Numerical Study of Cavitation Characteristics of Profiles for Use in Marine Current Turbines

2011 ◽  
Author(s):  
Alexander Ladino
Keyword(s):  
Numerical Study ◽  
Pressure Coefficient ◽  
Turbine Blades ◽  
Design Stage ◽  
Power Performance ◽  
Trailing Edge ◽  
Free Zone ◽  
Wide Range ◽  
Marine Current ◽  
Promising Source

Kinetic energy in the oceans offers an important and promising source of renewable energy which can be exploited by marine current turbines (MCT). One of the key issues related with design of MCT’s is the cavitation inception along turbine blades. Cavitation occurrence in MCT’s blades generates erosion and poor power performance with similar effect in the hydraulic turbine case. In this work, a numerical investigation using the vorticity–stream function code XFOIL in order to study cavitation characteristics in NACA 4 series profiles was performed. The study was developed systematically starting from NACA 4415 profiles and varying independently camber percentage, camber position and thickness. Other study carried out was the effect of trailing edge deflection in the cavitation bucket. Results show a symmetrical increment in cavitation free zone for profiles with increasing thickness. Also for camber increment, the cavitation free zone is incremented, especially at high angles of attack. For variation of camber percentage, increasing camber produces the cavitation bucket moves to high lift zone which suggest that the profile could cavitate at low and negative Cl in wide range of cavitation numbers. Finally the effect of trailing edge deflection produces a slight increment in cavitation free zone which is similar to the effect of camber increment. Also, the trailing edge deflection shows that a same Cl can be achieved with lower angle of attack and lower pressure coefficient compared with the standard profile, constituting a desired behavior from the cavitation point of view. Finally, local dimensionless correlations were developed which can be used for parametric studies of cavitation performance of MCT’s in the design stage.

scholarly journals Numerical Study on the Biomimetic Trailing Edge of a Turbine Blade Under a Wide Range of Outlet Mach Numbers

2021 ◽  
Vol 9 ◽  
Author(s):  
Fengbo Wen ◽  
Yuxi Luo ◽  
Shuai Wang ◽  
Songtao Wang ◽  
Zhongqi Wang
Keyword(s):  
Mach Number ◽  
Energy Loss ◽  
Numerical Study ◽  
Turbine Blades ◽  
Loss Coefficient ◽  
Detached Eddy Simulation ◽  
Trailing Edge ◽  
Loss Mechanism ◽  
Wide Range ◽  
Mach Numbers

This study was carried out to investigate the loss mechanism of a blade with a harbor seal whisker structure on the trailing edge under different Mach numbers. The loss of high-pressure turbine blades with four different trailing edge geometries, including a prototype, an elliptical trailing edge (ETE), a sinusoidal trailing edge (STE), and a biomimetic trailing edge (BTE) at Mach numbers of 0.38–1.21 is studied. The delayed detached-eddy simulation method is used to predict the detailed flow of the four cascades. The result shows that, when the Mach number is less than 0.9, the BTE can effectively reduce the energy loss coefficient compared with the other three cases. As the Mach number increases, the three-dimensional characteristics of the wake behind the BTE weaken. The energy loss coefficient of the blade with the BTE is close to that of the blade with the ETE and STE when the Mach number is greater than 0.9. Besides this, by controlling the wake, the BTE can effectively suppress the dynamic movement of shock waves in the cascade at high Mach numbers.

Numerical Study of Heat Transfer in Novel Wavy Trailing Edge Design for Gas Turbine Airfoils

2019 ◽  
Author(s):  
Sarwesh Parbat ◽  
Li Yang ◽  
Minking Chyu ◽  
Sin Chien Siw ◽  
Ching-Pang Lee
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Gas Turbine ◽  
Numerical Study ◽  
Turbine Blades ◽  
Suction Side ◽  
Inlet Temperature ◽  
Protective Film ◽  
Pressure Side ◽  
Trailing Edge

