Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session GM: Compressible Flows |
Hide Abstracts |
Chair: C.K. Law, Princeton University Room: Tampa Marriott Waterside Hotel and Marina Meeting Room 10 |
Monday, November 20, 2006 10:30AM - 10:43AM |
GM.00001: The transient start of supersonic jets Matei I. Radulescu, Chung K. Law The present study investigates the initial transient hydrodynamic evolution of highly under-expanded jets. Two-dimensional numerical simulations for slit and axisymmetric jets were performed to investigate the flow field during the initial stages over distances of approximately 1000 orifice radii. The parameters used in the simulations correspond to the release of pressurized hydrogen gas into ambient air, with pressure ratios varying approximately between 100 and 1000. The simulations indicate that the head of the jet is laminar at early stages, while a highly complex turbulent flowfield is established at the sides of the jet, involving shock interactions within the vortex rings. A closed form analytic similarity solution is derived for the pressure, density, and temperature temporal evolution at the jet head for vanishing diffusive fluxes generalizing a previous model of Chekmarev using Chernyi's boundary-layer method for hypersonic flows. Very good agreement is found between the present model, the numerical simulations and previous experimental results. The results are used to derive the criteria for Rayleigh-Taylor instability of the decelerating density gradients at the jet heads. The analytical results for the jet evolution could be used in the future to address the ignitability of unsteady expanding diffusive layers formed during the sudden release of pressurized fuel into an oxidizing atmosphere. [Preview Abstract] |
Monday, November 20, 2006 10:43AM - 10:56AM |
GM.00002: Double synthetic jets solely induced by acoustic wave Ming-Hao Wang, Li-Jun Xuan, Jie-Zhi Wu The dynamic process of a traveling acoustic wave in a duct with an orifice plate, where the fluid is otherwise at rest, is studied numerically and analytically. The computation by a compressible Navier-Stokes scheme, 6$^{th}$-order in space and 4$^{th}$-order in time, shows that the pressure wave produces a vorticity wave at the wall via the viscous momentum balance and no-slip condition. If the frequency is low, the amplitude is large, and the opening of the orifice is small, the vorticity can build up near the orifice and become concentrated vortices at both sides of the plate. The vortices shed off and form two double-row vortex streets moving away from the plate in opposite directions due to self induction, with \textit{two opposite synthetic jets} in between. In turn, the moving vortices emit new sound waves. This example may serve as a typical prototype of the closed-loop coupling between the shearing process measured by the vorticity and the compressing/expanding process measured by the pressure. An analytical solution for the generalized compressible Stokes layer with variable amplitude and wavelength in the straight-wall sections is obtained, of which all predicted flow variables are in excellent agreement with the numerical results. [Preview Abstract] |
Monday, November 20, 2006 10:56AM - 11:09AM |
GM.00003: Flows in micro-channels with side-wall mass injection Mark Short, David Kessler Incompressible, inviscid, rotational flows in rectangular and cylindrical large aspect ratio channels with side-wall mass injection form the basis for the study of the core flow in solid rocket motors (the Taylor-Proudman-Culick solutions). The assumption of incompressible inviscid flow is based on the relative magnitudes of the side-wall injection Mach number and the channel aspect ratio. Extensions to compressible inviscid flows have been considered by Balakrishnan, Linan, and Williams. Here we consider an analysis of steady flow in long, but very narrow, rectangular and cylindrical channels with side-wall mass injection where viscous effects must be accounted for, since the usual surface boundary layer flow cannot be blown off the injection surface due to the small injection surface separation. We develop asymptotic and numerical solutions for the viscous compressible rotational flow in the channel. The work has application to recent interest in the development of micro-propulsion systems. [Preview Abstract] |
Monday, November 20, 2006 11:09AM - 11:22AM |
GM.00004: Numerical investigation of three-dimensional transonic flows of Bethe-Zel'dovich-Thompson fluids Paola Cinnella, Christophe Corre Bethe-Zel'dovich-Thompson (BZT) fluids are fluids of the retrograde type (i.e. that superheat when expanded), which exhibit a region of negative values of the Fundamental Derivative of Gasdynamics $\Gamma $. As a consequence, they display, in the transonic and supersonic regime, nonclassical gasdynamic behaviours, such as rarefaction shock waves and mixed shock/fan waves. The peculiar properties of BZT fluids have received increased interest in recent years because of the possibility of enhancing turbine efficiency in Organic Rankine Cycles (ORCs). The present research provides for the first time a detailed investigation of transonic BZT flows past a 3D configuration, representative of an isolated turbine blade with infinite tip leakage, namely, the ONERA M-6 wing. Since BZT phenomena mainly affect the inviscid flow behavior, the analysis is restricted to the Euler equations, completed by the realistic Martin-Hou equation of state. The governing equations are solved numerically using a structured flow-solver based on a third-order accurate centred scheme. The results are validated through systematic comparisons with an unstructured multidimensional upwind solver. An investigation of the flow patterns for several choices of the upstream thermodynamic conditions is provided, showing the complexity of the 3D aerodynamics of BZT fluids, and confirming the advantages in terms of improved aerodynamic performance already demonstrated for 2D configurations. [Preview Abstract] |
