scholarly journals Embedding of a Blade-Element Analytical Model into the SHYFEM Marine Circulation Code to Predict the Performance of Cross-Flow Turbines

2020 ◽  
Vol 8 (12) ◽  
pp. 1010
Author(s):  
Micol Pucci ◽  
Debora Bellafiore ◽  
Stefania Zanforlin ◽  
Benedetto Rocchio ◽  
Georg Umgiesser
Keyword(s):  
Analytical Model ◽  
Fluid Dynamic ◽  
A Priori ◽  
Turbine Blades ◽  
Cross Flow ◽  
Tidal Energy ◽  
Operating Conditions ◽  
Geometrical Parameters ◽  
Simplified Approach ◽  
Blade Element

Our aim was to embed a 2D analytical model of a cross-flow tidal turbine inside the open-source SHYFEM marine circulation code. Other studies on the environmental impact of Tidal Energy Converters use marine circulation codes with simplified approaches: performance coefficients are fixed a priori regardless of the operating conditions and turbine geometrical parameters, and usually, the computational grid is so coarse that the device occupies one or few cells. In this work, a hybrid analytical computational fluid dynamic model based on Blade Element Momentum theory is implemented: since the turbine blades are not present in the grid, the flow is slowed down by means of bottom frictions applied to the seabed corresponding to forces equal and opposite to those that the blades would experience during their rotation. This simplified approach allowed reproducing the turbine behavior for both mechanical power generation and the turbine effect on the surrounding flow field. Moreover, the model was able to predict the interaction between the turbines belonging to a small cluster with hugely shorter calculation time compared to pure Computational Fluid Dynamics.

scholarly journals Passive flow control mechanisms with bioinspired flexible blades in cross-flow tidal turbines

2021 ◽  
Vol 62 (5) ◽  
Author(s):  
Stefan Hoerner ◽  
Shokoofeh Abbaszadeh ◽  
Olivier Cleynen ◽  
Cyrille Bonamy ◽  
Thierry Maître ◽  
...  
Keyword(s):  
Turbine Blades ◽  
Cross Flow ◽  
Tidal Energy ◽  
Control Mechanisms ◽  
Passive Flow Control ◽  
Turbine Efficiency ◽  
Tidal Turbines ◽  
Passive Flow ◽  
Axial Turbines ◽  
The Cost

Abstract State-of-the-art technologies for wind and tidal energy exploitation focus mostly on axial turbines. However, cross-flow hydrokinetic tidal turbines possess interesting features, such as higher area-based power density in array installations and shallow water, as well as a generally simpler design. Up to now, the highly unsteady flow conditions and cyclic blade stall have hindered deployment at large scales because of the resulting low single-turbine efficiency and fatigue failure challenges. Concepts exist which overcome these drawbacks by actively controlling the flow, at the cost of increased mechatronical complexity. Here, we propose a bioinspired approach with hyperflexible turbine blades. The rotor naturally adapts to the flow through deformation, reducing flow separation and stall in a passive manner. This results in higher efficiency and increased turbine lifetime through decreased structural loads, without compromising on the simplicity of the design. Graphic abstract

Development of a Design Approach for the Optimization of Steam Turbine Exhaust System Performance Through CFD Modelling

2021 ◽  
Author(s):  
Tommaso Diurno ◽  
Stella Grazia Tomasello ◽  
Tommaso Fondelli ◽  
Antonio Andreini ◽  
Bruno Facchini ◽  
...  
Keyword(s):  
Power Plants ◽  
Fluid Dynamic ◽  
Renewable Energy Sources ◽  
Computational Cost ◽  
Great Influence ◽  
Computational Effort ◽  
Operating Conditions ◽  
Cfd Modeling ◽  
Geometrical Parameters ◽  
Exhaust Hood

