteady structures and radiated noise. The baseline grid with periodic boundary conditions has a short span equal to 1/9th of the stowed chord, whereas the other, longer span grid adds stretched grids on both sides of the core, baseline grid to allow inviscid surface boundary conditions at both ends. The results indicate that the near-field mean statistics obtained using the two grids are similar to each other, as are the directivity and spectral shapes of the radiated noise. However, periodicity forces all acoustic waves with less than one wavelength across the span to be two-dimensional, without any variation in the span. The spanwise coherence of the acoustic waves is what is needed to make estimates of the noise that would be radiated from realistic span lengths. Simulations with periodic conditions need spans of at least six slat chords to allow spanwise variation in the low-frequencies associated with the peak of broadband slat noise. Even then, the full influence of the periodicity is unclear, so employing grids with a fine, central region and highly stretched meshes that go to slip walls may be a more efficient means of capturing the spanwise decorrelation of low-frequency acoustic phenomena.
- Published
- 2015
- Full Text
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34. Airframe Noise Research
- Author
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Lockard, David P
- Subjects
Aircraft Design, Testing And Performance ,Acoustics - Published
- 2015
35. Multi-Element Airfoil System
- Author
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Turner, Travis L, Khorrami, Mehdi R, Lockard, David P, McKenney, Martin J, Atherley, Raymond D, and Kidd, Reggie T
- Subjects
Aerodynamics - Abstract
A multi-element airfoil system includes an airfoil element having a leading edge region and a skin element coupled to the airfoil element. A slat deployment system is coupled to the slat and the skin element, and is capable of deploying and retracting the slat and the skin element. The skin element substantially fills the lateral gap formed between the slat and the airfoil element when the slat is deployed. The system further includes an uncoupling device and a sensor to remove the skin element from the gap based on a critical angle-of-attack of the airfoil element. The system can alternatively comprise a trailing edge flap, where a skin element substantially fills the lateral gap between the flap and the trailing edge region of the airfoil element. In each case, the skin element fills a gap between the airfoil element and the deployed flap or slat to reduce airframe noise.
- Published
- 2014
36. Grid Sensitivity Study for Slat Noise Simulations
- Author
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Lockard, David P, Choudhari, Meelan M, and Buning, Pieter G
- Subjects
Acoustics ,Numerical Analysis ,Aircraft Design, Testing And Performance - Abstract
The slat noise from the 30P/30N high-lift system is being investigated through computational fluid dynamics simulations in conjunction with a Ffowcs Williams-Hawkings acoustics solver. Many previous simulations have been performed for the configuration, and the case was introduced as a new category for the Second AIAA workshop on Benchmark problems for Airframe Noise Configurations (BANC-II). However, the cost of the simulations has restricted the study of grid resolution effects to a baseline grid and coarser meshes. In the present study, two different approaches are being used to investigate the effect of finer resolution of near-field unsteady structures. First, a standard grid refinement by a factor of two is used, and the calculations are performed by using the same CFL3D solver employed in the majority of the previous simulations. Second, the OVERFLOW code is applied to the baseline grid, but with a 5th-order upwind spatial discretization as compared with the second-order discretization used in the CFL3D simulations. In general, the fine grid CFL3D simulation and OVERFLOW calculation are in very good agreement and exhibit the lowest levels of both surface pressure fluctuations and radiated noise. Although the smaller scales resolved by these simulations increase the velocity fluctuation levels, they appear to mitigate the influence of the larger scales on the surface pressure. These new simulations are used to investigate the influence of the grid on unsteady high-lift simulations and to gain a better understanding of the physics responsible for the noise generation and radiation.
