Supersonic Jet Noise Reduction Research Articles

Investigation on supersonic jet noise reduction by water injection: Effects of water injection parameters

In order to protect the payload and the rocket structure from severe vibrations, water injection is commonly used on launch pads to reduce the high noise level radiated by supersonic plumes at lift-off. Even if this technique is widely used, the mechanisms behind sound reduction remain unclear. Sound reduction occurs due to multiple phenomena, each of them having different effects on the jet noise. Experiments based on acoustic measurements have been carried out on a hot supersonic jet on MARTEL facility (Mach number of 3 and a total temperature of 1700 K) to deeper identify the effect of evaporation and water injection parameters. Water flow rate, water injection speed and injection distance to the nozzle have been tested independently to identify the most important water injection parameters. It appears that water flow rate is the most important parameter to decrease noise level and that injecting water at high speed results in noise increase in the downstream direction. Results also highlight the importance of having liquid droplets at the end of the potential core to reduce noise.

Flow and acoustic fields investigation of noise reduction by micro vortex generators in supersonic nozzles

The role of micro-vortex generators (MVGs) in supersonic jet noise reduction is investigated. Studies are performed to understand the noise reduction mechanisms of these devices. MVGs are implemented on a scale model representative of GE-F404 nozzles. Configurations consisting of single and dual arrays of MVGs were tested for pressure ratios relevant to takeoff operating conditions. A combination of laboratory measurements and large-eddy simulations are used. Particle image velocimetry reveals that MVGs placed inside the nozzle form oblique shocks that interact with the jet plume's shock cell structure and greatly modify the shock-cell structure issued from the nozzle throat. This modification can weaken the jet plume shock-cell structure and even reduce the jet core velocities. Convective velocities estimated from the high-speed Schlieren imaging showed a significant reduction in magnitude caused by MVGs. When compared to the baseline design, the MVG nozzles showed noise reduction up to 10 dB in the upstream direction and near 5 dB in the peak downstream radiation angle at cold jet conditions. Near-field acoustic measurements showed a significant reduction of low-frequency turbulent mixing noise. Scaling analysis showed that MVGs are capable of delivering the same noise reduction performance across different model scales.

Optical-acoustics source analysis of supersonic jet noise reduction using micro vortex generators

A new supersonic jet noise reduction technology has been developed using Micro Vortex Generators (MVGs) by the collaboration between the University of Cincinnati and the Naval Research Laboratory. MVGs are used on model scale nozzles that are representative of GE F404 engine nozzles. Noise reductions up to −10 dB have been observed in both laboratory measurements and LES simulations at conditions related to take off in the overexpanded regime. Analysis of the acoustic field and flow field using Schlieren visualization reveal the noise reduction mechanisms associated with MVGs. Direct visualization of the changes in shock cell spacing, Large Coherent Structures (LCS) formation, and their convective velocity are identified and those changes modify the downstream propagating hydrodynamic waves and the upstream propagating acoustics waves. Spectral Proper Orthogonal Decomposition (SPOD) is utilized to examine the flow sources at frequencies associated with the noise components observed in the acoustic spectra to explain the noise reduction mechanisms of MVGs.

Spectral proper orthogonal decomposition analysis of flowfield for supersonic nozzle jet noise reduction

Spectral proper orthogonal decompositions (SPOD) is the frequency domain form of proper orthogonal decomposition (POD). SPOD is shown to be directly applicable to jet noise studies. A computational SPOD analysis is performed on the Large-Eddy Simulation (LES) computational data for both the baseline nozzle flow and a modified nozzle flow. The mode energy analysis from SPOD shows that for the baseline nozzle, the low-rank behavior is found at frequencies at which a large separation occurs. The low-rank behavior disappears for the modified nozzle flow where no significant peaks are detected. The coherent structures of the low frequency show the Kelvin–Helmholtz type instability. It is also shown that the reconstructed flow field using the first decades of SPOD modes can capture the major shock-expansion based interactions that are present within the original flow field. This suggests that the method of SPOD-based reconstruction can be used to carry out additional modal and acoustic analyses of jet flows.

