Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session G5: Compressible Flow: Shock Interactions |
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Chair: Veronica Eliasson, University of California, San Diego Room: B113 |
Monday, November 21, 2016 8:00AM - 8:13AM |
G5.00001: Optimization on the focusing of multiple shock waves. Shi Qiu, Veronica Eliasson Focusing of multiple shock waves can lead to extreme thermodynamic conditions, which are desired for applications like shock wave lithotripsy and inertial confinement fusion. To study shock focusing effects, multiple energy sources have been placed in a circular pattern around an intended target, while the distance between each source and the target is fixed. All the sources are set to release the same amount of energy at the same time in order to create multiple identical shock waves. The object is to optimize the thermodynamic conditions at the target by rearranging the initial placement of each source. However, dealing with this optimization problem can be challenging due to the high computational cost introduced by solving the Euler equations. To avoid this issue, both numerical and analytical methods have been applied to handle shock focusing more efficiently. A numerical method, an approximate theory named Geometrical Shock Dynamics (GSD), has been utilized to describe the motion of shock. Using an analytical method, a transition curve between regular and irregular reflection has been employed to predict shock interactions. Results show that computational cost can be reduced dramatically by combining GSD and a transition curve. In addition, optimization results based on varying initial setups is discussed. [Preview Abstract] |
Monday, November 21, 2016 8:13AM - 8:26AM |
G5.00002: Unsteadiness of a shock train in Mach 2.0 flow Robin Hunt, James Driscoll, Mirko Gamba Experimental observations of the progression of flow unsteadiness within a shock train are presented. A downstream control valve is used to generate a shock train in the constant area test section of a wind tunnel with a freestream Mach number of 2.0. Even with nominally constant boundary conditions the shock train exhibits inherent unsteady motion about the time average position. At the conditions presented the shocks can be displaced by up to 0.35 duct heights. Better knowledge of the shock train's dynamics may allow us to introduce control algorithms to reduce the system's unsteadiness and thus minimize the associated mechanical and thermal loads. An edge detection algorithm is applied to the instantaneous frames of high speed Schlieren movies to track the location of morphological features within the shock system. Simultaneously, high speed pressure transducers record the pressure fluctuations along the bottom wall of the duct. The results indicate a complex frequency dependent dynamical system. A strong component of the dynamics involves a disturbance traveling upstream through the boundary layer. Once the disturbance reaches the leading shock foot the shocks respond in order with the most upstream shock moving first. [Preview Abstract] |
Monday, November 21, 2016 8:26AM - 8:39AM |
G5.00003: Shock-Capturing Simulations of Multi-Fluid Shock-Turbulence Interactions Yifeng Tian, Farhad Jaberi, Daniel Livescu, Zhaorui Li The interaction between an isotropic multi-fluid turbulence with a planar shock wave is studied using turbulence resolved shock-capturing simulations. This problem is an extension of the canonical Shock-Turbulence Interaction (STI), with the effects of strong density variations (from compositional changes) taken into consideration. To establish shock-capturing simulation as a reliable method for studying STI, LIA convergence tests are conducted. These tests are consistent with previous DNS studies and indicate that LIA limits can be approximated at relatively high Reynolds numbers and low turbulent Mach numbers when the separation between numerical shock thickness and turbulent length scales is adequate. When variable density effects are introduced, turbulence structure is modified more by the normal shock, with a differential distribution of turbulent statistics in regions with different densities, resulting in a strong mixing asymmetry in the post-shock region. Turbulence achieves similar axisymmetric two-dimensional local state right after the shock wave in the multi-fluid case, but has a faster return to three-dimensional isotropic structure when compared to the single-fluid case. The characteristics of post-shock thermodynamic fluctuations are also affected and are dominated by shock strength fluctuations that result from the compositional changes. [Preview Abstract] |
Monday, November 21, 2016 8:39AM - 8:52AM |