Abstract Nowadays, the ever-increasing world electricity generation by renewable energy sources has brought about changes in conventional power plants, especially in those ones where large steam turbines work, which were widely used to meet the world’s energy needs by operating mostly at fixed conditions. Now, instead, they have to be capable to operate with greater flexibility, including rapid load changes and quick starts as well, in order to make the most of the renewable resources while guaranteeing the coverage of any shortcomings of the latter with traditional fossil fuel systems. Such service conditions are particularly challenging for the exhaust hoods, which have a great influence on the overall turbine performance, especially at off-design conditions. In fact, the complex and high rotational 3D flow generated within the diffuser and the exhaust hood outer casing can cause an increase in aerodynamic losses along with the detriment of the hood recovery performance. For these reasons, an optimized design and adequate prediction of the exhaust hood performance under all the machine operating conditions is mandatory. Since it has been widely proven that the exhaust hood flow strongly interacts with the turbine rear stage, the necessity to model this as well into a CFD modeling becomes crucial, requiring a remarkable computational effort, especially for full transient simulations. Even if adopting simplified approaches to model the last stage and exhaust hood interfaces, such as the so-called Frozen Rotor and the Mixing Plane ones, helps to keep the computational cost low, it can be not for an exhaust hood optimization process, which requires a significant number of CFD simulations to identify the most performing geometry configuration. For these reasons, a simplified model of the exhaust hood must be adopted to analyse all the possible design variants within a feasible time. The purpose of this work is to present a strategy for the exhaust hood design based on the definition of a simplified CFD model. A parametric model has been developed as a function of key geometrical parameters of both the exhaust hood and the diffuser, taking into account the strong fluid-dynamic coupling between these components. A periodic approximation has been introduced to model the exhaust hood domain, thus allowing to augment the number of the geometrical parameters of the DOE, while keeping the computational effort low. A response surface has been achieved as a function of the key geometrical parameters, therefore an optimization method has allowed identifying the best performing configuration. A 3D model of the optimized periodic geometry has been then generated to assess the effectiveness of the procedure here presented. Finally, the presented procedure has been applied in several off-design operating conditions, in order to find out an optimal geometry for each operating point, evaluating how much they differ from that one got for the design point.

scholarly journals Enhancement of Free Vortex Filament Method for Aerodynamic Loads on Rotor Blades

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Hamidreza Abedi ◽  
Lars Davidson ◽  
Spyros Voutsinas
Keyword(s):  
Wind Turbine ◽  
Potential Flow ◽  
Turbine Blades ◽  
Boundary Layer Separation ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Dynamic Stall ◽  
Aerodynamic Loads ◽  
Operational Conditions ◽  
Blade Element

The aerodynamics of a wind turbine is governed by the flow around the rotor, where the prediction of air loads on rotor blades in different operational conditions and its relation to rotor structural dynamics is one of the most important challenges in wind turbine rotor blade design. Because of the unsteady flow field around wind turbine blades, prediction of aerodynamic loads with high level of accuracy is difficult and increases the uncertainty of load calculations. An in-house vortex lattice free wake (VLFW) code, based on the inviscid, incompressible, and irrotational flow (potential flow), was developed to study the aerodynamic loads. Since it is based on the potential flow, it cannot be used to predict viscous phenomena such as drag and boundary layer separation. Therefore, it must be coupled to tabulated airfoil data to take the viscosity effects into account. Additionally, a dynamic approach must be introduced to modify the aerodynamic coefficients for unsteady operating conditions. This approach, which is called dynamic stall, adjusts the lift, the drag, and the moment coefficients for each blade element on the basis of the two-dimensional (2D) static airfoil data together with the correction for separated flow. Two different turbines, NREL and MEXICO, are used in the simulations. Predicted normal and tangential forces using the VLFW method are compared with the blade element momentum (BEM) method, the GENUVP code, and the MEXICO wind tunnel measurements. The results show that coupling to the 2D static airfoil data improves the load and power predictions while employing the dynamic stall model to take the time-varying operating conditions into consideration is crucial.

