Investigating High Turbulent Flows by Laser Doppler Anemometry

Author Name(s): Ilnar F. Ramazanov, Farit F. Ramazanov, Leysan F. Ryadninskaya
Author Email: kafiziki@mail.ru

Abstract

The article discusses the use of a laser Doppler anemometer for measuring flow parameters with a high degree of turbulence in power plants. Due to the lack of rigorous analytical solutions of the equations describing the turbulent flow regime of liquid and gas flows, the use of experimental methods for studying flows is an urgent scientific task. The precision method is the optical method of laser Doppler anemometry, with which you can determine the speed of flow. An automated system based on a two-color argon laser has been developed, which allows one to determine the flow velocity in two orthogonal planes with the determination of the sign of the velocity projection in the speed range from 0 to ± 150 m / s. The error of speed measurement is from 0.1 to 3%. Carrying out two series of measurements of the velocity projection at the same point in the flow allows us to determine the magnitude and direction of the velocity vector. The measuring volume is an ellipsoid of revolution with a section diameter of 144 μm. The flow velocity was measured in two sections of the cylinder of the internal combustion engine, as well as in the valve slit. During the study, it was revealed that the non-contact method of laser Doppler anemometry allows you to get a reliable picture of the distribution of the velocity field in the cylinder of an internal combustion engine.

Introduction

The measurement of fluid or gas flow rates with a high degree of turbulence is an urgent scientific problem due to the lack of rigorous analytical solutions. Therefore, experimental methods for studying turbulent flows are of particular importance. An absolute method for measuring the flow velocity is the laser Doppler anemometry (LDA) method described in the literature [1-3]. By measuring the Doppler frequency shift (DFS) caused by the scattering of light by optical inhomogeneities – light scattering particles (MF), one can determine the flow velocity, since there is an unambiguous, linear relationship between the DFS and the particle velocity. At subsonic flow velocities, the relative change in the radiation frequency is of the order of 10–8; therefore, the use of the Doppler effect for measuring flow velocities is possible only by scattering monochromatic laser radiation from optical inhomogeneities. In the study of turbulent flows of liquid and gas, it is not enough to know the average flow velocity and velocity pulsations; it is also necessary to determine the direction of the flow velocity vector. Therefore, to measure the speed of the midrange, two or three-component LDAs are used. Three-component LDAs are technically difficult to implement. Two-component LDAs are the most optimal, although they also have a significant drawback – to determine the orientation of the velocity vector at each point of the flow, it is necessary to measure the velocity in two planes.

Conclusion

In the course of experimental studies of gas-dynamic flows in the cylinder of an internal combustion engine, it was revealed that the LDA-based system allows one to obtain a reliable picture of the distribution of flows in the cylinder

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