涡产生器倾角对换热器内流动与换热特性的影响

为优化涡产生器强化传热的性能,通过改变三角翼式涡产生器的倾角,数值分析了倾角变化对板式换热器通道内流动与换热特性的影响,倾角变化范围为-30°～30°。获得了不同倾角下通道内的纵向涡、涡量分布,换热及阻力特性。结果表明涡产生器倾斜方向对流动与换热的影响不同,存在最佳的涡产生器倾角-10°,使得换热通道内涡产生器强化换热的性能最优;改变倾角可进一步提高涡产生器的强化传热性能,不同倾角对应努塞尔数和热性能评价因子间的最大差值分别达到8.9%和5.7%。     

超声速弱欠膨胀冲击射流流场结构

为了对超声速弱欠膨胀冲击射流的流场结构细节进行研究,使用大涡模拟方法对其进行了数值模拟。利用三阶迎风和四阶对称紧致格式对无量纲化轴对称可压缩滤波N-S方程进行空间离散,时间上推进采用的是三阶精度的TVD型Rugge-kutta法。亚格子尺度模型采用的是修正Sm agorinsky涡粘性模型。通过与经典的冲击射流实验比较,证明了程序的可靠性。数值模拟得到了剪切层以及壁面射流中的涡结构和主射流中的激波结构,并且在此基础上对涡合并和板前激波和涡干扰现象进行了深入研究。发现涡合并现象主要出现在流场的上游,越往下游出现的几率越小;涡和板前激波的相互作用会引起激波位置和强度以及冲击平板上冲击区的压强的显著变化,同时也会导致涡的变形。     

大功率合成射流激励器设计及其流场特性研究

为探寻新型高效的主动流动技术型式,对一种大功率合成射流激励器流场进行了详细的二维非定常数值模拟,并在此基础上进行优化设计研究,以期提高其作功能力和作功效率。结果表明,在激励器模型和有关参数不变的情况下,转速越大,激励器作用效果越明显;随着活塞位移增大,出口平均速度和最大速度都增加;在进行激励器设计时孔口段长度需要优化;激励器出口缝宽并不是越小越好。     

Numerical investigation of full scale coaxial main rotor aerodynamics in hover and vertical descent

The original free vortex wake model was used for numerical investigation. Calculation of the aerodynamic characteristics in hover and vertical descent modes in the range of vertical descent speed of 0–30 m/s including the Vortex Ring State (VRS) area was performed. The calculations were carried out under the condition of variable blade pitch angle values providing a fixed time-average thrust value. Visualization data of free vortex wake shapes, flow structures, and velocity fields were obtained and analyzed. The time-dependences of the rotor’s thrust and torque coefficients were obtained and analyzed. The obtained data allows determining the boundaries of the VRS area by various criteria such as rotor thrust and torque pulsations, growth of rotor power consumption relative to the hover, growth of rotor induced velocities relative to the hover, and growth of the required rotor blade pitch angles values. The results of the study are compared with experimental and calculated data of other authors and can significantly supplement the available results of experimental and computational studies in this area.     

Vortex dynamics and entropy generation in separated transitional flow over a compressor blade at various incidence angles

The transition process within a Laminar Separation Bubble（LSB） that formed on a compressor blade surface was investigated using Large Eddy Simulations（LESs） at a Reynolds number of 1.5×10⁵ and incidence angles of 0°,+3°,and+5°.The vortex dynamics in the separated shear layers were compared at various incidence angles and its effects on the loss generation were clarified through entropy analysis.Results showed that transition onset,which was accurately identified by the Linear Stabilit...     

一种新型布局方式的冲压发动机燃烧室

针对冲压发动机,在旁侧进气突扩燃烧室的基础上,结合凹腔火焰稳定器的特点,设计了一种新型布局的旁侧进气突扩凹腔燃烧室.采用三维两相数值计算方法,研究了凹腔位置、后壁倾角和长深比对燃烧室流场和性能的影响;针对所设计的旁侧进气突扩燃烧室和旁侧进气突扩凹腔燃烧室进行了设计点和非设计点的计算,给出了燃烧室性能参数,同时对燃烧室的...     

