The reliance on Computational Fluid Dynamics (CFD) simulations has drastically increased over time to evaluate the aerodynamic performance of small-scale wind turbines. With the rapid variability in customer demand, industrial requirements, economic constraints, and time limitations associated with the design and development of small-scale wind turbines, the trade-off between computational resources and the simulation’s numerical accuracy may vary significantly. In the context of wind turbine design and analysis, high fidelity simulation under full geometric and numerical complexity is more accurate but pose significant demands from a computational standpoint. There is a need to understand and quantify performance deterioration of high fidelity simulations under reduced geometric or numerical approximation on a single small scale turbine model. In the present work, the flow past a small-scale Horizontal Axis Wind Turbine (HAWT) was simulated under various geometric and numerical config... [more]

Computational fluid dynamics (CFD) was used to investigate the explosion characteristics of a Mg/air mixture in a 20 L apparatus via an Euler−Lagrange method. Various fluid properties, namely pressure field, velocity field, turbulence intensity, and the degree of particle dispersion, were obtained and analyzed. The simulation results suggested that the best delayed ignition time was 60 ms after dust dispersion, which was consistent with the optimum delayed ignition time adopted by experimental apparatus. These results indicate that the simulated Mg particles were evenly diffused in the 20 L apparatus under the effect of the turbulence. The simulations also reveal that the pressure development in the explosion system can be divided into the pressure rising stage, the maximum pressure stage, and pressure attenuation stage. The relative error of the maximum explosion pressure between the simulation and the experiments is approximately 1.04%. The explosion model provides reliable and usefu... [more]

This paper presents an unsteady flow analysis of a 3D wing with a morphing trailing edge flap (TEF) and a seamless side-edge transition between the morphed and static parts of a wing by introducing an unsteady parametrization method. First, a 3D steady Reynolds-averaged Navier−Stokes (RANS) analysis of a statically morphed TEF with seamless transition is performed and the results are compared with both a baseline clean wing and a wing with a traditional hinged flap configuration at a Reynolds number of 0.7 × 106 for a range of angles of attack (AoA), from 4° to 15°. This study extends some previous published work by examining the inherent unsteady 3D effects due to the presence of the seamless transition. It is found that in the pre-stall regime, the statically morphed wing produces a maximum of a 22% higher lift and a near constant drag reduction of 25% compared with the hinged flap wing, resulting in up to 40% enhancement in the aerodynamic efficiency (i.e., lift/drag ratio). Second,... [more]

The objective of this article is to review the methodologies used in the last 15 years to estimate the power loss in wind turbines due to their exposure to adverse meteorological conditions. Among the methods, the use of computational fluid dynamics (CFD) for the three-dimensional numerical simulation of wind turbines is highlighted, as well as the use of two-dimensional CFD simulation in conjunction with the blade element momentum theory (BEM). In addition, a brief review of other methodologies such as image analysis, deep learning, and forecasting models is also presented. This review constitutes a baseline for new investigations of the icing effects on wind turbines’ power outputs. Furthermore, it contributes to a continuous improvement in power-loss prediction and the better response of icing protection systems.

The nozzle which is applied in industrial pneumatic pulsators is studied. It is a part of the system for unclogging the drains and outlets of silos and hoppers for loose materials. The nozzle is required to achieve the lowest level of energy losses while directing the airflow, which impacts the loose material bed. The energy rate transferred into the bed depends on the temperature and pressure differences between the inlet and outlet of the nozzle. In this study, the available energy is determined assuming compressible and transient airflow through the nozzle, which is a part of the industrial pneumatic pulsator. Numerical simulations are performed using the OpenFOAM CFD toolbox. Energy analysis is carried out by using Reynolds Transport Theorem for specific energy for the variable temperature inside the silo on the basis of CFD results. In fact, the air parameters at the outlet of the nozzle are the ones inside the silo. The study showed that the design of the nozzle is not very suffi... [more]

The application of Computer-Aided Engineering (CAE) tools in mechanical design has consistently increased over the last decades. The benefits introduced by virtual models in terms of time and cost reductions are the main drivers for their exploitation in industry as well as for research purposes in academia. In this regard, Computational Fluid Dynamics (CFD) can be exploited to study lubrication and efficiency of gears. However, the mesh handling complexities deriving from the boundary motion is still a concern for its application to multi-stage gearboxes. In this work, an innovative multi domain partitioning method for the simulation of a two-stage industrial speed reducer is presented. The implemented solution foresees the combination of two remeshing strategies, namely GRA (Global Remeshing Approach) and GRAMC (GRA with Mesh Clustering), and resulted in a computationally effective performance. The results were compared with experimental data obtained with measurements on the real sy... [more]

Micro wind energy harvester (MWEH) can provide eco-friendly and sustainable energy for low-power electric devices like wireless sensors. The performance of the wind turbine can be enhanced by applying a duct with a brim. In this work, the characteristic study was performed when the duct is applied to the MWEH through the computational fluid dynamics analysis of the internal and external flow of the duct. The power generation performance for various cases was evaluated using the wind tunnel test. It is confirmed that the ducted MWEH is robust to the change of the wind direction and its performance can be further enhanced by the brim.

