Experimental analysis of the unsteady flow inside a Wells turbine

One of the most promising technologies for sea-wave energy conversion is the one based on the Oscillating Water Column (OWC) principle. The system is composed of two units, an open chamber that converts the sea water motion into an alternating air-flow, and a turbine driven by the latter. The alternating flow of air requires a turbine capable of maintaining the same direction of rotation. The Wells turbine represents the simplest and most reliable device for this purpose. It is a self-rectifying axial turbine characterized by a rotor with symmetric blades staggered at 90 degrees relative to the axis of rotation. The vast majority of experimental works on Wells turbines and OWC devices analyzed their performance from a global point of view, often under steady conditions, in order to evaluate the pressure drop through the rotor, the torque produced and thus the turbine efficiency. This paper presents an experimental analysis of the three-dimensional flow inside a Wells turbine which operates in a facility capable of reproducing the alternating air-flow typical of an OWC system. The investigation is based on local flow measurements using several probes in order to describe the non-stationary air-flow, both up- and down-stream of the rotor at different heights, along the span of the blade. The investigation, conducted on a high-solidity turbine, details the behavior of the flow field inside the machine, aiming to provide a detailed description that can guide the aerodynamic optimization of the entire system (chamber and turbine) for a better energy conversion.

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Preliminary Results of Numerical Simulations of a Bio-Mimetic Wells Turbine

Volume 6: Ocean Space Utilization; Ocean Renewable Energy ◽

10.1115/omae2016-54463 ◽

2016 ◽

Cited By ~ 1

Author(s):

Qiuhao Hu ◽

Ye Li ◽

Fangyi Wei

Keyword(s):

Energy Conversion ◽

Three Dimensional ◽

Turbine Rotor ◽

Navier Stokes ◽

Maximum Efficiency ◽

Wells Turbine ◽

Turbulence Effects ◽

Dimensional Simulation ◽

Lower Torque ◽

Good Agreement

Wells turbine is a kind of self-rectified air turbines used in an oscillatory water column (OWC) device for wave energy conversion. In this study, a steady three-dimensional simulation of a fan-shaped Wells turbine is performed on Star CCM+ commercial software by solving the Reynolds-averaged Navier-Stokes (RANS) equations. The turbulence effects are taken into account by using the Spalart-Allmaras turbulence model. Good agreement between the numerical results and the experimental results within the operation region (5< α <11 degrees) is observed. The geometry of the turbine rotor has a significant effect on the performance of energy conversion. Inspired by the aerodynamics of low Reynolds flyer, the normal fan-shaped Wells turbine is optimized by a bio-mimetic method in which the profile of a hawk moth wing of Manduca Sexta is applied on the blades. The modified turbine has a lower torque and pressure drop coefficient with higher efficiency. The maximum efficiency for the modified turbine is 0.61, compared to 0.48 for the normal fan-shaped one. By analysis of the detailed flow-field, it has also been found that only the middle parts of the blade can effectively generate the momentum. In order to acquire a higher efficiency, further optimization is carried out by refining some blade parts in the tip and the hub which cannot effectively produce power.

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Experimental investigation of the field of velocity gradients in turbulent flows

Journal of Fluid Mechanics ◽

10.1017/s0022112092002325 ◽

1992 ◽

Vol 242 ◽

pp. 169-192 ◽

Cited By ~ 239

Author(s):

A. Tsinober ◽

E. Kit ◽

T. Dracos

Keyword(s):

Turbulent Flows ◽

Strain Tensor ◽

Three Dimensional ◽

Outer Region ◽

Calibration Procedure ◽

Point Of View ◽

Strict Sense ◽

Hot Wire ◽

Special Equipment ◽

Flow Measurements

We present results of experiments on a turbulent grid flow and a few results on measurements in the outer region of a boundary layer over a smooth plate. The air flow measurements included three velocity components and their nine gradients. This was done by a twelve-wire hot-wire probe (3 arrays × 4 wires), produced for this purpose using specially made equipment (micromanipulators and some other auxiliary special equipment), calibration unit and calibration procedure. The probe had no common prongs and the calibration procedure was based on constructing a calibration function for each combination of three wires in each array (total 12) as a three-dimensional Chebishev polynomial of fourth order. A variety of checks were made in order to estimate the reliability of the results.Among the results the most prominent are the experimental confirmation of the strong tendency for alignment between vorticity and the intermediate eigenvector of the rate-of-strain tensor, the positiveness of the total enstrophy-generating term ωiωjsij (sij = ½(∂ui/∂xj+∂uj/∂xi), ωi = εijk∂uj/∂xk) even for rather short records and the tendency for alignment in the strict sense between vorticity and the vortex stretching vector Wi = ωjsij. An emphasis is put on the necessity to measure invariant quantities, i.e. independent of the choice of the system of reference (e.g. sijsij and ωiωjsij) as the most appropriate to describe physical processes. From the methodological point of view the main result is that the multi-hot-wire technique can be successfully used for measurements of all the nine velocity derivatives in turbulent flows, at least at moderate Reynolds numbers.

