Energy flow of high-speed separation shocks revealed with Schlieren imaging
DOI: 10.1063/10.0044345
Energy flow of high-speed separation shocks revealed with Schlieren imaging lead image
When a shock wave meets a supersonic boundary layer, low-frequency oscillations between the shock and detached boundary layer create a shock-induced flow separation.. At high Mach numbers, the separation can create shock trains, which can have dangerous structural loading effects when they occur in the nozzles of rocket engines and in ducts and wind tunnels with supersonic flows.
To better understand how the leading separation shock influences the flow, Anubhav Dasgupta and Surabhi Singh studied unstarted supersonic nozzles. They used high-speed Schlieren imaging to see the flow inside the nozzle, and then analyzed the images to track the separation of the shock.
The researchers also used two modal analysis techniques — spectral proper orthogonal decomposition (POD) and snapshot POD — to identify the most energetic flow structures and determine how they were related to the shock motion. The results showed the shock exhibited low-frequency spectral activity and energetic flow events.
“The most exciting finding was that the dominant snapshot POD mode captured the temporal behavior of the separation shock extremely well, even though it could not fully reconstruct the shock spatially,” Singh said. “This revealed that the dominant low-frequency energy of the flow is strongly organized by the global motion of the separation shock.”
The authors hope the findings can improve reduced-order modeling and flow-control strategies in high-speed propulsion systems by enabling more efficient modeling of unsteady high-speed flows. Ultimately, such work could enhance supersonic engine and isolator performance and structural safety.
The authors intend to continue studying shock-train flows in more complex 3D situations and developing reduced-order modeling.
Source: “Low-frequency spectral and energetic imprints of the separation shock in unstarted nozzles,” by Anubhav Dasgupta and Surabhi Singh, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0336549 .
