高速共轴刚性旋翼非定常流动高精度数值模拟

High-accuracy numerical-simulation of unsteady flow over high-speed coaxial rigidrotors

高速共轴刚性旋翼在前飞状态下会产生复杂的非定常涡干扰流动结构及较强的激波,对高速直升机的气动、噪声及振动特性有着重要的影响,这些流动现象的高分辨率捕捉是高速直升机CFD研究中的难点之一。发展了可在大规模并行计算中实现负载均衡的运动嵌套网格系统,提出了能够在人工边界上保持高阶精度的高效嵌套关系辨识及插值方法;在嵌套网格上应用了发展的谱特性自适应优化的五阶非多项式重构WENO格式(WENO-K)和改进的延迟脱体涡模拟(IDDES)方法,从而提高对非定常多尺度流动结构的空间数值分辨率及时间保持能力。针对简单四桨共轴旋翼及X-2验证机的八桨共轴旋翼,进行了非定常涡流场高精度数值模拟,研究了高速共轴刚性旋翼桨尖涡结构的生成、发展、演化过程及涡干扰机制。计算结果表明,高阶格式结合IDDES方法能够显著降低数值耗散并提高多尺度湍流结构的分辨率,捕捉到了桨尖涡的高速发展演化过程及桨-涡干扰现象,并能够分辨出桨叶后缘生成的马蹄状的精细涡面结构,有利于高速共轴旋翼涡流场干扰机制及气动噪声的深入研究。

High-speed coaxial rotor systems generate complex unsteady vortical flow structures and strong shock waves at forward flight,which significantly impact the aerodynamics,noise,and vibration characteristics of high-speed helicopters.Capturing these flow phenomena with high resolution is one of the challenges in computational fluid dy-namics research for high-speed helicopters.To address this challenge,a dynamic overset grid system capable of load balancing in large-scale parallel computations is developed.An efficient method for identifying overset relationships and an interpolation technique that maintains high-order accuracy at artificial boundaries are proposed.A novel fifth-order WENO-K scheme with adaptively optimized spectral characteristics has been introduced to enhance the numeri-cal resolution and preserve the structures of rotor tip vortices.Additionally,an improved Delayed Detached Eddy Simulation(IDDES)method is used to capture the smaller-scale vortex structures and their unsteady fluctuations in the wake region.High-accuracy numerical simulations of unsteady vortical flow fields of a simple four-blade coaxial ro-tor and an eight-blade coaxial rotor similar to the X-2 configuration have been conducted.The generation,develop-ment,evolution,and vortex interference mechanisms of blade tip vortices of the high-speed rigid rotors are analyzed.The computational results demonstrate that the high-order schemes,when combined with the IDDES method,can ef-fectively reduce numerical dissipation and enhance the resolution of multiscale turbulent structures,and successfully capture the rapid development and evolution of rotor tip vortices,as well as blade-vortex interactions.The sophisti-cated horseshoe-shaped vortex surface structures formed at the trailing edge of the rotor blades can be also dis-cerned.These findings contribute to a deeper understanding of the vortex interference mechanisms and aerodynamic noise in high-speed coaxial rotor flow fields.