Wake identification of stratified flows using dynamic mode decomposition

The wake behind a bluff body in the presence of a density gradient is characterized by competing effects of buoyancy, momentum, and ultimately viscosity as the flow decays. Consequently, there are a number of distinct flow regimes into which the wakes can be placed, and there is some interest in whether any given wake can be traced back to its source through interrogation of selected fluid mechanical properties in the wake. Here we use dynamic mode decomposition (DMD) to find modes that can be used to characterize and automate such a process. A custom-designed algorithm is proposed that can sort and classify stratified wakes based on a selection of the most energetic DMD modes. The approach is very, or partially successful, depending on the quality and dimension of the input data. The success of these first steps may be used to develop similar methods for more challenging and fully turbulent wakes, and also can serve as a guide for data-driven methods that require no prior knowledge of the flow structure.

Automated summary

This study investigates the wake characteristics behind a bluff body with a density gradient using dynamic mode decomposition (DMD) to find patterns for automated classification. The results show that the success of this method depends on the quality and dimension of input data, but the initial steps have achieved some level of success and can provide guidance for studying more complex turbulent wakes using data-driven methods.