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In the last few decades vertical axis wind turbines (VAWTs) have gained increased interest among researchers worldwide. This paper aims to present full two-way Fluid Structure Interaction (FSI) approach to model operation of the Savonius-type VAWT. The developed methodology couples the set of Unsteady Reynolds Averaged Navier-Stokes Equations (URANS) with the unsteady linear elasticity equations and dynamic mesh approach to comprehensively describe the deformations of the turbine rotor. The obtained results provide detailed information on the unsteady flow fields around the operating wind turbine as well as deformations of a turbine rotor caused by an interaction between solid and flowing air. This allowed us to determine the influence of the unsteady deformations of a turbine rotor on the instantaneous and average performance of a wind turbine. Computations were carried out for the wind speed equal to 15 m/s and the tip speed ratio equal to 0.8. The simulations were performed using the commercial ANSYS software. The obtained results showed that deformation of the turbine rotor increases the wind turbine power coefficient by around 5%. Moreover, it was shown that the centrifugal force has a significant effect on the rotor deformation and turbine operation, hence it cannot be neglected. • Development of the fully coupled Fluid Structure Interaction model of Savonius wind turbine. • Results of the fully coupled FSI model was compared with validated CFD model of the Savonius wind turbine. • The influence of the centrifugal force on the turbine operation was investigated. [ABSTRACT FROM AUTHOR]

The paper aims to present structural topology optimisation of the structural topology of the H-Rotor wind turbine combined with the one-way Fluid Structure Interaction (FSI) approach. The developed methodology couples the set of Unsteady Reynolds Averaged Navier–Stokes Equations (URANS) with the steady state linear elasticity equations and density based topology optimisation method. This approach allowed us to reduce the mass of the blades with respect to the maximum stress and deformation limits. The results obtained provide detailed information on the unsteady flow fields around the operating wind turbine, as well as optimised topology of the blade interior without affecting the external aerodynamic profile. The load of pressure profile from the CFD simulation was implemented at the point of rotation at which the force values observed on the blade surface were the highest. The centrifugal force was considered in the structural model. Computations were carried out for wind speed equal to 30 m/s and rotational velocity equal to 90 rad/s. The turbine operating parameters were chosen to represent extreme operating conditions. The results obtained showed that the blade mass, made of the same material, can be easily reduced by around 60% with the reduction of the observed stress values and deformation. [Display omitted] • One way FSI model of operating H-rotor wind turbine was developed. • Topological optimisation of blade under realistic loads has been carried out. • Two blade manufacturing processes in the optimisation have been considered. • Significant reduction of deformation and stress values and over 60% mass reduction. [ABSTRACT FROM AUTHOR]

The goal of the work is to determine unknown parameters of reactor heating in the process of biomass solar pyrolysis. The lab-scale reactor is heated by a xenon lamp, but the fraction of heat absorbed by the reactor is unknown, as well as the heat transfer coefficient from the reactor walls to the nitrogen flowing through internal reactor channels, and the overall heat transfer coefficient through the external reactor walls to the surroundings. The missing parameters are impossible to measure, therefore they need to be determined by solving the inverse problem. As the problem is strongly ill-conditioned, since the quantities are directly dependent on each other, two different inverse algorithms were used to retrieve them, namely, the Levenberg-Marquardt method and the Metropolis-Hastings method. The effectiveness of both approaches was assessed and then they were applied to the real data. The inverse problem was implemented in the MatLab software, while validation of the mathematical model and optimisation procedure was carried out with a CFD model built in Ansys Fluent 19.2. Calculations showed that 14.4% of the lamp power penetrates inside the reactor and heat transfer coefficients to the flowing nitrogen equal 8.74 W/m2K and 0.965 W/m2K to the surroundings. • Two inverse algorithms were used: Levenberg-Marquardt and Metropolis-Hastings. • The validation was carried out with a 3D CFD model. • Calculations showed that only 14.4% of the lamp power penetrates inside the reactor. [ABSTRACT FROM AUTHOR]

The article presents a review of works on mathematical modelling of biomass pyrolysis process. Models types, number of dimensions, captured phenomena, type and dimensions of the reactors and biomass particles as well as models validation methods were analysed. Particular attention was paid to descriptions of chemical reactions, which are the essence of biomass thermal decomposition simulation. The article briefly describes the most important issues related to biomass pyrolysis and provides a review of commonly used methods of modelling this process with emphasis on solutions "ready to employ" in CFD modelling. A summary of other review papers on this topic is also provided. The problem of mathematical modelling in the context of "model - an engineering tool" was also discussed. Mathematical model for an engineering applications must be prepared with consideration of necessary consensus between the calculations accuracy, calculation time, preparation efforts and analysis requirements. Therefore, in pyrolysis modelling context, the inclusion of chemical reactions and changes of heat transport conditions were considered as priority, while taking into account moisture evaporation and bed shrinkage should be conditioned by their actual contribution in the calculations accuracy and by their influence on the calculations time. • A review of research on mathematical modelling of biomass pyrolysis is presented. • Captured phenomena, kinetic models, properties change, reactor types are summarized. • Compromise between model precision and calculations costs is discussed. [ABSTRACT FROM AUTHOR]

