Dissertations / Theses on the topic 'Wind tunnel noise'

This project is intended to demonstrate the current state of knowledge in the prediction of the tonal and broadband noise radiation from a Sevik rotor. The rotor measurements were made at the Virginia Tech Stability Wind Tunnel. Details of the rotor noise and flow measurements were presented by Wisda et al(2014) and Murray et al(2015) respectively. This study presents predictions based on an approach detailed by Glegg et al(2015) for the broadband noise generated by a rotor in an inhomogeneous flow, and compares them to measured noise radiated from the rotor at prescribed observer locations. Discrepancies between the measurements and predictions led to comprehensive study of the flow in the wind tunnel and the discovery of a vortex upstream of the rotor at low advance ratios. The study presents results of RANS simulations. The static pressure and velocity profile in the domain near the rotor’s tip gap region were compared to measurements obtained from a pressure port array and a PIV visualization of the rotor in the wind tunnel

A high-frequency combination probe was used to measure dynamic flow quality in the test section of the NASA Langley 0.3-m Transonic Cryogenic Tunnel. The probe measures fluctuating stagnation (total) temperature and pressure, static pressure, and flow angles in two orthogonal planes. Simultaneous unsteady temperature and pressure measurements were also made in the settling chamber of the tunnel. The data show that the stagnation temperature fluctuations remain constant, and the stagnation pressure fluctuations increase by a factor of two, as the flow accelerates from the settling chamber to the test section. In the test section, the maximum rms value of the normalized fluctuating velocity is 0.7 percent. Correlation coefficients l failed to show vortlcity, entropy, or sound as the dominant mode of turbulence in the tunnel.

At certain tunnel operating conditions, periodic disturbances are seen in the data taken in the test section. A possible cause for the disturbances is found to be acoustic coupling of the test section and plenum chamber via the perforated side walls in the tunnel. The experimental data agree well with the acoustic coupling theory.

Master of Science

Much research and experiments have gone into studying idealized wing-body junction flows and their impact on horseshoe vortex and wake formation.  The vortices have been found to generate regions of high surface pressure fluctuations and turbulence that are detrimental to structural components and acoustics.  With the focus in the military and commercial industry on reducing the acoustical impact of aircraft and their engines, very little research has been done to examine the potential impact wing-body junctions may have on acoustics, especially for high lifting bodies such as propellers.  Two similar tests were conducted in the Virginia Tech Open Jet Wind Tunnel where boundary layer measurements, oil flow visualizations, acoustic linear array and surface pressure fluctuation measurements of a baseline Rood airfoil model and two novel junction fairing designs were all taken.  Boundary layer measurements were taken at four locations along the front half of the flat plate and the profiles were shown to be all turbulent despite the low Reynolds number of the flow, (test 1: Re_"<1400, test 2: Re_"<550).  Oil flow visualizations were taken and compared to those of previous researchers and the location of separation and line of low shear along with the maximum width of the wake and width of wake at the trailing edge all scaled relatively well with the Momentum Deficit Factor, defined for wing-body junction flows [Fleming, J. L., Simpson, R. L., Cowling, J. E. & Devenport, W. J., 1993. An Experimental Study of a Turbulent Wing-Body Junction and Wake Flow. Experiments in Fluids, Volume 14, pp. 366-378. ].  A linear microphone array was used to estimate the directivity of the facility acoustic background noise to be used to improve background subtraction methods for surface pressure fluctuation measurements.  Surface pressure fluctuation spectra were taken ahead of the leading edge of the plate and along the surface of the models.  These showed that the fairings reduced pressure fluctuations along the plate upstream of the leading edge, with fairing 1 reducing them to clean tunnel flow levels.  On the surface of the models, the fairings tended to reduce low frequency (<1000Hz) pressure fluctuation peaks when compared to the baseline model and increase the pressure fluctuations in the high frequency range.  Simple scaling arguments indicate that this spectral change may be more beneficial than detrimental as low frequency acoustics especially those between 800 Hz and 1200 Hz are the frequencies that humans perceive as the loudest noise levels.  Scaling the frequencies measured to those of full scale applications using Strouhal numbers show that frequencies below 1000 Hz in this experiment result in frequencies at the upper limit of the human hearing frequency range.  Low frequency acoustic waves also tend to travel farther and high frequency acoustic waves are more apt to be absorbed by the surrounding atmosphere.
Master of Science

