Burst digital correlator as laser-Doppler velocimetry signal processor

Area of Science:

• Fluid Dynamics
• Optical Measurement Techniques
• Signal Processing

Background:

• Laser-Doppler velocimetry (LDV) is a powerful technique for measuring fluid flow velocity.
• Obtaining accurate velocity data from low signal-to-noise ratio (SNR) LDV signals at high data rates presents a significant challenge.
• Existing correlator technologies may struggle with the demands of wideband signals and low SNR conditions.

Purpose of the Study:

• To develop and evaluate a novel burst digital correlator (BDC) for high-data-rate flow velocity measurements.
• To assess the BDC's performance with wideband laser-Doppler signals, particularly those with low SNR (below 0 dB).
• To validate the BDC's accuracy and data rate capabilities using both artificial and practical flow measurements.

Main Methods:

• Development of a burst digital correlator (BDC) specifically designed for wideband laser-Doppler signals.
• Testing with artificial signals across a 5-120 MHz bandwidth to determine measurement accuracy and data rates.
• Correlation of varying numbers of signal samples (64 and 512) to assess the impact on accuracy.
• Experimental validation using practical measurements in challenging flow conditions, including near-wall and recirculating flows.

Main Results:

• The BDC achieved a measurement accuracy of less than 0.4% at a data rate of 208 kHz with 64 correlated signal samples.
• Accuracy improved to better than 0.05% when using a sample size of 512.
• Successful performance evaluation in practical measurements of complex flow scenarios.

Conclusions:

• The developed burst digital correlator (BDC) effectively provides high-data-rate flow velocity information from low-SNR laser-Doppler signals.
• The BDC demonstrates high accuracy and robust performance across a wide signal bandwidth.
• This technology offers a significant advancement for fluid dynamics research requiring precise velocity measurements in challenging conditions.