The Experts below are selected from a list of 1332 Experts worldwide ranked by ideXlab platform

N Molin - One of the best experts on this subject based on the ideXlab platform.

  • Landing gear noise control using perforated Fairings
    Acta Mechanica Sinica Lixue Xuebao, 2010
    Co-Authors: K. Boorsma, Xin Zhang, N Molin
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using Fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these Fairings has been confirmed by flight tests to further enable noise reduction. Following an earlier fundamental study of the application of perforated Fairings, a study has been performed to investigate and optimize the benefits of bleeding air through landing gear Fairings. By means of wind tunnel tests, an aerodynamic and acoustic survey has been performed on a simplified generic main landing gear to explore the influence of (perforated) Fairings on the lower part of the gear. The results show that for this specific case, the application of impermeable Fairings reduces noise in the mid- and high frequency range by shielding sharp edged components from high velocity impingement. However, below 1kHz the noise is shown to increase significantly.Application of the perforations is shown to diminish this low frequency increase whilst maintaining the reduction in the mid- and high frequency range. The aerodynamic and acoustic measurements point in the direction of the separated flow of the Fairings interacting with the downstream gear components responsible for the low frequency noise increase. Bleeding of the air through the Fairings reduces the large scale turbulence in the proximity of these components and hence diminishes the low frequency noise increase.

  • bluff body noise control using perforated Fairings
    AIAA Journal, 2009
    Co-Authors: K. Boorsma, N Molin, Xin Zhang, Leung Choi Chow
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using Fairings to shield components from high-speed impingement reduces noise. Furthermore, perforating these Fairings has been confirmed by flight tests to enable a further reduction. A fundamental study has been performed to investigate and optimize the benefits of bleeding air through the fairing by application of perforations. Experiments have been performed with a simplified fairing–strut combination to clarify the influence of perforations on flow behavior and acoustics. The fairing self-noise is reduced significantly by breakdown of the vortex shedding process, resulting in a reduction of the associated broadband noise level. A redistribution of the velocities is achieved depending on the applied porosity. However, increasing the porosity can result in adverse noise effects due to the bled mass flow washing the strut. Self-noise of the perforations manifests itself at higher frequencies, although scaling of this phenomenon with orifice diameter opens up the possibility to shift it above the upper limit of the audible range.

  • perforated Fairings for landing gear noise control
    AIAA CEAS Aeroacoustics Conference, 2008
    Co-Authors: K. Boorsma, Xin Zhang, N Molin
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using Fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these Fairings has been confirmed by flight tests to further enable noise reduction. Following a more fundamental study on the application of perforated Fairings, a study has been performed to investigate and optimize the benefits of bleeding air through landing gear Fairings. By means of wind tunnel tests, an aerodynamic and acoustic survey has been performed on a simplified generic main landing gear to explore the influence of (perforated) Fairings on the lower part of the gear. The results show that for this specific case, the application of impermeable Fairings reduces noise in the mid- and high frequency range by shielding sharp edged components from high velocity impingement. However, below 1 kHz the noise is shown to increase significantly. Application of the perforations is shown to diminish this low frequency increase whilst maintaining the reduction in the mid- and high frequency range. The aerodynamic and acoustic measurements point in the direction of the separated flow of the Fairings interacting with the downstream gear components responsible for the low frequency noise increase. Bleeding of the air through the Fairings reduces the large scale turbulence in the proximity of these components and hence diminishes the low frequency increase. A sharp noise increase is present in the ground view direction at the 500 Hz centred tertsband for the solid fairing, which is confirmed to originate from the articulation link fairing. The flow around the wheels remains largely unaltered by application of the Fairings. Furthermore the application of Fairings is shown to suppress vortex shedding from the lower part of the main leg. A study on the effectiveness of perforation location reveals that the stagnation area perforations are responsible for most of the low frequency noise decrease. Both articulation link and undertray fairing contribute to the reduction. Exposing the perforate outside the stagnation area induces perforate self-noise, most significantly on the sides of the lower articulation link fairing. Agreeing with previous studies, the phenomenon scales with the local component of the shearing flow velocity and orifice diameter.

