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71.
A fast, efficient way to control loads on utility scale wind turbines is important for the growth of the wind industry. Microtabs and microjets are two Active Aerodynamic Load Control devices, which address this need. Both act perpendicular to the surface of the airfoil, and these actively controlled devices are used to mitigate changes in aerodynamic loading experienced by wind turbine rotors due to wind gusts, wind shear, or other atmospheric phenomena. This work explores the aerodynamic effects of microjets and then compares them to those of microtabs. Flow around an airfoil with an activated microjet at the trailing edge has been simulated using the Reynolds‐averaged Navier–Stokes solver OVERFLOW‐2. Using a Chimera overset grid topology, a microjet has been placed near the trailing edge of the lower surface of a NACA 0012 airfoil. For a jet velocity about half of the freestream velocity, the microjet can change the lift up to ΔCL = 0.2, but the amount of change varies with the momentum coefficient of the jet. The change in lift is not symmetric for positive and negative angles of attack due to changes in the boundary layer thickness with angle of attack. Increasing the Reynolds number reduces the effectiveness of the microjet only slightly. The effects of jet velocity, jet activation time, and airfoil angle of attack on airfoil lift, drag, and pitching moment are compared with previous work, which illustrates the deployment of a microtab at the 95% chord location of a NACA 0012 airfoil. This study shows that microjets and microtabs have very similar responses in lift and pitching moment, but the drag for the microjet is noticeably lower. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
72.
The purpose of this Letter to the Editor is to present a discussion on the physics of rotational augmentation based on existing work. One of the latest works by Gross et al. (2012) is highlighted here, and its conclusions are discussed. Based on the existing understanding of rotational augmentation, some inconsistencies seem to be present in the analysis of Gross et al. These are identified and discussed here, along with a brief survey of relevant literature. Copyright 2013 John Wiley & Sons, Ltd. 相似文献
73.
叶轮机械弯扭叶片的研究现状及发展趋势 总被引:34,自引:1,他引:33
弯扭叶片在20世纪90年代已在英、美等发达国家较普遍地得到应用,在我国也成功地应用于蒸汽轮机,在航空发动机涡轮中的应用也有了良好的开端。文章就叶片弯曲降低能量损失的机理以及静态和动态实验对采用弯曲叶片的效果做了综合评述,对压气机采用弯曲叶片的科研进展,以及遇到的难点也作了概要的介绍。根据我们的设计经验,在文章的最后总结了弯曲叶片级设计时应遵循的几条原则。 相似文献
74.
以某跑车模型为研究对象,探讨尾部小型扩散器对于车身气动性能的影响。在初始模型的基础上,进行CFD(Computational Fluid Dynamics)数值模拟计算,并对比风洞试验数据,验证仿真的可靠性。对初始模型的扩散器进行改进设计,加大扩散器的工作区域,研究其对于气动力的影响,并将改进后的扩散器与带有仿生凹坑型非光滑扰流器结合起来,通过数值模拟方法,得出压力和速度等流场参数,比较不同形式的扩散器对于气动性能的改进效果,分析气动力改善的原因。结果表明:通过对扩散器与非光滑扰流器的优化组合,能有效地提高气动负升力,减小气动阻力,达到了调谐车辆气动升力与气动阻力之间的耦合关系的目的。 相似文献
75.
为建立高超声速飞行器多学科设计优化软件系统,研究了一种面向多学科设计优化的建模方法.通过分析系统分解带来的学科设计冲突,建立了两种多学科连续性条件.据此连续性条件,结合现有飞行器设计流程,提出了一套建立多学科设计优化模型的方法,包括系统分析模型和系统优化模型.针对高超声速飞行器方案设计,研究了包含弹道/控制、气动、超燃冲压发动机、结构、热保护系统等五个学科的多学科设计优化问题.采用所研究的多学科设计优化建模方法,构造了系统级模型,并在框架软件中按照此模型集成各学科软件,建立了高超声速飞行器多学科设计优化软件系统. 相似文献
76.
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78.
