bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved Power for Wind Farm Savonius Rotors: Effect of Blade Shape and Rotors Position
Authors: Filali Abdelkader , Khezzar Lyes , Semmari Hamza 
Published: October 2020

Abstract
In the present study the effect of distance between five vertical Savonius rotors « Gap » on the total performance of the wind farm rotors is investigated. Numerical computations are conducted for a single Savonius turbine, and for the five clustered turbines aligned in perpendicular direction with respect to the upstream wind velocity. The study is carried out using ANSYS FLUENT commercial code and the moving mesh approach for the rotating zones is used. The turbulence model adopted in this work is the k-ω shear stress transport (SST) model. Numerical approach was first validated with previously published experimental and numerical data for a single rotating Savonius rotor case with semi-circular blades. Then, an improvement process based on the modification of the blades profiles to an elliptical shape was adopted. Subsequently, the change in distance between the five vertical Savonius rotors « Gap » has been considered with values of 0.25, 1 and 1.4 times the rotor radius (R). Results show that the Gap = 1R provides the optimum power coefficient for the wind farm rotors. However, the generated wake zone behind the five aligned rotors for this value is more important in particular for the 90 ° angle of the advanced and returned rotor blades. The field efficiency defined by the total power ratio of the five isolated rotors to the total power of the wind farm with five Savonius rotors is around 67%. All these geometrical considerations and propositions made it possible to define an optimal wind farm rotors arrangement.
Numerical Performance Predictions of Artificial Intelligence-Driven Centrifugal Compressor Designs
Authors: Fritsche Manuel , Epple Philipp , Kubrak Boris , Gast Stefan , Delgado Antonio , Barannik Valentyn 
Published: October 2020

Abstract
This paper demonstrates the application of artificial intelligence-driven turbomachinery design, its numerical performance predictions and their numerical validation. A common problem in the industrial application of turbomachinery is that readily available turbomachines are not necessarily matching the desired performance targets (performance characteristics) required for a specific application. Many machines operate under off-design conditions and hence are not operating at maximum efficiency. Traditional numerical analysis and response-driven optimization methods are ineffective and still too time-consuming and are particularly sensitive to changing performance targets. Most commercially available optimization algorithms are based on maximizing or minimizing a response function, for instance the standard error from a desired target performance characteristic of a turbomachine, by changing design variables.
This work uses a newly developed artificial intelligence-based approach that is not dependent on the specific design target using the turbomachinery design software AxSTREAM from SoftInWay. Here a neural network was trained within a constraint design space by many samples of design variables and their respective numerical performance predictions. For the numerical verification of the designs the solver Simcenter STAR-CCM+ from Siemens was used. Subsequently the trained neural network was applied to generate a set of design parameters that satisfied the physically feasible desired target performance characteristics very fast. This trained neural network enabled an effective reversal of the traditional iterative design process where now the desired target performance characteristics became the input and the geometry became the output, turning it into a generative inverse design process. This method was applied to generate a centrifugal compressor design within a given geometrically and physically constraint design space. A specific desired target performance characteristic was chosen. The generated designs and results are presented in detail.
Evaluation of Frictional Pressure Drop Correlations During Flow Boiling of Refrigerants in Micro-Fin Tubes
Authors: Tang Weiyu , Li Wei , Zhou Jianxin 
Published: October 2020

Abstract
Due to the widely commercial application of micro-fin tube and eco-friendly refrigerants, more general frictional pressure drop correlations is demanded for better prediction, and this study is aimed at compared existing correlations and provide guides for the furthermore improvement. Experimental data points for frictional pressure drop during flow boiling of refrigerants in horizontal micro-fin tubes were extracted from literature and our previous experimental work to evaluate numerous existing frictional pressure drop correlations and specify their applicability to meet the urgent demand of extensive application of eco-friendly refrigerants. The database consists of 949 data points covering eleven refrigerants (R1233zd(Z), R410A, R1234ze(E), R410A, R22, R32, R1234ze(Z), R22, R134a, R245fa and R1234yf included), and the involved operation conditions are as follows: mass velocity 94–888 kg m−2s−1, vapor quality 0.04–0.99, heat flux 3.9–85.2 kW m−2, and equivalent diameter 2.12–11.84mm. Eight existing general frictional pressure drop correlation including Cavallini et al., Kuo and Wang, Wongsangam et al. and Rollman and Spindler correlation were evaluated against the present database. In addition, the Churchill et al. model was employed in several correlation to improve their performance. It was found that none of these correlations was capable of providing a satisfactory prediction for a general operation condition. A detailed predictive ability of these correlation against specific work fluids were given for reference, and their individual parametric-trend predictive ability were also compared under varied operating conditions using several datasets.
Performance Assessment of a NACA-2412 Surrogate Model Using Non-Intrusive Polynomial Chaos Method
Authors: El Dine Matbouli Houssam , Fayssal Iyad 
Published: October 2020

