1,721,028 research outputs found
Numerical simulation of the aerodynamics and acoustics of a wall-mounted spoiler
No full textA steep descent with deployed spoilers is a potential noise abatement procedure. This study investigates noise sources solely due to spoilers by examining a spoiler mounted on a flat plate. An experimental database consisting of aerodynamic loads, microphone measurements, on-surface pressure distributions, hot wire anemometry, and particle image velocimetry is presented. Numerical simulations, performed using a lattice Boltzmann solver ProLB, are validated against these experimental data. While the geometry is relatively simple, this is still a challenging case to accurately predict numerically, particularly the boundary-layer separation bubble that occurs upstream of the spoiler. The flow is characterized by an arch-type broadband wake without any coherent vortex shedding. There is a horseshoe vortex that originates upstream of the spoiler and wraps around both sides of the spoiler. Inboard of the horseshoe vortex there are a pair of ground vortices with the opposite sign vorticity to the horseshoe vortex. A combination of band-filtered on-surface pressures and three-dimensional numerical beamforming was used to determine the noise sources. As well as the broadband bluff body wake and the horseshoe vortex, the beamforming showed that the ground edge vortices and the spoiler side edges were the dominant acoustic sources
Aerodynamics and aeroacoustics of flap side-edges
Full text linkAn experimental and computational investigation was carried out to determine the aerodynamics and aeroacoustics of a flap side-edge. A porous side-edge treatment was applied to the flap side-edge in an attempt to reduce airframe noise. Measurements taken as part of the experimental study were forces, on-surface pressures, particle image velocimetry, hotwire anemometry and on-surface microphones. Oil flow was performed to visualise the on-surface flow. A detached eddy simulation was performed on a geometry that consisted of a main element and a half span flap to understand the flowfield. From the experimental and computational investigation four sources of vorticity in the flowfield were identified, i.e. the main element cove, the main element trailing-edge, separation on the flap suction surface, and the flap side-edge vortical system. These sources of vorticity interacted to produce a significantly unsteady flowfield above the solid flap surface. Three potential acoustic sources on the flap were identified. The first two sources were the turbulent shear layers that rolled up to form the flap side-edge vortex, reattaching firstly on the side-edge and secondly on the suction surface of the flap. A mid-frequency broadband hump was measured by an on-surface microphone at the point of reattachment of the turbulent shear layer on the flap side-edge. The third source was a low frequency instability in the off-surface vortex due to non-linear vortical interactions upstream of the flap. This instability was measured by a hotwire in the downstream vortex and by an on-surface microphone in the main element flap cove. The application of a porous flap side-edge had two favourable effects. Firstly, it reduced the magnitude of vorticity in the turbulent shear layer and the vortex. This reduced the magnitude of the hydrodynamic instabilities induced by the flap side-edge vortex. Secondly, it displaced the vortex further away from the flap surface due to the finite mass flux allowed through the porous material. This reduced the magnitude of the disturbances that interacted with the solid flap surface by moving them further away. The effect of applying a porous flap side-edge was most noticeable in reducing the mid frequency broadband hump in the on-surface microphone measurements
Aeroacoustic study of strut braced ultra-high aspect ratio wings
No full textTo enhance aerodynamic efficiency, reduce fuel consumption, and minimize emissions in the next-generation of air transport, a strut-braced ultra-high aspect ratio wing (UHARW) is a promising solution. However, the addition of a bracing strut may have aeroacoustic implications. This paper assesses the noise generated by a strut-braced UHARW, focusing on two primary source types. The first is dipole noise, and the second is trailing-edge noise from both the main wing and bracing strut. Wall-modeled large-eddy simulations and the Ffowcs-Williams and Hawkings (FWH) equation are used to calculate the dipole noise. The results indicate a noise increase of approximately 3.5 dB over a wide frequency range due to the bracing strut at the local spanwise section where it is located. The trailing-edge noise of the main wing and strut is estimated using the trailing-edge noise prediction model of Brooks, Pope, and Marcolini. The noise of a full-span, realistic UHARW wing is estimated using a model based on the time domain FWH equations and spanwise strip theory. It is found that the addition of the bracing strut increases the maximum tone-corrected perceived noise level by approximately 0.8 PNdB at the wing source level, without considering other airframe or engine noise sources
Airy pattern approximation of a phased microphone array response to a rotating point source
