50 research outputs found
Design of a facility for shock-cells noise experimental investigation on a subsonic/supersonic coaxial jet
No full textShock-cell noise is an aeroacoustic phenomenon that occurs in aeronautic engines when the nozzle is not adapted to the atmospheric pressure. In civil aircraft at cruise the secondary ow is often supersonic, thus the onset of a shock-cells system in the wake and broadband shock-associated noise as a consequence. This paper aims to describe the design process of the new facility FAST (Free jet AeroacouSTic laboratory) at the von Karman Institute, built with the aim to investigate experimentally the shock-cell noise phenomenon on a dual stream jet. The rig consists of a coaxial open jet with supersonic capability for both primary and secondary ow. A coaxial silencer is used to remove the spurious noise coming from the feeding lines. The design has been validated by the use of CFD simulations. Preliminary experimental test campaigns with the single and coaxial supersonic jet are presented. Fine scale PIV coupled with a microphone array in the far field have been compared with analogous research in this field
Experimental characterization of the turbulent boundary layer over a porous trailing edge for noise abatement
No full textThe hydrodynamic and acoustic fields for a NACA 0018 with solid and porous trailing edge inserts are investigated. The porous inserts, covering 20% of the chord, are manufactured with metal foams with cell diameters of 450 and 800 μm and permeability values of 6 × 10−10 and 2.7 × 10−9 m2. The experiments are performed at a chord-based Reynolds number of 2.63 × 105 and an angle of attack of 0°. The porous trailing edge with higher permeability provides up to 11 dB noise attenuation with respect to the solid case for frequencies below a cross-over Strouhal number St = 0.26. Lower noise abatement (up to 7 dB) takes place below St = 0.3 for the insert with lower permeability. Conversely, noise increase with respect to the solid case is measured above the previously defined St value. A decrease in turbulence intensity is reported (up to 3% of the free-stream velocity), with lower intensity being measured for the insert with lower permeability. It is also observed that the permeability of the insert is linked to the increase of the anisotropy of highly energetic turbulent motions, being stretched in the streamwise direction, and the reduction of the eddy convection velocity (up to 20% with respect to the baseline case). In view of the results, the reduction of the velocity fluctuations is proposed as one of the mechanisms for low frequency noise abatement, being more relevant for the metal foam insert with lower permeability.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aircraft Noise and Climate EffectsWind EnergyNovel Aerospace Material
The internal and external flow fields of a structured porous coated cylinder and implications on flow-induced noise
No full textPorous coated cylinders have been shown to reduce the vortex shedding tone and broadband noise of a bare cylinder placed in uniform flow within specific Reynolds number regimes. The processes by which the vortex shedding and thus tone suppression take place are still uncertain despite numerous numerical and experimental studies. It is understood that adding a porous medium to a bare cylinder will have an influence on the Reynolds number of cylinder, yet the increase of outer diameter alone and the influences of surface roughness are insufficient to explain the changes in the shedding tone magnitude and frequency that are observed by many. Investigating the internal flow field of a porous coated cylinder could lead to a deeper understanding of the flow processes that result in the tonal noise reduction. This has not been achieved to date, as commonly used materials such as metal foam and polyurethane possess randomized porous structures, which make investigating the internal flow field nearly impossible without affecting the structure itself. This paper presents a preliminary analysis of the internal and external flow fields of two structured porous coated cylinders. The cylinders were manufactured using solid transparent materials that possess direct lines of sight through the pores in the axial and spanwise directions. Such structured porous coated cylinders have been previously successful in reducing the typical vortex shedding tone. Tomographic and 2-D planar Particle Image Velocimetry (PIV) were used in a water-tunnel facility to visualize the internal and external flow fields. To date only the 2-D planar PIV results have been post-processed that reveal differences in the wake for the two different cylinder types such as recirculation of flow around the pores. Vorticity flow structures are observed to vary along the cylinder span in the same pattern as the porous structure and streamlines at the windward cylinder side reveal the entry of flow into the porous medium.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aircraft Noise and Climate EffectsWind Energ
Mechanisms of broadband noise generation on metal foam edges
