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The article presents a method of purification of synthesis gas (syngas) produced as a result of biomass gasification with the use of a spray scrubber. The authors focus on the presentation of how individual elements of the geometry of a spray scrubber can influence its particle removal efficiency. The paper examines cases of dry particle removal, the use of demisters in purification process and wet scrubber collection efficiency with the use of numerical fluid mechanics (CFD). General equations are also used by authors to determine the initial predictions. The key part of the article is to present the results of the velocity and pressure distribution depending on the scrubber construction, determine the effect of the number of demisters used on the particle removal efficiency and to determine the probability of coalescence depending on the size of liquid droplets. Moreover, the authors formulate a simplified formula for the collection efficiency of a scrubber which is consistent with the results obtained from CFD calculations. The numerical results of collection efficiency were compared with experimental data from literature.

The occurrence of turbulent flows is quite common in nature and several industrial applications. The accurate simulation of these complex flows is still a great challenge in science. Large Eddy Simulation (LES) is an efficient technique based on the elimination of all scales of a flow smaller than a characteristic length ∆, considering that the flow pattern in small scales is homogeneous and isotropic. Therefore, modeling of turbulence in such scales is universal and independent of the flow type. This work present PMLES, a new OpenMP CUDA Fortran solver for complex turbulent flows at high Reynolds numbers and large computational domains (about 1 × 108 cells), using a single GPU card. This was possible by using an economical numerical scheme associated with a robust and efficient solution method that requires little variable storage. Theoretical and numerical aspects are firstly discussed, and then details of the computational implementation are given. Finally, the developed code is tested and validated by simulating a turbulent jet, and comparing the results with experimental and computational data from the literature. An analysis of performance gain is also carried out, demonstrating the code’s ability to solve this class of problems with a considerable reduction in computational time.

In any supersonic intake, the flow decelerates from supersonic to subsonic speed through a constant or divergent channel “isolator” by a series of bifurcated compression shock waves referred to as a shock train. It is important to understand the characteristics of the shock train which occur inside the isolator to improve the performance of scramjet engines. In the present work, numerical simulations were carried out to investigate the characteristics of the shock train occurring in the divergent channels using coupled implicit Reynolds Averaged Navier-Stokes (RANS) equations along with the two-equation k-w SST turbulence model. Results show that the downstream pressure variation causes the shock train length to decrease and the shock structure phenomenon varies from Mach reflection to Regular reflection. The variation of the inlet Mach number has less influence on the shock train length and the location of the shock train is determined by the area ratio. In comparison with the constant area duct, the shock train structure phenomena varies from Mach reflection to regular reflection in the divergent channel. Also, the increase in divergent angle raises the total pressure loss.

This paper presents experimental and numerical investigations on the modification of local spanwise skin-friction over triangular riblets under the total drag reduction condition. Specifically, the mean and fluctuating vortical flow fields were measured using 2-components X-wires and computed using LES, respectively. Besides, the relationship between local skin-friction along the riblet spanwise and associated vortex evolution was also built using the vortex dynamic method. Based on these results, it was found that, compared with the smooth case, the impaired and enhanced vortex strength, and resultant viscous diffusion/energy dissipation, determined the reduction and augment of the viscous drag force over the local spanwise riblet groove, i.e., decreasing and increasing cases of local drag, respectively. Furthermore, the mean normal diffusion fluxes of normal and spanwise vorticities contributed more to the viscous drag under these two cases. Correspondingly, the relevant flow physics related to these phenomena was discussed in detail.

Swirling flow has been widely used in gas turbine and aero-engine combustor to stabilize the flame. However, accurate numerical prediction of the swirling turbulent flow is difficult due to complex vortex movement in the flow, and turbulence modeling is a key factor. To assess the turbulence modeling in predicting the swirling flow, numerical studies are conducted for a well-documented swirling flow case. Three turbulence models are applied in the framework of scale resolved models, i.e. a newly developed VLES (Very-large eddy simulation) model, two LES (Large eddy simulation) models including the WALE (Wall-adapting local eddy viscosity model) and CSM (Coherent Structure Method). Numerical results are compared with the experimental results including the mean and RMS velocities. It is found that VLES model performs best among the three models and the other two LES models give comparable predictions. The complex vortex structures are explored based on the unsteady simulation results. The study demonstrates the high potential of VLES modeling for accurate prediction of complex swirling flow.