Passive jet noise reduction using contoured inserts

Successful supersonic jet noise reduction requires an approach that simultaneously (1) breaks up coherent structures in the jet shear layer turbulence, (2) reduces convection velocity of the acoustic sources, and (3) weakens the shock structure in the plume. If any one of these is done in isolation the result is typically a shift in frequency content and not an overall reduction in source amplitude. Using a set of contoured inserts placed within the expansion section of the nozzle allows all three of these design goals to be addressed. The contour weakens the shock structure while simultaneously generating strong streamwise vorticity the enhances mixing in the jet shear layer. Assuming that future high-performance aircraft would possess a variable area ratio nozzle with independent exit and throat area controls, multi-objective design optimization has yielded a design that maximizes noise reduction with minimal thrust penalty in a variable area ratio framework. Model-scale acoustic data are presented to demonstrate the efficacy of the design.Successful supersonic jet noise reduction requires an approach that simultaneously (1) breaks up coherent structures in the jet shear layer turbulence, (2) reduces convection velocity of the acoustic sources, and (3) weakens the shock structure in the plume. If any one of these is done in isolation the result is typically a shift in frequency content and not an overall reduction in source amplitude. Using a set of contoured inserts placed within the expansion section of the nozzle allows all three of these design goals to be addressed. The contour weakens the shock structure while simultaneously generating strong streamwise vorticity the enhances mixing in the jet shear layer. Assuming that future high-performance aircraft would possess a variable area ratio nozzle with independent exit and throat area controls, multi-objective design optimization has yielded a design that maximizes noise reduction with minimal thrust penalty in a variable area ratio framework. Model-scale acoustic data are presented to d...

Use of Thermal Nonuniformity to Reduce Supersonic Jet Noise

It is shown experimentally that thermal nonuniformity can reduce peak supersonic jet noise while keeping static thrust levels equivalent. A thermal nonuniformity is generated by introducing an unheated stream on the centerline of a plenum containing heated air. This axisymmetric arrangement was studied with the hypothesis that the convection and structure of plume turbulence could be changed by perturbations induced by the thermal nonuniformity. The results for ideally expanded and overexpanded jets indicate reductions in peak narrowband spectral sound pressure levels upstream of peak directivity directions for nonuniform jets compared with the baseline uniform jets, even for a modest temperature difference between the core jet and the unheated stream. The mechanisms for this reduction are examined based on wavenumber–frequency analyses using the far-field acoustic spectra, suggesting that peak spectral energies shift to higher wavenumbers when the thermal nonuniformity is introduced. Convection velocities of radiating structures calculated from the spectral peaks show a reduction of 10% for the design jet condition. These results indicate that temperature-driven velocity deficits may be useful for developing supersonic jet noise reduction strategies, while even greater reductions are thought feasible by increasing the ratio between the heated and unheated stream temperatures.

Elimination of Shock-Associated Noise in Supersonic Jets by Destructive Wave Interference

A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied, resulting in unique acoustic behavior and flowfield modifications. For most conditions, the acoustics are relatively unaffected or increased, but for very specific conditions, noise was drastically decreased. For optimized conditions, the shock noise was completely eliminated, and in other cases, a jet instability was generated that significantly decreased high-frequency noise. Measurements of the velocity field indicated that shock interaction, due to shocks from the injection jets, interacts with the primary jet shocks and significantly reduces the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with large-eddy simulation, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of overall sound pressure level of at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction and destructive interference of the shock structure in the jet is reported.

Partial-field decomposition analysis of full-scale supersonic jet noise using optimized-location virtual references.

