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Subsonic jet nozzles, commonly used in passenger aircrafts, generate significant noise that travels both downstream and upstream due to large-scale or fine-scale turbulences in the jet plume. To reduce jet noise, a novel wall treatment method, termed the wavy inner wall (WIW), is proposed. With this method, the smooth inner wall near the exit of the nozzle is replaced by treated walls that carry small wavy patterns. Numerical simulations are conducted to investigate the effects of the WIW treatment. Large eddy simulations (LES) were used to predict the unsteady flow field and the far-field noise, followed by the analogy method proposed by Ffowcs Williams and Hawkings. To better understand the mechanism behind the noise reduction achieved by the WIW treatment, the shear-layer instability, radial and azimuthal auto-correlation functions, turbulent kinetic energy, and acoustic source term from the Tam-Auriault (TA) jet-noise model were analyzed. Results indicated that the WIW treatment advances the onset of jet flow instability in the shear-layer, leading to the early breakdown of jet shear-layer and production of different scales of downstream turbulent structures. As a result, the distribution and production of turbulent kinetic energy are affected, and the generation and emission of jet noise are controlled. The WIW treatment enables the control of fine scale turbulence, resulting in the reduction of mid- to high-frequency noise in the far field, while ensuring a low thrust loss. This feature makes the WIW method a promising approach for jet noise control.

In this study, a numerical study based on Euler equations and coupled with detail chemistry model is used to improve the propulsion performance and stability of the rotating detonation engine. The proposed fuel injection called stratified injection functions by suppressing the isobaric combustion process occurring on the contact surface between fuel and detonation products, and thus the proportion of fuel consumed by detonation wave increases from 67% to 95%, leading to more self-pressure gain and lower entropy generation. A pre-mixed hydrogen-oxygen-nitrogen mixture is used as a reactive mixture. The computational results show that the propulsion performance and the operation stability of the engine with stratified injection are both improved, the temperature of the flow field is notably decreased, the specific impulse of the engine is improved by 16.3%, and the average temperature of the engine with stratified injection is reduced by 19.1%.

The relationship between the number of detonation waves and the evolution process of the flow field in a rotating detonation engine was investigated through a numerical analysis. The simulations were based on the Euler equation and a detailed chemical reaction model. In the given engine model, the flow-field evolution became unstable when a single detonation wave was released. New detonation waves formed spontaneously, changing the operational mode from single-wave to four-wave. However, when two or three detonation waves were released, the flow field evolved in a quasi-steady manner. Further study revealed that the newly formed detonation wave resulted from an accelerated chemical reaction on the contact surface between the detonation products and the reactive mixture. To satisfy the stable propagation requirements of detonation waves, we proposed a parameter called NL, which can be compared with the number of detonation waves in the combustor to predict the evolution (quasi-stable or unstable) of the flow field. Finally, we verified the effectiveness of NL in a redesigned engine. This study may assist the operational mode control in rotating detonation engine experiments.

Three anaerobic reactors for treating starch wastewater as the Anaerobic Digester (AD), Up-flow Anaerobic Sludge Blanket (UASB) reactor, and Internal Circulation (IC) reactor, were assessed in terms of energy supply and economic factors pertaining to biogas production. For all three reactors, more than 90% of heat loss was derived from the substrate heating loss. When the Chemical Oxygen Demand (COD) of wastewater exceeded 15,000mg/L, the UASB and IC reactors produced excess energy and achieved an economic surplus throughout the year. The UASB and IC reactors reached energy equilibrium throughout the year when the influent COD was 11,195.44mg/L, and 9,844.67mg/L, respectively. The economic equilibrium of the UASB and IC reactors was achieved for influent COD of 12,984mg/L and 11,561mg/L, respectively. The energy and economic equilibria of the AD could not be achieved throughout the year with influent COD concentrations ranging from 5,000mg/L to 20,000mg/L.

Dechlorane Plus (DP) is a chlorinated flame retardant that is currently in intensive use and has been detected extensively in the environment. In China, the temporal and spatial distribution of DP is characterized by sources of point emissions in the south and diffusion to the north and west, including to remote, high-elevation areas, which are characterized by different climatic conditions and topographies. Thus, relatively high and low concentrations of DP have been observed in areas without significant nearby pollution sources. High DP concentrations have been observed in South China because of the recycling of large amounts of electronic waste and the presence of a DP factory. DP in urban areas is not influenced by atmospheric transportation, whereas DP in rural areas originates from atmospheric transmission from specific sources, such as e-waste recycling areas, which vary seasonally. Furthermore, DP in Chinese forest soils has been observed to preferentially accumulate in the mineral horizon due to leaching by precipitation as well as erosion by weathering in the organic horizon. Although the hazard quotient (HQ) has been estimated to be far from 1 for DP manufacturing operators, the HQ might not reveal deleterious effects on humans. Extremely high DP concentrations have been observed in serum samples from DP manufacturing operators in China. Moreover, different isomer-specific accumulation in terrestrial species, except for aquatic biota, shows that syn-DP is preferentially accumulated. Finally, to achieve better understanding of the mechanisms of DP degradation both in nature and in organisms, further laboratory study is needed.

