Modeling the fuel injection process in modern gasoline direct injection engines plays a principal role in characterizing the in−cylinder mixture formation and subsequent combustion process. Flash boiling, which usually occurs when the fuel is injected into an ambient pressure below the saturation pressure of the liquid, is characterized by fast breakup and evaporation rates but could lead to undesired behaviors such as spray collapse, which significantly effects the mixture preparation. Four mono−component fuels have been used in this study with the aim of achieving various flashing behaviors utilizing the Spray G injector from the Engine Combustion Network (ECN). The numerical framework was based on a Lagrangian approach and was first validated for the baseline G1 condition. The model was compared with experimental vapor and liquid penetrations, axial gas velocity, droplet sizes and spray morphology and was then extended to the flash boiling condition for iso−octane, n−heptane, n−hexa... [more]

The subject of this work is the mathematical modelling of a counter-current moving-bed gasifier fuelled by wood-pellets. Two versions of the model have been developed: the one-dimensional (1D) version-solving a set of Ordinary Differential Equations along the gasifier height-and the three-dimensional (3D) version where the balanced equations are solved using Computational Fluid Dynamics. Unique procedures have been developed to provide unconditionally stable solutions and remove difficulties occurring by using conventional numerical methods for modelling counter-current reactors.The procedures reduce the uncertainties introduced by other mathematical approaches, and they open up the possibility of straightforward application to more complex software, including commercial CFD packages. Previous models of Hobbs et al., Di Blasi and Mandl et al. used a correction factor to tune calculated temperatures to measured values. In this work, the factor is not required. Using the 1D model, the Ma... [more]

The solar chimney is one of the uninvestigated areas in the possible selection in the field of renewable solar energy utilization. CFD can be demonstrated as a useful tool of figure confidence in the design and employment of a solar chimney. A realistic numerical model for a solar-based updraft power plant for power generation was established through this research work. Iraqi weather in Kirkuk, northern Iraq was considered for this case study. A three-dimensional (3D) simulation of the main geometric dimensions of the Spanish, Manzanares model integrated with a real turbine was performed using computational fluid dynamics (CFD). The turbulent model of RNG k-e, the nongrey discrete coordinate (DO) radiation model, and the solar raytracing algorithm were used. It was observed that the air velocity below the turbine was graded according to the seasons of the year and was at its maximum in July with 18.28 m/s due to the high ambient temperature, and the lowest value was recorded in January... [more]

Due to the existence of a Dean vortex in a U-tube, the flow and heat transfer process of supercritical methane is complex, and its thermophysical property are greatly influenced by different factors. Based on computational fluid dynamics theory, the numerical simulation of the turbulent flow and heat transfer characteristics of supercritical methane in a U-tube with an inner diameter of 10 mm and a radius of curvature of 27 mm carried out by using the finite volume method. On the basis of verifying the reliability of the model, the influences of inlet mass flux (G), heat flux on the tube wall boundary (q), pressure on the outlet (P), and gravity acceleration factors (g) on heat transfer characteristics were analyzed. The calculation results show that the sensitivity of the effects of G, q, P, and g on the heat transfer coefficient is, from large to small, in the order of P, G, g, and q. Compared with a horizontal straight tube, a U-tube can significantly improve heat transfer in the el... [more]

Workshops with a large area and a high ceiling height without compartments, such as large-scale assembly factories, have an uneven thermal comfort during heating, making it difficult to establish an effective heating strategy. In this study, we evaluate the heating performance of a large-scale factory based on thermal comfort and energy flow and discuss effective heating methods. In addition, an analysis of the heating performance of a large-scale factory is attempted for the first time. To analyze the heating performance, computational fluid dynamics (CFD) and building energy simulation (BES) were used to confirm thermal comfort distribution and energy flow in a large-scale factory. Temperature distribution and thermal comfort were evaluated through CFD, and the temperature of a large-scale assembly factory was compared with experimental data. Based on the CFD results, the current heating level of large factories was predicted to be 15.4 °C, and the ADPIrev was 70%. Moreover, the BES... [more]

