Showing papers in "International Journal of Aeroacoustics in 2016"
TL;DR: In this paper, the noise produced by aerodynamic interaction between a circular cylinder and an airfoil in a tandem arrangement was investigated numerically using incompressible large eddy simulations.
Abstract: Noise produced by aerodynamic interaction between a circular cylinder (rod) and an airfoil in a tandem arrangement is investigated numerically using incompressible large eddy simulations. Quasi-per...
32 citations
TL;DR: In this paper, the authors presented jet noise computations performed using the original and some recently proposed modified formulations of detached-eddy simulation, based on alternative definitions of the subgrid length-scale and/or a modified version of the Subgrid Spalart-Allmaras model, which involves the Wall-Adapting Local Eddy-viscosity model.
Abstract: The paper presents jet noise computations performed using the original and some recently proposed modified formulations of detached-eddy simulation, based on alternative definitions of the subgrid length-scale and/or a modified version of the subgrid Spalart-Allmaras model, which involves the Wall-Adapting Local Eddy-viscosity model. The modifications are aimed at the elimination or, at least, a significant weakening of a known flaw of detached-eddy simulation, namely, the severe delay of the Kelvin–Helmholtz instability and transition from fully modeled to mostly resolved turbulence in the free and separated shear layers. This flaw makes the original detached-eddy simulation formulation, in fact, non-applicable to the prediction of the noise of high Reynolds number jet flows when typical grids are used, and has led to the use of Implicit Large-Eddy Simulation instead. Based on examples of application of these modifications to such flows, already available in the literature, they were found capable of res...
28 citations
TL;DR: The results of computational fluid dynamics for flows around the propellers and compares their aerodynamic performance as well as their acoustics show that the wing, nacelle and fuselage around the blades influence the obtained level of noise but not the frequency content.
Abstract: This paper presents the results of computational fluid dynamics for flows around the propellers and compares their aerodynamic performance as well as their acoustics. After some validation of the employed computational fluid dynamics method, using wind tunnel experiments, a modern propeller design was assessed. Using the same baseline blade, different propellers were put together by adding stagger at the blade hub and small variations of the inter-blade angle. The employed method produced results showing differences in the propeller acoustics regarding the frequency spectrum produced by each design and the level of the acoustic tones. The effect of changing the hub was to generate frequencies in-between the tones of the baseline design while keeping the overall propeller performance the same. The effect of the employed hub changes was to generate tones in-between the harmonics of the fundamental blade passing frequency that dominated the baseline design. Installed and un-installed blades were compared and...
21 citations
TL;DR: In this paper, large-eddy simulations are performed for hot and cold jets with and without a flight stream, and the acoustic and flight stream Mach numbers are 0.875 and 0.3, respectively.
Abstract: Large-eddy simulations are performed for hot and cold jets with and without a flight stream. The acoustic and flight stream Mach numbers are 0.875 and 0.3, respectively. The temperature ratios for ...
21 citations
TL;DR: In this article, the flow induced by the clearance between the tip of an isolated airfoil and an end-plate is investigated numerically, using a zonal approach with large-eddy simulation in the region of interest.
Abstract: The flow induced by the clearance between the tip of an isolated airfoil and an end-plate is investigated numerically, using a zonal approach with large-eddy simulation in the region of interest. The results are analyzed in comparison with available experimental data, presented in a companion paper. The incoming boundary layer and the pressure distribution around the blade are evaluated. The description of the inflow-jet deviation, with an averaged approach, enables to represent the proper loading on the airfoil. Also, particular attention is paid to the powerful tipleakage vortex. The vortex characteristics are investigated using specific functions to locate its center and quantify its width. Overall, good results are obtained for the flow statistics and spectra. Furthermore, a very good description of the far-field pressure is achieved using the acoustic analogy, and the results confirm that the tip-flow essentially radiates in the central frequency range (0.7 kHz, 7 kHz).
20 citations
TL;DR: In this paper, a co-axial subsonic unheated jet with and without a swept lifting wing at free-stream conditions from a recent jet-wing TsAGI experiment is considered.
Abstract: A co-axial subsonic unheated jet with and without a swept lifting wing at free-stream conditions from a recent jet–wing TsAGI experiment is considered. For computational modelling, Monotonically In...
20 citations
TL;DR: In this article, a combined acoustic-aerodynamic diagnostics methodology is presented, involving the phased array microphone technique and an in-house rotating source identifier processing algorithm, which makes possible the industrial onsite investigation of unducted or short-ducted rotor-only axial fans.
