Detailed Flow Analysis Research Articles

Non-destructive evaluation of through-thickness permeability in 3D woven fabrics for composite fan blade applications

In this study, we propose a non-destructive modeling framework, with an ability to obtain computational models for numerical prediction of resin flow through 3D fabrics (commonly used in engine fan blade applications) at multiple fiber volume fractions using a single experiment. The work involves extracting real-time geometrical features of two types of 3D reinforcements during an in-situ compaction experiment using micro CT. The 3D image slices obtained at four different thicknesses were converted to computational models. The fiber tows and inter-tow gaps were modeled as distinct phases. The gap analysis and geometrical measurements revealed significant differences in the preform microstructure investigated at different thicknesses. This was followed by a detailed flow analysis using two different commercial software packages. The exported mesh was analyzed in GeoDict® and Ansys Fluent® for through-thickness permeability computations. The governing fluid dynamics equations were solved to obtain the flow field within the inter-tow gaps for representative volume elements. The predicted through-thickness permeability values were in very good agreement with the experimental data.

High-performance ocean energy harvesting turbine design – Detailed flow analysis with blade leaning strategy

Oscillating water column wave energy converter is having low efficiency because of its principal component, a bidirectional turbine. An analysis of the internal flow of the turbine gives an idea of improving the performance through optimization of geometrical parameters. In this study, an impulse turbine of 0.3 m diameter with fixed guide vanes is numerically simulated by solving three-dimensional incompressible steady Reynolds averaged Navier-stokes equation with two-equation turbulence closure model. This study shows that the numerical results very well match with the experimental results. The detailed flow physics demonstrates that different types of losses occur in this type of turbine and shows that the downstream diverging path of the rotor and guide vane is responsible for low performance. In this study, the effect of guide vane lean, as well as the combined rotor and guide vane lean on the performance of the turbine, has been discussed in detail and found to increase the efficiency of the turbine.

Kinematic optimization of a flapping foil power generator using a multi-fidelity evolutionary algorithm

Abstract For hydrodynamic optimization using computational fluid dynamics methods, the high computational cost impedes the use of evolutionary algorithms since they require evaluation of numerous solutions. In this paper, a multi-fidelity evolutionary algorithm, implemented with a dynamic stall model and a modified discrete vortex method, is used to find values of kinematic parameters for high energy extraction performance from a flapping foil. A single objective problem with two variables is first used to illustrate the benefits of the multi fidelity optimization strategy. Then the efficiency and the power output characterized by five design variables are optimized by the multi-fidelity evolutionary algorithm. The nondominated solutions obtained from the exercise are evaluated by the lattice Boltzmann method for detailed analysis. The results show that despite the use of low fidelity models and limited budget of computational resources, the multi-fidelity strategy is capable of finding kinematic conditions suitable for high energy extraction performance from a flapping foil. In addition, detailed flow analysis reveals that high energy extraction performance is associated with the detachment of the leading edge vortex near stroke reversal, resulting in a horseshoe-shaped vorticity wake with a width approximating the swept distance of the foil behind the turbine plane.

Developing a new energy performance indicator for the spindle system based on power flow analysis

The evaluation of the energy performance of spindle systems with a proper metric is extremely important for energy-efficient machine tools. However, there is a lack of appropriate index to achieve this evaluation. To close this gap, the additional power requirement, which is defined as the discrepancy between the material removal power and the power gap of the spindle system from air-cutting state to cutting state, was proposed as a new indicator based on a detailed power flow analysis. The additional power requirement universally exists in machining and results from the efficiency and power losses of the system, which makes it a good energy performance indicator candidate. A theoretical model for the additional power requirement of spindle systems was built and verified in a lathe machine, through which two causes of additional power requirement were pointed: less than 100% efficiency throughout the system and efficiency change of the spindle motor under a dynamic load and a variable speed. The first cause has a positive effect on the additional power requirement, whereas the second one generally plays a negative role. Furthermore, the additional power requirement can be negative because of the negative effect, which is different from previous studies. The close relation between the additional power requirement and the energy performance of the spindle is demonstrated by an in-depth analysis. This work is an important building block for energy-efficient machine tools.

