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Supersonic Flow (supersonic + flow)

Distribution by Scientific Domains

Engineering	58%
Physics and Astronomy	41%

Selected Abstracts

Development of the Detachment under the Influence of the Supersonic Flow in the Divertor Region

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2008
O. Marchuk
Abstract It is demonstrated in the framework of a one-dimensional model for the scrape-off layer that with increasing upstream plasma density and decreasing temperature near divertor target plates a supersonic flow develops in the front of the target. This flow is an important mechanism for the transition from high-recycling regime to a weak detached state and has a significant impact on the plasma parameters, in particular, the pressure and particle flux to the plates, after detachment. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Mach Probe Measurements in Unmagnetized Plasmas with Subsonicand Supersonic Flow

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 5-6 2006
A. Ando
Abstract Characteristics of an up-down type Mach probe are investigated by using a directional Langmuir probe (DLP) in unmagnetized plasmas with subsonic and supersonic flow produced by a magneto-plasma-dynamic arcjet (MPDA). The ion acoustic Mach number Mi is derived from plasma flow velocity Up and ion temperature Ti measured by spectroscopy and electron temperature Te by Langmuir probe. The obtained values of Mi are compared to the DLP data in various conditions of plasma flow and the coefficient of Mc in the Mach probe formula,Mi = Mc ln(Jup/Jdown ) , is evaluated. The obtained data are also compared with Hutchinson's PIC simulation results in an unmagnetized plasma and are in good agreement with each other. The dependence of ln(Jup/Jdown ) on cos, can be expressed as a quadratic function under subsonic (Mi < 1) and supersonic (Mi > 1) flow, so that the up-down type Mach probe can detect the components of plasma flow vector even when the probe collection surface inclines to plasma flow direction. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Development of the Detachment under the Influence of the Supersonic Flow in the Divertor Region

Mach Probe Measurements in Unmagnetized Plasmas with Subsonicand Supersonic Flow

On the use of anisotropic a posteriori error estimators for the adaptative solution of 3D inviscid compressible flows

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2009
Y. Bourgault
Abstract This paper describes the use of an a posteriori error estimator to control anisotropic mesh adaptation for computing inviscid compressible flows. The a posteriori error estimator and the coupling strategy with an anisotropic remesher are first introduced. The mesh adaptation is controlled by a single-parameter tolerance (TOL) in regions where the solution is regular, whereas a condition on the minimal element size hmin is enforced across solution discontinuities. This hmin condition is justified on the basis of an asymptotic analysis. The efficiency of the approach is tested with a supersonic flow over an aircraft. The evolution of a mesh adaptation/flow solution loop is shown, together with the influence of the parameters TOL and hmin. We verify numerically that the effect of varying hmin is concordant with the conclusions of the asymptotic analysis, giving hints on the selection of hmin with respect to TOL. Finally, we check that the results obtained with the a posteriori error estimator are at least as accurate as those obtained with anisotropic a priori error estimators. All the results presented can be obtained using a standard desktop computer, showing the efficiency of these adaptative methods. Copyright © 2008 John Wiley & Sons, Ltd. [source]

A posteriori pointwise error estimation for compressible fluid flows using adjoint parameters and Lagrange remainder

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2005
A. K. Alekseev
Abstract The pointwise error of a finite-difference calculation of supersonic flow is discussed. The local truncation error is determined by a Taylor series with the remainder being in a Lagrange form. The contribution of the local truncation error to the total pointwise approximation error is estimated via adjoint parameters. It is demonstrated by numerical tests that the results of the numerical calculation of gasdynamics parameter at an observation point may be refined and an error bound may be estimated. The results of numerical tests for the case of parabolized Navier,Stokes are presented as an illustration of the proposed method. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Numerical simulation of dense gas flows on unstructured grids with an implicit high resolution upwind Euler solver

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2004
P. Colonna
Abstract The study of the dense gas flows which occur in many technological applications demands for fluid dynamic simulation tools incorporating complex thermodynamic models that are not usually available in commercial software. Moreover, the software mentioned can be used to study very interesting phenomena that usually go under the name of ,non-classical gasdynamics', which are theoretically predicted for high molecular weight fluids in the superheated region, close to saturation. This paper presents the numerical methods and models implemented in a computer code named zFlow which is capable of simulating inviscid dense gas flows in complex geometries. A detailed description of the space discretization method used to approximate the Euler equations on unstructured grids and for general equations of state, and a summary of the thermodynamic functions required by the mentioned formulation are also given. The performance of the code is demonstrated by presenting two applications, the calculation of the transonic flow around an airfoil computed with both the ideal gas and a complex equation of state and the simulation of the non-classical phenomena occurring in a supersonic flow between two staggered sinusoidal blades. Non-classical effects are simulated in a supersonic flow of a siloxane using a Peng,Robinson-type equation of state. Siloxanes are a class of substances used as working fluids in organic Rankine cycles turbines. Copyright © 2004 John Wiley & Sons, Ltd. [source]

3-D Inviscid Transonic Condensing Flow around a Swept Wing

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003
K.A. Goodheart
Transonic condensing flow is an interesting phenomena because of the large change in temperature over a small area. This drop in temperature allows the moist air to condense. It is the purpose of this paper to examine the effect of sweep on condensing flow. The geometry of the wing model starts with NACA-0014 at the wall and reduces to a NACA-0010 at the tip. The span of the wing is 2.5 times the maximum chord length. The effect of sweep is examined by comparing a model wing with a sweep angle of 11.3 with a straight trailing edge that has no thickness and then a straight leading edge with a 11.3 trailing edge sweep. The free stream Mach number is 0.8 and angle of attack is 0. A 2-D calculation shows that the NACA-0014 and NACA-0010 have a region of supersonic flow but due to the effect of sweep the sonic line does not extend to the tip. This change of the supersonic region influences the area of condensation on the wing. The swept wing has a lower total drag coefficient for the adiabatic and all condensation cases compared to the straight leading edge wing and second for the each wing the trend of increasing drag with humidity is shown. [source]

