scholarly journals Blade-Resolved CFD Simulations of a Periodic Array of NREL 5 MW Rotors with and without Towers

Wind ◽  
2022 ◽  
Vol 2 (1) ◽  
pp. 51-67
Author(s):  
Lun Ma ◽  
Pierre-Luc Delafin ◽  
Panagiotis Tsoutsanis ◽  
Antonis Antoniadis ◽  
Takafumi Nishino
Keyword(s):  
Large Scale ◽  
Wind Farm ◽  
Computational Cost ◽  
Flow Characteristics ◽  
Sampling Period ◽  
Navier Stokes ◽  
Actuator Disc ◽  
Blade Tip ◽  
Large Wind ◽  
Turbine Model

A fully resolved (FR) NREL 5 MW turbine model is employed in two unsteady Reynolds-averaged Navier–Stokes (URANS) simulations (one with and one without the turbine tower) of a periodic atmospheric boundary layer (ABL) to study the performance of an infinitely large wind farm. The results show that the power reduction due to the tower drag is about 5% under the assumption that the driving force of the ABL is unchanged. Two additional simulations using an actuator disc (AD) model are also conducted. The AD and FR results show nearly identical tower-induced reductions of the wind speed above the wind farm, supporting the argument that the AD model is sufficient to predict the wind farm blockage effect. We also investigate the feasibility of performing delayed-detached-eddy simulations (DDES) using the same FR turbine model and periodic domain setup. The results show complex turbulent flow characteristics within the farm, such as the interaction of large-scale hairpin-like vortices with smaller-scale blade-tip vortices. The computational cost of the DDES required for a given number of rotor revolutions is found to be similar to the corresponding URANS simulation, but the sampling period required to obtain meaningful time-averaged results seems much longer due to the existence of long-timescale fluctuations.

scholarly journals Evaluation of Tip Loss Corrections to AD/NS Simulations of Wind Turbine Aerodynamic Performance

2019 ◽  
Vol 9 (22) ◽  
pp. 4919 ◽  
Author(s):  
Wei Zhong ◽  
Tong Guang Wang ◽  
Wei Jun Zhu ◽  
Wen Zhong Shen
Keyword(s):  
Wind Turbine ◽  
Wind Farm ◽  
Relative Difference ◽  
Superior Performance ◽  
Navier Stokes ◽  
Special Focus ◽  
Actuator Disc ◽  
Blade Tip ◽  
Blade Loads ◽  
Blade Element

The Actuator Disc/Navier-Stokes (AD/NS) method has played a significant role in wind farm simulations. It is based on the assumption that the flow is azimuthally uniform in the rotor plane, and thus, requires a tip loss correction to take into account the effect of a finite number of blades. All existing tip loss corrections were originally proposed for the Blade-Element Momentum Theory (BEMT), and their implementations have to be changed when transplanted into the AD/NS method. The special focus of the present study is to investigate the performance of tip loss corrections combined in the AD/NS method. The study is conducted by using an axisymmetric AD/NS solver to simulate the flow past the experimental NREL Phase Ⅵ wind turbine and the virtual NREL 5MW wind turbine. Three different implementations of the widely used Glauert tip loss function F are discussed and evaluated. In addition, a newly developed tip loss correction is applied and compared with the above implementations. For both the small and large rotors under investigation, the three different implementations show a certain degree of difference to each other, although the relative difference in blade loads is generally no more than 4%. Their performance is roughly consistent with the standard Glauert correction employed in the BEMT, but they all tend to make the blade tip loads over-predicted. As an alternative method, the new tip loss correction shows superior performance in various flow conditions. A further investigation into the flow around and behind the rotors indicates that tip loss correction has a significant influence on the velocity development in the wake.

scholarly journals Study of Vortex Systems as a Method to Weakening the Urban Heat Islands within the Financial District in Large Cities