Supersonic jet noise reduction efforts benefit from targeted source feature extraction and high-resolution acoustic imaging. Another useful tool for feature extraction is partial field decomposition of sources into independent contributors. Since such decomposition processes are nonunique, care must be taken in the physical interpretation of decomposed partially coherent aeroacoustic fields. The optimized-location virtual reference method (OLVR) is a partial field decomposition designed to extract physically meaningful source and field information through the strategic placement of virtual references within a reconstructed field. The OLVR method is applied here to obtain spatially distinct and ordered partial sources at multiple frequencies of a full-scale, high-performance supersonic jet engine operating at 100% engine power. Partial sources are shown to mimic behaviors of the total source distributions including monotonic growth and decay. Because of finite spatial coherence, multiple partial sources are used to reproduce far-field radiation away from the main lobe, and the number of required sources increases with increasing frequency. An analytical multiwavepacket model is fitted to the partial sources to demonstrate how OLVR partial fields can be leveraged to produce reduced-order models.

Noise Reduction in Supersonic Jets Exhausting over a Simulated Aircraft Carrier Deck

An innovative noise reduction method for supersonic exhaust jets was studied in a model-scale aircraft carrier environment. Acoustic measurements of model exhaust jets with (and without) distributed blowing, producing “fluidic inserts,” were performed. The model carrier environment consisted of a ground plane of adjustable distance below the jet, and a simulated jet blast deflector similar to those found in practice. The noise reduction of fluidic insert jets, above a ground plane, with steering of the “quiet planes” was examined with heat-simulated jets using near- and far-field pressure measurements. For jets exhausting over a ground plane, the fluidic inserts reduced the overall sound pressure level by 3–5 dB in the direction of maximum noise radiation. Upstream and sideline angles showed very little or no increase in sound level. Jets impinging on a modeled jet blast deflector were tested in addition to jets solely in the presence of a ground plane. The deflector resulted in downstream acoustic shielding and an increase in low-frequency noise. The region of maximum noise radiation for heat-simulated jets from nozzles with fluidic inserts impinging on the jet blast deflector was reduced in level by 4–7 dB. This region includes areas where carrier personnel are located.

Design and Analysis of a Supersonic Jet Noise Reduction Concept

The design and analysis of a simple jet noise reduction concept is discussed. The concept is intended for use on the type of supersonic exhaust nozzles typically employed on tactical aircraft. The concept addresses both broadband shock-associated noise and turbulent mixing noise. Broadband shock-associated noise is addressed through a reduction in the effective exhaust area, which reduces the strength of the shock cell structure in the jet. Turbulent mixing noise is reduced by enhancement of mixing in the jet shear layer, which creates a shorter region of strongly turbulent flow and breaks up the large-scale turbulent structures. This paper describes an active control device that deflects a fraction of the adjustable seals in the divergent section of the engine exhaust nozzle. After takeoff, the deflected seals are returned to their undeflected position. Very favorable jet noise reductions are demonstrated at multiple observer angles for nominal takeoff conditions.

Acoustics measurements of military-style supersonic beveled nozzle jets with interior corrugations

Increasingly powerful and noisy military aircraft have generated the need for research leading to the development of supersonic jet noise reduction devices. The hot, high speed supersonic jets exhausting from military aircraft during takeoff present a most challenging problem. The present study extends prior research on two methods of noise reduction. The first is the internal nozzle corrugations pioneered by Seiner et al. and the second is the beveled exit plane explored most recently by Viswanathan. A novel research idea of creating fluidic corrugations similar to the nozzle corrugations has been initiated by Penn State. To further the understanding and analysis of the fluidic corrugations, the present study focuses on the flow field and acoustic field of nozzles with two, three, and six conventional, hardwalled corrugations. The effect of the combination of the internal corrugations with a beveled nozzle is explored. The results show that significant noise reductions of over 3 dB of the mixing noise and the broadband shock-associated noise can be achieved. The combination of the beveled nozzle and the internal nozzle corrugations showed that there is less azimuthal dependence of the acoustic field than for the purely beveled nozzle. The combination nozzle was shown to reduce the noise over a wider range of polar angles and operating conditions than either the purely beveled nozzle or the purely corrugated nozzle.