- Published
- 2014
37. Aeroacoustic Evaluation of Flap and Landing Gear Noise Reduction Concepts
- Author
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Khorrami, Mehdi R, Humphreys, William M., Jr, Lockard, David P, and Ravetta, Patricio A
- Subjects
Aircraft Design, Testing And Performance ,Acoustics - Abstract
Aeroacoustic measurements for a semi-span, 18% scale, high-fidelity Gulfstream aircraft model are presented. The model was used as a test bed to conduct detailed studies of flap and main landing gear noise sources and to determine the effectiveness of numerous noise mitigation concepts. Using a traversing microphone array in the flyover direction, an extensive set of acoustic data was obtained in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the information was acquired with the model in a landing configuration with the flap deflected 39 deg and the main landing gear alternately installed and removed. Data were obtained at Mach numbers of 0.16, 0.20, and 0.24 over directivity angles between 56 deg and 116 deg, with 90 deg representing the overhead direction. Measured acoustic spectra showed that several of the tested flap noise reduction concepts decrease the sound pressure levels by 2 - 4 dB over the entire frequency range at all directivity angles. Slightly lower levels of noise reduction from the main landing gear were obtained through the simultaneous application of various gear devices. Measured aerodynamic forces indicated that the tested gear/flap noise abatement technologies have a negligible impact on the aerodynamic performance of the aircraft model.
- Published
- 2014
38. Acoustics and Surface Pressure Measurements from Tandem Cylinder Configurations
- Author
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Hutcheson, Florence V, Brooks, Thomas F, Lockard, David P, Choudhari, Meelan M, and Stead, Daniel J
- Subjects
Acoustics - Abstract
Acoustic and unsteady surface pressure measurements from two cylinders in tandem configurations were acquired to study the effect of spacing, surface trip and freestream velocity on the radiated noise. The Reynolds number ranged from 1.15x10(exp 5) to 2.17x10(exp 5), and the cylinder spacing varied between 1.435 and 3.7 cylinder diameters. The acoustic and surface pressure spectral characteristics associated with the different flow regimes produced by the cylinders' wake interference were identified. The dependence of the Strouhal number, peak Sound Pressure Level and spanwise coherence on cylinder spacing and flow velocity was examined. Directivity measurements were performed to determine how well the dipole assumption for the radiation of vortex shedding noise holds for the largest and smallest cylinder spacing tested.
- Published
- 2014
39. Elastically Deformable Side-Edge Link for Trailing-Edge Flap Aeroacoustic Noise Reduction
- Author
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Khorrami, Mehdi R, Lockard, David P, Moore, James B, Su, Ji, Turner, Travis L, Lin, John C, Taminger, Karen M, Kahng, Seun K, and Verden, Scott A
- Subjects
Acoustics ,Aircraft Design, Testing And Performance - Abstract
A system is provided for reducing aeroacoustic noise generated by an aircraft having wings equipped with trailing-edge flaps. The system includes a plurality of elastically deformable structures. Each structure is coupled to and along one of the side edges of one of the trailing-edge flaps, and is coupled to a portion of one of the wings that is adjacent to the one of the side edges. The structures elastically deform when the trailing-edge flaps are deployed away from the wings.
- Published
- 2014
40. Unsteady flowfield around tandem cylinders as prototype component interaction in airframe noise
- Author
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Khorrami, Mehdi R., Choudhari, Meelan M., Lockard, David P., Jenkins, Luther N., and McGinley, Catherine B.
- Subjects
Aerodynamic noise -- Properties ,Air flow -- Observations ,Wakes (Aerodynamics) -- Observations ,Aerospace and defense industries ,Business - Abstract
The current effort characterizes the details of flow interactions and wake interference effects between two cylinders in a tandem configuration. This setup is representative of several component-level flow interactions that occur when air flows over the main landing gear of aircraft. Such interactions are likely to have a significant impact on the noise radiation associated with the undercarriage. This paper focuses on two-dimensional, time-accurate flow simulations of two distinct tandem cylinder flow regimes, associated with short and intermediate separation distances between the two cylinders. Unsteady Reynolds averaged Navier-Stokes simulations using a two-equation turbulence model run at a Reynolds number of 1.66 x [10.sup.5] and a Mach number of 0.166 are presented. Emphasis is placed on understanding both the time-averaged and unsteady flow features between the two cylinders and in the wake of the rear cylinder. Predicted mean-flow quantities and vortex shedding frequencies show reasonable agreement with measured data for both cylinder spacings. Computations for the short separation distance exhibit a nonphysical decay of flow unsteadiness with time: however, the predicted sensitivity of the mean lift coefficient to small variations in the upstream flow angularity explains the asymmetric flowfield observed in the present and previous measurements.
