Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session G26: ReactIve Flows IV: Detonations |
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Chair: Kazhikathra Kailasanath, Naval Research Laboratory Room: 31B |
Monday, November 19, 2012 8:00AM - 8:13AM |
G26.00001: Multiplicity of detonation regimes in systems with a multi-peaked thermicity Matei I. Radulescu, Fan Zhang Bulk exothermicity in most gaseous detonation waves occurs in a single step. There are however several physical systems displaying multiple thermicity peaks. Examples are the nuclear fusion reactions sequence in supernovae explosions, hybrid detonations in multi-phase fuels and other reactive systems. The multiplicity of steady state detonation regimes in the presence of an endothermic internal or external loss is demonstrated through analysis of the reaction zone structure described by the reactive Euler equations with two sequential Arrhenius reactions. The steady Zel'dovich - Von Neumann- Doering reaction structure is obtained numerically. The reaction zone displays embedded sonic points where the net thermicity vanishes simultaneously. Depending on the magnitude of the losses or endothermic process, the detonation wave speed response was found to have multiple steady states and turning points, which are controlled by the magnitude of the kinetic parameters of each reaction. The dependence on system parameters is established analytically using the Fickett detonation analogue model with two sequential reactions. [Preview Abstract] |
Monday, November 19, 2012 8:13AM - 8:26AM |
G26.00002: Detonation and Transition to Detonation in Horizontal Water-Filled Pipes Neal P. Bitter, Joseph E. Shepherd Detonations and deflagration-to-detonation transition (DDT) are experimentally studied in horizontal pipes which are partially filled with water. The gas layer above the water is stoichiometric hydrogen-oxygen at 1 bar. The detonation wave produces oblique shock waves in the water, which focus at the bottom of the pipe due to the curvature of the walls. This results in peak pressures at the bottom of the pipe that are 4-6 times greater than the peak detonation pressure. Such pressure amplification is measured for water depths of 0.25, 0.5, 0.75, 0.87, and 0.92 pipe diameters. Focusing of the oblique shock waves is studied further by measuring the circumferential variation of pressure when the water depth is 0.5 pipe diameters, and reasonable agreement with theoretical modeling is found. Failure of the detonation waves was not observed, even for water depths as high as 0.92 pipe diameters. Transition to detonation also occurred at every water height, and transition distance did not vary significantly with water height. [Preview Abstract] |
Monday, November 19, 2012 8:26AM - 8:39AM |
G26.00003: Front Structure of Three-Dimensional Detonations in Gaseous Mixtures Boo Cheong Khoo, Hua-Shu Dou Numerical simulations have indicated that independent of how the disturbance is imposed at the beginning of the simulations the final stable detonation in a narrow duct is always the spinning detonation with 90 degree phase difference. With a simplified model, the detonation can be described by a process of energy release with a time periodic function corresponding to the motion of transverse waves, and the energy gradient in time can be a source of instability. It is proposed that the most stable energy release is such that the time derivative of energy release is the lowest. In the unsteady detonation, all the detonation structures always tend to approach this stable state. The calculations indicate that for spinning detonation and rectangular detonation in rectangular ducts, the 90 degree phase difference of transverse waves is the most stable and the in-phase detonation is the most unstable. For oblique detonation, the 180 degree phase difference is the most stable and the in-phase detonation is the most unstable. Under a sufficiently large disturbance, the oblique detonation can finally involve into rectangular mode with 90 degree phase difference. These results are in agreement with the numerical simulations and experiments. [Preview Abstract] |
Monday, November 19, 2012 8:39AM - 8:52AM |
G26.00004: Pressure Feedback in Rotating Detonation Engines Douglas Schwer, K. Kailasanath Rotating detonation engines (RDEs) represent a unique method for obtaining propulsion from the high efficiency detonation cycle. In order for the RDE to be a practical propulsive device, engines must be capable of running efficiently at low pressure ratios, however, this type of injection typically results in a large amount of pressure feedback into the injection system. This paper examines different aspects of the pressure feedback phenomena, and investigates approaches to injecting fresh mixture that reduce the amount of feedback. [Preview Abstract] |
Monday, November 19, 2012 8:52AM - 9:05AM |
G26.00005: The exhaust flow field of a rotating detonation-wave engine Kazhikathra Kailasanath, Douglas Schwer Rotating detonation-wave engines (RDE) are a form of continuous detonation-wave engine. They potentially provide further gains than an intermittent or pulsed detonation--wave engine (PDE). However, significantly less work has been done on this concept when compared to the PDE. Last year, we presented the details of the injection system on the overall flow field in an RDE. In this talk, we focus on the effects of adding an exhaust plenum to this idealized RDE. While the overall exhaust flow shows that a recirculation zone sets up behind the RDE when a plenum is added, the net effect on the flow field within the RDE and on performance is found to be small. However, the slight modification to the flow field may impact the design of suitable nozzles for this device. This is explored further with the addition of a simple conical nozzle. This nozzle reduces the size of the recirculation zone and also reduces the temperature in the plume but has little effect on the flow field inside the RDE. [Preview Abstract] |
Monday, November 19, 2012 9:05AM - 9:18AM |