Monday, November 20, 2006 11:22AM - 11:35AM |
GM.00005: High energy concentration in gas by shock focusing Veronica Eliasson, Nicholas Apazidis, Nils Tillmark The purpose of the present work is to study how the shape of a converging shock wave influences the stability and shock dynamics during the focusing and reflection process. Experiments are performed in a horizontal shock tube where a plane shock is transformed into an annular shape and then focused in a cylindrical test section. The shock wave is formed into different geometrical shapes by two separate methods. In the first method the desired shock shape is achieved by changing the shape of the outer boundary of the test section. In the second method cylindrical obstacles are placed at different positions and patterns inside the test section. Disturbances from the obstacles affect the shock and change its shape. During the focusing process the shock undergoes a successive change in shape. The coupling between the local strength of the shock and the shape of the shock front makes regions with higher curvature (i.e. corners) travel faster than regions with lower curvature (i.e. plane sides). Our results show that circular shock waves are unstable and hence easy to perturb while polygonal shock waves are stable. An interesting phenomenon, which occurs during the later stages of the focusing process, is the emission of light. The intensity of the emitted light depends on the gas used in the test section and on the shape and regularity of the shock wave. A symmetric shape (e.g. a square) emits more light than a non-symmetric shape (e.g. a shock wave disturbed by only one cylinder). [Preview Abstract] |
Monday, November 20, 2006 11:35AM - 11:48AM |
GM.00006: ABSTRACT WITHDRAWN |
Monday, November 20, 2006 11:48AM - 12:01PM |
GM.00007: The Effects of Streamwise Expansive Straining on Weakly Compressible Isotropic Turbulence Savvas Xanthos, Minwei Gong, Yiannis Andreopoulos The response of homogeneous and isotropic turbulence to streamwise straining action provided by planar expansion waves has been studied experimentally in the CCNY Shock Tube Research Facility. The reflection of a propagating shock wave at the open end wall of the shock tube generated an expansion fan traveling upstream and interacting with the induced flow behind the incident shock wave which has gone through a turbulence generating grid. A custom made hot-wire vorticity probe was used capable of measuring the time-dependent highly fluctuating three dimensional velocity and vorticity vectors, in non-isothermal and inhomogeneous flows. The longitudinal size of the straining zone was substantial so that measurements within it were possible. The flow accelerated from a Mach number of 0.23 to about 0.56 a value which is more than twice the initial one. Although the average value of the applied straining was only S$_{11}$=130 s$^{-1}$, the amplitude of fluctuations of the strain rate S$_{11}$ were of the order of 4000 s$^{-1}$ before the application of straining and reduced down by about 2.5 times downstream of the interaction. One of the most remarkable features of the suppression of the turbulence is that this process peaks shortly after the application of the straining where the pressure gradient has a minimum. [Preview Abstract] |
Monday, November 20, 2006 12:01PM - 12:14PM |
GM.00008: Evaluation of WENO Adaptation Modifications in DNS of Compressible Isotropic Turbulence Interacting with a Shock Wave Ellen Taylor, Pino Martin Weighted essentially non-oscillatory (WENO) methods have been developed to simultaneously provide robust shock-capturing in compressible fluid flow and avoid excessive damping of fine-scale flow features such as turbulence. Under certain conditions in compressible turbulence, however, numerical dissipation remains unacceptably high even after optimization of the linear component that dominates in smooth regions. We have therefore previously constructed and evaluated WENO schemes that also reduce dissipation due to two sources of \emph{non}linear error: the smoothness measurement that governs the application of stencil adaptation away from the linear optimal stencil, and the general lack of synchronization between adaptive numerical stencils pertaining to up- and downwind interpolated convective fluxes. In the present work, we extend our tested flow configurations from direct numerical simulations (DNS) of one-dimensional Euler solutions and three-dimensional compressible isotropic turbulence to also include DNS of compressible isotropic turbulence interacting with a strong shock wave. [Preview Abstract] |
Monday, November 20, 2006 12:14PM - 12:27PM |
GM.00009: Analysis of Shock Motion in a Compression Ramp Configuration using DNS data Minwei Wu, Pino Martin Large scale slow motion (LSSM) has been observed in shockwave and turbulent boundary layer interaction (STBLI) experimentally, while no evidence of LSSM has been found in numerical simulations. We perform a direct numerical simulation (DNS) of a 24$^{\circ}$ compression ramp configuration. The DNS is compared with experiments under the same flow conditions. Comparison shows good agreement in the mean wall-pressure distribution, the size of the separation bubble, and the velocity profile downstream of the interaction. Wall pressure signals near the separation point show evidence of large scale slow motions in the DNS. The relation of the LSSM and large scale structures in the incoming boundary layer is studied to verify if these structures are responsible for the LSSM. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700