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Radial Impulse Turbine for Wave Energy Conversion: A New Geometry

Volume 6: Nick Newman Symposium on Marine Hydrodynamics; Yoshida and Maeda Special Symposium on Ocean Space Utilization; Special Symposium on Offshore Renewable Energy ◽

10.1115/omae2008-57951 ◽

2008 ◽

Cited By ~ 2

Author(s):

B. Pereiras ◽

F. Castro ◽

A. El Marjani ◽

M. A. Rodriguez

Keyword(s):

Energy Conversion ◽

Wave Energy ◽

Flow Direction ◽

Mechanical Energy ◽

Research Work ◽

Flow Simulation ◽

Flow Behaviour ◽

Wells Turbine ◽

Impulse Turbine ◽

Local Flow

The Oscillating Water Column system (OWC) is an interesting concept for ocean wave energy extraction. Several kinds of air turbines have been used for pneumatic energy conversion to mechanical energy. The Wells turbine has been used widely in OWC plants. However, as an alternative the self-rectifying turbine called Impulse turbine has been studied during the last years. We are interested in the radial version of the Impulse turbine, which was initially proposed by McCormick. A former research work aimed to improve the knowledge of the local flow behaviour and the prediction of the performances for this kind of turbine has been carried out using CFD (FLUENT®). The objectives of that work were connected mainly to the elaboration of a suitable 3D model for air flow simulation in a radial Impulse turbine. Model validation was conducted through a comparison with available experimental results. In the present, the objective is, using the numerical model, to develop a new radial impulse turbine geometry that gets better performances than the original one. This new turbine geometry will be exploited next in a project for an OWC of 250 kW. In this paper we describe the flow behaviour and the performances of this new turbine. For that, we study the Torque and Input coefficients, the losses and flow direction in the turbine elements.

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Heat Transfer Characteristics of Turbulent Flames in Three-Dimensional Furnaces

2002 International Joint Power Generation Conference ◽

10.1115/ijpgc2002-26190 ◽

2002 ◽

Author(s):

Essam E. Khalil

Keyword(s):

Heat Transfer ◽

Flow Pattern ◽

Air Flow ◽

Three Dimensional ◽

Flow Regimes ◽

Turbulent Flames ◽

Shear Stresses ◽

Governing Equations ◽

Combustion Chambers ◽

Local Flow

The recent advances in numerical methods and the vast development of computers have directed the designers to better development and modifications to air-flow pattern and heat transfer in combustion chambers. Extensive efforts are exerted to adequately predict the air velocity and turbulence intensity distributions in the combustor zones, and to reduce the air pollution and noise abatement to ultimately produce quite and energy efficient combustor systems. The present work utilizes mathematical modeling techniques to primarily predict what happens in three-dimensional combustion chambers simulating boiler furnaces, and areo engines in terms of flow regimes and interactions. The present work also demonstrates the effect of chamber design and operational parameters on performance, wall shear stresses, and vorticity under various operating parameters. The governing equations of mass, momentum and energy are commonly expressed in a preset form with source terms to represent pressure radients, turbulence and viscous action. The physical and chemical characteristics of the air and fuel are obtained from tabulated data in the literature. The flow regimes and heat transfer plays an important role in the efficiency and utilization of energy. The behavior was found to be strongly dependent on turbulent shear, mixing, blockage, wall conditions and location of fuel and air inlets. Eddies can be strong enough to have higher velocities typically near reactants supply openings. Excessive transverse flow velocities cause extra macromixing; the air flow regimes are complex and of three-dimensional nature; with the advance of computational techniques it is possible to accurately simulate three-dimensional flows. The results reported in this work were obtained with the aid of the three-dimensional program 3DCOMB; applied to axisymmetrical and three-dimensional complex geometry with and without swirl. The present numerical grid comprises, typically, 144000-grid node covering the combustion chamber volume in the X, R or Y and Z coordinates directions. The numerical residual in the governing equations typically less than 0.001%. A modified grid generation formula was proposed and incorporated in the present work. Examples of large industrial furnaces are shown and were in good agreement with available measurements in the open literature. One may conclude that flow patterns, turbulence and heat transfer in combustors are strongly affected by the inlet swirl, inlet momentum ratios, combustor geometry; both micro and macro mixing levels are influential. Greater tangential velocities and turbulence characteristics are demonstrated in situations with higher swirl intensities. The present modeling capabilities can adequately predict the local flow pattern and turbulence kinetic energy levels in complex combustors.

