摘要 :
Sustained flight at hypersonic speeds presents an enduring challenge to robust vehicle design and control. An extreme aerothermal environment acting on geometrically-thin, multifunctional structures can result in significant struc...
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Sustained flight at hypersonic speeds presents an enduring challenge to robust vehicle design and control. An extreme aerothermal environment acting on geometrically-thin, multifunctional structures can result in significant structural deformations of the vehicle and/or its control surfaces. In particular, the adverse pressure gradient generated by a compression ramp can produce large regions of separated flow with the potential to adversely influence accurate prediction of the surface pressure using traditional hypersonic methods such as piston theory. The present work details high-fidelity, coupled aeroelastic simulations of laminar, unsteady 2D flow at M_∞ = 6.04 over a 35-degree compression ramp with an embedded compliant panel. Surface-pressure, skin friction, and heat transfer generated by the corner Shock Wave Boundary Layer Interaction (SWBLI) are compared between rigid and compliant configurations. A reduction in heat transfer is observed for a majority of compliant cases relative to the rigid case, while heat transfer analogies were found to be inaccurate for the compliant cases. Several aerodynamic reduced-order models (ROMs) are compared to the simulation data, and a simple modification is proposed which is found to improve the model accuracy considerably.
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摘要 :
Sustained flight at hypersonic speeds presents an enduring challenge to robust vehicle design and control. An extreme aerothermal environment acting on geometrically-thin, multifunctional structures can result in significant struc...
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Sustained flight at hypersonic speeds presents an enduring challenge to robust vehicle design and control. An extreme aerothermal environment acting on geometrically-thin, multifunctional structures can result in significant structural deformations of the vehicle and/or its control surfaces. In particular, the adverse pressure gradient generated by a compression ramp can produce large regions of separated flow with the potential to adversely influence accurate prediction of the surface pressure using traditional hypersonic methods such as piston theory. The present work details high-fidelity, coupled aeroelastic simulations of laminar, unsteady 2D flow at M_∞ = 6.04 over a 35-degree compression ramp with an embedded compliant panel. Surface-pressure, skin friction, and heat transfer generated by the corner Shock Wave Boundary Layer Interaction (SWBLI) are compared between rigid and compliant configurations. A reduction in heat transfer is observed for a majority of compliant cases relative to the rigid case, while heat transfer analogies were found to be inaccurate for the compliant cases. Several aerodynamic reduced-order models (ROMs) are compared to the simulation data, and a simple modification is proposed which is found to improve the model accuracy considerably.
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Indirect combustion noise is believed to be a key component of turbofan engine core noise, hut existing experimental data have not been able to definitively determine its importance. Instead, actuator disk theory (ADT) as develope...
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Indirect combustion noise is believed to be a key component of turbofan engine core noise, hut existing experimental data have not been able to definitively determine its importance. Instead, actuator disk theory (ADT) as developed by Cumpsty & Marble (Proceedings of the Royal Society of London A, 357, pp. 323-344, 1977), is commonly used to estimate its contribution based on combustor exit conditions and changes in the mean flow across blade rows. The theory, which assumes planar propagation of acoustic, entropic, and vortical waves in the long wavelength limit, is assessed by comparing its predictions to those from two-dimensional compressible Euler calculations of idealized entropy disturbances interacting with a 1980s era NASA turbine stator. Both low-frequency planar waves of constant frequency and higher-frequency, localized entropy disturbances are considered, with the former being within ADT's range of applicability and the latter outside of it. It is found that ADT performs well for the cut-on acoustic modes generated by the entropy-blade interaction but it's accuracy suffers for the cut-off acoustic modes, which could impact indirect combustion noise predictions for turbines with closely spaced blade rows.
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摘要 :
Indirect combustion noise is believed to be a key component of turbofan engine core noise, hut existing experimental data have not been able to definitively determine its importance. Instead, actuator disk theory (ADT) as develope...
