Adverse pressure gradient flows and their influence on boundary layer flashback

Adverse pressure gradient flows and their influence on boundary layer flashback

Penmathsa, Akhil (TU Delft Mechanical, Maritime and Materials Engineering)

Klein, S.A. (mentor)
Pecnik, R. (mentor)

Delft University of Technology

2021-01-25

Flame flashback is a failure mode in the operation of lean premixed combustion system. Due to higher flame speeds and lower quenching distances, hydrogen-rich fuel mixtures are prone to boundary layer flashback (BLF), where mixture flow speeds are low compared to the local flow velocity. Research at TU Munich (Eichler 2011) has resulted in new insights into the mechanism of BLF in confined geometries, revealing a strong interaction between the incoming flowfield and the flame. BLF occurs due to flow separation in confined geometries. Studies from Gruber (2012) also confirmed this effect and it was hypothesized that Darrieus Landau (DL) instability can cause the flow separation. Studies from TU Munich also showed increased flashback propensity in the presence of adverse pressure gradient. In this thesis, detailed study of the flow structure in the diffuser is performed. LES simulations are performed for the channel and diffuser and are validated with the results from the literature. First a comparison of subgrid scale models is performed for the channel case. Then, a detailed study of the time resolved structure for the channel and diffuser is performed with the two point correlations and cumulative distribution functions of instantaneous velocity. It has been observed that the turbulent structures are shorter in the diffuser compared to the channel. Then, the relevance of DL instability is investigated in the channel and diffuser geometries. It has been found that DL instability is more prevalent in the diffuser due to decrease in the turbulent frequencies. Together these effects could be the reason for the increased flashback propensity observed in adverse pressure gradient flows.

Gas Turbines
Hydrogen
Combustion Instability
Large Eddy Simulation
Boundary layer flashback

http://resolver.tudelft.nl/uuid:968bb3f5-0378-4872-9d05-cb0ec4fc629a

Student theses

master thesis

© 2021 Akhil Penmathsa