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Comparison of the reluctance laminated and solid rotor synchronous machine operating at high temperatures

COMPEL The International Journal for Computation and Mathematics in Electrical and Electronic Engineering ◽

10.1108/compel-10-2018-0405 ◽

2019 ◽

Vol 38 (4) ◽

pp. 1111-1119 ◽

Cited By ~ 2

Author(s):

Marcin Lefik ◽

Krzysztof Komeza ◽

Ewa Napieralska-Juszczak ◽

Daniel Roger ◽

Piotr Andrzej Napieralski

Keyword(s):

High Speed ◽

Design Methodology ◽

Three Dimensional ◽

Synchronous Machine ◽

Point Of View ◽

Heat Sources ◽

Model Calculations ◽

Content Type ◽

Thermal Phenomenon ◽

Practical Implications

Purpose The purpose of this paper is to present a comparison between reluctance synchronous machine-enabling work at high internal temperature (HT° machine) with laminated and solid rotor. Design/methodology/approach To obtain heat sources for the thermal model, calculations of the electromagnetic field were made using the Opera 3D program including effect of rotation and the resulting eddy current losses. To analyse the thermal phenomenon, the 3D coupled thermal-fluid (CFD) model is used. Findings The presented results show clearly that laminated construction is much better from a point of view of efficiency and temperature. However, solid construction can be interesting for high speed machines due to their mechanical robustness. Research limitations/implications The main problem, despite the use of parallel calculations, is the long calculation time. Practical implications The obtained simulation and experimental results show the possibility of building a machine operating at a much higher ambient temperature than it was previously produced for example in the vicinity of the aircraft turbines. Originality/value The paper presents the application of fully three-dimensional coupled electromagnetic and thermal analysis of new machine constructions designed for elevated temperature.

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ENHANCEMENT OF SCREEN FILM MAMMOGRAM UP TO A LEVEL OF DIGITAL MAMMOGRAM: EXPERIMENTAL ANALYSIS

International Journal of Image and Graphics ◽

10.1142/s0219467813400044 ◽

2013 ◽

Vol 13 (02) ◽

pp. 1340004

Author(s):

APARNA NARENDRA BHALE ◽

MANISH RATNAKAR JOSHI

Keyword(s):

Experimental Analysis ◽

Breast Imaging ◽

Point Of View ◽

Quality Analysis ◽

Digital Mammogram ◽

Total Recovery ◽

Clinical Observations ◽

Opinion Score ◽

Better Than

Breast cancer is one of the major causes of death among women. If a cancer can be detected early, the options of treatment and the chances of total recovery will increase. From a woman's point of view, the procedure practiced (compression of breasts to record an image) to obtain a digital mammogram (DM) is exactly the same that is used to obtain a screen film mammogram (SFM). The quality of DM is undoubtedly better than SFM. However, obtaining DM is costlier and very few institutions can afford DM machines. According to the National Cancer Institute 92% of breast imaging centers in India do not have digital mammography machines and they depend on the conventional SFM. Hence in this context, one should answer "Can SFM be enhanced up to a level of DM?" In this paper, we discuss our experimental analysis in this regard. We applied elementary image enhancement techniques to obtain enhanced SFM. We performed the quality analysis of DM and enhanced SFM using standard metrics like PSNR and RMSE on more than 350 mammograms. We also used mean opinion score (MOS) analysis to evaluate enhanced SFMs. The results showed that the clarity of processed SFM is as good as DM. Furthermore, we analyzed the extent of radiation exposed during SFM and DM. We presented our literally findings and clinical observations.