2021 ◽  
Vol 13 (23) ◽  
pp. 13206
Author(s):  
Luis Rodriguez-Lucas ◽  
Chen Ning ◽  
Marcelo Fajardo-Pruna ◽  
Yugui Yang
Keyword(s):  
Rural Areas ◽  
Large Scale ◽  
Flow Characteristics ◽  
Maximum Velocity ◽  
Vortex Generator ◽  
Urban Heat Islands ◽  
Navier Stokes ◽  
Specific Work ◽  
Heat Islands ◽  
Large Cities

This paper presents a new concept called the urban vortex system (UVS). The UVS couples a vortex generator (V.G.) that produces updraft by artificial vortex and a vortex stability zone (VSZ) consisting of an assembly of four buildings acting as a chimney. Through this system, a stable, upward vortex flow can be generated. The Reynolds Averaged Navier–Stokes (RANS) simulation was carried out to investigate the flow field in the UVS. The Renormalized Group (RNG) k–ε turbulent model was selected to solve the complex turbulent flow. Validation of the numerical results was achieved by making a comparison with the large-size experimental model. The results reported that a steady-state vortex could be formed when a vapor-air mixture at 2 m/s and 450 K enters the vortex generator. This vortex presented a maximum negative central pressure of −6.81 Pa and a maximum velocity of 5.47 (m/s). Finally, the similarity method found four dimensionless parameters, which allowed all the flow characteristics to be transported on a large scale. The proposed large-scale UVS application is predicted to be capable, with have a maximum power of 2 M.W., a specific work of 3 kJ/kg, buildings 200-m high, and the ability to generate winds of 6.1 m/s (20 km/h) at 200 m up to winds of 1.5 m/s (5 km/h) at 400 m. These winds would cause the rupture of the gas capsule of the heat island phenomenon. Therefore, the city would balance its temperature with that of the surrounding rural areas.

Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Energy Equations

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

Simulation of Wake Interactions in Wind Farms Using an Immersed Wind Turbine Model

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
S. Jafari ◽  
N. Chokani ◽  
R. S. Abhari
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Complex Terrain ◽  
Wind Farm ◽  
Wind Farms ◽  
Navier Stokes ◽  
The Novel ◽  
Wind Tunnel Experiments ◽  
Wake Interactions ◽  
Turbine Model

The accurate modeling of the wind turbine wakes in complex terrain is required to accurately predict wake losses. In order to facilitate the routine use of computational fluid dynamics in the optimized micrositing of wind turbines within wind farms, an immersed wind turbine model is developed. This model is formulated to require grid resolutions that are comparable to that in microscale wind simulations. The model in connection with the k-ω turbulence model is embedded in a Reynolds-averaged Navier–Stokes solver. The predictions of the model are compared to available wind tunnel experiments and to measurements at the full-scale Sexbierum wind farm. The good agreement between the predictions and measurements demonstrates that the novel immersed turbine model is suited for the optimized micrositing of wind turbines in complex terrain.

Simulation of Wake Interactions in Wind Farms Using an Immersed Wind Turbine Model

2013 ◽  
Author(s):  
S. Jafari ◽  
N. Chokani ◽  
R. S. Abhari
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Complex Terrain ◽  
Wind Farm ◽  
Wind Farms ◽  
Navier Stokes ◽  
The Novel ◽  
Wind Tunnel Experiments ◽  
Wake Interactions ◽  
Turbine Model

The accurate modelling of the wind turbine wakes in complex terrain is required to accurately predict wake losses. In order to facilitate the routine use of computational fluid dynamics in the optimised micrositing of wind turbines within wind farms, an immersed wind turbine model is developed. This model is formulated to require grid resolutions that are comparable to that in microscale wind simulations. The model in connection with the k-ω turbulence model is embedded in a Reynolds-Averaged Navier Stokes solver. The predictions of the model are compared to available wind tunnel experiments and to measurements at the full-scale Sexbierum wind farm. The good agreement between the predictions and measurements demonstrates that the novel immersed turbine model is suited for the optimised micrositing of wind turbines in complex terrain.

