12,967 research outputs found
Dataset for "On the reduction of aerofoil-turbulence interaction noise associated with wavy leading edges"Dataset for "On the reduction of aerofoil-turbulence interaction noise associated with wavy leading edges"
No full textThe data supports the paper by Kim, Haeri & Joseph (2016) 'On the reduction of aerofoil-turbulence interaction noise associated with wavy leading edges' Journal of Fluid Mechanics.</span
Dataset for "Improving the boundary efficiency of a compact finite difference scheme through optimising its composite template"
No full textThe data contains the ASCII, Tecplot and Matlab files used to generate the figures in the paper by Turner, Haeri & Kim (2016), 'Improving the boundary efficiency of a compact finite difference scheme through optimising its composite template', Computers & Fluids.</span
Airfoil noise reductions through leading edge serrations
No full textThis paper provides an experimental investigation into the use of leading edge (LE) serrations as a means of reducing the broadband noise generated due to the interaction between the aerofoil’s LE and impinging turbulence. Experiments are performed on a flat plate in an open jet wind tunnel. Grids are used to generate isotropic homogeneous turbulence. The leading edge serrations are in the form of sinusoidal profiles of wavelengths, ?, and amplitudes, 2h. The frequency and amplitude characteristics are studied in detail in order to understand the effect of LE serrations on noise reduction characteristics and are compared with straight edge baseline flat plates. Noise reductions are found to be insignificant at low frequencies but significant in the mid frequency range (500 Hz–8 kHz) for all the cases studied. The flat plate results are also compared to the noise reductions obtained on a serrated NACA-65 aerofoil with the same serration profile. Noise reductions are found to be significantly higher for the flat plates with a maximum noise reduction of around 9 dB compared with about 7 dB for the aerofoil. In general, it is observed that the sound power reduction level (?PWL) is sensitive to the amplitude, 2h of the LE serrations but less sensitive to the serration wavelength, ?. Thus, this paper sufficiently demonstrates that the LE amplitude acts as a key parameter for enhancing the noise reduction levels in flat plates and aerofoils
The effect of wavy leading edges on aerofoil-gust interaction noise
No full textHigh-order accurate numerical simulations are performed to investigate the effects of wavy leading edges (WLEs) on aerofoil–gust interaction (AGI) noise. The present study is based on periodic velocity disturbances predominantly in streamwise and vertical directions that are mainly responsible for the surface pressure fluctuation of an aerofoil. In general, the present results show that WLEs lead to reduced AGI noise. It is found that the ratio of the wavy leading-edge peak-to-peak amplitude (LEA) to the longitudinal wavelength of the incident gust (?g) is the most important factor for the reduction of AGI noise. It is observed that there exists a tendency that the reduction of AGI noise increases with LEA/?g and the noise reduction is significant for LEA/?g?0.3. The present results also suggest that any two different cases with the same LEA/?g lead to a strong similarity in their profiles of noise reduction relative to the straight leading-edge case. The wavelength of wavy leading edges (LEW), however, shows minor influence on the reduction of AGI noise under the present gust profiles used. Nevertheless, the present results show that a meaningful improvement in noise reduction may be achieved when 1.0?LEW/?g?1.5. In addition, it is found that the beneficial effects of WLEs are maintained for various flow incidence angles and aerofoil thicknesses. Also, the WLEs remain effective for gust profiles containing multiple frequency components. It is discovered in this paper that WLEs result in incoherent response time to the incident gust across the span, which results in a decreased level of surface pressure fluctuations, hence a reduced level of AGI noise
Implementation of genetic algorithm for the optimization of boundary characteristics of compact finite difference schemes
No full textAn advanced synthetic eddy method for the computation of aerofoil-turbulence interaction noise