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Indirect combustion noise is believed to be a key component of turbofan engine core noise, hut existing experimental data have not been able to definitively determine its importance. Instead, actuator disk theory (ADT) as developed by Cumpsty & Marble (Proceedings of the Royal Society of London A, 357, pp. 323-344, 1977), is commonly used to estimate its contribution based on combustor exit conditions and changes in the mean flow across blade rows. The theory, which assumes planar propagation of acoustic, entropic, and vortical waves in the long wavelength limit, is assessed by comparing its predictions to those from two-dimensional compressible Euler calculations of idealized entropy disturbances interacting with a 1980s era NASA turbine stator. Both low-frequency planar waves of constant frequency and higher-frequency, localized entropy disturbances are considered, with the former being within ADT's range of applicability and the latter outside of it. It is found that ADT performs well for the cut-on acoustic modes generated by the entropy-blade interaction but it's accuracy suffers for the cut-off acoustic modes, which could impact indirect combustion noise predictions for turbines with closely spaced blade rows.
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Acoustic liners usually operate in the presence of a high speed turbulent grazing flow. In this paper, numerous investigations of an acoustically excited flow field inside and outside a conventional honeycomb liner under Mach 0.5 ...
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Acoustic liners usually operate in the presence of a high speed turbulent grazing flow. In this paper, numerous investigations of an acoustically excited flow field inside and outside a conventional honeycomb liner under Mach 0.5 laminar or turbulent boundary layers are performed using DNS, with a focus on the interaction between the orifice and the boundary layer. The numerical simulations were conducted at different incident sound pressure levels (SPLs) and frequencies. Using flow visualization of the boundary layer-orifice interaction, basic flow features near and far away from the liner orifice are presented. A comparison of laminar and turbulent grazing flow conditions are also considered for the same incident acoustic field conditions. Impedance prediction applies the traditional Dean's method and the numerical predicted results are compared with experimental data from NASA Langley. Discussions of the impedance prediction including its precision and accuracy are also provided.
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摘要 :
Acoustic liners usually operate in the presence of a high speed turbulent grazing flow. In this paper, numerous investigations of an acoustically excited flow field inside and outside a conventional honeycomb liner under Mach 0.5 ...
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Acoustic liners usually operate in the presence of a high speed turbulent grazing flow. In this paper, numerous investigations of an acoustically excited flow field inside and outside a conventional honeycomb liner under Mach 0.5 laminar or turbulent boundary layers are performed using DNS, with a focus on the interaction between the orifice and the boundary layer. The numerical simulations were conducted at different incident sound pressure levels (SPLs) and frequencies. Using flow visualization of the boundary layer-orifice interaction, basic flow features near and far away from the liner orifice are presented. A comparison of laminar and turbulent grazing flow conditions are also considered for the same incident acoustic field conditions. Impedance prediction applies the traditional Dean's method and the numerical predicted results are compared with experimental data from NASA Langley. Discussions of the impedance prediction including its precision and accuracy are also provided.
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Single degree-of-freedom conventional acoustic liners are widely installed in jet engines to reduce internal engine noise. They work by converting acoustic energy into vorticity-bound fluctuations. Despite being widely used, effec...
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Single degree-of-freedom conventional acoustic liners are widely installed in jet engines to reduce internal engine noise. They work by converting acoustic energy into vorticity-bound fluctuations. Despite being widely used, effective design-stage models of acoustic liners placed in high sound amplitude conditions, possibly with a turbulent grazing flow, are not available due to the near-liner flow complexity and diagnostic challenges. The work presented in this thesis uses direct numerical simulations (DNS) of a compressible, viscous fluid to understand the inherent fluid mechanics and guide reduced-order-model development. In this work, detailed interaction of an incident acoustic field with a Mach 0.5 laminar and turbulent grazing flow with a cavity-backed circular orifice is studied. All results are for tonal excitation at 130 dB from 2.2 - 3.0 kHz, or at 3 kHz with 130 - 160 dB acoustic amplitude. The results suggest that the liner experiences a drag increase over the baseline geometry with acoustic excitation and that facesheet shear stress measurements, while dominant at low acoustic amplitudes, contribute less at higher acoustic amplitudes. The DNS data further show that the orifice discharge coefficient can be semi-empirically modeled effectively using an acoustic-hydrodynamic scaling. The results indicate that experimental in situ impedance measurements can be contaminated by microphone-orifice interaction. Finally, the time-domain model without grazing flow was extended to include grazing flow by properly modeling the discharge coefficient and the turbulent boundary layer effect. Reasonable agreement of the liner impedance prediction was found with the DNS data. Discrepancies of the prediction suggest the future improvement of the model development.
