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Dennis K. McLaughlin

Bio: Dennis K. McLaughlin is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Supersonic speed & Jet (fluid). The author has an hindex of 30, co-authored 148 publications receiving 3368 citations. Previous affiliations of Dennis K. McLaughlin include Oklahoma State University–Stillwater & Massachusetts Institute of Technology.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors studied the flow and acoustic properties of a jet at Reynolds number of 70,000 at Mach 2.1 with pitot tubes and hot-wire anemometry.
Abstract: Flow and acoustic properties of a jet at Reynolds number of 70,000 were studied at Mach 2.1. Measurements in a free jet test facility were made with pitot tubes and hot-wire anemometry. Center-line Mach number distributions for natural and excited jets were obtained. A slow initial growth rate was in the potential core region of the jet, indicating a transition from laminar to turbulent flow in moderate Reynolds number jets. The transition occurred within the first 2-3 diameters. Spectral components were calculated for the fluctuating flowfield, and sound pressure levels were measured for the overall near-field noise. The centroid of noise was located about 8 nozzle diameters downstream. The growth rates of instabilities were determined to be in agreement with linear stability theory predictions over a broad frequency range.

305 citations

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TL;DR: In this article, an experimental study of the flow field and acoustic properties of a low Reynolds number M = 0.9 jet has been performed in a low pressure anechoic test chamber.

236 citations

Journal ArticleDOI
TL;DR: In this article, an experimental investigation of the instability and the acoustic radiation of the low Reynolds number axisymmetric supersonic jet has been performed, and it was shown that the instability process in the perfectly expanded jet consists of numerous discrete frequency modes around a Strouhal number of 0·18.
Abstract: An experimental investigation of the instability and the acoustic radiation of the low Reynolds number axisymmetric supersonic jet has been performed. Hot-wire measurements in the flow field and microphone measurements in the acoustic field were obtained from different size jets at Mach numbers of about 2. The Reynolds number ranged from 8000 to 107000, which contrasts with a Reynolds number of 1·3 × 106 for similar jets exhausting into atmospheric pressure.Hot-wire measurements indicate that the instability process in the perfectly expanded jet consists of numerous discrete frequency modes around a Strouhal number of 0·18. The waves grow almost exponentially and propagate downstream at a supersonic velocity with respect to the surrounding air. Measurements of the wavelength and wave speed of the St = 0·18 oscillation agree closely with Tam's theoretical predictions.Microphone measurements have shown that the wavelength, wave orientation and frequency of the acoustic radiation generated by the dominant instability agree with the Mach wave concept. The sound pressure levels measured in the low Reynolds number jet extrapolate to values approaching the noise levels measured by other experimenters in high Reynolds number jets. These measurements provide more evidence that the dominant noise generation mechanism in high Reynolds number jets is the large-scale instability.

193 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used smoke visualization, hot-wire anemometry and acoustic excitation to study the dynamics of a swirling jet in the Reynolds number range from 20,000 to 60,000 and a nominal swirl number of 05.
Abstract: Instabilities present in a swirling jet in the Reynolds number range from 20 000 to 60 000 and a nominal swirl number of 05 were studied experimentally, using smoke visualization, hot‐wire anemometry and acoustic excitation Flow visualization photographs of the natural jet show vortex breakdown at the core and rolling up of the shear layer around the jet into weak, irregular, large‐scale organized structures When forced by acoustic excitation these structures became energetic and periodic Axisymmetric and helical instability waves in the Strouhal number range 075 to 15 were excited and their evolution along the axial direction were measured from velocity spectra and ensemble averaged measurements Compared to a nonswirling jet, the overall growth of the instability waves is considerably smaller, and vortex pairing is suppressed in a swirling jet However, the overall spread and mass entrainment rates are higher in the latter Measurements of the mean velocity components and turbulence fluctuations show that the vortex breakdown affects the axial velocity distribution and rapidly replaces the potential core with a large amount of turbulence Upon interacting with the vortex breakdown, the shear layer along the jet periphery loses its organized structure and, in general, ‘‘random turbulence’’ follows

178 citations

Journal ArticleDOI
TL;DR: An experimental investigation of noise generation by instabilities in low Reynolds number supersonic air jets has been performed by Morrison and McLaughlin this paper, where sound pressure levels, spectra and acoustic phase fronts were measured with a traversing condenser microphone in the acoustic field of axisymmetric, perfectly expanded, cold jets.

