Research objective
To simulate and investigate the internal fuel-air mixing, combustion, and unsteady flow in a combustion-powered actuator that is being experimentally studied for control of stall on rotorcraft blades.

Approach
A critical element of this flow control approach is the development of a pulsed generation of momentary, small-scale, high-speed jet with sufficient impulse to affect the advection of vorticity in the external cross flow. Gaseous fuel (Hydrogen) and air are injected from opposing ends within a miniature [O(1 cm3)] combustion chamber, and the mixture is ignited to yield [O(1 ms)] high pressure burst and the ejection of a high-speed exhaust jet. Computational prediction requires proper modeling of the geometry (including the opening and closing of the injection ports), the intense turbulent mixing, and the subsequent combustion process and exhaust.

Accomplishment Description
A large-eddy simulation approach with a subgrid kinetic energy closure is used to study the cyclic process in the COMPACT actuator. The injection, turbulent mixing, combustion and scavenging processes are all simulated with a highly parallel MPI based finite-volume solver running on RTJones. The cycle-to-cycle variability, and mixing and combustion efficiency have been studied for a set of initial experimentally defined conditions.

Future Plans
A more sophisticated ignition process to mimic the experimental approach will be used to further evaluate performance sensitivity to flame kernel growth. The dynamics during injection and turbulent mixing, and during the scavenging process will be studied in more details to understand the impact of design changes, e.g., the fuel and air injector placement and injection strategy. Moreover, simplified model to carry out scaling studies for various design parameters (volume, F/A ratio, etc.) will be carried out. Eventually, comparisons with PIV data (being acquired) are planned.

POC: Suresh Menon