  • perforated Fairings for blufi body noise control
    AIAA CEAS Aeroacoustics Conference, 2007
    Co-Authors: K. Boorsma, Xin Zhang, N Molin
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach conflguration. Using Fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these Fairings has been conflrmed by ∞ight tests to further enable noise reduction. A fundamental study has been performed to investigate and optimize the beneflts of bleeding air through the fairing by application of perforations. Wind tunnel tests have been performed with a simplifled fairing-cylindrical strut combination to clarify in∞uence of perforations on ∞ow behaviour and acoustics. The results show that for this speciflc case, the fairing self noise is reduced signiflcantly by breakdown of the vortex shedding process. The perforated Fairings, exhibiting difierent porosities between 33% and 55%, appear to be equally e‐cient in removing the spectral peak associated with the vortex shedding. A redistribution of the velocities is achieved depending on the applied porosity. Perforate selfnoise manifests itself at higher frequencies, although scaling of this phenomenon with oriflce diameter opens up the possibility to shift it above the upper limit of the audible range.

K. Boorsma - One of the best experts on this subject based on the ideXlab platform.

  • Landing gear noise control using perforated Fairings
    Acta Mechanica Sinica Lixue Xuebao, 2010
    Co-Authors: K. Boorsma, Xin Zhang, N Molin
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using Fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these Fairings has been confirmed by flight tests to further enable noise reduction. Following an earlier fundamental study of the application of perforated Fairings, a study has been performed to investigate and optimize the benefits of bleeding air through landing gear Fairings. By means of wind tunnel tests, an aerodynamic and acoustic survey has been performed on a simplified generic main landing gear to explore the influence of (perforated) Fairings on the lower part of the gear. The results show that for this specific case, the application of impermeable Fairings reduces noise in the mid- and high frequency range by shielding sharp edged components from high velocity impingement. However, below 1kHz the noise is shown to increase significantly.Application of the perforations is shown to diminish this low frequency increase whilst maintaining the reduction in the mid- and high frequency range. The aerodynamic and acoustic measurements point in the direction of the separated flow of the Fairings interacting with the downstream gear components responsible for the low frequency noise increase. Bleeding of the air through the Fairings reduces the large scale turbulence in the proximity of these components and hence diminishes the low frequency noise increase.

  • bluff body noise control using perforated Fairings
    AIAA Journal, 2009
    Co-Authors: K. Boorsma, N Molin, Xin Zhang, Leung Choi Chow
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using Fairings to shield components from high-speed impingement reduces noise. Furthermore, perforating these Fairings has been confirmed by flight tests to enable a further reduction. A fundamental study has been performed to investigate and optimize the benefits of bleeding air through the fairing by application of perforations. Experiments have been performed with a simplified fairing–strut combination to clarify the influence of perforations on flow behavior and acoustics. The fairing self-noise is reduced significantly by breakdown of the vortex shedding process, resulting in a reduction of the associated broadband noise level. A redistribution of the velocities is achieved depending on the applied porosity. However, increasing the porosity can result in adverse noise effects due to the bled mass flow washing the strut. Self-noise of the perforations manifests itself at higher frequencies, although scaling of this phenomenon with orifice diameter opens up the possibility to shift it above the upper limit of the audible range.

  • Aeroacoustic control of landing gear noise using perforated Fairings
    2008
    Co-Authors: K. Boorsma
    Abstract:

