Development of Flow Analysis Tools using Information Theory to Understand Flow Instability
Overview
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 any level 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 this theory 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 in signals 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 other characteristics controlling flow dynamics.
Funded by the Office of Naval Research.
In collaboration with Dr. Santosh Hemchandra, Indian Institute of Science – Bangalore
Swirling Flow Dynamics
Overview
Gas turbines are used every day, from power generation applications to jet engines. Modern day gas turbines face an increasing demand to reduce pollutant gas emissions, such as CO2 and NOx. To meet this challenge, many gas turbines use a lean premixed combustion process in which air and fuel are mixed upstream of the combustion chamber. Premixed systems are very effective at reducing emissions, but they present a problem during combustion: combustion instability. Combustion instability is caused by the coupling between combustor acoustics and flame heat release fluctuations. It can result in increased emissions, reduced hardware life, and catastrophic turbine failure. Flames in gas turbines are stabilized by use of a swirling flow field. A swirling flow field has many complex fluid-mechanical properties that directly influence combustion instability events. Namely, the velocity coupling mechanism that links the shear layer fluctuations of a swirling flow to combustor acoustic perturbations is key to understanding combustion instability in gas turbines.
The goal of this research is to explore the fundamental physics of swirling flows in order to understand the mechanisms by which velocity fluctuations are impacted by combustor acoustics. This knowledge will allow for the design of flow fields that mitigate and even prevent combustion instability events. Various experimental and analytical techniques are used, such as particle image velocimetry, pressure diagnostics, proper orthogonal decomposition, dynamic mode decomposition, and linear stability analysis.
In collaboration with Dr. Santosh Hemchandra, Indian Institute of Science – Bangalore
Publications
Manoharan, K., Frederick, M., Clees, S., O’Connor, J., Hemchandra, S., (2020) “A weakly nonlinear analysis of the precessing vortex core oscillation in a variable swirl turbulent round jet,” Journal of Fluid Mechanics, 884, p. A29. Accepted author pre-print available here.
Mason, D., Clees, S., Frederick, M., O’Connor, J., (2019) “The effects of exit boundary condition on precessing vortex core dynamics,” ASME Turbo Expo, Phoenix, AZ. Accepted author pre-print available here.
Clees, S., Lewalle, J., Frederick, M., O’Connor, J., (2018) “Vortex core dynamics in a swirling jet near vortex breakdown,” AIAA SciTech. Kissimmee, FL. Accepted author pre-print available here.
Frederick, M., Manoharan, K., Dudash, J., Brubaker, B., Hemchandra, S., O’Connor, J., (2018) “Impact of Precessing Vortex Core Dynamics on Shear Layer Response in a Swirling Jet,” Journal of Engineering for Gas Turbines and Power, 140(6), 061503. Accepted author pre-print available here.
O’Connor, J. (2017) “Disturbance Field Decomposition in a Transversely Forced Swirl Flow and Flame.” Journal of Propulsion and Power, 33(3), p. 750-763. Accepted author pre-print available here.
Mathews, B., Hansford, S., O’Connor, J. (2016) “Impact of Swirling Flow Structure on Shear Layer Vorticity Fluctuation Mechanisms,” ASME Turbo Expo, Seoul, South Korea. Accepted author pre-print available here.
O’Connor, J. (2015) “Visualization of Shear Layer Dynamics in a Transversely Forced Flow and Flame“ Journal of Propulsion and Power, 32(4), p. 1127-1136. Accepted author pre-print available here.
Hansford, S., Manoharan, K., Hemchandra, S., O’Connor, J. (2015) “Impact of flow non-axisymmetry on swirling flow dynamics and receptivity to acoustics,” in ASME Turbo Expo, Montreal, Canada. Accepted author pre-print available here.
Manoharan, K., Hansford, S., O’Connor, J., Hemchandra, S. (2015) “Instability mechanism in a swirl flow combustor: Precession of vortex core and influence of density gradient,” in ASME Turbo Expo, Montreal, Canada.
Interacting Flows
Overview
While the hydrodynamic stability characteristics of unit flows, like jets and wakes, have been studied extensively, the impact of flow interaction between unit flows on the hydrodynamic stability characteristics has not been explored. A limited number of studies have shown that flow interaction can change the stability characteristics of these flows. Recent work by the PI has investigated interacting wakes, where a single wake displays a global instability, referred to as the von Karman vortex street, as well as the Kelvin-Helmholtz shear layer instability. The interacting wakes, however, display very different dynamics, where the wake displays more intermittency and overall a more symmetric vortex shedding pattern. The three-wake system has several distinct features, including an extended region of K-H shear layer instability (as seen by the small-scale oscillations), and a more symmetric large-scale wake vortex shedding region downstream. Videos of the instantaneous velocity field also show that the three-wake system vortex shedding is more intermittent. These difference may indicate a change in the stability of the flow as a result of flow interaction. The goal of this work is to characterize the behavior of interacting flows, including wakes, in a quantitative manner.
Publications
Dorer, R., Meehan, M., O’Connor, J. (2023). “Investigation of Interacting Wake Instability using Complex Network Analysis.” AIAA SciTech Forum, National Harbor, MD. Accepted author pre-print here.
Dare, T. P., Berger, Z. P., Meehan, M., O’Connor, J. (2019). “Cluster-Based Reduced-Order Modeling to Capture Intermittent Dynamics of Interacting Wakes,” AIAA Journal, 57(7), p. 2819-2827. Accepted author pre-print available here.
Sebastian, J., Emerson, B., O’Connor, J., Lieuwen, T., (2018) “Spatio-temporal stability analysis of linear arrays of 2D density stratified wakes and jets,” Physics of Fluids, 30(11), P. 114103. Accepted author pre-print available here.
Meehan, M., Tyagi, A., O’Connor, J., (2018) “Flow dynamics in a variable-spacing, three bluff-body flowfield,” Physics of Fluids, 30, 025105. Accepted author pre-print available here and supplementary material.
Dare, T., Berger, Z., Meehan, M., O’Connor, J., (2018) “Cluster-based reduced-order modeling to capture intermittent dynamics of interacting wakes,” AIAA SciTech. Kissimmee, FL. Accepted author pre-print available here.