Piezoelectric Energy Harvesting Systems

Energy harvesting from wasted or unused power has been the topic of discussion for a long time. This paper focuses on harvesting energy from mechanical vibrations using piezoelectric transducers. We will consider comprehensively three major phases/steps associated with piezoelectric energy harvesting: (i) mechanical-mechanical energy transfer, including mechanical stability of the piezoelectric transducer under large stresses, and mechanical impedance matching, (ii) mechanical-electrical energy transduction, relating with the electromechanical coupling factor in the composite transducer structure, and (iii) electrical-electrical energy transfer, including electrical impedance matching, such as a DC/DC converter to accumulate the energy into a rechargeable battery. The problem found in the current research teams is on a narrow research area of each above phase. In order to provide comprehensive strategies on how to improve the efficiency of the harvesting system, I provide a general guideline for piezoelectric energy harvesting systems.We dealt with detailed energy flow analysis in piezoelectric energy harvesting systems with stiff “Cymbals” (∼100 mW) and flexible piezoelectric transducers (∼1 mW) under cyclic mechanical load, in order to provide comprehensive strategies on how to improve the efficiency of the harvesting system. Energy transfer rates are practically evaluated for all three steps above. For your information, the former “Cymbal” is to be applied to the automobile engine vibration, while the latter flexible transducer is to the human-wearable energy-harvesting system.We should also point out here that there is another research school of piezo-energy harvesting; that is, small energy harvesting (mW or lower) for signal transfer applications, where the efficiency is not a primary objective. This school usually treats a burst/pulse load to generate instantaneous electric energy for transmitting signals for a short period (100 ms ∼ 10 s) without accumulating the electricity in a rechargeable battery. Successful piezoelectric products in the commercial market belong mostly to this category at present, including “LightningSwitch” [remote switch for room lights, with using a piezoelectric unimorph component], and the 25 mm caliber “Programmable Ammunition” [electricity generation with a multilayer piezo-actuator under shot impact], both of which were originally designed in our group (spin-off company, Micromechatronics Inc., State College, PA).

Sustainability assessment of ecological intensification practices in coconut production

Environmental impact and economic performance assessments are important subjects for the definition of strategies for sustainable management in agriculture. The objective of the present study was to assess such impacts in a set of reference farms dedicated to coconut production, conforming a gradient with respect to the adoption of technologies and ecological intensification practices. Ranging in scale from smaller family farms to larger corporate enterprises, and from coconut monocultures to diversified crops and integrated coconut-livestock systems, the six cases were studied through a multi-attribute utility model comprising 62 indicators related to five sustainability dimensions: (i) Landscape ecology, (ii) Environmental quality, (iii) Sociocultural values, (iv) Economic values and (v) Management and administration. Detailed cash flow analyses permitted a critical view regarding the influence of technology adoption, ecological intensification, and management for sustainability as criteria for economic viability. The results attest to the value of produce diversification as opportunity toward technology integration, which correlated positively with higher sustainability indices in all dimensions. Tradeoff analysis showed a negative correlation between socio-environmental performance indices and profitability, whereas none of the cases studied showed constrained economic viability, indicating that ecological intensification in coconut production can also entail social improvements, by promoting fairer share of revenues and benefits among stakeholders. Recommendations issued to farmers and management teams, related with agronomic factors and practices adopted in production intensification, favor the communication of appropriate mechanisms for technology adoption, translating farm-level sustainability assessments into action for sustainability.

Towards improving the aerodynamic performance of a ducted wind turbine: A numerical study

This paper aims to study the aerodynamic performance of ducted wind turbines (DWT) using inviscid and viscous flow calculations by accounting for the mutual interaction between the duct and the rotor. Two generalized duct cross section geometries are considered while the rotor is modelled as an actuator disc with constant thrust coefficient. The analysis shows the opportunity to significantly increase the overall aerodynamic performance of the DWT by a correct choice of the optimal rotor loading for a given duct geometry. Present results clearly indicate that the increased duct cross section camber leads to an improved performance for a DWT. Finally, some insights on the changes occurring to the performance coefficients are obtained through a detailed flow analysis.

