Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A05: Compressible Flows: Shock Interactions and Shock Focusing |
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Chair: Veronica Eliasson, University of California San Diego Room: 204 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A05.00001: Normal shock wave attenuation during propagation in straight and branching ducts with grooves Seyed Mehdi Mortazawy, Kostas Kontis, John Ekaterinaris Experimental investigations and numerical simulations of normal shock waves of different strengths propagating inside ducts with roughness are presented. The roughness is added in the form of grooves. Straight and branching ducts are considered in order to better explore the mechanisms causing attenuation of the shock and the physics behind the evolution of the complex wave patterns resulting from diffraction and reflection of the primary moving shock. A well-established finite volume numerical method is used and further validated for several test cases relevant to this study. The computed results are compared with experimental measurements in ducts with grooves. Good agreement between high-resolution simulations and the experiment is obtained for the shock speeds and complex wave patterns created by the grooves. High frequency response time histories of pressure at various locations were recorded in the experiments. The recorded pressure histories and shock strengths were found in fair agreement with the two-dimensional simulation results as long as the shock stays in the duct. Overall, the physics of the interactions of the moving shock, and the diffracted and reflected waves with the grooves are adequately captured in the high-resolution simulations. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A05.00002: Combating shock waves: A study of shock wave cancellation mechanisms within linear turbine blade cascades Jorge Nunez, Veronica Eliasson Prior research has established that unsteady shock wave interactions on turbine blades negatively impact the fatigue life and performance of gas turbines. Current technology in gas turbines mitigates negative effects on turbine blades by way of cooling mechanisms. However, recent inventions seek to eliminate the adverse influence that unsteady shock wave interactions have on turbine blades by cancelling incident shock waves in gas turbines. The goal of this study is to ascertain the efficacy of shock cancellation mechanisms in gas turbines at preventing incident shock waves from reflecting off the turbine blades. A study of shock wave cancellation in linear turbine blade cascades has been performed to analyze the performance of shock wave cancelling mechanisms. CFD simulations are compared to shock tube experiments featuring high-speed schlieren photography and pressure measurements of unsteady shock wave impacts on linear turbine blade cascades. Different shock wave cancelling designs has been investigated and the benefits and drawbacks of the chosen designs will be discussed. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A05.00003: Scaling of compressible turbulent mixing Eunhye An, Eric Johnsen The decay of homogeneous, isotropic turbulence is well understood based on Kolmogorov theory in the incompressible limit. However, the roles of compressibilitity and inhomogeneities on the turbulence phenomenology are less well known. For this purpose, we conduct direct numerical simulation (DNS) to investigate the behavior of turbulent mixing, in which homogeneous isotropic turbulence regions of different intensities are juxtaposed. We investigate the scaling of the decay of turbulent kinetic energy (TKE) for this compressible, inhomogeneous flow. By considering the turbulent energy balance equation, we determine scaling coefficients predicting the observed behavior by accounting for dilatation. This scaling is verified by the DNS results of turbulent mixing as well as turbulent/non-turbulent interfaces. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A05.00004: Direct Simulation of Fluid-Structure Interaction in a Hypersonic Compression Ramp Flow Bryson Sullivan, Thomas Whalen, Stuart Laurence, Daniel Bodony Sustained hypersonic flight presents an enduring challenge to aircraft design and control. An extreme aerothermal environment acting on thin, multi-functional structures can yield significant fluid-thermal-structural interaction (FTSI) in control surfaces and/or a complete vehicle. While computationally efficient, the accuracy of reduced-order aerodynamic models can be compromised by local regions of subsonic/separated flow, highlighting the need for high-fidelity numerical simulations. The present talk outlines recent time-accurate FTSI simulations of a viscous flow at $M_\infty=6.0$ over a $35^\circ$ compression ramp with an embedded compliant panel. Reduced-order models are compared directly to FTSI simulation data, and a simple modification is proposed which can improve the accuracy of shock-expansion/local piston theory predictions. A reduction in surface heat flux is observed for most compliant cases, while traditional heat transfer analogies were found to be reliable only for the rigid case. Oscillation of the reattachment point was found to synchronize with the motion of the compliant panel for large-amplitude vibrations. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A05.00005: Simulation and Global Stability Analysis of a $35^o$ compression ramp in a uniform Mach 6 flow Fabian Dettenrieder, Daniel Bodony Aerothermal and structural loads of flows relevant to hypersonic vehicles pose a multi-disciplinary design problem. Of particular interest is the fluid-structure interaction associated with a deflected control surface at sufficiently high Mach number such that the compression shock sits on the control surface downstream of the corner, leading to large localized pressure and thermal loads. As a baseline for subsequent compliant analyses, we investigate the Mach 6 flow past a rigid $35$ degree compression ramp attached to a finite-length flat plate, which together model the control surface geometry, by means of direct numerical simulation (DNS). The three-dimensional DNS results include the boundary layer development from the plate's leading edge, through transition, and ultimate transition to turbulence. The unsteadiness of the separation bubble and observed ejection of mass and shocklets from the separation bubble are quantified and compared to experimental data. We use global stability analyses of the time-averaged flow to discuss the observed unsteadiness in terms of global modes. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A05.00006: Exploding Wire System for Use in Study of Two-Dimensional Shock Focusing Barry Lawlor, Lingzhi Zheng, Claire Mcguire, Jane Zanteson, Kevin Nguyen, Benjamin Katko, Veronica Eliasson Shock focusing is an area of interest within a wide range of disciplines, ranging from biomedical devices to structural design. Extensive study has been performed on shock waves by means of horizontal shock tube devices which typically only allow for the study of constant flow properties. A blast wave typically is defined as a shock front, followed by an exponential decay in flow properties. The intention of this study is to develop a tool with which to investigate and define the behavior of shock waves with decaying flow properties, including the transition from regular to irregular reflection. Such capability has been accomplished through an exploding wire system, which functions by subjecting a wire to a large and sudden voltage difference, producing a radially expanding explosion. The novelty of this system lies in (1) the ability to produce shock waves consistent with blast type flow conditions; (2) its modularity by virtue of the driver; and (3) its application in gaseous environments. The outcome has been an experimental setup with novel application in air, proven repeatability, as well as initial qualitative and quantitative results in its two-dimensional, cylindrical format. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A05.00007: 3D point-blast geometrical shock dynamics with moving least squares surface reconstruction for point sets Heng Liu, Veronica Eliasson Blast wave focusing can lead to extreme thermodynamic conditions and has been applied to a variety of fields such as medical treatment and civil engineering. Considering all difficulties and constraints to conduct full-filed multi-blast explosion experiments, oftentimes numerical simulation becomes the first option. As solving the inviscid Euler equations can be computationally expensive, Geometrical Shock Dynamics (GSD) is applied in this study to help reduce the computational cost. Whitham's original GSD method is proved to yield accurate results in the case of uniform flow states behind the shock front, but is inadequate if the non-uniformity exits such as in a blast wave. Some approaches have been proposed to address this issue, one of which is to apply the existing numerical data to account for the post-blast flow effect. Bach and Lee's analytical solution to point-blast is manipulated to drive the blast propagation in a modified GSD model, PGSD, and its extension to 3D only needs slight changes. As PGSD makes use of curvature-Mach relation instead of area-Mach relation as in GSD, triangulated meshes and connectivity information are not needed to compute surface patch areas. 3D surface shape is represented by point sets, from which Moving Least Squares (MLS) surface reconstruction is computed. MLS surface is capable of selectively keeping the local surface feature and projecting any point onto it that delivers convenience to mesh regularization. [Preview Abstract] |
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