An aeroacoustic study was conducted on a 26%-scale Boeing 777 main landing gear in the Virginia Tech (VT) Anechoic Stability Wind Tunnel. The VT Anechoic Stability Wind Tunnel allowed noise measurements to be carried out using both a 63-elements microphone phased array and a linear array of 15 microphones. The noise sources were identified from the flyover view under various flow speeds and the phased array positioned in both the near and far-field. The directivity pattern of the landing gear was determined using the linear array of microphones. The effectiveness of 4 passive noise control devices was evaluated. The 26%-scale model tested was a faithful reproduction of the full-scale landing gear and included most of the full-scale details with accuracy down to 3 mm. The same landing gear model was previously tested in the original hard-walled configuration of the VT tunnel with the same phased array mounted on the wall of the test section, i.e. near-field position. Thus, the new anechoic configuration of the VT wind tunnel offered a unique opportunity to directly compare, using the same gear model and phased array instrumentation, data collected in hard-walled and semi-anechoic test sections. The main objectives of the present work were (i) to evaluate the validity of conducting aeroacoustic studies in non-acoustically treated, hard-walled wind tunnels, (ii) to test the effectiveness of various streamlining devices (passive noise control) at different flyover locations, and (iii) to assess if phased array measurements can be used to estimate noise reduction. As expected, the results from this work show that a reduction of the background noise (e.g. anechoic configuration) leads to significantly cleaner beamforming maps and allows one to locate noise sources that would not be identified otherwise. By using the integrated spectra for the baseline landing gear, it was found that in the hard-walled test section the levels of the landing gear noise were overestimated. Phased array measurements in the near and far-field positions were also compared in the anechoic configuration. The results showed that straight under the gear, near-field measurements located only the lower-truck noise sources, i.e. noise components located behind the truck were shielded. It was thus demonstrated that near-field, phased-array measurements of the landing gear noise straight under the gear are not suitable. The array was also placed in the far-field, on the rear-arc of the landing gear. From this position, other noise sources such as the strut could be identified. This result demonstrated that noise from the landing gear on the flyover path cannot be characterized by only taking phased array measurement right under the gear. The noise reduction potential of various streamlining devices was estimated from phased array measurements (by integrating the beamforming maps) and using the linear array of individually calibrated microphones. Comparison of the two approaches showed that the reductions estimated from the phased array and a single microphone were in good agreement in the far-field. However, it was found that in the near-field, straight under the gear, phased array measurements greatly overestimate the attenuation.
Master of Science

Two experiments were conducted to investigate Adaptive Noise Cancelling and Cepstrum echo removal post-processing techniques on acoustic data from a linear microphone array in an anechoic chamber. A point source speaker driven with white noise was used as the primary signal. The first experiment included a background speaker to provide interference noise at three different Signal-to-Noise Ratios to simulate noise propagating down a wind tunnel circuit. The second experiment contained only the primary source and the wedges were removed from the floor to simulate reflections found in a wind tunnel environment. The techniques were applicable to both signal microphone and array analysis. The Adaptive Noise Cancellation proved successful in its task of removing the background noise from the microphone signals at SNRs as low as -20 dB. The recovered signals were then used for array processing. A simulation reflection case was analyzed with the Cepstral technique. Accurate removal of the reflection effects was achieved in recovering both magnitude and phase of the direct signal. Experimental data resulted in Cepstral features that caused errors in phase accuracy. A simple phase correction procedure was proposed for this data, but in general it appears that the Cepstral technique is and would be not well suited for all experimental data.
Master of Science

On-blade hot wire anemometry measurements as well as far field sound measurements at several receiving angles have been previously made for a rotor partially embedded in a boundary layer. The inflow distortion effect on the rotor angle of attack distribution was determined directly from the on-blade measurements, and was found to minimally affect the angle of attack at the blade tips and lower the angle attack in the rotor disk plane as the radial location moves towards the hub. A narrow, sharp increase in angle of attack as the rotor blades approached the wall was also observed, indicating blade interaction with flow reversal. The haystacking pattern, or spectral humps that appear at multiples of the blade passage frequency, was studied for a wide range of advance ratios. At high advance ratios, evidence of vortex shedding from the blade trailing edges was observed. For low advance ratios, the haystacks narrowed, became more symmetric and increased in number. A method of determining the average acoustic signature of an eddy passage through a rotor was developed from time delay aligning multiple microphone signals and eddy passages detected using the continuous wavelet transform. It was found that the eddy passage signatures were similar to a cosine wave with a Gaussian window. It was also found that normalized timescales obtained directly from the eddy passage signatures remained somewhat constant with advance ratio, but increases slightly for fixed free stream velocities with increasing rotor RPM. For advance ratios less than 0.6, the eddy passage signatures were dominated by a tonal component due to rotor ingestion of misaligned flow caused by a boundary layer separation at the wall. This indicates that flow reversal known as the Pirouette Effect is interacting with the rotor blades.
Master of Science