An improved constant volume cycle (CVC) model is developed to analyze the nozzle effects on the thrust and specific impulse of pulse detonation rocket engine (PDRE). Theoretically, this model shows that the thrust coefficient/specific impulse of PDRE is a function of the nozzle contraction/expansion ratio and the operating frequency. The relationship between the nozzle contraction ratio and the operation frequency is obtained by introducing the duty ratio, by which the key problem in the theoretical design can be solved. Therefore, the performance of PDRE can be accessed to guide the preliminary shape design of nozzle conveniently and quickly. The higher the operating frequency of PDRE is, the smaller the nozzle contraction ratio should be. Besides, the lower the ambient pressure is, the larger the expansion ratio of the nozzle should be. When the ambient pressure is 1.013 × 105 Pa, the optimal expansion ratio will be less than 2.26. When the ambient pressure is reduced to vacuum, the extremum of the optimal thrust coefficient is 2.236 9, and the extremum of the specific impulse is 321.01 s. The results of the improved model are verified by numerical simulation.

A novel wall treatment method, termed as the Slat Cove Wavy Wall (SCWW), is proposed to improve both the aero-acoustic and the aerodynamic performances of high-lift devices. By this treatment, a wavy pattern is imposed on the wall in the slat cove. In the present work, slats with three different SCWWs are designed and applied to a straight wing composed by 30P30N airfoil. Numerical simulations and analyses are conducted to unveil the underlying mechanisms of noise reduction. The unsteady flow field and the far-field noise are predicted by a hybrid SA-IDDES method followed by the integration of the Ffowcs Williams and Hawkings equation. The modified high-lift device is proved to be able to improve the aero-acoustic performance by reducing the low-frequency components of the radiated noise. Meanwhile, the aerodynamic performance is maintained or improved under proper design parameters. The boundary layer separation in the slat cove is accelerated by the SCWW, which transforms low-frequency periodic vortex shedding to high-frequency turbulent flow. This results in the sound energy shift from low-frequency noise to high-frequency broadband noise. The SCWW method is proved to be effective in redistribution of boundary vorticity flux on the slat lower surface. To reveal the mechanism of the SCWW's drag and noise reduction, the vortex dynamic processes near the slat lower surface in terms of the Lamb vector divergence are further investigated. It is found that the Lamb vector divergence is directly related to both the noise source and the drag. The interaction area of positive and negative Lamb vector divergence can be balanced and decreased by SCWW, resulting in the drag and noise reduction. As expressed by the vortex dynamic processes, this feature implies the SCWW method is of great potential in noise attenuation.

Decabromodiphenyl ether (BDE-209/decaBDE) is a high-production-volume brominated flame retardant in China, where the decaBDE commercial mixture is manufactured in Laizhou Bay, Shandong Province, even after the prohibition of penta- and octaBDE mixtures. The demand for flame retardants produced in China has been increasing in recent years as China not only produces electronic devices but also has numerous electronic waste (e-waste) recycling regions, which receive e-wastes from both domestic and foreign sources. High concentrations of BDE-209 have been observed in biotic and abiotic media in each of the different areas, especially within the decaBDE manufacturers and e-waste recycling areas. BDE-209 has been viewed as toxic and bioaccumulative because it might debrominate to less brominated polybrominated diphenyl ethers (PBDEs) (lower molecular weight and hydrophobicity), which are more readily absorbed by organisms. The highest concentration of PBDEs in dust within urban areas reached 40 236 ng g–1 in the Pearl River Delta, and BDE-209 contributed the greatest proportion to the total PBDEs (95.1%). Moreover, the maximum hazard quotient was found for toddlers (0.703) for BDE-209, which was close to 1. This suggests that exposure to BDE-209 might lead to increased potential for adverse effects and organ harm (e.g., the lungs) through inhalation, dust ingestion, and dermal absorption, especially for the group of toddlers compared to others. In daily food and human tissues, the amount of BDE-209 was also extensively detected. However, the toxicity and adverse effect of BDE-209 to humans are still not clear; thus, further studies are required to better assess the toxicological effects and exposure scenarios, a more enhanced environmental policy for ecological risks regarding BDE-209 and its debrominated byproducts in China.

