A large eddy simulation （LES） of the flows around an underwater vehicle model at intermediate Reynolds numbers is performed. The underwater vehicle model is taken as the DARPA SUBOFF with full appendages, where the ...A large eddy simulation （LES） of the flows around an underwater vehicle model at intermediate Reynolds numbers is performed. The underwater vehicle model is taken as the DARPA SUBOFF with full appendages, where the Reynolds number based on the hull length is 1.0x 105, An immersed boundary method based on the moving-least-squares reconstruction is used to handle the complex geometric boundaries. The adaptive mesh refinement is utilized to resolve the flows near the hull, The parallel scalabilities of the flow solver are tested on meshes with the number of cells varying from 50 million to 3.2 billion, The parallel solver reaches nearly linear scalability for the flows around the underwater vehicle model, The present simulation captures the essential features of the vortex structures near the hull and in the wake, Both of the time-averaged pressure coefficients and srreamwise velocity profiles obtained from the LES are consistent with the characteristics of the flows pass an appended axisymmetric body. The code efficiency and its correct predictions on flow features allow us to perform the full-scale simulations on tens of thousands of cores with billions of grid points for higher-Reynolds-number flows around the underwater vehicles.展开更多
Cavitating flows are dominated by large gradients of physical properties and quantities containing complicated interfacial structures and lots of multi-scale eddies that need to be accurately characterized using a hig...Cavitating flows are dominated by large gradients of physical properties and quantities containing complicated interfacial structures and lots of multi-scale eddies that need to be accurately characterized using a high-resolution mesh.The present work,within OpenFOAM,proposes an effective modeling framework using the large eddy simulation(LES)approach along with the volume of fluid(VOF)method to simulate the two-phase flow system and applies the Schnerr-Sauer model to calculate the mass-transfer rate between water and vapor.The adaptive mesh refinement(AMR)which is a powerful tool for allocating high-resolution grids only to the region of the greatest concern is adopted for improving the solution of interfacial structures.The effect of grid size is firstly investigated and the time-averaged quantities are verified against the experimental data,and then simulations of cavitating flows are successfully achieved to precisely characterize the features of cavitation with automatically and dynamically refining the mesh.As the refinement only takes place in the interfacial region,high-precision simulations can be achieved with limited computational resources,and the method shows promising prospects for modeling of the multi-scale,time-critical and computationally intensive cavitating flows.展开更多
研究了流体初始马赫数为2.0时,探测器的存在与否对刚性盘-缝-带型降落伞系统气动减速性能以及流场流体结构特性的影响.对于非定常可压缩流体的数值模拟,流场采用了三层块结构自适应网格加密技术,配合混合形式的TCD (tuned center differ...研究了流体初始马赫数为2.0时,探测器的存在与否对刚性盘-缝-带型降落伞系统气动减速性能以及流场流体结构特性的影响.对于非定常可压缩流体的数值模拟,流场采用了三层块结构自适应网格加密技术,配合混合形式的TCD (tuned center difference)和WENO (weighted essentially non-oscillatory)计算格式以及基于拉伸涡亚格子模型的大涡模拟方法来处理超音速流中的激波以及大尺度湍流旋涡结构等.结果表明:无探测器时,降落伞系统的流场结构稳定,扰动较小;有探测器存在时,探测器后端的湍流尾迹和伞衣内部逆向运动溢出的流体与伞衣前端的弓形激波周期性的相互作用,使得激波位置发生前移、激波倾角变小,伞衣内部流场难以达到平衡稳定状态.这加剧了降落伞系统的气动阻力振荡脉动变化,降低了降落伞系统气动阻力系数,同时也使得降落伞系统流场尾迹结构更加复杂.展开更多
Wake separation is crucial to aircraft landing safety and is an important factor in airport operational efficiency.The near-ground evolution characteristics of wake vortices form the foundation of the wake separation ...Wake separation is crucial to aircraft landing safety and is an important factor in airport operational efficiency.The near-ground evolution characteristics of wake vortices form the foundation of the wake separation system design.In this study,we analysed the near-ground evolution of vortices in the wake of a domestic aircraft ARJ21 initialised by the lift-drag model using large eddy simulations based on an adaptive mesh.Evolution of wake vortices formed by the main wing,flap and horizontal tail was discussed in detail.The horizontal tail vortices are the weakest and dissipate rapidly,whereas the flap vortices are the strongest and induce the tip vortex to merge with them.The horizontal tail and flap of an ARJ21 do not significantly influence the circulation evolution,height change and movement trajectory of the wake vortices.The far-field evolution of wake vortices can therefore be analysed using the conventional wake vortex model.展开更多
