Nonmechanical scanning laser Doppler velocimeter for cross-sectional two-dimensional velocity measurement

Abstract

We propose a two-dimensional scanning laser Doppler velocimeter (LDV) that does not require any moving mechanisms in its probe. In the proposed LDV, the measurement position can be scanned in two dimensions on a cross-sectional plane perpendicular to the direction of flow. The combination of the change in wavelength and change in port of the fiber array input to the probe is utilized for the scan. The experimental results using a sensor probe setup indicate that the measurement position can be scanned in two dimensions using the proposed method. The scanning range was estimated to be 39.7 mm in the axial direction over the wavelength range of 1536-1554 nm and 26.1 mm in the transverse direction for the use of 22 ports of the fiber array.

Nonmechanical cross-sectional scanning laser Doppler velocimeter with directional discrimination of transverse velocity component

“…1 In this model, the lenses were approximated to thin lenses. The measured results were compared with the theoretical values derived from a ray-tracing model under the paraxial approximation.…”

“…1,2 To measure the velocity distribution, various techniques for mechanically scanning the measurement position for a differential LDV have been proposed. Two-dimensional (2-D) velocity-distribution measurement on a cross-sectional plane of flow is highly desired for many applications.…”

“…1,2 To measure the velocity distribution, various techniques for mechanically scanning the measurement position for a differential LDV have been proposed. 1 In this LDV, the measurement position is scanned using a combination of changes in wavelength and port of the fiber array used as transmission paths between the main body and probe, instead of using moving mechanisms in the probe. 4,5 An LDV with a compact sensor probe is desirable for practical applications.…”

Acoustooptic Diffraction of Three-Color Radiation on a Single Acoustic Wave

“…The operation principle of Doppler anemometry is based on the change of the light frequency after reflection from the moving object. Deviation of light frequency Δ] is defined from the relation Δ]/] = V/b where ] and C are frequency and speed of the light and V is speed of the moving object [14][15][16]. For example, change of Δ] =100 MHz corresponds to V = 630 m/s for the reflected light at the wavelength of 0.63 m. Laser Doppler anemometry based on the differential scheme allows measuring the value Δ] with respect to the frequency f of the acoustic wave which propagates through the AO crystal; in this case the relation f > Δ] has to be fulfilled.…”

Fiber optic laser Doppler velocimeter with non-mechanical scanning of spatially encoded points for cross-sectional velocity distribution measurement

“…However, the direction of the scan is limited to one dimension in these LDVs. To measure two-dimensional cross-sectional velocity distribution, we proposed a non-mechanical scanning LDV combining the changes in wavelength and port of a fiber array input to the probe [7]. However, configuration and control of transmitting optics is complicated in this method.…”