固体火箭发动机涡声耦合特性数值研究

为了揭示固体火箭发动机内涡/声耦合机理,以VKI实验发动机为基础,使用大涡模拟方法,对不同温度下障碍物旋涡脱落诱发的振荡流场开展数值研究,获得了燃烧室内速度分布以及压力振荡的频率和幅值,并和实验数据进行了对比。结果表明,旋涡脱落频率与某阶声振频率相等不是涡/声耦合的必要条件;速度幅值对旋涡脱落频率的影响是主要的;平均马赫数对旋涡脱落频率的影响不大,对压力振幅的影响显著。     

叶片前缘旋流和常规冲击对比数值研究

为了寻求更好的叶片前缘内冷结构,对旋流冲击和常规冲击的流动和传热特性进行了数值模拟,对比研究了二者的涡流结构、传热强度、流动阻力、综合传热性能和热均匀性,研究了通道Re数和冲击间距对这些参数的影响。结果表明旋流冲击形成的旋涡有利于传热的增强和热均匀性的提高。在所研究的Re数（2×104~7.78×104）和冲击间距（3.3~5倍直径）范围内,旋流冲击与常规冲击相比平均传热增强18%~34%,增幅随Re数和冲击间距的增大而增大;流阻增大10%~26%,增幅随Re数和冲击间距的增大而减小;综合传热性能增强20%左右;热均匀性提高60%左右。     

Evaluation of pressure oscillations by a laboratory motor

Aeroacoustic pressure oscillation is one of the important challenges in segmented solid rocket motors with high slenderness ratio. The reason for these oscillations can be searched in vortex shedding due to grain burning surfaces, holes and slots. In this paper, a novel sub-scaled motor was used for evaluation of aeroacoustic pressure oscillations. First, the related parameters to scale down using Buckingham’s Pi-theorem were determined and then the sub-scaled motor was designed and manufactured. After this, Strouhal number in various grain forms and vortex shedding prediction criteria have been discussed. Then, one-dimensional linear and non-linear solution approaches have been presented. To understand the motor internal flow and vortex shedding formation, steady state computational fluid dynamic performed for seven regression steps and finally, two static tests have been performed. Results show that various definitions for Strouhal number are useful only for primarily glance on vortex shedding and pressure oscillations and so CFD solution and the test program are inevitable for a correct understanding of the ballistic operational condition of the motor. Experimental results demonstrated the existence of such oscillations with frequencies nearly equal to axial modes. It seems that non-linear parameters have small effects on aeroacoustic pressure oscillation and therefore the linear solution is acceptable to obtain approximate data. Of course, it should be emphasized that linear solution represents oscillations on overall motor action time, whereas the output of non-linear solution depends on thermochemistry properties of solid propellant and combustion products. Therefore, with a non-linear solution, oscillations maybe occur in some intervals of action time. FFT (Fast Fourier Transformation) results demonstrated that although both first and second acoustic modes have been excited, the position of longitudinal oscillation has an important role on which one is dominant.     

基于IDDES方法和γ-Re_θ转捩模型的粗糙颗粒诱导高速边界层强制转捩模拟

采用γ-Re_θ转捩模型与IDDES (Improved Delayed Detached Eddy Simulation)相结合的方法对BAM6QT (Boeing/AFOSR Mach-6 Quiet Tunnel)中的马赫6来流条件下粗糙颗粒诱导转捩情况进行了数值模拟研究,通过与试验测量的压力脉动均方根值、脉动主频和边界层内的皮托压分布的定量对比及与文献中DNS (Direct Numerical Simulation)流场结构的定性对比,表明该方法可以捕捉粗糙单元诱导出的流向涡,能够模拟颗粒前缘分离激波和弓形激波之间的震荡现象,能够模拟流向涡向下游的发展失稳过程及其脉动发展过程。计算结果表明流向涡结构在粗糙颗粒下游40倍颗粒直径位置开始破碎,非定常扰动能也在该点附近增长达到最大值。粗糙单元诱导出了明显的条带涡结构,其中低速条带处于边界层上层,在向下游发展的过程中逐渐扩散至边界层外缘并耗散掉。高速条带位于边界层底部,在向下游发展的同时往展向两侧拓展,最终展向上多条高速条带接触并互相耦合,导致最后条带涡结构的破碎和尾迹区边界层的转捩。     