In the case of road cars, road safety is the primary factor. The geometry of high-speed road cars has no regulatory restrictions. In addition to the high engine power and effective shape, they can use various types of additional movable aerodynamic elements to adjust their aerodynamic characteristics to the road conditions. Based on the geometry of a two-seater prototype of such a vehicle, a numerical analysis of the influence of a number of additional movable aerodynamic elements on its aerodynamic characteristics was performed. Several of them were installed on the prototype. An electronic system recording a number of motion parameters of the entire car body and some of its movable elements installed on the body was designed and built. The system has been adapted to program the motion of additional aerodynamic elements according to the set algorithms of their activation, temporarily changing the aerodynamic characteristics of the car. An experimental study of the effect of changes in... [more]

The AeroCity is a new form of transportation concept that has been developed to provide high-speed ground transportation at a much lower cost than the existing high-speed railway. Utilizing the Wing-in-Ground (WIG) effect, the AeroCity vehicle does not require complex infrastructures like other contemporary concepts, such as the Hyperloop or Maglev trains. In the current work, the aerodynamic characteristics of the AeroCity vehicle are examined through a Computational Fluid Dynamics (CFD) analysis. The results from the CFD analysis qualitatively match with the findings of wind tunnel experiments. Surface streamlines and boundary layer measurements correspond well with the numerical data. However, the force measurements show a discrepancy. It is found that the separation bubble over the side plates is not captured by the CFD, and this is responsible for an under-prediction of the drag at higher free-stream velocities. The Transition SST model improved the matching between the experiment... [more]

Biomass represents a programmable renewable energy source that is useful for reducing issues related to the transfer from fossil fuels to the renewable energy era. The exploitation of biomass is strongly related to the development of power technologies that are designed to improve efficiency; however, at the same time, they have to be designed to improve the life cycle of the entire installation—especially in relation to maintenance operations. In this paper, a numerical analysis is proposed to assess the performance of a heat exchanger used for separating condensing tar from syngas generated by the gasification of lignocellulosic wood chips and pellets. The analysis included clean, fouled, and clogged conditions. Flow maldistribution characterized the inlet section of shell-and-tube configurations and was responsible for clogging phenomena. Starting from field detection, analyses of fouled and clogged conditions showed a reduction in the effectiveness of the heat exchanger, causing da... [more]

The noise generated by different types of fans used in the turbomachinery industry is a topic that has been studied for many years. However, researchers are still looking for a universal solution to reduce noise while maintaining the performance of these machines. This paper, as a contribution to the research, presents the results of numerical investigations of an axial fan installed in a pipeline with a circular cross-section. In particular, the focus was on investigating the sensitivity of the sound power level to changes in selected design and operational parameters of this fan. The simulation studies used the unsteady Reynolds-averaged Navier−Stokes (URANS) approach and the Ffowcs Williams−Hawkings (FW-H) analogy implemented in Ansys Fluent.

Helicopters are used for offshore wind farms for maintenance and support flights. The number of helicopter operations is increasing with the expansion of offshore wind energy, which stresses the point that the current German regulations have not yet been validated through scientific analysis. A collaborative research project between DLR, the Technical University of Munich, the University of Stuttgart and the University of Tübingen has been conducted to examine the sizes of the flight corridors on offshore wind farms and the lateral safety clearance for helicopter hoist operations at offshore wind turbines. This paper details the results of piloted helicopter simulations in a realistic offshore wind farm scenario. The far-wake of rotating wind turbines and the near-wake of non-rotating wind turbines have been simulated with high-fidelity computational fluid dynamics under realistic turbulent inflow conditions. The resulting flow fields have been processed by superposition during piloted... [more]

With the increasingly stringent CO2 emission regulations, the degree of strengthening of the engines is increasing. Under high-pressure conditions, the airway throat parts of the intake and exhaust systems have a great influence on the flow loss of the diesel engine. The reasonable distribution of the throat area of the intake and exhaust ports in the limited cylinder headspace is key to improving the performance of supercharged engines. This study took a large-bore, high-pressure ratio diesel engine as the research object. Firstly, the three-dimensional (3D) flow simulation method was used to reveal the influence law of different throat areas on the engine intake and exhaust flow under steady-state conditions, and a steady-flow test bench was built to verify the accuracy of the simulation model and law. Secondly, based on the 3D steady-state calculation and test results, a more accurate one-dimensional simulation model was constructed, and a joint optimization simulation platform was... [more]