Modular life cycle assessment of municipal solid waste management

Life cycle assessment (LCA) is commonly applied to examine the environmental performance of waste management systems. The system boundaries are, however, often limited to either one tonne of material or to specific waste treatments and are, therefore, lacking a systems perspective. Here, a framework is proposed to assess complete waste management systems based on actual waste flows, assessed with a detailed material flow analysis (MFA) in a modular MFA/LCA approach. The transformation of the MFA into a product-process-matrix facilitates a direct link between MFA and LCA, therefore allowing for the assessment of variations in flows. To allow for an up-to-date and geographically specific assessment, 190 LCA modules were set up based on primary industrial data and the ecoinvent database. The LCA modules show where there have been improvements in different recycling processes over the past years (e.g. for paper recycling) and highlight that, from an environmental perspective, closed-loop recycling is not always preferable to open-loop recycling. In a case study, the Swiss municipal solid waste management system, of which there is already a detailed MFA, was modeled using the new LCA modules and applying the modular MFA/LCA approach. Five different mass flow distribution scenarios for the Swiss municipal solid waste management system were assessed to show the environmental impact of political measures and to test the sensitivity of the results to key parameters. The results of the case study highlight the importance of the dominant fractions in the overall environmental impacts assessment; while the metal fraction has the highest impact on a per kilogram basis, paper, cardboard, glass and mixed municipal solid waste were found to dominate the environmental impacts of the Swiss waste management system due to their mass. The scenarios also highlight the importance of the energy efficiency of municipal solid waste incineration plants and the credits from material substitution as key variables. In countries with advanced waste management systems such as Switzerland, there is limited improvement potential with further increases in recycling rates. In these cases, the focus of political measures should be laid on (i) the utilization of secondary materials in applications where they replace high-impact primary production, and (ii) an increased recovery of energy in waste-to-energy plants.

Detailed flow field measurements and analysis in highly viscous slug flow in horizontal pipes

The flow field in the liquid phase of high viscous oil and air two-phase slug flow were experimentally studied under laminar flow conditions. The horizontal 50.8-mm (2-in.) inner diameter (ID) pipe and high viscous fluid properties (nominal viscosity values of 0.51, 0.68 and 0.96 Pa·s) yielded mixture Reynolds numbers less than 100. Particle Image Velocimetry (PIV) was used to analyze the flow field in the liquid phase. Slug characteristics were measured with a set of capacitance probes (CPs). Based on velocity field measurements, the liquid phase mass is shown to be conserved within the slug body despite local spatial variations in volumetric flow rate – flow accelerates at slug front and decelerates at slug tail. A low momentum region inside the liquid phase is identified beneath the mixing zone and close to the lower sections of the pipe. Furthermore, based on a frame of reference moving with the slug front, a pair of vortices is identified at the slug front. Accordingly, a continuous increase in velocity is observed at lower sections of the pipe. From CPs data, the flow coefficient is estimated to be between 2.11 and 2.20 for the elongated bubble flow, and 2.26 and 2.38 for the slug flow in laminar conditions investigated. From PIV data, the flow coefficient is estimated to be between 2.28 and 2.34 for the elongated bubble, and 2.31 and 2.44 for the slug flow, respectively. These slight differences in the obtained values of flow coefficient indicate the possible misunderstands of 1.13 multiplier.

Edge curvature effects of a square cylinder on self-sustained oscillations

A square cylinder at zero angle of attack is known to exhibit a self-sustained response beyond the lock-in region. This self-sustained response is characterized by a frequency that is lower than the vortex shedding frequency and with large amplitudes. However, this self-sustained oscillation is not present for circular cylinders. Prior literature indicates that shape changes through altering the corner sharpness can help to reduce these self sustaining oscillations. In this work, shape changes are realized through altering the curvature of the edge(side) of the square cylinder. For different edge curvature and rounded corner combinations, characterization of these self-sustained oscillations is studied. Detailed flow analysis is performed to study the effect of straight edge, curved edge, sharp corner and rounded corner on the pressure distribution. A proper combination of edge curvature and corner sharpness proves to be beneficial in reducing self-sustaining oscillations.

