Direct numerical simulation of a tumbling short cylinder in low Reynolds number compressible flow

Embedded geometry method;immersed boundary method;fluid-structure interaction;direct numerical simulation;tumbling cylinder

Uddin, Hasib

关键词: Embedded geometry method;    immersed boundary method;    fluid-structure interaction;    direct numerical simulation;    tumbling cylinder;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/50381/Hasib_Uddin.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The delivery of fusion material to the center of a laser inertial confinement engine happensby injecting a frozen hydrogen isotope mixture that resides inside a carefully crafted capsulecalled hohlraum. Because of the injection mechanism, the capsule necessarily has the shape of a modified short cylinder traveling along its axis of symmetry. The flow details and stability of this geometry are of significant importance to the reliable operation of the device. The gas inside the fusion chamber is very hot and the viscosity is relatively high, which for the typical injection velocities of the capsule results in a low Reynolds number flow.In this connection, a low Reynolds number compressible flow past a dynamically moving rigid short cylinder has been investigated using three-dimensional direct numerical simulation (DNS) as a model of the real capsule. A Cartesian-based novel embedded geometry method for compressible fluid-structure interaction problems is developed and coupled with a low-numerical-dissipation compressible flow solver to perform simulations in a parallel multiprocessor environment. In this method, the surface of the cylinder is uniquely identifiedby a zero level set separating the fluid and solid region. A PDE-based global extension technique inspired by analytical continuation is used to smoothly propagate the surface boundary conditions inside the fictitious solid domain. This approach ensures smooth and noise-free reconstruction of pressure and viscous stresses on the surface of the solid body and utilization of a global high-order spatial discretization scheme due to the smooth nature of the flow quantities at each time step stage. The translational and rotational dynamics of the cylinder by modeling the 6-degree of freedom (DoF) motion employ a non-singular quaternion-based framework. The longitudinal stability of the cylinder is affected by the variation in angle of attack, aspect ratio and Reynolds number. The present work focuses on Reynolds number, Re = 60 and a Mach number, M = 0.25 to closely mimic the flow conditionsinside an inertial confinement fusion chamber. A critical angle of attack has been identified beyond which the short cylinder will start to tumble based on a set of stationary simulations. Additionally, the force coefficients and pitching moments from coupled moving boundary simulations are investigated.