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2010 Investigation of thermal nonequilibrium on hypersonic boundary-layer transition

By Jens Linn and Markus J. KlokerJens Linn and Markus J. Kloker


Abstract High-temperature gas effects are known as the physical processes which result in a deviation of the behavior of the calorically perfect gas in the hypersonicflow regime. These effects may have a significant impact on laminar-turbulent transition of the boundary layer, and thus affect the heat loads of hypersonic vehicles. In the present paper we deal with thermal effects, i.e. rotational and vibrational energy relaxation. A fundamental-breakdown scenario of a Mach-6.8 flat-plate boundary layer at flight conditions is simulated by high-order DNS using a calorically perfect gas, or thermal equilibrium, or a nonequilibrium model. A similar behavior is found for the calorically perfect gas and the thermal equilibrium case. In contrast, a stabilizing effect is observed in the thermal nonequilibrium case, leading to a fall off of fundamental breakdown. 1 Gas Models The Navier-Stokes Equations are altered in two ways to deal with thermal nonequilibrium (TNEQ), i.e. rotational and vibrational energy relaxation. First, a bulk viscosity or volumetric viscosity µ ⋆ v is added [3] to approximately account for rotational relaxation. Secondly, a vibrational-energy equation for each species has been added. In this case we deal with two temperatures. The translational temperature is T ⋆ = T ⋆ tra and the vibrational temperature T ⋆ vib i for each species, where the superscript ⋆ denotes dimensional quantities. The definition of the internal energy now reads: e ⋆ = e ⋆ trans + e ⋆ rot + e ⋆ vi

Year: 2009
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