Le bruit tonal rayonné au bord de fuite des profils à faible nombre de Reynolds est un phénomène observé sur les ailes de drones ou micro-drones qui sont utilisés partout dans la vie quotidienne. La diminution de ce bruit va augmenter la survivabilité et l'efficacité des appareils dans le domaine militaire. De plus, cela va augmenter le champ des applications civiles et minimiser la pollution par le bruit. La réduction efficace du bruit est indispensable et, par conséquent, une compréhension complète du processus de rayonnement du bruit tonal du profil est nécessaire. Malgré le fait que des essais dédiés aient été réalisés depuis les années 70, il reste beaucoup de détails à expliquer. Le travail présenté est dédié à une étude expérimentale et analytique du bruit tonal. C'est une partie de collaboration entre l'Ecole Centrale de Lyon et Embry- Riddle Aeronautical University. Le but est de réaliser une caractérisation exhaustive des paramètres acoustiques et aérodynamiques du bruit tonal de bord de fuite d'un profil et de produire une base de données qui pourra être utilisée pour valider les simulations numériques réalisées dans le futur. Le profil symétrique NACA-0012 ainsi que le profil asymétrique SD7003 ont été testés pour une série d'angles d'incidence (de -10° à 10°) dans la soufflerie anéchoïque à jet ouvert de l'Ecole Centrale de Lyon pour des nombres de Reynolds modérés (0.6x105 < Rec < 2.6x105). Les mesures de pression aux parois et de pression acoustique en champ lointain pour différentes configurations ont permis d'observer une structure en escalier de la signature du bruit, de déterminer quelle face du profil a produit le bruit et de distinguer le rôle de la boucle de rétroaction. Des techniques supplémentaires de post-traitement comme l'analyse temps-fréquence ont montré l'existence de plusieurs régimes (un régime de commutation entre deux états, un régime d'une seul fréquence et un régime à plusieurs fréquences) de l'émission de bruit. L'analyse de bi-cohérence a montré qu'il y a des couplages nonlinéaires entre les fréquences. Une étude par l'anémométrie à fil chaud et par des techniques de visualisation de l'écoulement a montré que la formation d'une bulle de décollement est une condition nécessaire mais pas suffisante pour la génération du bruit. De plus, la localisation de la bulle est aussi importante et elle doit être suffisamment proche du bord de fuite. En outre, l'analyse de stabilité linéaire des résultats de simulations numériques a montré que des ondes de Tollmien-Schlichting sont transformées en ondes de Kelvin-Helmholtz dans la zone du décollement. Une prédiction analytique de l'amplitude des fréquences pures émises dans le champ lointain a été effectuée sur la base du modèle d'Amiet en supposant que le champ de pression pariétal est bidimensionnel. Les mesures de pression proches du bord de fuite du profil ont été prises comme données d'entrée. Les amplitudes prédites sont globalement en accord avec les mesures acoustiques. Après l'analyse de tous les résultats la description suivante du processus de rayonnement de sons purs peut être proposée. Les ondes de Tollmien-Schlichting qui se développent initialement dans la couche limite se transforment en ondes de Kelvin-Helmholtz le long de la couche de cisaillement de la bulle de décollement. Au bord de fuite du profil elles sont converties en ondes acoustiques qui forment un couplage fort avec les instabilités de couche limite plus en amont de l'écoulement, pilotant elles-mêmes le déclenchement de ces instabilités
The tonal trailing-edge noise generated by transitional airfoils is a topic of interest because of its wide area of applications. One of them is the Unmanned Air Vehicles operated at low Reynolds numbers which are widely used in our everyday life and have a lot of perspectives in future. The tonal noise reduction will increase the survivability and effectiveness of the devices in military field. Moreover it will enlarge the range of civil use and minimize noise pollution. The effective noise reduction is needed and therefore the complete understanding of the tonal noise generation process is necessary. Despite the fact that investigation of the trailing-edge noise was started since the seventies there are still a lot of details which should be explained. The present work is dedicated to the experimental and analytical investigation of the tonal noise and is a part of the collaboration project between Ecole Centrale de Lyon and Embry-Riddle Aerospace University. The aim is to conduct an exhaustive experimental characterization of the acoustic and aerodynamic parameters of the trailing-edge noise and to produce a data base which can be used for further numerical simulations conducted at Embry-Riddle Aerospace University. A symmetric NACA-0012 airfoil and a slightly cambered SD7003 airfoil at moderate angles of attack (varied from -10° à 10°) were tested in an open-jet anechoic wind tunnel of Ecole Centrale de Lyon at moderate Reynolds numbers (0.6x105 < Rec < 2.6x105). Measurements of the wall pressure and far-field acoustic pressure in different configurations allowed to observe the ladder-type structure of the noise signature, to determine which side produced tones and to distinguish the role of the acoustic feedback loop. Additional post-processing techniques such as time-frequency analysis showed the existence of several regimes (switching regime between two tones, one-tone regime and multiple-tones regime) of noise emission. The bicoherence analysis showed that there are non-linear relationships between tones. The investigation of the role of the separation area by hot-wire anemometry and flow visualization techniques showed that the separation bubble is a necessary but not a suficient condition for the noise generation. Moreover the location of the bubble is also important and should be close enough to the trailing edge. Furthermore the linear stability analysis of accompanying numerical simulation results showed that the Tollmien-Schlichting waves transform to the Kelvin-Helmholtz waves at the separation area. An analytical prediction of the tone levels in the far-field was done using Amiet's model based on the assumption of perfectly correlated sources along the span. The wall-pressure measurements close to the trailing edge were used as an input data. The comparisons of the predicted levels and measured ones showed a good agreement. After analysis of all results the following description of the tonal noise mechanism is proposed. At some initial point of the airfoil the Tollmien-Schlichting instabilities start. They are traveling downstream and continued to Kelvin-Helmholtz waves along the shear-layer of the separation bubble. These waves reach the trailing edge, scatter from it as acoustic waves, which move upstream. The acoustic waves amplify the boundary layer instabilities at some frequencies for which the phases of both motions match and creates the feedback loop needed to sustain the process