In order to balance the intermittent supply of energy to the power grid, pumped storage units have to operate more and more in extended operating conditions and switch their mode frequently. During operation, the turbine unit has to withstand various axial forces that may cause deformation and fatigue damage to the key components of the machine. The excessive load could surpass the weight of the runner body, which is dangerous for the power plant. For the safe and stable operation, the simulation of the axial force under pump condition is performed by the computational fluid dynamics method (CFD) in this paper. The CFD simulation result has revealed the variation rule of the axial force with the operating condition. Besides, the conditions with pressure-balance pipelines (PBP) blockage are also investigated and the mechanism of PBP on reducing the axial force applied on the bracket has been revealed. The maximum stresses are calculated by means of Finite Element Method (FEM) and compar... [more]

The intake port structure optimization is very important for the uniflow scavenging opposed-piston two-stroke engine, as the intake port structure affects the scavenging efficiency and turbulence kinetic energy and thus further impacts the engine indicated efficiency. This paper aims at improving the indicated efficiency, presenting a comprehensive study on the intake port optimization concerning both scavenging efficiency and turbulence kinetic energy. First, a three-dimensional model based on computational fluids dynamics is established and validated. Subsequently, different numbers of intake ports are compared and analyzed from the perspectives of the scavenging efficiency and turbulence kinetic energy. Furthermore, the double-ports intake structure is selected with the consideration of the compact structure and high scavenging efficiency. Then, the radial angle and width of the double-ports structure are optimized based on the response surface method. The results show that the opti... [more]

Safety and reliable operation is one of the most important research areas for centrifugal pump systems, due to the interaction of complex flow, large structural load, and vibration caused by the operation of the impeller. To analyze the internal flow and impeller deformation of the centrifugal pump, the single-stage single-suction centrifugal pump titled IS100-80-160 was selected as the research object. Under the principle of single variable, the turbulent flow and structural response of three impellers designed by different parameters were calculated by CFX and ANSYS Workbench. A numerical simulation of steady flow at different flow rates of the centrifugal pump was carried out, and its hydraulic performance is consistent with the corresponding experimental results. By comparing the deformation of the impeller rotor system, it was found that the closed impeller has the worst stability with the best hydraulic performance; the impeller with split blades has the worst stability with the... [more]

The zigzag channel is the uppermost channel type of an industrial printed circuit heat exchanger (PCHE). The effect of geometric properties on the flow and heat transfer performance of the channel is significant to the PCHE design and optimization. Numerical investigations were conducted on the flow and heat transfer characteristics of supercritical CO2 (sCO2) in semicircular zigzag channels by computational fluid dynamics method. The shear stress transfer (SST) k−ω model was used as turbulence model and the National Institute of Standards and Technology (NIST) real gas model with REFPROP database was used to evaluate the thermophysical parameters of sCO2 in this numerical method. The effectiveness of the simulation method is verified by experimental data. Thermal hydraulic performance for zigzag channels with different pitch lengths, bending angles, and hydraulic diameters are studied comparatively based on this numerical method, with the boundary conditions which cover the pseudocrit... [more]

The Special Issue entitled “Novel Numerical Methods in Heat and Mass Transfer” focuses on such issues as CFD modeling of fluid flow, heat transfer characteristics, mass transfer, phase-change and heat exchangers. The Guest Editors of this Special Issue, under the support and auspices of the publishing house, and through its editors, invited the authors to publish their latest achievements in the area of numerical methods used in the area of heat and mass transfer. A short overview of the successful invited submission articles devoted to the above-mentioned subject is presented with the hope that these valuable works will be of interest to a wide range of readers, as the topic is important and worth further scientific attention.

High temperatures and non-uniform temperatures both have a negative bearing on the performance of proton exchange membrane fuel cells. The temperature of proton exchange membrane fuel cells can be lowered by reasonably distributed cooling channels. The flow field distribution of five different cooling plates is designed, and the temperature uniformity, pressure drop and velocity of each cooling flow field are analyzed by computational fluid dynamics technology. The results show that while the pressure drop is high, the flow channel distribution of a multi-spiral flow field and honeycomb structure flow field contribute more to improving the temperature uniformity. As the coolant is blocked by the uniform plate, it is found that although the flow field channel with a uniform plate has poor performance in terms of temperature uniformity, its heat dissipation capacity is still better than that of the traditional serpentine flow field. The multi-spiral flow field has the strongest ability t... [more]