3D Simulation of Flow in a Vortex Cell Using RANS and Hybrid RANS-LES Turbulence Models

2017 ◽  
Author(s):  
Tausif Jamal ◽  
D. Keith Walters ◽  
Varun Chitta
Keyword(s):  
Large Scale ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
General Information ◽  
Navier Stokes ◽  
Test Case ◽  
Computational Domain ◽  
Vortex Cell ◽  
Curvature Effects ◽  
Low Dissipation

A vortex cell is a cylindrical aerodynamic cavity that traps separated vortices to prevent the formation of large-scale vortex shedding. Due to the presence of complex vortical structures, regions with varying turbulent intensities, and rotation-curvature effects on turbulent structure; the flow inside a vortex cell is a valuable test case for newly proposed turbulence models and numerical schemes. In the present study, numerical simulations were carried using a Reynolds-averaged Navier-Stokes (RANS) turbulence model and two hybrid RANS/large-eddy-simulation (LES) models. The computational domain consists of a cylindrical cavity with an incoming transitional boundary layer and a Reynolds number of 9.4 × 104 based on the diameter of the cavity. Results indicate that the RANS model provides general information about the flow characteristics, while the hybrid RANS-LES models predict the flow characteristics with more accuracy but suffer inaccuracies due to the details of the RANS to LES transition. Most significantly, the dynamic hybrid RANS-LES (DHRL) model in combination with a low-dissipation numerical scheme overpredicts the turbulent mixing in the vortex cell and fails to provide an accurate representation of the physics of the trapped vortex. It is concluded that the hybrid RANS-LES models used in this study need further work to be able to fully and accurately predict the flow in a vortex cell.

scholarly journals Structural Optimization Design of Large Wind Turbine Blade considering Aeroelastic Effect

2017 ◽  
Vol 2017 ◽  
pp. 1-7
Author(s):  
Yuqiao Zheng ◽  
Yongyong Cao ◽  
Chengcheng Zhang ◽  
Zhe He
Keyword(s):  
Structural Optimization ◽  
Wind Turbine ◽  
Turbine Blade ◽  
Optimization Design ◽  
Large Scale ◽  
Wind Turbine Blade ◽  
Mathematical Simulations ◽  
Blade Tip ◽  
And Performance ◽  
Large Wind

This paper presents a structural optimization design of the realistic large scale wind turbine blade. The mathematical simulations have been compared with experimental data found in the literature. All complicated loads were applied on the blade when it was working, which impacts directly on mixed vibration of the wind rotor, tower, and other components, and this vibration can dramatically affect the service life and performance of wind turbine. The optimized mathematical model of the blade was established in the interaction between aerodynamic and structural conditions. The modal results show that the first six modes are flapwise dominant. Meanwhile, the mechanism relationship was investigated between the blade tip deformation and the load distribution. Finally, resonance cannot occur in the optimized blade, as compared to the natural frequency of the blade. It verified that the optimized model is more appropriate to describe the structure. Additionally, it provided a reference for the structural design of a large wind turbine blade.

Computational Flow Analysis of Wind Farms Using a Simplified Rotor Disc Model With Radially Varying Thrust Coefficient

2014 ◽  
Author(s):  
K. Vafiadis ◽  
N. Stergiannis ◽  
A. Tourlidakis
Keyword(s):  
Wind Turbines ◽  
Transient Analysis ◽  
Large Scale ◽  
Wind Farm ◽  
Wind Farms ◽  
Present Contribution ◽  
Axial Thrust ◽  
Thrust Coefficient ◽  
Disc Model ◽  
Actuator Disc

