Linear Instability of Shock-Dominated Laminar Hypersonic Separated Flows

Abstract

The self-excited spanwise homogeneous perturbations arising in shockwave/boundary-layer interaction (SWBLI) system formed in a hypersonic flow of molecular nitrogen over a double wedge are investigated using the kinetic Direct Simulation Monte Carlo (DSMC) method. The flow has transitional Knudsen and unit Reynolds numbers of 3.4 × 10 −3 and 5.2 × 10 4 m −1 , respectively. Strong thermal nonequilibrium exists downstream of the Mach 7 detached (bow) shock generated due to the upper wedge surface. A linear instability mechanism is expected to make the pre-computed 2-D base flow potentially unstable under spanwise perturbations. The specific intent is to assess the growth rates of unstable modes, the wavelength, location, and origin of spanwise periodic flow structures, and the characteristic frequencies present in this interaction.

On the synchronisation of three-dimensional shock layer and laminar separation bubble instabilities in hypersonic flow over a double wedge

“…This ratio is between 0.9 and 1, however, in close proximity to the corner of two wedges, also known as the hinge, inside the recirculation region, where the expected errors in transport coefficients of shear viscosity and thermal conductivity are within 6.2 and 3.7 %, respectively (see Alexander, Garcia & Alder 1998). Finally, figure 6(e) of Sawant et al (2022) also shows that the effect of doubling the number of particles produced the same transient behaviour, where the instantaneous, spanwise-averaged, streamwise velocity differed by at most 7 % in the small region where λ/ x = 0.9 and by 1.5 % outside of it.…”

“…Figure 6(b,c) of Sawant et al (2022) show that the ratio τ/ t is greater than unity in the entire flow domain and the smallest collision cells contain at least eight particles, respectively. With respect to λ/ x, figure 6(a) of Sawant et al (2022) shows that the ratio is greater than unity in the entire flow domain, including the interior zones of shock structures and regions of triple, separation and reattachment points. This ratio is between 0.9 and 1, however, in close proximity to the corner of two wedges, also known as the hinge, inside the recirculation region, where the expected errors in transport coefficients of shear viscosity and thermal conductivity are within 6.2 and 3.7 %, respectively (see Alexander, Garcia & Alder 1998).…”

“…isothermal. The appendix of Sawant et al (2022) describes the DSMC numerical criteria and convergence study for flows presented here. Figure 6(b,c) of Sawant et al (2022) show that the ratio τ/ t is greater than unity in the entire flow domain and the smallest collision cells contain at least eight particles, respectively.…”

“…The appendix of Sawant et al (2022) describes the DSMC numerical criteria and convergence study for flows presented here. Figure 6(b,c) of Sawant et al (2022) show that the ratio τ/ t is greater than unity in the entire flow domain and the smallest collision cells contain at least eight particles, respectively. With respect to λ/ x, figure 6(a) of Sawant et al (2022) shows that the ratio is greater than unity in the entire flow domain, including the interior zones of shock structures and regions of triple, separation and reattachment points.…”