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The cycle-to-cycle variations (CCVs) in reciprocating internal combustion engines may cause negative influence on diving performance, fuel economy, and emissions. Especially, lean-burn technology or exhaust gas recirculation (EGR) was used to improve engine combustion efficiency and reduce NOx, and the combustion boundary was limited by increased CCVs. Therefore, it was important to identify the complex dynamics of CCVs and to take measures for inhibiting them. The CCVs based on indicated mean effective pressure (IMEP) time series were examined in a lean-burn natural gas engine with a non-uniform pre-mixture based on statistical and multifractal theories. Tests were conducted at an engine speed of 1000 rpm and low loads of 10% and 25%, and combustion data at an engine load of 10% were analysed in detail because the CCVs are less sensitive to changes of gas injection timing (GIT) at the higher engine load. The nonlinear dynamics of the CCVs was revealed at the different GIT from 1° to 120°CA ATDC. The statistical properties of IMEP time series were characterised by distributions of probability density functions (PDF), the multifractal complexities of the combustion fluctuations were quantitatively analysed by the singularity spectra in terms of the Hölder exponent based on the theory of wavelet transform modulus maxima, and the primary source leading to the increased CCVs and complex dynamics in a natural gas engine with a non-uniform pre-mixture was identified using 3D-computational fluid dynamics simulations. Results show that as the GIT increased, the kurtosis of the IMEP time series systematically decreased from 592 to 1.8, the fast dynamics transitions from super-Gaussian to quasi-Gaussian distributions in combustion system were revealed, and the lower value of kurtosis implied the lower degree of intermittency. Except for the GIT of 60°CA ATDC, the value of the Hölder exponent h 0 > 0.5 , which implies that the CCVs for the other GITs behaved like a persistent walk or positive correlation. For GITs of 60° and 90°CA ATDC, the narrow broadness of the singularity spectrum implicated a monofractality, while the obvious multifractal properties could be identified for the other GITs. The transitions of the dynamic behaviours may be caused by the degree of mixture in-homogeneity combined with a new mechanism of “prior-cycle effects” proposed in this paper, and the effect mechanism was not only associated with the residual gas in the cylinder but also with the residual gas fuel in the intake port, rather than independent effect of residual gas in cylinder reported in previous researches. Our research results provided the deeper understanding on the dynamics of combustion system in multi-point injection natural gas engines and may be beneficial to achieve nonlinear prediction and to develop improved control strategies for inhibiting the CCVs.

In order to ascertain the hazard of thermal radiation during the overhead flare combustion under accident conditions in an enterprise, the CFD simulation is used to obtain the thermal radiation superposition nephogram under the water failure of the whole plant with two flare discharge and combustion at the same time. According to the regulation of maximum operating heat radiation value of flare system in Standard SH3009 -2013, the influence range of different thermal radiation intensities is calculated, which provides a basis for the height design of overhead flare system and the determination of reasonable safety distance between elevated torch system and surrounding facilities and personnel concentration places.

Recent work on ejector performance enhancement indicates that more information on ejector internal flow structure is needed to have a clearer picture of factors and conditions affecting operation and performance of these devices. This paper relies on experimental studies and CFD simulations to identify flow structures occurring under typical ejector refrigeration conditions and primary nozzle geometry and position. Effects on parameter distributions and the resulting operation of the device are given particular attention. The CFD model used for this purpose was validated by using in-house data, generated from an experimental prototype and over a wide range of conditions. The experiments for the selected condition were predicted very satisfactorily by numerical model. The study then focused on the role of the primary nozzle geometry and the distance of the nozzle from the beginning of the mixing chamber (NXP), in locally shaping the flow structure and the related consequences on ejector operation. Simulations on NXP for given operating conditions have shown that an optimum value was always found, and slightly varied the operating conditions within the range considered. Primary nozzle shape changes in terms of outlet diameters for given upstream conditions directly affected the expansion level of the flow. The simulations showed that an optimum range of nozzle exit diameters could be found, for which ejector performance was highest. Moreover, under these conditions it was observed that pressure fluctuations inside the ejector were reduced.

Ionic mass transfer in a novel electrocoagulation reactor (ECR) using a rotating impeller anode is studied experimentally using the limiting current density method. The CFD simulation is also conducted for characterizing the novel electrocoagulation reactor (ECR) and validating the experimental study of ionic mass transfer. Variables included rotational speed and anode diameter. The Bland-Altman method was used to verify the accuracy of experimental and simulation results. Data for the condition 11852 < Re < 58550 and 88 < Sc < 285 were found to fit the equation for the largest diameter of 11.2 cm; Sh = 2.1Re0.93Sc0.33. Based on COD removal efficiency, optimal EC performance is realized at the largest anode diameter of 11.2 cm, confirming the enhancement of aluminum mass transfer by increasing the anode diameter. The experimental values of current density and mass transfer coefficient are validated by CFD simulation for all the rotational speeds and anode diameters. The accuracy is up to 95% for the experimental current densities compared with simulation values.