No full textThis paper presents an advanced method to synthetically generate flow turbulence via an inflow boundary condition particularly designed for three-dimensional aeroacoustic simulations. The proposed method is virtually free of spurious noise that might arise from the synthetic turbulence, which enables a direct calculation of propagated sound waves from the source mechanism. The present work stemmed from one of the latest outcomes of synthetic eddy method (SEM) derived from a well-defined vector potential function creating a divergence-free velocity field with correct convection speeds of eddies, which in theory suppresses pressure fluctuations. In this paper, a substantial extension of the SEM is introduced and systematically optimised to create a realistic turbulence field based on von Kármán velocity spectra. The optimized SEM is then combined with a well-established sponge-layer technique to quietly inject the turbulent eddies into the domain from the upstream boundary, which results in a sufficiently clean acoustic field. Major advantages in the present approach are: a) that genuinely three-dimensional turbulence is generated; b) that various ways of parametrisation can be created to control/characterise the randomly distributed eddies; and, c) that its numerical implementation is efficient as the size of domain section through which the turbulent eddies should be passing can be adjusted and minimised. The performance and reliability of the proposed SEM are demonstrated by a three-dimensional simulation of aerofoil-turbulence interaction nois
Improving the boundary efficiency of a compact finite difference scheme through optimising its composite template
No full textThis paper presents efforts to improve the boundary efficiency and accuracy of a compact finite difference scheme, based on its composite template. Unlike precursory attempts the current methodology is unique in its quantification of dispersion and dissipation errors, which are only evaluated after the matrix system of equations has been rearranged for the derivative. This results in a more accurate prediction of the boundary performance, since the analysis is directly based on how the derivative is represented in simulations. A genetic algorithm acts as a comprehensive method for the optimisation of the boundary coefficients, incorporating an eigenvalue constraint for the linear stability of the matrix system of equations. The performance of the optimised composite template is tested on one-dimensional linear wave convection and two-dimensional inviscid vortex convection problems, with uniform and curvilinear grids. In all cases, it yields substantial accuracy and efficiency improvements while maintaining stable solutions and fourth-order accuracy
On the reduction of aerofoil-turbulence interaction noise associated with wavy leading edges
No full textAn aerofoil leading-edge profile based on wavy (sinusoidal) protuberances/tubercles is investigated to understand the mechanisms by which they are able to reduce the noise produced through the interaction with turbulent mean flow. Numerical simulations are performed for non-lifting flat-plate aerofoils with straight and wavy leading edges (denoted by SLE and WLE, respectively) subjected to impinging turbulence that is synthetically generated in the upstream zone (free-stream Mach number of 0.24). Full three-dimensional Euler (inviscid) solutions are computed for this study thereby eliminating self-noise components. A high-order accurate finite-difference method and artefact-free boundary conditions are used in the current simulations. Various statistical analysis methods, including frequency spectra, are implemented to aid the understanding of the noise-reduction mechanisms. It is found with WLEs, unlike the SLE, that the surface pressure fluctuations along the leading edge exhibit a significant source-cutoff effect due to geometric obliqueness which leads to reduced levels of radiated sound pressure. It is also found that there exists a phase interference effect particularly prevalent between the peak and the hill centre of the WLE geometry, which contributes to the noise reduction in the mid- to high-frequency range
Author Correction: Evaluation of skin cancer resection guide using hyper‑realistic in‑vitro phantom fabricated by 3D printing
No full textThe original version of this Article contained an error in the spelling of the author Taehun Kim which was incorrectly given as Teahun Kim. The original Article has been corrected
Self-Diagnosing GAN: Diagnosing Underrepresented Samples in Generative Adversarial Networks
No full textDespite remarkable performance in producing realistic samples, Generative Adversarial Networks (GANs) often produce low-quality samples near low-density regions of the data manifold, e.g., samples of minor groups. Many techniques have been developed to improve the quality of generated samples, either by post-processing generated samples or by pre-processing the empirical data distribution, but at the cost of reduced diversity. To promote diversity in sample generation without degrading the overall quality, we propose a simple yet effective method to diagnose and emphasize underrepresented samples during training of a GAN. The main idea is to use the statistics of the discrepancy between the data distribution and the model distribution at each data instance. Based on the observation that the underrepresented samples have a high average discrepancy or high variability in discrepancy, we propose a method to emphasize those samples during training of a GAN. Our experimental results demonstrate that the proposed method improves GAN performance on various datasets, and it is especially effective in improving the quality and diversity of sample generation for minor groups
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