CFD Analysis of Stall in a Wells Turbine

2018 ◽  
Author(s):  
Kellis Kincaid ◽  
David W. MacPhee
Keyword(s):  
Source Code ◽  
Turbulence Models ◽  
Ocean Waves ◽  
Cfd Analysis ◽  
Oscillating Water Column ◽  
Blade Profile ◽  
Flow Conditions ◽  
Wells Turbine ◽  
Sst Model ◽  
Blade Shape

The Wells turbine is a self-rectifying device that employs a symmetrical blade profile, and is often used in conjunction with an oscillating water column to extract energy from ocean waves. The effects of solidity, angle of attack, blade shape and many other parameters have been widely studied both numerically and experimentally. To date, several 3-D numerical simulations have been performed using commercial software, mostly with steady flow conditions and employing various two-equation turbulence models. In this paper, the open source code Open-FOAM is used to numerically study the performance characteristics of a Wells turbine using a two-equation turbulence model, namely the Menter SST model, in conjunction with a transient fluid solver.

Wells Turbine With Variable Blade Profile for Wave Energy Conversion

2018 ◽  
Author(s):  
Celia Miguel González ◽  
Ginés Rodríguez Fuertes ◽  
Manuel García Díaz ◽  
Bruno Pereiras García ◽  
Francisco Castro ◽  
...  
Keyword(s):  
Rotation Speed ◽  
Incidence Angle ◽  
Main Flow ◽  
Performance Curve ◽  
Oscillating Water Column ◽  
Blade Profile ◽  
Wave Energy Conversion ◽  
Wells Turbine ◽  
Sharp Drop ◽  
Ansys Fluent

It is well known among the researchers involved in the field of turbines for Oscillating Water Column systems (OWC) that the main problem for Wells turbines is the stall, which appears when the main flow incidence angle exceeds certain value and leads to a sharp drop in the efficiency. It also causes problems during the starting, driving the turbine to not reach the designing rotation speed. Delaying the stall apparition is the key to improve the performance of the Wells turbine. is necessary to delay the flow separation at the trailing edge because it is the reason which leads to the sharp efficiency drop at the stall point. One of the solutions proposed by researchers in this field is using a variable blade profile instead of the traditional ones, built using constant chord and profile from hub to tip. This work tries to dig deeper in this line by analysing a blade with variable chord and shape among the blade span. The work has been developed numerically by using commercial software ANSYS FLUENT®. A CFD code was created in order to obtain the performance curve of the turbine proposed to be compared with those assumed as reference, which were taken from the bibliography and also used to validate the numerical model. The results have shown that an improvement has been achieved. It confirms that using a variable blade profile is a suitable solution to delay the stall apparition.

An Assessment of Turbulence Models for S-Duct Diffusers With Flow Control

2013 ◽  
Author(s):  
S. P. Bhat ◽  
R. K. Sullerey
Keyword(s):  
Experimental Data ◽  
Flow Control ◽  
Turbulence Model ◽  
Flow Analysis ◽  
Turbulence Models ◽  
Experimental Results ◽  
Cfd Analysis ◽  
Duct Flow ◽  
Ansys Fluent ◽  
Sst Model

The selection of a turbulence model for a problem is not trivial and has to be done systematically after comparison of various models with experimental data. It is a well known fact that there is no such turbulence model which fits all problems ([3], [13]). The flow in S-duct diffuser is a very complex one where both separation and secondary flow coexist. Previous work by the author on CFD analysis of S-duct diffuser was done using k-ε-Standard model [1], however it has been seen that choosing other turbulence model may result in better capturing of the physics in such a problem. Also flow control, to reduce energy losses, is achieved using a technique called Zero Net Mass Flow (ZNMF), in which suction and vortex generation jets (VGJ) are combined and positioned at optimum location. A proper turbulence model has to be chosen for capturing these phenomena effectively. Extensive experimental data is available on this problem and ZNMF technique from previous work done by one of the authors which is used for validating the CFD results. Here the focus is on choosing the best turbulence model for the S-duct diffuser. Numerical (CFD) analysis is carried out using Ansys Fluent 13.0 with six turbulence models for the geometry with (ZNMF) and without (Bare duct) flow control and then compared with the experimental results. The turbulence models used are Spalart-Allmaras, three variants of k-ε – Standard, RNG and Realizable and two variants of k-ω – Standard and SST model. All the parameters of comparison are non-dimensionalized using the free stream properties, so that the results are applicable to a wider range of problems. This work is limited to incompressible flow analysis, as the experimental data is only available for low Mach number flows. Comparison of all these models clearly shows that results obtained using k-ω-SST model are very comparable to the experimental results for the bare duct (without flow control) and flow controlled duct both in terms of distribution of properties and aggregate results. Compressible flow analysis can be attempted to achieve reliable results in future with ZNMF using the best turbulence model based on this study.