In recent decades, the use of wind turbines has been successfully increasing in power generation. Various types of wind turbine configurations as well as possible blade geometries are been proposed and are still under development for extracting the maximum possible energy extraction. Vertical axis wind turbine (VAWT) found to have enhanced adaptable physiognomies to the unsteady wind of urban terrains. These turbines can yield electricity from the wind of any direction with low-slung cut-in wind speed. These turbines are ominously quieter than the old-fashioned HAWTs, light-weight, and can be straightforwardly unified into buildings. Hence, the main idea of the present work to numerically evaluate the design performance of a C-shaped Savonius turbine for wind-energy conversion thus obtaining a higher output. During computational fluid dynamic (CFD) simulations, 3 different symmetric and non-symmetric airfoils are examined. After authenticating the numerical procedure against experimental measurements, precise CFD simulations of the unsteady flow around an H-rotor Darrieus turbine have been carried out and presented here. Based on the various configuration of the H-rotor Darrieus turbine tested the DU-06-W-200 found to be capable of wind energy generation, particularly in urban areas.

The scarcity of land resources and food security challenges have prompted more effective uses of the rooftop as well as façade spaces in the urban city of Singapore. Urban rooftop spaces are used for mechanical and electrical (M&E) amenities such as air-conditioning cooling units and water tanks, so the spacious span of the roof area on HDB flats in Singapore is not available. Urban-metabolic farming modules (UmFm) built on 1.5 to 2 m terrace-step terrains have been modelled using BIM Revit to mimic such constraints in rooftop spaces. CFD simulation was conducted for the structure with consideration of the prevailing wind directions at different months of the year. The airflow with the inclusion of mesh netting and varying tiltings of the polycarbonate side façade was simulated to understand their impact on airflow in the growth envelope of the UmFm units under different prevailing wind directions. The amount of solar irradiance received by the crops at different heights in the UmFm due to the sun’s path, and shading of crops grown on the A-frame, was studied using Climate Studio. A comparative verification was done with a scaffold modular unit mounted with temperature, humidity, airflow, and Photosynthesis Photon Flux Density (PPFD) sensors. The digital model of the UmFm unit enables a prior assessment of site feasibility before actual physical implementation on an existing rooftop. It also facilitates plug and play for the UmFm unit to generate an eco-resilient farmscape for an urban city.

This paper utilizes the CFD simulation analysis method, calculates and analyzes the distribution characteristics of streaming around the typical steel tubular transmission tower body and the pressure field, researches the change law of wind load force (torque) coefficient along with each main shaft direction o tower body, and then compares it with corresponding wind tunnel test result, and verifies the adaptability of this CFD simulation result. The result shows that the pole member in the upwind direction on the steel tubular tower has obvious disturbance and shielding effect to wind speed distribution around the pole member of downwind direction. The wind direction has obvious influence on the aerodynamic (torque) parameters of tower body, especially the steel tubular - angle steel combined tower body. The above research result provides a certain theoretical support and value taking basis for the wind-resistant design of steel tubular transmission tower body.

Three-dimensional Eulerian-Eulerian transient simulations were conducted to represent the gas-liquid flow of a heterogeneous bubble column. Different drag closures, breakup and coalescence models were evaluated in order to verify their influence on the model prediction. Numerical simulations were compared to experimental data, with industrial conditions of gas superficial velocities: 20cm/s and 40cm/s, in order to select the most suitable models to describe the bubble’ dynamics in the heterogeneous flow. The standard k − ε model for both phases was set for turbulence. 12 combinations of breakup and coalescence models were compared and analyzed. In the case of coalescence, Models of Prince and Blanch, and Luo presented similar behavior and good agreement with experimental data, while for breakup, a breakage forming three daughter bubbles appeared to be the best choice. Simulations presented relative errors around 7.7% and 14.0%, for 20cm/s and 40cm/s respectively, for the gas axial velocity, and around 14% and 21.9%, for gas holdup. For drag force, density and viscosity were accounted by an average of the phases, which resulted in an improvement about 7% on model validation

Simulating transient processes of pumped-storage power plants is essential for the design and optimization of pump-turbine and water conveyance system. Because pressure pulsations and runner forces cannot be obtained from the traditional 1D transient simulation methods, 3D CFD simulations are necessary. In this study, the fast runaway transient process, occurring after the pump trip of a pumped-storage plant with a head of 700m, was simulated by using the CFD method that couples the 1D water conveyance system and 3D turbine. The phenomena, composed of water hammer fluctuations, pressure pulsation transitions, and flow pattern evolutions, were described and analyzed. We found that the flow patterns and pressure pulsations change violently as the working point goes through different regions. Especially, the pressure pulsations and unbalanced radial runner forces are the most severe in the S-shaped characteristic region. The strong impact on blades, large scale recirculating vortices in blade passages, obvious rotating stalls in vane and blade regions, transitional backflows at runner inlet and outlet, and strong circumferential velocity in vaneless space are the main sources. The dynamic working trajectory does not follow the measured static characteristic curve and demonstrates an undamped loop in the S-shaped region. This paper provides some evidence on the relations between flow structure and pressure pulsation features, although the mechanism of dynamic characteristics needs further investigations.

A mathematical simulation was developed using CFD in this study for the nonpremixed combustion of two co-axial jets of a mixture consisted of propane, hydrogen, and air. The combustion chamber is represented in a three-dimensional cylindrical shape. The study aimed to evaluate the chemical and thermal properties of the mixture in the burner by adopting the following variables: temperature, axial velocity, and emitted CO. The study aims to identify and reduce carbon monoxide emissions to the environment as it is toxic pollutant. The addition of hydrogen to propane because it is a clean fuel that does not emit carbon monoxide as is the case with propane. In this study, the flame propagation velocity of hydrogen gas was compared to that of propane fuel.