Laser velocimeter measurements in a dump combustor

The mean velocity and turbulence intensity of isothermal and reacting highly turbulent flows following a sudden pipe expansion are measured experimentally by laser Doppler velocimetry (LDV). The flow system comprises a 3.032-mm-diameter steel inlet section with gaseous-propane injectors and torch igniter, a 609-mm-long, 152.34-mm-diameter fused-quartz downstream section, and a radial blower with DOP and Al2O3 seeders. A one-component LDV system is operated in dual-beam forward-scattering mode with a net frequency shift of 10 MHz. The results are presented graphically and analyzed. While the peak normalized turbulence is found to be 22 percent in both cool and hot flows, the local turbulence intensities in the hot flow are typically 40-60 percent of the cold-flow values, indicating that combustion suppresses turbulence away from the shear layer. The velocity-bias effect on the LDV measurements is also evaluated and found to be significant, confirming the findings of Roesler et al. (1980) and Stevenson el al. (1982).