Aerodynamic periodicity of transient aerodynamic forces of flexible plunging airfoils

For flapping micro-air vehicles, periodical aerodynamics in every plunging period is always desired in the design of aircraft controlling system. During the periodic plunges of rigid airfoil, either periodical or non-periodical aerodynamic forces can be generated. Real airfoils are usually flexible so that the effect of flexibility on unsteady characteristics of aerodynamic periodicity should be considered. In this study, a fluid structure interaction analysis is employed to systematically investigate the aerodynamic periodicity of a periodically plunging flexible airfoil. The influences of several dimensionless kinematic and structural parameters on aerodynamic periodicity are investigated. The results show that the aerodynamic periodicity of plunging flexible airfoil qualitatively resembles that of rigid airfoil as the mechanisms contributing to aerodynamic periodicity are kept for airfoil with various flexibilities. However, aerodynamic periodicity at small plunging amplitude and high Reynolds number can be improved as airfoil becomes medium flexible but worsened as airfoil is very flexible. The reason is that the deformation of the airfoil changes the strength and structure of the nearby vortices, thereby leading to weak vortex–vortex and vortex–airfoil interactions. The extent of improvement in aerodynamic periodicity is also found significantly influenced by incoming velocity.     

有翼飞行器大攻角分离涡模拟

基于势流方程,采用涡格法和三维离散涡相结合,模拟具有升力面分离涡的大攻角弹冀、弹体、尾翼组合体绕流。该方法适用于高亚音速、小攻角或大攻角有翼飞行器的压力分布、法向力和压力中心等气动特性的数值计算,并具有显示三维涡流场的能力。     

高压比离心压气机二次流旋涡结构研究

为揭示高压比离心压气机的流动特性,采用数值方法对高压比离心压气机的旋涡结构和流动损失的产生及演变规律进行了研究。根据不同类型旋涡的具体特征,给出了分别适用于受迫涡和自由涡的二次流识别方法,包括截面旋线法和拟定主流的截面流线法。应用给出的二次流识别方法并结合耗散函数,探讨了压气机内旋涡的形成机理以及旋涡与损失的关联性。研究表明:当涡量与截面法矢量夹角的余弦值大于零时,旋线方向与实际气流方向定性一致,否则相反;旋线显示的涡轴方向与截面法矢量夹角大于90°时,识别出的旋涡不存在;刮削涡和泄漏涡既是低能流体的聚集区也是能量的耗散区,是影响离心压气机损失产生及分布的关键因素;诱导轮尾迹会抑制导风轮流道内叶表通道涡的形成。     

高马赫数来流条件下斜激波与流向涡对相互作用

针对斜激波入射流向涡对形成的复杂流动干扰现象,在来流马赫数6条件下,利用后掠斜坡式涡流发生器生成流向涡对,采用数值模拟结合激波风洞实验,研究了斜激波与流向涡对相互作用引起的激波变形和旋涡演变。结果表明,斜激波与流向涡对相互作用的剧烈程度大致分为强、中、弱三种。在强相互作用下,激波面向上游凸起的程度最剧烈,呈现类“T”字型特征,其对称面处接近于一道正激波,波后出现回流区和局部流动滞止,使得流向涡对发生破碎;在中等相互作用下,对称面处存在局部正激波,但没有出现回流区;在弱相互作用下,不再出现局部正激波。进一步地分析发现,斜激波与流向涡对相互作用产生的流向涡对破碎现象,不符合经典的激波作用下单个流向涡破碎理论的预测。采用流向涡对对称面处的气流参数,对经典的流向涡破碎理论进行修正后,能够预测本文流向涡对在斜激波作用下是否发生破碎。本文为掌握激波作用下流向涡对破碎现象的规律,提供了重要参考。