Into the Lab: Aerospace Engineering

01 majJoseph Majdalani, Auburn Alumni Engineering Council endowed professor and chair of aerospace engineering, and Joshua Batterson, assistant professor of aerospace engineering, are studying the oscillatory behavior and vibratory response, known as combustion instability, of chemical rockets, gas turbines and large combustors.

These researchers are investigating the behavior of resonant combustion modes and acoustic instabilities which are known to appear suddenly and inexplicably in combustion devices under otherwise normal operating conditions. The corresponding acoustic instabilities arise due to a natural coupling between chamber acoustics and thermal energy. In many cases involving chemical propulsion and power generation devices (which are constantly driven toward high efficiency and low emission margins), the resulting instabilities materialize as large amplitude limit cycle oscillations in the flow variables.

Including efficiency, combustion stability remains the most important aspect to evaluate by new engine designers. In the past four decades, these uncontrolled oscillations have become the leading cause of new rocket program cancellations. For this reason, acoustic and stability engineers are among the most sought after in the aerospace community. Majdalani and Batterson have focused their research on creating a comprehensive stability algorithm that can be used as a diagnostic tool in the developmental stages of these combustors. Their newly constructed approach is based on the latest technological advances that suggest incorporating the effects of acoustical, hydrodynamic, thermal, and vortical waves into the energy balance equation.

Their representation is expected to enhance the accuracy of both linear and nonlinear stability equations adopted by various industries. Moreover, their gains in acoustic energy help to explain experimental findings that elude stability assessment codes in use today. Finally, their work helps to explain the origins of injection-driven instabilities observed in solid, liquid and hybrid rocket motors.

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