The primary objective of this study is to provide an analytical comparison between CFD and experimental efforts of non-reacting flows from a 7-point lean direct injector (LDI) array. Previous work has been completed to conduct a parametric study of the 7-point LDI to understand the effects of air swirler angle, air swirler direction (clockwise or counter-clockwise), and center element offset. Part of the parametric study involved observing the effects on velocity flow fields with particular investigations on central recirculation zone (CRZ) formation. Several different 7-point configurations were experimentally tested. Two of those configurations included 1) the baseline 60˚ co-rotating swirlers on all 7 elements and 2) a 60˚ center swirler with six co-rotating 52˚ outer swirlers. Numerical results of these two configurations were also carried out using NASA’s multi-dimensional unsteady flow solver (OpenNCC), which is the publicly releasable version of the National Combustion Code (NCC). This paper aims to compare the numerical and experimental results of these two particular configurations in order to prove the fidelity of the computational model as well as confirm the experimental findings.

Studies of velocity flow fields were experimentally collected through particle image velocimetry (PIV) using water-seeded spray through the center nozzle. Past studies on the baseline configuration, co-rotating 60˚ swirlers, of the 7-point LDI have shown recirculation zones downstream of each of the 7 elements. However, the volume and magnitude of axial velocities within the central recirculation zone on the outer elements were found to be much greater than that of the center element recirculation zone. Since the individual elements are closely arranged together, the center element was found to be strongly influenced by the six outer elements thus leading to a smaller center element recirculation zone. Cold-flow results from OpenNCC showed qualitatively similar results in that a recirculation zone was formed on each of the 7 elements. A significantly smaller and weaker center element recirculation zone relative to the outer swirlers was found from the OpenNCC results and further corroborates the experimental measurements.

A second configuration of the 60˚ center elements with co-rotating 52˚ outer swirlers was investigated both experimentally and numerically as well. The velocity flow fields from the experimental results showed a central recirculation zone formed downstream of the 60˚ swirler and no recirculation zones on any of the 52˚ outer swirlers. Besides the number of central recirculation zones present, the other unique feature to this configuration was the shape of the center swirler CRZ. Unlike the baseline 60˚ configuration, the center element in the counter-rotating configuration displayed a CRZ with a narrow tail that extended considerably further downstream. Cold-flow numerical results from OpenNCC have confirmed similar qualitative velocity flow fields, including the characteristically tail-like CRZ.

Further analysis will include detailed quantitative comparisons of velocity profiles along the PIV and axial planes as well as discussions on comparing the size and strength of CRZs. Such discussions will enable better understanding of non-reacting flow structures and how that may affect turbulent fuel-air mixing for this particular LDI hardware design.


Experimental and Numerical Comparison of Non-Reacting Flow Formation From a 7-Point Lean Direct Injector Array

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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