Abstract The strive to achieve increasingly higher efficiencies in gas turbine power generation has led to a continued rise in the turbine inlet temperature. As a result, novel cooling approaches for gas turbine blades are necessary to maintain them within the material’s thermal mechanical performance envelope. Various internal and external cooling technologies are used in different parts of the blade airfoil to provide the desired levels of cooling. Among the different regions of the blade profile, the trailing edge (TE) presents additional cooling challenges due to the thin cross section and high thermal loads. In this study, a new wavy geometry for the TE has been proposed and analyzed using steady state numerical simulations. The wavy TE structure resembled a sinusoidal wave running along the span of the blade. The troughs on both pressure side and suction side contained the coolant exit slots. As a result, consecutive coolant exit slots provided an alternating discharge between the suction side and the pressure side of the blade. Steady state conjugate heat transfer simulations were carried out using CFX solver for four coolant to mainstream mass flow ratios of 0.45%, 1%, 1.5% and 3%. The temperature distribution and film cooling effectiveness in the TE region were compared to two conventional geometries, pressure side cutback and centerline ejection which are widely used in vanes and blades for both land-based and aviation gas turbine engines. Unstructured mesh was generated for both fluid and solid domains and interfaces were defined between the two domains. For turbulence closer, SST-kω model was used. The wall y+ was maintained < 1 by using inflation layers at all the solid fluid interfaces. The numerical results depicted that the alternating discharge from the wavy TE was able to form protective film coverage on both the pressure and suction side of the blade. As a result, significant reduction in the TE metal was observed which was up to 14% lower in volume averaged temperature in the TE region when compared to the two baseline conventional configurations.

Numerical Prediction of Turbine Profile Loss

1990 ◽  
Author(s):  
L. Xu ◽  
J. D. Denton
Keyword(s):  
Turbine Blades ◽  
Surface Friction ◽  
Trailing Edge ◽  
Integral Boundary ◽  
Wide Range ◽  
Boundary Layer Method ◽  
Time Marching ◽  
Flow Through ◽  
Euler Solver ◽  
Profile Loss

A simple numerical method for predicting the profile loss of turbine blades in subsonic and transonic flows is presented. A time marching Euler solver is used to obtain the main flow through the blade passages, the loss due to the surface friction is calculated using an integral boundary layer method, the total mixed out loss is evaluated from the mass flow and momentum balances between the trailing edge plane and an imaginary downstream plane where the flow is uniform. The base pressure acting on the trailing edge of the blade is calculated directly from the inviscid calculation without empirical correlations. The spurious numerical loss in the Euler calculation is separated from the real loss. The rationality of the approach is justified by the agreement of the prediction with a wide range of experimental measurements.

scholarly journals Effects of Micro-Tab on the Lift Enhancement of Airfoil S-809 with Trailing-Edge Flap

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 547
Author(s):  
Jianjun Ye ◽  
Shehab Salem ◽  
Juan Wang ◽  
Yiwen Wang ◽  
Zonggang Du ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Flow Behavior ◽  
Air Flow ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Turbine Blades ◽  
Lower Surface ◽  
Wind Turbine Blades ◽  
Trailing Edge ◽  
Trailing Edge Flap

Recently, the Trailing-Edge Flap with Micro-Tab (TEF with Micro-Tab) has been exploited to enhance the performance of wind turbine blades. Moreover, it can also be used to generate more lift and delay the onset of stall. This study focused mostly on the use of TEF with Micro-Tab in wind turbine blades using NREL’s S-809 as a model airfoil. In particular, the benefits generated by TEF with Micro-Tab may be of great interest in the design of wind turbine blades. In this paper, an attempt was made to evaluate the influence of TEF with Micro-Tab on the performance of NREL’s S-809 airfoils. Firstly, a computational fluid dynamics (CFD) model for the airfoil NREL’s S-809 was established, and validated by comparison with previous studies and wind tunnel experimental data. Secondly, the effects of the flap position (H) and deflection angle (αF) on the flow behaviors were investigated. As a result, the effect of TEF on air-flow behavior was demonstrated by augmenting the pressure coefficient at the lower surface of the airfoil at flap position 80% chord length (C) and αF = 7.5°. Thirdly, the influence of TEF with Micro-Tab on the flow behaviors of the airfoil NREL’s S-809 was studied and discussed. Different Micro-Tab positions and constant TEF were examined. Finally, the effects of TEF with Micro-Tab on the aerodynamic characteristics of the S-809 with TEF were compared. The results showed that an increase in the maximum lift coefficient by 25% and a delay in the air-flow stall were accomplished due to opposite sign vortices, which was better than the standard airfoil and S-809 with TEF. Therefore, it was deduced that the benefits of TEF with Micro-Tab were apparent, especially at the lower surface of the airfoil. This particularly suggests that the developed model could be used as a new trend to modify the designs of wind turbine blades.

scholarly journals Marine Turbine Hydrodynamics by a Boundary Element Method with Viscous Flow Correction

2018 ◽  
Author(s):  
Francesco Salvatore ◽  
Zohreh Sarichloo ◽  
Danilo Calcagni
Keyword(s):  
Viscous Flow ◽  
Numerical Models ◽  
Turbine Blades ◽  
Integral Equation Method ◽  
Boundary Integral ◽  
Operating Conditions ◽  
Hydrodynamic Performance ◽  
Numerical Predictions ◽  
Wide Range ◽  
Marine Current