scholarly journals CFD analysis of the energy conversion process in a fixed oscillating water column (OWC) device with a Wells turbine

2018 ◽  
Vol 148 ◽  
pp. 1026-1033 ◽  
Author(s):  
Pasquale G.F. Filianoti ◽  
Luana Gurnari ◽  
Marco Torresi ◽  
Sergio M. Camporeale
Keyword(s):  
Energy Conversion ◽  
Water Column ◽  
Conversion Process ◽  
Cfd Analysis ◽  
Oscillating Water Column ◽  
Wells Turbine ◽  
Energy Conversion Process

Wells Turbines With 3-Dimensional Blades: The Performance Under Unsteady Flow Conditions

2015 ◽  
Author(s):  
Manabu Takao ◽  
Katsuya Takasaki ◽  
Tomohiro Tsunematsu ◽  
Miah Md. Ashraful Alam ◽  
Toshiaki Setoguchi
Keyword(s):  
Unsteady Flow ◽  
Flow Separation ◽  
Blade Profile ◽  
Wave Energy Conversion ◽  
Flow Conditions ◽  
Suction Surface ◽  
Wells Turbine ◽  
3 Dimensional ◽  
Profile Changes ◽  
The Mean

The effect of the 3-dimentional (3D) blade on the turbine characteristics of Wells turbines for wave energy conversion has been investigated numerically by a quasi-steady analysis under unsteady flow conditions in this study in order to improve the peak mean efficiency characteristics. The aim of use of the 3D blade is to prevent flow separation on the suction surface near the tip. The chord length is constant in the radius and the blade profile changes gradually from the mean radius to the tip. The proposed blade profiles in the study are NACA0015 from the hub to mean radius and NACA0025 at the tip. The performance of the Wells turbine with 3D blades has been compared with those of the original Wells turbine, i.e., the turbine with 2-dimentional blades. As a result, it was concluded that although the peak mean efficiency of a Wells turbine can be improved by the use of the proposed 3D blade, its blade does not overcome the stall characteristic.

scholarly journals Effect of Blade Profile on the Performance of Wells Turbine under Unidirectional Sinusoidal and Real Sea Flow Conditions

2007 ◽  
Vol 2007 ◽  
pp. 1-9 ◽  
Author(s):  
A. Thakker ◽  
R. Abdulhadi
Keyword(s):  
Unsteady Flow ◽  
Numerical Results ◽  
Blade Profile ◽  
Flow Conditions ◽  
Wells Turbine ◽  
Hysteretic Characteristics ◽  
The One ◽  
Good Agreement

This paper presents the effect of blade profile and rotor solidity on the performance of Wells turbine operating under unidirectional unsteady flow conditions. In the study, four kinds of blade profile were selected, that is, NACA0020, NACA0015, CA9, and HSIM 15-262123-1576. The experiments have been carried out for two solidities,σ= 0.48 andσ= 0.64, under sinusoidal and irregular unsteady flow conditions based on Irish waves (site2). As a result, it was found that the preferable rotor geometry is the one with blade profile of CA9 with solidityσ= 0.64. In addition, the effect of blade profile and rotor solidity on hysteretic characteristics of the turbine has been clarified experimentally and it was found to be in good agreement qualitatively when compared to numerical results (Setoguchi et al. (2003)).

scholarly journals Analysis of Flow Characteristics and Effects of Turbulence Models for the Butterfly Valve

2021 ◽  
Vol 11 (14) ◽  
pp. 6319
Author(s):  
Sung-Woong Choi ◽  
Hyoung-Seock Seo ◽  
Han-Sang Kim
Keyword(s):  
Turbulence Model ◽  
Dissipation Rate ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Flow Properties ◽  
Nominal Diameter ◽  
Large Pressure ◽  
Sst Model ◽  
Turbulence Effect ◽  
Valve Opening

In the present study, the flow characteristics of butterfly valves with different sizes DN 80 (nominal diameter: 76.2 mm), DN 262 (nominal diameter: 254 mm), DN 400 (nominal diameter: 406 mm) were numerically investigated under different valve opening percentages. Representative two-equation turbulence models of two-equation k-epsilon model of Launder and Sharma, two-equation k-omega model of Wilcox, and two-equation k-omega SST model of Menter were selected. Flow characteristics of butterfly valves were examined to determine turbulence model effects. It was determined that increasing turbulence effect could cause many discrepancies between turbulence models, especially in areas with large pressure drop and velocity increase. In addition, sensitivity analysis of flow properties was conducted to determine the effect of constants used in each turbulence model. It was observed that the most sensitive flow properties were turbulence dissipation rate (Epsilon) for the k-epsilon turbulence model and turbulence specific dissipation rate (Omega) for the k-omega turbulence model.