- Published
- 2007
41. Evaluation of PowerFLOW for Aerodynamic Applications
- Author
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Lockard, David P., Luo, Li-Shi, Milder, Seth D., and Singer, Bart A.
- Published
- 2002
- Full Text
- View/download PDF
42. Aeroacoustic Simulation of Nose Landing Gear on Adaptive Unstructured Grids With FUN3D
- Author
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Vatsa, Veer N, Khorrami, Mehdi R, Park, Michael A, and Lockard, David P
- Subjects
Aerodynamics - Abstract
Numerical simulations have been performed for a partially-dressed, cavity-closed nose landing gear configuration that was tested in NASA Langley s closed-wall Basic Aerodynamic Research Tunnel (BART) and in the University of Florida's open-jet acoustic facility known as the UFAFF. The unstructured-grid flow solver FUN3D, developed at NASA Langley Research center, is used to compute the unsteady flow field for this configuration. Starting with a coarse grid, a series of successively finer grids were generated using the adaptive gridding methodology available in the FUN3D code. A hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) turbulence model is used for these computations. Time-averaged and instantaneous solutions obtained on these grids are compared with the measured data. In general, the correlation with the experimental data improves with grid refinement. A similar trend is observed for sound pressure levels obtained by using these CFD solutions as input to a FfowcsWilliams-Hawkings noise propagation code to compute the farfield noise levels. In general, the numerical solutions obtained on adapted grids compare well with the hand-tuned enriched fine grid solutions and experimental data. In addition, the grid adaption strategy discussed here simplifies the grid generation process, and results in improved computational efficiency of CFD simulations.
- Published
- 2013
43. Slat Noise Control Using a Slat Gap Filler
- Author
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Zhang, Yang, primary, Cattafesta, Louis N., additional, Pascioni, Kyle A., additional, Choudhari, Meelan M., additional, Lockard, David P., additional, Khorrami, Mehdi R., additional, and Turner, Travis, additional
- Published
- 2020
- Full Text
- View/download PDF
44. CFD and Experimental Data Comparisons for Conventional and AFC-Enabled CRM High-Lift Configurations (Invited)
- Author
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Vatsa, Veer N., primary, Lin, John C., additional, Pack Melton, LaTunia G., additional, Lockard, David P., additional, and Ferris, Ryan, additional
- Published
- 2020
- Full Text
- View/download PDF
45. Computational aeroacoustic analysis of slat trailing-edge flow
- Author
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Singer, Bart A., Lockard, David P., and Brentner, Kenneth S.
- Subjects
Acoustic emission -- Analysis ,Airplanes -- Noise ,Reynolds number -- Usage ,Vortex-motion -- Analysis ,Fluid dynamics -- Analysis ,Aerospace and defense industries ,Business - Abstract
Results demonstrate that high-amplitude, high-frequency acoustic signal, similar to those obtained in high-lift system, is caused by vortex shedding from the trailing-edge slat. The acoustic analysis is based on the Ffowcs Williams and Hawkings equation.
- Published
- 2000
46. The Influence of Realistic Reynolds Numbers on Slat Noise Simulations
- Author
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Lockard, David P and Choudhari, Meelan M
- Subjects
Aerodynamics - Abstract
The slat noise from the 30P/30N high-lift system has been computed using a computational fluid dynamics code in conjunction with a Ffowcs Williams-Hawkings solver. Varying the Reynolds number from 1.71 to 12.0 million based on the stowed chord resulted in slight changes in the radiated noise. Tonal features in the spectra were robust and evident for all Reynolds numbers and even when a spanwise flow was imposed. The general trends observed in near-field fluctuations were also similar for all the different Reynolds numbers. Experiments on simplified, subscale high-lift systems have exhibited noticeable dependencies on the Reynolds number and tripping, although primarily for tonal features rather than the broadband portion of the spectra. Either the 30P/30N model behaves differently, or the computational model is unable to capture these effects. Hence, the results underscore the need for more detailed measurements of the slat cove flow.