A computational methodology for the hydrodynamic analysis of horizontal axis marine current turbines is presented. The approach is based on a boundary integral equation method for inviscid flows originally developed for marine propellers and adapted here to describe the flow features that characterize hydrokinetic turbines. To this purpose, semi-analytical trailing wake and viscous-flow correction models are introduced. A validation study is performed by comparing hydrodynamic performance predictions with two experimental test cases and with results from other numerical models in the literature. The capability of the proposed methodology to correctly describe turbine thrust and power over a wide range of operating conditions is discussed. Viscosity effects associated to blade flow separation and stall are taken into account and predicted thrust and power are comparable with results of blade element methods that are largely used in the design of marine current turbines. The accuracy of numerical predictions tend to reduce in cases where turbine blades operate in off-design conditions.

scholarly journals Experimental and CFD Analysis of Impact of Surface Roughness on Hydrodynamic Performance of a Darrieus Hydro (DH) Turbine

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 928 ◽  
Author(s):  
Mohammad Hassan Khanjanpour ◽  
Akbar A. Javadi
Keyword(s):  
Surface Roughness ◽  
Drag Coefficient ◽  
Output Power ◽  
Negative Impact ◽  
Pressure Coefficient ◽  
Turbine Blades ◽  
Roughness Height ◽  
Hydrodynamic Performance ◽  
Cfd Modeling ◽  
Wide Range

Although improving the hydrodynamic performance is a key objective in the design of ocean-powered devices, there are some factors that affect the efficiency of the device during its operation. In this study, the impacts of a wide range of surface roughness as a tribological parameter on stream flow around a hydro turbine and its power loss are studied. A comprehensive program of 3D Computational Fluid Dynamics (CFD) modeling, as well as an expansive range of experiments were carried out on a Darrieus Hydro (DH) turbine in order to measure reduction in hydrodynamic performance due to surface roughness. The results show that surface roughness of turbine blades plays an important role in the hydrodynamics of the flow around the turbine. The surface roughness increases turbulence and decreases the active fluid energy that is required for rotating the turbine, thereby reducing the performance of the turbine. The extent of the negative impact of surface roughness on the drag coefficient, pressure coefficient, torque, and output power is evaluated. It is shown that the drag coefficient of a turbine with roughness height of 1000 μm is about 20% higher than a smooth blade (zero roughness height) and the maximum percentage of reduction of output power could be up to 27% (numerically) and 22% (experimentally).

Numerical Study of Conventional and Biomimetic Marine Current Turbines in Tandem by Using Openfoam®

2017 ◽  
Vol 34 (5) ◽  
pp. 679-693 ◽  
Author(s):  
Y. J. Chu ◽  
W. T. Chong
Keyword(s):  
Renewable Energy ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Turbine Blades ◽  
Fabrication Method ◽  
Tandem Configuration ◽  
Marine Current Turbine ◽  
Current Design ◽  
Marine Current ◽  
Current Turbine

AbstractThe increasing demands on renewable energy nowadays caused the development of marine current turbine industry. In order to improve the current design of marine current turbines, studies were conducted to analyse their hydrodynamic performances during operation. Since most of the time marine current turbines operate in arrays, it is important to understand the interactions between the turbines in order to design the optimum turbine farm. OpenFOAM® was used to simulate the turbine interactions of conventional and biomimetic marine current turbines in tandem configuration. The conventional marine current turbines were referred to Pinon et al. (2012) and Mycek et al. (2013) while the biomimetic marine current turbine was adopted from Chu (2016). The numerical simulations were conducted with turbines in different inter-device distances, A/D. The percentage differences of ‘‘efficiency’’, η between the IFREMER-LOMC and the biomimetic turbine case of inter-device distances, A/D = 4, 6, 8 and 10 are 14.3%, 6.4%, 3% and 1.92% respectively. The results show that the power produced by the biomimetic turbines in tandem is comparable with the IFREMER-LOMC turbines when A/D > 4. The biomimetic marine current turbines can be a fair choice due to their potential to have alternative fabrication method of their sheet-like turbine blades.