Abstract
Computational Fluid Dynamics (CFD) models have been regarded as inevitable tools in the design of various aerodynamics applications like formula 1 cars, wind turbines, airfoil design, and many others. Such models rely on applying advanced numerical methods to solve the set of Navier-Stokes equations and other auxiliary models to quantify the aerodynamics performance, such as lift and drag in airfoil applications. However, currently adopted advanced mathematical models that are used to predict airfoil performance, though are essential tools in the advancement of aviation industry, incur large computational costs. As a primary step, an approximate model of an airfoil is built for the sake of reducing computational cost while preserving accuracy. The approximate model is based on creating a simplified algebraic model which is suitable then to perform aerodynamic design optimization rather than solving the highly non-linear set of continuity and momentum equations. In this work, the non-intrusive polynomial chaos expansion (NIPC) technique is employed on a NACA-2412 airfoil. The main objective of this research is to investigate the performance of the NIPC model with different orders on solution accuracy. A methodology is designed by first developing a full CFD model of the NACA-2412 airfoil. An experimental setup of the airfoil was then prepared with the variations of lift and drag coefficients under different operative conditions were reported. The experimental data were used to validate the numerical results generated by the CFD simulations. The surrogate model was then constructed via the NIPC technique. The performance of the surrogate model was then benchmarked with CFD results under different flow and operating conditions. Analysis was also performed to investigate the effect of polynomial order on the solution accuracy. Results showed that for a given data set size, increasing the order of the polynomial would deteriorate the solution accuracy. At a certain order k, the analytical solution starts diverging especially for values of angle of attack close to −60 and 60°.
Novel Propulsion System for VTOL Aircraft Based on Cycloidal Rotors Coupled With Wings
Authors: Rodrigues F. F. , Habibnia M. , Pascoa J. 
Published: October 2020

Abstract
Aircraft being capable of Vertical Take-off and Landing (VTOL) and hover are increasingly emerging in various critical and routine applications. Rescue missions in roads and environmental disasters, observance and monitoring-based carriers, surveillance and payload carriage in environments that require high maneuverability and controllability are just a few examples in which this type of aircraft is essential. Helicopters are the most typical aircraft in this kind, but concerning the thrusting mechanism, several alternatives are yet in hand. The tendency to equip aircraft with cycloidal rotors (shortly say, cyclorotors) as means of Vertical Take-Off and Landing thrusters has increased in recent years. These devices present several advantages such as considerably lower noise production and more stable hover and vertical displacements in comparison with conventional screw propellers as used in helicopters. In the present work a novel concept of propulsion system combining two cycloidal rotors with a pair-wing system is presented. A double wing assembly is designed to place in between the two cyclorotors on each side of the aircraft. The bottom wing is intended to divide the flow in two separate portions through the downwash region of the front cycloidal rotor. To improve the efficiency of this propulsion system, the implementation of plasma actuators in the pair-wing system will be experimentally studied. The concept behind this novel propulsion system is explained and numerical and experimental results, that support its operation concept, are presented.
Numerical Simulation of Non-Stationary Turbulent Flows Using Double Exponential Dynamic Time Filtering Technique
Authors: Jamal Tausif , Bhushan Shanti , Walters D. Keith 
Published: October 2020

Abstract
Temporally varying turbulent flows are of considerable interest in complex engineering problems such as combustion, hydrodynamics, and hemodynamics. These types of flows are often associated with complex flow physics such as varying mean pressure gradients, interactions of different scales of motion, and complex boundary layer separations. Hybrid Reynolds-averaged Navier-Stokes (RANS)/Large-Eddy Simulation (LES) methods have recently shown promise for accurate and computationally efficient simulation of these flows. One such method is the dyanamic hybrid RANS-LES (DHRL) model which has been demonstrated for numerous statistically stationary turbulent flows. More recently, it has been shown that Exponential Time-Averaging (ETA) and Dynamic Time Filtering (DTF) methods for obtaining resolved flow statistics have significantly improved the predictive capabilities of the Dynamic Hybrid RANS-LES (DHRL) model performance for a non-stationary turbulent flows with periodically time-varying statistics. However, for non-periodic temporally evolving flows with monotonically varying statistics, a more suitable alternative is desired. In this study, the performance of the Dynamic Hybrid RANS-LES (DHRL) model with a double exponential dynamic time filtering (DDTF) methodology is evaluated against a Reynolds-Averaged Navier-Stokes (RANS) model, a conventional Hybrid RANS-LES (HRL) model, implicit LES, and the DHRL model with DTF for a pulsating channel and a temporally-varying turbulent mixing layer. Model performance is evaluated based on comparisons to existing experimental and Direct Numerical Simulation (DNS) results. A comprehensive analysis of the results highlights key similarities and differences between the models and indicates that the use of a double exponential DTF technique improves the accuracy of the baseline DHRL model. It is concluded that the DDTF is a useful alternative to simulate unsteady non-periodic temporally evolving turbulent flows.
Order of Accuracy and Sensitivity to Freestream Conditions of a Modified k-ω Turbulence Model for High-Order Finite Element Methods
Authors: Bagheri-Sadeghi Nojan , Helenbrook Brian T. , Visser Kenneth D. 
Published: October 2020