Experimental and Computational Fluid Dynamic Analysis of Laboratory-Scaled Counter-Rotating Cross-Flow Turbines in Marine Environment

2018 ◽  
Author(s):  
Minh N. Doan ◽  
Ivan H. Alayeto ◽  
Claudio Padricelli ◽  
Shinnosuke Obi ◽  
Yoshitaka Totsuka
Keyword(s):  
Fluid Dynamic ◽  
Magnetic Hysteresis ◽  
Turbine Blades ◽  
Water Channel ◽  
Cross Flow ◽  
Vertical Axis ◽  
Computational Domain ◽  
Computational Fluid Dynamic Analysis ◽  
Angular Velocities ◽  
Marine Hydrokinetic

Power generation of laboratory-scaled marine hydrokinetic (MHK) cross-flow (vertical axis) turbines in counter-rotating configurations was scrutinized both experimentally and numerically. A tabletop experiment, designed around a magnetic hysteresis brake as the speed controller and a Hall-effect sensor as the speed transducer was built to measure the rotor rotational speed and the hydrodynamic torque generated by the turbine blades. A couple of counter-rotating straight-three-bladed vertical-axis turbines were linked through a transmission of spur gears and timing pulleys/belt and coupled to the electronic instrumentation via flexible shaft couplers. A total of 6 experiments in 3 configurations, with various relative distances and phase angles, were conducted in the water channel facility (3.5 m long, 0.30 m wide, and 0.15 m deep) at rotor diameter base Reynolds number of 20,000. The power curve of the counter-rotating turbines (0.068-m rotor diameter) was measured and compared with that of a single turbine of the same size. Experimental results show the tendency of power production enhancement of different counter-rotating configurations. Additionally, the two-dimensional (2D) turbine wakes and blade hydrodynamic interactions were simulated by the shear stress transport k-omega (SST k-omega) model using OpenFOAM. The computational domain included a stationary region and two rotating regions (for the case of counter-rotating turbines) set at constant angular velocities. The interface between the rotating and stationary region was modeled as separated surface boundaries sliding on each other. Velocity, pressure, turbulent kinetic energy, eddy viscosity, and specific dissipation rate field were interpolated between these boundaries.

scholarly journals Numerical Investigations on the Blade Tip Clearance Excitation Forces in an Unshrouded Turbine

2020 ◽  
Vol 10 (4) ◽  
pp. 1532 ◽  
Author(s):  
Yang Pan ◽  
Qi Yuan ◽  
Gongge Huang ◽  
Jiawei Gu ◽  
Pu Li ◽  
...  
Keyword(s):  
Fluid Dynamic ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Geometrical Parameters ◽  
Deformation Method ◽  
Flow Angle ◽  
Rotordynamic Coefficients ◽  
Blade Tip ◽  
Positive Direct

The purpose of this study was to investigate the characteristics of the blade tip excitation forces represented as the rotordynamic coefficients (stiffness and damping coefficients) in an unshrouded turbine using the three-dimensional computational fluid dynamic (CFD) numerical method. The blade geometrical parameters were based on a SNECMA transonic experimental rig. The simulations were performed by solving the compressible Reynolds-averaged Navier–Stokes (RANS) equations. The multi-frequency elliptical whirling orbit model and an improved mesh deformation method based on the transient analysis were utilized. The effects of operating conditions on the rotordynamic coefficients and the unsteady flow were also found. The results show that the positive direct stiffness, which confirmed the direct force contribution in the tip excitation forces and the cross-coupling stiffness, were dependent on the whirling frequencies. Damping effects were shown to be negligible. The rotational speed, inlet flow angle, eccentric ratio (ER), and mean tip clearance had impacts on the stiffness, and some effects of these variables on the rotordynamic coefficients were found to be frequency dependent. Additionally, increasing the rotor eccentricity and the mean tip clearance led to the nonuniformity of the circumferential pressure distributions.

Proposal of a Load Sensing Two-Way Valve Model, Applying “Design of Experiments” Techniques to Simulations

2006 ◽  
Author(s):  
Andrea Vacca
Keyword(s):  
Design Of Experiments ◽  
Analytical Model ◽  
Flow Rate ◽  
Operating Conditions ◽  
Fractional Factorial ◽  
Geometrical Parameters ◽  
Screening Analysis ◽  
Load Sensing ◽  
Actual Behaviour ◽  
Wide Range

