Stability of highly cooled hypervelocity boundary layers

Bitter, Neal; Shepherd, Joseph E.

doi:10.1017/jfm.2015.358

Cited by 101 publications

(63 citation statements)

References 72 publications

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“…Surprisingly, the supersonic mode in Case 2 (Cold Wall) actually had a higher magnitude than the traditional second mode and could impact transition unexpectedly if not accounted for. Overall, however, the results are consistent with previous research 24 showing that a colder wall produces a stronger supersonic mode. In both the hot and cold wall cases, the radiated sound from the wall may have an impact on the stability of the boundary layer, and it is possible the sound radiation acts as an energy sink for the second mode, as suggested by Chuvakhov and Fedorov.…”

Section: Discussionsupporting

confidence: 91%

The Supersonic Mode and the Role of Wall Temperature in Hypersonic Boundary Layers with Thermochemical Nonequilibrium Effects

Knisely

Zhong

2018

2018 Fluid Dynamics Conference

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There has been a renewed interest in studying the stability of the supersonic mode in hypersonic boundary layers. The supersonic mode, sometimes also referred to as the spontaneous radiation of sound, is associated with an unstable Mack's second mode synchronizing with the slow acoustic spectrum, causing the disturbance to travel upstream supersonically relative to the meanflow outside the boundary layer. Recent theoretical results have shown the possibility of the supersonic mode existing in hot-wall flows, which is contrary to decades of research on the supersonic mode suggesting it is an artifact of hypersonic cold-wall (Tw/T∞ < 1) flows. The flow conditions leading to the supersonic mode have not been thoroughly and systematically investigated. As a result, it is unknown whether or not the supersonic mode can become the dominant boundary layer instability over the traditional second mode. This work uses thermochemical nonequilibrium Direct Numerical Simulation (DNS) along with thermochemical nonequilibrium Linear Stability Theory (LST) to replicate the flow conditions used in the theoretical study to obtain a more complete investigation of the supersonic mode in both hot-wall and cold-wall flow conditions. The purpose is to analyze the effect of wall temperature on the supersonic mode at high-enthalpy conditions. The simulation is Mach 10 flow over a 1mm nose radius axisymmetric cone 1 meter in length. LST results indicate that the supersonic mode does not exist in neither the hot-wall nor the cold-wall flows, however unsteady DNS results indicate the presence of the spontaneous radiation of sound in both cases, going against LST predictions. Further FFT analysis indicated that this sound radiation was an artifact of the interaction between an unstable subsonic mode S, stable supersonic mode F1, and the slow acoustic spectrum. The supersonic mode found in the cold-wall case had a significantly higher magnitude than the hot-wall case, demonstrating that a colder wall produces a stronger supersonic mode. Additionally, the magnitude of the supersonic mode in the cold-wall case was higher than the magnitude of the traditional second mode and could impact transition unexpectedly if not accounted for.

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Section: Discussionsupporting

confidence: 91%

The Supersonic Mode and the Role of Wall Temperature in Hypersonic Boundary Layers with Thermochemical Nonequilibrium Effects

Knisely

Zhong

2018

2018 Fluid Dynamics Conference

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“…disturbances predicted by linear instability theory is shown in figure 1. This pattern convects with a velocity close to the edge value, and the spatial growth rate is inversely proportional to the boundary-layer thickness (Bitter 2015). The presence of these propagating disturbances can be measured by a variety of means, as discussed subsequently ( § 2), and the analysis of the frequency content, propagation speed and amplitude can be used to experimentally characterize boundary-layer instability.…”

Section: Compressible Boundary-layer Instabilitymentioning

confidence: 99%

“…Calculations of the boundary-layer flow indicate that there is a pronounced temperature maximum within the boundary layer, as shown in figure 1. Stability computations (Mack 1975(Mack , 1984(Mack , 1999Bitter & Shepherd 2014;Bitter 2015) indicate that the shape of the mean temperature profile has a profound influence on the stability characteristics of the boundary layer. A cold wall stabilizes the first mode and destabilizes the second mode; at sufficiently high edge Mach number and wall cooling, the first mode is completely eliminated.…”

Section: Hypervelocity Flowmentioning

confidence: 99%

Observations of hypervelocity boundary-layer instability

2015

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A novel optical method is used to measure the high-frequency (up to 3 MHz) density fluctuations that precede transition to turbulence within a laminar boundary layer in a hypervelocity flow. This optical method, focused laser differential interferometry, enables measurements of short-wavelength, high-frequency disturbances that are impossible with conventional instrumentation such as pressure transducers or hot wires. In this work, the T5 reflected-shock tunnel is used to generate flows in air, nitrogen and carbon dioxide with speeds between 3.5 and 5 km s ), density fluctuations are observed to grow in amplitude and transition from a single narrow band of frequencies consistent with the Mack or second mode of boundary-layer instability to bursts of large-amplitude and spectrally broad disturbances that appear to be precursors of turbulent spots. Disturbances that are sufficiently small in initial amplitude have a wavepacket-like signature and are observed to grow in amplitude between the upstream and downstream measurement locations. A cross-correlation analysis indicates propagation of wavepackets at speeds close to the edge velocity. The free stream flow created by the shock tunnel and the resulting boundary layer on the cone are computed, accounting for chemical and vibrational non-equilibrium processes. Using this base flow, local linear and parabolized stability (PSE) analyses are carried out and compared with the experimental results. Reasonable agreement is found between measured and predicted most unstable frequencies, with the greatest differences being approximately 15 %. The scaling of the observed frequency with the inverse of boundary-layer thickness and directly with the flow velocity are consistent with the characteristics of Mack's second mode, as well as results of previous researchers on hypersonic boundary layers.

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“…The eigenfunctions and eigenvalues were computed by Bitter [21] using parallel flow linear stability theory for a boundary layer on a cone with flow conditions given in Table 3. The real and imaginary eigenfunctions are plotted versus height above the cone surface in Fig.…”

Section: Simulated Measurements a Descriptionmentioning

confidence: 99%

Analysis of Focused Laser Differential Interferometry

Schmidt

Shepherd

2015

31st AIAA Aerodynamic Measurement Technology and Ground Testing Conference

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A computational method for predicting the output of a focused laser differential interferometer (FLDI) given an arbitrary density field is presented. The method is verified against analytical predictions and experimental data. The FLDI simulation software is applied to the problem of measuring Mack-mode wave packets in a hypervelocity boundary layer on a 5°half-angle cone. The software is shown to complement experiments by providing the necessary information to allow quantitative density fluctuation magnitudes to be extracted from experimental measurements.

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Stability of highly cooled hypervelocity boundary layers

Cited by 101 publications

References 72 publications

The Supersonic Mode and the Role of Wall Temperature in Hypersonic Boundary Layers with Thermochemical Nonequilibrium Effects

The Supersonic Mode and the Role of Wall Temperature in Hypersonic Boundary Layers with Thermochemical Nonequilibrium Effects

Observations of hypervelocity boundary-layer instability

Analysis of Focused Laser Differential Interferometry

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