SBIR Phase I: A Fast Parallel Grid-Free Method for Simulating Turbulent Incompressible Flow In/Around Time-Varying Geometries

该小型企业创新研究(SBIR)第一阶段项目为开发第一个商业可用的计算流体动力学程序包奠定了基础，该程序包用于复杂时变几何结构中湍流不可压缩涡控流动的真正无网格大涡模拟(LES)。该计算引擎基于拉格朗日涡旋边界元方法的并行、快速多极实现。湍流通过大涡模拟，使用拉格朗日动态斯马戈林斯基亚格子网格模式。该方法是：(1)在流体域完全无网格，(2)无数值扩散，(3)固有解自适应，(4)能够模拟非均匀非定常壁面湍流流动。为此，在第一阶段将开发两个新的想法：无网格方法，预测扩散变粘性，这是大涡模拟的前提条件；和非扩散涡旋合并策略，以遏制粒子的扩散和保持长期精度。然后将这些结合到拉格朗日涡元方法中，以自由空间中初始扰动的无限雷诺数涡环的演化为例，展示基于无网格涡流的大涡模拟的显著特征。该软件是模拟和分析复杂湍流现象的理想软件。这包括涡流破裂、(大量)流分离、涡流脱落、横流中的瞬时喷流、尾迹干扰、高旋流等。所有这些都与先进的流动控制机制的设计有关，例如，用于减少流动诱导的噪音和振动，以及在降低能耗的情况下改善升力/阻力性能。例如，水流在钝体上流动，如地面或水下车辆；在发动机中；在旋转机械中/周围，如泵和风扇；直升机；或在具有旋转和移动部件的数据存储单元中。

This Small Business Innovation Research (SBIR) Phase I project prepares the ground-work for the development of the first commercially available Computational Fluid Dynamics package for a truly grid-free Large Eddy Simulation (LES) of turbulent incompressible vortex dominated flow in complex time-varying geometries. The computational engine is based on the parallel, fast multi-pole implementation of a Lagrangian vortex-boundary element method. Turbulence is accounted for via LES, using a Lagrangian dynamic Smagorinsky sub-grid scale model. The method is: (1) fully grid-free in the fluid domain, (2) free of numerical diffusion, (3) inherently solution-adaptive, and (4) capable of modeling inhomogeneous unsteady wall-bounded turbulent flow. To this end, two new ideas will be developed during Phase I: A grid-free method for predicting diffusion with variable-viscosity, which is a pre-requisite for LES modeling; and a non-diffusive vortex merging strategy to curb the proliferation of particles and maintain long-time accuracy. These will then be incorporated into the Lagrangian vortex element method to demonstrate the salient features of grid-free vortex-based LES modeling of turbulent flows, using the prototypical example of the evolution of an initially perturbed infinite-Reynolds-number vortex ring in free space.The software is ideal for simulation and analysis of complex turbulent flow phenomena. This includes vortex breakdown, (massive) flow separation, vortex shedding, transient jets in cross-stream, wake-body interaction, high-swirl flow, etc. All are associated with the design of advanced flow control mechanisms used, for example, to reduce flow-induced noise and vibration, and to improve lift/drag performance at reduced energy consumption rates. Examples are flow over bluff bodies such as ground or under-water vehicles; in engines; in/around rotating machinery such as pumps and fans; helicopters; or in data storage units with rotating and moving parts.