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1.
Spencer P. Kuo 《Shock Waves》2007,17(4):225-239
Two types of plasma spikes, generated by on-board 60 Hz periodic and pulsed dc electric discharges in front of two slightly
different wind tunnel models, were used to demonstrate the non-thermal plasma techniques for shock wave mitigation. The experiments
were conducted in a Mach 2.5 wind tunnel. (1) In the periodic discharge case, the results show a transformation of the shock
from a well-defined attached shock into a highly curved shock structure, which has increased shock angle and also appears
in diffused form. As shown in a sequence with increasing discharge intensity, the shock in front of the model moves upstream
to become detached with increasing standoff distance from the model and is eliminated near the peak of the discharge. The
power measurements exclude the heating effect as a possible cause of the observed shock wave modification. A theory using
a cone model as the shock wave generator is presented to explain the observed plasma effect on shock wave. The analysis shows
that the plasma generated in front of the model can effectively deflect the incoming flow; such a flow deflection modifies
the structure of the shock wave generated by the cone model, as shown by the numerical results, from a conic shape to a curved
one. The shock front moves upstream with a larger shock angle, matching well with that observed in the experiment. (2) In
the pulsed dc discharge case, hollow cone-shaped plasma that envelops the physical spike of a truncated cone model is produced
in the discharge; consequently, the original bow shock is modified to a conical shock, equivalent to reinstating the model
into a perfect cone and to increase the body aspect ratio by 70%. A significant wave drag reduction in each discharge is inferred
from the pressure measurements; at the discharge maximum, the pressure on the frontal surface of the body decreases by more
than 30%, the pressure on the cone surface increases by about 5%, whereas the pressure on the cylinder surface remains unchanged.
The energy saving from drag reduction is estimated to make up two-thirds of the energy consumed in the electric discharge
for the plasma generation. The measurements also show that the plasma effect on the shock structure lasts much longer than
the discharge period.
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2.
The generation of high-speed liquid (water and diesel fuel) jets in the supersonic range using a vertical single-stage powder
gun is described. The effect of projectile velocity and mass on the jet velocity is investigated experimentally. Jet exit
velocities for a set of nozzle inner profiles (e.g. straight cone with different cone angles, exponential, hyperbolic etc.)
are compared. The optimum condition to achieve the maximum jet velocity and hence better atomization and mixing is then determined.
The visual images of supersonic diesel fuel jets (velocity about 2000 m/s) were obtained by the shadowgraph method. This provides
better understanding of each stage of the generation of the jets and makes the study of their characteristics and the potential
for auto-ignition possible. In the experiments, a pressure relief section has been used to minimize the compressed air wave
ahead of the projectile. To clarify the processes inside the section, additional experiments have been performed with the
use of the shadowgraph method, showing the projectile travelling inside and leaving the pressure relief section at a velocity
of about 1100 m/s.
Received 23 January 2001 / Accepted 2 July 2001 相似文献
3.
This paper discusses gas-dynamic aspects of intense explosions in uniform environments. In experiments, the energy of a laser
is almost instantaneously released in a volume of air shaped as either a flattened or stretched cylinder generating a blast
wave. Its shape evolves in time and ultimately becomes spherical. But momentum transferred to the air when the blast wave
is strongly nonspherical is anisotropic. As a result, a subsonic jet and a vortex are induced and propagate along the symmetry
axis or along the perpendicular plane, depending on the initial configuration of the blast wave. Simulations based on a free-Lagrangian
method for a nonviscous gas are in good agreement with the experiments. Velocities, circulation, and positions of fluid particles
found in computations give an insight into the causes and details of the flow. Two simultaneous and contrary processes take
place – vorticity production by the anisotropic shock wave and baroclinical generation of vorticity at the boundary of the
heated gas – which give rise to net circulation.
Received 21 April 1997 / Accepted 27 June 1997 相似文献
4.
A Free-Lagrange method for unsteady compressible flow: simulation of a confined cylindrical blast wave 总被引:1,自引:0,他引:1
G. J. Ball 《Shock Waves》1996,5(5):311-325
A Free-Lagrange numerical procedure for the
simulation of two-dimensional inviscid compressible flow
is described in detail. The
unsteady Euler equations are solved on an unstructured
Lagrangian grid based on a density-weighted Voronoi mesh.
The flow solver is of the Godunov type, utilising either the
HLLE (2 wave) approximate Riemann solver or the more recent HLLC
(3 wave) variant, each adapted to the Lagrangian frame.
Within each mesh cell, conserved properties are
treated as piece-wise linear, and a slope limiter of the MUSCL type
is used to
give non-oscillatory behaviour with nominal
second order accuracy in space.
The solver is first order accurate in time.
Modifications to the slope limiter to minimise
grid and coordinate dependent
effects are described.
The performances of the HLLE and HLLC solvers are compared for
two test problems; a one-dimensional
shock tube and a two-dimensional blast wave confined
within a rigid cylinder. The blast wave is initiated by impulsive
heating of a gas column whose centreline is parallel to,
and one half of the cylinder radius from,
the axis of the cylinder.
For the shock tube problem, both solvers predict shock and expansion
waves in good agreement with theory.
For the HLLE solver, contact resolution
is poor, especially in the blast wave problem. The HLLC solver achieves
near-exact contact capture in both problems.
Received May 25, 1995 / Accepted September 11, 1995 相似文献
5.
Comparison of kinetic and continuum approaches for simulation of shock wave/boundary layer interaction 总被引:1,自引:0,他引:1
I.A. Graur M.S. Ivanov G.N. Markelov Y. Burtschell E. Valerio D. Zeitoun 《Shock Waves》2003,12(4):343-350
The present paper, which is a collaboration between three different research groups, analyzes the efficiency of various numerical
approaches to describe the complex problem of shock wave/boundary layer interaction. Computations were carried out based on
a kinetic approach (Direct Simulation Monte Carlo method) and on two continuum approaches (Navier-Stokes equations and quasigasdynamic
equations), which are validated by comparison with experimental results obtained in the R5Ch blowdown Hypersonic Wind Tunnel
in ONERA. The influence of the slip boundary conditions for two continuum approaches are also studied. The results obtained
by all models display the good prediction of the main structure of the flow and the levels of the flux coefficients are very
close to those measured. The implementation of the slip boundary condition for the continuum approaches improves the agreement
with the experimental data.
Received 12 July 2001 / Accepted 24 May 2002 /Published online 4 December 2002
Correspondence to: D. Zeitoun (e-mail: David.Zeitoun@polytech.univ-mrs.fr)
An abridged version of this paper was presented at the 23rd Int. Symposium on Shock Waves at Fort Worth, Texas, from July
22 to 27, 2001 相似文献
6.
In the Shock Wave Journal Vol. 2, No. 4 a benchmark test for shock wave reflection over wedges was announced. International
scientists who are interested in shock wave research were invited to participate. The benchmark test aimed at comparison of
various advanced numerical schemes as well as experimental results. During the last three years more than twenty results,
including both CFD and experiments, were collected from all over the world. Efforts contributed by these scientists made the
present benchmark test reach to a standard of the state of the art of the computational fluid dynamics applied to the shock
wave research. However, it was regrettable not to publish all the results collected due to limitation on the available page
number.
Received 5 November 1994 / Accepted 9 September 1996 相似文献