Abstract
Instability evolution in a transitional hypersonic boundary layer and its effects on aerodynamic heating are investigated over a 260 mm long flared cone. Experiments are conducted in a Mach 6 wind tunnel using Rayleigh-scattering flow visualization, fast-response pressure sensors, fluorescent temperature-sensitive paint (TSP) and particle image velocimetry (PIV). Calculations are also performed based on both the parabolized stability equations (PSE) and direct numerical simulations (DNS). Four unit Reynolds numbers are studied, 5.4, 7.6, 9.7 and$11.7\times 10^{6}~\text{m}^{-1}$. It is found that there exist two peaks of surface-temperature rise along the streamwise direction of the model. The first one (denoted as HS) is at the region where the second-mode instability reaches its maximum value. The second one (denoted as HT) is at the region where the transition is completed. Increasing the unit Reynolds number promotes the second-mode dissipation but increases the strength of local aerodynamic heating at HS. Furthermore, the heat generation rates induced by the dilatation and shear processes (respectively denoted as$w_{\unicode[STIX]{x1D703}}$and$w_{\unicode[STIX]{x1D714}}$) were investigated. The former item includes both the pressure work$w_{\unicode[STIX]{x1D703}1}$and dilatational viscous dissipation$w_{\unicode[STIX]{x1D703}2}$. The aerodynamic heating in HS mainly arose from the high-frequency compression and expansion of fluid accompanying the second mode. The dilatation heating, especially$w_{\unicode[STIX]{x1D703}1}$, was more than five times its shear counterpart. In a limited region, the underestimated$w_{\unicode[STIX]{x1D703}2}$was also larger than$w_{\unicode[STIX]{x1D714}}$. As the second-mode waves decay downstream, the low-frequency waves continue to grow, with the consequent shear-induced heating increasing. The latter brings about a second, weaker growth of surface-temperature HT. A theoretical analysis is provided to interpret the temperature distribution resulting from the aerodynamic heating.
Highlights
Aerodynamic heating is a key issue in hypersonic flow research due to its strong relevance to the safety of ultra-high-speed flight
Laminar-to-turbulence transition is one of the most important sources bringing about uncertain aerodynamic heating that might adversely impact a vehicle’s thermal protection system (TPS) (Berry et al 2006; Greene & Hamilton 2006; McGinley et al 2006)
Power spectrum distributions (PSD) of PCB-measured time series are calculated. Their streamwise evolutions at different unit Reynolds numbers are shown in figure 3
Summary
Aerodynamic heating is a key issue in hypersonic flow research due to its strong relevance to the safety of ultra-high-speed flight. Recent investigations of hypersonic boundary layers have indicated the appearance of an additional peak in heat transfer (denoted as HS) within the transitional region, as well as a second rapid growth of heat transfer near the end of transition (HT) Schneider and his group (Berridge et al 2010) were the first to observe this phenomenon on a Mach 6 flared cone under quiet flow conditions. Very recently, Zhang et al (2015) and Zhu et al (2016) have conducted twodimensional PIV measurements, combined with PCB sensors, over a 0.26 m long, 5◦ half-angle flared cone in the Mach 6 wind tunnel at Peking University They found that the second-mode instability initially grew fast, reached its maximum and decayed to zero along the streamwise direction. A theoretical analysis of heat transfer is described to explain the relationship between aerodynamic heating and surface-temperature distribution
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