Mesoscale numerical weather prediction models usually provide information regarding environmental parameters near urban areas at a spatial resolution of the order of thousands or hundreds of meters, at best. If detailed information is required at the building scale, an urban-scale model is necessary. Proper definition of the boundary conditions for the urban-scale simulation is very demanding in terms of its compatibility with environmental conditions and numerical modeling. Here, steady-state computational fluid dynamics (CFD) microscale simulations of the wind and thermal environment are performed over an urban area of Kozani, Greece, using both the k-ε and k-ω SST turbulence models. For the boundary conditions, instead of interpolating vertical profiles from the mesoscale solution, which is obtained with the atmospheric pollution model (TAPM), a novel approach is proposed, relying on previously developed analytic expressions, based on the Monin Obuhkov similarity theory, and one-way... [more]

In the Global South, pico- and micro-hydropower turbines are often made by local workshops. Despite several advantageous features, e.g., a high power density and capacity to handle silt, there is no commonly available Turgo turbine design appropriate for local manufacture. Technological developments including the internet, CAD, and additive manufacturing increase the opportunity to precisely transfer designs around the world. Consequently, design improvements can be shared digitally and used by manufacturers in their local context. In this paper, a rationalised CFD approach was used to guide simple design changes that improve the efficiency of a Turgo turbine blade. The typical manufacturing capacity of the micro-hydropower industry in Nepal was used to rationalise the variation of potential design changes. Using the geometry and operational parameters from an existing design as a benchmark, a two-blade, homogenous, multiphase model was developed and run using the commercial code ANSYS... [more]

A tubular reactor based on the disk and doughnut concept was designed as an engineering solution for biogas upgrading via CO2 methanation. CFD (Computational Fluid Dynamics) benchmarks agreed well with experimental and empirical (correlation) data, giving a maximum error of 8.5% and 20% for the chemical reaction and heat transfer models, respectively. Likewise, hot spot position was accurately predicted, with a 5% error. The methodology was used to investigate the effect of two commercially available coolants (thermal oil and molten salts) on overall reactor performance through a parametric study involving four coolant flow rates. Although molten salts did show higher heat transfer coefficients at lower coolant rates, 82% superior, it also increases, by five times, the pumping power. A critical coolant flow rate (3.5 m3/h) was found, which allows both a stable thermal operation and optimum pumping energy consumption. The adopted coolant flow range remains critical to guarantee thermal... [more]

A natural-gas-diesel dual-fuel marine engine with a pre-chamber is a promising solution for ocean transportation to meet the International Maritime Organization (IMO) emission regulations. This engine system employs a pre-chamber with direct injection of diesel to ignite premixed natural gas due to its higher ignition energy, which can enable lower lean limit and higher thermal efficiency. The dual-fuel pre-chamber marine engine presents complex multi-regime combustion characteristics in- and outside the pre-chamber, thus posing challenges in its numerical simulation in a cost-effective manner. Therefore, this paper presents a three-dimensional modeling study for the multi-regime combustion in a large-bore two-stroke marine dual-fuel engine, proposing a novel mapping approach, which couples the well-stirred reactor (WSR) model with the G-equation model to achieve high computational accuracy and efficiency simultaneously. In-depth analysis is performed using representative exothermic re... [more]

The paper provides novel insights into the physics behind the wind turbine and wind farm blockages as well as their effects on the energy yield based on the momentum and energy balance. The current work presents blockage effects at two scales: the local scale and the wind farm scale. We clarify the combined effect of local blockages when more than one turbine is present. The work demonstrates why two turbines, which are positioned one behind the other, induce a mutual decrease in energy yield. When the turbines are placed in a row, there is an increase of energy from the end to the middle of the row because of the restriction of the expansion flow. As in the case of two turbines placed behind each other, back rows induce a power decrease for the rows in front of them and the effect increases from the edge to the center. The work also elucidates for the first time how the power output of an isolated row has a maximum in the center, whereas, in a wind farm, wind turbines on the edge of t... [more]