No full textThe turbulent flow over a porous trailing edge of a NACA 0018 airfoil is experimentally investigated to study the link between the hydrodynamic flow field and the acoustic scattering. Four porous trailing edges, obtained from open-cell metal foams, are tested to analyze the effects on far-field noise of the permeability of the material and of the hydrodynamic communication between the two sides of the airfoil. The latter is assessed by filling the symmetry plane of two of the porous trailing edges with a thin layer of adhesive that acts as a solid membrane. Experiments are performed at a zero degree angle of attack. Far-field noise measurements show that the most permeable metal foam reduces noise (up to 10 dB) with respect to the solid trailing edge for Strouhal numbers based on the chord below 16. At higher nondimensional frequencies, a noise increase is measured. The porous inserts with an adhesive layer show no noise abatement in the low frequency range, but only a noise increase at higher frequency. The latter is, therefore, attributed to surface-roughness noise. Flow field measurements, carried out with time-resolved planar particle image velocimetry, reveal correlation of near-wall velocity fluctuations between the two sides of the permeable trailing edges only within the frequency range where noise abatement is reported. This flow communication suggests that permeable treatments abate noise by distributing the impedance jump across the foam in the streamwise direction, promoting noise scattering from different chordwise locations along the inserts. This is further confirmed by noise source maps obtained from acoustic beamforming. For the frequency range where noise reduction is measured, the streamwise position of the main noise emission depends on the permeability of the insert. At higher frequencies, noise is scattered from upstream the trailing edge independently of the test case, in agreement with the roughness-generated noise assumption.Aircraft Noise and Climate EffectsWind EnergyNovel Aerospace Material
Broadband Trailing-Edge Noise Reduction Using Permeable Metal Foams
No full textAircraft Noise and Climate EffectsWind EnergyNovel Aerospace Material
Numerical and Experimental Investigation of the Mitigation of Landing Gear Noise Using Diamond Lattice Fairings
No full textTwo passive add-on porous fairings, comprised of diamond grids varying in size, are numerically and experimentally investigated for their effectiveness in mitigating landing gear noise. The baseline landing gear, a modified version of the LAGOON landing gear with its inner rim cavities closed, along with two configurations equipped with diamond-lattice fairings, are numerically simulated using the Improved Delayed Detached-Eddy Simulation (IDDES) in combination with the Ffowcs Williams and Hawkings (FW-H) analogy. Instead of resolving the detailed flow features through the diamond-lattice fairings, a numerical model is employed to represent the effect of fairing. Prior to integrating the numerical model into the simulations of landing gears, rigorous validation of the model against experimental data in a channel flow is performed. Subsequently, the predicted flow fields and far-field noise spectra of the baseline and controlled landing gears are validated against the experiments conducted in the anechoic A-Tunnel at Delft University of Technology. The results indicate that implementing a diamond-lattice fairing upstream of the landing gear can effectively diminish far-field noise in the frequency range exceeding 200 Hz. For the baseline landing gear, the torque link and brakes are potent noise sources. For the controlled landing gears, both diamond-lattice fairings mitigate the pressure fluctuations on the torque link and brakes, leading to a reduction of surface noise sources. The noise directivity shows that the DL 4.5mm fairing produces a noise reduction of 2-6 dB whereas the DL 2.5mm fairing generates a noise reduction of 3-7 dB across all radial directions. These findings pave the way for the low-noise design of aircraft landing gears
Quantitative criteria to design optimal permeable trailing edges for noise abatement
No full textAn experimental study on broadband noise scattered by permeable trailing edges with different pore arrangements is performed. A NACA 0018 airfoil with chord c = 0.2 m is investigated at chord-based Reynolds numbers ranging from 1.4 × 105 to 3.8 × 105 and angles of attack of 0.2 and 5.4 degrees. Noise emission from five 3D-printed perforated trailing-edge inserts, with channels normal to the chord, is measured with a microphone antenna. For comparison, inserts manufactured with metallic foams, with comparable flow permeability K but more tortuous pore paths, are also analysed. All the inserts have a permeable extension s equal to 20% of the chord (s/c = 0.2). It is shown that noise mitigation ΔLp, computed as the difference between far-field noise scattering from solid and permeable edges, collapse when nondimensionalizing frequency as Strouhal number based on the chord. From the collapsed data, it is observed that the maximum noise attenuation reported for each insert ΔLp,max reaches an asymptotic value of 9.3 dB for increasing K. To parameterize such asymptotic behaviour, noise reduction levels are fitted to a newly proposed relation ΔLp,max=γ1tanh(γ2K) (where γ1 and γ2 are fitting coefficients, that depend on the type of insert and angle of attack). Following this analysis, limit permeability values for perforated and