Research Symposium Series: Tejas Pant, Animesh Sharma, & Tristan Fuller
|Event Date:||March 26, 2018|
|Hosted By:||Aero Assist
|School or Program:||Aeronautics and Astronautics
Study of two-way coupling between transient flame dynamics and thermo-acoustic instabilities in a self-excited model rocket combustor
Combustion instabilities in high-speed propulsion devices such as gas turbines and rocket engines result from pressure waves with very large amplitudes propagating back and forth in the combustion chamber. Exposure to the pressure fluctuations over a long period of time can lead to a cataclysmic failure of engines. The underlying physics governing the generation of combustion instabilities is a complex coupling among a number of unit physics like heat release, chemical kinetics, turbulence and acoustic waves. Currently, it is very difficult to accurately predict the expected level of oscillations in a combustor. Hence development of strategies and engineering solutions to mitigate combustion instabilities is an active area of research in both academia and industry. In this study, we carry out numerical modeling of combustion instabilities in a self-excited, laboratory scale, model rocket combustor developed at Purdue University for a stable and an unstable operating condition using the popular turbulent combustion model, the flamelet model. The steady flamelet model (SFL) model and the flamelet/progress variable (FPV) model are used in this study. For the stable operating condition, the performance of the SFL model and the FPV model is quite similar in terms of predictions of pressure fluctuation. For the unstable operating condition, the predictions of both the models are widely different. It is demonstrated that this difference is mainly due to a two-way coupling between transient flame dynamics like flame extinction reignition, ignition delay and combustion instabilities.
Measuring number of electrons in plasma filament produced by ultra-fast laser pulse through elastic scattering of microwaves
Focusing laser pulses in gaseous medium results in ionization of the gas around the focal region thereby producing a filament of plasma. This ionization of gaseous medium is a highly non linear process having exponential dependence on laser intensity. Multiphoton ionization (MPI) is a fundamental first step in high-energy laser-matter interaction and is important for understanding the mechanism of plasma formation. Elastic Microwave Scattering allows us to directly measure the number of electron produced in the plasma filament and determine the fundamental coefficients of the ionization process such as cross-sections and ionization rates. Here we have report first direct measurement of absolute plasma electron numbers generated at multi-photon ionization of air and subsequently we precisely determined cross-section of eight-photon ionization of oxygen molecule by 800 nm photons σ8 = (3.30.3) 10-130 W-8m16s-1. MPI of O2, N2 and Ar was studied at standard atmospheric pressure and temperature. We found that ionization rate of O2 is much greater than that of N2. We observed that ionization rate and cross-section is same for N2 and Ar. Elastic Microwave scattering technique established a general approach to directly measure and tabulate basic constants of MPI process for various gases and photon energies.
Model validation of a thermoacoustically self-excited rocket combustor
Combustion instabilities experienced in rocket development programs are expensive and detrimental to progress. To provide a robust and faster approach toward developing rocket engines, computer simulated models (CFD) validated by experimental measurements are required to enhance understanding of this complex coupled problem. A rocket combustor operating with an oxidizer rich staged combustion cycle at 12 bar with methane and oxygen was developed to provide high-fidelity data for model validation. The experiment is designed with well characterized flow, wall, and acoustic boundary conditions to enable direct comparison with simulations. Measurements of pressure and chemiluminescence radiation (photomultiplier tubes) were taken with high temporal and spatial resolution. The combustor presents self-excited longitudinal combustion instabilities and the spatio-temporally resolved measurements show clear evidence of combustion response enhanced by complex mixing and flame stabilization processes described by the simulation. Significant variations in the instability behavior is observed by changing the oxidizer temperature from 440 K to 730 K, accentuating longitudinal instability modes while damping bulk modes of the combustor. The simulation is able to match these trends as well as main periodic features of the experiment to within 2.5%. The dominant physics described by the simulation have been reproduced in the experiment and thus the simulation has been validated.
What is the Research Symposium Series?
The Research Symposium Series is a department-sponsored forum for graduate students and advanced-level undergraduates to present their research to a general audience.
The Research Symposium Series is designed to:
- Facilitate the exchange of ideas and knowledge among faculty and graduate students.
- Provide opportunities for students to develop their technical presentation skills.
- Promote the research activities of the department to undergraduates and other interested individuals.
- $500, $300, $200 for best three presentations
- $150 for best undergraduate presentation
- $150 for best abstract
Questions about the Research Symposium Series may be directed to:
*Winners in the presentation category cannot compete in that category the following year. The same applies for winners in the abstract category.