Laboratory-scale Jet Research Articles

Source characterization of afterburning laboratory-scale jet noise with vector acoustic intensity

This paper presents an intensity-based characterization of noise sources in a highly heated laboratory-scale jet with a 3-inch exit diameter. Run conditions had nozzle pressure ratios between 2.7 and 3.5 and temperature ratios of ∼7. Measurements were performed using a microphone scanning rig containing 8 four-microphone intensity probes. Probes were separated by 1.5 nozzle diameters and the microphones were spaced 0.5 nozzle diameters apart. Each scan mapped out over 3,000 measurement locations to produce an intensity field map. Vector intensity was processed over a 200 Hz to 20 kHz bandwidth using the phase and amplitude gradient estimator (PAGE) method [D. C. Thomas, et al., J. Acoust. Soc. Am. 137, 3366–3376 (2015)]. Results show the dominant source region as a function of frequency and are compared to the acoustical holography source reconstruction of the T7-A afterburner engine condition [L. T. Mathews and K. L. Gee, AIAA J., in press (2024)]. Additionally, the intensity-derived source locations are connected to the jet’s supersonic and subsonic flow regions. [Work supported by ONR Grant No. N00014-21-1-2069].

A tale of two curves and their influence on rocket and supersonic jet noise research.

This letter describes how a landmark 1960s supersonic jet noise experiment influenced subsequent noise models. A discrepancy in other researchers' application of Potter and Jones's axial decomposition of the sound power generated from a laboratory-scale jet can be traced to an erroneous plot in the original report. Whereas most jet noise research indicates the dominant sound power is generated upstream of the supersonic core tip, propagation of this error in the ubiquitous NASA SP-8072 report has caused rocket noise modelers for five decades to disproportionately allocate sound power generation to the subsonic flow.

Holographic reconstructions of large-eddy simulations of a highly heated laboratory-scale jet

Near-field acoustical holography allows for the reconstruction of a sound field from a limited measurement. For aeroacoustic noise generated by military aircraft, reconstructions of the pressure field within the jet plume have provided insight into equivalent acoustic noise source distributions, though the relationship between these equivalent sources and actual flow pressures and velocities within the plume remain unknown. This study reconstructs the sound field of a highly heated laboratory-scale jet simulated by the Naval Research Lab's Jet Noise Reduction (JENRE) large eddy simulation solver. The simulated data allow for comparisons of the holographic reconstructions of the pressure and particle velocity fields to points along the nozzle lipline, to the Ffowcs Williams and Hawkings integration surface (FWHS), and to the far field. Pressure field reconstructions outside and inside of the FWHS match well, while particle velocity reconstructions follow similar trends as the velocities generated by the LES but severly underestimate the time harmonic complex amplitdues.

Coherence Analysis of the Noise from a Simulated Highly Heated Laboratory-Scale Jet

Measurements of full-scale high-performance military aircraft reveal phenomena that are not widely seen at laboratory scales. However, recent modifications to large eddy-simulation (LES) methods allow for simulations of jets operating at a high-temperature ratio in a similar regime as military aircraft operating at afterburner. This work applies coherence analyses that have been previously used to study the jet noise field produced by military aircraft to the LES of a highly heated laboratory-scale jet. The coherence of the complex pressures along a near-field line approximately parallel to the shear layer as well as along the nozzle lip line shows evidence of distinct noise production mechanisms that transfer information differently from the flow to the field. A phenomenological comparison between the LES and measurements of an afterburning F-35 aircraft is then made. Although the LES is not run at the exact same conditions as the aircraft and does not reproduce all of the phenomena present in the aircraft’s jet noise field, differences between noise production mechanisms observed in the LES may describe some of the spatiospectral lobe phenomena observed in the measurements of the F-35.

