Non-intrusive Velocity and Density Measurements in Subsonic Turbulent Boundary Layer

Sontag, John M.; Gordeyev, Stanislav

doi:10.2514/6.2015-3247

Cited by 9 publications

(16 citation statements)

References 13 publications

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“…First, the flow is expected to be primarily spanwise-uniform. Second, as the beam traverses the 4-inch-long region of the flow, aero-optical distortions become stronger thus improving the signal-to-noise ratio [44] . After exiting the test section, the beam is reflected off the return mirror, which sends the beam back along the same path.…”

Section: Aero-optical Measurementsmentioning

confidence: 99%

“…The 2-component deflection angle is a local gradient of the wavefront, so knowing both components of the deflection angle the wavefront (or equivalently, Optical Path Difference or OPD) can be computed. OPD is proportional to the spanwise-integrated density field, ( , , ) = ∫ ′ ( , , , ) [46] , where K GD is the Gladstone-Dale constant, and knowing OPD, the amplitude of the density fluctuation over a subaperture can be estimated [44] . In contrast, time-resolved Schlieren images provide good spatial and temporal information, but density information is not easily extracted from them.…”

Section: Aero-optical Measurementsmentioning

confidence: 99%

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Transient Plasma Impact on Spectra of Flow Disturbances in a Corner Separation Zone at Mach 4.5

Houpt

Hedlund

Gordeyev

et al. 2016

47th AIAA Plasmadynamics and Lasers Conference

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This work was performed to study the effect on flow disturbances in the corner separation zone of a compression surface with a hypersonic boundary layer caused by a weakly ionized transient plasma generated upstream. Schlieren imaging was used to distinguish the corner separation zone for 15°, 20°, and 25° compression ramps at Mach 4.5 (nozzle exit). A Shack-Hartmann wavefront sensor was used to determine the dominant frequencies of flow oscillations at different locations in the flow field and the resulting effect of repetitively pulsed plasma actuators. A significant rise in amplitudes of high-frequency (>80 kHz) flow perturbations was found when pulsing the plasma at a frequency (100 kHz) higher than the natural dominant frequency of the boundary layer (~65 kHz). The plasma effect was negligible when operated below this frequency (50 kHz). PCB pressure sensors were used to determine the dominant frequencies of pressure oscillations present at the surface on the flat plate and compression ramp inside the separation zone. This technique can potentially be used for active control of the boundary layer condition and supersonic flow structure on the compression surface.

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Section: Aero-optical Measurementsmentioning

confidence: 99%

Section: Aero-optical Measurementsmentioning

confidence: 99%

Transient Plasma Impact on Spectra of Flow Disturbances in a Corner Separation Zone at Mach 4.5

Houpt

Hedlund

Gordeyev

et al. 2016

47th AIAA Plasmadynamics and Lasers Conference

Self Cite

View full text Add to dashboard Cite

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“…Away from the wall, the dominant structures shift towards larger structures and the distortions increase in magnitude. For further commentary on spectra shape and its relation to the structures in the boundary layer, see the discussion in [17].…”

Section: Resultsmentioning

confidence: 99%

“…The ratio continuously increases, from about 1.5 near the wall to almost 3.5 at y/δ = 0.8, and then shows a slight decrease. 9 American Institute of Aeronautics and Astronautics Sontag and Gordeyev AIAA-2017-3835 However, the region y/δ > 0.6 was shown to be partially contaminated by the presence of the sidewall boundary layers [17], so this decreasing trend might be related to this corrupting effect. For all cooled wall cases in Figure 7, the fluctuating density ratio is less than unity.…”

Section: Figure 6 Convective Velocity Profiles Calculated From Deflementioning

confidence: 99%

“…(6) This allows for direct measurements of the product 2 ( ) ( ) as a fuction of the distance from the wall and gaining a further insight into the density structure in turbulent boundary layers. This approach was investigated in the earlier paper [17] and it was demonstrated to provide valuable information about wall-normal variation of convective speed and the product 2 ( ) ( ).…”

Section: Introductionmentioning

confidence: 99%

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Studies of Density Fields in Non-Adiabatic Boundary Layers Using Wavefront Sensors

Sontag

Gordeyev

2017

48th AIAA Plasmadynamics and Lasers Conference

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Measurements of time-resolved aero-optical distortions caused by subsonic boundary layers in the spanwise direction were performed at different heights away from the wall. The wall upstream of the measurement station was either heated or cooled to introduce heat-fluxrelated density variations into the boundary layer. It was demonstrated that the aero-optical deflection angle spectra are self-similar across the boundary layer and the convective speeds of aero-optical structures at different heights are approximately the same for all tested cases. From the collected aero-optical data, the fluctuating density profiles were directly calculated at different heights and compared with the ones predicted by the Extended SRA. It was shown that the Extended SRA incorrectly predicts fluctuating density profiles for strong cooling and heating cases and possible reasons for this discrepancy are discussed. Finally, it was shown that the experimentally-measured fluctuating density profiles correctly predict the aerooptical distortions in the wall-normal direction.

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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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Non-intrusive Velocity and Density Measurements in Subsonic Turbulent Boundary Layer

Cited by 9 publications

References 13 publications

Transient Plasma Impact on Spectra of Flow Disturbances in a Corner Separation Zone at Mach 4.5

Transient Plasma Impact on Spectra of Flow Disturbances in a Corner Separation Zone at Mach 4.5

Studies of Density Fields in Non-Adiabatic Boundary Layers Using Wavefront Sensors

Measurement of Flow Perturbation Spectra in Mach 4.5 Corner Separation Zone

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