This paper defines an analytical model, based on results of simulations, for the description of the actual behaviour of a particular load sensing valve. The component considered for the analysis is typically applied in steering systems, with a load sensing control strategy, in presence of other actuators. Controlling the primary port flow rate is the valve's scope, the exceeding flow being discharged to the secondary port. A simple analytical model of the valve is commonly used in the industrial field and is useful for the understanding of its operation in a generic hydraulic system. However, experiments show that the actual behaviour is strongly influenced by the flow rate through the valve, and depends also on many geometrical parameters (i.e. shape of spool grooves, spool edges distance, etc.). The simple empirical model presented in this paper is defined considering only parameters primarily affecting the valve operation. As it often happens in searching for new models, the discovery of the most influencing factors presents several difficulties, because of their large number and, mainly, because it is difficult to consider all possible mutual interactions. Therefore, in this analysis, a stochastic-based method has been chosen, according to a technique known as "Design of Experiments" (DOE). In the first part of the paper, the author presents a screening analysis of the valve, under all the possible operating conditions. This procedure allows the identification of the most influencing parameters, for the development of the enhanced model of the valve. The configurations examined were chosen defining an optimal experimental plan, that allows an high significance of results with a restricted number of tests, through fractional factorial strategies. Further, this analysis gives a lot of useful information for the improvement of the valve design. In the remaining section of this paper, the author presents a correlative model of actual valve behaviour. This is generalized to a wide range of possible spool geometries, and is characterized by a simple formulation, accounting for only a few parameters, highlighted by the screening analysis. All results processed by DOE algorithms, implemented with MATLAB® scripts, are evaluated through simulations, instead of experiments. For this purpose, a previously developed AMESim® model of the valve (validated on the basis of laboratory tests) has been utilized.

Inclusion of a Simple Dynamic Inflow Model in the Blade Element Momentum Theory for Wind Turbine Application

2014 ◽  
Author(s):  
Xiaomin Chen ◽  
Ramesh Agarwal
Keyword(s):  
Steady State ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Operating Conditions ◽  
Phase Iii ◽  
Speed Ratio ◽  
Horizontal Axis Wind Turbine ◽  
Bem Theory ◽  
Blade Element

It is well established that the power generated by a Horizontal-Axis Wind Turbine (HAWT) is a function of the number of blades B, the tip speed ratio λr (blade tip speed/wind free-stream velocity) and the lift to drag ratio (CL/CD) of the airfoil sections of the blade. The previous studies have shown that Blade Element Momentum (BEM) theory is capable of evaluating the steady-state performance of wind turbines, in particular it can provide a reasonably good estimate of generated power at a given wind speed. However in more realistic applications, wind turbine operating conditions change from time to time due to variations in wind velocity and the aerodynamic forces change to new steady-state values after the wake settles to a new equilibrium whenever changes in operating conditions occur. The goal of this paper is to modify the quasi-steady BEM theory by including a simple dynamic inflow model to capture the unsteady behavior of wind turbines on a larger time scale. The output power of the wind turbines is calculated using the improved BEM method incorporating the inflow model. The computations are performed for the original NREL Phase II and Phase III turbines and the Risoe turbine all employing the S809 airfoil section for the turbine blades. It is shown by a simple example that the improved BEM theory is capable of evaluating the wind turbine performance in practical situations where operating conditions often vary in time.

scholarly journals A Double Multiple Stream Tube (DMST) routine for site assessment to select efficient turbine aspect ratios and solidities in real marine environments

2021 ◽  
Vol 312 ◽  
pp. 08001
Author(s):  
Micol Pucci ◽  
Stefania Zanforlin ◽  
Debora Bellafiore ◽  
Stefano Deluca ◽  
Georg Umgiesser
Keyword(s):  
Aspect Ratio ◽  
Fluid Dynamic ◽  
Energy Resource ◽  
Cross Flow ◽  
Power Coefficient ◽  
Geometrical Parameters ◽  
Northern Adriatic Sea ◽  
Stream Tube ◽  
Northern Adriatic ◽  
Aspect Ratios

