scholarly journals Unsteady Heat-Flux Measurements of Second-Mode Instability Waves in a Hypersonic Boundary Layer

2016 ◽  
Author(s):  
Michael A. Kegerise ◽  
Shann J. Rufer
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Hypersonic Boundary Layer ◽  
Mode Instability ◽  
Instability Waves ◽  
Second Mode ◽  
Flux Measurements

Experimental study of second-mode instability growth and breakdown in a hypersonic boundary layer using high-speed schlieren visualization

2016 ◽  
Vol 797 ◽  
pp. 471-503 ◽  
Author(s):  
S. J. Laurence ◽  
A. Wagner ◽  
K. Hannemann
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Porous Ceramic ◽  
Propagation Speed ◽  
Mode Instability ◽  
Instability Waves ◽  
Local Maxima ◽  
High Enthalpy ◽  
Reflected Shock ◽  
Second Mode

Visualization experiments are performed to investigate the development of instability waves within the boundary layer on a slender cone under high Mach number conditions. The experimental facility is a reflected-shock wind tunnel, allowing both low (Mach-8 flight equivalent) and high-enthalpy conditions to be simulated. Second-mode instability waves are visualized using a high-speed schlieren set-up, with pulse bursting of the light source allowing the propagation speed of the wavepackets to be unambiguously resolved. This, in combination with wavelength information derived from the images, enables the calculation of the disturbance frequencies. At the lower-enthalpy conditions, we concentrate on the late laminar and transitional regions of the flow. General characteristics are revealed through time-resolved and ensemble-averaged spectra on both smooth and porous ceramic surfaces of the cone. Analysis of the development of individual wavepackets is then performed. It is found that the wavepacket structures evolve from a ‘rope-like’ appearance to become more interwoven as the disturbance nears breakdown. The wall-normal disturbance distributions of both the fundamental and first harmonic, which initially have local maxima at the wall and near $y/{\it\delta}=0.7$–0.75, exhibit an increase in signal energy close to the boundary-layer edge during this evolution. The structure angle of the disturbances also undergoes subtle changes as the wavepacket develops prior to breakdown. Experiments are also performed at high-enthalpy ($h_{0}\approx 12~\text{MJ}~\text{kg}^{-1}$) conditions in the laminar regime, and the visualization technique is shown to be capable of resolving wavepacket propagation speeds and frequencies at such conditions. The visualizations reveal a somewhat different wall-normal distribution to the low-enthalpy case, with the disturbance energy concentrated much more towards the wall. This is attributed to the highly cooled nature of the wall at high enthalpy.

scholarly journals Time-Resolved Visualization of Instability Waves in a Hypersonic Boundary Layer

AIAA Journal ◽  
2012 ◽  
Vol 50 (1) ◽  
pp. 243-246 ◽  
Author(s):  
S. J. Laurence ◽  
A. Wagner ◽  
K. Hannemann ◽  
V. Wartemann ◽  
H. Lüdeke ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Hypersonic Boundary Layer ◽  
Time Resolved ◽  
Instability Waves

Interactions between second mode and low-frequency waves in a hypersonic boundary layer

2017 ◽  
Vol 820 ◽  
pp. 693-735 ◽  
Author(s):  
Xi Chen ◽  
Yiding Zhu ◽  
Cunbiao Lee
Keyword(s):  
Boundary Layer ◽  
Parametric Resonance ◽  
Low Frequency ◽  
Frequency Mode ◽  
Linear Stability Theory ◽  
Hypersonic Boundary Layer ◽  
Reynolds Stresses ◽  
Second Mode ◽  
Low Frequency Mode ◽  
Low Frequency Waves

The stability of a hypersonic boundary layer on a flared cone was analysed for the same flow conditions as in earlier experiments (Zhang et al., Acta Mech. Sinica, vol. 29, 2013, pp. 48–53; Zhu et al., AIAA J., vol. 54, 2016, pp. 3039–3049). Three instabilities in the flared region, i.e. the first mode, the second mode and the Görtler mode, were identified using linear stability theory (LST). The nonlinear-parabolized stability equations (NPSE) were used in an extensive parametric study of the interactions between the second mode and the single low-frequency mode (the Görtler mode or the first mode). The analysis shows that waves with frequencies below 30 kHz are heavily amplified. These low-frequency disturbances evolve linearly at first and then abruptly transition to parametric resonance. The parametric resonance, which is well described by Floquet theory, can be either a combination resonance (for non-zero frequencies) or a fundamental resonance (for steady waves) of the secondary instability. Moreover, the resonance depends only on the saturated state of the second mode and is insensitive to the initial low-frequency mode profiles and the streamwise curvature, so this resonance is probably observable in boundary layers over straight cones. Analysis of the kinetic energy transfer further shows that the rapid growth of the low-frequency mode is due to the action of the Reynolds stresses. The same mechanism also describes the interactions between a second-mode wave and a pair of low-frequency waves. The only difference is that the fundamental and combination resonances can coexist. Qualitative agreement with the experimental results is achieved.

Measurements and Computations of Second-Mode Instability Waves in Several Hypersonic Wind Tunnels

2010 ◽  
Author(s):  
Dennis Berridge ◽  
Katya Casper ◽  
Shann Rufer ◽  
Christopher Alba ◽  
Daniel Lewis ◽  
...  
Keyword(s):  
Wind Tunnels ◽  
Mode Instability ◽  
Instability Waves ◽  
Second Mode

scholarly journals Pressure fluctuations beneath instability wavepackets and turbulent spots in a hypersonic boundary layer

2014 ◽  
Vol 756 ◽  
pp. 1058-1091 ◽  
Author(s):  
Katya M. Casper ◽  
Steven J. Beresh ◽  
Steven P. Schneider
Keyword(s):  
Boundary Layer ◽  
Pressure Fluctuation ◽  
Electrical Breakdown ◽  
Pressure Fluctuations ◽  
Spanwise Direction ◽  
Hypersonic Boundary Layer ◽  
Nozzle Wall ◽  
Turbulent Spots ◽  
Fluctuation Field ◽  
Second Mode

AbstractTo investigate the pressure-fluctuation field beneath turbulent spots in a hypersonic boundary layer, a study was conducted on the nozzle wall of the Boeing/AFOSR Mach-6 Quiet Tunnel. Controlled disturbances were created by pulsed-glow perturbations based on the electrical breakdown of air. Under quiet-flow conditions, the nozzle-wall boundary layer remains laminar and grows very thick over the long nozzle length. This allows the development of large disturbances that can be well-resolved with high-frequency pressure transducers. A disturbance first grows into a second-mode instability wavepacket that is concentrated near its own centreline. Weaker disturbances are seen spreading from the centre. The waves grow and become nonlinear before breaking down to turbulence. The breakdown begins in the core of the packets where the wave amplitudes are largest. Second-mode waves are still evident in front of and behind the breakdown point and can be seen propagating in the spanwise direction. The turbulent core grows downstream, resulting in a spot with a classical arrowhead shape. Behind the spot, a low-pressure calmed region develops. However, the spot is not merely a localized patch of turbulence; instability waves remain an integral part. Limited measurements of naturally occurring disturbances show many similar characteristics. From the controlled disturbance measurements, the convection velocity, spanwise spreading angle, and typical pressure-fluctuation field were obtained.

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