No full textDeconvolution of phased microphone array source maps is a commonly applied technique in order to improve the dynamic range and resolution of beamforming. Most deconvolution algorithms require a point spread function (PSF). In this work, it is shown that the conventional definition of the PSF, based on steering vectors, is changed when the source is rotating. The effect of rotation results in an increase in the resolution and aperture of the array. The concept of virtual array positions created by source rotation is used to derive an approximation of the PSF based on an Airy pattern. The Airy pattern approximation is suitable for use in deconvolution of rotating source maps as it is more accurate and computationally less expensive than the conventional PSF definition. The proposed Airy pattern approximation was tested with both CLEAN and DAMAS deconvolution algorithms. On the same hardware, it was significantly faster when compared to the conventional definition. The limitations of the Airy pattern approximation are shown in a synthesized broadband test case with a high dynamic range. However, in most practical beamforming applications, the proposed Airy pattern approximated PSF for deconvolution is a suitable option considering its accuracy and speed
Parametric investigation of the fluid mechanic performance of an AC dielectric barrier discharge plasma actuator
No full textThe aim of this work is to systematically quantify and rank the effects of nine different design parameters on the fluid mechanic abilities of a Dielectric Barrier Discharge (DBD) plasma actuator supplied with an Alternating Current. The ranking and quantification not only consider the parameters themselves but also their interactions with each other. In order to perform this ranking, a Design of Experiment approach is used. This allows the most significant design parameters for the thrust generation, power consumption and thrust to power consumed ratio (force efficiency) of DBD actuator performance to be determined in a systematic way. The results show that the thrust generation is driven by the voltage, distance between the electrodes, AC frequency, and geometry of the exposed electrode, in that order. A high voltage and high frequency, with a thin dielectric, a narrow inter-electrode gap, and a thin and narrow air-electrode results in an increase in the thrust generation.The thrust to power ratio of a DBD is employed as a proxy for the fluid mechanic efficiency. The analysis of the force efficiency shows that the voltage, frequency, distance between the electrodes, and geometry of the air electrode have significant effects. The higher force efficiency is obtained for a high voltage, low frequency, short inter-electrode gap, thin dielectric of low permittivity with a narrow and thin exposed electrode. Finally, two actuators are investigated to determine the best scaling laws for the power consumption as a function of voltage and frequency. In these experiments, the power consumption was a function of voltage to the power of 2.5 and frequency to the power of 1.5. This systematic study of the parameters and their interactions allows general guidelines to be obtained for the best fluid mechanic performance of a DBD, viz. its thrust generation and force efficiency
Aeroacoustic study of a strut braced ultra high aspect ratio wing
No full textTo address the imperative of enhancing aerodynamic efficiency, reducing fuel consumption, and minimizing emissions in the next generation of air transportation, a substantial advancement in aircraft performance is essential. One of the configurations investigated for achieving these goals is the strut-braced Ultra-High Aspect Ratio Wing (UHARW). The addition of a bracing strut may have an aeroacoustic impact. In this paper, a noise assessment of the strut braced UHARW is performed. There are two types of sources in this configuration. The first is the dipole noise source due to the unsteady flow on the high-lift wing and in the wake of the bracing strut for example. The second is the trailing-edge noise of the main wing and the strut. To calculate the dipole noise sources, a Wall Modelled Large Eddy Simulation (WMLES) with a weakly compressible solver is employed to simulate the flow field around the basic elements of the high-lift wing. Subsequently, the time-varying pressure data on their surfaces serves as input for the Ffowcs Williams-Hawkings (FW-H) equation to calculate the far-field noise. These numerical methods are validated on the flow around a 30P30N three-element airfoil. The simulation results of the basic elements of the UHARW indicate that the joint of the strut and the wing increases the noise by approximately 3.5 dB over a wide frequency range locally. It is also shown that the noise of the existing flap side-edge is greater at frequencies between 300 and 1400 Hz. The noise of the full-span high-lift wing are estimated through the superposition of the noise generated by the individual basic elements in the time domain. The trailing edge noise of the main wing and strut is estimated using a semi-empirical method developed by Brooks, revealing that the noise spectrum of the strut contributes more at frequencies over 600 Hz, while that of the main wing contributes more at frequencies lower than 600 Hz. Based on a model of a realistic full-span UHARW wing, changes in the tone corrected Perceived Noise Level (PNLT) are estimated to quantity the potential impact on noise certification. The installation of the bracing strut results in an increase in the maximum PNLT of the wing source by approximately 0.76 PNLdB. This value does not consider the other airframe or engine noise sources on an aircraft