A MATLAB routine, based on a Double Multiple Stream Tube model, developed to quickly predict the performance of cross-flow hydrokinetic turbine, here is presented. The routine evaluate flow data obtained with the open-source marine circulation code SHYFEM. The tool can establish the best locations to place tidal devices taking into account bathymetric constraints and the hydrokinetic potential. Hence, it can be used to decide the best set of geometrical parameters. The geometrical variables of our analysis are turbine frontal area, aspect ratio and solidity. Several sub-models, validated with 3D and 2D CFD simulations, reproduce phenomena such as dynamic stall, fluid dynamic tips losses and the lateral deviation of streamlines approaching the turbine. As a case study, the tool is applied to an area of the northern Adriatic Sea. After having identified some suitable sites to exploit the energy resource, we have compared behaviours of different turbines. The set of geometrical parameters that gives the best performance in terms of power coefficient can vary considering several locations. Conversely, the power production is always greater for turbine with low aspect ratio (for a fixed solidity and area). Indeed, shorter devices benefit from higher hydrokinetic potentials at the top of the water column.

A physically-based SPICE model for the leakage current in a-Si:H TFTs accounting for its dependencies on process, geometrical, and bias conditions

2000 ◽  
Vol 609 ◽  
Author(s):  
Peyman Servati ◽  
Arokia Nathan ◽  
Andrei Sazonov
Keyword(s):  
Leakage Current ◽  
Analytical Model ◽  
Measurement Data ◽  
Diffusion Profile ◽  
Operating Conditions ◽  
Geometrical Parameters ◽  
Temperature Dependent ◽  
Current Voltage ◽  
Physically Based ◽  
Hydrogenated Amorphous

ABSTRACTWe have developed a physically-based analytical model of the static current-voltage characteristics of hydrogenated amorphous silicon (a-Si:H) inverted staggered thin film transistors (TFTs) in the reverse (leakage) regime (VG<0,VD>0). We studied analytically (based on measurement data) the dependence of the leakage current on process parameters (i.e. the deposition-temperature-dependent phosphorus diffusion profile in the a-Si:H active layer), geometrical parameters (i.e. a-Si:H thickness, source/drain overlap areas), and operating conditions (i.e. VG, VD). The derived analytical model is implemented in HSPICE. The simulated and measured results are in good agreement with a discrepancy of less than 5%.

Numerical and Experimental Characterization of a Plate Compact Multipass Counter Flow and Locally Cross-Flow Recuperator

2006 ◽  
Author(s):  
Paolo M. Congedo ◽  
Giuseppe Starace
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Cross Flow ◽  
Operating Conditions ◽  
Geometrical Parameters ◽  
Total Efficiency ◽  
Operating Pressure ◽  
Counter Flow ◽  
The Real

A compact and efficient heat exchanger for exhaust gas recovery energy was needed to raise the total efficiency of a thermo-photovoltaic system TPV (Thermo-Photo-Voltaic) for automotive applications (see [1]). In order to respect the strict condition of a high heat transfer surface to volume ratio, a heat exchanger configuration with a plate compact multi-pass counter flow and locally cross-flow recuperator has been chosen. The goal of this work is the understanding of the behaviour of the heat exchanger with numerical and experimental analysis for different geometrical and operating conditions. A high number of dimensions and manufacturing constraints was evaluated before reaching a definite design of a compact and efficient heat exchanger to be tested in the lab for initial experiments. The experimental work was needed in order to validate the numerical model. As the material needed for the real application could not be easily manufactured and instrumented in a workshop, a simplified real model, made of brass, was built, in order to compare numerical results and experimental findings. It was supposed that results obtained in this way would be sufficient to be considered valid when extrapolated in the real heat exchanger high temperature operating conditions and manufacturing material. The experimental results have been successfully compared with numerical ones obtained with the Fluent CFD code (release 6.2.16) Curves of performance (ε-NTU diagram plotted as a function of the ratio between the minimum and the maximum thermal capacities of the flows and pressure drop -mass flowrate diagram as a function of the average temperature) have been obtained and were useful to choose the adequate configuration for different applications, depending on the requested heat transfer and maximum allowable pressure drop. The output of the investigation was: heat transfer, outlet temperatures for both air flows, heat exchanger efficiency, differential pressure drop for both hot and cold sides. After this validation final numerical simulations have been carried out in order to understand the dependence of the heat exchanger efficiency on other geometrical parameters and operating conditions such as plates dimensions, numbers and height of vanes, operating pressure and so on.

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