RESEARCH

Our Vision

As more and more computational resources become available to everyday research, physics-based high-fidelity models play increasingly vital roles in energy and propulsion research. CTF@UConn is interested in the general research areas of efficient energy utilization and propulsion solutions, with emphasis on developing high-fidelity modeling techniques to fundamental laboratory-scale combustion, device-relevant deflagration and detonation, fire modeling and thermal radiation modeling.

With recent development in computational power and experimental apparatus, the ability of experimental research and computational studies are converging. Computational analysis and experimental investigation can complement each other in many different aspects. CTF@UConn is actively pursuing the change of paradigm in model validation and data assimilation for computational models.

The detailed data from high-fidelity models provide insight into the physical process, which will in turn inspire proposal of theoretical models. CTF@UConn is aiming at advancing the theories of reacting flow in the long run.

Heat Transfer in gas turbine relevant conditions

Heat transfer to the wall is a significant contributor to gas turbine and internal combustion engine efficiency and durability. However, understanding of the magnitude and characteristics of radiative heat transfer is still lacking, due to challenges in measuring and modeling radiation in complex combustors. CTF@UConn has been working on assessing and modeling radiation within realistic gas turbine combustors since 2020, leveraging the line-by-line capability of our in-hour Monte Carlo ray tracing radiation solver and advanced turbulent combustion modeling capabilities. Through detailed modeling, we have identified the importance of radiative redistribution within the combustor and identified key species contributing to the redistribution and to the wall. We have since developed radiation solvers for capturing radiation within thermal barrier coatings, considering the particular spectral window of the materials. Related softwares can be found in the Codes page.

Our latest effort on understanding the role of radiative versus convective heat transfer in wall-confined geometries is demonstrate below. In collaboration with experimental partners at Penn State University, a backward-facing step combustor is modeled using wall-resolved LES. Radiation data are extracted accounting for facility reality (spectral window of sapphire windows, field of view limitation). Good agreement with experiment is achieved, where we show that radiation is at least comparable to convection, downstream the impingement point.

This research direction has been funded by ONR, RTRC, and Pratt&Whitney since 2020.

Transient OH mass fraction iso-surface characterizing flame front for 5 flow through times for the backward-facing step combustor. Credit: Jonathan Denman.

Transient OH mass fraction contour showing flame surface 1mm below step height in xz-plane. Credit: Jonathan Denman

Local and global extinction in turbulent combustion

Turbulent combustion is encountered in nearly all practical power generation devices, e.g., gas turbines, internal combustion engines, and industrial furnaces. With increasingly stringent emission control and demand for efficiency enhancement, turbulent flames that are burning in mixed modes and near limit become more and more common. Computational modeling as an efficient design and testing tool is frequently used nowadays to study the fundamental behaviors of the flames, and to help shorten the design cycle. Models that are not specific to any combustion regime are desirous and are developed in CTF@UConn. The objective of these projects is to develop high-fidelity efficient computational tools that can better predict local flame phenomenon (local extinction, reignition, premixed flame fronts, etc. ) that are closely related to global catastrophic events such as blow off.

The research direction has been financially supported by ACS PRF and AFOSR over the past 10 years.

A swirling flame from the Cambridge bluff-body stabilized burner is modeled using a LES/transported-PDF approach. Very good agreement with experiment is achieved, where local extinction is captured. Credit: Hasret Turkeri.

Lean blowoff of a bluff-body stabilized premixed propane/air flame is simulated using well-resolved LES with finite-rate chemistry. The blowoff process was captured by the simulation, indicating a two-stage blowoff phenomenon. Results are compared with experimental measurements from Dr. Baki Cetegen’s group, and good agreement in terms of flame surface statistics and time-to-blowoff with experiment is achieved. Credit: Bifen Wu.

Direct numerical simulations of methane/air flame kernels are conducted to determine the critical laminar flame properties that are critical for turbulent flame extinction. The study is designed to test hypotheses that local and global extinction in turbulent flames are controlled by these two canonical flame properties: the laminar flame speed and extinction strain rate. Reduction of total heat release rates and surface areas are quantified to distinguish the roles of volumetric burning versus surface burning. The displacement speed, which is connected to the laminar flame speed, is identified to be the more controlling canonical property in determining the probability of global extinction, although the flame is the broken flames regime. Credit: Patrick Meagher.

Detonation: fundamental and application

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Multiphase combustion

Multiphase transport and reactions are encountered in many practical combustion systems, such as in spray and coal combustion, in soot emission, and in flame synthesis for batch nano-material productions, etc.. Accurate predictions of the locations of different phases, heat and mass transfer for each phase, and the coupling between different phases are required to provide insights into these processes. The objective of these projects are to improve modeling accuracy based on theory and high-fidelity simulations, carry out comprehensive simulations for laboratory-scale/industrial-scale multiphase flow, and provide insights into the combustion (synthesis) process.

Fire research

Large-scale fires (wildland fire, forest fire, warehouse fire, large fuel spill pool fire, etc.) are major causes for property and human loss. CTF@UConn is working on developing accurate and efficient radiation models for fire simulations. The role of radiative heat transfer in fire propagation and the interactions between turbulence, chemistry, soot and radiation are emphasized.

Direct numerical simulation was conducted for a small (4kW) heptane pool fire. Good agreement with experiment is achieved. The abundant data were analyzed to study radiation characteristics, soot/gas interactions, and turbulence-radiation interactions. Credit: Bifen Wu.

FM Visitor day: A group of UConn students visited the research campus of FM, a long term collaborator, in 2018. The video demonstrates the importance of having sprinklers in residential homes. (Left room: with sprinklers. Right room: without sprinklers). This photo shows the onset of fire before sprinkler is activated. Credit: Joseph Squeo.

Interplay between experiments and computations

CTF@UCONN is working on using direct numerical simulation and experimental measurements to evaluate experimental procedures (spatial and temporal resolution, post-processing models, etc.). CTF@UCONN is also actively pursuing direct comparison between numerical prediction and experimental signals, in order to reduce the uncertainty involved in the signal conversion and data processing procedures.