Abstract: A combined acoustic-aerodynamic diagnostics methodology is presented herein, involving the phased array microphone technique and an in-house rotating source identifier processing algorithm. The methodology makes possible the industrial onsite investigation of unducted or short-ducted rotor-only axial fans. Its application is illustrated in a case study of a free-inlet, free-exhausting fan, surveyed from the upstream direction. A methodology is outlined for guaranteeing the appropriateness of averaging of the phased array microphone records. A technique is proposed for eliminating the ambiguity of the angular position of the rotor noise sources. A complete set of noise source maps of various frequencies have been evaluated. Noise sources, such as tip leakage flow and suction side blade boundary layer flow, have been identified. Empirical correlations have been pointed out between indicators of aerodynamic noise and aerodynamic loss along the blade span. Such correlations may contribute to redesign guidelines for simultaneous reduction of noise and improvement of efficiency at prescribed fan performance.
17 citations
TL;DR: In this article, the use of a single optimized bump placed on the leading edge of the front blade of a counter rotating open rotor is proposed as a passive device to reduce the interaction noise at low-speed and high-speed.
Abstract: The use of a single optimized bump placed on the leading edge of the front blade of a counter rotating open rotor is envisaged as passive device to reduce the interaction noise at low-speed and hig...
16 citations
TL;DR: In this article, the effect of the upstream edge geometry on attenuating undesirable effects is investigated experimentally for flows over shallow rectangular cavities with two different aspect ratios of L/D 1 and 1.67.
Abstract: The flow-excited acoustic resonance phenomenon is created when the flow instability oscillations are coupled with one of the acoustic modes of a confined duct, which in turn generates acute noise problems and/or excessive vibrations. In this study, the effect of the upstream edge geometry on attenuating these undesirable effects is investigated experimentally for flows over shallow rectangular cavities with two different aspect ratios of L/D = 1 and 1.67, where L is the cavity length and D is the cavity depth, for Mach number up to 0.45. The acoustic resonance modes of the cavity are self-excited due to the development of free shear layers over the cavity mouth. Twenty four different upstream cavity edges are investigated in this study, including round edges, chamfered edges, vortex generators, and spoilers with different sizes and configurations. The results for each upstream cavity edge are compared with the base case where sharp edge is used. Most of the spoiler edges are found to be effective in suppr...
16 citations
TL;DR: In modern ultra-high bypass ratio turboengines, the noise contribution of both turbine stages and combustion chamber is expected to increase drastically as discussed by the authors, and in the present work, both noise sources are considered.
Abstract: In modern ultra-high by-pass ratio turboengines, the noise contribution of both turbine stages and combustion chamber is expected to increase drastically. In the present work, both noise sources ar...
15 citations
TL;DR: In this paper, a coherent vortex shedding from blunt and beveled trailing edges generates tonal noise, which is usually undesired, and to obtain a better understanding of the noise generation under such conditions, the authors used a probabilistic model.
Abstract: Coherent vortex shedding from blunt and beveled trailing edges generates tonal noise, which is usually undesired. To obtain a better understanding of the noise generation under such conditions, the...
TL;DR: In this article, a better understanding of both contra-rotating open rotors and open-rotor open-robot propulsion systems is presented, which is a major obstacle to the adoption of this fuel efficient technology as a viable aircraft propulsion system.
Abstract: Noise from contra-rotating open rotors is a major obstacle to the adoption of this fuel efficient technology as a viable aircraft propulsion system. A better understanding of both contra-rotating o...
TL;DR: In this article, the authors explore the use of a second-order unstructured-grid, finite-volume code for direct noise prediction with a Mach 1.5 jet impinging on a perpendicular flat plate.
Abstract: In this paper, we explore the use of a second-order unstructured-grid, finite-volume code for direct noise prediction. We consider a Mach 1.5 jet impinging on a perpendicular flat plate. Hybrid LES...
TL;DR: In this article, the authors proposed an extension to the triple plane pressure mode matching method to improve the splitting between acoustics and the rest of the unsteady flow field in turbomachinery components.
Abstract: Time-periodic computational fluid dynamics simulations are widely used to investigate turbomachinery components. The triple plane pressure mode matching method developed by Ovenden and Rienstra extracts the acoustic part in such simulations. Experience shows that this method is subject to significant errors when the amplitude of pseudo-sound is high compared to sound. Pseudo-sounds are unsteady pressure fluctuations with a convective character. The presented extension to the triple plane pressure improves the splitting between acoustics and the rest of the unsteady flow field. The method is simple: (i) the acoustic eigenmodes are analytically determined for a uniform mean flow as in the original triple plane pressure mode matching method; (ii) the suggested model for convective pressure perturbations uses the convective wavenumber as axial wavenumber and the same orthogonal radial shape functions as for the acoustic modes. The reliability is demonstrated on the simulation data of a low-pressure fan. As ac...
