Hot luminescent gas core at the middle of the convergence chamber.
Schematic drawing of the shock tube: (A) driver section, (B) inlet pipe, (C) transformation section, (D) annular tube, and (E) test section. and , shock sensors; and , glass windows framing the test section.
Test section: (a) drawing of the wing profiles where the outer ring represents the annular channel; (b) photograph of the test section with the profiles installed in the chamber.
Arrangement of the schlieren optics: (L) lens, (M) mirror, and (S) the schlieren stop. and are the temperature sensors used for triggering and measuring the shock speed in the annular tube.
Spectrometric setup. The spectrometer is triggered by the shock wave passing and deflecting the HeNe laser beam detected by a photodiode. The time between the signal and capture is determined with a delay unit.
Schlieren images of converging cylindrical shock waves in air at 13.3 kPa. The Mach number of the initial annular shock was . The time between image capture and focusing instant is displayed under each image. Images (a)–(e) show the converging shocks before focusing while (f) shows the reflected diverging shock. The distance between opposite wing tips is 40 mm.
Idealized diagram over the shock interactions responsible for forming the polygonal shape. Detail from Fig. 6(c) is inserted.
Two examples of the multiply exposed schlieren photographs used for determining shock position and velocity: (a) in air and (b) in argon. The light spot seen in the middle of (b) is the luminescent gas core.
Propagation of polygonal shock wave in air and argon (○) compared with circular Guderley solutions (dashed lines). Power law fits (full lines) to the experimental data are added for comparison.
Mach number from fits to experimental data (full lines) and circular cylindrical Guderley solution (dashed lines). The upper curves represent the shock in argon with initial and the lower in air with initial . The experimental fit represents averaged Mach number of the polygonal wave.
Linear fits to the shock front position to determine Mach numbers of incident shock and Mach stems for shock wave in air and in argon (○).
Deviation of the shock wave shape vs radius.
Photographs of the light emitting gas core: (a) photo showing the full view of the test section; (b) a photo taken from a closer distance.
Photomultiplier records of light emissions from converging polygonal shock waves in argon with helium as driver: mean value and standard deviation (dashed lines) from 20 runs.
Raw time-integrated emission spectrum of the entire light flash. A continuum and two groups of lines from electron transitions in neutral argon atoms were especially notable.
Time-resolved spectra of the light flash. The spectra, taken with exposure times of 60 ns, show the evolution of the continuum and the appearance of the argon emission lines. The spectra have been corrected for CCD sensitivity. Each spectrum is taken at a separate run.
Spectra taken during 60 ns at three different times after the implosion instant: (a) photomultiplier signal with marks indicating the time of each spectrum; (b) ; (c) ; (d) . The intensity scales differ between the graphs.
Filtered spectra with blackbody curve fits. The blackbody curves are corrected for the quantum efficiency of the camera and the glass window transmission losses. The times at start of exposure and blackbody temperature are (a) , ; (b) , .
Temperatures acquired from blackbody fits of time-resolved spectra with 60 ns exposure time. Each data point represents measurements made on separate runs. The temporal errors are ±20 ns.
The computational domain (a) and a magnification of a small circular region around the right tip of the left horizontal wing (b).
Numerical schlieren images of the global shock system in the air-filled chamber at equidistant times. Initial Mach number .
Numerical schlieren images of the central part of the air-filled chamber showing the converging shock fronts at the time instants corresponding to the experimental schlieren photographs shown in Fig. 6. Initial Mach number .
Comparison of a detail of a schlieren photograph, Fig. 6(d), computational mesh, and numerical schlieren image computed at the same instant prior to implosion.
Effective radius of converging and diverging polygonal shock fronts. Experimental and numerical data for the shock in air with air as driver gas (, full line) and argon with helium as driver gas (○, dashed line).
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