基金supported by the National Natural Science Foundation of China (11302238, 11232011. and 11572331)support from the Strategic Priority Research Program (XDB22040104)+1 种基金the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (QYZDJ-SSW-SYS002)the National Basic Research Program of China (973 Program 2013CB834100: Nonlinear science)
文摘A large eddy simulation （LES） of the flows around an underwater vehicle model at intermediate Reynolds numbers is performed. The underwater vehicle model is taken as the DARPA SUBOFF with full appendages, where the Reynolds number based on the hull length is 1.0x 105, An immersed boundary method based on the moving-least-squares reconstruction is used to handle the complex geometric boundaries. The adaptive mesh refinement is utilized to resolve the flows near the hull, The parallel scalabilities of the flow solver are tested on meshes with the number of cells varying from 50 million to 3.2 billion, The parallel solver reaches nearly linear scalability for the flows around the underwater vehicle model, The present simulation captures the essential features of the vortex structures near the hull and in the wake, Both of the time-averaged pressure coefficients and srreamwise velocity profiles obtained from the LES are consistent with the characteristics of the flows pass an appended axisymmetric body. The code efficiency and its correct predictions on flow features allow us to perform the full-scale simulations on tens of thousands of cores with billions of grid points for higher-Reynolds-number flows around the underwater vehicles.
基金Project supported by the China Postdoctoral Science Foundation(Grant No.2018M630502)This work was supported by the Jiangsu Province Science Foundation for Youths(Grant No.BK20180505)the Fundamental Research Funds for the Central Universities(Grant No.2019B14914)。
文摘Cavitating flows are dominated by large gradients of physical properties and quantities containing complicated interfacial structures and lots of multi-scale eddies that need to be accurately characterized using a high-resolution mesh.The present work,within OpenFOAM,proposes an effective modeling framework using the large eddy simulation(LES)approach along with the volume of fluid(VOF)method to simulate the two-phase flow system and applies the Schnerr-Sauer model to calculate the mass-transfer rate between water and vapor.The adaptive mesh refinement(AMR)which is a powerful tool for allocating high-resolution grids only to the region of the greatest concern is adopted for improving the solution of interfacial structures.The effect of grid size is firstly investigated and the time-averaged quantities are verified against the experimental data,and then simulations of cavitating flows are successfully achieved to precisely characterize the features of cavitation with automatically and dynamically refining the mesh.As the refinement only takes place in the interfacial region,high-precision simulations can be achieved with limited computational resources,and the method shows promising prospects for modeling of the multi-scale,time-critical and computationally intensive cavitating flows.
文摘研究了Mach数为2时,流场不同块结构自适应网格加密精度对探测器-刚性盘-缝-带型降落伞系统的气动减速性能以及流场结构特性的影响.对于非定常可压缩流体流动,采用了兼顾激波与湍流的WENO(weighted essentially non-oscillatory)和TCD(tuned center difference)混合计算格式以及拉伸涡亚格子模型的大涡模拟方法.结果表明:在较低的流场块结构自适应网格分辨率下,是难以准确模拟计算降落伞系统重要的气动阻力系数和捕捉流场流动特征细节的.随后验证了流场自适应网格的收敛性.
基金financial support from the National Natural Science Foundation of China(Grant 91752205)Civil Aviation Joint Fund of NSFC(Grant U1733203)Civil Aviation Safety Capacity Building Project(Grant TM 2019-16-1/3)。
文摘Wake separation is crucial to aircraft landing safety and is an important factor in airport operational efficiency.The near-ground evolution characteristics of wake vortices form the foundation of the wake separation system design.In this study,we analysed the near-ground evolution of vortices in the wake of a domestic aircraft ARJ21 initialised by the lift-drag model using large eddy simulations based on an adaptive mesh.Evolution of wake vortices formed by the main wing,flap and horizontal tail was discussed in detail.The horizontal tail vortices are the weakest and dissipate rapidly,whereas the flap vortices are the strongest and induce the tip vortex to merge with them.The horizontal tail and flap of an ARJ21 do not significantly influence the circulation evolution,height change and movement trajectory of the wake vortices.The far-field evolution of wake vortices can therefore be analysed using the conventional wake vortex model.