The novel diesel engines with advanced fuel injection systems are equipped with solenoid injectors comprising multiple small nozzle orifices which makes considerable improvement in fuel spray characteristics and engine performance along with providing high pressure fuel injection system. On the other hand, poor fuel quality, impurities and heavy metal elements in the diesel fuel, and high temperature medium in the diesel engines combustion chamber lead to remarkable deposits formation in the small holes of the nozzle. In addition, it results in partial or complete nozzle hole obstruction which is called injector nozzle coking having detrimental effects on discharged spray ideal behavior and proper engine performance. In this work, the analysis of coking phenomenon influences on diesel spray macroscopic characteristics have been done. Initially, the coked injectors with different time operation and deposit amounts are prepared under experimental and specific operating conditions. Then, the images recorded from the spatial and temporal evolution of a diesel spray in various injection and chamber pressures, are processed through the extended code in MATLAB software in order to analyze discharged fuel spray characteristics. The SCHLIEREN Imaging Method with high speed camera has been utilized in a CVC (constant volume chamber) without combustion. Non-Destructive Electron Microscopy Method of SEM (Scanning Electron Microscope) imaging was utilized in order to analyze sediments quantity and construction changes during injector working in the real engine conditions. The results show that, sediments occupy 20, 40, 75 and 90% of the total hole opening surface, respectively in the injectors with 300, 700, 800 and 900 hours operating time. By increasing the injector operation time and accumulated sediment amount on the nozzle, the discharged injector spray exhibits a more inappropriate behavior. Moreover, The Results revealed that coking has considerable effects on the spray tip penetration at low injection pressures. As injection pressure increases, the decreasing rate of the penetration length alleviates gently. In other words, at high injection pressures (1500 bar and higher) the penetration length has minor drop compared with non-utilized injectors even at 900 hours operating time, but the spray projected area can be reduced up to 28% in high chamber pressures.

Erosion wear of the centrifugal pump impeller are the key issues since its operating in sediment-laden flow. Experiment and numerical method are adopted in this study to investigate the erosion wear of the impeller in a double-suction pump in the Jingtai Yellow River Irrigation Project (JYRIP). Observation during operation combined with morphology study is carried out to verify erosion mechanisms at the different sections of the impeller blade. For numerical study, the Eulerian-Lagrangian approach combined with the Mclaury model is employed to predict the trajectories of the particles under different particle parameters. Also the effects of particle size and concentration on impeller erosion wear is studied. Numerical results are consistent with experimental data. The surface wear of the blade changes obviously from circular shape to strip shape in the direction from the Leading Edge (LE) to the Trailing Edge (TE), and the wear damage area increases correspondingly. Trajectories of larger particles are more uniform and tend to cause more severe erosion wear damage. The wear damage tends to be slow after the particle size increases to a certain extent under the same sediment concentration. Besides, erosion rate increases with an increase in sediment concentration, and the erosion rate of the suction side is greater than the pressure side at the same position of the blade surface. These results can offer a good reference for the design of wear resistance impeller of the double suction pump.

Onsite utilization of wind energy in the urban environment is an effective solution to environmental protection and energy security. The typically micro wind turbines, including Savonius vertical axis wind turbine, H-type vertical axis wind turbine and micro horizontal axis wind turbine are more suitable for distributed generation, relative to centralized generation of large scale wind turbines. However, the wind in the urban environment characterized by low wind speed, high levels of turbulence and strongly unsteady direction and speed, directly affecting the aerodynamic characteristics of wind turbine. In the present work, wind tunnel tests have been conducted to investigate the low Reynolds number effect on aerodynamic characteristics for these three typical micro wind turbines, and the aerodynamic differences among them have been compared qualitatively and quantitatively. The experimental results show that micro horizontal axis wind turbine and H-type vertical axis wind turbine, belonging to lift-type wind turbine, have relatively higher startup wind speed and lower power coefficient due to deteriorative aerodynamic performance of airfoil at low wind speed. However, Savonius vertical axis wind turbine, as a drag-type wind turbine, exhibits excellent aerodynamic performance at low Reynolds number. The Savonius wind turbine has apparent output power at 5m/s, and the peak power coefficient exceeding 0.2 at 9m/s being superior to that of two other lift-type wind turbines at the same wind speed. In addition, in consideration of natural advantage of vertical axis wind turbine, Savonius wind turbine is the best option for applying at low Reynolds number urban environment.

Electroosmotic flow of salt-free power-law fluids through planar slit and cylindrical micro and nanochannels with fluid slip is theoretically analyzed. Analytical solutions are obtained to investigate the effects of flow behavior index, channel size, applied electric field strength, Gouy-Chapman length (or surface charge density), and fluid slip length on the velocity distribution and volumetric flow rate. The results show that the electroosmotic flow velocity and thereby the flow rate for shear-thinning fluids are many times larger than those for Newtonian and shear-thickening fluids for the ranges of applied electric field strength and surface charge density usually encountered in practice. Such augmentation can be further amplified by increasing the surface charge density, applied electric field strength and fluid slip. Furthermore, the electroosmotic flow velocity profile of shear-thinning fluids becomes more plug-like as the ratio of channel half-width (or radius) to Gouy-Chapman length increases. However, such a profile for shear-thickening fluids always exhibits a parabolic-like flow pattern regardless of the ratios of channel half-width (or radius) to Gouy-Chapman length.