This work explores the mechanism of bubble and droplet breakup caused by turbulence in turbulent dispersions. Considering the deformation properties of the particle during the particle-eddy interaction process, a breakup model for bubbles and droplets of the Taylor length scale size is developed. The particle-eddy interaction frequency is modeled based on bubbles/droplets interacting with both larger and smaller eddies, in contrast with the usual collision frequency. Breakup criteria are demonstrated to depend on the degree of surface deformation prior to breakup. The relationship between the local characteristics of surrounding flows, such as the turbulent eddies’ variance and dissipation rate and the breakage rate as well as the daughter size distribution is then established and quantified. In particular, the contribution of turbulent eddies to the total breakage rate is clarified. This work provides a further understanding of breakup observations in complex turbulent fields and offers a more fundamental breakup kernel for the population balance model.

Endocrine-disrupting chemicals (EDCs) that exist in the aquatic system bring severe environmental risks. In this study, we investigate the dissolved organic matter (DOM) effect on the release and distribution of EDCs under varied hydrodynamic conditions. A water chamber mesocosm was designed to simulate the hydrodynamic forces in a shallow lake. The contents of bisphenol A (BPA) and nonylphenol (NP) in colloid-bound and soluble phases were measured under four increasing hydrodynamic intensities that were 5%, 20%, 50%, and 80% of the critical shear stress. The total BPA and NP contents in overlying water grew linearly with the hydrodynamic intensity (R2 = 0.997 and 0.987), from 108.28 to 415.92 ng/L of BPA and 87.73 to 255.52 ng/L of NP. The exponential relationships of EDC content and hydrodynamic intensity in soluble phase (R2 = 0.985 of BPA and 0.987 of NP) and colloid phase (R2 = 0.992 of BPA and 0.995 of NP) were also detected. The DOM concentrations in colloid-bound phase (cDOM) and in soluble phase (sDOM) were measured and the linear relationships with BPA content (R2 = 0.967 of cDOM and 0.989 of sDOM) and NP content (R2 = 0.978 of cDOM and 0.965 of sDOM) were detected. We analyzed the ratio (&alpha, DOM) of sDOM and cDOM that grew logarithmically with the hydrodynamic intensity (R2 = 0.999). Moreover, the ratio (&alpha, EDCs) of BPA and NP contents in soluble and colloid-bound phases varied differently with &alpha, DOM. The results suggested that BPA tended to be in the soluble phase and NP tended to be in the colloid-bound phase due to the increasing value of &alpha, DOM.

With the rapid development of national modern industry, people begin to pay attention to environmental pollution and harm caused by industrial dust. Based on above, a numerical study on the dedusting technology of industrial environment was conducted. The dynamic models of multicomponent particles collision and coagulation, breakage and deposition are developed, and the interaction of water droplet and aerosol particle in 2-Dimension flow field was researched by Eulerian-Lagrangian method and Multi-Monte Carlo method. The effects of the droplet scale, movement speed of droplet and the flow field structure on scavenging efficiency were analyzed. The results show that under the certain condition, 30μm of droplet has the best scavenging efficiency. At the initial speed 1m/s of droplets, droplets and aerosol particles have more time to interact, so it has a better scavenging efficiency for the particle., {"references":["Xu Licheng,Sun Heping. The fine water mist dust theory and application, Building Energy & Environment,1996(4): 16~18","Zhang Xiaoyan. Design and experimental study of dusting system by fine water-spray, Industrial Safety and Environmental Protection,2001, 27(8): 1~4","Balachandran, W. Jaworek, A., Krupa, A. Efficiency of smoke removal by charged water droplets, Journal of Electrostatics, 2003, 58(3-4): 209~220","Tawatchi Charinpanitku, Wiwut Tanthapanichakoon. Deterministic model of open-space dust removal system using water spray nozzle: Effects of polydispersity of water droplet and dust particle, Separation and Purification Technology, 2011, 77( 3):382~388","Fan S. M., Walter J. Implications of droplet nucleation to mineral dust aerosol deposition and transport. Geophysical Research Letters, 2005,32, L10805, doi:10.1029/2005GL022833, pp. 1~4","Zhao Hai-bo, Zheng Chu-guang. Dynamics balance model on evolution process of discrete system, Science Press,2008,04","Ding Jue Wang Qingtao Liu Yi. Numerical study on the growth process of secondary aerosol in the fog. Chinese Journal of Theoretical and Applied Mechanics. 2013,45(2): 164-170","Jung, C. H., Kim, Y. P., Lee, K. W., A moment model for simulating raindrop scavenging of aerosols. Journal of Aerosol Science. 2003, 34(9): 1217~1233","Jung, C. H., Kim, Y. P., Lee, K. W., Analytic solution for polydispersed aerosol dynamics by a wet removal process, Journal of Aerosol Science. 2002, 33(5): 753~767.\n[10]\tSlinn, W. G. N., Precipitation scavenging//Raderson D, editor. Atmospheric Sciences and Power Production. Washington DC: Division of Biomedical Environmental Research, US Department of Energy, 1983."]}