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

Abstract

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.

Free transition on a slender cone in a quiet and a conventional wind tunnel and the effect of ultrasonically absorptive materials

“…11e). This is consistent with the measurements of free transition on a §at panel at 0 degree angle of attack as shown in [13].…”

Shock-induced heating and transition to turbulence in a hypersonic boundary layer

“…The sensitivity of the transition process to the free-stream disturbances is greatly reduced as the shock incidence angle increases, in which case an absolute instability engendered in the separation bubble dominates the transition process (Hildebrand et al 2018). Experiments at shock incidence angles higher than the ones considered in Sandham et al (2014), Schülein (2014) and Willems et al (2015) have been recently addressed by Currao et al (2020) in an experimental investigation performed concurrently with the present study. They studied the interaction between a Mach-5.8 laminar hypersonic boundary layer and a shock generated by a 10 • wedge.…”

Transitional shock-wave/boundary-layer interactions in hypersonic flow

“…Measurements with PCB and ALTP sensors also have a high degree of uncertainty, due to the difficulty of calibration and the unknown mechanical oscillation properties of the transducer, but it is possible to detect periods of high fluctuations compared with less noisy times, allowing a measure of intermittency to be extracted. More results from the H2K unsteady signals, including a wavelet analysis, are presented in Willems & Guelhan (2014) PCB sensors and S q for ALTP heat flux sensors) was used to separate laminar from turbulent regions. Figure 13 shows the resulting intermittency distributions for cases (a) without a shock and (b) with shock impingement at two locations.…”