Multiscale simulation of erosive wear in a prototype-scale Pelton runner

The technical capacity to predict the erosion process is instrumental for the optimization of the runner designs and operation strategies of hydroelectric plants. A multiscale model of erosion recently formulated by the authors and validated on a laboratory-scale jet impingement case is used to study the erosion of a prototype-scale Pelton runner. The model is shown to provide physically-sound descriptions of the sediment impact condition distributions on the bucket surface; furthermore, the erosion distribution obtained is explained in terms of these underlying impact condition distributions. The model predictions for the erosion depth distribution on the bucket surface are validated with the corresponding experimental data, resulting in an average error of 35% for eight point-wise comparisons, 14% for line-averaged values along four transversal sections, and 4% for the surface-averaged erosion depth, directly linked to the total eroded mass. A careful error propagation analysis of the comparison between simulation and field data yields an uncertainty of ±22%. Based on these considerations, the modeling error is estimated to be 26±22%. The results obtained, namely quantitative predictions of the erosion of industrial-scale hydraulic machines, have no precedent in the literature; they demonstrate the accuracy and transferability of the multiscale model of erosion and suggest an improvement over the state-of-the-art computational fluid dynamics models based on empirical erosion correlations.

Partial field decomposition of the simulated noise from a highly heated laboratory-scale jet

The decomposition of jet noise fields into self-coherent and mutually incoherent parts is an important step preliminary to the application of acoustical holography techniques. Cross-spectral matrices of point arrays sampled from large eddy simulations of a laboratory-scale jet operating at a high temperature ratio are decomposed using a singular value decomposition to obtain partial fields. The shape and relative strengths of the individual partial fields highlight the difference between the coherent radiation in the aft direction and the incoherent portion of the radiation towards the sideline. Azimuthally, levels are mostly constant but require multiple partial fields to accurately represent the low coherence at high frequency.

Coherence analysis of the simulated sound field of a highly-heated laboratory-scale jet

Large eddy simulations (LES) have successfully reproduced the flow and acoustic fields generated by laboratory-scale jets. However, laboratory-scale test conditions ordinarily do not match those of full-scale military aircraft. Recently, Liu et al. (AIAA 2016–2125) showed that accounting for a variable ratio of specific heats leads to increased accuracy in LES simulations of heated jets. As a step towards modeling operating parameters similar to military aircraft, they produced a simulation of a highly-heated jet with a temperature ratio of seven. This paper shows the levels in the field as well as the axial and azimuthal coherence trends of this simulated jet. Large axial coherence lengths are found in the direction of maximum radiation with decreased coherence towards the sideline. Azimuthally, coherence length scales are greatest in the region of maximum radiation and generally decrease with increasing frequency. Additionally, evidence is seen for multiple self-coherent and mutually-incoherent radiation lobes within the region of maximum radiation. [Work supported by USAFRL through ORISE.]

Influence of inlet boundary conditions in computations of turbulent jet flames

PurposeThis paper aims to assess the sensitivity of numerical simulation results of turbulent reactive flow to the formulation of inlet boundary conditions. The analysis concerns the profiles of the mean velocity the turbulence kinetic energy k and its dissipation rate ϵ. It is intended to provide guidance to the determination of inlet conditions when only global flow data are available. This situation can be met both in simple laboratory experiments and in industrial full-scale applications, when measurements are either incomplete or infeasible, resulting in lack of detailed inlet data.Design/methodology/approachTwo turbulence–chemistry interaction models were studied: eddy dissipation concept and partially stirred reactor. Three different velocity profiles and related turbulence statistics were applied to present feasible scenarios and their consequences. Simulations with the most appropriate inlet data were accompanied with profiles of turbulent quantities obtained with a proposed method. This method was contrasted to other approaches popular in the literature: the pre-inlet pipe and the separate cold flow simulations of a burner. The methodology was validated on two laboratory-scale jet flames: Delft Jet-in-Hot-Coflow and Sandia CHN B. The simulations were carried out with open source code OpenFOAM.FindingsThe proposed relations for turbulence kinetic energy and its dissipation rate at the inlet are found to provide results comparable to those obtained with the use of experimental data as inlet boundary conditions. Moreover, from a certain location downstream the jet, weakly dependent on the Reynolds number, the influence of inlet conditions on flow statistics was found to be negligible.Originality/valueThis work reveals the consequences of the use of rather crude assumptions made for inlet boundary conditions. Proposed formulas for the profiles for k and epsilon are attractive alternatives to other approaches aiming to determine the inlet boundary conditions for turbulent jet flows.

Experimental validation of acoustic intensity bandwidth extension by phase unwrapping.