In this study, the development and testing of a hybrid thermal energy storage (TES) including phase change material (PCM) macro-capsules inside a vertical sensible tank is presented. The storage was specifically developed for delivering hot water on board of ships. Accordingly, a commercial PCM was selected and tested. Subsequently, the hybrid TES was designed and tested under mimicked boundary conditions at lab scale, showing the possibility of increasing the volumetric energy storage density up to 30% compared to the sensible configuration. On this basis, two numerical models were developed: a detailed one, implemented in a Fluent environment, aiming at investigating the main parameters affecting the heat transfer efficiency inside the TES and a second one, implemented in an ESP-r environment to simulate the TES as a component to be implemented inside a more complex system, thus helping its accurate design and operation through a reliable modelling phase. Both models were satisfactor... [more]

When a hydrokinetic turbine operates in a confined flow, blockage effects are introduced, altering the flow at and downstream of the rotor. Blockage effects have a significant effect on the loading and performance of turbines. As a result, understanding them is critical for hydrokinetic turbine design and performance prediction. The current study examines the main and interaction effects of solidity (σ), tip speed ratio (TSR), blockage ratio (ε), and pitch angle (θ) on how the blockage influences the performance (CP) of a three-bladed, untwisted, untapered horizontal axis hydrokinetic turbine. The investigation is based on validated 3D computational fluid dynamics (CFD), design of experiments (DOE), and the analysis of variance (ANOVA) approaches. A total number of 36 CFD models were developed and meshed. A total of 108 CFD cases were performed as part of the analysis. Results indicated that the effect of varying θ was only noticeable at the high TSR. Additionally, the rate of incremen... [more]

The design features of a centrifugal compressor must guarantee high performance and a wide operating range. The ported shroud was developed specifically to extend the operating limit. It is a passive flow control device based on a cavity for flow recirculation to avoid blade passage blocking in near surge conditions. A CFD simulation campaign using a simplified model identified the differences in the performance of the centrifugal compressor with ported shroud, compared to the baseline case. The use of a stability criterion to determine the limit mass flow rate, developed in a previous study by the authors, highlighted and quantified the extension of the surge margin in the case with ported shroud for different rotational speeds. An increase in the surge margin of 11% was detected at design speed, but with a lower trend at higher speeds. An in-depth flow analysis showed the main physical mechanisms in the compressor that occur for different operating conditions: at near surge condition... [more]

This paper presents some results from a computational fluid dynamics (CFD) model of a multi-megawatt crosswind kite spinning on a circular path in a straight downwind configuration. The unsteady Reynolds averaged Navier-Stokes equations closed by the k−ω SST turbulence model are solved in the three-dimensional space using ANSYS Fluent. The flow behaviour is examined at the rotation plane, and the overall (or global) induction factor is obtained by getting the weighted average of induction factors on multiple annuli over the swept area. The wake flow behaviour is also discussed in some details using velocity and pressure contour plots. In addition to the CFD model, an analytical model for calculating the average flow velocity and radii of the annular wake downstream of the kite is developed. The model is formulated based on the widely-used Jensen’s model which was developed for conventional wind turbines, and thus has a simple form. Expressions for the dimensionless wake flow velocity a... [more]

This paper compares three different numerical models to evaluate their accuracy for predicting the performance of an H-rotor vertical-axis wind turbine (VAWT) considering the influence of struts. The strut of VAWTs is one factor that makes the flow feature around the turbine more complex and thus influences the rotor performance. The focus of this study is placed on analyzing how accurately three different numerical approaches are able to reproduce the force distribution and the resulting power, taking the strut effect into account. For the 12 kW straight-bladed VAWT, the blade force is simulated at three tip speed ratios by the full computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier−Stokes (RANS) equations, the actuator line model (ALM), and the vortex model. The results show that all the models do not indicate a significant influence of the struts in the total force over one revolution at low tip speed ratio. However, at middle and high tip speed ratio, th... [more]

Energy consumption is steadily increasing with the ever-growing population, leading to a rise in global warming. Building energy consumption is one of the major sources of global warming, which can be controlled with renewable energy installations. This paper deals with an advanced evacuated hybrid solar photovoltaic−thermal collector (PVT) for simultaneous production of electricity and domestic hot water (DHW) with lower carbon emissions. Most PVT projects focus on increasing electricity production by cooling the photovoltaic (PV). However, in this research, increasing thermal efficiency is investigated through vacuum glass tube encapsulation. The required area for conventional unglazed PVT systems varies between 1.6−2 times of solar thermal collectors for similar thermal output. In the case of encapsulation, the required area can decrease by minimizing convective losses from the system. Surprisingly, the electrical efficiency was not decreased by encapsulating the PVT system. The per... [more]