TL;DR: In this article, a cambered airfoil with a 16.5° angle of attack between two horizontal plates, a 10 mm gap was maintained between the tip and the lower plate, which significantly reduced the interaction between upstream turbulence and the leading edge as well as the resulting interaction noise.
Abstract: Time-resolved PIV and time-resolved stereo PIV measurements are carried out in the tip leakage vortex of a single non-rotating airfoil placed in the potential core of a flanged rectangular jet in free field conditions. The experiment is based on the improvement of an existing rig: a cambered airfoil (NACA5510) now mounted with a 16.5° ± 0.5° angle of attack between two horizontal plates, a 10 mm gap being maintained between the airfoil tip and the lower (casing) plate. The mean flow velocity is 70 m/s, which corresponds to a 0.2 Mach number and a chord-based Reynolds number of 933, 000. Unlike in the former experiment carried out with this rig, the boundary layer thickness is now smaller than the gap, which significantly reduces the interaction between the upstream turbulence and the airfoil leading edge as well as the resulting interaction noise. The measurements described here include the far field. The upstream flow is characterised with hotwire anemometry.LDV profiles are also obtained in the tip leakage region and compared to the PIV measurements. The experiment is also designed to provide validation data for unsteady CFD computations of the same configuration as shown in a companion paper.
TL;DR: This paper presents two test articles that have contributed to turbo-machinery aero-acoustics studies and suggests that scaled versions of turbofan components depending on the physical process of interest should be considered.
Abstract: The study of turbo-machinery aero-acoustics encompasses source generation, duct propagation, and radiation to the far field for the purposes of physical understanding, evaluation, and noise reduction. Further, the acoustics subset can be divided into overall, broadband, or tone emphasis. Ultimately, assessments on full-scale turbofans are required. However, for isolating specific effects, or for costs reasons, it is useful to test models. These models may be scaled versions of turbofan components depending on the physical process of interest. The advantage of using models is the lower cost allows for a wider range of conditions to be studied. Even so, the cost of manufacturing and testing scale model fans in mid-technology readiness level can be limiting. A potentially useful supplement to turbo-machinery aero-acoustics studies is the use of artificial sources to generate acoustic signatures. The advantage is that a wide range of signatures can be quickly and efficiently studied, particularly useful for n...
TL;DR: In this paper, the authors attempt to provide a repertoire of measures to forewarn the onset of impending flow-induced mechanical oscillations via online health monitoring using a suitably placed pressure transducer.
Abstract: In this study, we attempt to provide a repertoire of measures to forewarn the onset of impending flow-induced mechanical oscillations via online health monitoring. To illustrate the principles, the flow of air through a pipe terminated by a circular orifice plate is investigated at various flow velocities using a suitably placed pressure transducer. It is observed that the regimes corresponding to the production of a tone is presaged by operating conditions that display temporarily intermittent bursts of periodic pressure oscillations that emerge from a background of lower-amplitude aperiodic fluctuations. The various model-free measures prescribed in this paper serve as efficient precursors by characterizing these intermittent states, which can potentially arise in aeroacoustic systems when the flow is highly unsteady or turbulent.
TL;DR: The influence of modeling choices on a low-order method for predicting broadband interaction noise downstream of a fan stage in a turbofan engine is explored in this article, which relies on experimentally or computationally obtained rotor-wake turbulence parameters as input.
Abstract: The influence of modeling choices on a low-order method for predicting broadband interaction noise downstream of a fan stage in a turbofan engine is explored. The general method relies on experimentally or computationally obtained rotor-wake turbulence parameters as input. These parameters are used together with the Liepmann spectrum to define the inflow into the exit guide vane. Strip-theory allows the full 3D vane response to be constructed using a gust response model for a 2D vane. The sound power in the duct downstream of the exit guide vanes is calculated using the Green’s method for an annular duct. Comparison is made between the predictions obtained with a 2D flat-plate cascade gust response and a 2D flat-plate airfoil gust response. In addition, the effect of the inclusion of real vane geometry via an asymptotic gust response method is investigated. It is shown that for the current modeling method, a cascade response must be used and that the asymptotic method does not extend to high enough camber...