Piezoelectric Energy Harvesting Systems—Essentials to Successful Developments

AbstractIn recent years, industrial and academic research units have focused on harvesting energy from mechanical vibrations using piezoelectric transducers. These efforts have provided research guidelines and have brought to light the problems and limitations of piezoelectric systems. There are three major phases associated with piezoelectric energy harvesting: (i) mechanical–mechanical energy transfer, including mechanical stability of the piezoelectric transducer under large stresses, and mechanical impedance matching, (ii) mechanical–electrical energy transduction, relating to the electromechanical coupling factor in the composite transducer structure, and (iii) electrical–electrical energy transfer, including electrical impedance matching, such as a direct current (DC/DC) conversion to transfer the energy to a rechargeable battery. This Review starts from the historical background of piezoelectric energy harvesting, followed by several misconceptions by current researchers. The main part deals with step‐by‐step detailed energy flow analysis energy harvesting systems with lead zirconate titanate (PZT)‐based devices to provide comprehensive strategies on how to improve the efficiency of the harvesting system.

Mode decomposition and Lagrangian structures of the flow dynamics in orbitally shaken bioreactors

In this study, two mode decomposition techniques were applied and compared to assess the flow dynamics in an orbital shaken bioreactor (OSB) of cylindrical geometry and flat bottom: proper orthogonal decomposition and dynamic mode decomposition. Particle Image Velocimetry (PIV) experiments were carried out for different operating conditions including fluid height, h, and shaker rotational speed, N. A detailed flow analysis is provided for conditions when the fluid and vessel motions are in-phase (Fr = 0.23) and out-of-phase (Fr = 0.47). PIV measurements in vertical and horizontal planes were combined to reconstruct low order models of the full 3D flow and to determine its Finite-Time Lyapunov Exponent (FTLE) within OSBs. The combined results from the mode decomposition and the FTLE fields provide a useful insight into the flow dynamics and Lagrangian coherent structures in OSBs and offer a valuable tool to optimise bioprocess design in terms of mixing and cell suspension.

A modified anisotropic [formula omitted] model for predicting flow and heat transfer in a rotating channel

A modified anisotropic k-ω model that takes into account turbulence pulsation was proposed. The model was then used to study the flow and heat transfer characteristics of a rotating channel. The study considered Reynolds numbers ranging from 3000 to 15,000, rotation numbers from 0 to 1.31, and temperature ratios of 0.1, 0.17, and 0.22. The results obtained by the anisotropic k-ω model were compared with those obtained by the standard k-ω model. The anisotropic k-ω model was demonstrated to accurately predict the flow and heat transfer characteristics of the rotating channel and the results were in good agreement with the experimental data. By contrast, the standard k-ω model underestimated the heat transfer effect, especially for the trailing edge. Detailed flow analysis using the anisotropic k-ω model showed an inversely proportional relationship between the critical rotation number and the dimensionless distance. In addition, the study also found that the change of temperature ratio had an impact on the location of the fluid separation, the greater the temperature ratio, the earlier the fluid separation appears.