Supersonic Jet Noise: Main Sources and Reduction Methodologies

The large velocity ratio and the presence of Shocks in the exhaust plume from low bypass engines or supersonic jetliners cause jet noise to be dominant component of overall aircraft noise, and therefore is an important issue in design of the next generation of civil supersonic transport. Jet noise reduction technology also has application in the design of high- performance tactical aircraft. Jet noise is of particular concern on aircraft carriers where it is necessary for deck crew to be in relatively close proximity to the aircraft at takeoff and landing. In this paper, a brief discussion about supersonic jet noise sources and a review of the main passive technologies employed for the reduction of supersonic jet noise are presented.

Fluidically Enhanced Chevrons for Supersonic Jet Noise Reduction

An experimental and computational investigation of a combination of fluidic injection and chevrons (fluidically enhanced chevrons) for supersonic jet noise reduction was performed. Previous studies have shown that chevrons underperform in overexpanded flow due to reductions in effective penetration. Consequently, this study focuses on improvements gained by fluidic enhancement in the overexpanded regime. Acoustic results indicated the fluidically enhanced chevrons outperform the chevrons, with additional overall sound pressure level reductions of 2 dB in the upstream direction and nearly 1.5 dB in the downstream direction. Spectral results indicated that primary benefits were in shock and low-frequency noise. A small high-frequency penalty was the only observed detriment. Time-averaged velocity and turbulence quantities as well as shock cell spacing, were computed by large-eddy simulation and then compared to particle imaging velocimetry and shadowgraph results. These flowfield measurements indicated that the fluidically enhanced chevrons modify the flowfield by reducing the shock cell spacing and shock strength and increasing the upstream jet half-width, peak and integrated turbulence values, and shear-layer thickness. These modifications were caused by the introduction of streamwise vortices with over four times the magnitude of the unenhanced chevrons. Noise reductions were attributed to flowfield modifications through the use of several theoretical models, such as Powell’s screech formula.

Supersonic Jet Noise Reduction by Chevrons and Fluidic Injection

This work focuses on the noise reduction capabilities of chevrons, fluidic injection, and a combination of both. The control mechanisms were experimentally investigated for over, under, and ideally expanded operating conditions. Acoustic far-field data was collected to quantify noise reductions and changes to the flow field through use of theoretical relations. Results show appreciable noise reduction by both fluidic injection and chevrons. Optimal performance of the two technologies occured at opposite ends of the operation envelope, with the chevrons performing better in the underexpanded regime and the fluidics in the overexpanded regime. The combination of the two technologies was also shown to achieve substantial noise reduction, but direct additive benefits were not always gained. This result is still important as it shows fluidic injection can be employed on complex geometry nozzles, such as that on the F-35, and still achieve noise reduction.

Recently investigated subsonic and supersonic jet noise reduction techniques

Recently investigated subsonic and supersonic jet noise reduction techniques

Noise reduction in supersonic jets by nozzle fluidic inserts

Professor Philip Doak spent a very productive time as a consultant to the Lockheed-Georgia Company in the early 1970s. The focus of the overall research project was the prediction and reduction of noise from supersonic jets. Now, 40 years on, the present paper describes an innovative methodology and device for the reduction of supersonic jet noise. The goal is the development of a practical active noise reduction technique for low bypass ratio turbofan engines. This method introduces fluidic inserts installed in the divergent wall of a CD nozzle to replace hard-wall corrugation seals, which have been demonstrated to be effective by Seiner (2005) [1]. By altering the configuration and operating conditions of the fluidic inserts, active noise reduction for both mixing and shock noise has been obtained. Substantial noise reductions have been achieved for mixing noise in the maximum noise emission direction and in the forward arc for broadband shock-associated noise. To achieve these reductions (on the order of greater than 4 and 2dB for the two main components respectively), practically achievable levels of injection mass flow rates have been used. The total injected mass flow rates are less than 4% of the core mass flow rate and the effective operating injection pressure ratio has been maintained at or below the same level as the nozzle pressure ratio of the core flow.