TL;DR: In this article, the fluid and aero-acoustic properties of jets with two or four chevrons were investigated in the form of Schlieren imaging. But the results were limited to the case of two-lobe nozzles.
Abstract: An experimental study was conducted into the fluid and aeroacoustic properties of jets issuing from nozzles with two or four chevrons. Flow visualisation in the form of schlieren imaging was utilised to investigate the general change in jet structure. Schlieren imaging revealed a highly asymmetric flow field produced by the azimuthal asymmetry at the nozzle lip. The shock structures within the flow were significantly altered in both symmetry and spacing by the introduction of chevrons. A spatial two-point correlation was used to classify the dominant azimuthal instability mode produced by each of the respective nozzles. It was found that the two-lobe nozzle favoured a lateral flapping mode towards the chevron sides of the nozzle. The four-lobe nozzle, when coherent structures were visible, produced a mode somewhat more difficult to classify, being either a helical mode or a multi-axial flapping mode.A complex relationship was observed between the range of pressure ratios over which strong screech tones ar...
TL;DR: In this paper, a hybrid method combining a three-dimensional unsteady Reynolds-Averaged Navier-Stokes simulation of a cropped counter-Rotating open rotors at approach conditions and an acoustic analogy was proposed.
Abstract: A hybrid method combining a three-dimensional unsteady Reynolds-Averaged Navier–Stokes simulation of a cropped Counter-Rotating Open Rotors at approach conditions and an acoustic analogy either bas...
TL;DR: In this paper, an extension of the rotational rake mode measurement system has been proposed to measure the modal content propagating in hard-wall ducts in the NASA Glenn Research Center.
Abstract: The NASA Glenn Research Center’s rotating rake mode measurement system has been successful in measuring the modal content propagating in hard-wall ducts. This paper proposes an extension of the rot...
TL;DR: In this paper, the authors used both time-averaged and instantaneous snapshots of the flow field for a 37.6 mm round convergent nozzle over the jet Mach number range of 1.0 to 1.7 to investigate shock-spaces in a supersonic jet during stage-jumps associated with the screech phenomenon.
Abstract: Flow visualization is used to investigate shock-spacings in a supersonic jet during stage-jumps associated with the screech phenomenon. Conventional schlieren and shadowgraphy techniques as well as a new projection focusing schlieren technique are employed. Both time-averaged and instantaneous snapshots of the flow field are analyzed for a 37.6 mm round convergent nozzle over the jet Mach number range of 1.0 < Mj < 1.7. Shock-spacing is studied especially during hysteresis of the stage-jumps where two different screech frequencies could be realized at exactly the same Mj depending on whether the latter variable was increased or decreased. The data follow a monotonic trend without any discontinuity at any Mj. This establishes the fact that the stage-jumps in frequency are not associated with abrupt changes in the shock-spacing.
Abstract: Analysis and understanding of the noise generation processes in high-speed, high-Reynolds number jets are hampered by the broad range of turbulent scales and the disparate fluctuation intensities of the acoustic response hidden under the hydrodynamic source. Towards providing insight into these processes, the irrotational near-field of an unheated, Mach 0.9 jet is decomposed into its constitutive hydrodynamic and acoustic components using three separate filters in the present work. Previous work had decomposed the full near-field pressure signal into its hydrodynamic and acoustic components using a linear filter in Fourier space. The presence of numerical artifacts in the results prompted the current study, in which a new algorithm is developed to filter the pressure field in wavelet space. Results from the new method are then compared against those obtained using the standard Fourier-based algorithm, as well as another algorithm based upon the empirical mode decomposition. The ability of the wavelet-base...
TL;DR: In this paper, a condenser microphone was used to monitor the far-field acoustic fluctuations of a two-stage solid rocket motor during five static burns of the motor, and time histories and spectra measured for the two thrust conditions were presented.
Abstract: Near-plume fluctuating pressures were measured during five static burns of a two-stage solid rocket motor. An array of 11 water-cooled dynamic pressure sensors was used for the near-field survey, and a condenser microphone was used to monitor the far-field acoustic fluctuations. During the initial high-thrust phase of the burn, the plume was nearly ideally expanded, while in the following low-thrust phase, it was highly over-expanded and showed the presence of clear shock patterns. This paper presents time histories and spectra measured for the two thrust conditions. Spectra from very close to the plume show high levels of low-frequency fluctuations which are known to produce significant vibro-acoustic response of the spacecraft structures. The far-field microphone signal was dominated by mixing noise with little evidence of contribution from shock-associated noise, even for the over-expanded condition. The work was performed in support of an effort to improve predictions of the acoustic environment of a ...
