Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session B06: Acoustics: Noise Reduction |
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Chair: Daniel Bodony, University of Illinois at Urbana-Champaign Room: 205 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B06.00001: Reducing noise from twin supersonic jets using very-low-frequency control Sandeep Murthy, Daniel Bodony The intense jet noise radiated by closely-spaced, twin supersonic hot jets leads to sound-induced structural vibration, fatigue and operational difficulties for carrier-borne aircraft. Experimental, theoretical, and computational investigations into the physics and control of jet noise have identified several important sound sources, including wavepackets, screech, Mach wave radiation, and broadband shock associated noise. Reducing the loudest sources of jet noise has relied on intuition, parametric survey, or optimal control techniques. With the aim of developing a more general method of jet noise reduction (JNR), we present a physics-based approach that leverages very-low-frequency jet dynamics in order to achieve JNR whilst preserving propulsive performance. Our approach formulates the control problem using the very-low-frequency global modes of the compressible Navier-Stokes operator linearized about the jet mean flow to disrupt the nonmodal transient growth processes. The presentation will showcase uncontrolled and controlled single and twin supersonic hot jets issuing from biconical nozzles, with conditions and geometries motivated by tactical Naval aircraft. The predictions utilize fully-resolved simulations whose data informs the control development and its performance. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B06.00002: On passive noise control in a tandem airfoil configuration using leading-edge serrations SH Sankarasarma Vemuri, Xiao Liu, Bin Zang, Mahdi Azarpeyvand This study focuses on experimental investigation of passive noise control for a tandem NACA 65-710 airfoil configuration by applying serrations to the leading edge of the rear airfoil. Wake-profile measurements on an isolated airfoil are used to determine the maximum turbulence intensity locations for the optimal positioning of the rear airfoil for near-field and far-field acoustic measurements. The far-field noise measurements and noise directivity analysis have demonstrated that the use of leading-edge serrations can lead to significant noise reduction from the tandem airfoil configuration. Near-field measurements have been carried out to understand the mechanism leading to the noise reduction by studying how surface pressure fluctuations vary over the serration root and tip planes. The near-field hydrodynamic analysis obtained using remote-sensing of the fluctuating pressure field over the airfoil has shown that the use of leading-edge serrations causes significant reduction in the unsteady aerodynamic load acting on the airfoil, particularly along the serration tip plane. This is believed to be due to a strong flow separation from the serration tip region. This study might have practical application for noise reduction from outlet guide vanes. [Preview Abstract] |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B06.00003: Noise Signature Study of a Rim Driven Thruster Hasan Raza, Maxwell Kogler, Conor Pace, Michael Vu, Oleg Goushcha A unique propulsion system has been assembled in which a flow is driven using a fan actuated at its outer diameter rim. This fan configuration eliminates the need for a shaft and a centerline hub required by the conventional fan designs allowing for an undisturbed flow through the centerline region. Also, in our design the fan blades extend from the rim inward towards the centerline. Blades at the outer radius are connected to the rim. The inner radius blade tips are located in a relatively low-flow region associated with small tangential velocity of the fan near the centerline. Therefore, the tip vortices and the associated noise produced by the tip vortices should be minimized compared to the conventional propeller configuration where bade tips are located in a high-tangential velocity region associated with the outer radius. We present an experimental study of noise signature from the rim driven thruster and compare our results to the noise signature of a conventional propeller and fan to comment on any high-frequency noise reduction. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B06.00004: The Propeller-Induced Cavitation Noise Source: Experimental Measurements and Numerical Solutions Duncan McIntyre, Mostafa Rahimpour, Giorgio Tani, Fabiana Miglianti, Michele Viviani, Zuomin Dong, Peter Oshkai Propeller-induced cavitation dominates the mid- to high-frequency range of underwater radiated noise emitted by ships, representing a significant threat to marine ecosystems. The development of mitigation strategies for noise pollution requires predictive models, which are challenging to develop due to the varied, multiscale, and multi-physical nature of the phenomenon. One promising technique for predicting the detailed behaviour of the propeller cavitation noise relies on the use of uRANS solutions of the cavitating flow with a volume-of-fluid cavitation model as an input for acoustic modelling with a porous surface formulation of the Ffwocs Williams-Hawking analogy. We present an application of this methodology involving the reproduction of model-scale experiments in a cavitation tunnel. We focused on ten loading conditions of a controllable pitch propeller that resulted in four distinct regimes of cavitation. Performance of the hydrodynamic model varied depending on the c avitation regime. Cavities attached to propeller blades well, but regimes involving cavities within shed vortices were not reproduced well. The numerical model was effective in predicting the shapes of acoustic spectra, but the absolute sound levels were overpredicted. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B06.00005: Noise Reduction Mechanism of a High-Lift Airfoil's Leading-Edge Device. Rinie Akkermans, Paul Bernicke Airframe noise is a major part of the total noise produced by an aircraft during its landing phase, of which the wing's leading-edge device (i.e., slat) is a major contributor. In this contribution, the noise reduction of such slat devices is investigated by means of Overset-LES simulations. It solves the compressible Navier-Stokes equations in perturbation form over a background flow, supplemented by a sub-filter-stress model. Two geometries are considered, i.e., a reference and a modified long-cord slat geometry. The effect of the long-cord slat on the turbulent sound sources is investigated by mainly considering turbulence statistics and span-wise coherence length in the slat cove region. Furthermore, acoustic far-field propagation reveals the influence of long-cord slat on the directivity. Results show that the noise reduction is mainly resulting from a shielding effect by the long-cord slat, rather than modification of the turbulent sound source in the slat cove region itself. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B06.00006: An experimental analysis on efficacy of perforated plates of varying orifice quantity T Dhanachandran Thanapal, JinLiang Heng, Basman Elhadidi, Wai Lee Chan Combustion engines typically generate significant noise signatures and the latter constitutes a source of noise pollution. One method of reducing such noise is by disrupting the acoustic waves using acoustic dampers, which in this work is in the form of perforated plates. As air flows through the orifices of the plates, an unsteady jet flow is generated, which will further interact with the acoustic noise and, through viscous dissipations, convert the acoustic fluctuations into non-radiating vortical fluctuations. With the recognition of this fundamental mechanism, the objective of this work is to understand the effectiveness of the perforated plates as acoustic dampers. Fast Fourier transformation was used to analyse the resulting microphone data, showing that the single-orifice plate functioned as an acoustic resonator instead of a damper. In contrast, the multiple-orifice plate functioned as acoustic damper, producing approximately 50{\%} reduction in noise. This finding is consistent with prior investigation where plates with higher open area ratios perform better at reducing acoustic noise. Both single- and multiple-orifice plates were relatively insensitive to the bias flow rate, although the single-orifice plate performance did improve slightly when the bias flow rate was increased. [Preview Abstract] |
Saturday, November 23, 2019 5:58PM - 6:11PM |
B06.00007: Numerical analysis of the characteristics of Helmholtz resonators with multiple necks JinLiang Heng, T Dhanachandran Thanapal, Wai Lee Chan, Basman Elhadidi Helmholtz resonators are commonly used in combustion engines to reduce engine noise and tackle combustion instability issues. A resonator, typically consisting of a fixed volume cavity and a neck has a resonant frequency that is a function of the speed of sound, neck cross-sectional area, cavity volume, and neck length. For a resonator with multiple necks, the analytical expression is able to determine a single value for its resonant frequency. However, in this work involving a cavity with multiple necks, experiments have shown that multiple frequencies are present. Subsequent numerical simulations utilizing the Lattice Boltzmann method also yield reasonable agreement with experiments, suggesting that the multiple-frequency phenomenon may be attributed to interactions between different necks, and may be specific to the current experimental setup. Further simulations with sinusoidal and pulse acoustic source will be performed for further insights to the flow associated with a resonator with multiple necks, from which the multiple-frequency phenomenon may be explained. [Preview Abstract] |
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