DMD and POD of time-resolved schlieren on a multi-stream single expansion ramp nozzle

Berry, Matthew; Ali, Mohd Y.; Magstadt, Andrew; Glauser, Mark

doi:10.1016/j.ijheatfluidflow.2017.05.007

Cited by 27 publications

(8 citation statements)

References 7 publications

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“…been carried out on the time-resolved shadowgraph images to supplement the findings from the unsteady pressure measurements. The classic snapshot method of modal analysis has been adopted with the obtained shadowgraph images ( [31][32][33], [34], [35], [36]). The images have been pre-processed to remove anomalies from the parasite reflections from the glass window or the fluctuations in the utilized light source ( [37]).…”

Section: Measurement Methodologymentioning

confidence: 99%

Parametric experimental studies on the shock related unsteadiness in a hemispherical spiked body at supersonic flow

Sahoo,

Karthick,

Das

et al. 2019

Preprint

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Experimental studies are carried out to investigate the effects of the geometrical parameters with a drag reducing spike on a hemispherical forebody in a supersonic freestream of M ∞ = 2.0 at 0 • angle of attack. The spike length (l/D = 0.5, 1.0, 1.5, 2.0), spike stem diameter (d/D = 0.06, 0.12, 0.18), and spike tip shapes are varied and their influence on the time-averaged, and time-resolved flow field are examined. When l/D increases, a significant reduction in drag (c d ) is achieved at l/D = 1.5, whereas the variation in d/D has only a minor effect. The intensity of the shock-related unsteadiness is reduced with an increase in d/D to d/D = 0.18, whereas changes in l/D have a negligible effect. The effects of spike tip geometry are studied by replacing the sharp spike tip with a hemispherical one having three different base shapes (vertical base, circular base, and elliptical base). Hemispherical spike tip with a vertical base is performing better by reducing c d and flow unsteadiness. The dominant Spatio-temporal mode arising due to the shock-related unsteadiness is represented through modal analysis of time-resolved shadowgraph images and the findings are consistent with the other measurements.

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Section: Measurement Methodologymentioning

confidence: 99%

Parametric experimental studies on the shock related unsteadiness in a hemispherical spiked body at supersonic flow

Sahoo,

Karthick,

Das

et al. 2019

Preprint

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“…Experimental measurements of flowfield and acoustics as can be reviewed in numerous studies of Krothapalli et al [3], Henderson [16], Henderson et al [17], Sinibaldi et al [18], Alvi and Iyer [43], and Guariglia et al [55], to name a few. With the recent improvement in digital imaging cameras, high-speed schlieren is enable to acquire large datasets of time-resolved flowfield information (Berry et al [56]), although the measured quantities are scalars derived from density gradients (Berry et al [54]). The statistical dominant flow structures and dynamical evolution of large-scale flow structures can be extracted from the time-resolved schlieren images or from the time-resolved velocity fields obtained from large-eddy simulations using POD (Weightman et al [10], Berry et al [54], Nair et al [57], Berry et al [58], Weightman et al [59]), spectral POD (Karami and Soria [60]), and dynamic mode decomposition (DMD) (Berry et al [56]) techniques.…”

Section: Free Jetsmentioning

confidence: 99%

Effects of Nozzle Pressure Ratio and Nozzle-to-Plate Distance to Flowfield Characteristics of an Under-Expanded Jet Impinging on a Flat Surface

2019

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The current work experimentally investigates the flowfield characteristics of an under-expanded turbulent jet impinging on a solid surface for various nozzle-to-plate distances 2.46 D j , 1.64 D j , and 0.82 D j ( D j is the jet hydraulic diameter), and nozzle pressure ratios (NPRs) ranging from 2 to 2.77 . Planar particle image velocimetry (PIV) measurements were performed in the central plane of the test nozzle and near the impingement surface. From the obtained PIV velocity vector fields, flow characteristics of under-expanded impinging jets, such as mean velocity, root-mean-square fluctuating velocity, and Reynolds stress profiles, were computed. Comparisons of statistical profiles obtained from PIV velocity measurements were performed to study the effects of the impingement surface, nozzle-to-plate distances, and NPRs to the flow patterns. Finally, proper orthogonal decomposition (POD) analysis was applied to the velocity snapshots to reveal the statistically dominant flow structures in the impinging jet regions.

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“…analyses were performed on time-resolved shadowgraphs, and the extracted frequencies agreed remarkably well with those obtained using traditional microphone measurements made in the same study. Other studies that have applied POD upon time-resolved schlieren images of supersonic jets had also been reported in recent literature [108,144,145]. These studies share similar methodology in that the frequencies that were extracted were based on spectral analysis of the POD mode coefficients.…”

Section: Overviewmentioning

confidence: 92%

“…This allows useful information to be extracted from experimental or simulation data, and the most important and energetic structures that are dominant within the flow field can be identified and studied. There have been many successful applications of POD analysis in a wide variety of flow scenarios, such as flow past cylinders [100], turbulent jets [101][102][103][104][105], flow past backward-facing step [106], laminar separation bubble [107] and time-resolved schlieren images of a supersonic ramp nozzle [108].…”

Section: Proper Orthogonal Decompositionmentioning

confidence: 99%

“…While there have been many examples of POD applications in fluid mechanics studies, such as those associated with the vortex-shedding frequency of flow past a shallow cylinder[109], shear layer generated by a groyne in shallow flow[109] and in turbulent jets[101,102,147], applications of POD upon time-resolved schlieren images have only been reported in recent literature[108,[143][144][145]. To the best of the author's knowledge, schlieren-based POD methods for jet screech studies of circular bevelled nozzles remain relatively scarce.…”

mentioning

confidence: 99%

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Development of schlieren-image based flow diagnostics and analysis for supersonic jet flows

Lim¹

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The primary focus of this thesis is on the developments of image-based flow diagnostics for supersonic jet flow and noise control. Three different in-house techniques are presented: (1) 3D shock wave reconstruction technique based on schlieren imaging and visual hull concepts, (2) schlieren image velocimetry based on the optical flow algorithm (SIVOF), and (3) a data-driven approach to identify and characterize intermittent jet screech based on proper orthogonal decomposition (POD) of time-resolved schlieren images. The secondary focus is to provide experimental data and improve understanding on problems associated with the supersonic jet. To this end, the in-house techniques are applied in conjunction with conventional experimental techniques to Mach number 1.45 supersonic cold jets produced from convergent-divergent circular nozzles. In order to achieve flow and noise control,

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DMD and POD of time-resolved schlieren on a multi-stream single expansion ramp nozzle

Cited by 27 publications

References 7 publications

Parametric experimental studies on the shock related unsteadiness in a hemispherical spiked body at supersonic flow

Parametric experimental studies on the shock related unsteadiness in a hemispherical spiked body at supersonic flow

Effects of Nozzle Pressure Ratio and Nozzle-to-Plate Distance to Flowfield Characteristics of an Under-Expanded Jet Impinging on a Flat Surface

Development of schlieren-image based flow diagnostics and analysis for supersonic jet flows

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