- Published
- 2012
47. Aeroacoustic Simulation of a Nose Landing Gear in an Open Jet Facility Using FUN3D
- Author
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Vatsa, Veer N, Lockard, David P, Khorrami, Mehdi R, and Carlson, Jan-Renee
- Subjects
Acoustics - Abstract
Numerical simulations have been performed for a partially-dressed, cavity-closed nose landing gear configuration that was tested in NASA Langley s closed-wall Basic Aerodynamic Research Tunnel (BART) and in the University of Florida s open-jet acoustic facility known as UFAFF. The unstructured-grid flow solver, FUN3D, developed at NASA Langley Research center is used to compute the unsteady flow field for this configuration. A hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) turbulence model is used for these computations. Time-averaged and instantaneous solutions compare favorably with the measured data. Unsteady flowfield data obtained from the FUN3D code are used as input to a Ffowcs Williams-Hawkings noise propagation code to compute the sound pressure levels at microphones placed in the farfield. Significant improvement in predicted noise levels is obtained when the flowfield data from the open jet UFAFF simulations is used as compared to the case using flowfield data from the closed-wall BART configuration.
- Published
- 2012
48. Slat Noise Simulations: Status and Challenges
- Author
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Choudhari, Meelan M, Lockard, David P, Khorrami, Mehdi R, and Mineck, Raymond E
- Subjects
Acoustics - Abstract
Noise radiation from the leading edge slat of a high-lift system is known to be an important component of aircraft noise during approach. NASA's Langley Research Center is engaged in a coordinated series of investigations combining high-fidelity numerical simulations and detailed wind tunnel measurements of a generic, unswept, 3-element, high-lift configuration. The goal of this effort is to provide a validated predictive capability that would enable identification of the dominant noise source mechanisms and, ultimately, help develop physics inspired concepts for reducing the far-field acoustic intensity. This paper provides a brief overview of the current status of the computational effort and describes new findings pertaining to the effects of the angle of attack on the aeroacoustics of the slat cove region. Finally, the interplay of the simulation campaign with the concurrently evolving development of a benchmark dataset for an international workshop on airframe noise is outlined.
- Published
- 2011
49. CFD-CAA Coupled Calculations of a Tandem Cylinder Configuration to Assess Facility Installation Effects
- Author
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Redonnet, Stephane, Lockard, David P, Khorrami, Mehdi R, and Choudhari, Meelan M
- Subjects
Fluid Mechanics And Thermodynamics - Abstract
This paper presents a numerical assessment of acoustic installation effects in the tandem cylinder (TC) experiments conducted in the NASA Langley Quiet Flow Facility (QFF), an open-jet, anechoic wind tunnel. Calculations that couple the Computational Fluid Dynamics (CFD) and Computational Aeroacoustics (CAA) of the TC configuration within the QFF are conducted using the CFD simulation results previously obtained at NASA LaRC. The coupled simulations enable the assessment of installation effects associated with several specific features in the QFF facility that may have impacted the measured acoustic signature during the experiment. The CFD-CAA coupling is based on CFD data along a suitably chosen surface, and employs a technique that was recently improved to account for installed configurations involving acoustic backscatter into the CFD domain. First, a CFD-CAA calculation is conducted for an isolated TC configuration to assess the coupling approach, as well as to generate a reference solution for subsequent assessments of QFF installation effects. Direct comparisons between the CFD-CAA calculations associated with the various installed configurations allow the assessment of the effects of each component (nozzle, collector, etc.) or feature (confined vs. free jet flow, etc.) characterizing the NASA LaRC QFF facility.
- Published
- 2011
50. The Variation of Slat Noise with Mach and Reynolds Numbers
- Author
-
Lockard, David P and Choudhari, Meelan M
- Subjects
Acoustics - Abstract
The slat noise from the 30P30N high-lift system has been computed using a computational fluid dynamics code in conjunction with a Ffowcs Williams-Hawkings solver. By varying the Mach number from 0.13 to 0.25, the noise was found to vary roughly with the 5th power of the speed. Slight changes in the behavior with directivity angle could easily account for the different speed dependencies reported in the literature. Varying the Reynolds number from 1.4 to 2.4 million resulted in almost no differences, and primarily served to demonstrate the repeatability of the results. However, changing the underlying hybrid Reynolds-averaged-Navier-Stokes/Large-Eddy-Simulation turbulence model significantly altered the mean flow because of changes in the flap separation. However, the general trends observed in both the acoustics and near-field fluctuations were similar for both models.
- Published
- 2011
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