摘要 :
The work develops a high-accuracy numerical viscous analysis of nonlinear interaction of SD7003 airfoil with nonuniform, unsteady incoming flow. The study is focused on the low-Re number unsteady flows typical of MAV applications ...
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The work develops a high-accuracy numerical viscous analysis of nonlinear interaction of SD7003 airfoil with nonuniform, unsteady incoming flow. The study is focused on the low-Re number unsteady flows typical of MAV applications in which a gust encounter can induce a particularly significant aerodynamic and aeroelastic response. Efficient source models are developed to introduce sharp-edge and time-harmonic gust perturbations with specified amplitude, frequency and duration inside the computational domain through the source terms in the governing momentum equations. Parametric analysis of gust-airfoil interactions for different steady airfoil loads is conducted in comparison with equivalent pitch-ramp and time-harmonic pitching simulations. In addition, all obtained solutions are compared with corresponding predictions based on the inviscid, incompressible unsteady aerodynamic theory. The study reveals complex interaction of inviscid and viscous unsteady forces observed for different gust and pitching excitations, and identifies the degree of similarity between the corresponding gust and pitching airfoil responses.
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High-fidelity simulations of the unsteady flow and radiated noise of a UAV propeller are presented herein. We aim at capturing the broad-band noise associated with both the propeller and its wake. The current results are found to ...
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High-fidelity simulations of the unsteady flow and radiated noise of a UAV propeller are presented herein. We aim at capturing the broad-band noise associated with both the propeller and its wake. The current results are found to be in good agreement with several data including the thrust generated, the unsteady flow structure, as well as the radiated sound spectra and directivity. We focus on understanding the physics of the turbulence-generated noise and how it propagates to the near- and the far- acoustic fields. This is analyzed by computing the dilatation field, the Lighthill-stress terms, and each term in the integrand of FWH integral solution of the far field.
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摘要 :
High-fidelity simulations of the unsteady flow and radiated noise of a UAV propeller are presented herein. We aim at capturing the broad-band noise associated with both the propeller and its wake. The current results are found to ...
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High-fidelity simulations of the unsteady flow and radiated noise of a UAV propeller are presented herein. We aim at capturing the broad-band noise associated with both the propeller and its wake. The current results are found to be in good agreement with several data including the thrust generated, the unsteady flow structure, as well as the radiated sound spectra and directivity. We focus on understanding the physics of the turbulence-generated noise and how it propagates to the near- and the far- acoustic fields. This is analyzed by computing the dilatation field, the Lighthill-stress terms, and each term in the integrand of FWH integral solution of the far field.
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摘要 :
This work focuses on elucidating the intricate connection between
unsteady dynamics of laminar separation bubble (LSB) and feedback-loop
resonant interactions observed in boundary layers of transitional airfoils.
A complex tone...
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This work focuses on elucidating the intricate connection between
unsteady dynamics of laminar separation bubble (LSB) and feedback-loop
resonant interactions observed in boundary layers of transitional airfoils.
A complex tones-producing phenomenon is examined by means of
theoretical, numerical and experimental studies, with the most recent
results reported in the current paper. High-accuracy numerical studies
are performed for selected transitional-flow regimes for NACA-0012 and
SD7003 airfoils for which experimental measurements recorded strong
flow-acoustic resonant interactions characterized by multiple-tone acoustic
spectra. Numerical studies employ a 6th-order Navier-Stokes solver
implementing low-pass filtering of poorly resolved high-frequency solution
content to retain numerical accuracy and stability over the range of
transitional flow regimes. The numerical results of this study clearly
indicate the effect of various parameters such as upstream flow conditions,
angle of attack, and mean flow velocity on the transition between toneproducing
and no-tone-producing flow regime.
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摘要 :
This work focuses on elucidating the intricate connection between
unsteady dynamics of laminar separation bubble (LSB) and feedback-loop
resonant interactions observed in boundary layers of transitional airfoils.
A complex tones-p...
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This work focuses on elucidating the intricate connection between
unsteady dynamics of laminar separation bubble (LSB) and feedback-loop
resonant interactions observed in boundary layers of transitional airfoils.
A complex tones-producing phenomenon is examined by means of
theoretical, numerical and experimental studies, with the most recent
results reported in the current paper. High-accuracy numerical studies
are performed for selected transitional-flow regimes for NACA-0012 and
SD7003 airfoils for which experimental measurements recorded strong
flow-acoustic resonant interactions characterized by multiple-tone acoustic
spectra. Numerical studies employ a 6th-order Navier-Stokes solver
implementing low-pass filtering of poorly resolved high-frequency solution
content to retain numerical accuracy and stability over the range of
transitional flow regimes. The numerical results of this study clearly
indicate the effect of various parameters such as upstream flow conditions,
angle of attack, and mean flow velocity on the transition between toneproducing
and no-tone-producing flow regime.
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摘要 :
This work examines the effects of bi-modal excitation on a Mach 1.5 heated shear layer of a planar jet. A reduced order model is derived, turning the Navier-Stokes equations into a set of coupled ordinary differential equations. A...
