Instantaneous Velocity Measurements in Laminar and Turbulent Premixed Flames Using On-Line PIV

Abstract

Particle Image Velocimetry (PIV) is used to measure the instantaneous velocity field in laminar and turbulent premixed flames formed at the exit of a round Bunsen burner. The seeding levels were adjusted to provide data simultaneously in the unburned as well as burned gases. The PIV system employs a double-pulsed laser with a solid state sensor as the recording device. Customized image acquisition is used to quickly process the data, thus rapidly providing the velocity field. Two-dimensional, instantaneous velocity fields are measured in a steady laminar flame and captures the sudden change in flow speed at the flame sides as well as the high speeds sustainable at the flame tip. A wake profile downstream of the flame cone is revealed. Vorticity, strain rates and dilatation are possible with these datasets and are also reported; the strain rate is seen to be a reasonably good approximation to the flame shape with magnitudes measured to be below the extinction stretch rate; the dilatation is seen to provide the closest approximation to the instantaneous flame shape. Turbulent flame tips show similar phenomena occurring instantaneously on convoluted flame shapes. The overall accuracy of the measurements is discussed.

Key Words:

• PIV
• velocimetry
• premixed flame
• strain rates
• vorticity