Intermittency determination in the near-field region of a transitional jet by LDV

The intermittency factor is an important parameter for describing the intermittent behaviors in the flow field of turbulent flows or flows near the transition to turbulence. Many methods have been developed to calculate this parameter using different detector functions and threshold value selection. However, for most methods the determination of the threshold value is very subjective. A recent proposal identifies a method for determining a single threshold value and has been demonstrated in a boundary layer flow with Hot-wire Anemometer (HWA) velocity signals. This method remains to be validated in other type of flows using Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) data.

In this talk, I will present a modified method for calculating the intermittency factor in the near-field region of a transitional jet using LDV signals, a significant complication. Our modified method changes the step order of the general calculation procedure and determines the single threshold value (STV) from the radial skewness distribution. The results are validated by comparing with results calculated using other well-known methods and published results at similar flow conditions. The three-fold novelty of the present work is: determination of the intermittency in a jet using an extension of the STV method, with signals obtained from LDV and focused on the near-field region of a transitional round jet.