Development of Flow Analysis Tools using Information Theory to Understand Flow Instability
Abstract
Project Summary: Flow instability drives many of the operability issues found in Navy aviation technologies. For example, feedback between vortex shedding and shock-cell structure in supersonic jets drives screech. Additionally, coupling between vortex shedding and combustor acoustic modes drives thermoacoustic oscillations. Prediction of these instabilities can be difficult in flows with anylevel of complexity. Hydrodynamic instability theory, which can identify the unstable modes of a system and their modal characteristics, can be applied to a variety of flows. This theory allows us to predict mode frequencies, growth rates, and structural sensitivity, and provides mathematical insight into the instability modes and their mechanisms.However, flow complexity may make use of thistheory intractable. For example, flows with fluctuating density gradients like partially-premixed flames or highly three-dimensional flows are not well posed for the use of hydrodynamic instability analysis.Additionally, the data from flows that may be well-suited for instability analysis is often incomplete or highly noisy due to limitations in optical diagnostics. In this work, we proposed to use methods from information theory to investigate the instability behaviors of complex flows. Measures of information content insignals from these flows such as mutual information and transfer entropy will be used to construct a general, multi-layer complex network representation of flow dynamics. This network representation will be interrogated to identify critical flow regions and othercharacteristics controlling flow dynamics.The proposed work includes four tasks. First, a suite of tools combining ideas from information theory and complex networks will be developed to understand flow instabilities and the spatio-temporal structure of critical regions that can influence their dynamics. Second, these tools will be tested on systems of two-dimensional multi-element flow fields, which are an ideal case study for these types of methods. By varying a few simple parameters in multi-element flows, including their number and spacing, we can create a wide variety of high dimensional flow behaviors that are still tractable to analyze using traditional stability analysis. Third, we will compare results obtained using stability analysis and the new information-based tools for these tractable flows to establish links between the results of the two families of methods. Finally, the new methods will be tested on more complex flows of Navy relevance, including swirling flows and twin jets to explain dynamics.The final outcomes of the work are twofold. First, this work will implement novel analysis methodologies combining complex networks and information theory for hydrodynamic instability in flows that can cause operability issues in Navy-relevant systems. These methods will be used to identify critical flow regions driving instabilities from time-resolved measurements and/or computations. This new capability will allow for fundamental understanding of driving mechanisms, their dependence on key operational parameters, and identification of interventionsthat can influence flow dynamics in critical regions and thus enable suppression of these dynamics. These methods will be applicable to all data, including highly complex flows and low-quality or noisy experimental data, which will provide insight into a range ofkey flow configurations. The fact that this tool development is done in conjunction with hydrodynamic stability analysis for tractable configurations will provide a rigorous theoretical basis for interpretation of the results and extension to complex cases where stability analysis is challenging. Second, these methods will be used to understand behaviors of several key families of flows, including multi-element flows, swirling flows, and twin jets, enhancing our fundamental understanding of canonical flows of Navy interest.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 09, 2024
- Source ID
- N629092412090
Entities
People
- Santosh Hemchandra
Organizations
- Office of Naval Research
- United States Navy