Characterisation of the Instantaneous Velocity and Mixture Field Issuing From a Lean Premixed Module (LPM)

Abstract

Measurements have been made on the non-reacting flow field issuing from a Lean Premixed module (LPM) that incorporates a radial swirler, mixing duct section and nozzle. The geometry contains many features that are thought typical of LPM systems in which gaseous fuel is introduced into a swirling flow at a discrete number of locations. Hot wire anemometry measurements have been used to define the velocity field issuing from the module whilst additional experiments have utilised heated air to simulate gaseous fuel. In this way temperature measurements, using Constant Current Anemometry, have been used to infer the fuel-air mixture field issuing from the module. The velocity data indicates a highly turbulent flow field and the basic spectral characteristics of this velocity field are defined. In addition, within certain regions a strong periodic flow component is observed and is indicative of the instabilities typically associated with swirling flows. The spectral characteristics of the mixture field are also presented and the method by which the mixture and velocity spectra should be compared is outlined. Using this method the measurements indicate the basic spectral characteristics are virtually identical and, furthermore, a periodic fluctuation in the mixture field is also observed. For these types of LPM systems fluctuations in the mixture and velocity fields are therefore strongly correlated. In addition it is shown that the flow fields are dominated by the relatively large time and length scales associated with the main velocity field rather than, say, the much smaller velocity and mixing scales associated with the individual fuel jets.