Current status of circularity for aluminum from household waste in Austria

Aluminum (Al) represents the metal with the highest consumption growth in the last few decades. Beside its increasing usage in the transport (lightweight construction of vehicles) and building sector, Al is used ever more frequently for household goods like packaging material, which represents a readily available source for secondary aluminum due to its short lifetime.The present paper investigates the extent to which this potential source for recycling of Al is already utilized in Austria and highlights areas for future improvements. Thereto a detailed material flow analysis for Al used in packaging & household non-packaging in 2013 was conducted. In practice, all Al flows starting from market entrance through waste collection and processing until its final recycling or disposal have been investigated. The results indicate that about 25,100 t/a (2.96 kg/cap/a) of Al packaging & household non-packaging arose as waste. At present about 9800 t/a, or 39%, are recycled as secondary Al, of which 26% is regained from separate collection and sorting, 8% from bottom ash and 5% from mechanical treatment. The type of Al packaging & household non-packaging affects the recycling rate: 82% of the total recycled quantities come from rigid packaging & household non-packaging, while only 3% of the total recycled Al derives from flexible materials. A significant amount of Al was lost during thermal waste treatment due to oxidation (10%) and insufficient recovery of Al from both waste incineration bottom ash and municipal solid waste treated in mechanical biological treatment plants (49%). Overall it can be concluded that once Al ends up in commingled waste the recovery of Al becomes less likely and its material quality is reduced. Although Austria can refer to a highly developed recycling system, the Austrian packaging industry, collection and recovery systems and waste management need to increase their efforts to comply with future recycling targets.

Fuzzy Based Network Assignment and Link‐Switching Analysis in Hybrid OCC/LiFi System

In recent times, optical wireless communications (OWC) have become attractive research interest in mobile communication for its inexpensiveness and high‐speed data transmission capability and it is already recognized as complementary to radio‐frequency (RF) based technologies. Light fidelity (LiFi) and optical camera communication (OCC) are two promising OWC technologies that use a photo detector (PD) and a camera, respectively, to receive optical pulses. These communication systems can be implemented in all kinds of environments using existing light‐emitting diode (LED) infrastructures to transmit data. However, both networking layers suffer from several limitations. An excellent solution to overcoming these limitations is the integration of OCC and LiFi. In this paper, we propose a hybrid OCC and LiFi architecture to improve the quality‐of‐service (QoS) of users. A network assignment mechanism is developed for the hybrid system. A dynamic link‐switching technique for efficient handover management between networks is proposed afterward which includes switching provisioning based on user mobility and detailed network switching flow analysis. Fuzzy logic (FL) is used to develop the proposed mechanisms. A time‐division multiple access (TDMA) based approach, called round‐robin scheduling (RRS), is also adopted to ensure fairness in time resource allocation while serving multiple users using the same LED in the hybrid system. Furthermore, simulation results are presented taking different practical application scenarios into consideration. The performance analysis of the network assignment mechanism, which is provided at the end of the paper, demonstrates the importance and feasibility of the proposed scheme.

Enhancing operation of decentralized energy systems by a regional economic optimization model DISTRICT

In this paper, a regional energy system model is introduced. The model targets the cost minimal operation of a regional energy system with the possibility of trading electricity at a spot and reserve market outside of the system borders. The system boundaries are set to be around the regional energy system, with one connection point to the rest of the system and hence the possibility to trade across the system border. Within the system boundaries, the system is divided into model areas where demand and generation are located, using a transport model approach to account for grid restrictions between the model areas. In addition to generation technologies, the model allows for demand side management and storage usage. For the trade at central markets, spot and reserve markets are integrated, using a price-taker approach. The paper shows the mathematical formulation in detail. To test the formulation and methodology of the model presented here, a case study based on real data is conducted. The case study highlights the fact that the model accounts for operational interconnections of technologies at distribution grid level. It also enables looking at effects on the grid and indicates where a more detailed power flow analysis might be required. If the proclaimed flexible energy systems come to reality, the model enables stakeholders to improve their knowledge of their distributed system, the effects of small-scale technologies and the interplay with the central system. Hence, the application demonstrates that the model adds value to closing the knowledge gap between stakeholders’ concerns about efficient operation planning of their system at distribution grid level.

On the Feasibility of Independently Controllable Transmissions

The present research is carried out to determine whether the independently controllable transmission (ICTs) are able to transmit the energy/power from the arbitrary variable speed input shaft to the variable or constant speed of the output shaft, independent of each other and without a control system. For this purpose, the novel ICT proposed in this study has the required features and is simpler than those proposed so far. However, this ICT and any other proposed ICT, while being feasible from a kinematic point of view, results in the conclusion that the transmissions are practically inapplicable, as will be demonstrated from the detailed power flow analysis carried out and presented in this paper. This is because either one shaft, the so called “free shaft”, has variable uncontrollable speed, or a couple of the shafts have powers close to zero.