涡轮转子凹槽叶尖泄漏流动气动热力特征

为探索总结凹槽叶尖泄漏流动气动热力特征,利用实验和数值模拟方法,对叶尖凹槽内部旋涡相互作用机理和叶顶流动换热与泄漏流能量再分布等问题进行研究,并对凹槽叶尖参数化设计方法进行探讨。结果表明:搭建的考虑多因素实验台和可视化泄漏流动测量方案可以精确地捕捉到叶顶区域的流动结构;刮削涡在凹槽中起到"气动篦齿"作用,其形态特征的变化直接影响凹槽叶尖对泄漏流动的控制效果;高温泄漏流流体对叶片表面的冲击是叶尖热负荷提高的主要原因;合理选择叶尖气动参数和凹槽的几何参数可以有效控制刮削涡形态,最终提升叶尖气动热力性能。     

短舱涡流发生器流动控制机理初探

首先回顾了短舱涡流发生器在民机研制中的应用及发展历程,然后结合民用飞机研发实践,借助于CFD工具初步计算并着重分析了短舱涡流发生器的流动控制机理。结果分析表明合理设计的短舱涡流发生器能够产生能量较强的集中涡,在分离敏感的短舱后翼面区域产生下洗流场并为边界层注入能量,降低短舱后气流的当地有效迎角,延缓由于"挂架涡"提前破裂而导致的大面积分离,从而能够改善失速区形态。     

无人机近距编队飞行建模与仿真

无人机编队飞行有着单架无人机无法比拟的优点,但属于较新的研究领域。从无人机未来发展需求出发,根据近距编队的特点,提出了一种近距编队控制方法,并以双机近距编队为基础对控制律设计和算法实现进行了研究。通过建立僚机旋转参考系下的双机编队相对运动模型,同时考虑长机翼尖涡对僚机产生的气动耦合效应,基于PI控制设计了一种无人机近距编队飞行控制器,通过仿真验证和比较分析,证明僚机可以很好地跟随长机的机动保持编队构型,验证了提出的编队飞行控制方法的可行性和有效性。     

气浮陀螺空气轴承涡流力矩的有限元分析

气浮陀螺K0项漂移精度的控制一直是陀螺研制中的难点,而空气轴承涡流力矩是影响陀螺K0项漂移精度最主要因素。因此,本文根据气浮陀螺研制中的实际问题,结合机加工中空气轴承出现的误差形式,建立了空气轴承制造误差对涡流力矩影响的数学模型,并采用有限元方法分析了空气轴承制造误差对涡流力矩的影响规律,得出了浮子圆度误差和窄缝装配误差是引起涡流力矩最主要因素,并通过空气轴承结构参数与涡流力矩的灵敏度分析,得到了径向平均间隙和窄缝平均间隙结构参数的最优值。针对上述研究结论,提出了控制陀螺涡流力矩的技术方法,并通过试验验证了本文理论计算结果的正确性。     

单凹坑壁面的瞬态红外传热测量与流场显示

为了揭示凹坑冷却结构的强化传热机理,基于第三类边界条件下的一维半无限大瞬态导热模型,用红外热成像仪的瞬态测温技术和金属网快速加热技术,对矩形通道内壁面进行了瞬态传热测量,获得了光滑壁面和带有单个球面凹坑壁面的局部对流换热系数分布,并用油-粉末法对凹坑壁面进行了壁面流场显示,实验雷诺数范围1.58×104~6.36×104。实验发现凹坑强化换热与其诱导形成的涡流结构密切相关,单个球面凹坑引起的涡流可以使凹坑下游边缘附近的局部换热最大增强80%左右,凹坑下游尾迹区域的平均换热增强20%~30%。     

Compact Car-Body Surface Design with T-spline Surface

Creating proper B-spline surface models is a very challenging task for designers in car-body surface design. Due to the tensor-product structure of B-spline surface, some undesirable issues of the redundant control points addition, incomplete surface definition and the difficulty of trimming boundary alteration frequently occur, when designing the car-body surface with B-spline surfaces in local-feature-lines construction, full-boundary-merging and visual surface trimming. A more efficient approach is proposed to design the car-body surface by replacing B-spline surface with classical T-spline surface. With the local refinability and multilateral definition offered by T- spline surface, those designing issues related with B-spline surface can be overcomed. Finally, modeling examples of the door, hood and rear-window are given to demonstrate the advantage of T-spline surface over B-spline surface in car-body surface design.