    A study was performed to investigate and optimize the application of perforated Fairings for landing gear noise control. The sparse knowledge about this new subject has necessitated a more fundamental study involving a basic fairing-strut configuration, followed by wind tunnel tests on a simplified landing gear configuration incorporating perforated Fairings. For the basic configuration, various exchangeable perforated half-cylindrical shells shrouding a circular cylinder were the subject of aerodynamic and acoustic tests. A qualitative and quantitative description has been given of the influence of perforated Fairings on time averaged and unsteady flow and the related acoustics. The bled air through the shell prevents the formation of large scale vortices associatedwith the shell and thereby reduces low frequency noise. However, a test with a noisy H-beam replacing the circular cylinder has indicated that increasing porosity can result in adverse noise effects due to the bled mass flow washing the strut. Shearing flow past the perforate has been shown to create adverse self-noise of which both intensity and spectral content are dictated by the local velocity past the perforate. The application of perforated Fairings to the simplified landing gear model reduces the low frequency noise introduced by the solid Fairings to values below the baseline landing gear configuration in both side and ground view directions. Exposing the perforate outside the stagnation area does not yield extra noise reduction but introduces perforate self-noise. The synthesis of the conducted studies has shed new light on the application of perforated Fairings for landing gear noise control. In particular the effects of porosity and perforation location have been clarified. However more research is needed for further optimization of these parameters.

  • perforated Fairings for landing gear noise control
    AIAA CEAS Aeroacoustics Conference, 2008
    Co-Authors: K. Boorsma, Xin Zhang, N Molin
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using Fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these Fairings has been confirmed by flight tests to further enable noise reduction. Following a more fundamental study on the application of perforated Fairings, a study has been performed to investigate and optimize the benefits of bleeding air through landing gear Fairings. By means of wind tunnel tests, an aerodynamic and acoustic survey has been performed on a simplified generic main landing gear to explore the influence of (perforated) Fairings on the lower part of the gear. The results show that for this specific case, the application of impermeable Fairings reduces noise in the mid- and high frequency range by shielding sharp edged components from high velocity impingement. However, below 1 kHz the noise is shown to increase significantly. Application of the perforations is shown to diminish this low frequency increase whilst maintaining the reduction in the mid- and high frequency range. The aerodynamic and acoustic measurements point in the direction of the separated flow of the Fairings interacting with the downstream gear components responsible for the low frequency noise increase. Bleeding of the air through the Fairings reduces the large scale turbulence in the proximity of these components and hence diminishes the low frequency increase. A sharp noise increase is present in the ground view direction at the 500 Hz centred tertsband for the solid fairing, which is confirmed to originate from the articulation link fairing. The flow around the wheels remains largely unaltered by application of the Fairings. Furthermore the application of Fairings is shown to suppress vortex shedding from the lower part of the main leg. A study on the effectiveness of perforation location reveals that the stagnation area perforations are responsible for most of the low frequency noise decrease. Both articulation link and undertray fairing contribute to the reduction. Exposing the perforate outside the stagnation area induces perforate self-noise, most significantly on the sides of the lower articulation link fairing. Agreeing with previous studies, the phenomenon scales with the local component of the shearing flow velocity and orifice diameter.

  • perforated Fairings for blufi body noise control
    AIAA CEAS Aeroacoustics Conference, 2007
    Co-Authors: K. Boorsma, Xin Zhang, N Molin
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach conflguration. Using Fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these Fairings has been conflrmed by ∞ight tests to further enable noise reduction. A fundamental study has been performed to investigate and optimize the beneflts of bleeding air through the fairing by application of perforations. Wind tunnel tests have been performed with a simplifled fairing-cylindrical strut combination to clarify in∞uence of perforations on ∞ow behaviour and acoustics. The results show that for this speciflc case, the fairing self noise is reduced signiflcantly by breakdown of the vortex shedding process. The perforated Fairings, exhibiting difierent porosities between 33% and 55%, appear to be equally e‐cient in removing the spectral peak associated with the vortex shedding. A redistribution of the velocities is achieved depending on the applied porosity. Perforate selfnoise manifests itself at higher frequencies, although scaling of this phenomenon with oriflce diameter opens up the possibility to shift it above the upper limit of the audible range.

George Em Karniadakis - One of the best experts on this subject based on the ideXlab platform.