Numerical study of flow structure and aerodynamic noise characteristics of rectangular jets with different nozzle shapes at low Mach number
No full textThis study numerically investigates the flow and aeroacoustic characteristics of rectangular jets with different nozzle geometries but with the same mass flow rate. Turbulence statistics in the near field are compared, and the influence of nozzle shape on jet dynamics and associated noise is assessed. The configurations analyzed include a planar nozzle and orifice-type nozzles with square, beveled, and filleted edges. The Reynolds number based on the nozzle height is 1:1 × 10
4 and the maximum Mach number is approximately 0.17. Flow fields are computed using Delayed Detached Eddy Simulation with the Spalart–Allmaras turbulence model, while far-field noise is obtained using Farrasat’s 1A formulation from permeable integration surfaces. The numerical framework is validated against experimental data. Results demonstrate that square and beveled orifices induce the vena contraction effect by their sharp edges, resulting in higher exit velocities and elevated near-field turbulence. In contrast, planar and filleted nozzles exhibit weaker turbulence, delayed shear layer roll-up, and longer potential cores. The beveled orifice in particular exhibits pronounced tonal noise peaks at 4.3, 8.5, and 12.7 kHz in the turbulent velocity spectrum. Spectral proper orthogonal decomposition identified dominant energetic modes near the potential core boundary where vortex roll-up and shear-layer interaction occur. The sharp-edged orifices produce overall sound pressure levels approximately 10 dB higher when integrating across the full frequency spectrum (including the tones) and 7 dB higher for the broadband component, compared to the planar and filleted nozzles. These findings underscore the trade-off between jet mixing and noise mitigation in nozzle design, offering insights for optimizing rectangular jets for engineering.</p
Parametric study of the DBD fluid mechanic performance
No full textDataset for the parametric investigation led on Dielectric Barrier Discharge plasma actuator to determine its fluid mechanic abilities (thrust generation and force efficiency).
These data support the submitted article:
S. Grosse, D. Angland, Parametric investigation of the fluid mechanic performance of an AC dielectric barrier discharge plasma actuator, Journal of Physics D: Applied Physics DOI:https://doi.org/10.1088/1361-6463/aba298</span
Scaling laws for aerodynamic loads and acoustics of wall-mounted plates at different deflection angles
No full textInclined flat plates mounted on horizontal surfaces have applications in the aerospace, renewable energy and automotive sectors. While previous studies have examined how aspect ratio and proximity to a mounting surface affect aerodynamic loads on a plate, a systematic investigation of scaling laws for aerodynamic loads and acoustics is lacking. This paper establishes scaling relationships for the aerodynamic loads and the flow-induced noise generated by a wall-mounted flat plate inclined to the flow. Wind tunnel experiments were conducted using a Kevlar-walled test section, with a wall-mounted flat plate deflected between 10◦ and 90◦ across various Reynolds numbers. A correction method based on the bluff body blockage corrections of Maskell and calibrated using open test section wind tunnel data is presented in this work to account for solid and wake blockage effects in the Kevlar test section experiments. For aerodynamic loads, the normalised normal force coefficient collapses when scaled with projected frontal area, converging to a fixed value of the drag coefficient at 90◦. This provides a simple predictive methodology for the aerodynamic loads with maximum errors of ΔCD = 0.073 and ΔCL = 0.081. The scaling law presented in this work is unique for wall-mounted flat plates and differs for flat plates in freestream. Aeroacoustic analysis reveals broadband noise without coherent vortex shedding. The noise scales approximately, but not perfectly, with the sixth power of velocity. The slight variations in the value of the velocity exponent at different deflection angles highlight that it does not simply scale as a compact dipole but other effects are present, including non-compactness and edge scattering effects. The acoustic scaling with projected area exhibits different behaviour at low and high deflection angles. At low deflection angles, the plate is partially immersed in the boundary layer, reducing the acoustic intensity variation with deflection angle. At higher deflection angles (> 30◦), the acoustic intensity scaled with the projected area to a power of 1.2 again indicating additional sources besides the scaling of pure compact dipole sources
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