Siniša Krajnovi? Lars Davidson 《Journal of Wind Engineering & Industrial Aerodynamics》2005,93(9):677-696
The effect of a moving floor on the flow around a simplified car with a typical fastback geometry is investigated. Two large-eddy simulations of the flows with stationary and moving floors are made and both instantaneous and time-averaged results are compared. It is found that the floor motion reduces drag by 8% and lift by 16%. Changes in the flow are found to be global but are largest close to the floor and on the rear slanted surface of the vehicle. The wake flow is found to be relatively insensitive to the floor movement, in agreement with previous experimental observations. The periodicity of the flow events is found to be dependent on whether the floor is moving. Power spectral density of both the lift and the drag contain only one dominant frequency peak when the moving floor is adopted as compared to scattered spectra in the stationary floor case. Changes in the qualitative picture of the flow are limited to the flow near the floor and on the slanted surface of the body. However, changes in the surface pressure on the body and the history of the flow show the need of a moving floor in experimental and numerical simulations. 相似文献
79.
Hassan Hemida Siniša Krajnovi? 《Journal of Wind Engineering & Industrial Aerodynamics》2010,98(1):34-164
Large-eddy simulation (LES) is made of the flow around a generic train model at two different yaw angles of 90° and 35°. The Reynolds numbers, based on the freestream velocity and the height of the train, are 3×105 and 3.7×105 for the yaw angles of 90° and 35°, respectively. The primary objective is to investigate the influence of the nose shape and yaw angles on the flow structures and the train aerodynamics. Both the time-averaged and instantaneous flows are explored. In the case of the 90° yaw angle, the LES results show that the influence of the three-dimensional flow from the nose of the train on the time-averaged wake flow is limited to a region of a length of 3.5 train heights from the tip of the nose in the direction of the length of the train. The instantaneous flow shows an unsteady vortex shedding due to the shear layer instabilities on the periphery of the recirculation region and the exterior flow. In the case of the 35° yaw angle, weak vortex shedding is found in the wake. Instead, unstable vortices are found in the lower part of the recirculation region. These vortices detach from and reattach to the train surface in a regular fashion leaving disturbances on the train surface and hence affecting the aerodynamic coefficients. The influence of the shape of the nose on the flow structures is investigated by repeating the simulations at the 90° yaw angle on a short nose model. The short nose model is identical to the long nose model whilst the length of its nose is half that of the long nose. The short-nose simulation shows highly unsteady and three-dimensional flow around the nose yielding more vortex structures in the wake. These structures result in a surface flow that differs from that in the long-nose train flow. They also influence the dominating frequencies that arise due to the shear layer instabilities. 相似文献
80.
The concept of moving surface boundary-layer control, as applied to a Joukowsky airfoil, is investigated through a planned
experimental programme complemented by numerical studies. The moving surface was provided by rotating cylinders located at
the leading edge and/or trailing edge as well as top surface of the airfoil. Results suggest that the concept is quite promising,
leading to a substantial increase in lift and a delay in stall. Depending on the performance desired, appropriate combinations
of cylinder geometry, location and speed can be selected to obtain favourable results over a wide range of angle of attack.
Next, effectiveness of the concept in reducing drag of bluff bodies such as a two-dimensional flat plate at large angles of
attack, rectangular prisms and three-dimensional models of trucks is assessed through an extensive wind tunnel test-programme.
Results show that injection of momentum through moving surfaces, achieved here by introduction of bearing-mounted, motordriven,
hollow cylinders, can significantly delay separation of the boundary-layer and reduce the pressure drag. The momentum injection
procedure also proved effective in arresting wind-induced vortex resonance and galloping type of instabilities. A flow visualization
study, conducted in a closed-circuit water tunnel using slit lighting and polyvinyl choride tracer particles, adds to the
wind-tunnel and numerical investigations. It shows, rather dramatically, the effectiveness of the moving surface boundary-layer
control (MSBC).
The Sabita Chaudhury Memorial Lecture
The models were fabricated in the Mechanical Engineering Workshop. The assistance of M/s E Abell, P Hurren and D Camp in the
design and construction of the models is gratefully acknowledged. The investigation was supported by the Natural Sciences
and Engineering Research Council of Canada, Grant No. A-2181. 相似文献