Proper Orthogonal Decomposition Analysis of Swept-Ramp Shock-Wave/Boundary-Layer Unsteadiness at Mach 2

Dynamics of strong swept-shock/turbulent-boundary-layer interactions

“…We classify this unsteadiness as mid-frequency unsteadiness rather than low-frequency unsteadiness, because it is largely associated with convective coherent structures formed in the separated shear layer (see § 4.2), not stationary large-scale ('breathing') unsteadiness of the separated region as a whole; necessarily, its mechanism is more similar to mid-frequency unsteadiness in comparable spanwise-homogeneous interactions, rather than the low-frequency unsteadiness in such interactions. Recent experiments also confirm this observation that the prominence of the mid-frequency fluctuation band is increased relative to the that of the low-frequency fluctuation band in swept interactions (Arora, Mears & Alvi 2019;Vanstone & Clemens 2019). We note that, by an absolute measure, the mid-frequency content in swept interactions may comprise lower or FIGURE 9.…”

Interactions between a shock and turbulent features in a Mach 2 compressible boundary layer

“…Evidence exists which indicate different levels of influence from the upstream and downstream effects on the separation bubble unsteadiness as a function of its frequency content. For example, Vanstone & Clemens (2019) show based on band-pass filtered high-speed PIV data that, while the low ( f δ I /U ∞ < 10 −2 ) and medium (10 −2 < f δ I /U ∞ < 10 −1 ) frequency contents exhibit strong correlation with the low-and high-momentum events in the upstream boundary layer, the high ( f δ I /U ∞ > 10 −1 ) frequency contents appear to be primarily driven by shear layer flapping from the downstream region. Hence for cases when the separation is stronger, the perturbation at time scales corresponding to the unstable global mode may be dominated by sources other than the perturbations from the incoming boundary layer, leading to reduced influence of the upstream boundary layer for these cases, as reported by Piponniau et al (2009), Clemens & Narayanaswamy (2014) and others.…”

Shock-Boundary Layer Interactions in Supersonic Turbine Cascades

“…Modal decomposition techniques have emerged as powerful tools for analyzing the unsteady flows [43] facilitating the assessment of organized structures which may play an important role in the flow dynamics. In recent years, these techniques have been applied for the investigation of low-frequency unsteadiness in SBLIs [28,[44][45][46][47][48][49][50][51][52].…”