Using correlated noise of turbulent flow in a long-wavelength acoustic flowmeter to measure the average flow speed

Abstract

Current methods to measure the flow of gaseous emissions from coal-burning power plant smokestacks have uncertainties of 5% to 20%, which is unsuitable if a carbon pricing program is implemented. As part of its Greenhouse Gas and Climate Science Measurements Program, the Fluid Metrology Group at the National Institute of Standards and Technology (NIST) is investigating methods to reduce the uncertainty of flow measurements from smokestacks. In particular, NIST’s scale model long-wavelength acoustic flowmeter (LWAF) uses low-frequency plane waves to measure the average axial flow speed, V, of turbulent fluid flow in a duct with an uncertainty of 1%. To apply this technology to smokestacks, we are investigating cross-correlations of low-frequency flow noise. The spectral density of the measured flow noise is consistent with fluctuations smaller than the duct diameter D for f >> V/D. The amplitude and width of the correlation peak for broadband flow noise is shown to be dependent on V, and a model of this de...