The Development of an Accuracy of a Doppler Global System for One Dimensional Velocity Measurement

Abstract

The development of a Doppler Global System for one dimensional velocity measurement including both hardware and software development is described. The Doppler Global Velocimetry (DGV) system is a whole field measurement system based on Doppler shifting of the light frequency reflected by seeded particles or rotating disc surface speed. The relationship between the Doppler shift and the transmission ratio is a key part of the DGV system to calculate measured velocity. The absorption line filter is a device to determine the Doppler shift by converting a frequency to an intensity.

This study describes the optical system and software developments to increase the accuracy of the DGV system. The new light source and two charged coupled device cameras are the main hardware developments. A LabView code was created to calibrate the ALF cell automatically as a software development.

The DGV system spatial and intensity calibration was completed for accurate measurement, and the ALF cell was calibrated to maintain the relationship between the transmission ratio and frequency shift of the laser. The system was tested by measuring the surface speed across a 99.06 mm white painted disc at 18000 and 10020 rpm when the transmission ratios of the ALF cell are 1.1, 0.5 and 0.085.

As a result, the error of the system was -8 to 12 m/s when the transmission ratio was 1.1. The measured velocity had ±5 m/s when the transmission ratio was 0.5. However, the error was significantly high at the bottom right and top left part of the disc because these regions did not receive enough light. Also, the measurement was not accurate when the transmission ratio was 0.08. The change of transmission ratio was almost constant when the transmission ratio was 0.08, so Doppler shift calculation was not calculated accurately because of that reason.

In conclusion, the rotating disc horizontal surface speed was measured at different rotational speeds and transmission ratios. Results prove that new two Dalsa Pantera TF 1M30 cameras and, Oxxius continuous wave diode pumped solid state laser as a light source work properly to measure velocity in our DGV system.