A chromospheric dark-cored fibril in Ca II IR spectra

ASTRONOMISCHE NACHRICHTEN, Issue 6 2010
C. Beck
Abstract We investigate the thermodynamical and magnetic properties of a "dark-cored" fibril seen in the chromospheric Ca II IR line at 854.2 nm to determine the physical process behind its appearance. We analyse a time series of spectropolarimetric observations obtained in the Ca II IR line at 854.2 nm and the photospheric Fe I line at 630.25 nm. We simultaneously invert the spectra in both wavelength ranges with the SIR code to obtain the temperature and velocity stratification with height in the solar atmosphere and the magnetic field properties in the photosphere. The structure can be clearly traced in the line-of-sight (LOS) velocity and the temperature maps. It connects from a small pore with kG fields to a region with lower field strength. The flow velocity and the temperature indicate that the height of the structure increases with increasing distance from the inner footpoint. The Stokes V signal of 854.2 nm shows a Doppler-shifted polarization signal with the same displacement as in the intensity profile, indicating that the supersonic flow seen in the LOS velocity is located within magnetized plasma. We conclude that the chromospheric dark-cored fibril traces a siphon flow along magnetic field lines, driven by the gas pressure difference caused by the higher magnetic field strength at the inner footpoint. We suggest that fast flows guided by the magnetic field lead to the appearance of "dark-cored" fibrils in intensity images. Although the observations included the determination of the polarization signal in the chromospheric Ca II IR line, the signal could not be analysed quantitatively due to the low S/N. Chromospheric polarimetry will thus require telescopes of larger aperture able to collect a sufficient number of photons for a reliable determination of polarization in deep and only weakly polarized spectral lines (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A cut-cell non-conforming Cartesian mesh method for compressible and incompressible flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2007
J. Pattinson
Abstract This paper details a multigrid-accelerated cut-cell non-conforming Cartesian mesh methodology for the modelling of inviscid compressible and incompressible flow. This is done via a single equation set that describes sub-, trans-, and supersonic flows. Cut-cell technology is developed to furnish body-fitted meshes with an overlapping mesh as starting point, and in a manner which is insensitive to surface definition inconsistencies. Spatial discretization is effected via an edge-based vertex-centred finite volume method. An alternative dual-mesh construction strategy, similar to the cell-centred method, is developed. Incompressibility is dealt with via an artificial compressibility algorithm, and stabilization achieved with artificial dissipation. In compressible flow, shocks are captured via pressure switch-activated upwinding. The solution process is accelerated with full approximation storage (FAS) multigrid where coarse meshes are generated automatically via a volume agglomeration methodology. This is the first time that the proposed discretization and solution methods are employed to solve a single compressible,incompressible equation set on cut-cell Cartesian meshes. The developed technology is validated by numerical experiments. The standard discretization and alternative methods were found equivalent in accuracy and computational cost. The multigrid implementation achieved decreases in CPU time of up to one order of magnitude. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Parallel computing of high-speed compressible flows using a node-based finite-element method

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2003
T. Fujisawa
Abstract An efficient parallel computing method for high-speed compressible flows is presented. The numerical analysis of flows with shocks requires very fine computational grids and grid generation requires a great deal of time. In the proposed method, all computational procedures, from the mesh generation to the solution of a system of equations, can be performed seamlessly in parallel in terms of nodes. Local finite-element mesh is generated robustly around each node, even for severe boundary shapes such as cracks. The algorithm and the data structure of finite-element calculation are based on nodes, and parallel computing is realized by dividing a system of equations by the row of the global coefficient matrix. The inter-processor communication is minimized by renumbering the nodal identification number using ParMETIS. The numerical scheme for high-speed compressible flows is based on the two-step Taylor,Galerkin method. The proposed method is implemented on distributed memory systems, such as an Alpha PC cluster, and a parallel supercomputer, Hitachi SR8000. The performance of the method is illustrated by the computation of supersonic flows over a forward facing step. The numerical examples show that crisp shocks are effectively computed on multiprocessors at high efficiency. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Acoustic upwinding for sub- and super-sonic turbulent channel flow at low Reynolds number

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2007
H. C. de LangeArticle first published online: 13 FEB 200
Abstract A recently developed asymmetric implicit fifth-order scheme with acoustic upwinding for the spatial discretization for the characteristic waves is applied to the fully compressible, viscous and non-stationary Navier,Stokes equations for sub- and super-sonic, mildly turbulent, channel flow (Re,=360). For a Mach number of 0.1, results are presented for uniform (323, 643 and 1283) and non-uniform (expanding wall-normal, 323 and 643) grids and compared to the (incompressible) reference solution found in (J. Fluid. Mech. 1987; 177:133,166). The results for uniform grids on 1283 and 643 nodes show high resemblance with the reference solution. Expanding grids are applied on 643 - and 323 -node grids. The capability of the proposed technique to solve compressible flow is first demonstrated by increasing the Mach number to 0.3, 0.6 and 0.9 for isentropic flow on the uniform 643 -grid. Next, the flow speed is increased to Ma=2. The results for the isothermal-wall supersonic flows give very good agreement with known literature results. The velocity field, the temperature and their fluctuations are well resolved. This means that in all presented (sub- and super-sonic) cases, the combination of acoustic upwinding and the asymmetric high-order scheme provides sufficient high wave-number damping and low wave-number accuracy to give numerically stable and accurate results. Copyright © 2007 John Wiley & Sons, Ltd. [source]