TL;DR: An extended method has been developed and implemented based on mode decomposition that is much shorter than the International Organization for Standardization rig and does not require anechoic terminations, and both methods have been used to characterise the same fan.
Abstract: Air-moving devices such as fans are routinely characterised experimentally in terms of their sound power, and sound quality which depends on both broadband and tonal noise levels The International Organization for Standardization method 5136, widely used in industry and academia, estimates sound power in third-octave bands radiated into a duct Since the International Organization for Standardization method is not designed for tone measurements and overlooks the unevenness of the modal power distribution, an extended method has been developed and implemented based on mode decomposition The ‘two-port’ source model is formulated to include higher-order modes and applied for the first three modes which require six independent stationary measurements on each side or ‘port’ The resulting experimental rig is much shorter than the International Organization for Standardization rig and does not require anechoic terminations Both methods have been used to characterise the same fan, and the results compared to
TL;DR: In this article, the sum and difference frequency scattering of narrowband noise as it interacts with ducted rotating turbomachinery is studied experimentally, and it is shown that this phenomenon will aff...
Abstract: The phenomenon of sum and difference frequency scattering of narrowband noise as it interacts with ducted rotating turbomachinery is studied experimentally in this article. This phenomenon will aff...
TL;DR: In this article, the effect on the normal incidence acoustic impedance of a non-circular orifice shape relative to a circular orifice was examined relative to an adjustable porosity perforate, formed from two identical perforates sliding over each other.
Abstract: The effect on normal incidence acoustic impedance of a non-circular orifice shape is examined relative to a circular orifice. The impedance of an adjustable porosity perforate, formed from two identical perforates sliding over each other, is measured. As the orifice shape becomes more non-circular, the measured impedance is found to deviate from the predicted results for a circular orifice of the same area. Several isolated orifices of the same open area but different shapes are tested and compared with a circular orifice. Both low incident sound pressure levels using broadband noise and high incident sound pressure levels using sinusoidal tones are used to evaluate the impedance performance of these isolated orifices. One orifice mimics the unique shape produced by the adjustable perforate and results in a smaller attached mass (or mass end correction) compared with a round orifice. This is consistent with the perforate impedance results. The unique orifice shape does not appear to have measurable differ...
TL;DR: In this paper, a frequency domain analysis of turbofan inlets is performed by a statistical distribution of propagating duct modes, and the required number of modes is estimated by Rice's approximations.
Abstract: Broadband noise in turbofan inlets is represented in a frequency domain analysis by a statistical distribution of propagating duct modes. The required number of modes is estimated by Rice’s approxi...
TL;DR: In this article, it was shown that the tonal sound emission of a high-pressure turbine stage may increase considerably when the mean temperature of the inflow is spatially not uniform.
Abstract: It is shown in a simulation that the tonal sound emission of a high-pressure turbine stage may increase considerably when the mean temperature of the inflow is spatially not uniform The tonal sound power emitted in the downstream direction is increased by 59 dB at the blade passing frequency fb and by 117 dB at 2fb The mean total temperature of the incoming flow is assumed to vary periodically in the azimuthal direction with a temperature amplitude of ±9% as a result of 14 discrete burners inside the annular combustion chamber The temperature also varies radially with minima at the inner and outer walls of the annular channel The turbine stage consists of a stator with 70 vanes and a rotor with 73 blades, while the temperature field in the simulation has 14 periods in the circumference
TL;DR: The results demonstrate that the exhaust rotor–stator interaction tone power levels can be predicted to within ± 1 dB on a consistent basis for rotor at subsonic tip relative speeds by including the three-dimensional geometry of the fan stage and its flowfield.
Abstract: This paper describes in detail the process for predicting, from first principles, the rotor–stator interaction tone levels for two realistic model-scale fans that are representative of high bypass ratio and ultrahigh bypass ratio turbofans. The prediction scheme relies on a suite of three-dimensional computational tools that include Reynolds Averaged Navier–Stokes aerodynamic models and linearized inviscid aeroacoustic models. The goal of the study was to assess the accuracy of tone-level predictions for realistic fans operating under realistic conditions. The predictions were carried out over a wide range of operating conditions that include, but were not limited to the approach, cutback, and sideline conditions for each of the two fans. The in-duct and external tonal sound fields were computed at a representative blade passing frequency harmonic tone. The predicted tone sound pressure level and sound power level have been compared with the measurements acquired at a NASA anechoic wind tunnel. The data–t...