Dynamics of shock wave diffraction over sharp splitter geometry using entropy-based artificial viscosity method

This paper reports the numerical analysis of shock wave diffraction over a convex sharp splitter geometry, focusing on the mechanism of the shock diffraction and the longtime behavior of shock–vortex dynamics. The flow evolution with shock–vortex dynamics for incident shock Mach number, \({M}_{{\mathrm {s}}} = 1.59\), is found to be in excellent agreement with the previous experimental results. We use a recent entropy-generation-based artificial viscosity (AV) method in conjunction with a high-order explicit discontinuous spectral element method (DSEM) to resolve these complex interactions. The AV is coupled with a shock sensor switch to attain optimal dissipations. Simulations capture the essential wave diffraction, transverse wave interaction with the deforming and growing primary vortex, and weaker secondary vortices arising from the Kelvin–Helmholtz instability. A quantification of the artificial dissipation of the numerical scheme is made by comparing the components of the kinetic energy dissipation rate and the pressure dilatation term. A new detailed transient flow analysis is also presented to address the shock dynamics, shock–vortex interaction, and the evolution of the flow topology with the probability density functions of various parameters of the enstrophy transport equation and the invariants of the velocity gradient tensor. The analysis reveals the mechanism of unwinding of vortices and its link with the divergence of the Lamb vector. A positive correlation is found between enstrophy and the imaginary part of the eigenvalues. Real parts of the two eigenvalues are associated with high dilatation shock regions and the outer edges of the vortices, respectively.

Integral Plus Resonant Sliding Mode Direct Power Control for VSC-HVDC Systems under Unbalanced Grid Voltage Conditions

An integral plus resonant sliding mode direct power control (IRSMC DPC) strategy for voltage source converter high voltage direct current (VSC-HVDC) systems under unbalanced grid voltage conditions is proposed in this paper. Through detailed instantaneous power flow analysis, a generalized power compensation method, by which the ratio between the amplitude of active and reactive power ripples can be controlled continuously, is obtained. This enables the system to provide flexible power control, so that the desired performance of the system on both the ac and dc sides can be attained under different operating conditions. When the grid voltage is unbalanced, one or both of the active and reactive power terms contain ripples, oscillating at twice the grid frequency, to obtain non-distorted ac current. A power controller consisting of the proportional, integral and resonant control laws is designed using the sliding mode control approach, to achieve accurate power control objective. Simulation studies on a two-terminal VSC-HVDC system using MATLAB/SIMULINK (R2013b, Mathworks, Natick, MA, USA) are conducted to verify the effectiveness of the IRSMC DPC strategy. The results show that this strategy ensures satisfactory performance of the system over a wide range of operating conditions.

Study of the Effect of Fin-and-Tube Heat Exchanger Fouling on its Structural Performance

ABSTRACTThis paper presents the thermal and structural analysis of high temperature fin-and-tube heat exchanger. Water flowing in tubular space and flue-gas flowing in the intertubular space, were considered as working fluids. The effect of limescale fouling on thermal and structural performance of heat exchanger was studied. The analysis considered an industrial heat exchanger, which failure occur from time to time. The expert inspection, after the failure indicated the existence of fouling layer within the heat exchanger tubes. In order to understand the reasons of heat exchanger failure, a detailed fluid flow analysis (both in the tubular and intertubular spaces) was performed. The analysis indicated that the silicate limescale fouling layer with thermal conductivity of 0.35 W/(mK) and thickness up to 1.5 mm existing in the tube, may increase the tube wall temperature even more than 150°C. The study also includes the impact of outer tube wall surface fouling with thickness of 0.2 mm and heat transfer coefficient of 2 W/(mK). As a result, the compressible stresses may increase over three times compared to the situation where the tube wall fouling does not exist.