The phase and amplitude gradient estimator (PAGE) method for active acoustic intensity uses pairwise microphone transfer functions to obtain the phase gradient, which improves the calculation bandwidth over the traditional weighted quadspectral method. Additionally, for broadband sources, the PAGE theory indicates that the transfer function phase can be unwrapped to further extend the usable frequency range to beyond the spatial Nyquist frequency. Here, two experiments demonstrate intensity bandwidth extension by more than an order of magnitude using phase unwrapping. First, plane-wave tube results show accurate one-dimensional intensity calculations with the microphones separated by five wavelengths, 30 times the traditional limit. Second, two-dimensional measurements of a laboratory-scale jet with a four-microphone probe yield physically reasonable calculations at frequencies 15 times the traditional limit.

Spatial variation in similarity spectra decompositions of a Mach 1.8 laboratory-scale jet

The primary source of noise from supersonic jets is turbulent mixing noise. Tam et al. [AIAA Paper 96-1716 (1996)] proposed similarity spectra for a two-source model of turbulent mixing noise corresponding to noise from omnidirectional fine-scale turbulence structures and directional large-scale turbulent structures. These empirical similarity spectra have been compared with reasonable success to the spectra of both military and laboratory-scale jets. Most application have looked at the variation in angle: fine-scale similarity spectra matches sideline of the jet nozzle, large-scale in the maximum radiation lobe, and a combination needed in between. A similarity spectra decomposition of from an ideally expanded, Mach 1.8 laboratory-scale jet allows for a spatial comparison between the near and far-field spectra. The sound from the convergent-divergent nozzle was collected at the Hypersonic and High-Enthalpy Wind Tunnel at Kashiwa Campus of the University of Tokyo at a variety of near, mid, and far field locations. Comparison of similarity spectra decompositions over distance yield insights into the sound propagation from this supersonic jet. In addition, results from a preliminary wavenumber eduction technique to build a wavepacket-based equivalent source model of the large-scale turbulent mixing noise. [Work supported by Office of Naval Research grant.]

Intensity-based laboratory-scale jet noise source characterization using the phase and amplitude gradient estimator method

A new method for the calculation of vector acoustic intensity from pressure microphone measurements has been applied to the aeroacoustic source characterization of an unheated, Mach 1.8 laboratory-scale jet. Because of the ability to unwrap the phase of the transfer functions between microphone pairs in the measurement of a broadband source, physically meaningful near-field intensity vectors are calculated up to the maximum analysis frequency of 32 kHz. This result improves upon the bandwidth of the traditional cross-spectral intensity calculation method by nearly an order of magnitude. The new intensity method is used to obtain a detailed description of the sound energy flow near the jet. The resulting intensity vectors have been used in a ray-tracing technique to identify the dominant source region over a broad range of frequencies. Additional aeroacoustics analyses provide insight into the frequency-dependent characteristics of jet noise radiation, including the nature of the hydrodynamic field and the sharp transition between the Mach wave and sideline radiation.

Computational Fluid Dynamic Design of Jet Stirred Reactors for Measuring Intrinsic Kinetics of Gas‐Phase and Gas‐Solid Reactions

ABSTRACTNonreactive and reactive computational fluid dynamic simulations were applied to optimize the design of a laboratory scale jet stirred reactor for measuring intrinsic kinetics of gas‐phase and gas‐solid reactions, i.e. kinetics determined by chemical steps only and not by heat or mass transfer. In the past these reactors were designed and tested based on empirical design criteria and residence time distribution experiments. This work shows that these do not always capture important local effects that are vital for kinetic studies. First the degree of macro–mixing was evaluated for three different geometries (down case, 45° case and 90° case) by performing in silico residence time distribution experiments at 900 K, showing that with these type of experiments only minor differences are observed. However, the ethane steam cracking simulations revealed major differences, with the 45° case being the most uniform in terms of temperature and the 90° case being by far the worst. The species nonuniformity in all geometries was acceptable and was in some cases even partly masked by important shortcut streams such as those observed in the 90° case. The existing gradients on the substrate surface are sufficiently small to be neglected in modeling efforts. As temperature is the major parameter determining the rate of the surface reactions, the 45° case is suggested as the best geometry for measuring intrinsic kinetics.

