High-enthalpy models for boundary-layer stability and transition

Abstract

The prediction of the transition dynamics of high-enthalpy boundary-layer flows requires appropriate thermodynamic and transport models. This work quantifies the influence of transport, diffusion, collision, equilibrium, and chemical-kinetics modeling on the stability characteristics and the estimated transition-onset location of canonical boundary layers. The computed behavior of second-mode instabilities is consistently highly dependent on the base-flow’s boundary-layer height. The Blottner-Eucken-Wilke transport model is seen to underpredict the boundary-layer height, hence overpredicting the growth-rate distribution and forecasting the transition onset to occur ∼38% sooner. The other low-order transport models (Brokaw and Yos) returned very close results to the most-accurate Chapman-Enskog model. The use of Gupta et al.’s collisional data instead of Wright et al.’s more accurate data is also seen to predict the transition onset to occur ∼8% closer to the leading edge. The modeling of mass diffusion and the chemical-equilibrium constant is observed to have a negligible influence on the boundary-layer height and transition-onset-location estimations (less than 5% and 2%, respectively). For the analyzed conditions, all chemical models predict the same transition-onset location (±1%); since at the streamwise positions where perturbations have reached sufficiently large amplitudes, the flow is close to equilibrium and thus independent of the reaction rates. The use of different transport models for the perturbation terms, while maintaining the same model for the basic state, leads to negligible differences in the predictions. This further reinforces the thesis that the boundary-layer height calculation is paramount to the simulation of the development of second-mode instabilities.

Decoupling ablation effects on boundary-layer stability and transition

“…This is what was observed by Miró Miró et al. (2019 a ), who reported an underprediction by 38 % of the expected transition-onset location when employing the BEW transport model (appendix A.2) instead of the state-of-the-art CE model (appendix A.1).…”

“…This comparison also assesses whether the strong dependency of the predictions on the transport model, observed by Miró Miró et al. (2019 a ), extends to more complex physical scenarios.

Figure 1.Sketch of the various physical phenomena under consideration.

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“…In addition, another less-accurate (see the quantitative analysis in Miró Miró et al. 2019 a ) combination of transport and diffusion models is compared with the previous: the BEW transport model (appendix A.2) and the constant Schmidt number (§ 4). This corresponds to the modelling framework adopted by Mortensen & Zhong (2016).…”

Local analysis of absolute instability in plasma jets

“…Recent work on hypersonic boundary layers by Miró Miró et al. (2019) has further shown the influence of using different high temperature TTP models on LST results. The integration of equilibrium chemistry in parabolized stability equations by Zanus, Miró Miró & Pinna (2019) revealed different effects depending on the instability mode considered.…”

Ionization and dissociation effects on boundary-layer stability

“…The transport model was seen to be the one mostly conditioning such predictions: Miró Miró et al. (2019) reported that a transport model with a 10 % error with respect to the state of the art could lead to the prediction of a 38 % sooner transition onset location. Klentzman & Tumin (2013) investigated the receptivity and stability of boundary layers with a dissociating binary oxygen mixture, assuming viscous and inviscid perturbations.…”