Localized fluid flow measurements with an He-Ne laser spectrometer

This article describes the use of the Fabry–Perot laser interferometer in the fringe mode to measure velocities of fast‐moving reflecting surfaces, and includes a review of previously published work. We begin by describing the theory of the Doppler shift that applies to these situations, and include an experimental test of whether surface normal direction affects Doppler shift. Formulas are derived for the analysis of the effects of shocked, dispersive, moving transparent media on velocity measurements, including expressions for the velocity of light in a moving medium with moving boundaries. The Fabry–Perot method is compared with other techniques such as the VISAR interferometer. We then describe in detail a standard configuration developed at our facilities, discuss other configurations using optical fibers and more than one cylinder lens, and describe a new laser amplifier developed specifically for velocimetry. Methods of alignment, instrument calibration, surface preparation, and operation are inclu...

Velocimetry of fast surfaces using Fabry–Perot interferometry

The existence of large-scale structures in the form of a vortical double helix in a swirling Ranque flow is observed for the first time. The structure of the vortical double helix is visualized in real time by the method of Hilbert bichromatic filtering. The experimental result is interpreted on the basis that the most probable physical mechanism for the spatial energy separation in the gas flow (i.e., for the so-called Ranque effect) is viscous heating of the gas in a thin boundary layer at the walls of the vortex chamber and the adiabatic cooling at the center owing to the formation of an intense vortex braid near the axis.

Observation of large-scale hydrodynamic structures in a vortex tube and the Ranque effect

An overview of measurements of particle velocities and diameters by laser techniques, with emphasis on thermal plasmas, is given. As far as veloities are concerned, laser-Doppler velocimetry is discussed as a well-established technique. Diameter measurements are much less developed. The state of the art is described and prospective considerations are stressed.

A review on measurements of particle velocities and diameters by laser techniques, with emphasis on thermal plasmas

The present paper gives an introduction to laser Doppler anemometry. The fundamental principles of this measuring technique, as well as the basic features of its instrumental realizations, are explained. The application of laser Doppler anemometry to fluid investigations often requires an adaptation of the LDA-system to the measuring problem. Basic formulas for the lay-out and adaptation are given.

Laser Doppler Anemometry – a non‐intrusive optical measuring technique for fluid velocity

A device for simultaneously measuring the three orthogonal components of a velocity vector is described. The system uses a laser beam passing twice through the region of flow under investigation. This allows one to determine the third component using only forward scattering. Vector diagrams which explain the mode of operation and experimental signals are given.

A laser Doppler velocimeter which measures the three components of velocity

The possibility of using an electro-optical frequency modulator with a rotating electric field (MREF) in LDV is discussed. Prototype systems measuring one component of the velocity vector are described. Photographs of the experimental signals obtained are given.

The application of an electro-optical frequency modulator with a rotating electric field in optical Doppler velocimeters

A coloured real-time visualizer of optical inhomogeneities comprising a bichromatic schlieren system, video camera and colour monitor has been developed. The schlieren system represents a function Foucault-Hilbert transformation provided with an amplitude spatial frequency filter, or a quadrant Foucault knife edge. Two colour-coded complementary Toepler-grams are obtained in the exit plane of this schlieren system. Their summed image is then recorded by the video camera and displayed on the screen of the colour monitor. The schlieren photograph of internal gravity waves, generated by the cylindrical body motion in the reservoir filled with the stratified liquid, is presented.

Real-time coloured visualization of phase flows by the schlieren method

A laser velocimeter is described which uses an optical Doppler frequency discriminator in the form of a spherical mirror confocal Fabry-Perot interferometer (SFPI). The SFPI pass band is made to coincide with the laser frequency using a system of external control. Experimental results are given.

The application of an optical Doppler frequency discriminator in a laser velocimeter

Basic forms of the optical systems of laser Doppler velocimeters with supression of the additive noise component in the output signal are investigated by the Jones matrix method. The expressions for the resulting Doppler signal, taking into account the parameters and orientation of phase elements and the receiving polarization analyser, have been obtained and analysed. Experimental results are given.

Yu.N. Dubnistchev

Papers

A laser Doppler velocimeter which measures the three components of velocity

The application of an electro-optical frequency modulator with a rotating electric field in optical Doppler velocimeters

Real-time coloured visualization of phase flows by the schlieren method

The application of an optical Doppler frequency discriminator in a laser velocimeter

Analysis of optical compensating schemes of laser Doppler velocimeters