Flowfield Investigation in a Non-Reacting Reverse Flow Isothermal Combustor

摘要

The non-reacting isothermal flow field of a reverse flow distributed combustor is examined here using high-speed particle image velocimetry (PIV). The focus of this study is to determine the flow field and turbulent stress for better mixture preparation under distributed combustion condition. High frequency data acquisition had little impact on mean velocity distribution but significantly impacted the fluctuating velocities and turbulent stresses. Reduction in oxygen concentration from increased dilution of the oxidizer resulted in enhanced velocity fluctuations to promote mixing. Additionally, shear strain and vorticity increased in the inlet stream that helped to promote mixing. Reynold's stress, indicative of the amount of turbulent mixing increased with increased dilution. High Reynold's stress occurred in the entrained flow regime that was formed between the inlet fresh air and exit gas stream. Turbulent kinetic energy, a measure of the energy distribution within the combustor, showed more spatially uniform behavior with increased dilution to the fresh reactant stream. The Kolomogorov and turbulence length scales were much different at low and high frequency data acquisition. The effect of data sampling rate using Fourier transform provided examination of the power spectral density of the axial and radial velocity components. High sampling rate of 3kHz (in contrast to low frequency sampling) provided a better representation on actual contributions to velocity fluctuations present in the flow. These results provide clear role of high-speed data acquisition in particle image velocimetry on determining turbulence stresses present in the flow.