Combined PIV and DGV applied in a combustion facility

Kurzfassung

Whole field velocity information obtained from combustion test facilities is of special interest to the numerical computation community as it permits validation of advanced simulation methods. Both particle image velocimetry (PIV) and Doppler global velocimetry (DGV) currently are the most suited candidates for efficiently providing this sort of data at a reasonably high spatial resolution. Recent efforts have successfully qualified DGV for use in reactive flows using a specially designed frequency-stabilized laser. However, in order to obtain three-component velocity data with DGV typically four optical access ports are required to achieve at least three light sheet – camera viewing angles. A combination of DGV with PIV is very attractive as only two access ports are required: one for the light sheet, the other for the receiving optics camera(s). While PIV provides the in-plane velocity component, the frequency shifts measured by DGV can be used to estimate the out-of-plane velocity component given knowledge of the PIV components. The combined technique was recently applied to investigate the mixing zone of a single sector combustor rig at pressures at 2 and 10 bar. Optical access to the mixing zone was only possible through two opposing windows as well as through narrow windows at the downstream end of the combustor. Once the applied arrangement was set up the entire combustor test rig could be traversed in all three coordinates to allow a convenient volumetric mapping of the combustor’s flow field. The final volumetric data sets consist of 41 individual planes spaced at 2 mm increments. The in-plane spatial resolution is about 1.2 x 1.2 mm₂. The accumulation of the solid particulate seeding during the measurements led to continuous deterioration of both the PIV and DGV signals such that the measurement uncertainties increased from typically 1-2 m/s to the order of 3-5 m/s. Preliminary analysis of the volumetric data sets already show the influence of the mixing jets in the secondary zone on the global flow field.