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Cyclopean Vision, Size Estimation, and Presence in Orthostereoscopic Images

Presence Teleoperators & Virtual Environments ◽

10.1162/105474601300343630 ◽

2001 ◽

Vol 10 (3) ◽

pp. 312-330 ◽

Cited By ~ 15

Author(s):

Bernard Harper ◽

Richard Latto

Keyword(s):

Visual System ◽

Three Dimensional ◽

Point Of View ◽

Psychophysical Experiment ◽

Size Estimation ◽

Human Form ◽

Image Capture ◽

Series Of Experiments ◽

Abstract Shapes ◽

And Control

Stereo scene capture and generation is an important facet of presence research in that stereoscopic images have been linked to naturalness as a component of reported presence. Three-dimensional images can be captured and presented in many ways, but it is rare that the most simple and “natural” method is used: full orthostereoscopic image capture and projection. This technique mimics as closely as possible the geometry of the human visual system and uses convergent axis stereography with the cameras separated by the human interocular distance. It simulates human viewing angles, magnification, and convergences so that the point of zero disparity in the captured scene is reproduced without disparity in the display. In a series of experiments, we have used this technique to investigate body image distortion in photographic images. Three psychophysical experiments compared size, weight, or shape estimations (perceived waist-hip ratio) in 2-D and 3-D images for the human form and real or virtual abstract shapes. In all cases, there was a relative slimming effect of binocular disparity. A well-known photographic distortion is the perspective flattening effect of telephoto lenses. A fourth psychophysical experiment using photographic portraits taken at different distances found a fattening effect with telephoto lenses and a slimming effect with wide-angle lenses. We conclude that, where possible, photographic inputs to the visual system should allow it to generate the cyclopean point of view by which we normally see the world. This is best achieved by viewing images made with full orthostereoscopic capture and display geometry. The technique can result in more-accurate estimations of object shape or size and control of ocular suppression. These are assets that have particular utility in the generation of realistic virtual environments.

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Numerical Simulation of Droplets Moving on Surface of Three-Dimensional Trapezoidal Object in Air Flow(Fluids Engineering)

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.76.768_1134 ◽

2010 ◽

Vol 76 (768) ◽

pp. 1134-1143 ◽

Cited By ~ 1

Author(s):

Katsunori DOI ◽

Takeshi KAWANABE ◽

Naoki HAMAMOTO ◽

Yoshiaki NAKAMURA

Keyword(s):

Numerical Simulation ◽

Air Flow ◽

Three Dimensional

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A Four-Channel Low-Noise Readout IC for Air Flow Measurement Using Hot Wire Anemometer in 0.18 μm CMOS Technology

Sensors ◽

10.3390/s21144694 ◽

2021 ◽

Vol 21 (14) ◽

pp. 4694

Author(s):

Kyeongsik Nam ◽

Hyungseup Kim ◽

Yongsu Kwon ◽

Gyuri Choi ◽

Taeyup Kim ◽

...

Keyword(s):

Supply Voltage ◽

Air Flow ◽

Low Noise ◽

Cmos Process ◽

Significant Information ◽

Flow Measurements ◽

Pass Filter ◽

Low Pass Filter ◽

Op Amp ◽

Noise Characteristics

Air flow measurements provide significant information required for understanding the characteristics of insect movement. This study proposes a four-channel low-noise readout integrated circuit (IC) in order to measure air flow (air velocity), which can be beneficial to insect biomimetic robot systems that have been studied recently. Instrumentation amplifiers (IAs) with low-noise characteristics in readout ICs are essential because the air flow of an insect’s movement, which is electrically converted using a microelectromechanical systems (MEMS) sensor, generally produces a small signal. The fundamental architecture employed in the readout IC is a three op amp IA, and it accomplishes low-noise characteristics by chopping. Moreover, the readout IC has a four-channel input structure and implements an automatic offset calibration loop (AOCL) for input offset correction. The AOCL based on the binary search logic adjusts the output offset by controlling the input voltage bias generated by the R-2R digital-to-analog converter (DAC). The electrically converted air flow signal is amplified using a three op amp IA, which is passed through a low-pass filter (LPF) for ripple rejection that is generated by chopping, and converted to a digital code by a 12-bit successive approximation register (SAR) analog-to-digital converter (ADC). Furthermore, the readout IC contains a low-dropout (LDO) regulator that enables the supply voltage to drive digital circuits, and a serial peripheral interface (SPI) for digital communication. The readout IC is designed with a 0.18 μm CMOS process and the current consumption is 1.886 mA at 3.3 V supply voltage. The IC has an active area of 6.78 mm2 and input-referred noise (IRN) characteristics of 95.4 nV/√Hz at 1 Hz.

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