107 citations


Cited by
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Journal Article
01 Jun 1978
TL;DR: In this paper, the authors evaluated the applicability of the standard κ-ϵ equations and other turbulence models with respect to their applicability in swirling, recirculating flows.
Abstract: The standard κ-ϵ equations and other turbulence models are evaluated with respect to their applicability in swirling, recirculating flows. The turbulence models are formulated on the basis of two separate viewpoints. The first perspective assumes that an isotropic eddy viscosity and the modified Boussinesq hypothesis adequately describe the stress distributions, and that the source of predictive error is a consequence of the modeled terms in the κ-ϵ equations. Both stabilizing and destabilizing Richardson number corrections are incorporated to investigate this line of reasoning. A second viewpoint proposes that the eddy viscosity approach is inherently inadequate and that a redistribution of the stress magnitudes is necessary. Investigation of higher-order closure is pursued on the level of an algebraic stress closure. Various turbulence model predictions are compared with experimental data from a variety of isothermal, confined studies. Supportive swirl comparisons are also performed for a laminar flow case, as well as reacting flow cases. Parallel predictions or contributions from other sources are also consulted where appropriate. Predictive accuracy was found to be a partial function of inlet boundary conditions and numerical diffusion. Despite prediction sensitivity to inlet conditions and numerics, the data comparisons delineate the relative advantages and disadvantages of the various modifications. Possible research avenues in the area of computational modeling of strongly swirling, recirculating flows are reviewed and discussed.

5,396 citations

Journal ArticleDOI
TL;DR: A comprehensive review of the advances made over the past two decades in this area is provided in this article, where various swirl injector configurations and related flow characteristics, including vortex breakdown, precessing vortex core, large-scale coherent structures, and liquid fuel atomization and spray formation are discussed.

1,048 citations

Journal ArticleDOI
TL;DR: In this article, the mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation and the results show that the phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed.
Abstract: The mechanisms of sound generation in a Mach 0.9, Reynolds number 3600 turbulent jet are investigated by direct numerical simulation. Details of the numerical method are briefly outlined and results are validated against an experiment at the same flow conditions (Stromberg, McLaughlin & Troutt 1980). Lighthill's theory is used to define a nominal acoustic source in the jet, and a numerical solution of Lighthill's equation is compared to the simulation to verify the computational procedures. The acoustic source is Fourier transformed in the axial coordinate and time and then filtered in order to identify and separate components capable of radiating to the far field. This procedure indicates that the peak radiating component of the source is coincident with neither the peak of the full unfiltered source nor that of the turbulent kinetic energy. The phase velocities of significant components range from approximately 5% to 50% of the ambient sound speed which calls into question the commonly made assumption that the noise sources convect at a single velocity. Space–time correlations demonstrate that the sources are not acoustically compact in the streamwise direction and that the portion of the source that radiates at angles greater than 45° is stationary. Filtering non-radiating wavenumber components of the source at single frequencies reveals that a simple modulated wave forms for the source, as might be predicted by linear stability analysis. At small angles from the jet axis the noise from these modes is highly directional, better described by an exponential than a standard Doppler factor.

632 citations

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TL;DR: A hierarchy of computational approaches that range from semi-empirical schemes that estimate the noise sources using mean-flow and turbulence statistics, to high-fidelity unsteady flow simulations that resolve the sound generation process by direct application of the fundamental conservation principles is discussed in this paper.

520 citations

Journal ArticleDOI
TL;DR: In this paper, the authors review evidence of the existence, energetics, dynamics, and acoustic efficiency of wave packets and highlight how extensive data available from simulations and modern measurement techniques can be used to distill acoustically relevant turbulent motions.
Abstract: Turbulent jet noise is a controversial fluid mechanical puzzle that has amused and bewildered researchers for more than half a century. Whereas numerical simulations are now capable of simultaneously predicting turbulence and its radiated sound, the theoretical framework that would guide noise-control efforts is incomplete. Wave packets are intermittent, advecting disturbances that are correlated over distances far exceeding the integral scales of turbulence. Their signatures are readily distinguished in the vortical, turbulent region; the irrotational, evanescent near field; and the propagating far field. We review evidence of the existence, energetics, dynamics, and acoustic efficiency of wave packets. We highlight how extensive data available from simulations and modern measurement techniques can be used to distill acoustically relevant turbulent motions. The evidence supports theories that seek to represent wave packets as instability waves, or more general modal solutions of the governing equations, and confirms the acoustic importance of these structures in the aft-angle radiation of high subsonic and supersonic jets. The resulting unified view of wave packets provides insights that can help guide control strategies.

517 citations