The paper presents a Computational Fluid Dynamics (CFD) model of the cold alpha-type Stirling engine. The developed mathematical model comprises of Unsteady Reynolds Averaged Navier-Stokes (URANS) set of equations, i.e. continuity, momentum and energy equations. Moreover, the developed mathematical model comprises a non-equilibrium description of the regenerator, by the introduction of the energy conservation equation for the regenerator matrix. It was implemented in the framework of commercial CFD software ANSYS Fluent. The work presents an in-depth analysis of the influence of the numerical mesh and applied turbulence model on the obtained results. The model was used to analyse the influence of the regenerator on the performance of the cold Stirling engine at different operating conditions. It appeared that on an average application of the regenerator increased the engine specific work by 10 J/kg and this increase is significantly higher at a high rotational speed of the engine. At the same time, the engine efficiency averagely was increased by 10 percent points and again this increase was significantly higher at higher rotational speeds of the engine. Especially, the influence of the heat source and sink temperatures on the engine operation were analysed. It appears that the lower are temperatures of a heat source and sink the more pronounced is the presence of the regenerator in the engine. Finally, the influence of the elementary parameters: particle diameter and porosity of the solid matrix which constitute the regenerator filling was investigated. It was shown that for the analysed engine the optimal value of the regenerator packing porosity equals about 0.72 it results in the specific area of the regenerator equal around 1675 m2/m3. Obtained results can be used to analyse the possibility of application of Stirling engines to recover low-temperature exergy of regasified Liquified Natural Gas (LNG), which for small regasification units can be alternative for commonly utilised Ambient Air Vaporizers (AAV) and it aside for regasification of LNG it could produce electric energy. [ABSTRACT FROM AUTHOR]

This paper deals with the Bayesian estimation of flow parameters in a porous material based on the measurements of local temperature at selected points inside the packed-bed. The unknown probability distribution function of estimated parameters was sampled using a Markov Chain Monte Carlo (MCMC) method. The MCMC method is efficient in sampling unknown distributions, but it is extremely time-consuming. The Proper Orthogonal Decomposition was used to construct off-line, low order approximation of the porous media flow problem. This model was further incorporated into the Metropolis-Hastings algorithm to retrieve the posterior distribution of the unknown parameters. This approach allowed us to decrease the computational time necessary to generate an ergodic Markov Chain. The efficiency of the proposed approach was tested on the simulated data generated with commercial CFD tools, and finally, it was applied to the real data acquired on the dedicated experimental stand. • Research highlight are summarized as follows: • Development of the mathematical model of biomass drying process. • Development of the coupled POD-MCMC inverse methodology estimate unknown parameters of the model. • Analysis of the accuracy of the developed approach. • Application of the inverse method to estimate model parameters for a real measurement data. [ABSTRACT FROM AUTHOR]

In the paper, a second order thermodynamic analysis of a small scale alpha-type Stirling engine is presented. The developed mathematical model is based on the Finite Time Thermodynamics (FFT) approach and it is derived from the differential time dependent equations of energy and mass conservation. The engine model consists of three spaces: compression, expansion and regenerator. In contrast to available models, the model presented in this paper assumes polytropic processes in the compression and expansion spaces, which corresponds to the non-ideal heat transfer in these spaces. The results, obtained using the developed second order model, were compared with the results obtained using the Computational Fluid Dynamics (CFD) analysis of the same engine. A very good agreement between the second order model and the CFD model was achieved. Finally, the developed model was applied to analyse potential to recover cryogenic exergy of the Liquefied Natural Gas (LNG). The paper presents the results of the dimensional upscaling of the engine and the influence of the average working pressure. It was revealed that increasing the size of the engine or the average working pressure moves the engine to practically unachievable working conditions. [ABSTRACT FROM AUTHOR]