Bubble-Distribution Measurement in a Flotation Column

ABSTRACTWith improvement in mineral processing, column flotation technology has undergone enormous changes, and various flotation columns have emerged in large numbers. In this study, three types of laboratory-scale flotation columns, including countercurrent, cyclone, and jet flow, were designed, and their bubble sizes were measured by using an image-analysis technique. The effect of circulating rates on bubble distribution was discussed. The bubble sizes decreased as the circulating rate increased. The bubble diameters in the countercurrent and jet flow mineralization environments were the maximum and minimum, respectively, when the circulating rate was the same.

Spatiotemporal-Correlation Analysis of Jet Noise from a High-Performance Military Aircraft

Correlation analyses of ground-based acoustic-pressure measurements of noise from a tethered F-22A provide insights into the sound-field characteristics with position and engine condition. Time-scaled single-point (auto)correlation functions show that, to the side of the nozzle exit, the temporal-correlation envelope decays rapidly, whereas the envelope decays more slowly in the maximum radiation region and farther downstream. This type of spatial variation has been previously attributed to a transition from fine- to large-scale mixing noise in laboratory-scale jets. Two-point space–time (cross) correlation functions demonstrate that noise from a single engine operating at intermediate power is similar to that from a heated, convectively subsonic laboratory-scale jet, whereas additional features are seen at afterburner, relative to supersonic laboratory jets. A complementary coherence analysis provides estimates of coherence lengths as a function of frequency and location. Acoustic coherence lengths across the ground microphone array are used to analyze one-dimensional, equivalent-source-coherence lengths obtained from the DAMAS-C beamforming algorithm. The source coherence reaches its maximum downstream of the maximum source level, suggesting that uncorrelated sources meaningfully contribute to the dominant source region. In addition to revealing further the nature of the sound field near an advanced tactical engine, the characteristics seen should be useful as a phenomenological comparison point for those trying to model military-scale results both experimentally and numerically.

Electrical Resistivity Imaging of Laboratory Soilcrete Column Geometry

AbstractGround improvement via jet grouting is commonly used to strengthen weak ground and/or create hydraulic barriers. Delivering soilcrete columns with tightly controlled and known diameters is critical to performance; however, techniques to assess jet grout geometry during construction are lacking. This paper reports the results of a study on electrical resistivity imaging of soilcrete by investigating the effects of electrode configuration and electrical protocol type on laboratory scale soilcrete columns constructed in a tank filled with sand. Experimental results are verified via numerical modeling and the model is used to analyze the changes in soilcrete resistivity that result from geometric variation. The results of this study indicate that resistivity imaging with direct contact electrodes can estimate the diameter of laboratory scale jet grout columns to within ±5% of the as-built column diameter. A relationship between electrode spacing and column diameter is identified and quantified to more...

Numerical Modelling of Turbulent Particle-laden Sonic CO2 Jets with Experimental Validation

Under-expanded particle-laden flows resulting in velocities greater than the local speed of sound are a feature of a wide number of applications in aviatic, astronautical, and process engineering scenarios including those relating to the accidental release of high-pressure fluids from reservoirs or pipelines. Such pipelines are considered to be the most likely method for transportation of captured carbon dioxide (CO2) from power plants and other industries prior to subsequent storage in carbon capture and storage (CCS) applications. Their safe operation is of paramount importance as their contents are likely to be in the region of several thousand tonnes. CO2 poses a number of dangers upon release due to its physical properties. It is a colourless and odourless asphyxiant which has a tendency to sublimation and solid formation, and is directly toxic if inhaled in air at concentrations around 5%, and likely to be fatal at concentrations around 10%. The developments presented in this paper concern the formulation of a multi-phase homogeneous discharge and dispersion model capable of predicting the near-field fluid dynamic, phase and particle behaviour of such CO2 releases, with validation against measurements of laboratory-scale jet releases of CO2 recently obtained by our group.