Depuis plusieurs décennies, le trafic aérien ne cesse de croître. Ainsi, près de 6 milliards de passagers transitent dans le monde par an. Les objectifs européens à l'horizon 2020 en terme d'émission sonore des aéronefs imposent une réduction de 10 dB par point de mesure par rapport aux aéronefs de l'an 2000. Dans ce contexte, le projet européen VALIANT (VALidation and Improvement of Airframe Noise prediction Tools) a pour but principal de tester, valider et améliorer les codes numériques et les modèles de prédiction du bruit de cellule (trains d'atterrissage + voilure) sur des géométries simplifiées afin de disposer de cas tests pour les recherches futures. L'objectif de la thèse, associé à la contribution de l'ECL dans ce projet, est de créer des bases de données expérimentales fiables sur des systèmes à deux éléments - bec/aile et aile/volet - et de modéliser analytiquement le bruit issu de tels systèmes. La thèse s'est concentrée sur un système aile/volet non porteur et parallèle dans un écoulement de soufflerie à veine ouverte, en configuration d'alignement ou de recouvrement partiel, menant à de possibles interactions aérodynamiques et/ou acoustiques. Les mesures ont été faites pour différentes vitesses d'écoulement (30 − 100 m~s), avec une attention particulière à 50 m~s (M0 ∼ 0, 15). Le taux de turbulence de l'écoulement incident est modifiable par l'ajout d'une grille de turbulence à maille large placée dans la section de sortie du convergent. Les résultats aérodynamiques (fil chaud, pression en paroi) ont révélé la présence d'une forte interaction lorsque la distance entre les deux corps est de l'ordre de grandeur de la couche limite turbulente au bord de fuite de l'aile. De plus, le couplage acoustique a lieu lorsque la longueur de recouvrement est positive ou nulle. Des mesures de localisation de sources menées par l'ONERA/DSNA ont permis de valider les mesures de champ lointain en confirmant l'absence de sources de bruit d'installation en dessous de 10 kHz. Par ailleurs, des comparaisons avec les simulations numériques donnent de bons accords. Du point de vue analytique, le problème mathématique de deux plaques planes en recouvrement partiel dans un écoulement uniforme a été posé et une réduction bidimensionnelle a été justifiée. Le problème n'ayant pas de solution exacte, plusieurs modèles issus de la littérature - théories de Howe et d'Amiet - ont été étudiés. Les plus pertinents ont été confrontés aux résultats expérimentaux, révélant les limites asymptotiques de ces modèles. Un modèle original est alors proposé pour la géométrie du problème posé, sans hypothèse restrictive. La démarche est basée sur une procédure de diffraction itérative permettant de prendre en compte la proximité des deux corps et utilisant la fonction de Green exacte du demi-plan en écoulement uniforme. Le modèle prédit des comportements qualitatifs angle/fréquence proches des résultats expérimentaux. La prise en compte de la statistique des rafales incidentes reste néanmoins à effectuer afin de procéder à des comparaisons quantitatives. Une campagne expérimentale complémentaire avec une marche descendante permet de mettre en évidence les écoulements de cavité arrière d'une aile, plus proche de la réalité. De même, des mesures sur une configuration bec/aile a été testée et la prise en compte de la déflexion du jet de la soufflerie pour la réfraction des ondes sonores par la couche de cisaillement a été proposée.