In many engineering applications one can find periodically variable gas temperatures. Possible examples include the temperature inside the cylinders of Stirling Engines and other reciprocating machines. New methods are proposed and evaluated for the measurement of periodically varying temperature by thermocouples. A Computational Fluid Dynamics model is created to assess the method viability and efficacy in a realistic setting while avoiding measurement errors. The first method is based on matrix analysis, the two others on the particle filter algorithm used to estimate either the heat transfer coefficients with the additional use of other flow information, or to estimate the thermocouple constants without said information. It is shown that the matrix method is sufficient for cases with constant velocities. For variable velocities, the PF algorithm shows promising results as based on measurements generated from the numerical simulation. • Periodic gas temperature measurement is treated as an inverse heat transfer problem. • Two-thermocouple mechanistic solutions are generalized into an overdetermined system. • Application of 'Particle filter', utilizing other heat transfer information. • Methods are tested using CFD generated measurement data. • Particle Filter provides a high quality reconstruction of the actual temperature. [ABSTRACT FROM AUTHOR]

A 2D transient model of coupled heat and mass transfer phenomena occurring in a single coke chamber is developed. The interior of the chamber is partially filled by the coal charge, which is assumed to be a porous media. The standard equations of continuity, species transport, momentum and energy describing the flow of the single-phase fluid are applied. The model considers a range of aspects associated with the carbonization process, such as the evaporation and condensation of the water, the evolution of the volatile components, the change in the density and the flow resistance during the coking process. Conductive, convective and radiative types of heat transfer are included in the model. The model also provides for the creation of the lateral gap near the walls. Water evaporation and condensation are modeled with the modified Hertz–Knudsen equation linked to the sorption isotherm. The model of the specific process is implemented in the commercial CFD software ANSYS Fluent. Results of the CFD simulation are compared with thermocouple measurements performed at the Centre de Pyrolyse de Marienau test unit. Commonly known information regarding raw gas evolution and energy consumption are also used for validation purposes. The model agrees well with both experimental data and data from the literature. [ABSTRACT FROM AUTHOR]

• A zero dimensional model of an α type Stirling engine is created and explained. • Heat transfer models for internal convection in the engine are compared. • Those correlations are implemented in the model and the results are shown. • It is found the models produce starkly different results. In the paper the authors present a zero-dimensional model of an alpha type Stirling engine and special consideration is paid to the problems of the evaluation of internal heat transfer between the heat exchange surfaces and the working fluid. Furthermore, a thermodynamic model of the engine, developed by the authors is shown. The model can be classified as zero-dimensional. Energy and mass conservation equations are written in a differential form, and solved for finite time steps for control volumes, that is the expansion cylinder, the compression cylinder, the regenerator, the regenerator matrix and the engine as a whole, which allows to transform the differential equations into a solvable system of algebraic equations. Unlike most models shown in literature, the one created by the authors evaluates the gas properties based on a real gas model. The impl ementation of a real gas model further helps to evaluate parameters such as viscosity and thermal conductivity of the gas, which is necessary for calculating the heat transfer coefficients. Those are calculated for each volume from known correlations, for a given moment in time. That is, the gas parameters needed are not evaluated as an average for the stroke, rather, they are calculated from instantaneous gas parameters and implemented as variables in the energy equations. The engine working fluid is atmospheric air. The influence of different heat transfer models on the predicted engine performance is shown in the form of engine characteristics for different models, based on variables such as pressure, and rotational. It can be shown, that further research into in-cylinder heat transfer is necessary, as the established models, when implemented into the Stirling engine, predict starkly different engine performance. Furthermore, non-physical results based on those models are shown. [ABSTRACT FROM AUTHOR]

The paper presents a thermo-ecological analysis of a liquefied natural gas regasification system equipped with a Stirling engine. The proposed system includes an alpha configuration machine, working as a cold engine with the heat sink acting as the evaporator for the LNG and the upper heat source being at ambient temperature (sea water) or moderately higher. The engines are modelled using two approaches developed by the authors, that is a CFD model and a second-order one-dimensional model. First a small engine is modelled by both CFD and the second order approach to compare results and after confirming their similarity, due to a lower computational cost a larger machine is modelled with the second order model. Due to the heat transfer conditions being crucial for a Stirling cycle machine's performance, those are investigated. It is shown that the internal, convective heat transfer coefficients are much higher in cryogenic conditions than in typical ones. The results of engine assessment are used for the Thermo-ecological cost (TEC) analysis. Within the thermo-ecological analysis, the influence of selected parameters is demonstrated. Additionally the TEC of electricity generated in cold power plant is presented for different configurations. In the case of analysed Stirling systems savings of natural gas reach the level of only 0.5%. However, when TEC of electricity is calculated, the savings are at the level of 72%. The proposed theoretical investigations are the base for the acquisition of new knowledge in the field of possible ways of converting cryogenic exergy of LNG into electricity and optimization of this cycle with strong focus on ecological effects, including the TEC. [ABSTRACT FROM AUTHOR]