A single cylinder diesel engine was tested under different loading conditions with its piston crown coated with the Thermal Barrier Coating (TBC). The main objective of this work is to investigate the effect of the TBC on performance and emission characteristics in the diesel engine. The top surface of the piston was coated with 100 µm thick NiCrAl as lining layer by plasma spray method. A mixture of 88% Yttria stabilized Zirconia, 4% MgO and 8% TiO2 of 150 µm thick were coated over the lining layer. Exhaust emission (HC, NOx, CO and CO2) parameters were investigated using AVL exhaust gas analyzer. The results showed that the brake thermal efficiency was increased by 10% and brake specific fuel consumption was decreased by 9.8% for coated piston in comparison with the uncoated piston engine. It was also observed that, smoke, CO and HC emissions were decreased in the TBC engine as compared with the baseline engine. In addition carbon di oxide (CO2) and nitrogen oxide (NOx) emissions were partially increased.

Developing an accurate and reliable model for the pressure strain correlation is a critical need for the success of the Reynolds Stress Modeling approach. This is challenging because replicating the non-local effects of pressure using a modeling basis composed of local tensors is limiting. In this paper we use physics based arguments and analysis of simulation data to select additional tensors to extend this modeling basis for pressure strain correlation modeling to formulate models with improved precision and robustness. We integrate these tensors in the modeling basis and develop separate models for the slow and rapid pressure strain correlation. This complete pressure strain correlation model is tested for different turbulent flows and its predictions are compared to prior pressure strain correlation models. We show that the new model with an extended tensor basis is able to show improvements in accuracy and reliability.

The limitation of energy resources in the world has cut the attention of many researchers to find new resources of clean energy and develop methods for recovering exergy losses. Twin screw expander (TSE) is one of the positive displacement machines that has been widely applied in recent years to recover mechanical power from fluids due to its lower installation, operation, and maintenance costs in comparison with common expansion turbines (CET). In this paper, technical and economic conditions of a city gate station (CGS) were studied with the aim of recovering exergy loss using a TSE. A computational fluid dynamic code was used to simulate the three-dimensional fluid flow in the TSE. The simulation results for Shahroud station —a CGS located in the east of Iran— revealed that, unlike CET, flow and pressure fluctuations in different seasons of the year did not put any restrictions on the use of TSE whereby 85.3% of annual loss exergy was recovered. Economic studies showed that the internal rate of return (IRR) and payback period of TSE utilization were obtained of 27.6% and 4.4 years, respectively, making the investment in CGS stations more practical compared to the CET.

Sediment transport in the aquatic environment is one of the complex two-phase problems in flow mechanics and sediment hydraulics. In this study, the interaction between water and sediment is explored using the SPH method and developed SPHysics2D in which the pressure values are calculated using the state equation. In this study, the non-Newtonian rheological model µ(I) is used for modeling the sediment phase where it is developed based on the properties of granular particles. Also, the effective pressure is used for the study of sediment behavior. The method used in this research is compared with the methods used by other researchers. The Owen equation is utilized to determine the effect of viscosity within the two-phase area. The developed method is evaluated by the dam break on a dynamic bed and then, the experimental model of submerged sediment column collapse is investigated in the aquatic environment. The results of the modeling demonstrate the capabilities of the developed code for the use in the flow and sediment hydraulics.

This paper explores the use of Two-Dimensional sinusoidal surface features to delay transition and/or reduce drag. The authors, in this paper demonstrated that the presence of low amplitude sinusoidal surface features might damp the disturbances in the laminar boundary layer, reduce wall shear stress and maintain laminar flow for longer than a conventional flat plate. The hypothesis of the paper is inspired by the simplification of the dermal denticle on the surface of the shark-skin. Simulations are carried out using the Transition SST model in FLUENT based on the evidences of the transition model being suitable for a wider variety of high curvature scenarios. The surface waves are simulated for different amplitudes and wavelengths and their impact on transition onset and drag reduction are quantified at different velocities. Results presented in this paper indicate that a transition delay of 10.8% and a drag reduction of 5.2% are achievable. Furthermore, this paper adds credence to the notion that biomimicry is a very promising avenue for future drag reducing methods.