Acoustic and aerodynamic measurements have been carried out on a rotor operating in a planar turbulent boundary layer near a wall for a variety of thrust conditions and yaw angles with respect to the inflow. At the highest thrust condition a strong flow reversal in the wall-rotor tip gap was observed. Average velocity fields filtered by the angular position of the rotor show that the flow reversal is fed by jets of fluid that tend to form below the blade as it passes by the wall. Instantaneous velocity measurements show the presence of strong vortices in the tip gap. These vortices were characterized and found to be both stronger and more numerous on the downstroke side of the tip gap. Additionally, vortices with the same handedness as the bound circulation in the blade were more numerous and only located on the downstroke side of the tip gap. Those with the opposite handedness were found to be only located on the upstroke side. Unexpectedly strong far-field acoustic response at the blade passage frequency at this highest thrust condition and is believed to be due to an interaction of the blade tip with these vortices. At moderate thrust, when the rotor was yawed toward the downstroke side the far field acoustic response at the blade passage frequency was found to increase. The opposite was true as it was yawed toward the upstroke side. At the highest thrust, however the unyawed rotor had the strongest blade passage frequency response which is believed to be due to stronger vortex-tip interaction in this case.
Master of Science

Cette étude vise à caractériser en soufflerie les mécanismes aérodynamiques à l’origine de la génération puis la transmission des fluctuations de bruit dans un modèle d’habitacle automobile. Le banc d’essai conçu en soufflerie anéchoïque consiste en un écoulement dont la vitesse incidente est modulée par un volet mobile, et qui par interaction avec une marche montante rayonne un bruit aéroacoustique transmis à travers une vitre dans un caisson anéchoïque. L’approche retenue consiste, pendant le temps de maniement du volet, à mesurer et relier le champ de vitesse externe mesuré à l’aide de la technique de vélocimétrie laser par images de particules (TR-PIV échantillonnée à 20 kHz) à la pression pariétale d’une part, puis au champ acoustique interne obtenu par transmission d’autre part. Des outils de corrélation spatio-temporelle sont alors utilisés pour mettre en évidence les zones de l’écoulement les plus corrélées avec les fluctuations d’énergie de la pression pariétale et celles du niveau de bruit intérieur. La fluctuation du chargement aérodynamique de la vitre sous la bulle de recirculation est logiquement liée à l’activité instationnaire de cette dernière, puis plus en aval, au lâcher tourbillonnaire. Quant au bruit transmis dans le modèle d’habitacle, il semble principalement lié aux fluctuations de vitesse dans la couche de cisaillement. Enfin, une procédure spécifique a permis d’évaluer le caractère quasi-stationnaire des variations temporelles des quantités fluctuantes ainsi que la réponse acoustique de la vitre
This study aims at characterizing in a wind tunnel the aerodynamic mechanisms contributing to the generation and transmission of the noise fluctuations into a car interior model. The test bench designed in anechoic wind tunnel consists of a flow whose incoming flow velocity is modulated by a mobile flap, and which by interaction with a forward-facing step radiates an aeroacoustic noise transmitted through a glass into an anechoic box. The adopted approach consists, during the flap handling time, in measuring and connecting the external velocity field measured using the Time-Resolved laser Particle Image Velocimetry technique (TR-PIV at sampling frequency 20 kHz) to the wall pressure on the one hand, and then to the internal acoustic field obtained by transmission on the other hand. Spatio-temporal correlation tools are then used to highlight the flow areas that are the most correlated with the energy fluctuations of the wall pressure and with those of the internal noise level. The fluctuation of the aerodynamic loading of the window under the recirculation bubble is logically related to the unsteady activity of the latter, then further downstream to the vortex stream. As for the noise transmitted into the cabin model, it seems mainly related to the speed fluctuations in the shear layer. Finally, a specific procedure allows to evaluate the quasi-steady nature of the temporal variations of the fluctuating quantities, as well as the acoustic response of the window