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This work examines the effects of bi-modal excitation on a Mach 1.5 heated shear layer of a planar jet. A reduced order model is derived, turning the Navier-Stokes equations into a set of coupled ordinary differential equations. A prior Large-Eddy Simulation's data from the minor plane of a Mach 1.5 heated rectangular jet is used to fit the mean flow profiles at various streamwise locations in the form of a hyperbolic tangent profile. Locally-parallel linear stability theory is then used to obtain the transverse shapes of the coherent structure components involved. The set of ordinary differential equations is first solved for the nonlinear development of a single mode, and then for bi-modal excitation at a pair of fundamental and harmonic frequencies. The trends for the single mode excitation qualitatively compared well with previous work. Bi-modal excitation is then examined for the fundamental Strouhal number 0.10, which has been identified as a dominant noise source. Cases were considered separately with adding the subharmonic and the harmonic as a means of reducing the amplitude of the fundamental. Adding the subharmonic had minimal effects on reducing the fundamental unless both initial amplitudes are large. However, adding the harmonic could be very effective at reducing the fundamental even at low initial amplitudes.
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The noise generation by moderate-Reynolds number airfoils is still a topic of major interest because of the wide area of its applications. However, the underlying mechanism is not totally clear. The present paper is dealing with a...
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The noise generation by moderate-Reynolds number airfoils is still a topic of major interest because of the wide area of its applications. However, the underlying mechanism is not totally clear. The present paper is dealing with an exhaustive experimental characterization addressing aerodynamic and acoustic quantities. The symmetric NACA-0012 airfoil and the slightly cambered SD7003 airfoil at moderate incidence (angles of attack varied from -5° to +7°) are tested in the free-jet anechoic wind tunnel of Ecole Centrale de Lyon. Measurements of wall pressure, far-field acoustic pressure and velocity fluctuations using the hot-wire anemometry are described. In addition advanced post-processing techniques are applied, such as the time-frequency analysis and the bicoherence in order to highlight some non-linear features and/or intermittency. Three regimes of noise emission are identified depending on the configuration and flow velocity. The results complement the database started in previous investigations. They are used for comparison with numerical simulations presented in the second part of the paper.
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摘要 :
The noise generation by moderate-Reynolds number airfoils is still a topic of major interest because of the wide area of its applications. However, the underlying mechanism is not totally clear. The present paper is dealing with a...
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The noise generation by moderate-Reynolds number airfoils is still a topic of major interest because of the wide area of its applications. However, the underlying mechanism is not totally clear. The present paper is dealing with an exhaustive experimental characterization addressing aerodynamic and acoustic quantities. The symmetric NACA-0012 airfoil and the slightly cambered SD7003 airfoil at moderate incidence (angles of attack varied from -5° to +7°) are tested in the free-jet anechoic wind tunnel of Ecole Centrale de Lyon. Measurements of wall pressure, far-field acoustic pressure and velocity fluctuations using the hot-wire anemometry are described. In addition advanced post-processing techniques are applied, such as the time-frequency analysis and the bicoherence in order to highlight some non-linear features and/or intermittency. Three regimes of noise emission are identified depending on the configuration and flow velocity. The results complement the database started in previous investigations. They are used for comparison with numerical simulations presented in the second part of the paper.
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The current preliminary study initiates complementary experimental and numerical efforts to re-examine resonant feedback mechanism of flow-acoustic interactions in airfoil transitional boundary layers and its contribution to low-s...
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The current preliminary study initiates complementary experimental and numerical efforts to re-examine resonant feedback mechanism of flow-acoustic interactions in airfoil transitional boundary layers and its contribution to low-speed airfoil trailing-edge noise. Furthermore, the impact of impinging vortical flow disturbances and the corresponding interaction of leading and trailing edge noise sources is considered. Recorded unsteady responses of loaded, transitional NACA0012 airfoil with tripped suction or pressure sides indicate the presence of shifted ladder-type tonal structures with dual velocity dependence in the acoustic signal previously reported in the literature. The installation of upstream grid generating low-intensity turbulence appears to eliminate the feedback mechanism leaving just a single velocity dependence for the dominant spectral components. Numerical efforts employ a high-order Navier-Stokes solver implementing low-pass filtering of poorly resolved high-frequency solution content to retain numerical accuracy and stability over the range of flow regimes. Upstream flow disturbances are introduced inside the computational domain through a source term in the momentum equations.
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摘要 :
The current preliminary study initiates complementary experimental and numerical efforts to re-examine resonant feedback mechanism of flow-acoustic interactions in airfoil transitional boundary layers and its contribution to low-s...
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The current preliminary study initiates complementary experimental and numerical efforts to re-examine resonant feedback mechanism of flow-acoustic interactions in airfoil transitional boundary layers and its contribution to low-speed airfoil trailing-edge noise. Furthermore, the impact of impinging vortical flow disturbances and the corresponding interaction of leading and trailing edge noise sources is considered. Recorded unsteady responses of loaded, transitional NACA0012 airfoil with tripped suction or pressure sides indicate the presence of shifted ladder-type tonal structures with dual velocity dependence in the acoustic signal previously reported in the literature. The installation of upstream grid generating low-intensity turbulence appears to eliminate the feedback mechanism leaving just a single velocity dependence for the dominant spectral components. Numerical efforts employ a high-order Navier-Stokes solver implementing low-pass filtering of poorly resolved high-frequency solution content to retain numerical accuracy and stability over the range of flow regimes. Upstream flow disturbances are introduced inside the computational domain through a source term in the momentum equations.
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