Abstract
Using turbulence models with finite element methods (FEM) can be challenging as the turbulence variables can assume negative non-physical values and hinder solution convergence. A modified k–ω model was recently proposed by Stefanski et al. (2018) to be used with finite element solvers of compressible flows. The model overcomes this issue by replacing k and ω with working variables that ensure positivity and smoothness of k and ω. In this work the applicability of this model for high-order FEM simulations of incompressible flows was examined. The model was implemented for incompressible flow in an hp-FEM solver using streamline Petrov-Galerkin discretization and was validated and verified using a fully-developed channel flow and a boundary layer flow over a flat plate. Several aspects of the turbulence model behavior were studied. These included the possibilitty of getting orders of accuracy higher than 2, and the model’s sensitivity to freestream values of k and ω. The results suggested that higher orders of accuracy are possible when quadratic and quartic basis functions are used. However, this depended on the way the boundary condition for ω was defined. The commonly used boundary condition for ω, which depends on the wall-distance of the first grid point resulted in poor orders of accuracy compared to the so-called slightly-rough-surface boundary condition which is independent of the wall distance of the first grid point. Additionally, results indicated that increasing the nondimensional wall distance of the first gridpoint makes it more sensitive to the value of ω on the wall. Adding a cross-diffusion term to the transport equation for ω is known to significantly improve the accuracy of turbulence model prediction for certain flows and reduce the sensitivity of the original k–ω model to freestream values of turbulence variables. Following a more recent version of k–ω model, this term was added to the turbulence model and some other modifications including a different production term with a stress-limiter were applied. The drag coefficient of the flat plate from the new turbulence model showed similar sensitivity to the freestream values of turbulence variables as the model of Stefanski et al. (2018).
A Correction to the Barotropic Model of Gaseous Cavitation in Choked Converging-Diverging Nozzle Flows
Authors: Waldrop Michael , Thomas Flint 
Published: October 2020

Abstract
The Barotropic Cavitation Model describes the behavior of a homogeneous mixture of liquid and gas bubbles (gaseous cavitation) as it traverses a converging-diverging (CD) nozzle. Its normal shock formulation makes reliable and accurate predictions of streamwise static pressure distribution from the nozzle inlet to just downstream of the throat and in the diverging section as the flow approaches the nozzle outlet. It fails in the intermediate portion of the divergence with maximum pressure prediction errors (as a fraction of nozzle inlet pressure) roughly equivalent to the back pressure ratio (as high as 0.46). A correction to the streamwise static pressure distributions predicted by the normal shock solution of the Barotropic Cavitation Model is proposed, applied and compared to experiments with aerated and non-aerated cavitation in several fluids. When used to simulate aerated cavitation of dodecane in a CD nozzle it predicts the location of first disagreement between the normal shock solution and experimental static pressure measurements within 4% of nozzle length. A polynomial curve fit between this predicted point (xcorr) and the normal shock location (xshock) then reduces maximum prediction error for static pressure in the correction region to no more than 0.11 (as a fraction of inlet pressure) for the aerated dodecane cases examined. For non-aerated gaseous cavitation in dodecane, water or JP8 jet fuel this error ratio does not exceed 0.13 and typical values are less than 0.07.
Large Eddy Simulation of Slurry Erosion in Submerged Impinging Jets
Authors: Wang Qiuchen , Huang Qiyu , Sun Xu , Zhang Jun , Karimi Soroor , Shirazi Siamack A. 
Published: October 2020

Abstract
Submerged impingement jets are widely used in erosion/corrosion investigation as it is easy to control standoff distance as well as jet angle and flow velocities in experiments. In addition to experiments, typically Computational Fluid Dynamics (CFD) technique has been used to simulate slurry flow in this geometry to investigate erosion process and develop and verify erosion equations. This is done by solving Reynolds Averaged Navier-Stokes (RANS) equations with turbulence models, time-averaged fluid flow is revealed, and thus time-averaged erosion rate can be obtained by tracking particles in the fluid flow field. The current work shows that this seemingly simple flow displays unsteady flow structures in the stagnation zone of the flow field and its effects on erosion process was unclear. In this study, Large Eddy Simulation (LES) is used to simulate unsteady fluid flow in different impingement jets in Eulerian scheme. Then particles are injected randomly in the surface and tracked transiently to simulate unsteady erosion process in Lagrangian scheme. Finally, an erosion equation is used to calculate solid particle erosion rates. The LES Eulerian-Lagrangian erosion modeling are further validated by experimental fluid velocities and erosion profile measured before. It was found the accuracy of erosion prediction of small particles can be improved and unsteady properties can be well resolved by using this method.
Lattice Boltzmann Method Based on Large-Eddy Simulation (LES) Used to Investigate the Unsteady Turbulent Flow on Series of Cavities
Authors: Mehrez Insaf , Gheith Ramla , Aloui Fethi 
Published: October 2020

