Hypersonic Instability Waves Measured Using Fast-Response Heat-Flux Gauges

Roediger, Tim; Knauss, H.; Smorodsky, B. V.; Estorf, Malte; Schneider, Steven P.

doi:10.2514/1.37026

Cited by 30 publications

(5 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The ALTP sensors can measure frequencies above 300 kHz (Roediger et al 2008(Roediger et al , 2009). They were tested in several wind tunnels and calibrated dynamically up to 1 MHz with a modulated diode laser.…”

Section: Data Acquisitionmentioning

confidence: 99%

Experiments on the effect of laminar–turbulent transition on the SWBLI in H2K at Mach 6

2015

View full text Add to dashboard Cite

than two and an increase in the heat flux by a factor of more than four. Therefore, big areas of laminar flow are desirable to increase the performance of a propelled vehicle and to reduce the weight of the necessary thermal protection systems of a propelled or re-entry vehicle. On the other hand, turbulent boundary layers have a lower tendency to separate and are preferred in regions of large pressure gradients. Hence, the correct prediction of the transition is essential for the design of future hypersonic vehicles and their thermal protection systems.Shock wave-boundary layer interactions (SWBLI) are inevitable for most of the practical applications. They can cause locally increased pressure and thermal loads, cause separations and have a great influence onto the transition process. Most of the existing publications in this field deal with interactions of shock waves with turbulent boundary layers (Dupont et al. 2006; Schülein 2006;Humble et al. 2009; Helmer 2011;Grilli et al. 2012), some handle the case of interactions of shock waves with laminar boundary layers (Boin et al. 2006;Lüdeke and Sandham 2009;Brown and Boyce 2009) but investigations of the interaction between shock waves and transitional boundary layers are rare (Dolling 2001;Arnal and Delery 2004;Benay et al. 2006;Vanstone et al. 2013). In order to study these phenomena in detail within the framework of the ESA-TRP "laminar to turbulent transition in hypersonic flows," experiments in three different facilities using several measuring techniques have been carried out (Sandham et al. 2014). This paper describes the results of the experiments performed in the hypersonic wind tunnel H2K at DLR in Cologne.The transition process of undisturbed hypersonic boundary layers is most likely driven by instabilities called second (Mack) modes (Mack 1975). These are acoustic waves trapped between the wall and the sonic line. Therefore, Abstract This paper presents the results of the experiments performed in the hypersonic wind tunnel H2K in the framework of the ESA technology research project "laminar to turbulent transition in hypersonic flows". The investigations include the free boundary-layer transition on a flat plate as well as the influence of a shock wave-boundary layer interaction on the transition. The shock is created by a wedge with a small angle of attack resulting in a moderate shock intensity. The experiments were performed at Mach 6.0, at three different unit Reynolds numbers and with a translational displacement of the shock generator. Besides the optical methods-Schlieren photography and infrared thermography-several intrusive sensors were used. High-speed measurements were carried out using PCB and atomic layer thermo pile sensors. Kulite sensors were used for low-and mid-speed pressure measurements. The data analysis includes the comparison of the absolute values, the frequency spectra and wavelets and their distributions in time and space.

show abstract

Section: Data Acquisitionmentioning

confidence: 99%

Experiments on the effect of laminar–turbulent transition on the SWBLI in H2K at Mach 6

2015

View full text Add to dashboard Cite

show abstract

“…15,24 This is in contrast to measurements on conical geometries, where harmonics of the second-mode instability are observed. 13,24 Another point of interest is the significant growth of low-frequency energy (for frequencies < 10 kHz). Again, that was observed in previous stability measurements on planar geometries, but the exact mechanism for this low-frequency energy growth is unknown.…”

Section: Resultsmentioning

confidence: 99%

“…More recently, a new class of fast-response heat-flux sensors, the Atomic Layer Thermopile (ALTP), was applied to the measurement of surface heat-flux fluctuations induced by transitional hypersonic boundary layers. [11][12][13][14][15] These sensors are reported to have a bandwidth of ∼ 1 MHz, a spatial resolution of 1 mm 2 , and a linear static response from milliwatts to kilowatts per square centimeter. 16 Being a surface-based measurement, however, these sensors can provide only a partial picture of the transition process.…”

mentioning

confidence: 99%

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

Kergerise

Rufer

2016

54th AIAA Aerospace Sciences Meeting

View full text Add to dashboard Cite

In this paper we report on the application of the atomic layer thermopile (ALTP) heatflux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are in agreement with data previously reported in the literature. Heat flux time series, and the Morlet-wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was developed to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

show abstract

“…The atomic layer thermopile (ALTP) developed by Roediger et al (2008) is claimed to have a frequency response of up to 1 MHz. Roediger et al (2009) utilized ALTP gauges to measure the second-mode instability waves and compared the experimentally observed growth rates to growth rates calculated from linear-stability theory. Heitmann et al (2011) used such heat-flux gauges to measure instabilities that were artificially excited in a hypersonic boundary layer.…”

Section: Measurement Of Second-mode Instabilitymentioning

confidence: 99%

Observations of hypervelocity boundary-layer instability

2015

View full text Add to dashboard Cite

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.

show abstract

Hypersonic Instability Waves Measured Using Fast-Response Heat-Flux Gauges

Cited by 30 publications

References 7 publications

Experiments on the effect of laminar–turbulent transition on the SWBLI in H2K at Mach 6

Experiments on the effect of laminar–turbulent transition on the SWBLI in H2K at Mach 6

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

Observations of hypervelocity boundary-layer instability

Contact Info

Product

Resources

About