Scaling of Composite Wind Turbine Blades for Rotors of 80 to 120 Meter Diameter

2001 ◽  
Vol 123 (4) ◽  
pp. 310-318 ◽  
Author(s):  
Dayton A. Griffin ◽  
Michael D. Zuteck
Keyword(s):  
Wind Turbine ◽  
Turbine Blades ◽  
Scaling Up ◽  
Rotor Blades ◽  
Design Parameters ◽  
Power Performance ◽  
Wind Turbine Blades ◽  
Baseline Design ◽  
Scaling Model ◽  
Wide Range

As part of the U.S. Department of Energy’s Wind Partnerships for Advanced Component Technologies (WindPACT) Program, a scaling study was performed on composite wind turbine blades. The study’s objectives were to assess the scaling of current commercial blade materials and manufacturing technologies for rotors of 80 to 120 meters in diameter, to develop scaling curves of estimated weight and cost for rotor blades in that size range, and to identify practical limitations to the scaling of current conventional blade manufacturing and materials. Aerodynamic and structural calculations were performed for a matrix of baseline blade design parameters, and the results were used as a basis for constructing a computational scaling model. The scaling model was then used to calculate structural properties for a wide range of aerodynamic designs and rotor sizes. Blade designs were evaluated on the basis of power performance, weight, static strength in flapwise bending, fatigue life in edgewise bending, and tip deflection under design loads. Calculated results were compared with weight data for current commercial blades, and limitations were identified for scaling up the baseline blade configurations. A series of parametric analyses was performed to quantify the weight reductions possible by modifying the baseline design and to identify the practical limits of those modifications. The model results provide insight into the competing design considerations involved in scaling up current commercial blade designs.

Energy Harvesting Using Flapping Dynamics of Piezoelectric Inverted Flexible Foil

2015 ◽  
Author(s):  
Pardha S. Gurugubelli ◽  
Rajeev K. Jaiman
Keyword(s):  
Energy Harvesting ◽  
Limit Cycle ◽  
Numerical Study ◽  
Electric Energy ◽  
Leading Edge ◽  
Ocean Current ◽  
Limit Cycle Oscillations ◽  
Bending Rigidity ◽  
Trailing Edge ◽  
Wide Range

This paper presents a numerical study on the self-induced flapping dynamics of an inverted flexible foil in the context of energy harvesting using piezoelectric elements. The inverted foil considered in this study is clamped at the trailing edge and the leading edge is free to oscillate. To simulate the nonlinear flapping dynamics of an inverted flexible foil, a high-order coupled fluid-structure solver based on the combined field with explicit interface (CFEI) has been developed. Additionally, a simplified piezoelectric model has been presented to determine the electric energy that can be harvested through flapping. The coupled solver is validated over a flexible foil fixed at the leading edge and trailing edge free to oscillate. A systematic study on the flapping response of an inverted flexible foil has been performed for a wide range of non-dimensional bending rigidity for a fixed Reynolds number of 1000 and mass ratio of 0.1. As a function of decreasing bending rigidity, four flapping regimes have been observed: (i) fixed-point stable, (ii) inverted limit-cycle oscillations, (iii) deformed flapping and (iv) flipped flapping. The inverted limit-cycle oscillations are characterized by low-frequency large amplitude oscillations which generate O(103) times greater strain energy than a flexible foil fixed at the leading edge, which has a profound impact on the development of ocean current based energy harvesting devices.

scholarly journals Strain Sensor via Wood Anomalies in 2D Dielectric Array

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 1022
Author(s):  
Rashid G. Bikbaev ◽  
Ivan V. Timofeev ◽  
Vasiliy F. Shabanov
Keyword(s):  
Higher Plants ◽  
Numerical Study ◽  
Reciprocal Lattice ◽  
Strain Sensing ◽  
Photonic Materials ◽  
Sensing Applications ◽  
Wide Range ◽  
Sensor Structure ◽  
Optical Behavior ◽  
Chlorophyll Absorption

Optical sensing is one of many promising applications for all-dielectric photonic materials. Herein, we present an analytical and numerical study on the strain-responsive spectral properties of a bioinspired sensor. The sensor structure contains a two-dimensional periodic array of dielectric nanodisks to mimic the optical behavior of grana lamellae inside chloroplasts. To accumulate a noticeable response, we exploit the collective optical mode in grana ensemble. In higher plants, such a mode appears as Wood’s anomaly near the chlorophyll absorption line to control the photosynthesis rate. The resonance is shown persistent against moderate biological disorder and deformation. Under the stretching or compression of a symmetric structure, the mode splits into a couple of polarized modes. The frequency difference is accurately detected. It depends on the stretch coefficient almost linearly providing easy calibration of the strain-sensing device. The sensitivity of the considered structure remains at 5 nm/% in a wide range of strain. The influence of the stretching coefficient on the length of the reciprocal lattice vectors, as well as on the angle between them, is taken into account. This adaptive phenomenon is suggested for sensing applications in biomimetic optical nanomaterials.

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