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Aeroacoustic analysis based on FW–H analogy to predict low-frequency in-plane harmonic noise of a helicopter rotor in hover

Suresh T., Szulc O., Flaszynski P.

Archives of Mechanics

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2022

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Vol. 74, nr 2-3

201--246

EN

The integral formulation of the Ffowcs-Williams and Hawkings (FW–H) analogy, developed by Farassat (known as Farassat’s formulation 1A), is implemented to study the sound generation and propagation of rotating slender bodies. The general post-processing numerical code utilizes the linear acoustic theory to predict the thickness and loading noise terms for bodies in subsonic motion. The developed numerical code is validated for elementary acoustic sources (rotating monopole and dipole) against analytical solutions. The validated code is then applied for prediction of lowfrequency in-plane harmonic noise (LF-IPH) of a model helicopter rotor of Sargent and Schmitz in a low-thrust hover with full-scale tip Mach number. The required loading distribution of the rotor blade is obtained with CFD (RANS) and Blade Element Momentum Theory (BEMT) methods and also validated against literature data. The developed acoustic code, supplemented by CFD and BEMT loading analyses, allows for a detailed comparison (thickness and loading, near- and far-field, etc.) of the LFIPH noise of a helicopter rotor in both, time and frequency domains. The predicted (FW–H) acoustic signals are compared not only with the reference code solutions, but also with the experimental data. Moreover, the paper quantifies the impact of computational grid density and time-step size (used by CFD and FW–H codes) on the final solution accuracy. Additionally, a simplified analytical code is developed (based on elementary dipole solutions, compact chord assumption and BEMT method) allowing for the initial loading noise analysis with highly reduced computational resources. The acquired results are fully compatible with the classical FW–H analysis in terms of the impact of the in-plane and out-of-plane forces on the generated noise. The FW–H code predictions of the acoustic pressure and its components are in satisfactory agreement with the reference and experimental data of Sargent and Schmitz.

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Growth and study of 4-sulfobenzenaminium potassium dihydrogenphosphate for mechanical, dielectric and photonics applications

Vinoth E., Vetrivel S., Gopinath S., Mullai R. U., Aruljothi R., Suresh T.

Materials Science Poland

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2020

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Vol. 38, No. 4

619--628

EN

This article describes the growth and characterization of 4-sulfobenzenaminium potassium hydrogen phosphate (SPH) sulphanilic acid with potassium dihydrogen phosphate (KDP) doped semi-organic single crystals. The crystal was grown by the slow evaporation method. Examination of the crystalline nature of the sample was carried out by single crystal X-ray diffraction and it confirmed that the sample crystallizes in orthorhombic structure in the centrosymmetric space group P212121. The optical transmittance behavior was tested by UV-Vis spectral analysis. FT-IR spectral investigations have been carried out to indicate the presence of functional groups. The chemical structure of the compound was established by 1H and 13C NMR spectra. The SHG efficiency of the powdered SPH crystal is around 1.7 times that of pure KDP. The grown crystal was stable up to 270 °C as observed from TGA and DTA curves. The microhardness test was carried out to study the load dependency of hardness. The result of this study indicates that SPH crystal is a malleable material. From the hardness values, the stiffness constant and yield strength were calculated. The dielectric response of the novel crystal was studied in the frequency range of 50 Hz to 5 MHz at various temperatures. By employing FE-SEM, the surface morphology and the particle size of the crystal were assessed.

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Growth and characterization of 4-(((4-aminophenyl)sulfonyl)oxy)-2,3-dihydroxy-4-oxobutanoic acid with Ce3+: for semiorganic nonlinear optical application

Vinoth E., Vetrivel S., Gopinath S., Aruljothi R., Suresh T., Mullai R. U.

Materials Science Poland

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2020

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Vol. 38, No. 4

584--593

EN

This work aims at the growth and characterization of novel semi-organometallic nonlinear optical (NLO) crystal 4-(((4- aminophenyl) sulfonyl) oxy)-2,3-dihydroxy-4-oxobutanoic acid (ASODA) with ammonium ceric (II) sulfate dehydrate (ACS). The crystal 4-(((4-aminophenyl) sulfonyl) oxy)-2,3-dihydroxy-4-oxobutanoic acid with Ce3+ (STA) was grown by slow evaporation solution growth technique using deionized water as a solvent. Crystalline system of the grown STA crystal was identified by a single crystal X-ray diffraction study and confirmed as monoclinic crystalline system with non-centrosymmetric space group P21/C. The powder X-ray diffraction study confirmed the purity and crystallinity of the crystal. The presence of functional groups and hydrogen bonds (–O–H–O–) was confirmed by FT-IR spectroscopy. UV-Vis spectra showed that the grown crystal had a low cutoff wavelength at 219 nm. The position of protons and carbons were determined by structural studies based on NMR technique. The grown crystal was thermally stable up to 130 °C and its melting point was 163 °C. The SHG studies were performed by Quanta Ray Model laser source using Kurtz powder technique. The NLO efficiency of the STA crystal was 0.5 times greater than that of standard KDP. The dielectric constant and dielectric loss of the grown crystal were studied at different temperatures. The surface morphology and the particle size of the crystal were determined by FE-SEM technique. From the mechanical studies, it was found that the grown crystal is a soft material.