  • u shaped Fairings suppress vortex induced vibrations for cylinders in cross flow
    Journal of Fluid Mechanics, 2015
    Co-Authors: Fangfang Xie, Yiannis Constantinides, Michael S Triantafyllou, George Em Karniadakis
    Abstract:

    We employ three-dimensional direct and large-eddy numerical simulations of the vibrations and flow past cylinders fitted with free-to-rotate U-shaped Fairings placed in a cross-flow at Reynolds number . Such Fairings are nearly neutrally buoyant devices fitted along the axis of long circular risers to suppress vortex-induced vibrations (VIVs). We consider three different geometric configurations: a homogeneous fairing, and two configurations (denoted A and AB) involving a gap between adjacent segments. For the latter two cases, we investigate the effect of the gap on the hydrodynamic force coefficients and the translational and rotational motions of the system. For all configurations, as the Reynolds number increases beyond 500, both the lift and drag coefficients decrease. Compared to a plain cylinder, a homogeneous fairing system (no gaps) can help reduce the drag force coefficient by 15 % for reduced velocity , while a type A gap system can reduce the drag force coefficient by almost 50 % for reduced velocity , and, correspondingly, the vibration response of the combined system, as well as the fairing rotation amplitude, are substantially reduced. For a homogeneous fairing, the cross-flow amplitude is reduced by about 80 %, whereas for Fairings with a gap longer than half a cylinder diameter, VIVs are completely eliminated, resulting in additional reduction in the drag coefficient. We have related such VIV suppression or elimination to the features of the wake flow structure. We find that a gap causes the generation of strong streamwise vorticity in the gap region that interferes destructively with the vorticity generated by the Fairings, hence disorganizing the formation of coherent spanwise cortical patterns. We provide visualization of the incoherent wake flow that leads to total elimination of the vibration and rotation of the fairing–cylinder system. Finally, we investigate the effect of the friction coefficient between cylinder and fairing. The effect overall is small, even when the friction coefficients of adjacent segments are different. In some cases the equilibrium positions of the Fairings are rotated by a small angle on either side of the centreline, in a symmetry-breaking bifurcation, which depends strongly on Reynolds number.

  • suppression of vortex induced vibrations by Fairings a numerical study
    Journal of Fluids and Structures, 2015
    Co-Authors: Fangfang Xie, Yiannis Constantinides, Hongmei Yan, Owen H Oakley, George Em Karniadakis
    Abstract:

    Abstract Fairings are nearly neutrally buoyant devices, fitted along the axis of long circular risers to suppress vortex-induced vibrations (VIV) and possibly reduce the drag force. Here we study numerically how VIV can be practically eliminated by using free-to-rotate Fairings. Since the rotational inertia is low for the Fairings, direct numerical simulations based on standard fluid–structure interaction algorithms may fail because of the so-called added mass effect. To resolve this problem we introduce fictitious methods and successfully stabilize the simulations. We then investigate the effect of rotational friction Cf on the stabilization effect of the Fairings. In particular through two-dimensional (2D) simulations we find that when the Reynolds number is low (Re=100), Cf=0 is the most effective choice in suppressing VIV. Moreover, at this low Reynolds number there exists a critical value of Cf around which large oscillations and non-symmetric trajectories are observed. On the other hand, at higher Reynolds number (Re=500) a different behavior emerges, i.e. VIV are suppressed continuously as Cf increases. At Re=1000, we perform 3D simulations to investigate the effects of three-dimensionality of the flow on the vibration and rotation responses. In this work we quantify numerically for the first time various salient features of free-to-rotate devices for VIV suppression and relate them to modified flow structures in the near wake.

Fangfang Xie - One of the best experts on this subject based on the ideXlab platform.

  • u shaped Fairings suppress vortex induced vibrations for cylinders in cross flow
    Journal of Fluid Mechanics, 2015
    Co-Authors: Fangfang Xie, Yiannis Constantinides, Michael S Triantafyllou, George Em Karniadakis
    Abstract:

    We employ three-dimensional direct and large-eddy numerical simulations of the vibrations and flow past cylinders fitted with free-to-rotate U-shaped Fairings placed in a cross-flow at Reynolds number . Such Fairings are nearly neutrally buoyant devices fitted along the axis of long circular risers to suppress vortex-induced vibrations (VIVs). We consider three different geometric configurations: a homogeneous fairing, and two configurations (denoted A and AB) involving a gap between adjacent segments. For the latter two cases, we investigate the effect of the gap on the hydrodynamic force coefficients and the translational and rotational motions of the system. For all configurations, as the Reynolds number increases beyond 500, both the lift and drag coefficients decrease. Compared to a plain cylinder, a homogeneous fairing system (no gaps) can help reduce the drag force coefficient by 15 % for reduced velocity , while a type A gap system can reduce the drag force coefficient by almost 50 % for reduced velocity , and, correspondingly, the vibration response of the combined system, as well as the fairing rotation amplitude, are substantially reduced. For a homogeneous fairing, the cross-flow amplitude is reduced by about 80 %, whereas for Fairings with a gap longer than half a cylinder diameter, VIVs are completely eliminated, resulting in additional reduction in the drag coefficient. We have related such VIV suppression or elimination to the features of the wake flow structure. We find that a gap causes the generation of strong streamwise vorticity in the gap region that interferes destructively with the vorticity generated by the Fairings, hence disorganizing the formation of coherent spanwise cortical patterns. We provide visualization of the incoherent wake flow that leads to total elimination of the vibration and rotation of the fairing–cylinder system. Finally, we investigate the effect of the friction coefficient between cylinder and fairing. The effect overall is small, even when the friction coefficients of adjacent segments are different. In some cases the equilibrium positions of the Fairings are rotated by a small angle on either side of the centreline, in a symmetry-breaking bifurcation, which depends strongly on Reynolds number.

  • suppression of vortex induced vibrations by Fairings a numerical study
    Journal of Fluids and Structures, 2015
    Co-Authors: Fangfang Xie, Yiannis Constantinides, Hongmei Yan, Owen H Oakley, George Em Karniadakis
    Abstract:

    Abstract Fairings are nearly neutrally buoyant devices, fitted along the axis of long circular risers to suppress vortex-induced vibrations (VIV) and possibly reduce the drag force. Here we study numerically how VIV can be practically eliminated by using free-to-rotate Fairings. Since the rotational inertia is low for the Fairings, direct numerical simulations based on standard fluid–structure interaction algorithms may fail because of the so-called added mass effect. To resolve this problem we introduce fictitious methods and successfully stabilize the simulations. We then investigate the effect of rotational friction Cf on the stabilization effect of the Fairings. In particular through two-dimensional (2D) simulations we find that when the Reynolds number is low (Re=100), Cf=0 is the most effective choice in suppressing VIV. Moreover, at this low Reynolds number there exists a critical value of Cf around which large oscillations and non-symmetric trajectories are observed. On the other hand, at higher Reynolds number (Re=500) a different behavior emerges, i.e. VIV are suppressed continuously as Cf increases. At Re=1000, we perform 3D simulations to investigate the effects of three-dimensionality of the flow on the vibration and rotation responses. In this work we quantify numerically for the first time various salient features of free-to-rotate devices for VIV suppression and relate them to modified flow structures in the near wake.

Xin Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Landing gear noise control using perforated Fairings
    Acta Mechanica Sinica Lixue Xuebao, 2010
    Co-Authors: K. Boorsma, Xin Zhang, N Molin
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using Fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these Fairings has been confirmed by flight tests to further enable noise reduction. Following an earlier fundamental study of the application of perforated Fairings, a study has been performed to investigate and optimize the benefits of bleeding air through landing gear Fairings. By means of wind tunnel tests, an aerodynamic and acoustic survey has been performed on a simplified generic main landing gear to explore the influence of (perforated) Fairings on the lower part of the gear. The results show that for this specific case, the application of impermeable Fairings reduces noise in the mid- and high frequency range by shielding sharp edged components from high velocity impingement. However, below 1kHz the noise is shown to increase significantly.Application of the perforations is shown to diminish this low frequency increase whilst maintaining the reduction in the mid- and high frequency range. The aerodynamic and acoustic measurements point in the direction of the separated flow of the Fairings interacting with the downstream gear components responsible for the low frequency noise increase. Bleeding of the air through the Fairings reduces the large scale turbulence in the proximity of these components and hence diminishes the low frequency noise increase.

