Kazuo Maeno

Computed-tomographic density measurement of supersonic flow field by colored-grid background oriented schlieren (CGBOS) technique

The background oriented schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. The principle of BOS is similar to the conventional schlieren technique, which exploits the bending of light caused by refractive index change corresponding to density change in the medium and both techniques are sensible to density gradient. In this report we propose colored-grid background oriented schlieren (CGBOS) technique. The experiments were carried out in a supersonic wind tunnel of test section size 0.6 × 0.6 m2 at JAXA-ISAS. A colored-grid pattern was used as background image and density gradient in vertical and horizontal direction was obtained. Computed tomographic reconstructions of 3D density information of the supersonic flow field around an asymmetric body from multi-directional CGBOS images were examined.

Measurement of Gas Temperature Profile in Discharge Region of Excimer Laser with Laser Schlieren Method

Shock waves are generated by pulse discharges in the cavity of excimer lasers. The shock waves cause arcing, nonhomogeneous excitation of laser gas and limitation of repetition rate of a high-repetition-rate excimer laser. Distribution of temperature rise by pulse discharge is an essential factor for generation and propagation of shock waves. Gas temperature profiles in the discharge region of the excimer laser cavity are measured by a laser schlieren method for single-pulse operations. The results show that the temperature distribution depends on the xenon concentration. In the cases of pure helium and higher xenon concentration, the temperature distributions are steeper than those in the cases of lower xenon concentration.

Interferometric signal measurement of shock waves and contact surfaces in small scale shock tube

In this study we have performed the experiment under the several pressure conditions by using the mini-shock tube of 3mm diameter, which was developed by Garen, by using the interferometric signal measurement with the collimated and polarized laser beams. It is confirmed that the shock waves do not propagate at constant velocity in this mini-shock tube. We have also performed a numerical simulation by using two-dimensional and axi-symmetric N-S equation to compare with the experimental results. The experimental results are shown with the numerical results on the x-t diagram. It is confirmed that the influence of the friction between the test gas and the wall produces the difference between the inclinations of x - t curves of the diagram.

Laser interferometric CT measurement of the unsteady supersonic shock-vortex flow field discharging from two parallel and cylindrical nozzles

Three-dimensional flow phenomena with unsteady shock waves and vortices have been observed in a shock tube experiment by using an interferometric CT (computed tomography) technique. A model with small ducts, which has a pair of cylindrical nozzles, is introduced in the test section of the shock tube. The model can be rotated around its central axis to change the observation angle. The projection image of density distribution for each observation angle is obtained by using a fixed Mach–Zehnder interferometer. The three-dimensional density distribution is reconstructed from these projection images. The shock Mach numbers are fixed to 2.3 at the exits of the nozzles in nitrogen gas of 19.4 kPa initial pressure. The resultant 3D density flow fields are illustrated by several visualizing methods to clarify the 3D features of shock waves, vortices and their mutual interactions.

An Investigation on the Behavior of Laser Induced Bubble in Cryogenic Liquid Nitrogen

There have been few experimental reports on cryogenic two-phase fluids and cavitation phenomena using the irradiation of pulsed high-power laser. This paper describes an investigation of the behavior of laser induced cavitation bubble in cryogenic liquid nitrogen. The bubble is produced by a pulsed ruby laser focused in the special cryostat. The production, growth, and rebound phenomena of the bubbles are visualized by diffusive shadowgraph technique with an image-converter camera. To compare with the experimental results, a numerical study has also been performed on the dynamics of a single spherical bubble in liquid nitrogen under the conditions of nonequilibrium phase change.

Shock waves in mini-tubes: influence of the scaling parameter S

Weak shock waves have been investigated in a glass tube of 1 mm diameter and a length of 600 mm. The distance between shock and contact surface is approximately 10 mm and both travel nearly with the same speed at the measuring position of 410 mm. For a laminar flow behind the shock wave an identical Mach number M 1 can be generated with two different shock strength values p 41 as a consequence of friction effects.

Three-Dimensional Density Measurement of Supersonic and Axisymmetric Flow Field by Colored Grid Background Oriented Schlieren (CGBOS) Technique

The background oriented schlieren (BOS) technique is one of the visualization techniques that enable the quantitative measurement of density information in the flow field with very simple experimental setup. BOS requires only a background and a digital still camera and it can realize the quantitative measurement of density. In this report we propose the colored grid background image for BOS technique (CGBOS). The experiments were carried out in the 0.6 m x 0.6 m test section of supersonic wind tunnel at JAXA-ISAS. The measurement setup consisted of metal halide ramps, a colored grid background image and a digital still camera. A colored grid pattern was used as background image and density gradient in vertical and horizontal direction was obtained. The measurement result and prospect of CGBOS technique are reported.

CARS Measurement of Vibrational/Rotational Temperatures with Total Radiation Visualization behind Strong Shock Waves of 5–7 km/s

In the development of aerospace technology the design of space vehicles is important in phase of reentry flight. The space vehicles reenter into the atmosphere with range of 6–8 km/s. The non‐equilibrium flow with radiative heating from strongly shocked air ahead of the vehicles plays an important role on the heat flux to the wall surface structure as well as convective heating. The experimental data for re‐entry analyses, however, have remained in classical level. Recent development of optical instruments enables us to have novel approach of diagnostics to the re‐entry problems. We employ the CARS (Coherent Anti‐Stokes Raman Spectroscopy) method for measurement of real gas temperatures of N2 with radiation of the strong shock wave. The CARS signal can be acquired even in the strong radiation area behind the strong shock waves. In addition, we try to use the CCD camera to obtain 2D images of total radiation simultaneously. The strong shock wave in front of the reentering space vehicles is experimentally r...

Observation of Nonequilibrium Radiation behind Strong Shock Waves in Low-density Air

Nonequilibrium radiation phenomena behind strong shock waves in low-density air are observed by using a couple of CCD camera systems in a shock tube experiment. The simultaneous observation for total radiation and its spectral radiation is carried out in order to elucidate spaced-ependent contribution of an individual radiation spectrum to the total radiation intensity. The results are shown for the shock velocity range from 9.0 km/s to 12.1 km/s at the initial pressure 13.3 Pa. Wavelength range is selected from 300 nm to 445 nm to investigate mainly the contributions from UV radiation. It is found that the band spectra due to the molecular species N2+ and CN mainly contribute to the first-peak, while the spectra due to the atomic species O+ and N mainly contribute to the formation of the second-peak. It is also found that the Balmer series in H spectra strongly contributes to the second-peak. The radiation along the tube wall surfaces is composed of the same constituents as those around the tube axis as well as the spectra coming from the impurities.

Interferometric Measurement in Shock Tube Experiments

This chapter describes applications of interferometry to the shock tube experiments. The first topic is Laser Interferometric Computed Tomography (LICT) technique to realize the three-dimensional (3D) density measurement of high-speed and unsteady flow field behind shock waves discharging from nozzles. The second topic is measurement of propagating shock wave in micro-scale shock tube by interferometic approach. Micro-scale shock tube is being researched in several fields of science recently and micro-scale shock wave has possibilities of applications for various fields medical, engineering, ...etc. Clarifying the characteristics of micro-scale shock tube to generate the micro-scale shock wave is very important step for the application.