Supersonic Jet Noise Reduction by Microjet Injection

The effect of microjet (μjet) injection on the noise from supersonic jets is investigated. One convergent and three convergent-divergent (C–D) nozzles, covering design Mach numbers ( MD) 1.0 to 2.2, are used in the study; all nozzles have the same exit diameter ( D). The μjets are injected perpendicular to the primary jet at the nozzle lip from six equally-spaced ports; each port has a diameter of 0.0054 D. Effects in the over-expanded and under-expanded regimes as well as one case of fully expanded condition are explored. Relative to the effect on subsonic jets, larger reduction in the overall sound pressure level (OASPL) is achieved in most supersonic conditions. While the injection readily eliminates screech tones with the convergent nozzle it becomes increasingly ineffective in screech reduction with nozzles of higher MD. With all nozzles, the injection is often found to amplify the broadband shock-associated noise; the overall noise reduction occurs due to a suppression of broadband levels especially at lower frequencies. With the shock still within the divergent section of the C–D nozzles, there is ‘excess broadband noise’ and sometimes there are ‘transonic tones’; the injection is found to affect the tones very little but reduce the broadband noise component significantly. For shock-free, fully expanded condition, the OASPL reduction in the peak noise radiation direction is comparable to that in a subsonic case; the same correlation, found earlier for subsonic cases, applies.

Acoustic assessment of small-scale military-style nozzles with chevrons

With the emergence of more powerful fighter aircraft, supersonic jet noise reduction devices are being intensively researched. Small-scale measurements are a crucial step in evaluating the potential of noise reduction concepts at an early stage in the design process. With this in mind, the present study provides an acoustic assessment of small-scale military-style nozzles with chevrons. Comparisons are made between the present measurements and those made by NASA at moderate scale. Measurements made with baseline nozzles (without chevrons) show excellent agreement with NASA data establishing the accuracy of the scaling methodology. The effect of chevrons on supersonic jets is then investigated for cold jets, highlighting the crucial role of the jet operating conditions on the effects of chevrons on the jet flow and subsequent acoustic benefits. At low Reynolds numbers (small scale) the penetration of the chevrons in the jet flow is the most important chevron parameter in reducing the generated noise. A small-scale heat simulated jet is investigated in the over-expanded condition and shows no substantial noise reduction from the chevrons. This is contradictory to moderate-scale measurements. The discrepancy is attributed to a Reynolds number low enough to sustain an annular laminar boundary layer in the nozzle that separates in the over-expanded flow condition. Transition of the boundary layer to turbulent flow is induced with inner roughness of the nozzle and results in more noise reduction with the chevrons. The resulting effect is comparable to results from NASA, seemingly validating the hypothesis made that jets of too low Reynolds number cannot be used directly to accurately measure chevron noise reduction. These results are important in assessing the limitations of small-scale measurements in this particular jet noise reduction method. © 2012 Institute of Noise Control Engineering.

Control of supersonic jet noise using a wire device

The present study describes a new technique for the reduction of supersonic jet noise using a control wire device that is placed into the supersonic jet stream. The control wire device is composed of long cylinders with a very small diameter and its location is varied to investigate the control effectiveness of supersonic jet noise. The jet pressure ratio is varied to obtain the supersonic jets which are operated in a wide range of over-expanded to moderately under-expanded conditions. A high-quality Schlieren optical system is used to visualize the flow field of supersonic jets both with and without the control wire device. In order to quantify the control effect of the wire device on a supersonic jet, pressure measurements are also accomplished. Acoustic measurements are performed to obtain the overall sound pressure level and noise spectra. The results obtained show that the present wire device effectively breaks the shock-cell structure, reduces the shock strength, and consequently leads to a substantial suppression of supersonic jet noise. The location of the control wire device is an important factor in reducing the supersonic jet noise. The present wire device suppresses the screech tones and the broadband shock-associated noise as well as the overall sound pressure level, when it is placed at a location smaller than three times the exit diameter of nozzle in the downstream of the nozzle exit. For over-expanded jets, the noise control effectiveness of the wire device appears more significant, compared to under-expanded jets.

408 クラウン型ノズルを用いた超音速ジェットの騒音の低減(流体工学 : 圧縮性流れI)

408 クラウン型ノズルを用いた超音速ジェットの騒音の低減(流体工学 : 圧縮性流れI)