  • bluff body noise control using perforated Fairings
    AIAA Journal, 2009
    Co-Authors: K. Boorsma, N Molin, Xin Zhang, Leung Choi Chow
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using Fairings to shield components from high-speed impingement reduces noise. Furthermore, perforating these Fairings has been confirmed by flight tests to enable a further reduction. A fundamental study has been performed to investigate and optimize the benefits of bleeding air through the fairing by application of perforations. Experiments have been performed with a simplified fairing–strut combination to clarify the influence of perforations on flow behavior and acoustics. The fairing self-noise is reduced significantly by breakdown of the vortex shedding process, resulting in a reduction of the associated broadband noise level. A redistribution of the velocities is achieved depending on the applied porosity. However, increasing the porosity can result in adverse noise effects due to the bled mass flow washing the strut. Self-noise of the perforations manifests itself at higher frequencies, although scaling of this phenomenon with orifice diameter opens up the possibility to shift it above the upper limit of the audible range.

  • perforated Fairings for landing gear noise control
    AIAA CEAS Aeroacoustics Conference, 2008
    Co-Authors: K. Boorsma, Xin Zhang, N Molin
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach configuration. Using Fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these Fairings has been confirmed by flight tests to further enable noise reduction. Following a more fundamental study on the application of perforated Fairings, a study has been performed to investigate and optimize the benefits of bleeding air through landing gear Fairings. By means of wind tunnel tests, an aerodynamic and acoustic survey has been performed on a simplified generic main landing gear to explore the influence of (perforated) Fairings on the lower part of the gear. The results show that for this specific case, the application of impermeable Fairings reduces noise in the mid- and high frequency range by shielding sharp edged components from high velocity impingement. However, below 1 kHz the noise is shown to increase significantly. Application of the perforations is shown to diminish this low frequency increase whilst maintaining the reduction in the mid- and high frequency range. The aerodynamic and acoustic measurements point in the direction of the separated flow of the Fairings interacting with the downstream gear components responsible for the low frequency noise increase. Bleeding of the air through the Fairings reduces the large scale turbulence in the proximity of these components and hence diminishes the low frequency increase. A sharp noise increase is present in the ground view direction at the 500 Hz centred tertsband for the solid fairing, which is confirmed to originate from the articulation link fairing. The flow around the wheels remains largely unaltered by application of the Fairings. Furthermore the application of Fairings is shown to suppress vortex shedding from the lower part of the main leg. A study on the effectiveness of perforation location reveals that the stagnation area perforations are responsible for most of the low frequency noise decrease. Both articulation link and undertray fairing contribute to the reduction. Exposing the perforate outside the stagnation area induces perforate self-noise, most significantly on the sides of the lower articulation link fairing. Agreeing with previous studies, the phenomenon scales with the local component of the shearing flow velocity and orifice diameter.

  • perforated Fairings for blufi body noise control
    AIAA CEAS Aeroacoustics Conference, 2007
    Co-Authors: K. Boorsma, Xin Zhang, N Molin
    Abstract:

    Landing gears of commercial aircraft make an important contribution to total aircraft noise in the approach conflguration. Using Fairings to shield components from high speed impingement reduces noise. Furthermore, perforating these Fairings has been conflrmed by ∞ight tests to further enable noise reduction. A fundamental study has been performed to investigate and optimize the beneflts of bleeding air through the fairing by application of perforations. Wind tunnel tests have been performed with a simplifled fairing-cylindrical strut combination to clarify in∞uence of perforations on ∞ow behaviour and acoustics. The results show that for this speciflc case, the fairing self noise is reduced signiflcantly by breakdown of the vortex shedding process. The perforated Fairings, exhibiting difierent porosities between 33% and 55%, appear to be equally e‐cient in removing the spectral peak associated with the vortex shedding. A redistribution of the velocities is achieved depending on the applied porosity. Perforate selfnoise manifests itself at higher frequencies, although scaling of this phenomenon with oriflce diameter opens up the possibility to shift it above the upper limit of the audible range.