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摘要 :
Single degree-of-freedom conventional acoustic liners are widely installed in jet engines to reduce internal engine noise. They work by converting acoustic energy into vorticity-bound fluctuations. Despite being widely used, effec...
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Single degree-of-freedom conventional acoustic liners are widely installed in jet engines to reduce internal engine noise. They work by converting acoustic energy into vorticity-bound fluctuations. Despite being widely used, effective design-stage models of acoustic liners placed in high sound amplitude conditions, possibly with a turbulent grazing flow, are not available due to the near-liner flow complexity and diagnostic challenges. The work presented in this thesis uses direct numerical simulations (DNS) of a compressible, viscous fluid to understand the inherent fluid mechanics and guide reduced-order-model development. In this work, detailed interaction of an incident acoustic field with a Mach 0.5 laminar and turbulent grazing flow with a cavity-backed circular orifice is studied. All results are for tonal excitation at 130 dB from 2.2 - 3.0 kHz, or at 3 kHz with 130 - 160 dB acoustic amplitude. The results suggest that the liner experiences a drag increase over the baseline geometry with acoustic excitation and that facesheet shear stress measurements, while dominant at low acoustic amplitudes, contribute less at higher acoustic amplitudes. The DNS data further show that the orifice discharge coefficient can be semi-empirically modeled effectively using an acoustic-hydrodynamic scaling. The results indicate that experimental in situ impedance measurements can be contaminated by microphone-orifice interaction. Finally, the time-domain model without grazing flow was extended to include grazing flow by properly modeling the discharge coefficient and the turbulent boundary layer effect. Reasonable agreement of the liner impedance prediction was found with the DNS data. Discrepancies of the prediction suggest the future improvement of the model development.
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Acoustic liners play an important role in aircraft gas turbine engine noise reduction by converting acoustic fluctuations into nonradiating vortical disturbances through small openings, or apertures. In the recent years, numerical...
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Acoustic liners play an important role in aircraft gas turbine engine noise reduction by converting acoustic fluctuations into nonradiating vortical disturbances through small openings, or apertures. In the recent years, numerical investigations of acoustic liners have become a popular tool to analyze their characteristics. Although most of the previous efforts focused on 2D simulations to uncover many of the working mechanisms of acoustic liners, a better understanding requires 3D simulations. Hence, in this paper, a 3D model of a honeycomb liner with circular apertures is used. The configuration of this model is based on one of the designs investigated at the NASA Langley Research Center. The goal of the simulations is to analyze the flow characteristics of normal incident sound interacting with the liner aperture. A series of simulations were performed by varying the intensity and frequency of the incident sound. Through the numerical simulation data, a detailed flow visualization and acoustic energy dissipation quantification at different sound pressure levels and frequencies are presented. Impedance values were predicted using the traditional two microphone method. Reasonable agreement between the experimental measurements and numerical predictions of the normalized impedance are found. Finally, a time domain analysis of the data is also presented.
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摘要 :
Acoustic liners play an important role in aircraft gas turbine engine noise reduction by converting acoustic fluctuations into nonradiating vortical disturbances through small openings, or apertures. In the recent years, numerical...
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Acoustic liners play an important role in aircraft gas turbine engine noise reduction by converting acoustic fluctuations into nonradiating vortical disturbances through small openings, or apertures. In the recent years, numerical investigations of acoustic liners have become a popular tool to analyze their characteristics. Although most of the previous efforts focused on 2D simulations to uncover many of the working mechanisms of acoustic liners, a better understanding requires 3D simulations. Hence, in this paper, a 3D model of a honeycomb liner with circular apertures is used. The configuration of this model is based on one of the designs investigated at the NASA Langley Research Center. The goal of the simulations is to analyze the flow characteristics of normal incident sound interacting with the liner aperture. A series of simulations were performed by varying the intensity and frequency of the incident sound. Through the numerical simulation data, a detailed flow visualization and acoustic energy dissipation quantification at different sound pressure levels and frequencies are presented. Impedance values were predicted using the traditional two microphone method. Reasonable agreement between the experimental measurements and numerical predictions of the normalized impedance are found. Finally, a time domain analysis of the data is also presented.
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