This study examined the conditions under which excitation of a single jet will enhance the mixing between many jets of different fluids. The experimental apparatus consisted of three colinear, parallel, turbulent air jets. Information on fluids mixing was obtained with planar laser induced fluorescence measurements, and the velocity field with a hot wire anemometer. Coupling, resulting in enhanced mixing between adjacent jets, was observed. The effect of the separation between adjacent jets and the effect of the excitation magnitude were examined. Increasing the separation between the jets in the range from 2.2 to 3.2 diameters adversely effected the mixing between the jets, but even at the widest separation tested, the improvement in the side jets over the unexcited case was greater than 10 percent after 10 diameters downstream. The magnitude of the excitation to the central jet was varied between zero and 38 percent of the centerline flow velocity at the jet exit. The effect of increasing magnitude appears to saturate around 25 percent, both in the forced central jet and the unforced side jets. Centerline concentrations in the side jets are 50 percent lower than in the unexcited case. (Author) ABSTRACTThe present work, where only few out of several fluid streams are excited, while the remaining couple with that excitation, was motivated by the recognition of the virtues of active flow excitation while keeping in mind the industry desire to minimize complication and moving parts. This study, therefore, examined the conditions under which excitation of a single jet will enhance the mixing between many jets of different fluids.The experimental apparatus consisted of 3 co-linear, parallel, turbulent air jets. Information on fluids mixing was obtained with Planar Laser Induced Fluorescence (PLIF) measurements, and the velocity field with a hot wire anemometer.Coupling, resulting in enhanced mixing between adjacent jets, was observed. The effect of the separation between adjacent jets and the effect of the excitation magnitude were examined.Increasing the separation between the jets in the range from 2.2 to 3.2 diameters adversely effected the mixing between the jets, but even at the widest separation tested the improvement in the side jets over the unexcited case was greater than 10% after 10 diameters downstream. The magnitude of the excitation to the central jet was varied between zero and 38% of the centerline flow velocity at the jet exit. The effect of increasing magnitude appears to saturate around 25%, both in the forced central jet and the unforced side jets. Centerline concentrations in the side jets are 50% lower than in the unexcited case. BACKGROUND

Solid and molten ash particles from coal derived syngas in the hot gas path can deposit on and erode turbine blade surfaces causing issues with performance that potentially could result in failure. Conducting experiments at the firing temperatures of actual turbine engines (∼ 1500 K) is difficult, so an experimental method of substituting the ash particles for particles with a lower melting temperature is presented. This allows particle deposition tests to be run at more reasonable laboratory conditions. To fully simulate ash deposition, dynamic similitude was used to design a lower-temperature experiment with using PVC and Teflon particles with an average size of 24 and 6 microns respectively. The carrier flow, air, varies over a temperature range of 350–475 K, and the deposition surface varies over a temperature range of 400–475 K. The data and geometry from other experiments were also scaled and compared directly to the results of the current study. The deposition surface was a polished flat plate angled 45° normal to the flow. Initial observations indicate trends with PVC and Teflon particles in the scaled experiment agree with that of coal ash. Observed trends were an increase in capture efficiency with fluid temperature and decrease in capture efficiency as the deposition surface temperature is lowered. Capture efficiencies are all in the range of 0.5–10%. Further tests will be conducted using this scaling method with PVC particles on leading edge geometry with film cooling.

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A detailed examination of the coupling observed between adjacent turbulent jets, one of which was externally excited, is presented. The study is relevant to the active control of combustion and mixing devices; applications which demand maximum reliability and minimal power consumption by their active elements. To this end, it is desirable for each active component to affect several simple, non-active components in the system. An initial study of three collinear turbulent air jets was seen to enhance the mixing of adjacent, unforced jets with ambient fluid by 15–20%. The work presented here examines this phenomena using quantitative PLIF mixing measurements, three component and single-wire velocity measurements, qualitative flow visualization, and reduced singular value decomposition (SVD). This analysis of the data shows that the mixing improvement in the adjacent, unforced jets is primarily due to the low level perturbation at the exit of the unforced jets induced by the periodic forcing in the active center jet. This improved mixing is shown to be a result of amplification of the +/-1 spatial mode. Large scale structures in the central, forced jet are shown not to effect the behavior of the adjacent jets.