Large scale horizontal axis wind turbines are one of the most promising renewable energy technologies. When they are installed in wind farms (onshore and offshore) they can exploit the most of the available wind energy of a site. The accurate calculation of their aerodynamic interaction due to the wake development is crucial for the design of the layout and the operation of a wind farm. Simulating a wind farm with more than one fully detailed wind turbines and possibly complex terrain geometry requires significant computational power and time. Therefore, the turbine rotors are approximated as discs which behave as momentum sinks. This approach has been adopted in the present study which focuses on the development of a simplified rotor disc model. However, in the present contribution, in order to approximate the axial thrust across the disc in a more accurate manner, a novel model that involves a radially varying thrust coefficient is utilized which is extracted from the CFD full rotor transient analysis results. The analysis is carried out with the use of two commercial CFD codes, ANSYS CFX and ANSYS Fluent for the full rotor and the simplified model, respectively. For the development of the radial distribution of thrust along the blades, both steady and transient computations are carried out and the results are compared against available experimental data. For the full rotor simulation the time-averaged transient results are compared against the steady ones and with the results of the actuator disc approach. Two different turbulence models, k-epsilon and Shear Stress Transport, were used along with the three dimensional RANS equations. The detailed assessment of the differences in the flow field as it is obtained from the steady and transient analysis of both full rotor and actuator disc approximations indicated that a good agreement exists between the two distributions and the existing differences are identified and quantified.

scholarly journals From numerical prototypes to real models: a progressive study of aerodynamic parameters of nonconventional concrete structures with Computational Fluid Dynamics

2020 ◽  
Vol 13 (3) ◽  
pp. 628-643
Author(s):  
C. V. S. SARMENTO ◽  
A. O. C. FONTE ◽  
L. J. PEDROSO ◽  
P. M. V. RIBEIRO
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Performance ◽  
Large Scale ◽  
Computational Models ◽  
Computational Cost ◽  
Concrete Structures ◽  
Navier Stokes ◽  
Small Scale ◽  
Aerodynamic Parameters

Abstract The practical evaluation of aerodynamic coefficients in unconventional concrete structures requires specific studies, which are small-scale models evaluated in wind tunnels. Sophisticated facilities and special sensors are needed, and the tendency is for modern and slender constructions to arise with specific demands on their interaction with the wind. On the other hand, the advances obtained in modern multi-core processors emerge as an alternative for the construction of sophisticated computational models, where the Navier-Stokes differential equations are solved for fluid flow using numerical methods. Computations of this kind require specialized theoretical knowledge, efficient computer programs, and high-performance computers for large-scale calculations. This paper presents recent results involving two real-world applications in concrete structures, where the aerodynamic parameters were estimated with the aid of computational fluid dynamics. Conventional quad-core computers were applied in simulations with the Finite Volume Method and a progressive methodology is presented, highlighting the main aspects of the simulation and allowing its generalization to other types of problems. The results confirm that the proposed methodology is promising in terms of computational cost, drag coefficient estimation and versatility of simulation parameters. These results also indicate that mid-performance computers can be applied for preliminary studies of aerodynamic parameters in design offices.

3-D Navier-Stokes Simulation of Large-Scale Regions of the Bronchopulmonary Tree

2009 ◽  
Author(s):  
D. Keith Walters ◽  
William H. Luke
Keyword(s):  
Large Scale ◽  
Cfd Simulation ◽  
Computational Cost ◽  
Three Dimensional ◽  
Flow Distribution ◽  
Mesh Size ◽  
Flow Path ◽  
Navier Stokes ◽  
Small Scale ◽  
Flow Geometry

A new methodology for CFD simulation of airflow in the human bronchopulmonary tree is presented. The new approach provides a means for detailed resolution of the flow features via three-dimensional Navier-Stokes CFD simulation without the need for direct simulation of the entire flow geometry, which is well beyond the reach of available computing power now and in the foreseeable future. The method is based on a finite number of flow paths, each of which is fully resolved, to provide a detailed description of the entire complex small-scale flowfield. A stochastic coupling approach is used for the unresolved flow path boundary conditions, yielding a virtual flow geometry allowing accurate statistical resolution of the flow at all scales for any set of flow conditions. Results are presented for multi-generational lung models based on the Weibel morphology and the anatomical data of Hammersley and Olson. Validation simulations are performed for a portion of the bronchiole region (generations 4–12) using the flow path ensemble method, and compared to simulations that are geometrically fully resolved. Results are obtained for three inspiratory flowrates and compared in terms of pressure drop, flow distribution characteristics, and flow structure. Results show excellent agreement with the fully resolved geometry, while reducing the mesh size and computational cost by as much as 94%.

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