Dapeng Yan

Methods of extracting and registering shock wavefronts from series interferograms of transient flow field

This paper describes the methods of extracting shock wavefront deleting fringes from the interferograms of transient flow field and registering time series shock wavefront on a single image. These methods have been used to extract and register time-series shock wavefront from the interferograms of explosive flow field and muzzle flow field and to calculate the propagation velocity of the shock wavefront.

Temperature measurement of combustion process of detonating powder by using serial pulsed laser interferometry

In this paper, experimental results are presented of using a small pulsed YAG laser to ignite detonating powder to produce the temperature field of transient combustion, and of using a method of serial pulsed laser interferometry to obtain time series interferograms of the combustion process of detonating powder. By means of a computer, a detecting method of fringes thinning is used to thin the fringes of time series interferograms, and fringe displacements are read automatically. The transient temperature distribution of the combustion field of detonating powder and the changes of temperature with time in the combustion process are calculated quantitatively.

Moire interference measurement of boundary layer in hypersonic shock tunnel

This paper presents the interference measurement of the boundary layer in hypersonic shock tunnel with a new large aperture, high sensitive moire interferometer. The principle of the interferometer is presented. This paper shows that the conjugate relation between the model in the tunnel and the observing plate can eliminate the diffracting affection due to the model and therefore the boundary layer can be visualized. The moire interferograms of the boundary were processed with computer digital image process technique. From the deformation of moire fringe, the density profile is presented.

Pulse moire interferogram of rocket exhaust plume and its quantitative anaylsis

This paper presented the measurement of the exhaust plume field of solid rocket with a moire interferometer. The principle of the moire interferometer is presented. The moire interferograms of the plume were processed with computer digital image process technique. It was found that the grey distribution of the moire interferograms has a sharp valley, and from the analysis this paper presented a method to thin and trace a deformated moire fringe on one step. This paper presented the result of the quantitative measurement.

Large-aperture high-accuracy lateral shearing interferometer utilizing a Twyman-Green interferometer

This paper puts forward a new large-aperture high-accuracy interferometer for flow visualization and optical shop testing. The interferometer uses a Twyman-Green interferometer as a beam splitter, and a grating as a detector. Using this interferometer to measure the flow fields in a shock tunnel and to test optical elements obtained some satisfactory results.

Design and application of a moiré interferometer

The optical layout, the application, and the working principle of a large-aperture long-range moire interferometer (MI) for the quantitative measurement of flow properties are introduced. The interferometer is easily converted from a schlieren, and is easily tuned by practitioners of experimental flow mechanics.

Eliminating system errors of a large-aperture and high-sensitivity moire deflector by real-time holography

The design principles of a large-aperture high-sensitivity and high-precision moire deflector in which two error-correction methods of real-time holography are used to make grating are presented. Theories and experiments show that this moire deflector has high sensitivity and high precision in measurement, and its system errors are eliminated.

Generalized Talbot effect

Self-imaging phenomena still exist when a plane grating is illuminated by a monochromatic arbitrary wavefield. The surfaces of the self images are curved, the curvature is determined by the second partial derivatives of wavefront functions. The larger the distance between the grating and a self image the more curved the surface is. The fringe density in self images is affected by the first partial derivatives of wavefront functions. Wavefront functions must satisfy some conditions so that self-images appear.

Analysis of moire deflectometry by wave optics

In this paper, the equations and the contrast of moire fringes, the sensitivity, and the maximum distance allowed between the two gratings in moire deflectometry (MD) are studied in detail on the basis of wave optics. In the analysis the affection of the transfer function for the propagation of a wavefield and the object-image conjugation are considered.