metal foam inserts of K = 3.5 × 10−9 and 1 × 10−9 m2 are found, respectively; above these thresholds, less than 1 dB additional noise mitigation is reported; below, a difference in ΔLp,max of up to 4 dB for a given K is measured depending on the pore organization. Consequently, the tortuosity of the permeable structure is identified as an additional parameter (to K) controlling noise attenuation. It is also observed that the acoustic performance of lower-permeability edges is less sensitive to changes in the angle of attack. Tests for permeable lengths equal to s/c = 0.05 and 0.1 are performed: the change of ΔLp,max with increasing s/c is also properly described with a hyperbolic tangent, evidencing equally good performance in noise reduction for all measured extents. Finally, for the most permeable insert with periodic pore arrangement, an extremely loud tonal noise caused by vortex shedding (+30 dB higher than broadband levels) from the blunt solid-permeable junction at s/c=0.8 is reported. Since applying a longer permeable surface, or increasing the permeability at the trailing edge decreases the aerodynamic performance of the blade, a permeable trailing edge with s/c = 0.05, K = 1 × 10−9 m2 and tortuosity of 1.15 is recommended to optimize broadband noise abatement and avoid shedding-related tones for the conditions explored in the current study.Aircraft Noise and Climate EffectsWind EnergyNovel Aerospace Material
Aeroacoustic design and characterization of the 3D-printed, open-jet, anechoic wind tunnel of Delft University of Technology
No full textThe newly refurbished vertical tunnel (V-tunnel) at Delft University of Technology has been redesigned as a state-of-the-art facility for research in aeroacoustics (A-tunnel), as well as fundamental studies in laminar-turbulent transition and flow control. This manuscript focuses on the design and refurbishment aspects of the facility, including a description of the main modifications in the supporting structures and the drive system of the fan, with details of the flow conditioning and anechoic performance. A rigorous aeroacoustic and aerodynamic characterization of the facility is also presented, benchmarking the flow quality and acoustic performance of the new wind tunnel with respect to other aeroacoustic facilities across the world.Aircraft Noise and Climate EffectsWind EnergyEMSD policy / communications/ scientific developmentAerodynamic
On the mitigation of landing gear noise using a solid fairing and a dense wire mesh
No full textA solid fairing and a wire-mesh fairing consisting of very fine wires and pores are numerically and experimentally investigated for the mitigation of landing gear noise. A slightly modified LAGOON landing gear and two configurations, one equipped with a solid fairing and the other with a wire-mesh fairing, are numerically simulated using the Improved Delayed Detached-Eddy Simulation (IDDES) in combination with the Ffowcs Williams and Hawkings (FW-H) analogy. Instead of resolving the detailed flow features through the wire mesh, a recently proposed numerical model is used to represent the effect of the wire-mesh fairing. The simulated flow fields and the far-field noise spectra are validated against the experiments conducted in an anechoic wind tunnel. The superiority of the recently proposed wire-mesh model over a classical wire-mesh model in modelling both the aerodynamic and aeroacoustic effects of the wire mesh is demonstrated. Results also show that the dense wire-mesh fairing functions very similarly to the solid fairing and that significant noise can be reduced through the installation of a solid fairing or a wire-mesh fairing upstream of the landing gears. For the baseline landing gear, the torque link and the brakes are identified noise sources. With the aerodynamic penalty of a 50% increase in drag, both fairings mitigate the pressure fluctuation on the torque link and brakes, resulting in the reduction of surface noise sources. The noise directivity shows that a solid fairing or a dense wire-mesh fairing contributes to a noise reduction of 4-6 dB in all radial directions. The findings in this study pave the way for the low-noise design of aircraft landing gears
Desarrollo de una metodología experimental para la caracterización de la transmisión de calor en un compresor centrífugo
No full textEl presente Proyecto Final de Carrera aborda el desarrollo de una metodo-logía que permite medir la transferencia de calor a través de la pared de la voluta de un compresor centrífugo. Mediante esta metodología se puede au-mentar el rango de valores de flujo de calor medido, mejorando la calidad de las correlaciones realizadas a partir de estos datos. En este proyecto, además del desarrollo teórico, también se lleva a cabo una campaña de ensayos sobre el compresor de baja presión de un turbocompresor de doble etapa siguien-do la metodología expuesta. Por una parte, esto permite validarla, y por otra, también permite hallar los coeficientes de una correlación que permite calcular el flujo de calor en condiciones distintas de las medidas.Rubio Carpio, A. (2015). Desarrollo de una metodología experimental para la caracterización de la transmisión de calor en un compresor centrífugo. Universitat Politècnica de València. https://riunet.upv.es/handle/10251/55461Archivo delegad
