Influence of Laminar Boundary-Layer Transition on Entry Vehicle Designs

Lin, Tony

doi:10.2514/1.30047

Cited by 29 publications

(9 citation statements)

References 21 publications

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“…Transition of the boundary layer from laminar to turbulent can increase surface heating loads by a factor of 4-10 (Lau 2008;Lin 2008;Hollis 2012), thereby increasing the cooling requirements and the weight of the thermal protection system. The location of the transition region is therefore a key design consideration, yet it remains extremely challenging to predict reliably.…”

mentioning

confidence: 99%

Stability of highly cooled hypervelocity boundary layers

2015

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The influence of high levels of wall cooling on the stability of hypervelocity boundary layers is investigated. Such conditions are relevant to experiments in high-enthalpy impulse facilities, where the wall temperature is much smaller than the free-stream temperature, as well as to some real flight scenarios. Some effects of wall cooling are well known, for instance, the stabilization of the first mode and destabilization of the second mode. In this paper, several new instability phenomena are investigated that arise only for high Mach numbers and high levels of wall cooling. In particular, certain unstable modes can travel supersonically with respect to the free stream, which changes the nature of the dispersion curve and leads to instability over a much wider band of frequencies. The cause of this phenomenon, the range of parameters for which it occurs and its implications for boundary layer stability are examined. Additionally, growth rates are systematically reported for a wide range of conditions relevant to high-enthalpy impulse facilities, and the stability trends in terms of Mach number and wall temperature are mapped out. Thermal non-equilibrium is included in the analysis and its influence on the stability characteristics of flows in impulse facilities is assessed.

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confidence: 99%

Stability of highly cooled hypervelocity boundary layers

2015

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“…2, a single still image captures the complex thermal footprints (higher temperature shown in lighter gray) associated with turbulent flow at the Orbiter surface. The time of appearance and the spatial extent of flow turbulence is crucial for an optimal TPS design [46][47]. This particular image was acquired with the Shuttle located near the point of closest approach relative to the imaging system yielding a spatial resolution of approximately 4-inches per pixel.…”

Section: Thermal Imaging (Shuttle Orbiter)mentioning

confidence: 99%

Remote observations of reentering spacecraft including the space shuttle orbiter

Horvath

Cagle

Grinstead

et al. 2013

2013 IEEE Aerospace Conference

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Abstract-Flight measurement is a critical phase in development, validation and certification processes of technologies destined for future civilian and military operational capabilities. This paper focuses on several recent NASA-sponsored remote observations that have provided unique engineering and scientific insights of reentry vehicle flight phenomenology and performance that could not necessarily be obtained with more traditional instrumentation methods such as onboard discrete surface sensors. The missions highlighted include multiple spatially-resolved infrared observations of the NASA Space Shuttle Orbiter during hypersonic reentry from 2009 to 2011, and emission spectroscopy of comparatively small-sized sample return capsules returning from exploration missions. Emphasis has been placed upon identifying the challenges associated with these remote sensing missions with focus on end-to-end aspects that include the initial science objective, selection of the appropriate imaging platform and instrumentation suite, target flight path analysis and acquisition strategy, pre-mission simulations to optimize sensor configuration, logistics and communications during the actual observation. Explored are collaborative opportunities and technology investments required to develop a next-generation quantitative imaging system (i.e., an intelligent sensor and platform) with greater capability, which could more affordably support cross cutting civilian and military flight test needs.

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“…This activity is indicative of the difficult but potentially rewarding nature of these efforts. In the design of hypervelocity vehicles, the location of transition critically determines not only the drag, but also the degree to which thermal protection needs to be applied, because both friction and heating rate jump significantly at the transition point (Saric, Reed & Kerschen 2002;Schneider 2004;Lau 2008;Lin 2008;Reshotko 2008;Schmisseur & Erbland 2012). The receptivity and growth of the disturbances that precede transition within an initially laminar boundary layer in hypervelocity (characterized by speeds exceeding 3-4 km s −1 ) flow are less understood than in subsonic flows, particularly at conditions where gas dissociation and vibrational excitation must be considered.…”

Section: Introductionmentioning

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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Influence of Laminar Boundary-Layer Transition on Entry Vehicle Designs

Cited by 29 publications

References 21 publications

Stability of highly cooled hypervelocity boundary layers

Stability of highly cooled hypervelocity boundary layers

Remote observations of reentering spacecraft including the space shuttle orbiter

Observations of hypervelocity boundary-layer instability

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