En soufflerie subsonique, on genere un tourbillon a partir du decrochage dynamique d'un volet mis rapidement en incidence par commande numerique. Ce tourbillon unique et reproductible se detache et est convecte par l'ecoulement sur un profil naca0012. Cette maquette, montee sur une balance de portance et de trainee instationnaires est munie de prises de pression multiplexees sur un capteur par un commutateur pneumatique

Rising fuel cost has motivated increased fuel efficiency for freight trains. At cruising speed,the largest contributing factor to the fuel consumption is aerodynamic drag. As a result of stagnationand flow separation on and around lead and trailing cars, the first and last railcars experiencegreater drag than intermediate cars. Accordingly, this work focused on reducing drag on lead locomotivesby designing and optimizing an add-on nose fairing that is feasible for industrial operation.The fairing shape design was performed via computational fluid dynamic (CFD) software.The simulations consisted of two in-line freight locomotives, a stretch of rails on a raised subgrade,a computational domain, and a unique fairing geometry that was attached to the lead locomotive ineach non-baseline case. Relative motion was simulated by fixing the train and translating the rails,subgrade, and ground at a constant velocity. An equivalent uniform inlet velocity was applied atzero degree yaw to simulate relative motion between the air and the train.Five fairing families-Fairing Families A-E (FFA-FFE)-are presented in this thesis.Multidimensional regressions are created for each family to approximate drag as a function ofthe design variables. Thus, railroad companies may choose an alternative fairing if the recommendedfairing does not meet their needs and still have a performance estimate. The regression forFFE is used as a surrogate model in a surrogate based optimization. Results from a wind tunneltest and from CFD are reported on an FFE geometry to validate the CFD model. The wind tunneltest predicts a nominal drag reduction of 16%, and the CFD model predicts a reduction of 17%.A qualitative analysis is performed on the simulations containing the baseline locomotive, the optimalfairings from FFA-FFC, and the hybrid child and parent geometries from FFA & FFC. Theanalysis reveals that optimal performance is achieved for a narrow geometry from FFC becausesuction behind the fairing is greatly reduced. Similarly, the analysis reveals that concave geometriesboost the flow over the top leading edge of the locomotive, thus eliminating a vortex upstreamof the windshields. As a result, concave geometries yield greater reductions in drag.The design variable definitions for each family were strategically selected to improve manufacturability,operational safety, and aerodynamic performance relative to the previous families.As a result, the optimal geometry from FFE is believed to most completely satisfy the constraintsof the design problem and should be given the most consideration for application in the railroadindustry. The CFD solution for this particular geometry suggests a nominal drag reduction of 17%on the lead locomotive in an industrial freight train.

Low disturbance wind tunnels, such as the Klebanoff–Saric Wind Tunnel (KSWT), offer an ideal environment to study boundary layer transition. In particular, the leading-edge receptivity of sound can be measured by creating acoustic disturbances that interact with the leading edge of a model to create Tollmien–Schlichting Waves. The magnitude and composition (sound, turbulence) of the background disturbances can affect these experiments, so the background disturbances should be minimized and documented thoroughly. The purpose of this thesis is to document the background acoustic signature of the KSWT and describe infrastructure upgrades for acoustic receptivity experiments. The measurements presented in this thesis will support future receptivity measurements in the KSWT. Microphone measurements revealed several important acoustic features in the tunnel. Cross correlations showed that two sources of low-frequency unsteadiness (the extended diffuser and corner two) create large pressure fluctuations that dominate the pressure spectrum. Directional separation of waves in the test section revealed that motor and blade passing noise travels primarily upstream into the test section. Finally, the acoustic treatments in the plenum are effective at removing sound from the tunnel. A wall of speakers was installed in the plenum to enable acoustic receptivity experiments. The speakers create both the primary downstream traveling waves and reflected upstream traveling waves in the test section. An adaptive closed loop control system was installed to reduce the amplitude of the reflected waves during acoustic forcing. Although the performance of the control system is frequency dependent, the technique was implemented successfully. The reduction in the diffuser reflection will increase the quality of future acoustic receptivity experiments in the KSWT.