Modal decomposition analysis to extract the coherent behaviors in transitional pulsatile pipe flows

Investigation of mechanisms triggering the transition to turbulence in pulsatile pipe flows are of interest due to the detrimental effect of intermittent flow structures on hemodynamics behaviors. However, conventional metrics such as critical Reynolds number or turbulence intensity fail to represent these intermittent flow mechanisms adequately because of the time-varying nature of pulsatile flow as well as the interdependent mechanism between mean and oscillatory flow components. Data driven modal decomposition methods such as proper orthogonal decomposition (POD), dynamic mode decomposition (DMD) and spectral proper orthogonal decomposition (SPOD) have generally been found to be well-suited for extracting the underlying coherent interdependent mechanism in the data. In this work, we perform several modal decomposition analyses on 2D particle image velocimetry (PIV) data of transitional pulsatile pipe flow to extract the spatial, temporal, and spectral coherent mechanisms triggering the transition to turbulence. Furthermore, we explore the relation between the resulting modes to traditionally obtained coherent structures as well as our novel instantaneous frequency structures of the flow field.