Spatiotemporal correlation of wall pressure fluctuations generated in scramjet inlet

Wall pressure fluctuations in the scramjet inlet are a significant aerodynamic load that requires special consideration in aircraft structural design. This study focuses on understanding the physical essence behind these pressure fluctuations by conducting wind tunnel measurements to analyze their time-frequency and spatiotemporal correlation characteristics. The working condition of the scramjet inlet is assessed based on the observed wall pressure fluctuations. A relatively accurate disturbance velocity is calculated by using the phase-array technique and a statistical algorithm, which indicates that the two dominant oscillations responsible for the unsteady flow and significant pressure fluctuations in the unstarted inlet should correspond to the acoustic mode, as their propagation speed is equivalent to the speed of sound. Wall pressure fluctuations in time-space domain reveals the second oscillation originating from to the first oscillation at the inlet lip. A spatiotemporal correlation analysis is conducted to investigate the generation mechanism of wall pressure fluctuations by examining the direction of energy flow on both temporal and spatial scales. The started inlet is primarily influenced by localized random fluctuations, while the un-started inlet is predominantly affected by the overflow-induced acoustic modes.