Finely resolved spatial variation in F-22 spectra

Examination of the spatial variation in the spectrum from ground-based microphones near an F-22 Raptor has revealed spectral features at high engine power that are not seen at intermediate power or in laboratory-scale jet noise. At military and afterburner powers, a double peaked spectrum is detected around the direction of maximum radiation. In this region, there is not a continuous variation in peak frequency with downstream distance, as seen in lab-scale studies, but a transition between the relative levels for two discrete one-third octave bands. Previous attempts to match similarity spectra for turbulent mixing noise to a few of these measurements split the difference between the two peak frequencies [Neilsen et al., J. Acoust. Soc. Am. 133, 2116–2125 (2013)]. The denser spatial resolution afforded by examining the spectral variation on all 50 ground-based microphones, located 11.6 m to the sideline and spanning 30 m, provides the opportunity to further investigate this phenomenon and propose a more complete formulation of expected spectral shapes. Special care must be given to account for the relative amount of waveform steepening, which varies with level, distance, and angular position. [Work supported by ONR.]

On cumulative nonlinear acoustic waveform distortions from high-speed jets

AbstractA model is proposed for predicting the presence of cumulative nonlinear distortions in the acoustic waveforms produced by high-speed jet flows. The model relies on the conventional definition of the acoustic shock formation distance and employs an effective Gol’dberg number$\Lambda $for diverging acoustic waves. The latter properly accounts for spherical spreading, whereas the classical Gol’dberg number$\Gamma $is restricted to plane wave applications. Scaling laws are then derived to account for the effects imposed by jet exit conditions of practical interest and includes Mach number, temperature ratio, Strouhal number and an absolute observer distance relative to a broadband Gaussian source. Surveys of the acoustic pressure produced by a laboratory-scale, shock-free and unheated Mach 3 jet are used to support findings of the model. Acoustic waveforms are acquired on a two-dimensional grid extending out to 145 nozzle diameters from the jet exit plane. Various statistical metrics are employed to examine the degree of local and cumulative nonlinearity in the measured waveforms and their temporal derivatives. This includes a wave steepening factor (WSF), skewness, kurtosis and the normalized quadrature spectral density. The analysed data are shown to collapse reasonably well along rays emanating from the post-potential-core region of the jet. An application of the generalized Burgers equation is used to demonstrate the effect of cumulative nonlinear distortion on an arbitrary acoustic waveform produced by a high-convective-Mach-number supersonic jet. It is advocated that cumulative nonlinear distortion effects during far-field sound propagation are too subtle in this range-restricted environment and over the region covered, which may be true for other laboratory-scale jet noise facilities.

Autocorrelation analysis of lab-scale jets

Autocorrelation (AC) analysis is useful in examining temporal relationships in a waveform and can be used to provide insight into properties of jet noise. Using techniques developed by Harker et al. [J. Acoust. Soc. Am. 133, EL458 (2013)] for full-scale jet data, AC analysis has been applied to unheated, laboratory-scale jet noise data. To more consistently compare the AC at various locations around the jet, it is important to account for the spatial variation in the spectrum by scaling with the peak frequency. In addition to this frequency scaling, the spatiotemporal variations in the autocorrelation are more plainly seen when an envelope function is applied. Calculated AC envelope functions from measured data are compared with theoretical curves for fine and large-scale jet noise radiation. Results are compared against those from a full-scale, military jet aircraft. [Work supported by ONR.]

Comparison of supersonic full-scale and laboratory-scale jet data and the similarity spectra for turbulent mixing noise

Broadband, partially correlated noise radiated from supersonic jets has characteristics that scale with nozzle size and flow properties. In particular, the spectral content of jet noise and variation with angle in many cases agree with empirically derived similarity spectra for large and fine-scale components of turbulent mixing noise [Tam et al., AIAA paper 96-1716]. In previous studies, measurements made near the F-22A Raptor agreed remarkably well with the similarity spectra, with two exceptions. First, the high-frequency slopes seen in the data were shallower than the similarity spectra at many angles. Second, the data exhibit a double frequency peak, which is absent from the similarity spectra [Neilsen et al., J. Acoust. Soc. Am. 132, 1993 (2012)]. These observations are explored further by examining the spectral characteristics of noise from a different military jet and a laboratory-scale, unheated jet. In both cases, there is evidence that for supersonic cases the measured spectra are shallower than the similarity spectra due to nonlinear propagation effects. In addition, the military data support the observation that the double spectral peak is a feature of full-scale jet noise. Recommendations are made for applying the similarity spectra to predict spectral levels for full-scale jets. [Work supported by ONR.]