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Tambe, Samir B.Liquid Jets Injected into Non-Uniform Crossflow
PhD, University of Cincinnati, 2010, Engineering : Aerospace Engineering

An experimental study has been conducted with liquid jets injected transversely into a crossflow to study the effect of non-uniformities in the crossflow velocity distribution to the jet behavior. Two different non-uniform crossflows were created during this work, a shear-laden crossflow and a swirling crossflow.

The shear-laden crossflow was generated by merging two independent, co-directional, parallel airstreams creating a shear mixing layer at the interface between them. The crossflow exhibited a quasi-linear velocity gradient across the height of the test chamber. By varying the velocities of the two airstreams, the sense and the slope of the crossflow velocity gradient could be changed. Particle Image Velocimetry (PIV) studies were conducted to characterize the crossflow. The parameter, UR, is defined as the ratio of the velocities of the two streams and governs the velocity gradient. A positive velocity gradient was observed for UR > 1 and a negative velocity gradient for UR < 1. PIV and Phase Doppler Particle Anemometry (PDPA) studies were conducted to study the penetration and atomization of 0.5 mm diameter water jets injected into this crossflow. The crossflow velocity gradient was observed to have a significant effect on jet penetration as well as the post breakup spray. For high UR (> 1), jet penetration increased and the Sauter Mean Diameter (SMD) distribution became more uniform. For low UR (< 1), low penetration, higher droplet velocities and better atomization were observed.

The second crossflow tested was a swirling flow generated using in-house designed axial swirlers. Three swirlers were used, with vane exit angles of 30°, 45° and 60°. Laser Doppler Velocimetry (LDV) was used to study the crossflow velocities. The axial and the tangential components of the crossflow velocity were observed to decrease with increasing radial distance away from the centerbody. The flow angle of the crossflow was smaller than the vane exit angle, with the difference increasing with the vane exit angle. Water jets were injected from a 0.5 mm diameter orifice located on a cylindrical centerbody. Multi-plane PIV measurements were conducted to study the penetration and droplet velocity distribution of the jets. The jets were observed to follow a path close to the helical trajectory of the crossflow with a flow angle slightly less than the crossflow. This deficit in flow angle is attributed to the centrifugal acceleration experienced by the jet. Mie-Scattering images obtained from PIV were used to recreate the jet plume and to obtain the jet trajectory for penetration analysis. In cylindrical coordinate system, the jet penetration can be described in terms of radial and “circumferential” penetration, where circumferential penetration relates to the difference in the circumferential displacement of the jet and the crossflow over the same streamwise displacement. Radial penetration increased with q while circumferential penetration increased with swirl angle. PIV results from cross-sectional and streamwise planes were combined to generate three-dimensional droplet velocity distribution throughout the jet plume. The three-dimensional velocity distribution yielded further insight into the evolution of the jet plume.

Committee:

San-Mou Jeng, PhD (Committee Chair); Milind Jog, PhD (Committee Member); Shaaban Abdallah, PhD (Committee Member); George Hsiao, PhD (Committee Member)

Subjects:

Aerospace Materials

Keywords:

jet in crossflow;liquid jet in crossflow;swirling flow;non-uniform crossflow;jet penetration

Sharma, Arvindh RLiquid Jet in Oscillating Crossflow: Characterization of Near-Field and Far-Field Spray Behavior
MS, University of Cincinnati, 2015, Engineering and Applied Science: Aerospace Engineering
An experimental investigation of response characteristics of a liquid jet in oscillating crossflow is undertaken to understand the behavior of a liquid fuel spray in the presence of combustion instabilities. The effect of crossflow oscillations on the liquid jet is studied in the near-field (within x/d˜8) and the far-field (x/d˜50) spray region. Experiments are conducted in bag breakup, multimode and shear breakup regimes by varying crossflow Weber number from 18 to 250, while momentum flux ratio is varied between 10 and 30. The crossflow is modulated in the frequency range of 90 Hz to 450 Hz, with modulation level varying between 5% and 20%, using a mechanical modulating device. High speed shadowgraph is employed to study the near-field and far-field spray movement while intensified high-speed camera images of laser Mie-scattering intensity are utilized in studying the spray cross-section in the far-field. A technique to extract time-varying momentum flux ratio from the windward trajectory of liquid jet in the near-field is developed. The response of near-field spray is quantified in terms of a ratio of the observed momentum flux ratio extracted from a correlation of upper penetration to the expected momentum flux ratio corresponding to the instantaneous crossflow velocity. The liquid jet penetration is found to respond to oscillations in the crossflow at all oscillation frequencies in the near-field. The strength of the response is found to be mainly dependent on the crossflow oscillation frequency, with the strength of response decreasing with increase in frequency. The momentum flux ratio and the modulation level are found to have relatively negligible effects on the level of normalized spray response. The spray response in the far-field is studied by observing the high-speed shadowgraphs and Mie-scattering intensity images at an axial distance of x/d=50. The spray field in the axial location is divided into ten bins and the intensity change in each bin is analyzed to quantify spray response. The spray is found to respond to crossflow oscillations by exhibiting a “flapping” behavior in the far-field. The binning method and Mie-scattering intensity image analysis suggest that the spray oscillation decreases with increasing crossflow frequency. The spray width and height fluctuate in the spray cross-section in the presence of crossflow oscillation. The amplitude of spray height fluctuation is higher in low frequency crossflow, and decreases with an increase in frequency. The total Mie-scattering intensity in the cross-section also exhibits a periodic response to crossflow oscillation, suggesting that the droplet characteristics are affected by crossflow fluctuation. The liquid spray near-field and far-field study indicates that the crossflow oscillation frequency plays a large role in determining spray response.

Committee:

Jongguen Lee, Ph.D. (Committee Chair); Milind Jog, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Jet in crossflow;Inlet air modulation;Oscillating crossflow;Liquid spray penetration;Near-field spray;Far-field spray;Aerospace Propulsion;Experimental Fluid Dynamics