Shack-Hartmann Wavefront Measurements of Supersonic Turbulent Boundary Layers in the TGF

Smith, Adam E.; Gordeyev, Stanislav; Ahmed, Hamza; Ahmed, Anwar; Wittich, Donald J.; Paul, Michael

doi:10.2514/6.2014-2493

Cited by 15 publications

(15 citation statements)

References 16 publications

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“…Although the aero-optics of turbulent boundary layers has been extensively studied in recent years ( [2,18] and references therein), including experimental measurements [19][20][21][22][23] and numerical simulations [24][25][26] in high supersonic and hypersonic turbulent boundary layers, aero-optical measurements of transitional events in laminar boundary layers at high speeds are limited and many important questions about the details of the dynamics and topology of underlying structures remain unanswered. The highly spatially and temporally resolved optical data yielded by the Shack-Hartmann WFS can provide valuable quantification of the amplification and propagation of disturbances within a transitional boundary layer.…”

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confidence: 99%

Optical Measurements of Transitional Events in a Mach-6 Boundary Layer

Gordeyev

Juliano

2017

AIAA Journal

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Results of aero-optical measurements of naturally occurring transitional structures-turbulent spots and secondmode wave packets-in a hypersonic laminar boundary layer are presented. Optical spectra of turbulent spots were similar to spectra for fully turbulent boundary layers, and the average thickness of the boundary layer during the turbulent spot was approximately 50% of the fully turbulent boundary layer. The convective speed of the leading edge of the spot was measured to be 0.95 of the freestream speed, whereas the trailing edge moves at 0.7 of the freestream speed. The dominant frequency of the wave packet structures was about 70 kHz, consistent with the theoretically predicted second-mode frequency; the average convective speed of the packets was measured to be 0.88 of the freestream speed. Using the frozen field hypothesis, the wave fronts were stitched together to reveal streamwise/ spanwise topology of the packets. The packets were found to be fairly narrow, about 2-3δ in the spanwise direction, extending for 30-60δ in the streamwise direction.

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confidence: 99%

Optical Measurements of Transitional Events in a Mach-6 Boundary Layer

Gordeyev

Juliano

2017

AIAA Journal

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“…The computed value of 7.30 nm for the boundary layer is slightly lower than the experimental value of 8.0 nm presented in Ref. 7. At the time of writing the experimental OPDRMS,S values for the cavity flow were not available; however, due to the overall higherthan-expected levels of OPDRMS seen in the LES/RANS data in Figure 8, it is expected that the values from the simulation are moderately higher than those of the experiment.…”

Section: A Aero-optical Analysismentioning

confidence: 60%

“…OPD levels are compared to empty wind tunnel data given in Ref. 7 for validation, and the density integral along the beam path is added to that of the cavity simulation when computing the total OPD.…”

Section: B Experiments Descriptionmentioning

confidence: 99%

LES/RANS Modeling of Aero-Optical Effects in a Supersonic Cavity Flow

Zilberter

Edwards

2016

47th AIAA Plasmadynamics and Lasers Conference

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A hybrid Large Eddy simulation / Reynolds-Averaged Navier-Stokes turbulence model is applied to compute the wavefront aberrations in an optical beam passing through a supersonic open cavity flow. The turbulence model blends a RANS-type closure near solid walls with a subgrid model in the free-stream based on the ratios of estimated inner and outer turbulent length scales. The cavity geometry is modeled using an immersed boundary method, and an auxiliary flat plate simulation is performed to replicate the effects of the wind-tunnel boundary layer on the computed optical path difference. Two-dimensional proper orthogonal decomposition modes of the optical wavefront are computed and compare favorably with wind tunnel data despite uncertainties about inflow turbulence levels and boundary layer thicknesses over the wind tunnel window. Dynamic mode decomposition of a planar wavefront spanning the entire cavity reveals that wavefront distortions are driven by shear layer oscillation at the Rossiter frequencies; these disturbances create eddy shocklets that propagate into the free-stream and create additional optical path disturbances.

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“…The flow characteristics for varying stagnation pressures are shown in Table 1, with the flow velocities determined by direct measurements using SH wavefront sensor at the nozzle exit [6]. Specifically, this approach used a multipoint cross-correlation technique [29] to allow for the measurement of convective speeds of naturally occurring, optically active small-scale turbulent structures in the freestream exiting the nozzle and invoking Taylor's frozen field assumption. While the Reynolds number Re x is calculated based on the model length from the leading edge to the ramp corner, the unit Reynolds number Re l is used to describe the flow conditions independently of model length scales.…”

Section: A Test Arrangementmentioning

confidence: 99%

“…Unlike the LDI technique, which is discussed in the following, the SH wavefront sensor measures two quantities, the streamwise and the spanwise deflection angles, per each point, and thus provides more information about the flow. Also, any corrupting effects from mechanically related vibrations imposed on the laser beam are easily removed from SH wavefront data [29]; these corrupting effects are still present in the data for LDI. Therefore, it is the most adequate wavefront sensor to measure aerooptical distortions [35].…”

Section: Flow Measurementsmentioning

confidence: 99%

Measurement of Flow Perturbation Spectra in Mach 4.5 Corner Separation Zone

et al. 2018

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Characterization of the M 4.5 flow over a flat-plate model with a 30 deg compression ramp was performed with low-enthalpy (T 0 300 K) and high-enthalpy (T 0 800-1250 K) flow conditions for a wide range of unit Reynolds numbers (Re l 4 ⋅ 10 5 − 1 ⋅ 10 7 m −1). Three measurement techniques were employed to measure the frequency spectrum of flow perturbations: a high-frequency Shack-Hartmann wavefront sensor (aerooptical method), highfrequency PCB™ pressure sensors, and a laser differential interferometer. The magnitude and frequency of flow oscillations measured by all three methods provide comprehensive and complementary results in determining spectra of gas disturbances within the flow. Of these measurement methods, the Shack-Hartmann wavefront sensor is shown to be the most suitable tool for analysis of the high-speed flow. Aerooptical measurements detect modification to the flow structure when plasma actuation is employed or when Re l is varied. In this work, flow characterization by the Shack-Hartmann sensor at individual points over the ramp has shown three flow regimes depending on the unit Reynolds number: turbulent, transitional, and laminar. At higher Re l , the freestream disturbances become strong enough to significantly affect the perturbations in the boundary-layer and the separation zone on the compression ramp. Frequency spectrum measurements during high-frequency plasma actuation (F 100 kHz) indicate amplification of the perturbations from the natural state that occur over the separation region.

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Shack-Hartmann Wavefront Measurements of Supersonic Turbulent Boundary Layers in the TGF

Cited by 15 publications

References 16 publications

Optical Measurements of Transitional Events in a Mach-6 Boundary Layer

Optical Measurements of Transitional Events in a Mach-6 Boundary Layer

LES/RANS Modeling of Aero-Optical Effects in a Supersonic Cavity Flow

Measurement of Flow Perturbation Spectra in Mach 4.5 Corner Separation Zone

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