G26.00006: Capturing the Dynamics of Unsteady Inviscid and Viscous Hydrogen-Air Detonations Christopher Romick, Tariq Aslam, Joseph Powers We consider the calculation of one-dimensional unsteady detonation in a mixture of calorically imperfect ideal gases with detailed kinetics. Both inviscid and viscous detonations of an initially stoichiometric hydrogen-air mixture at ambient conditions of $293.15~K$ and $0.421~atm$ are considered using a chemical mechanism composed of $19$ reversible reactions, containing $9$ species and $3$ elements. The use of detailed kinetics introduces multiple reaction length scales, and their interaction gives rise to complex dynamics. In the inviscid limit, both shock-capturing and shock-fitting are used on a uniform grid. The diffusive behavior is predicted using a wavelet-based adaptive mesh refinement technique and includes multi-component species, momentum, and energy diffusion, as well as DuFour and Soret effects. In the inviscid limit when using shock-capturing, finer resolutions are necessary to accurately capture the dynamics in the unstable regime than when using shock-fitting. At the resolutions necessary for accurate shock-capturing, diffusion can play a crucial role in determining the overall behavior. Near the neutral stability point, the addition of physical diffusions dampens the amplitude of oscillations significantly. [Preview Abstract] |
Monday, November 19, 2012 9:18AM - 9:31AM |
G26.00007: Developing Subgrid Models for Shock-to-Detonation Mesoscale Simulations Thomas Jackson Determining the thermal and mechanical sensitivity of new and existing energetic materials is important for transportation, safety and storage concerns. Initiation of an energetic material can occur when an impulse delivered to the material evolves into a self-sustaining detonation wave. The microstructure can lead to local regions of high temperature, so-called ``hot spots.'' Temperatures in these hot spots can exceed the bulk temperature expected from shock heating, which in turn can trigger ignition even when a homogenized model might fail to predict it. If the chemical and mechanical energy release within hot spots exceeds cooling by diffusion and join up, a localized ignition can occur. Ignition spread due to evolution and growth of high-temperature regions, potentially with reinforcement from neighboring regions or preconditioning of the material, can then lead to detonation. Hot spots are thought to be formed due to shock interaction with microscale and molecular-scale material inhomogeneities through processes such as void collapse, shear banding, debonding, and grain sliding. The most important question at the device scale is whether or not the individual hot spots will coalesce to create a local ignition front, and whether the ignition front or fronts are in turn sufficient to initiate the entire device. Our approach has two principal steps. We first develop sub-grid models based on hot-spot dynamics, and then use the sub-grid model in our mesoscale simulations using our shock dynamics code. In this talk we present recent efforts into developing subgrid models that can be incorporated into mesoscale simulation codes. [Preview Abstract] |
Monday, November 19, 2012 9:31AM - 9:44AM |
G26.00008: A model for shock wave chaos Luiz Faria, Aslan Kasimov, Rodolfo Rosales We propose the following simple model equation that describes chaotic shock waves: \[ u_{t}+\frac{1}{2}\left(u^{2}-uu_{s}\right)_{x}=f\left(x,u_{s}\right). \] It is given on the half-line $x<0$ and the shock is located at $x=0$ for any $t\ge0$. Here $u_{s}\left(t\right)$ is the shock state and $f$ is a given source term [1]. The equation is a modification of the Burgers equation that includes non-locality via the presence of the shock-state value of the solution in the equation itself. The model predicts steady-state solutions, their instability through a Hopf bifurcation, and a sequence of period-doubling bifurcations leading to chaos. This dynamics is similar to that observed in the one-dimensional reactive Euler equations that describe detonations. We present nonlinear numerical simulations as well as a complete linear stability theory for the equation. [Preview Abstract] |
Monday, November 19, 2012 9:44AM - 9:57AM |
G26.00009: On gaseous detonation in a radially expanding flow Aslan Kasimov, Svyatoslav Korneev We investigate two-dimentional converging detonation in a radially expanding flow of ideal gas. The steady state structure is computed analytically and its stability and nonlinear dynamics are explored using numerical simulation. Intricate cellular patterns are observed. [Preview Abstract] |
Monday, November 19, 2012 9:57AM - 10:10AM |
G26.00010: Numerical Simulations of Detonation Wave - Magnetic Field Interactions Lord Cole, Ann Karagozian Numerical simulations of one- and two-dimensional detonation waves subjected to an applied magnetic field are performed, with applications to flow control and MHD thrust augmentation in Pulse Detonation Engines and their design variations.\footnote{Zeineh, et al., {\bf J. Prop. \& Power}, Vol. 28, No. 1, pp. 146-159, 2012} The evolution of the ionization processes and the diffusive and convective transport of the magnetic field are examined in the context of their effect on detonation dynamics. As with prior studies on hydrogen-air detonation dynamics,\footnote{Cole, et al., {\bf Comb. Sci. \& Tech.}, to appear, 2012} the present studies explore hydrogen-air-cesium detonations via high order shock capturing schemes and complex reaction kinetics, in addition to a two-temperature relaxation model for the plasma. One-dimensional simulations examining the non-coupled effect of the magnetic field on the unsteady detonation indicate that the stabilizing effect of the dilluent, cesium, becomes less effective when it becomes an active participant under the influence of strong magnetic fields. Two-dimensional dynamics allow a more complete coupling between the magnetic field and the detonation kinetics to be represented, with implications for an alteration in stability characteristics. [Preview Abstract] |
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