D. S. Dolling

Effects of upstream boundary layer on the unsteadiness of shock-induced separation

The relationship between the upstream boundary layer and the low-frequency, large-scale unsteadiness of the separated flow in a Mach 2 compression ramp interaction is investigated by performing wide-field particle image velocimetry (PIV) and planar laser scattering (PLS) measurements in streamwise–spanwise planes. Planar laser scattering measurements in the upstream boundary layer indicate the presence of spanwise strips of elongated regions of uniform momentum with lengths greater than 40?. These long coherent structures have been observed in a Mach 2 supersonic boundary layer (Ganapathisubramani, Clemens & Dolling 2006) and they exhibit strong similarities to those that have been found in incompressible boundary layers (Tomkins & Adrian 2003; Ganapathisubramani, Longmire & Marusic 2003). At a wall-normal location of y/?=0.2, the inferred instantaneous separation line of the separation region is found to oscillate between x/?=?3 and ?1 (where x/?=0 is the ramp corner). The instantaneous spanwise separation line is found to respond to the elongated regions of uniform momentum. It is shown that high- and low-momentum regions are correlated with smaller and larger size of the separation region, respectively. Furthermore, the instantaneous separation line exhibits large-scale undulations that conform to the low- and high-speed regions in the upstream boundary layer. The low-frequency unsteadiness of the separation region/shock foot observed in numerous previous studies can be explained by a turbulent mechanism that includes these elongated regions of uniform momentum

Relationship Between Upstream Turbulent Boundary-Layer Velocity Fluctuations and Separation Shock Unsteadiness

Particle image velocimetry and high-frequency response wall pressure measurements have been used to investigate the relationship between upstream turbulent boundary-layer properties and the unsteady separation shock behavior in a Mach 5 unswept compression ramp interaction. No correlation is found between variations in the incoming boundary-layer thickness and the separation shock foot position, as has been suggested in earlier work. However, themean velocity proe le, conditioned on theseparation shock foot position, exhibits a subtly fullershape when the shock is downstream than when it is upstream. More signie cantly, a clear correlation is observed between positivestreamwisevelocity e uctuations in thelowerthird of the upstream boundary layer and downstream shock motions, and vice versa. The strongest correlations are found for velocity e uctuations with frequencies of about4‐10 kHz, which is signie cantly lowerthan the frequencies that characterize the large-scale structures in the boundary layer (40 kHz), although spatial limitations in the transducer array may limit the instrument sensitivity to this lower range. These results are qualitatively consistent with the simple physical principle that a fuller velocity proe le imparts increased resistance to separation to the boundary layer and, hence, causes downstream shock motion, whereas a less-full velocity proe le is associated with lower resistance to separation and, hence, upstream shock motion.

Large-scale motions in a supersonic turbulent boundary layer

Wide-field particle image velocimetry measurements were performed in a Mach 2 turbulent boundary layer to study the characteristics of large-scale coherence at two wall-normal locations (

Low-frequency dynamics of shock-induced separation in a compression ramp interaction

y/delta,{=},0.16

Cavity Oscillation Mechanisms in High-Speed Flows

and 0.45). Instantaneous velocity fields at both locations indicate the presence of elongated streamwise strips of uniform low- and high-speed fluid (length

Experimental Study of Shear-Layer/Acoustics Coupling in Mach 5 Cavity Flow

,{>},8delta

Control of Supersonic Inlet-Isolator Unstart Using Active and Passive Vortex Generators

). These long coherent structures exhibit strong similarities to those that have been found in incompressible boundary layers, which suggests an underlying similarity between the incompressible and supersonic regimes. Two-point correlations of streamwise velocity fluctuations show coherence over a longer streamwise distance at

Large-scale structure evolution in supersonic interacting shear layers

y/delta,{=},0.45

Planar laser imaging of a supersonic side-facing cavity

than at

PIV Investigation of Role of Boundary Layer Velocity Fluctuations in Unsteady Shock-Induced Separation

y/delta,{=},0.16