G5.00004: Shock wave-free interface interaction Roman Frolov, Peter Minev, Rouslan Krechetnikov The problem of shock wave-free interface interaction has been widely studied in the context of compressible two-fluid flows using analytical, experimental, and numerical techniques. While various physical effects and possible interaction patterns for various geometries have been identified in the literature, the effects of viscosity and surface tension are usually neglected in such models. In our study, we apply a novel numerical algorithm for simulation of viscous compressible two-fluid flows with surface tension to investigate the influence of these effects on the shock-interface interaction. The method combines together the ideas from Finite Volume adaptation of invariant domains preserving algorithm for systems of hyperbolic conservation laws by Guermond and Popov and ADI parallel solver for viscous incompressible NSEs by Guermond and Minev. This combination has been further extended to a two-fluid flow case, including surface tension effects. Here we report on a quantitative study of how surface tension and viscosity affect the structure of the shock wave-free interface interaction region. [Preview Abstract] |
Monday, November 21, 2016 8:52AM - 9:05AM |
G5.00005: Predictive Analytical Model for Isolator Shock-Train Location in a Mach 2.2 Direct-Connect Supersonic Combustion Tunnel Joe Lingren, Leon Vanstone, Kelley Hashemi, Sivaram Gogineni, Jeffrey Donbar, Maruthi Akella, Noel Clemens This study develops an analytical model for predicting the leading shock of a shock-train in the constant area isolator section in a Mach 2.2 direct-connect scramjet simulation tunnel. The effective geometry of the isolator is assumed to be a weakly converging duct owing to boundary-layer growth. For some given pressure rise across the isolator, quasi-1D equations relating to isentropic or normal shock flows can be used to predict the normal shock location in the isolator. The surface pressure distribution through the isolator was measured during experiments and both the actual and predicted locations can be calculated. Three methods of finding the shock-train location are examined, one based on the measured pressure rise, one using a non-physics-based control model, and one using the physics-based analytical model. It is shown that the analytical model performs better than the non-physics-based model in all cases. The analytic model is less accurate than the pressure threshold method but requires significantly less information to compute. In contrast to other methods for predicting shock-train location, this method is relatively accurate and requires as little as a single pressure measurement. This makes this method potentially useful for unstart control applications. [Preview Abstract] |
Monday, November 21, 2016 9:05AM - 9:18AM |
G5.00006: The pressure impulse of a laser-induced underwater shock wave Yoshiyuki Tagawa, Shota Yamamoto, Keisuke Hayasaka, Masaharu Kameda We investigate the pressure impulse, the time integral of pressure evolution, of a laser-induced underwater shock wave. We simultaneously observe plasma formation, shock-wave expansion, and pressure in water using a combined measurement system that obtains high-resolution nanosecond-order image sequences. Remarkably, pressure impulse is found to distribute symmetrically for a wide range of experimental parameters even when the shock waves are emitted from an elongated plasma. In contrast, distribution of pressure peak is found to be non-spherically-symmetric. We rationalize aforementioned results by considering the structure of the underwater shock wave as a collection of multiple spherical shock waves originated from point-like plasmas in an elongated region. [Preview Abstract] |
Monday, November 21, 2016 9:18AM - 9:31AM |
G5.00007: ABSTRACT WITHDRAWN |
Monday, November 21, 2016 9:31AM - 9:44AM |
G5.00008: Experimental and numerical investigation of cylindrical and hemispherical jet formation Matthew Betney, Peta Foster, Tim Ringrose, Thomas Edwards, Brett Tully, Hugo Doyle, Nicholas Hawker This paper presents a detailed investigation of the formation of jets in cylindrical and spherical cavities, when impacted by shocks at extreme pressures. As the shock pressure increases the effects of material strength lessen in proportion. Beyond a certain magnitude the behaviour is referred to as “hydrodynamic”. In this domain both cylindrical and spherical cavities involute to form jets, which go on to strike the leeward cavity wall, compressing the cavity contents to high pressures and temperatures. In this study, the jet formation process is isolated by cutting hemispherical and half-cylindrical cavities from the rear side of PMMA and copper blocks. This allows direct measurement of the jet speed and shape using high speed imaging, providing data against which numerical models may be compared. Shock waves at pressures of up to 30 GPa are formed in the targets by the impact of projectiles from a two-stage light gas gun, at velocities of up to 7 km/s. Numerically, the jet formation process is modelled using our in-house front-tracking code. This code uses Lagrangian hypersurfaces to model the interfaces between different media, with an underlying Eulerian mesh used to model the bulk flow. Detailed comparisons between numerical and experimental results are presented. [Preview Abstract] |
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