Investigating Unsteady Dynamics of Cylinder-Induced Shock-Wave/Transitional Boundary-Layer Interactions

Spectral Proper Orthogonal Decomposition Analysis of Shock-Wave/Boundary-Layer Interactions

“…A Photron FASTCAM Mini UX100 high-speed camera was used to capture the images at a frame rate of 80 kHz. 1…”

“…SWBLIs generate low-frequency unsteadiness in many aerodynamicapplications and often lead to flow separation and an increased possibility of engineunstart in scramjet engines. 1,2 The majority of existing research on SWBLIs has been conducted in either fully laminar or fully turbulent boundary layers. 3 Despite the breadth of research conducted, a definitive driving mechanism of this unsteadiness is still yet to be determined, though there has been some evidence suggesting that strong interactions with larger separation bubbles are the result of oscillations of a downstream instability while weaker interactions with smaller separations are driven by fluctuations in the incoming boundary layer.…”

“…While turbulent and laminar interactions have been the focus of the majority of previous studies, research on shock-wave/transitional boundary-layer interactions (XSWBLI) is an emerging area focusing on the internal mechanisms of these interactions. 1,4,5,6 Previous research conducted by Murphree et al 5,7 examined SWBLIs generated by a cylinder mounted on a flat plate in a Mach 5 flow. Planar laser scattering (PLS) and particle image velocimetry (PIV) were used to visualize the flow structure as the cylinder was moved farther from the leading edge of the plate.…”

“…These findings were confirmed by the PIV measurements. More recently, Combs et al 1,6 studied cylinder-induced SWBLIs in transitional and fully turbulent boundary layers in a Mach 1.78 flow. High-speed Schlieren images were used to track the positions of the upstream influence shock, forward lambda shock, and trailing lambda shock in a time-resolved manner.…”

“…Building upon previous work by Combs et al, Murphree et al, and Towne et al, the current research focuses on analyzing high-speed Schlieren images of cylinder-induced SWBLIs in a Mach 5 wind tunnel using spectral proper orthogonal decomposition (SPOD). 1,6,8,10 The advantage of using SPOD analysis over similar methods like dynamic mode decomposition (DMD) or proper orthogonal decomposition (POD), is that SPOD is coherent in both space and time. For this reason, SPOD may be a better option for identifying physically meaningful coherent structures in fluid flows and investigating the driving mechanisms behind SWBLI unsteadiness.…”