Hydrodynamics plays a major role in transport of heat and mass transfer in microchannels. This includes flow patterns and flow regimes in which the micro-channels are operated. The flow patterns have a major impact the transport properties. Another important aspect is the pressure drop in micro-channels. In the present review, the experimental and Computational Fluid Dynamics (CFD) studies covering all the above aspects have been covered. The effect of geometrical parameters like shape of channel, channel size, material of construction of channels; operating parameters like flow velocity, flow ratio and fluid properties have been presented and analyzed. Experimental and analytical work of different pressure drop models has also been presented. All the literature related to influence of flow patterns on transport properties like volumetric mass transfer coefficients (VMTC) and heat transfer coefficients (HTC) have been presented and analyzed. It is found that most works in Liquid-Liquid... [more]

As global power generation is currently relying on fossil fuel-based power plants, more anthropogenic CO2 is being released into the atmosphere. During the transition period to alternative energy sources, carbon capture and storage seems to be a promising solution. Chemical-looping combustion (CLC) is an energy conversion technology designed for combustion of fossil fuel with advantageous carbon capture capabilities. In this work, a 1D computational fluid dynamics (CFD) multiscale model was developed to study the reduction step in a syngas-based CLC system and was validated using literature data (R=0.99). In order to investigate mass transfer effects, flow rate and particle dimension studies were carried out. Sharper mass transfer rates were seen at lower flow rates and smaller granule sizes due to suppression of diffusion limitations. In addition, a 3D CFD particle model was developed to investigate in depth the reduction within an ilmenite particle, with focus on heat transfer effect... [more]

At Université Libre de Bruxelles (ULB), research was performed on a 1 kN lab-scale Hybrid Rocket Motor (the ULB-HRM). It has a single-port solid paraffin fuel grain and uses liquid N2O as an oxidizer. The first Computational Fluid Dynamics (CFD) model of the motor was developed in 2020 and improved in 2021, using ANSYS Fluent software. It is a 2D axisymmetric, two-phase steady-state Reynolds-Averaged Navier−Stokes (RANS) model, which uses the average fuel and oxidizer mass flow rates as inputs. It includes oxidizer spray droplets and entrained fuel droplets, therefore adding many additional parameters compared to a single-phase model. It must be investigated how they affect the predicted operating conditions. In this article, a sensitivity analysis is performed to determine the model’s robustness. It is demonstrated that the CFD model performs well within the boundaries of its purpose, with average deviations between predicted and experimental values of about 1% for the chamber pressur... [more]

Details on the hydrothermal characteristics of turbulent flows in a solar channel heat exchanger (CHE) are highlighted. The device has transverse T-shaped vortex generators (VGs). Two staggered VGs (baffles) are inserted on the lower and upper walls of the CHE. The working fluid is Newtonian and incompressible, with constant physical properties. The ANSYS Fluent 17.0 is utilized in this survey. The second-order upwind and QUICK schemes were utilized to perform the discretization of pressure and convective terms, respectively. The SIMPLE algorithm was employed to achieve the speed-pressure coupling. The residual target 10−9 was selected as a convergence criterion. The effects of the T-VGs’ geometrical shape and Reynolds numbers were inspected. At the baffle level, the wall effect was augmented due to the reduction of the passage area of flows, which is estimated here to be 55%, resulting thus in a considerable resistance to the movement of fluid particles. The thermal distribution is hi... [more]

Runner and distributor blockages in hydraulic turbines occur due to the ingestion of external bodies such as rocks or logs. These obstructions can change the amplitude and uniformity of the pressure pulsations in the machine, creating large unbalanced forces that can lead to reduced efficiency, increased vibration and mechanical damage. In this paper, the effects of obstructions caused by ingested bodies in the runner and the distributor of a pump turbine on its internal pressure pulsation were investigated by means of computational fluid dynamics. A numerical model of an unobstructed pump turbine is presented and validated against experimental data. Several cases of runner or distributor blockage were studied, and their RSI pressure pulsations were recorded and analyzed at different locations. The results obtained allow us to characterize the effect of these blockages on the machine’s RSI, which can be helpful for the correct diagnosis of these types of damage.

