Combustion chambers are naturally prone to acoustic instabilities that originate from flame propagation. Passive devices such as combustor chamber baffles, resonators, and injection liners have proven to attenuate acoustic instabilities degradate the integrity of engine components. Acoustic energy viscous dissipation effects are measured and quantified for new designs and arrangements implemented in tested suppression devices. Two passive suppression devices are introduced which exhibit new baffle arrangement and combustion liner design. Audio acoustic equipment excites chamber acoustic instabilities and microphones receive acoustic pressure wave amplitudes. Using this technique viscous damping effects from acoustic sound waves are measured in un-reacting static and flow conditions. An extensive study on damping enhancements to tangential acoustic mode instabilities was explored. A baffle insert was designed with staggered offset injector baffle blades to evaluate viscous damping effects on tangential acoustic instabilities. Tangential acoustic wave energy dissipation is characterized through decay rates measurements. It was concluded that a staggered offset baffle blades with a constant outer versus inner varying injector exhibits the highest attenuation rate. Changes to baffle blades shows a 2T mode experiences the greatest damping enhancement. An empirical expression is derived from curve fitting decay rates for tangential modes and demonstrates acoustic behavior to follow a non-linear correlation. A new auxetic s-shape structure is incorporated into a combustion liner that was coupled with a Helmholtz resonator. The investigation focuses on viscous damping acoustic effects comparing circles to auxetic designs within grazing and bias flow conditions. A series of experiments were conducted that characterized flow discharge behavior, acoustic impedance, acoustic rig that couples bias and grazing flow. Auxetic designs display enhanced absorption qualities at high frequency bandwidths compared to traditional circles. S-shapes with a 60° injection angle demonstrates superior viscous damping absorption characteristics. A higher differential pressure highlights a reduction in absorption coefficient measurements.


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Graduation Date





Ahmed, Kareem


Doctor of Philosophy (Ph.D.)


College of Engineering and Computer Science


Mechanical and Aerospace Engineering

Degree Program

Mechanical Engineering









Release Date

August 2024

Length of Campus-only Access

5 years

Access Status

Doctoral Dissertation (Campus-only Access)

Restricted to the UCF community until August 2024; it will then be open access.