Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


47906.pdf (7.72 MB)

ETD Abstract Container

Abstract Header

Validation of Convective Wave-Based Reduced Order Model of Combustion Instabilities in a Lean Premixed Bluff Body Combustor

Ikwubuo, Melvin-Eddy
http://orcid.org/0009-0008-3937-4022
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1712916155178978

Abstract Details

2024, PhD, University of Cincinnati, Engineering and Applied Science: Aerospace Engineering.
A rigorous literature survey on combustion instability, acoustic modeling, dynamic flame modeling, and reduced-order modeling (ROM) was presented to acknowledge the difficulty of accurately predicting combustion instability for a lean, fully premixed combustor operating at speed beyond 5% of the speed of sound while producing significantly long flame. The objective is to validate the feasibility of predicting thermoacoustic instability using ROM for changes in boundary condition (exit blockage ratio) and flow rate on a combustor that produces a non-compact flame. A revised ROM was derived with convective flow rather than assuming stationary flow to predict combustion instability in the combustor that operates at a speed beyond 5% of the speed of sound. The structure of the ROM was revised to account for spatially distributed heat release rather than assuming a singular compact flame. A proposed end boundary condition model was used to improve the solution of the ROM. A bluff body combustor was tested to establish a combustor that can operate at speeds greater than 5% of the speed of sound. The bluff body combustor produced stable and unstable non-compact flame under the same flow condition (inlet mach number and equivalence ratio) as the combustor configuration changes (combustor length and blockage ratio). The stable flame combustor configuration is used for flame transfer function measurement. In contrast, the unstable flame combustor configuration is used for ROM prediction validation. The exit pressure reflection coefficients were measured for three different blockage ratios (69%, 56%, 0%) without combustion as the temperature, flow rate, and frequency change to validate the end boundary model proposed in the literature. The model used to characterize the acoustic exit boundary condition for the revised ROM was successfully validated using the multiple microphone method downstream of the bluff body flame holder. An inlet Mach number of 0.06-0.13 at an equivalence ratio of 0.85 produces an unstable flame that fluctuates between 185-280Hz. The same combustion flow condition produces a stable flame by changing the combustor length for each exit blockage ratio case. The Helmholtz number of the flame (He=k_unstable L_flame) ranges between 0.29 to 0.60, signifying a long flame. As the inlet Mach number increases, the instability frequency increases, regardless of combustor length or exit blockage ratio. The proposed ROM was able to predict instability frequencies for bluff body combustor within 5hz as the operating conditions change using Ikwubuo and Lee's exit acoustic boundary condition model and spatially distributed flame transfer function with respect to the flame length. However, the traditional ROM could not accurately predict the instability frequencies but was able to map a similar trend of the instability frequencies as the flow operating condition changes. The traditionally theoretical acoustic boundary conditions or traditional ROM overpredict the frequency. Using a global flame transfer function in ROM can significantly wayward the model's frequency prediction when the flame length exceeds 21% of the combustor domain. Flame length exceeding 21% of the combustor domain requires multiple flame segments to maintain frequency prediction accuracy. Based on the outcome of the two ROMs shown in the paper and the effects of the flame segments, there is significant evidence that suggests the instability frequency for the short combustor case is influenced by the changes in flame length.
Jongguen Lee, Ph.D. (Committee Chair)
Kwanwoo Kim, Ph.D. (Committee Member)
Paul Orkwis, Ph.D. (Committee Member)
Prashant Khare, Ph.D. (Committee Member)
142 p.
Aerospace Materials
Combustion Dynamic; Flame Transfer Function; Orifice; Aeroacoustics; Reduced Order Model; Thermoacoustic Instability

Recommended Citations

Citations

  • Ikwubuo, M.-E. (2024). Validation of Convective Wave-Based Reduced Order Model of Combustion Instabilities in a Lean Premixed Bluff Body Combustor [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1712916155178978

    APA Style (7th edition)

  • Ikwubuo, Melvin-Eddy. Validation of Convective Wave-Based Reduced Order Model of Combustion Instabilities in a Lean Premixed Bluff Body Combustor. 2024. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1712916155178978.

    MLA Style (8th edition)

  • Ikwubuo, Melvin-Eddy. "Validation of Convective Wave-Based Reduced Order Model of Combustion Instabilities in a Lean Premixed Bluff Body Combustor." Doctoral dissertation, University of Cincinnati, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1712916155178978

    Chicago Manual of Style (17th edition)

ucin1712916155178978
28
© 2024, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.