Dynamic Stall Alleviation Using a Deformable Leading Edge Concept-A Numerical Study

2003 ◽  
Vol 40 (1) ◽  
pp. 77-85 ◽  
Author(s):  
Mehmet Sahin ◽  
Lakshmi N. Sankar ◽  
M. S. Chandrasekhara ◽  
Chee Tung
Keyword(s):  
Numerical Study ◽  
Leading Edge ◽  
Dynamic Stall

A Numerical Study on the Performance Improvement for a Vertical-Axis Wind Turbine at Low Tip-Speed-Ratios

2017 ◽  
Author(s):  
Zhenyu Wang ◽  
Mei Zhuang
Keyword(s):  
Wind Speed ◽  
Wind Energy ◽  
Wind Turbines ◽  
Flow Separation ◽  
Power Output ◽  
Numerical Study ◽  
Leading Edge ◽  
Vertical Axis ◽  
Dynamic Stall ◽  
Energy Extraction

Vertical-axis wind turbines (VAWTs) are a promising solution for the use of renewable energy in residential areas. Compared to traditional horizontal-axis wind turbines (HAWTs), VAWTs are usually smaller, quieter, and insensitive to the wind direction and can be installed in a wide range of urban, suburban and rural places such as top of buildings, backyard, etc. In addition, VAWTs require a lower wind speed to self-start which increases the capability of wind energy extraction in the areas with low wind speed. However, VAWTs are less efficient and the power output of VAWTs is substantially affected by the phenomenon of dynamic stall induced by the variations of angle of attack of rotating blades, especially at low tip speed ratios (λTSR<4). When the dynamic stall vortices, formed near the leading-edge, are transported downstream, it creates large and sudden fluctuations in torques. At low values of the tip speed ratio and relatively low Reynolds number (Re<105), dynamic stall occurs periodically throughout the rotation of the blades. This results a sharp drop in lift coefficient and therefore rotor torque and power output are substantially reduced. The purpose of the present study is to investigate the prospects for improving the flow performances of small VAWTs using serrated leading-edge configurations on straight blades in a conventional H-type VAWT design to control dynamic flow separation. A numerical study is carried out to obtain the detailed flow fields for analysis and visualization. The results show that the turbine blade with the serration profiles of h = 0.025c (amplitude) and λs = 0.33c (wavelength) not only increased the power generation at low TSRs, but also enhanced the capability of wind energy extraction at the optimum TSR in comparison to the baseline model. The dynamic stall was suppressed significantly in the range of the azimuth angle from 80° to 160°. The flow separation induced by large angles of attack was essentially alleviated in the modified turbine model due to the serrated configuration implemented on the blade leading-edge.

scholarly journals Numerical Study of the Dynamic Stall Effect on a Pair of Cross-Flow Hydrokinetic Turbines and Associated Torque Enhancement due to Flow Blockage

2021 ◽  
Vol 9 (8) ◽  
pp. 829
Author(s):  
Minh N. Doan ◽  
Shinnosuke Obi
Keyword(s):  
Power Output ◽  
Numerical Study ◽  
Cross Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Dynamic Stall ◽  
Navier Stokes ◽  
Hydrokinetic Turbines ◽  
Hydrokinetic Turbine ◽  
Direction Of Movement

An open-source 2D Reynolds-averaged Navier–Stokes (RANS) simulation model was presented and applied for a laboratory-scaled cross-flow hydrokinetic turbine and a twin turbine system in counter-rotating configurations. The computational fluid dynamics (CFD) model was compared with previously published experimental results and then used to study the turbine power output and relevant flow fields at four blockage ratios. The dynamic stall effect and related leading edge vortex (LEV) structures were observed, discussed, and correlated with the power output. The results provided insights into the blockage effect from a different perspective: The physics behind the production and maintenance of lift on the turbine blade at different blockage ratios. The model was then applied to counter-rotating configurations of the turbines and similar analyses of the torque production and maintenance were conducted. Depending on the direction of movement of the other turbine, the blade of interest could either produce higher torque or create more energy loss. For both of the scenarios where a blade interacted with the channel wall or another blade, the key behind torque enhancement was forcing the flow through its suction side and manipulating the LEV.