Performance enhancement of Savonius wind turbine by blade shape and twisted angle modifications

2021 ◽  
pp. 095765092098794
Author(s):  
Ahmed M Nagib Elmekawy ◽  
Hassan A Hassan Saeed ◽  
Sadek Z Kassab
Keyword(s):  
Wind Turbine ◽  
Performance Enhancement ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Vertical Axis ◽  
Cfd Simulations ◽  
Sliding Mesh ◽  
Blade Shape ◽  
Rotor Shape ◽  
Twisting Angle

Three-dimensional CFD simulations are carried out to study the increase of power generated from Savonius vertical axis wind turbines by modifying the blade shape and blade angel of twist. Twisting angle of the classical blade are varied and several proposed novel blade shapes are introduced to enhance the performance of the wind turbine. CFD simulations have been performed using sliding mesh technique of ANSYS software. Four turbulence models; realizable k -[Formula: see text], standard k - [Formula: see text], SST transition and SST k -[Formula: see text] are utilized in the simulations. The blade twisting angle has been modified for the proposed dimensions and wind speed. The introduced novel blade increased the power generated compared to the classical shapes. The two proposed novel blades achieved better power coefficients. One of the proposed models achieved an increase of 31% and the other one achieved 32.2% when compared to the classical rotor shape. The optimum twist angel for the two proposed models achieved 5.66% and 5.69% when compared with zero angle of twist.

scholarly journals An approach to the modeling of a virtual thermal manikin

2014 ◽  
Vol 18 (4) ◽  
pp. 1413-1423 ◽  
Author(s):  
Dragan Ruzic ◽  
Sinisa Bikic
Keyword(s):  
Turbulence Models ◽  
Thermal Conditions ◽  
Heat Fluxes ◽  
Thermal Manikin ◽  
Flow Conditions ◽  
Body Segments ◽  
Nominal Size ◽  
Natural Flow ◽  
Good Agreement ◽  
Made In

The aim of the research described in this paper, is to make a virtual thermal manikin that would be simple, but also robust and reliable. The virtual thermal manikin was made in order to investigate thermal conditions inside vehicle cabins. The main parameters of the presented numerical model that were investigated in this paper are mesh characteristics and turbulence models. Heat fluxes on the manikin's body segments obtained from the simulations were compared with published results, from three different experiments done on physical thermal manikins. The presented virtual thermal manikin, meshed with surface elements of 0.035 m in nominal size (around 13,600 surface elements) and in conjunction with the two-layer RANS Realizable k-? turbulence model, had generally good agreement with experimental data in both forced and natural flow conditions.

Prediction of the Flow and Force Characteristics of Safety Relief Valves

2006 ◽  
Author(s):  
W. Dempster ◽  
C. K. Lee ◽  
J. Deans
Keyword(s):  
Operating Conditions ◽  
Cfd Analysis ◽  
Flow Conditions ◽  
Relief Valve ◽  
Good Correspondence ◽  
Geometry Modeling ◽  
Valve Opening ◽  
Satisfactory Prediction ◽  
Force Characteristics

The design of safety relief valves depends on knowledge of the expected force-lift and flow-lift characteristics at the desired operating conditions of the valve. During valve opening the flow conditions change from seal-leakage type flows to combinations of sub-sonic and supersonic flows It is these highly compressible flow conditions that control the force and flow lift characteristics. This paper reports the use of computational fluid dynamics techniques to investigate the valve characteristics for a conventional spring operated 1/4” safety relief valve designed for gases operating between 10 and 30 bar. The force and flow magnitudes are highly dependent on the lift and geometry of the valve and these characteristics are explained with the aid of the detailed information available from the CFD analysis. Experimental determination of the force and flow lift conditions has also been carried out and a comparison indicates good correspondence between the predictions and the experiment. However, attention requires to be paid to specific aspects of the geometry modeling including corner radii and edge chamfers to ensure satisfactory prediction.

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