Abstract
A numerical study is proposed to analyze the turbulent flow structures. This paper aims to determine the effect of the series of the cavities. The configuration is similar to that represented by two walls with infinite width, one of which is mobile and the other is fixed. The series of cavity are placed on the fixed wall. The objectives are to study the aero acoustic capabilities of LBM and to build and to assess the efficiency of the Lattice Boltzmann Equation (LBE) as a new computational tool to perform the Large-Eddy Simulations (LES) for turbulent flows. In the first part, the background of LBM is presented and the construction of Navier-Stokes equations from Boltzmann equation is discussed. The LBM-LES model for solving transition is developed and turbulence modeling is implemented. In the second part, the dynamics of the flows in the vicinity of cavities with symmetric or asymmetric edges are considered, to then discuss the oscillation phenomenon. The effect of the geometric of the cavity and the Reynolds numbers were studied to investigate the fluid flow dynamics. We were focusing on the dynamics of asymmetric deep cavity flows, to put forward the topology of the cavity flow and to highlight the effects of dissymmetry and aspect ratio.
Optimal Design of Thermally Stressed Turbocharger Blade Using Response Surface Method
Authors: Jung Kuk Jin , Lee Jin-Woo , Kim Youn-Jea 
Published: October 2020

Abstract
RI turbine is a device that rotates the shaft by the working fluid enters the radial direction and exit in the axial direction. It is mainly used in automobile turbochargers and helicopters. Turbocharger is an important part of reducing fuel use as part of the vehicle’s power source. It is largely divided into compressor part and turbine part, and rotates the compressor by the power received from the turbine part. The gas emitted after combustion in the engine is the working fluid and the driving force for rotating the turbine. In this process the turbine is directly exposed to hot combustion gases. There is an intermediate cooling process, but the trend is to reduce and simplify it. Therefore, thermal stress analysis and optimal design process for the blades of the turbocharger turbine is required. In this study, the optimal design of turbine blade was carried out to alleviate thermally vulnerable areas without compromising efficiency through CFD (computational fluid dynamics) and RSM (response surface method). After preliminary design, numerical analysis was used to identify thermal weakness, and the optimal design was carried out with vulnerable area and efficiency as output parameters. As a result, a blade design that can lower the temperature from the weakness was derived, and a thermal optimization design process of the RI turbine was presented.
Fabrication of a Microchannel Device With a Three-Dimensional Pore Network Using a Sacrificial Sugar Template
Authors: Zhang Haipeng , Palmon Tomer , Kim Seunghee , Ryu Sangjin 
Published: October 2020

Abstract
Porous media compressed air energy storage (PM-CAES) is an emerging technology that stores compressed air in an underground aquifer during the off-peak periods, to mitigate the mismatch between energy supplies and demands. Thus, PM-CAES involves repeated two-phase fluid flow in porous media, and ensuring the success of PM-CAES requires a better understanding of repetitive two-phase fluid flow through porous media. For this purpose, we previously developed microfluidic channels that retain a two-dimensional (2D) pore network. Because it was found that the geometry of the pore structure significantly affects the patterns and occupational efficiencies of a non-wetting fluid during the drainage-imbibition cycles, a more realistic microfluidic model is needed to reflect the three-dimensional (3D) nature of pore structures in the underground geologic formation.
In this study, we developed an easy-to-adopt method to fabricate a microfluidic device with a 3D random pore network using a sacrificial sugar template. Instead of using a master mold made in photolithography, a sacrificial mold was made using sugar grains so that the mold could be washed away after PDMS curing. First, we made sugar templates with different levels of compaction load, and found that the thickness of the templates decreased as the compaction load increased, which suggests more packing of sugar grains and thus lower porosity in the template. Second, we fabricated PDMS porous media using the sugar template as a mold, and imaged their pore structure using micro computed tomography (micro-CT). Pores within PDSM samples appeared more tightly packed as the compacting force increased. Last, we fabricated a prototype PDMS channel device with a 3D pore network using a sugar template, and visualized flow through the pore network using colored water. The flow visualization result shows that the water was guided by the random pores and that the resultant flow pattern was three dimensional.