Numerical simulation of aerodynamic noise for the two-stage adjustable-blade axial-flow fan

In order to research the noise generated by gas–liquid two-phase flow within capillary tubes in refrigeration systems, this study employs a numerical simulation method based on the volume of fluid model and evaporation-condensation model. The noise of gas–liquid two-phase flows is generated by refrigerant vaporization in capillary tubes under different inlet temperatures and diameters. The results of this study showed that two-phase flow noise in capillary tubes predominantly exists in the frequency range of 0–200 Hz, corresponding to low-frequency noise. Under different inlet temperature and diameter conditions, the total sound pressure level (TSPL) of a two-phase flow noise increased with the increase in the capillary tube diameter. Moreover, when the inlet temperature was 316.6 K, as the diameter increased from 1 to 1.9 mm, TSPL increased from 32.02 to 34.36 dB. In addition, as the inlet temperature gradually decreased, TSPL increased. Furthermore, it was found that the lower the inlet temperature, the greater the increase in TSPL. When the inlet temperatures were 316.6, 313.6, 310.6, and 307.6 K, and the diameter increased from 1 to 1.9 mm, TSPL increased by 2.34, 3.41, 4.1, and 5.38 dB, respectively, corresponding to the relative increase of 7.31%, 10.23%, 11.85%, and 15.34%. Finally, using an orthogonal analysis, a criterion relationship was obtained for predicting the TSPL of gas–liquid two-phase flow noises in capillary tubes under different conditions. This study provides guidance for noise control and structural optimization of capillary tubes considering the gas–liquid two-phase flow.

Investigation on the noise induced by gas–liquid two-phase flow in a capillary tube

2023

Investigation on accuracy of numerical simulation of aerodynamic noise of single-stage axial fan

Lu,

Xiao,

Liu

et al. 2023

The prediction accuracy of turbomachinery aerodynamic noise, particularly in relation to broadband noise with uncertain factors, has long been a challenging issue. Previous studies have not fully comprehended the factors influencing its prediction accuracy, lacking an objective and comprehensive evaluation method. An improved approach combining orthogonal experiment design and principal component analysis is employed to address these limitations. The evaluation method expands the noise metrics and provides a comprehensive assessment of the accuracy of numerical simulation for aerodynamic noise. The evaluation method is utilized to optimize and quantitatively analyze the impact of the refinement size of the core area on noise prediction for single-stage axial fans. Subsequently, the three metrics, namely, Z1, Z2, and broadband noise Z3, are integrated using PCA to form a new integrated optimal metric Ztotal. The influence of different refinement sizes, particularly on Ztotal, is quantitatively examined. The findings reveal that the mesh size of the stator wake (D area) exhibits the most significant influence on noise prediction accuracy, with a calculated weight of 81.3% on noise accuracy. Furthermore, a comprehensive investigation is conducted on the influence of turbulence models and the wall Y+ value on aerodynamic noise. Detached-eddy simulation and large eddy simulation demonstrate effective capabilities in simulating both upstream and downstream turbulent flow characteristics of the stator, enabling accurate prediction of broadband noise. This study presents a set of numerical simulation schemes that achieve precise prediction of turbomachinery aerodynamic noise.

Numerical prediction and optimization of aerodynamic noise of straw crushers by considering the straw-crushing process

Zhao,

Zhai,

Gao

et al. 2024

Straw crops are struck and broken into soft filaments by the high-speed rotating hammers of straw crushers, which disturb the internal airflow field and generate much noise during the operation of straw crushers. To accurately estimate and reduce the aerodynamic noise of straw crushers at the design stage, in this study, first, the coupling method of the discrete element method, bonded-particle model, and computational fluid dynamics were used to obtain the acoustics source data. Next, the Ffowcs Williams–Hawkins theory and the indirect boundary element method were used to predict the aerodynamic noise generated during the straw crushing process. The multi-island genetic algorithm was used to optimize the aerodynamic noise of straw crushers. The results indicate that the simulated and measured total sound pressure levels (TSPLs) at the outlet and inlet differed by 1.43 and 2.12 dB(A), respectively. Additionally, aerodynamic noise at the inlet appears to be primarily influenced by the sound pressure level at the excitation fundamental frequency, while noise at the outlet is primarily influenced by the sound pressure level at the double frequency. Higher sound pressure levels were mainly concentrated at the fundamental frequency and its lower harmonic frequencies, and the sound pressure level gradually decreased with the increase in the frequency. After optimization, the aerodynamic noise TSPL at the inlet decreased from 100.87 to 88.58 dB(A) and at the outlet decreased from 102.26 to 89.62 dB(A). This study provides a methodological reference for aerodynamic noise prediction and the design of low-noise straw crushers.