Shear flows are commonly found within the combustors that are necessary in high-speed air breathing propulsion engines (gas turbines, ramjets & scramjets). These combustors require a fluidic mechanism to “anchor” the flame and various geometries have been employed to accomplish this, some include: backward facing steps, cavities and bluff bodies are some of the more common designs. While these create a recirculation zone that serves to use high temperature products to mix with and ignite the incoming reactants in order to maintain the constant combustion process, they also have various challenges. Understanding the performance of these steady pre-mixed, pre-vaporized combustors requires quantifying various metrics; compact design, stable, low drag and high turn-down ratios are some examples.
Quantifying the performance of these combustors is a challenge due to the reacting flowfield. In our laboratory we have studied the isothermal (non-reacting) behavior and the reacting flow behavior to further our understanding of these shear flows in a combustion application. Many combustors have been build and operated in order to leverage various control techniques. In addition to building and operating these combustors (run on various fuels), we have been able to take chemiluminescence measurements in order to understand thermal energy release and perform reacting PIV measurements in order to quantify the turbulence flowfield and determine instantaneous flame interfaces.
Suppressing combustor instabilities, minimizing drag losses and increasing the volumetric heat release over a variety of operating conditions is explored using a variety of control techniques. Various passive control techniques have been studied trying to mitigate the challenges including using enhanced counter-current shear, microjets and other geometric variations with the goal of creating compact and efficient combustor designs.
High-speed video of a themo-acoustic instability in a planer dump combustor