Multiple jet impingement is a widely implemented convective process for enhancing heat transfer over target surfaces. Depending on the engineering application, the impinging plate can have different configurations. However, the increased complexity of the surface induces complicated thermal behaviors that must be analyzed. In that sense, this study consisted of the experimental and numerical analysis of multiple jets impinging on a step surface. A particle image velocimetry technique was applied to measure velocity fields, while a heat flux sensor was mounted on the surface to determine the heat transfer. Numerical simulations, for both flat and non-flat plates, were conducted in ANSYS FLUENT applying the SST k-ω model, and experimental results were used to validate the model. Three surface configurations were analyzed, flat, 1 D, and 2 D steps, and the results show an increase in the average Nusselt number compared with the flat plate, 9% and 20%, respectively. This increase was mainl... [more]

Recent studies have demonstrated that ammonia is an emerging energy vector for the distribution of hydrogen from stranded sources. However, there are still many unknown parameters that need to be understood before ammonia can be a substantial substitute in fuelling current power generation systems. Therefore, current attempts have mainly utilised ammonia as a substitute for natural gas (mainly composed of methane) to mitigate the carbon footprint of the latter. Co-firing of ammonia/methane is likely to occur in the transition of replacing carbonaceous fuels with zero-carbo options. Hence, a better understanding of the combustion performance, flame features, and radical formation of ammonia/methane blends is required to address the challenges that these fuel combinations will bring. This study involves an experimental approach in combination with numerical modelling to elucidate the changes in radical formation across ammonia/methane flames at various concentrations. Radicals such as OH... [more]

Erosion caused by solid particles in a pipeline is one of the main problems endangering the safety production of the oil and gas industry, which may lead the equipment to malfunction or even fail. However, most of the previous studies focused on the standard elbow, and the erosion law of right-angle elbow and blind tee is rarely reported in the literature. This work aims to investigate the erosion law of different pipeline structures including 90° elbow, right-angle pipe, and tee pipe based on the production characteristics and engineering parameters of the gas field. An integrated CFD-DPM method is established including a realizable k-ε turbulence model, discrete phase model, and erosion rate prediction model. The accuracy of the model is evaluated by a series of experimental data of flow conditions of our previous work. Further, the erosion rate, pressure distributions, and particle trajectories in 90° elbow, right-angle pipe, and tee pipe under different flow velocities, particle ma... [more]

Despite their simplicity, photovoltaic (PV) modules are often arranged in structures that can be affected by severe and complex wind loads: in this context, the wind flow and the dynamic excitation induced by vortex shedding can introduce unexpected aeroelastic responses. This work introduces a novel wind tunnel application of experimental techniques to address this issue by the use of flow visualisation and video postprocessing, through the optical flow algorithm. Numerical simulations based on unsteady Reynolds-averaged Navier−Stokes (RANS) models are performed and compared against the experimental wind tunnel tests on a PV panel that was also instrumented with pressure taps. A setup with a 65∘ tilt angle was examined because, based on preliminary analyses, it was considered interesting for the free flow−wake transition associated with the dynamic response of the PV panel. The comparison of the experimental and numerical average wind fields supported that the proposed optical flow me... [more]

The previously developed approaches for fuel droplet heating and evaporation processes, mainly using the Discrete Multi Component Model (DMCM), are investigated for the aerodynamic combustion simulation. The models have been recently improved and generalised for a broad range of bio-fossil fuel blends so that the application areas are broadened with an increased accuracy. The main distinctive features of these models are that they consider the impacts of species’ thermal conductivities and diffusivities within the droplets in order to account for the temperature gradient, transient diffusion of species and recirculation. A formulation of fuel surrogates is made using the recently introduced model, referred to as “Complex Fuel Surrogate Model (CFSM)”, and analysing their heating, evaporation and combustion characteristics. The CFSM is aimed to reduce the full composition of fuel to a much smaller number of components based on their mass fractions, and to formulate fuel surrogates. Such... [more]

