Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M03: Compressible Flows: General |
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Chair: Suman Muppidi, NASA Ames Room: Georgia World Congress Center B204 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M03.00001: Preliminary results for the Study of Blast Driven Turbulence (RTI & RMI) Benjamin Musci, Sam Petter, Devesh Ranjan The presented work focuses on the initial testing and validation of a new experimental facility in the Georgia Tech Shock Tube and Advanced Mixing Laboratory, which allows for the study of blast-driven turbulence in a cylindrical geometry. The facility uses detonators to generate a blast wave, causing the flow to expand through a diverging test-chamber. The blast wave then interacts with a gaseous, membrane-less, interface of differing density, also allowing for the fundamental study of the combined Richtmyer-Meshkov (RMI) and Rayleigh-Taylor Instabilities (RTI). Validation of the crucial aspects of the facility's performance are being completed to show that these phenomena can be faithfully and repeatedly reproduced. These include the following: Pressure readings taken at various locations along the blast trajectory. The creation of a non-diffuse gaseous interface and its trajectory after interaction with the blast wave has also been investigated using Mie Scattering in order to determine shot-to-shot variation of the facility. High speed Mie scattering data is presented as a preliminary result to understand the qualitative development of the instability in this new facility. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M03.00002: On the Similarity of the Pseudo-Shock Structure Mirko Gamba, Robin L Hunt We experimentally investigate the dependence of the steady state structure, such as pressure rise and length, of shock trains on the conditions approaching a pseudo-shock generated by mechanically imposing a range of pressure ratios across a supersonic isolator. A range of Ma, θ, Re_{θ} and confinement ratio C_{θ} approaching the pseudo-shock are considered. A combination of wall static pressure measurements, schlieren and PIV is used. It is found that the impact of approach conditions can adequately be captured by the Waltrup and Billig correction factor Q = (Ma^{2} − 1)Re_{θ}¼C_{θ}^{-½} based on local approach conditions. Once corrected by Q, the axial length of the shock train is nearly constant and the pressure raise is nearly a constant fraction of the value across a normal shock at the approach Ma. Therefore, the additional pressure raise has to be provided by the mixing region, which ineffectively provides flow compression, resulting in an elongation of the pseudo-shock. Overall, the pressure raise per unit length along the shock train is independent of approach conditions and approximately three times larger than that along the mixing region, which still exhibits some Ma dependence. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M03.00003: Energetic Dispersal of a Carefully Perturbed Bed of Particles Frederick Ouellet, Rahul Babu Koneru, Joshua R Garno, Bertrand Rollin, S Balachandar Accurate characterization of the evolution of a particle cloud following interactions with detonation waves and contact interfaces is a challenging problem for simulations and experiments. In experiments, precise descriptions of the initial states of the explosive and the surrounding particle bed are hard to achieve. Also, diagnostic tools and data for early times following detonation are limited. In simulations, modeling the particle compaction regime is difficult and the uncertainties of other physical models are hard to quantify under extreme conditions. This work makes use of Eulerian-Lagrangian, compressible flow simulations to analyze the effects of carefully designed perturbations to a uniformly distributed but initially low volume fraction particle bed surrounding an explosive. The analysis focuses on the sequence of events, multiphase instabilities and late time behavior displayed by the particle cloud. Inspired by behaviors of two-fluid instabilities, increasingly complex perturbations are used to unravel the effects of the initial particle distribution. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M03.00004: Improving the discrete unified gas kinetic scheme for efficient simulation of three-dimensional compressible turbulence Lian-Ping Wang, Zhaoli Guo, Jianchun Wang The discrete unified gas-kinetic scheme (DUGKS) is a relatively new, finite-volume formulation of the Boltzmann equation. It has two major advantages over the lattice Boltzmann method (LBM) in that it can simulate compressible (and even non-continuum) flows, and can naturally incorporate a non-uniform mesh. Recently, we have successfully simulated three-dimensional (3D), incompressible turbulent flows including homogeneous isotropic turbulence (Phys. Rev. E., 94, 043304, 2016) and turbulent channel flow (Computers & Fluids, 2017, doi: 10.1016/j.compfluid.2017.03.007). In this talk, we report results on using DUGKS to simulate compressible isotropic homogeneous turbulence. The relevant issues in simulating 3D compressible flows using DUGKS include the choice of the set of discrete velocities, efficient and accurate numerical integration method, numerical limiter to treat local discontinuity, and parallel implementation. We use the standard Maxwellian equilibrium but adjust the heat flux to achieve variable Prandtl numbers. We also introduce a method (L. Mieussems, J. Comp. Phys. 162, 429-466) to restore the physically correct entropy balance. A series of test simulations will be reported for both decaying and forced compressible turbulences. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M03.00005: Asymptotic scaling laws for spherical and cylindrical finite-source blast waves Yue Ling, S Balachandar, Xiangzhou Jian In this study we consider the spherical and cylindrical blast waves generated by the sudden release of a sphere or cylinder of compressed gas. The model problems are useful to understand explosion flow physics, such as the instability at the gas contact discontinuity and the interaction between the shock wave and the gas contact. The explosion flows here are dictated by the initial pressure and sound-speed ratios between the compressed gas and the ambience, which can vary over a wide range in practical applications. Therefore, it is of interest to investigate the scaling laws for the spherical symmetric or axisymmetric explosion flows. Numerical simulations for a wide range of initial pressure and sound-speed ratios are performed. A long-term length scale that incorporates the initial charge radius and the initial pressure ratio is introduced, which is shown to collapse the trajectories of the main shock, the gas contact, and the secondary shock for a wide range of parameters. The results indicate that an asymptotic similarity solution exists for both the far and near fields in the long term. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M03.00006: Making cereal: extrusion of a viscous compressible fluid. Michael McPhail, James Oliver, Ian M Griffiths Extrusion of viscous bubbly mixtures is an important stage in the manufacture of a range of products including: plastic foams, pet food and breakfast cereals. The complicated dynamics associated with multiphase flows, and the presence of a free boundary make numerical simulations of these processes difficult. By taking an average over the phases, the mixture can be treated as a single-phase compressible fluid coupled to a model describing the microscale dynamics. Using ideas from lubrication theory, we are able to derive a reduced model for the free expansion of a compressible fluid analogous to the Trouton model for an incompressible fluid. The result is a much simpler set of equations, which retains all of the necessary physics. In the limit of small surface tension and small Reynolds number, this model reduces to a single ordinary differential equation whose solution we can write analytically. |
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M03.00007: Group classification of self-similar, linear velocity fluid flow. James D McHardy, Jason Albright, Scott D Ramsey Self-similar motions describe flow in which the spatial profiles of velocity, pressure and density vary with time while remaining geometrically similar to themselves. Viewed in the appropriately scaled coordinate frame, the spatial distributions of these variables are invariant with respect to time. Under the ansatz of a linear velocity flow, a flow in which the velocity is linearly proportional to the spatial parameter multiplied by R’(t)/R(t), the Euler equations admit self-similar solutions for certain R. Such solutions appear across the literature. For example, density profiles associated with a linear velocity are used to model uniform heating compression of ICF targets. This work unifies these solutions under a common framework and classifies them according to their group properties. To achieve this, we apply the symmetry analysis methods of Lie within the context of equivalence transformations proposed by Ovsiannikov. We then construct and solve a system of constraining equations to find the admissible functions R leading to solutions that are invariant under the determined group. As well as group characterization, the applied analysis easily identifies the vector fields pertaining to each solution, the characteristics of which correspond to the propagation of the flow. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M03.00008: Determination of the scalar index of refraction field with BOS in a supersonic jet Catalina Stern, David Porta, Carlos Echeverria In this work, the scalar field of the refractive index of an axisymmetric supersonic jet was measured with the Background Oriented Schlieren (BOS) technique. The jet was generated by passing compressed air through a straight nozzle with a diameter of 4 mm. An apparently stationary shock pattern had been visualized previously with shadowgraphs and Rayleigh Scattering. However, the use of BOS allowed a precise measurement of the width, a few tenths of a millimeter, of the shock waves. This result is important because usually, when they are modelled, shock waves are considered infinitely narrow discontinuities. Additionally, real images obtained with schlieren and shadowgraph techniques were compared with images derived from the BOS data. The correspondence is excellent for schlieren but not for shadowgraphs, due to numerical errors. |
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