Unsteady heat-flux measurements of second-mode instability waves in a hypersonic flat-plate boundary layer

Kegerise, Michael A.; Rufer, Shann J.

doi:10.1007/s00348-016-2214-9

Cited by 28 publications

(9 citation statements)

References 24 publications

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“…Mack's modes are potential precursors of transition in compressible boundary layers, and both the first-and second-mode waves have been observed in various experiments (see e.g. Kendall 1975;Lysenko & Maslov 1984;Stetson & Kimmel 1992;Casper et al 2016;Kegerise & Rufer 2016;Laurence, Wagner & Hannemann 2016;Zhu et al 2018;Liu et al 2019). At high-subsonic and moderate-supersonic speeds, boundary-layer transition in low-disturbance environments occurs as a result of excitation and amplification of instabilities that resemble Mack's first-mode waves.…”

Section: Stability Of High-speed Boundary Layersmentioning

confidence: 99%

Optimal two-dimensional roughness for transition delay in high-speed boundary layer

Jahanbakhshi,

Zaki

2023

J. Fluid Mech.

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The influence of surface roughness on transition to turbulence in a Mach 4.5 boundary layer is studied using direct numerical simulations. Transition is initiated by the nonlinearly most dangerous inflow disturbance, which causes the earliest possible breakdown on a flat plate for the prescribed inflow energy and Mach number. This disturbance primarily comprises two normal second-mode instability waves and an oblique first mode. When localized roughness is introduced, its shape and location relative to the synchronization points of the inflow waves are confirmed to have a clear impact on the amplification of the second-mode instabilities. The change in modal amplification coincides with the change in the height of the near-wall region where the instability wave speed is supersonic relative to the mean flow; the net effect of a protruding roughness is destabilizing when placed upstream of the synchronization point and stabilizing when placed downstream. Assessment of the effect of the roughness location is followed by an optimization of the roughness height, abruptness and width with the objective of achieving maximum transition delay. The optimization is performed using an ensemble-variational (EnVar) approach, while the location of the roughness is fixed upstream of the synchronization points of the two second-mode waves. The optimal roughness disrupts the phase of the near-wall pressure waves, suppresses the amplification of the primary instability waves and mitigates the nonlinear interactions that lead to breakdown to turbulence. The outcome is a sustained non-turbulent flow throughout the computational domain.

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Section: Stability Of High-speed Boundary Layersmentioning

confidence: 99%

Optimal two-dimensional roughness for transition delay in high-speed boundary layer

Jahanbakhshi,

Zaki

2023

J. Fluid Mech.

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“…An atomic-layer thermopile (ALTP) probe was used to make measurements of freestream heat transfer. These sensors are a fairly new technology and have been used in previous studies of boundary-layer instabilities 18,19 and stagnation point heating measurements. 20 The ALTP sensor comes with an in-line amplifier that amplifies the AC signal of the sensor by a fixed gain of 5000.…”

Section: Heat Transfer Sensorsmentioning

confidence: 99%

“…Calibrations with a diode laser corroborated the approximate bandwidth. 19 For this experiment, the ALTP sensor was mounted into a 7.94-mm-diameter body with a 3-degree taper to the front end of the probe. This sensor was mounted flush to the end of the probe tip.…”

Section: Heat Transfer Sensorsmentioning

confidence: 99%

Measurements of Freestream Fluctuations in the NASA Langley 20-Inch Mach 6 Tunnel

Chou

Leidy

Bathel

et al. 2018

2018 Fluid Dynamics Conference

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An experimental campaign was conducted to measure and to characterize the freestream disturbance levels in the NASA Langley Research Center 20-Inch Mach 6 Wind Tunnel. A pitot rake was instrumented with fast pressure transducers, hot wires, and an atomic layer thermopile to quantify the fluctuation levels of pressure, mass flux, and heat flux, respectively. In conjunction with these probe-based measurements, focused laser differential interferometry was used to optically measure density fluctuations. Measurements were made at five nominal different unit Reynolds numbers ranging from 3.28-26.5×10 6 /m. The rake was positioned at two different streamwise locations and several different roll angles to measure flow uniformity within the test section. In general, noise levels were spatially consistent within the tested region. Pitot pressure fluctuation levels ranged from 0.84% at the highest Reynolds number tested to 1.89% at the lowest Reynolds number tested. Freestream mass-flux fluctuations remained relatively constant between 1.8-2.5% of the freestream. The pressure transducers were also used to determine the dominant disturbance speed and angle of propagation. The disturbances were estimated to travel at approximately 54-81% of the freestream speed at an angle of approximately 21-44°from the freestream direction, but these measurements had a significant amount of uncertainty. A comparison to previous measurements of pressure made in 2012 and of mass flux made in 1994 show almost no change in the RMS fluctuation of these flow quantities.

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“…Kegerise, M. A measured the instability of the medium heat flux in the 6 Mach plate boundary layer. 8 The medium-pressure instability of the 6-Mach model boundary layer is measured by Fong, K. D., et al 9 Owen, F. K., et al measured the temperature instability in the Mach 7 free flow. 10 Unfortunately, as so far, there is no direct way to diagnose the time-varying electron density of the plasma sheath, which is most concerned in EM propagation.…”

Section: Introductionmentioning

confidence: 97%

An integrative time-varying frequency detection and channel sounding method for dynamic plasma sheath

et al. 2018

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The plasma sheath-surrounded hypersonic vehicle is a dynamic and time-varying medium and it is almost impossible to calculate time-varying physical parameters directly. The in-fight detection of the time-varying degree is important to understand the dynamic nature of the physical parameters and their effect on re-entry communication. In this paper, a constant envelope zero autocorrelation (CAZAC) sequence based on time-varying frequency detection and channel sounding method is proposed to detect the plasma sheath electronic density time-varying property and wireless channel characteristic. The proposed method utilizes the CAZAC sequence, which has excellent autocorrelation and spread gain characteristics, to realize dynamic time-varying detection/channel sounding under low signal-to-noise ratio in the plasma sheath environment. Theoretical simulation under a typical time-varying radio channel shows that the proposed method is capable of detecting time-variation frequency up to 200 kHz and can trace the channel amplitude and phase in the time domain well under –10 dB. Experimental results conducted in the RF modulation discharge plasma device verified the time variation detection ability in practical dynamic plasma sheath. Meanwhile, nonlinear phenomenon of dynamic plasma sheath on communication signal is observed thorough channel sounding result.

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Unsteady heat-flux measurements of second-mode instability waves in a hypersonic flat-plate boundary layer

Cited by 28 publications

References 24 publications

Optimal two-dimensional roughness for transition delay in high-speed boundary layer

Optimal two-dimensional roughness for transition delay in high-speed boundary layer

Measurements of Freestream Fluctuations in the NASA Langley 20-Inch Mach 6 Tunnel

An integrative time-varying frequency detection and channel sounding method for dynamic plasma sheath

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