Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session E10: Jets II |
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Chair: Mark Glauser, Syracuse University Room: 334 |
Sunday, November 24, 2013 4:45PM - 4:58PM |
E10.00001: Reduced-order modeling of wavepackets in controlled jets with corrugated profiles Aniruddha Sinha, Ali Uzun, Tim Colonius Reduced noise from high-speed turbulent jets has been achieved through passive and active devices distributed uniformly around the nozzle lip. These devices include chevrons as well as a spinning valve fluidic injection actuator that can deliver steady or harmonic excitation. On a time-averaged basis, all these actuators introduce corrugations in the mean shear layer, and our analysis shows that such corrugations give rise to new instability mechanisms in addition to the usual Kelvin-Helmholtz modes. We study these controlled jets using parallel-flow linear stability analysis, as well as the theory of linear parabolized stability equations (PSE) that accounts for mild streamwise variations of the mean flow. For unforced (round) subsonic and supersonic jets, PSE models have previously been shown to give accurate predictions for the large-scale coherent structures (wavepackets) educed from experimental data. We examine similar data for forced jets, as well as jets issuing from serrated nozzles, and seek to explain the observed modifications in wavepacket dynamics and the reduced noise radiation as changes in the instability characteristics of the corrugated mean flows. [Preview Abstract] |
Sunday, November 24, 2013 4:58PM - 5:11PM |
E10.00002: Towards High Speed Jet Noise Reduction Using Time-Resolved PIV Zachary Berger, Matthew Berry, Patrick Shea, Barry Kiel, Naibo Jiang, Bernd Noack, Sivaram Gogineni, Mark Glauser In this investigation, the flow field of a Mach 0.6 turbulent, compressible jet is studied using time-resolved particle image velocimetry (TRPIV). The hydrodynamics and acoustics are simultaneously sampled using pressure sensors in the near-field and microphones in the far-field, respectively. Two-component velocity measurements are taken in the streamwise plane of the jet, just before the collapse of the potential core. Several planes are obtained off of the jet's centerline, providing information across the entire nozzle and beyond the expanding shear layer. These measurements will provide a three-dimensional view of the flow field in the spanwise direction of the jet. Low-dimensional modeling tools are implemented to extract the energetic modes in the flow. In addition, correlations between the near-field velocity and the far-field acoustics are computed using similar techniques. These results will assist in identifying the structures and events in the near-field responsible for the far-field noise. The goal is to use the time-evolution of the flow field to identify these events both spatially as well as temporally. Ultimately, active flow control schemes will then be developed based on these findings. [Preview Abstract] |
Sunday, November 24, 2013 5:11PM - 5:24PM |
E10.00003: Analysis and comparison of non-axisymmetric and circular nozzle configurations of a high speed jet Matthew Berry, Barry Kiel, Zachary Berger, Naibo Jiang, Sivaram Gogineni, Mark Glauser The main focus of this experiment is on the analysis and comparison of different nozzle configurations of a high speed jet. We used 3 different non-axisymmetric nozzle designs placed in 7 different orientations as well as our standard 2 inch circular nozzle. The flow field was investigated at Mach 0.6 using two-component time-resolved PIV simultaneously sampled with far-field acoustic measurements. The velocity was examined in the streamwise direction of the r-z plane using 10 kHz TRPIV with a window size of about 5 inches. An array of 12 G.R.A.S. microphones were placed about 150 inches from the jet nozzle. Low-dimensional modeling was performed on the velocity data to extract and compare the structures associate with the different nozzle designs. The overall sound pressure level at several polar angles with respect to the jet axis was also compared. [Preview Abstract] |
Sunday, November 24, 2013 5:24PM - 5:37PM |
E10.00004: The influence of the density ratio on the linear frequency response of low-density jets Wilfried Coenen, Alejandro Sevilla, Lutz Lesshafft Low-density jets support global self-sustained oscillations when the jet-to-ambient density ratio is sufficiently small, a phenomenon that has been linked to the presence of a region of local absolute instability in the underlying parallel base flow. However, the use of local stability analysis requires introducing ad-hoc criteria to match the experimental observations (see Coenen \& Sevilla, J.~Fluid Mech.\ 713, 2012, and references therein). In this work we therefore use a global approach, where the wavepacket structures are temporal eigenmodes of the linearized equations of motion in a 2D domain. The resulting eigenvalue spectra show that, when the density ratio is decreased, a discrete eigenmode becomes increasingly dominant, eventually reaching a positive growth rate for a certain critical density ratio. For the particular case of a He/air jet, this critical density ratio, as well as the corresponding oscillation frequency, is in good quantitative agreement with the experiments of Hallberg \& Strykowski (J.~Fluid Mech.\ 569, 2006). The influence of the density ratio on the linear frequency response of the jet under globally stable conditions is also investigated. [Preview Abstract] |
Sunday, November 24, 2013 5:37PM - 5:50PM |
E10.00005: Structure of backward facing step flow in low Reynolds number controlled by synthetic jet array with different injection velocities Saneyuki Takano This study presents detailed structure of separated flow downstream of a backward facing step affected by a non-uniform periodic disturbance along spanwise direction induced by synthetic jet array. The Reynolds number based on the step height ranged from 300 to 900. The frequency of the synthetic jet actuation was selected within the acceptance frequency range of separating shear layer. The periodic disturbance generates periodic transverse vortices whose size and shape change corresponding to the strength of the disturbance. The effect of different injection velocities in the synthetic jet array from those of adjacent jets on the transverse vortex structure and resulting reattachment process is discussed based on the wall shear stress measured by the Micro Flow Sensor (MFS) and flow visualization. Near wall behavior of the transverse vortex above the MFS was related to the sensor output. The results show that non-uniform injection velocity manipulated in the jet array induces difference in the distorted vortex structure and reattachment process in spanwise direction, which strongly depend on the Reynolds number and injection velocities of the synthetic jets. [Preview Abstract] |
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