The scavenging process of two-stroke engines plays a fundamental role in cylinder flow patterns and in the overall engine performance. In this work, 3D CFD simulations of the scavenging in a uniflow, two-stroke, compression ignition engine for general aviation, named GF56, have been performed by using a 3D finite-volume FANS equations solver with k-ϵ closure. The GF56 engine consists of six cylinders, separated into two quasi-symmetric banks. Both the right and the left banks, together with the corresponding cylinders, are carefully analyzed. Charging and trapping efficiencies are computed as a function of the delivery ratio for different mass flow rates entering into the plenum, and the influence of the exhaust pressure and of the cylinder’s location in the bank are analyzed. The results show that the fresh air trapped during the scavenging process is quite similar for each cylinder of the right bank and it is about 92% of the in-cylinder mass. The cylinder’s location in the bank by i... [more]

A swirling pulverized coal flame is computationally investigated. A Eulerian−Lagrangian formulation is used to describe the two-phase flow. Turbulence is modelled within a RANS (Reynolds averaged numerical simulation) framework. Four turbulence viscosity- (TV) based models, namely the standard k-ε model, realizable k-ε model, renormalization group theory k-ε model, and the shear stress transport k-ω model are used. In addition, a Reynolds stress transport model (RSM) is employed. The models are assessed by comparing the predicted velocity fields with the measurements of other authors. In terms of overall average values, the agreement of the predictions to the measurements is observed to be within the range 20−40%. A better performance of the RSM compared to the TV models is observed, with a nearly twice as better overall agreement to the experiments, particularly for the swirl velocity. In the second part of the investigation, the resolution of the discrete particle phase in modelling... [more]

In order to study the matching characteristics of the positive displacement air compressor and the PEMFC (proton exchange membrane fuel cells), air supply subsystem, the basic operating performance parameters of the scroll and single-screw air compressors were analyzed with the focus on the oil-free double-wrap scroll compressor. According to the thermodynamic model and three-dimensional unsteady-state numerical simulation, the variation of the temperature, pressure, and velocity was obtained. Besides, under the rated operating condition of the compressor, the inlet and outlet mass flow rate of the fluid in the working chamber with the orbiting angle of the crank was achieved. Based on the built test platform, the actual working process of scroll and screw compressors was analyzed. This study indicates that the volume flow can be significantly increased by improving the speed of the positive displacement compressor. Based on the experimental measurement, when the height of the scroll t... [more]

High concentration of dissolved oxygen within microalgae cultures reduces the performance of corresponding microalgae cultivation system (MCS). The main aim of this study is to provide a reliable computational fluid dynamics (CFD)-based methodology enabling to simulate two relevant phenomena governing the distribution of dissolved oxygen within MCS: (i) mass transfer through the liquid−air interface and (ii) oxygen evolution due to microalgae photosynthesis including the inhibition by the same dissolved oxygen. On an open thin-layer cascade (TLC) reactor, a benchmark numerical study to assess the oxygen distribution was conducted. While the mass transfer phenomenon is embedded within CFD code ANSYS Fluent, the oxygen evolution rate has to be implemented via user-defined function (UDF). To validate our methodology, experimental data for dissolved oxygen distribution within the 80 meter long open thin-layer cascade reactor are compared against numerical results. Moreover, the consistency... [more]

This paper proposes the analysis of real monitored data for evaluating the relationship between occupants’ comfort conditions and the energy balance inside an existing, nearly zero-energy building under different operational strategies for the heating, ventilation, and air-conditioning system. During the wintertime, the adaptive comfort approach is applied for choosing the temperature setpoint when an air-to-air heat pump provides both heating and ventilation. The results indicate that in very insulated buildings with high solar gains, the setpoint should be decided taking into consideration both the solar radiation and the outdoor temperature. Indeed, when the room has large glazed surfaces, the solar radiation can also guarantee acceptable indoor conditions when a low setpoint (e.g., 18.7 °C) is considered. The electricity consumption can be reduced from 17% to 43% compared to a conventional setpoint (e.g., 20 °C). For the summertime, the analysis suggests the adoption of a dynamic a... [more]