Domain of dependence of wall-pressure measurements in attached and separated hypersonic boundary layers*

The accuracy of assimilating wall-pressure measurements in separated hypersonic boundary layers is dependent on the placement of the sensors relative to the onset of separation. The reverse flow significantly alters the boundary-layer disturbance spectra, and therefore sensors upstream/downstream of separation serve different roles. We use adjoint-variational methods to study the sensitivity of these sensors on precursor and upstream events in the flow, in Mach 6 flow over a cone-flare. Sensors within the attached region can accurately estimate the boundary-layer instability waves. However, these sensors are insensitive to important modes that can alter the downstream flow, and therefore sensors within the separated region are necessary. We introduce the notion of the domain of dependence (DOD) of a sensor and compare the two placements, upstream and downstream of separation onset. In the latter case, we explore the influence of the corner-shock on the interpretation of wall-pressure data.