Dynamic stall alleviation using a deformable leading edge concept - A numerical study

2000 ◽  
Author(s):  
Mehmet Sahin ◽  
Lakshmi Sankar ◽  
M. Chandrasekhara ◽  
Chee Tung
Keyword(s):  
Numerical Study ◽  
Leading Edge ◽  
Dynamic Stall

Numerical study of dynamic stall on several airfoil sections

AIAA Journal ◽  
1999 ◽  
Vol 37 ◽  
pp. 128-130
Author(s):  
Emmanuel Guilmineau ◽  
Patrick Queutey
Keyword(s):  
Numerical Study ◽  
Dynamic Stall

Numerical Study on Control of Sunroof Buffeting

2021 ◽  
Vol 13 (2) ◽  
Author(s):  
K. Vijaykumar ◽  
S. Poonkodi ◽  
A.T. Sriram
Keyword(s):  
Numerical Study ◽  
Leading Edge ◽  
Dominant Frequency ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Ansys Fluent ◽  
Flow Modification ◽  
Numerical Result ◽  
Modification Technique ◽  
Commercial Solver

Sunroof has become one of the essential features of a luxury car, and it provides natural air circulation and good illumination into the car. But the primary problem associated with it is the buffeting noise which causes discomfort to the passengers. Though adequate studies were carried out on sunroof buffeting, efficient control techniques are needed to be developed from fundamental mechanism. To reduce the buffeting noise, flow modifications at the entrance of the sunroof is considered in this study. The internal portion of the car with sunroof is simplified into a shear driven open cavity, and two-dimensional numerical simulations are carried out using commercial solver, ANSYS Fluent. Reynolds averaged Navier-Stokes equation is used with the realizable k-? turbulence model. The unsteady numerical result obtained in this study is validated with the available experimental results for the dominant frequency. The prediction is good agreement with experiment. Flow modification technique is proposed to control the sunroof buffeting by implementing geometric modifications. A hump has been placed near the leading edge of the cavity which resulted in significant reduction of pressure oscillations. Parametric studies have been performed by varying the height of hump and the distance of hump from the leading edge. There is no prominent difference when the height of the hump is varied. As the distance of the hump from the leading edge is reduced, the sound pressure level decreases.

Numerical Study on the Influence of Trench Width on Film Cooling Characteristics of Double-Wave Trench

2017 ◽  
Author(s):  
Bo-lun Zhang ◽  
Li Zhang ◽  
Hui-ren Zhu ◽  
Jian-sheng Wei ◽  
Zhong-yi Fu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Numerical Study ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Trench Width

Film cooling performance of the double-wave trench was numerically studied to improve the film cooling characteristics. Double-wave trench was formed by changing the leading edge and trailing edge of transverse trench into cosine wave. The film cooling characteristics of transverse trench and double-wave trench were numerically studied using Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment. The film cooling effectiveness and heat transfer coefficient of double-wave trench at different trench width (W = 0.8D, 1.4D, 2.1D) conditions are investigated, and the distribution of temperature field and flow field were analyzed. The results show that double-wave trench effectively improves the film cooling effectiveness and the uniformity of jet at the downstream wall of the trench. The span-wise averaged film cooling effectiveness of the double-wave trench model increases 20–63% comparing with that of the transverse trench at high blowing ratio. The anti-counter-rotating vortices which can press the film on near-wall are formed at the downstream wall of the double-wave trench. With the double-wave trench width decreasing, the film cooling effectiveness gradually reduces at the hole center-line region of the downstream trench. With the increase of the blowing ratio, the span-wise averaged heat transfer coefficient increases. The span-wise averaged heat transfer coefficient of the double-wave trench with 0.8D and 2.1D trench width is higher than that of the double-wave trench with 1.4D trench width at the high blowing ratio conditions.

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